HomeMy WebLinkAbout20061800.tiff •
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FINAL DRAINAGE- • •
AND . •
EROSION CONTROL .
REPORT
FOR
KITELEY RANCH AT
FOSTER LAKE
Decembef 7, 2005
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M I R 0 ..
S. A. Ml% Inc.
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• PREPARED BY: •
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S. A:Miro, Inc.
Consulting Engineers
3500 JFK Pkwy
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Suite 310
Fort Collins, Colorado 80525-2635
(970)266-1900 '
Bryan E. Clerico, P.E. •
S. A. Miro Job No '04190
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r. •
2006-1800
"This report for the drainage design of Kiteley Ranch at Foster Lake was prepared under my direct supervision
in accordance with the provisions of the Urban Storm Drainage Criteria Manual,and was designed to comply
with the provisions thereof. I understand that Weld County does not and will not assume liability for drainage
facilities'design:
Registered Professional Engineer State
of Colorado No. 36722
Kiteley Ranch at Foster Lake
TABLE OF CONTENTS
GENERAL LOCATION AND DESCRIPTION 1
HISTORIC DRAINAGE BASINS 1
DRAINAGE DESIGN CRITERIA 1
-
DRAINAGE FACILITY DESIGN 2
EROSION CONTROL PLAN 3
CONCLUSIONS 8
REFERENCES 9
APPENDIX A_1
I. GENERAL LOCATION AND DESCRIPTION
This Drainage and Erosion Control report has been prepared for the Kiteley Ranch at Foster Lake site. It is
located in the Northwest quarter of Section 27, Township 3 North, Range 68 West, of the 6t1 Principal
Meridian, County of Weld, State of Colorado. More specifically, the site is bounded on the west by County
Road 7 and north by Highway 66. Foster Reservoir is located to the south and Meade Crossing is located to
the east, across from an irrigation ditch entering Foster Reservoir.
The site is approximately 140 acres,of which 116 acres will flow into Pond 1 and 4 acres will flow into Pond 2.
The remaining area will flow off-site. The development of the site will include subdividing the land into 429
single family lots with associated roads and open space.
II. HISTORIC DRAINAGE BASINS
A small portion of the project in the southeast corner may be located in the FEMA floodplain per FIRM
Community Panel Number 080266 0850 C last revise September 28, 1982. It is difficult to place the
actual floodplain boundary from FEMA mapping onto surveyed topography. An analysis shall be
conducted to verify the actual floodplain location in comparison to the actual field surveyed topography.
FEMA floodplain requirements shall be adhered to.
Historically, runoff from the site flows in a southeasterly direction into Foster Reservoir. The historic basin
is approximately 126.5 acres of cultivated farm land with slopes averaging roughly 3.0%. A wet area is
located in the southeast corner of the property, but is not considered jurisdictional wetlands. The soils
have a medium surface runoff, which corresponds to a Type C soil. All calculations are based on a Type
C soil. The 5-year historic flow is 33.2 CFS and the 100-year historic flow is 217.4 CFS.
III. DRAINAGE DESIGN CRITERIA
The Urban Storm Drainage Criteria Manual Volumes 1 and 3 are utilized as a guideline for design.
Hydrologic Criteria
The Rational Method was used for this study to calculate runoff for the 5-year and the 100-year rainfall
events, minor and major respectively. The Intensity-Duration-Frequency Curves used were derived from
Urban Storm Drainage Criteria Manual Vol. 1, equation RA-3. The value for P, is 1.4 for the 5-year event
and 2.7 for the 100-year event and is obtained from Figure RA-2 and RA-6, respectively. The Runoff
coefficients were obtained from Table RO-5 and Figure RO-5. Assuming 3,000 SF homes and 3 units/
acre density, the impervious value for the developed lots is 40% including roadways.
Hydraulic Criteria
This report does not determine storm sewer sizes. On-site storm system pipes shall be designed to
convey the 5-year event without causing damage to structures during the 100-year event. Currently, an
open channel is utilized to convey flows from Basin 1C to Pond 1. The channel has an 8 foot bottom
width, 4:1 sidelopes and 3 foot depth. The channel has a 0.3% longitudinal slope which can convey 78
CFS with 1 foot of freeboard.
Each of the proposed ponds shall have a level spreader at the outlet end of the discharge pipe. A level
spreader is a shallow basin, elongated in the direction perpendicular to the slope of the ground. The level
spreader will discharge the runoff from the pond at a constant elevation, spread out over the length of the
Kiteley Ranch at Foster Lake
level spreader. This shall promote a sheet flow pattern rather than concentrated flow in order to minimize
erosion downstream of the project.
IV. DRAINAGE FACILITY DESIGN
General Concept
On-site runoff will travel to three different primary design points: Pond 1, Pond 2 or off-site. Much of the
south and east portions of the project have grading that is influenced by providing proper cover over the
storm sewer. These areas will require fill. Another constraint that has influenced the drainage design is
the existing overhead powerline easement in the south portion of the site. Pond 1 was placed on the north
side of the easement in order to minimize disturbance to the easement. The easement also isolated a
portion of lots in the southeast corner of the project which required Pond 2 to be designed to provide water
quality.
All of the site detention takes place in Pond 1 because Pond 2 is for water quality purposes only. Table
SO-1 in Urban Storm Drainage Criteria Manual Vol. 2 provides a recommended allowable release rate per
area of tributary catchment. The table allows for 0.17 CFS/acre for the 5 year storm and 1.0 CFS/acre for
the 100-year storm. Since the historic drainage area is 126.5 acres, the allowable release rate from the
site under developed conditions is 21.5 CFS for the 5-year storm and 126.5 CFS for the 100-year storm.
Under developed conditions, there is 13.2 CFS flowing off-site for the 5-year storm and 91.6 CFS flowing
off-site for the 100-year storm. So, the developed flows are within the recommended range and well
below the historic rates of 33.2 CFS for the 5-year event and 217.4 CFS for the 100-year event. It
assumed that the water quality volume required for the pond is included in the required detention storage.
Pond 1 has 7.0 acre-ft. of storage between the bottom elevation of 4956.24 and the spillway elevation of
4959.18. Pond 2 currently has 0.7 acre-ft. of storage between the bottom elevation of 4956.78 and the
_ spillway elevation of 4961.00. This volume is much larger than necessary due to the bottom of pond
elevation being dictated by cover over storm pipe and also the surrounding grades dictating the spillway
elevation. The discharge structure shall be sized such that stormwater releases above Water Quality
levels are made such that unnecessary extra detention does not occur.
It should be noted that the developed peak 100-year flow leaving the site is 91.61 CFS at 31 minutes.
Historically, there is 151.39 CFS flowing off-site at 31 minutes and a peak flow of 217.4 CFS at 41
minutes. So, the peak flow under developed conditions occurs earlier than under historic conditions. But,
at that same point in time, the rate of flow is actually less under developed conditions than historic
conditions due to the detention.
Treatment for water quality will be provided to minimize the number of pollutants being discharged off-site
from the proposed project. Pond 1 shall be a Constructed Wetlands Basin that contains depressions that
are intended to hold permanent water and shall be planted with a wetland vegetation mixture. Pond 1
requires 1.90 acre-ft. for water quality storage which includes a 20% volume increase for sedimentation.
The 1.90 acre-ft.of water quality is included as part of the 7.0 acre-ft. of required detention.
Pond 2 shall achieve water quality by being designed as an extended detention basin (dry). The pond will
have a sloping bottom to drain the pond at the end of a storm event. Pond 2 requires 0.07 acre-ft. for
water quality storage which includes a 20%volume increase for sedimentation. Calculations for the water
quality portion of the ponds follow the procedure outlined in UDFCD Volume 3 and are provided in the
appendix.
Developed Basins
2
Kiteley Ranch at Foster Lake
The site is divided into six on-site drainage basins plus one off-site basin. The on-site basins flow into
either Pond 1 or Pond 2 where they are detained and water quality is provided.
Each sub-basin is described as follows:
Sub-basin 1A is 47.7 acres in size and is located in the northwest corner of the
site. This sub-basin drains the entire northwest portion of the project and
discharges directly into Pond 1 at Design Point 1. The 5 year flow is 43.3 CFS
and the 100 year flow is 140.5 CFS.
Sub-basin 1B is 18.6 acres in size and is located in the middle-north portion of
the site. This sub-basin flows towards the south into a storm sewer system that
discharges into a channel and into Pond 1 at Design Point 2. The 5 year flow is
20.0 CFS and the 100 year flow is 64.9 CFS.
Sub-basin IC is 7.8 acres in size and is located in the northeast corner of the
site. This area flows towards the south into a sump condition in the road that
discharges into a grass-lined channel and into Pond 1 at Design Point 3. The 5
year flow is 7.9 CFS and the 100 year flow is 25.6 CFS.
Sub-basin 1D is 31.0 acres in size and is located in the southwest corner of the
site. This area flows eastward into a storm sewer system that discharges directly
into Pond 1 at Design Point 4. The 5 year flow is 31.4 CFS and the 100 year flow
is 101.8 CFS.
Sub-basin 1E is 11.4 acres in size and encompasses an area that discharges
directly into Pond 1 at Design Point 5. The 5 year flow is 8.1 CFS and the 100
year flow is 40.1 CFS.
Sub-basin 2A is 3.8 acres in size and is located in the southeast portion of the
site. This area flows directly into Pond 2 at Design Point 6. The 5 year flow is 4.5
CFS and the 100 year flow is 14.7 CFS.
Sub-basin OS1 is 13.9 acres and is located along the south and east perimeter
of the project. Flows from this area travel off-site and into Foster Reservoir at
Design Point 7. The 5 year flow is 8.5 CFS and the 100 year flow is 48.1 CFS.
V. EROSION CONTROL PLAN
The proposed erosion control program for this site will include the installation of structural erosion control
measures including silt fencing, sediment basins and traps, rough cut street control and straw bale channel
protection. Non-structural measures will include maintaining established grasses until striping is necessary
and the establishment of temporary and permanent grasses in idol or completed areas during construction
sequencing.
The following construction phases are anticipated during construction of the site. There potential pollutants
are identified and BMP solutions are addressed for these pollutants.
CONSTRUCTION PHASES
3
Kiteley Ranch at Foster Lake
The proposed sequence of major construction activity is as follows:
1. Clearing, grubbing and grading
Potential Pollutants
_ • Sediment
• Vehicle fuels and lubricants
2. Underground utility installation
Potential Pollutants
• Sediment
• Vehicle fuels and lubricants
• Paints
• Solvents
• Concrete
• Various types of pipe material
3. Building construction
Potential Pollutants
• Vehicle and equipment fuels
• Solvents and paint
• Adhesives
• Cleaners
• Asphalts and tars
• Concrete
4. Street, sidewalk, and curb and gutter installation.
Potential Pollutants
• Vehicle and equipment fuels
• Solvents and Paints
• Bituminous products
• Concrete
5. Landscaping
Potential Pollutants
• Sediment
• Fertilizer
• Chemicals
4
Kiteley Ranch at Foster Lake
There may be overlap between construction sequences two (2), three (3), four(4), and five (5).
A more detailed construction schedule will be available from the contractor as it is developed.
BMP FOR STORM WATER POLLUTION PREVENTION
The following controls and measures will be implemented prior to and during the various sequence of
construction:
1. Clearing and Grubbing - Install vehicle tracking pad at entrance to site. Define
limits of clearing, place silt fence at all future toe of slope as defined by the
approved erosion control plan (See included drawing). Designate area to
stockpile topsoil. Follow requirements of approved erosion control plan.
2. Grading- Construct sediment traps and basins as shown on approved erosion
control plans. Install rock check structures and rough cut street protection along
flowline of newly graded drainage channels and rough cut roads, and silt fencing
at down slope side of newly disturbed areas. As construction progresses,
designate areas for construction trailer, trash container, vehicle and equipment
refueling, vehicle and equipment parking, and for material storage. Stored
materials shall be free of contact with soil. Materials in containers shall be stored
within a covered area. Fueling and storage areas shall be protected with a
minimum 1'high berm, to prevent migration of any spills.
—
3. Underground utility main installation (sanitary sewer, water and storm drain)-
Maintain all previous controls and measures from clearing, grubbing and grading
construction. Trenches shall be backfilled as soon as possible (after inspection).
Excess material shall be salvaged when possible, waste material shall be disposed
of in a proper manner. Empty containers that held hazard material such as
solvents, lubricants, fuels, etc., shall be disposed of in a proper manner. Refueling
and vehicle maintenance shall be done at designated areas. Fueling and storage
areas shall be protected with a minimum 1' high berm, to prevent migration of any
spills
During installation of the storm sewer system, inlet and outlet sediment protection
will be provided. During flushing and testing of utilities sediment control
measures shall be in place.
When trenching for utilities located outside of protected areas, silt fencing and/or
hay bales shall be provided, at down slope areas of disturbance. At completion of
construction disturbed areas shall be reseeded. Erosion control measures shall
remain in place until stabilization has been achieved.
4. Building Construction - Designate areas for vehicle fueling and maintenance,
concrete truck washout, and material storage. Material stored outdoors will be
5
Kiteley Ranch at Foster Lake
free of contact with the soil and covered when possible. Materials in containers
will be covered and stored in sheltered areas. All flammable materials shall be
stored in proper containers and checked daily for leaks and spills.
5. Paving and Curb and Gutter Installation - Designate areas for vehicle fueling and
_ maintenance, concrete truck washout, and material storage. Material stored
outdoors will be free of contact with the soil. Materials in containers will be
stored indoors within covered areas.
6. Landscaping - Designate areas for vehicle fueling and maintenance, concrete truck
washout, and material storage. Material stored outdoors will be free of contact
with the soil and covered when possible. Materials in containers will be stored
indoors within covered areas. Avoid excess watering and placing of fertilizers
and chemicals.
OTHER CONTROLS
Control Practices for Cleared Vegetation
Remove only what is needed; leave native vegetation in place when possible. Compost
vegetation away from detention ponds or at regional composting areas.
Erosion and Sediment Control
Soil Stabilization Practices - Where significant ground cover exists on-site it will be left in place,
if possible, or removed just prior to grading. Landscaping shall be installed as soon as possible
after grading is completed.
Sediment and Erosions Control Practices = Construct temporary sediment traps. Follow the
approved erosion control plan.
Tracking of Sediment Onto Roads and Streets - Streets shall be kept clean and free of mud, soil,
and construction waste. Street sweeping or other acceptable methods shall be used to prevent
sediment from being washed from the project site. Streets shall not be washed with water if
prohibited by local ordinances.
Control Practices for Wind Erosion - Wind erosion shall be controlled on the site by maintaining
appropriate levels of surface moisture, or application of surface binding materials if necessary,
seeding and mulching of the site will occur as soon as practicable after completion of grading
activities.
NON-STORM WATER MANAGEMENT
6
Kiteley Ranch at Foster Lake
Non-storm water discharges will be eliminated or reduced to the extent feasible. No materials
shall be discharged in quantities which will have an adverse effect on the receiving waters. The
measures listed below will be implemented to achieve these objectives.
Proper and lawful disposal of all waste materials.
Control any spills and leaks that may occur and clean up (mitigate).
Use of designated areas for equipment repair and cleaning.
Careful application of irrigation water.
FINAL STABILIZATION AND LONG TERM STORM WATER MANAGEMENT
Management of storm water after completion of construction will be accomplished by utilizing
the practices listed below.
Upon completion of construction, the site shall be inspected to ensure that all equipment,
waste materials, and debris have been removed.
The site will be inspected to make certain that all graded surfaces have been landscaped
or seeded with an appropriate ground cover. The following ground covers will be
provided to minimize erosion from stormwater runoff:
—
SPECIES Drilled PLS/Acre @ Desired % OF MIX PLS /Acre in Mix
100%
Buchloe dactyloides 7.7 35 2.7
(Buffalo Grass)
Bouteloua gracilis 6.5 20 1.3
(Blue Grama)
Bouteloua curtipendula 13.3 15 2.0
(Side Oats Grama)
Agropyron smithii 20.0 15 3.0
(Western Wheatgrass)
Schizachyrium 10.0 10 1.0
scoparium
(Little Bluestem)
Agropyron trachyculum 20.0 5 1.0
(Slender Wheatgrass)
7
Kiteley Ranch at Foster Lake
All inlet protection, perimeter fencing, rock check dams, and all other control practices and
measures that are to remain after completion of construction will be inspected to ensure their
proper functioning.
Permanent riprap basins will be installed at the storm sewer outfall to the detention ponds in order
to minimize erosion and sedimentation at the discharge points.
The property owner/contractor shall be responsible for maintaining the storm water controls in good
working order and shall also be responsible for the costs incurred until such time as they are accepted by
the County or no longer required, including removal of measures.
VI. CONCLUSIONS
This drainage and erosion control report and plans comply with the Urban Storm Drainage Criteria
Manual2. The drainage system is designed to convey the runoff to the designated on site detention
facilities and provides water quality treatment prior to discharging off-site. The peak flow released from
the site under proposed conditions is less than the historic flow at that same time.
8
Kiteley Ranch at Foster Lake
VII. REFERENCES
Urban Storm Drainage Criteria Manual (Volumes 1 and 3), Urban Drainage and Flood
Control District, June 2001.
9
Kiteley Ranch at Foster Lake
APPENDIX
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DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF
90
80 15.000 sq.R.homes I-
/
70
/ ' 4.000 sp.ft.homes '
•
a /
— p /� 13.000 sp.rt.homes I.
1 50 , •
8 /
2 / f • 2.000 sp.R homes I.
— &a 40 +'
_�.J •
,/ —
O
r / . ♦ - , /
H 30 /. . ' / - _i 11,000 sp.R homes l..
.e • # •••••
we. • • /
.r
20 ,
i
10
0
_ 0 1 2 3 4 5 8
Single Family Dwelling Units per Acre
— FIGURE RO-5
Watershed Imperviousness, Single-Family Residential Two-Story Houses
1.00 - -
0.90
080 __
i /. -...
080 _. _.. 1 t50-yr !!
-4.-25 !,
9 050 —_.. t _{ tirv-t0yr
0
_ t5y
5 000 _ .. y-2-yr
_ 0.30 -_ -
020
0.10 .. ..__ _
—
000
0% 10% 20% 30% 40% 50% 60% 70% B0% 90% 100%
Watershed Percentage Imperviousness
-^ FIGURE RO-6
Runoff Coefficient, C, vs. Watershed Percentage Imperviousness NRCS Hydrologic Soil Group A
—
06/2001 RO-17
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 1) RUNOFF
TABLE RO-5
Runoff Coefficients, C
Percentage
Imperviousness Type C and D NRCS Hydrologic Soil Groups
2-yr 5-yr 10-yr 25-yr 50-yr 100-yr
0% 0.04 0.15 0.25 0.37 0.44 0.50
5% 0.08 0.18 0.28 0.39 0.46 0.52
_
10% 0.11 0.21 0.30 0.41 0.47 0.53
15% 0.14 0.24 0.32 0.43 0.49 0.54
20% 0.17 0.26 0.34 0.44 0.50 0.55
- 25% 0.20 0.28 0.36 0.46 0.51 0.56
30% 0.22 0.30 0.38 , 0.47 0.52 0.57
35% 0.25 0.33 0.40 0.48 0.53 0.57
- 40% 0.28 0.35 0.42 0.50 0.54 0.58
45% 0.31 0.37 0.44 0.51 0.55 0.59
50% 0.34 0.40 0.46 0.53 0.57 0.60
- 55% 0.37 0.43 0.48 0.5F 0.58 0.62
60% 0.41 0.46 0.51 0.57 0.60 0.63
65% 0.45 0.49 0.54 0.59 0.62 0.65
70% 0.49 0.53 0.57 0.62 0.65 0.68
75% 0.54 0.58 0.62 0.66 0.68 0.71
80% 0.60 0.63 0.66 0.70 0.72 0.74
85% 0.66 0.68 0.71 0.75 0.77 0.79
-
90% 0.73 0.75 0.77 0.80 0.82 0.83
95% 0.80 0.82 0.84 0.87 0.88 0.89
100% 0.89 0.90 0.92 0.94 0.95 0.96
- Type B NRCS Hydrologic Soils Group
0% 0.02 0.08 0.15 0.25 0.30 0.35
5% 0.04 0.10 0.19 0.28 0.33 0.38
- 10% 0.06 0.14 0.22 0.31 0.36 0.40
15% 0.08 0.17 0.25 0.33 0.38 0.42
20% 0.12 0.20 0.27 , 0.35 0.40 0.44
- 25% 0.15 0.22 0.30 0.37 0.41 0.46
30% 0.18 0.25 0.32 0.39 0.43 0.47
35% 0.20 0.27 0.34 0.41 0.44 0.48
40% 0.23 0.30 0.36 0.42 0.46 0.50
-
45% 0.26 0.32 0.38 0.44 0.48 0.51
50% 0.29 0.35 0.40 0.46 0.49 0.52
55% 0.33 0.38 0.43 0.48 0.51 0.54
_
60% 0.37 0.41 0.46 0.51 0.54 0.56
65% 0.41 0.45 0.49 0.54 0.57 0.59
70% 0.45 0.49 0.53 0.58 0.60 0.62
- 75% 0.51 0.54 0.58 0.62 0.64 0.66
80% 0.57 0.59 0.63 0.66 0.68 0.70
85% 0.63 0.66 0.69 0.72 0.73 0.75
- 90% 0.71 0.73 0.75 0.78 0.80 0.81
95% 0.79 0.81 0.83 0.85 0.87 0.88
100% 0.89 0.90 0.92 0.94 0.95 0.96
06/2001 RO-11
Urban Drainage and Flood Control District
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STORAGE DRAINAGE CRITERIA MANUAL(V. 2)
attempt to account for the effects of the WQCV on all control levels whenever it performs watershed-level
drainage and flood control system master plans.
3.2 Sizing of On-Site Detention Facilities
3.2.1 Maximum Allowable Unit Release Rates for On-Site Facilities. The maximum allowable unit
release rates per acre for on-site detention facilities for a number of design retum periods are listed in
Table SO-1. These rates apply unless other rates are recommended in a District-approved master plan.
The predominant soil group for the total tributary catchment shall be used for determining the allowable
release rates. Multiply the unit rates provided in Table SO-1 by the tributary catchment's area to obtain
the actual design release rates in cubic feet per second (cfs). Whenever Natural Resources
Conservation Service (NRCS)soil surveys are not available for the portion of a county being studied,
extrapolate their types using soil investigations at the site.
TABLE SO-1
Recommended Maximum Allowable Unit Flow Release Rates (cfs/acre)of Tributary Catchment
Design Return NRCS Hydrologic Soil Group
Period
(Years) A B C &D
2 0.02 0.03 0.04
5 0.07 0.13 0.17
10 0.13 0.23 0.30
25 0.24 0.41 0.52
50 0.33 • 0.56 0.68
100 0.50 0.85 1.00
3.2.2 Empirical Equations for the Sizing of On-Site Detention Storage Volumes. Urbonas and
Glidden (1983), as part of the District's ongoing hydrologic research, conducted studies that evaluated
peak storm runoff flows along major drainageways. The following set of empirical equations provided
preliminary estimates of on-site detention facility sizing for areas within the District. They are not intended
for use when off-site inflows are present or when multi-stage controls are to be used (e.g., 10-and 100-
year peak control) at the storage facility. In addition, these equations are not intended to replace detailed
hydrologic and flood routing analysis, or even the analysis using the Rational Formula-based FAA method
for the sizing of detention storage volumes. The District does not promote the use of these empirical
equations. It does not object, however, to their use by local governments who have adopted them or
want to adopt them as minimum requirements for the sizing of on-site detention for small catchments
within their jurisdiction. If the District has a master plan that contains specific guidance for detention
SO-8 06/2001
Urban Drainage and Flood Control District
5-YEAR STORM
Hydrograph Summary Report
-
ad. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph
type flow interval peak hyd(s) elevation storage description
_ (origin) (cfs) (min) (min) (cult) (ft) (cuff)
1 Rational 43.28 1 21 54,539 — — — 1A
—
2 Rational 19.99 1 15 17,991 — — 18
3 Rational 7.89 1 17 8,049 — — — 1C
4 Rational 31.36 1 17 31,990 -- - 1O
5 Rational 8.13 1 12 5,851 — — 1E
6 Combine 96.36 1 17 118,420 1,2,3,4,5 — POND 1 INFLOW
—
7 Reservoir 4.14 1 40 97,770 6 4957.43 114,869 POND1 OUTFLOW
8 Rational 33.19 1 41 81,636 — — — HISTORIC
9 RaaiunA , 4.51 1 12 3,251 — — — 2A
10 Rational 8.49 1 12 6,115 — — — OS-1
11 Combine 13.23 1 12 107,135 7,9,10 - - TOTAL FLOW OFF-SITE
se
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•
•
•
•
•
KITELEY-COZ-5YR.gpw I Return Period: 5 Year Thursday, Sep 29 2005, 6:45 AM
Hydraflow Hydrographs by Intelisolve
3
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 1
1A
Hydrograph type = Rational Peak discharge = 43.28 cfs
- Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 47.7 ac Runoff coeff. = 0.35
Intensity = 2.593 in/hr Tc by User = 21 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=54,539 cuft
Ianmeevdmes#+xaonl
Hydrograph Discharge Table
Time --Outflow Time - Outflow
- (min cfs) (min cfs)
1 2.06 35 14.43
2 4.12 36 12.37
3 6.18 37 10.31
4 8.24 38 8.24
5 10.31 39 6.18
6 12.37 40 4.12
7 14.43 41 2.06
8 16.49
9 18.55
_ 10 20.61 ...End
11 22.67
12 24.73
13 26.80
14 28.86
15 30.92
16 32.98
17 35.04
18 37.10
19 39.16
20 41.22
21 43.28«
22 41.22
23 39.16
24 37.10
25 35.04
26 32.98
27 30.92
28 28.86
29 26.80
30 24.73
31 22.67
32 20.61
33 18.55
34 16.49
Hydrograph Report
Hydra low Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 2
1B
Hydrograph type = Rational Peak discharge = 19.99 cfs
Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 18.6 ac Runoff coeff. = 0.35
Intensity = 3.071 in/hr Tc by User = 15 min
IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=17,991 cuff
Hydrograph Discharge Table ("iledv "ue°"'%aop)
Time --Outflow
(min cfs)
1 1.33
2 2.67
3 4.00
4 5.33
5 6.66
6 8.00
7 9.33
8 10.66
9 11.99
10 13.33
11 14.66
12 15.99
13 17.33
14 18.66
15 19.99«
16 18.66
17 17.33
18 15.99
19 14.66
20 13.33
21 11.99
22 10.66
23 9.33
24 8.00
25 6.66
26 5.33
27 4.00
28 2.67
29 1.33
...End
Hydrograph Report 5
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 3
1C
Hydrograph type = Rational Peak discharge = 7.89 cfs
Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 7.8 ac Runoff coeff. = 0.35
Intensity = 2.891 in/hr Tc by User = 17 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=8,049 cult
- Hydrograph Discharge Table (Printed values>-•1%dop.)
Time -- Outflow
(min cfs)
1 0.46
2 0.93
3 1.39
4 1.86
5 2.32
6 2.79
7 3.25
8 3.71
9 4.18
10 4.64
11 5.11
12 5.57
13 6.03
14 6.50
15 6.96
16 7.43
17 7.89 «
18 7.43
19 6.96
20 6.50
21 6.03
22 5.57
23 5.11
24 4.64
25 4.16
26 3.71
27 3.25
28 2.79
29 2.32
30 1.86
31 1.39
32 0.93
33 0.46
.,.End
6
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 4
10
Hydrograph type = Rational Peak discharge = 31.36 cfs
- Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 31.0 ac Runoff coeff. = 0.35
Intensity = 2.891 in/hr Tc by User = 17 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=31,990 cuft
Hydrograph Discharge Table (RI s uesn1%wop.)
Time -Outflow
- (min cfs)
1 1.84
2 3.69
3 5.53
4 7.38
5 9.22
6 11.07
7 12.91
8 14.76
9 16.60
.� 10 18.45
11 20.29
12 22.14
13 23.98
14 25.83
15 27.67
16 29.52
17 31.36«
18 29.52
19 27.67
20 25.83
21 23.98
22 22.14
23 20.29
24 18.45
25 16.60
26 14.76
27 12.91
28 11.07
29 9.22
30 7.38
31 5.53
32 3.69
33 1.84
...End
7
Hydrograph Report
Hydra(low Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
_ Hyd. No. 5
1E
Hydrograph type = Rational Peak discharge = 8.13 cfs
Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 11.4 ac Runoff coeff. = 0.21
Intensity = 3.395 in/hr Tc by User = 12 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=5,851 cuft
Hydrograph Discharge Table (Pnnted values'=1%mop,
Time —Outflow
- (min cfs)
1 0.68
2 1.35
3 2.03
4 2.71
5 3.39
6 4.06
7 4.74
8 5.42
9 6.09
— 10 6.77
11 7.45
12 8.13 «
13 7.45
14 6.77
15 6.09
16 5.42
17 4.74
— 18 4.06
19 3.39
20 2.71
21 2.03
22 1.35
23 0.68
...End
Hydrograph Report 13
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 6
POND 1 INFLOW
Hydrograph type = Combine Peak discharge = 96.36 cfs
- Storm frequency = 5 yrs Time interval = 1 min
Inflow hyds. = 1, 2, 3, 4, 5
-
Hydrograph Volume=118,420 cuff
Hydrograph Discharge Table (Minted values.=1%af Op)
- Time Hyd. 1 + Hyd.2+ Hyd. 3+ Hyd.4+ Hyd.5= Outflow
(min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs)
1 2.06 1.33 0.46 1.84 0.68 6.38
- 2 4.12 2.67 0.93 3.69 1.35 12.76
3 6.18 4.00 1.39 5.53 2.03 19.14
4 8.24 5.33 1.86 7.38 2.71 25.52
5 10.31 6.66 2.32 9.22 3.39 31.90
- 6 12.37 8.00 2.79 11.07 4.06 38.28
7 14.43 9.33 3.25 12.91 4.74 44.66
8 16.49 10.66 3.71 14.76 5.42 51.04
9 18.55 11.99 4.18 16.60 6.09 57.42
"" 10 20.61 13.33 4.64 18.45 6.77 63.80
11 22.67 14.66 5.11 20.29 7.45 70.18
12 24.73 15.99 5.57 22.14 8.13 « 76.56
_ 13 26.80 17.33 6.03 23.98 7.45 81.59
14 28.86 18.66 6.50 25.83 6.77 86.61
15 30.92 19.99« 6.96 27.67 6.09 91.64
16 32.98 18.66 7.43 29.52 5.42 94.00
- 17 35.04 17.33 7.89« 31.36« 4.74 96.36«
18 37.10 15.99 7.43 29.52 4.06 94.10
19 39.16 14.66 6.96 27.67 3.39 91.84
20 41.22 13.33 6.50 25.83 2.71 89.59
- 21 43.28 « 11.99 6.03 23.98 2.03 87.33
22 41.22 10.66 5.57 22.14 1.35 80.95
23 39.16 9.33 5.11 20.29 0.68 74.57
24 37.10 8.00 4.64 18.45 0.00 68.19
- 25 35.04 6.66 4.18 16.60 0.00 62.48
26 32.98 5.33 3.71 14.76 0.00 56.78
27 30.92 4.00 3.25 12.91 0.00 51.08
28 28.86 2.67 2.79 11.07 0.00 45.38
- 29 26.80 1.33 2.32 9.22 0.00 39.67
30 24.73 0.00 1.86 7.38 0.00 33.97
31 22.67 0.00 1.39 5.53 0.00 29.60
32 20.61 0.00 0.93 3.69 0.00 25.23
33 18.55 0.00 0.46 1.84 0.00 20.86
34 16.49 0.00 0.00 0.00 0.00 16.49
35 14.43 0.00 0.00 0.00 0.00 14.43
- 36 12.37 0.00 0.00 0.00 0.00 12.37
37 10.31 0.00 0.00 0.00 0.00 10.31
38 8.24 0.00 0.00 0.00 0.00 8.24
-
Continues on next page...
9
POND 1 INFLOW
Hydrograph Discharge Table
ime Hyd. 1 + Hyd. 2+ Hyd. 3 + Hyd.4+ Hyd. 5= Outflow
(min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs)
39 6.18 0.00 0.00 0.00 0.00 6.18
— 40 4.12 0.00 0.00 0.00 0.00 4.12
41 2.06 0.00 0.00 0.00 0.00 2.06
...End
r.,
Hydrograph Plot
Hydra(low Hydrographs by Intelisolve Wednesday,Sep 28 2005,7:3 PM
Hyd. No. 7
POND1 OUTFLOW
Hydrograph type = Reservoir Peak discharge = 4.14 cfs
- Storm frequency = 5 yrs Time interval = 1 min
Inflow hyd. No. = 6 Max. Elevation = 4957.43 ft
Reservoir name = POND 1 Max. Storage = 114,869 cuft
Storage Indication method used. Hydrograph Volume=97,770 cuft
POND1 OUTFLOW
Q(cfs) Hyd. No. 7—5 Yr Q(cfs)
100.00 100.00
90.00 90.00
80.00 80.00
70.00 70.00
- 60.00 - — — — 60.00
50.00 50.00
40.00 40.00
30.00 — 30.00
20.00 - 20.00
— 10.00 10.00
0.00 - 0.00
0 290 580 870 1160 1450 1740 2030 2320 2610 2900
Time(min)
Hyd No. 7 Hyd No. 6
2
Pond Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,7:3 PM
—
Pond No. 2 - POND 1
Pond Data
— Pond storage is based on known contour areas.Average end area method used.
Stage/Storage Table
Stage(ft) Elevation(ft) Contour area(sqft) incr.Storage(cuft) Total storage(cult)
—
0.00 4956.24 89,312 0 0
0.76 4957.00 97,678 71,056 71,056
1.76 4958.00 108,651 103,165 174,221
- 2.76 4959.00 119,311 113,981 288,202
3.76 4960.00 129,487 124,399 412,601
Culvert/Orifice Structures Weir Structures
— [A] [B] [C] [D] [A] [B] [C] [D]
Rise(in) = 42.00 18.00 0.00 0.00 Crest Len(ft) = 10.00 0.00 0.00 0.00
Span(in) = 42.00 18.00 0.00 0.00 Crest El.(ft) = 4957.24 0.00 0.00 0.00
�.. Na Barrels = 1 1 0 0 Weir Coeff. = 3.33 0.00 0.00 0.00
Invert El.(ft) = 4956.04 4956.24 0.00 0.00 Weir Type = Rect — — —
Length(ft) = 135.00 0.00 0.00 0.00 Multi-Stage = No No No No
Slope(X) = 0.01 0.00 0.00 0.00
—
N-Value = .013 .013 .000 .000
Orif.Coeff. = 0.60 0.60 0.00 0.00
Multi-Stage = Na Yes No No Exflflration= 0.000 in/hr(Contour) Tailwater Elev.= 0.00 ft
Note'.Culvert/Orifice outflows have been analyzed under inlet and cutlet control.
— ,re"-s•
ww
Stage(ft) Stage/Discharge Stage(ft)
- 4.00 ..___. ___. __. _ _ _ - __. .__ 4.00
_ . _. - _ _. _ __ 3.00- 3.00 - . _ - _.. .._
2.00 - -__ - . _ _ - - - . 2.00
- _ • 1.00
1.00 -(
I
0.00 0.00
0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00
Discharge(cfs)
• ---. Total Q
- I
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Thursday,Sep 29 2005,6:29 AM
Hyd. No. 8
HISTORIC
Hydrograph type = Rational Peak discharge = 33.19 cfs
— Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 126.5 ac Runoff coeff. = 0.15
Intensity = 1.749 in/hr Tc by User = 41 min
— IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=81,636 cuft
-
Hydrograph Discharge Table (PnnIed values>-1%Mop.)
Time -- Outflow Time -- Outflow Time -- Outflow
- (min cfs) (min cfs) (min cfs)
1 0.81 35 28.33 69 10.52
2 1.62 36 29.14 70 9.71
3 2.43 37 29.95 71 8.90
4 3.24 38 30.76 72 8.09
5 4.05 39 31.57 73 7.28
6 4.86 40 32.38 74 6.48
-
7 5.67 41 33.19« 75 5.67
8 6.48 42 32.38 76 4.86
9 7.28 43 31.57 77 4.05
- 10 8.09 44 30.76 78 3.24
11 8.90 45 29.95 79 2.43
12 9.71 46 29.14 80 1.62
13 10.52 47 28.33 81 0.81
- 14 11.33 48 27.52
15 12.14 49 26.71
16 12.95 50 25.90 ...End
17 13.76 51 25.09
- 18 14.57 52 24.28
19 15.38 53 23.47
20 16.19 54 22.66
21 17.00 55 21.85
- 22 17.81 56 21.04
23 18.62 57 20.23
24 19.43 58 19.43
_ 25 20.23 59 18.62
26 21.04 60 17.81
27 21.85 61 17.00
28 22.66 62 16.19
- 29 23.47 63 15.38
30 24.28 64 14.57
31 25.09 65 13.76
32 25.90 66 12.95
- 33 26.71 67 12.14
34 27.52 68 11.33
69
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
s—.-
Hyd. No. 9
2A
Hydrograph type = Rational Peak discharge = 4.51 cfs
Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 3.8 ac Runoff coeff. = 0.35
Intensity = 3.395 in/hr Tc by User = 12 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=3,251 cult
Hydrograph Discharge Table (Pnnted values>=1%Mop)
Time —Outflow
- (min cfs)
1 0.38
2 0.75
3 1.13
4 1.50
5 1.88
6 2.26
7 2.63
8 3.01
9 3.39
_ 10 3.76
11 4.14
12 4.51 «
13 4.14
14 3.76
15 3.39
16 3.01
17 2.63
18 2.26
19 1.88
20 1.50
21 1.13
22 0.75
23 0.38
...End
70
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:28 PM
Hyd. No. 10
OS-1
Hydrograph type = Rational Peak discharge = 8.49 cfs
Storm frequency = 5 yrs Time interval = 1 min
Drainage area = 13.9 ac Runoff coeff. = 0.18
Intensity = 3.395 in/hr Tc by User = 12 min
IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=6,115 cull
Hydrograph Discharge Table (Printea values>.l%alCM)
Time —Outflow
(min cfs)
1 0.71
2 1.42
3 2.12
4 2.83
5 3.54
6 4.25
7 4.95
8 5.66
9 6.37
10 7.08
11 7.79
12 8.49 <<
13 7.79
_ 14 7.08
15 6.37
16 5.66
17 4.95
18 4.25
19 3.54
20 2.83
21 2.12
22 1.42
23 0.71
End
71
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:29 PM
Hyd. No. 11
TOTAL FLOW OFF-SITE
Hydrograph type = Combine Peak discharge = 13.23 cfs
- Storm frequency = 5 yrs Time interval = 1 min
Inflow hyds. = 7, 9, 10
Hydrograph Volume=107,135 cuft
Hydrograph Discharge Table 'Pnmod values
"'%aQp)
- Time Hyd. 7+ Hyd.9+ Hyd. 10= Outflow
(min) (cfs) (cfs) (cfs) (cfs)
1 0.00 0.38 0.71 1.08
- 2 0.00 0.75 1.42 2.17
3 0.01 1.13 2.12 3.26
4 0.01 1.50 2.83 4.35
5 0.02 1.88 3.54 5.44
- 6 0.03 2.26 4.25 6.53
7 0.06 2.63 4.95 7.64
8 0.09 3.01 5.66 8.76
9 0.12 3.39 6.37 9.87
-
10 0.15 3.76 7.08 10.99
11 0.19 4.14 7.79 12.11
12 0.23 4.51 « 8.49 « 13.23 «
13 0.27 4.14 7.79 12.20
14 0.33 3/6 7.08 11.17
15 0.40 3.39 6.37 10.15
16 0.48 3.01 5.66 9.15
- 17 0.55 2.63 4.95 8.14
18 0.62 2.26 4.25 7.13
19 0.70 1.88 3.54 6.12
20 0.77 1.50 2.83 5.11
- 21 0.85 1.13 2.12 4.10
22 0.92 0.75 1.42 3.08
23 0.98 0.38 0.71 2.07
24 1.05 0.00 0.00 1.05
- 25 1.18 0.00 0.00 1.18
26 1.41 0.00 0.00 1.41
27 1.60 0.00 0.00 1.60
28 1.87 0.00 0.00 1.87
-
29 2.30 0.00 0.00 2.30
30 2.66 0.00 0.00 2.66
31 2.97 0.00 0.00 2.97
_ 32 3.22 0.00 0.00 3.22
33 3.43 0.00 0.00 3.43
34 3.61 0.00 0.00 3.61
35 3.77 0.00 0.00 3.77
- 36 3.91 0.00 0.00 3.91
37 4.01 0.00 0.00 4.01
38 4.08 0.00 0.00 4.08
Continues on next page...
_
100-YEAR STORM
I
Hydrograph Summary Report
-
,..wd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph
type flow interval peak hyd(s) elevation storage description
— (origin) (cfs) (min) (min) (cult) (ft) (cuft)
1 Rational 140.58 1 21 177,136 — — 1A
—
2 Rational 64.89 1 15 58,405 -- — 1B
3 Rational 25.62 1 17 26,133 — — IC
— 4 Rational 101.82 1 17 103,860 -- — — 10
5 Rational 40.18 1 12 28,927 — — — 1E
6 Combine 320.93 1 17 394,461 1,2,3,4,5 — POND 1 INFLOW
7 Reservoir 91.61 1 31 372,426 6 4959.15 306,536 PONDI OUTFLOW
8 Rational 217.41 1 41 534,827 — — — HISTORIC
— 9 Rational 1 1456 1 I 12 10,552 — — — 2A
10 Rational' 48.06 1 12 34,605 — — — OS-1
P1 Combine 91.61 1 31 417,582 7,9,10 — — TOTAL FLOW OFF-SITE
—
— L.
—
I
L-• II I I III
KITELEY-COZ-100YR.gpw Return Period: 100 Year Thursday, Sep 29 2005, 6:46 AM
Hydraflow Hydrographs by Intelisolve
3
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
Hyd. No. 1
1A
Hydrograph type = Rational Peak discharge = 140.58 cfs
Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 47.7 ac Runoff coeff. = 0.58
Intensity = 5.081 in/hr Tc by User = 21 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=177,136 cuft
Hydrograph Discharge Table (Pnnted values>=1%of0P)
Time —Outflow Time -- Outflow
- (min cfs) (min cfs)
1 6.69 35 46.86
2 13.39 36 40.17
3 20.08 37 33.47
4 26.78 38 26.78
5 33.47 39 20.08
6 40.17 40 13.39
7 46.86 41 6.69
8 53.56
9 60.25
10 66.94 ...End
11 73.64
12 80.33
13 87.03
14 93.72
15 100.42
16 107.11
17 113.81
18 120.50
19 127.20
20 133.89
21 140.58 <<
22 133.89
23 127.20
24 120.50
25 113.81
26 107.11
27 100.42
28 93.72
29 87.03
30 80.33
31 73.64
32 66.94
33 60.25
34 53.56
4
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
Hyd. No. 2
1B
Hydrograph type = Rational Peak discharge = 64.89 cfs
Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 18.6 ac Runoff coeff. = 0.58
Intensity = 6.015 in/hr Tc by User = 15 min
IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=58,405 cult
Hydrograph Discharge Table (Riotedvalues'.l%u/op.)
Time —Outflow
(min cfs)
1 4.33
2 8.65
3 12.98
4 17.31
5 21.63
6 25.96
7 30.28
8 34.61
9 38.94
10 43.26
11 47.59
12 51.92
13 56.24
14 60.57
15 64.89«
16 60.57
17 56.24
18 51.92
19 47.59
20 43.26
21 38.94
22 34.61
23 30.28
24 25.96
25 21.63
26 17.31
27 12.98
28 8.65
29 4.33
...End
Hydrograph Report
Hydra'low Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
Hyd. No. 3
1C
Hydrograph type = Rational Peak discharge = 25.62 cfs
Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 7.8 ac Runoff coeff. = 0.58
Intensity = 5.663 in/hr Tc by User = 17 min
IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=26,133 tuft
Hydrograph Discharge Table (Punted values'v.1%of°P)
Tine -Outflow
Amin cfs)
1 1.51
2 3.01
3 4.52
4 6.03
5 7.54
6 9.04
7 10.55
8 12.06
9 13.56
10 15.07
11 16.58
12 18.08
13 19.59
14 21.10
15 22.61
16 24.11
17 25.62 «
18 24.11
19 22.61
20 21.10
21 19.59
22 18.08
23 16.58
24 15.07
25 13.56
26i 12.86
2A 10.55
28 9:04
29 7.54
30 6.03
31 4.52
32 3.01
33 1.51
...End
6
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
_ Hyd. No. 4
1O
Hydrograph type = Rational Peak discharge = 101.82 cfs
- Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 31.0 ac Runoff coeff. = 0.58
Intensity = 5.663 in/hr Tc by User = 17 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=103,860 cuft
Hydrograph Discharge Table (Printed values>.1%af Op.)
Time -Outflow
- (min cfs)
1 5.99
2 11.98
3 17.97
4 23.96
5 29.95
6 35.94
7 41.93
8 47.92
9 53.91
10 59.90
11 65.89
12 71.88
13 77.87
14 83.85
15 89.84
16 95.83
17 101.82 «
18 95.83
19 89.84
20 83.85
21 77.87
22 71.88
23 65.89
24 59.90
25 53.91
26 47.92
27 41.93
28 35.94
29 29.95
30 23.96
31 17.97
32 11.98
33 5.99
...End
7
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
Hyd. No. 5
1E
Hydrograph type = Rational Peak discharge = 40.18 cfs
- Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 11.4 ac Runoff coeff. = 0.53
Intensity = 6.649 in/hr Tc by User = 12 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=28,927 cult
Hydrograph Discharge Table (Printed values»1%ofQP)
Time —Outflow
(min cfs)
1 3.35
2 6.70
3 10.04
4 13.39
5 16.74
6 20.09
7 23.44
8 26.78
9 30.13
10 33.48
11 36.83
12 40.18<<
13 36.83
14 33.48
15 30.13
16 26.78
17 23.44
18 20.09
19 16.74
20 13.39
21 10.04
22 6.70
23 3.35
8
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:21 PM
Hyd. No. 6
POND 1 INFLOW
Hydrograph type = Combine Peak discharge = 320.93 cfs
— Storm frequency = 100 yrs Time interval = 1 min
Inflow hyds. = 1, 2, 3, 4, 5
— Hydrograph Volume=394,461 cuff
Hydrograph Discharge Table `p"'ed vat".1%of°`'
— Time Hyd. 1 + Hyd.2+ Hyd. 3+ Hyd.4+ Hyd.5= Outflow
(min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs)
1 6.69 4.33 1.51 5.99 3.35 21.87
— 2 13.39 8.65 3.01 11.98 6.70 43.73
3 20.08 12.98 4.52 17.97 10.04 65.60
4 26.78 17.31 6.03 23.96 13.39 87.46
5 33.47 21.63 7.54 29.95 16.74 109.33
- 6 40.17 25.96 9.04 35.94 20.09 131.19
7 46.86 30.28 10.55 41.93 23.44 153.06
8 53.56 34.61 12.06 47.92 26.78 174.92
9 60.25 38.94 13.56 53.91 30.13 196.79
10 66.94 43.26 15.07 59.90 33.48 218.66
11 73.64 47.59 16.58 65.89 36.83 240.52
12 80.33 51.92 18.08 71.88 40.18 c< 262.39
13 87.03 56.24 19.59 77.87 36.83 277.56
14 93.72 60.57 21.10 83.85 33.48 292.73
15 100.42 64.89« 22.61 89.84 30.13 307.89
16 107.11 60.57 24.11 95.83 26.78 314.41
- 17 113.81 56.24 25.62« 101.82« 23.44 320.93«
18 120.50 51.92 24.11 95.83 20.09 312.45
19 127.20 47.59 22.61 89.84 16.74 303.98
20 133.89 43.26 21.10 83.85 13.39 295.50
- 21 140.58 « 38.94 19.59 77.87 10.04 287.02
22 133.89 34.61 18.08 71.88 6.70 265.16
23 127.20 30.28 16.58 65.89 3.35 243.29
24 120.50 25.96 15.07 59.90 0.00 221.43
- 25 113.81 21.63 13.56 53.91 0.00 202.91
26 107.11 17.31 12.06 47.92 0.00 184.39
27 100.42 12.98 10.55 41.93 0.00 165.87
28 9332 8.65 9.04 35.94 0.00 147.36
-
29 87.03 4.33 7.54 29.95 0.00 128.84
30 80.33 0.00 6.03 23.96 0.00 110.32
31 73.64 0.00 4.52 17.97 0.00 96.13
- 32 66.94 0.00 3.01 11.98 0.00 81.94
33 60.25 0.00 1.51 5.99 0.00 67.75
34 53.56 0.00 0.00 0.00 0.00 53.56
35 46.86 0.00 0.00 0.00 0.00 46.86
- 36 40.17 0.00 0.00 0.00 0.00 40.17
37 33.47 0.00 0.00 0.00 0.00 33.47
38 26.78 0.00 0.00 0.00 0.00 26.78
— Continues on next page...
9
POND 1 INFLOW
Hydrograph Discharge Table
Time Hyd. 1 + Hyd.2+ Hyd. 3+ Hyd.4+ Hyd.5= Outflow
(min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs)
39 20.08 0.00 0.00 0.00 0.00 20.08
40 13.39 0.00 0.00 0.00 0.00 13.39
41 6.69 0.00 0.00 0.00 0.00 6.69
...End
-
Hydrograph Plot
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,7:4 PM
Hyd. No. 7
POND1 OUTFLOW
Hydrograph type = Reservoir Peak discharge = 91.61 cfs
-- Storm frequency = 100 yrs Time interval = 1 min
Inflow hyd. No. = 6 Max. Elevation = 4959.15 ft
Reservoir name = POND 1 Max. Storage = 306,536 cuft
Storage Indication method used. Hydrograph Volume=372,426 cuft
POND1 OUTFLOW
Q(cfs) Hyd. No. 7—100 Yr Q (cfs)
350.00 - -- - ---- 350.00
-
300.00
•
- 250.00 - ... ----.... - - -- — - • - — 250.00
•
200.00 • --- — ---- - - 200.00
150.00 -. . _ ._. . ._ ... ... ... ..-- - ----- -- -_ 150.00
100.00 - . . . -.. . • -..-- - ..._... - - ? -_ _ _ 100.00
50.00 - - 50.00
0.00 l - 0.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
Time(hrs)
Hyd No. 7 Hyd No.6
Pond Report 2
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,7:4 PM
Pond No. 2 - POND 1
.—.
Pond Data
— Pond storage is based on known contour areas. Average end area method used.
Stage/Storage Table
Stage(ft) Elevation(ft) Contour area(sqft) Incr.Storage(cult) Total storage(cuft)
-
0.00 4956.24 89,312 0 0
0.76 4957.00 97,678 71,056 71,056
1.76 4958.00 108,651 103,165 174,221
_ 2.76 4959.00 119,311 113,981 288,202
3.76 4960.00 129,487 124,399 412,601
Culvert/Orifice Structures Weir Structures
— [A] [B] [C] [DI [A] [B] [C] [DI
Rise(in) = 42.00 18.00 0.00 0.00 Crest Len(ft) = 10.00 0.00 0.00 0.00
Spar PI) = 42.00 18.00 0.00 0.00 Crest El.(ft) = 4957.24 0.00 0.00 0.00
-- Its Barrels. = I I 0 0 Weir Coeff. = 3.33 0.00 0.00 0.00
Invert El.(ft) = 4956.04 4956.24 0.00 0.00 Weir Type = Rect — — —
Length(ft) = 135.00 0.00 0.00 0.00 Multistage = No No No No
Slope(X) = 0.01 0.00 0.00 0.00
N-Value = .013 .013 .000 .000
Orii.Coeff. = 0.60 0.60 0.00 0.00
Multi-Stage = n/a Yes No No Exflltratlon= 0.000 in/hr(Contour) Tailwater Elev.= 0.00 ft
— Note:CuivervOrifice outflows have been analyzed under inlet and outlet contra.
Stage(ft) Stage/Discharge stage(ft)
— 400 _ _ _ __ ___. 4.00
— 3.00 - _ • _ _ _. _ . . 3.00
-
2.00 . - __ _ _. 2.00
. .
•
—
1.00 •
_. . •
• - • 1.00
I
I •
0.00 I 0.00
0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00
Discharge(cfs)
— Total CI
1
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Thursday,Sep 29 2005,6:30 AM
Hyd. No. 8
HISTORIC
Hydrograph type = Rational Peak discharge = 217.41 cfs
— Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 126.5 ac Runoff coeff. = 0.5
Intensity = 3.437 in/hr Tc by User = 41 min
- IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=534,827 cuft
- Hydrograph Discharge Table °""'°°values""6d°°'
Time -Outflow Time --Outflow Time -- Outflow
- (min cfs) (min cfs) (min cfs)
1 5.30 35 185.59 69 68.93
2 10.61 36 190.90 70 63.63
- 3 15.91 37 196.20 71 58.33
4 21.21 38 201.50 72 53.03
5 26.51 39 206.80 73 47.72
6 31.82 40 212.11 74 42.42
7 37.12 41 217.41 « 75 37.12
8 42.42 42 212.11 76 31.82
9 47.72 43 206.80 77 26.51
10 53.03 44 201.50 78 21.21
11 58.33 45 196.20 79 15.91
12 63.63 46 190.90 80 10.61
13 68.93 47 185.59 81 5.30
14 74.24 48 180.29
15 79.54 49 174.99
16 84.84 50 169.69 ...End
17 90.15 51 164.38
- 18 95.45 52 159.08 •
19 100.75 53 153.78
20 106.05 54 148.47
21 111.36 55 143.17
- 22 116.66 56 137.87
23 121.96 57 132.57
24 127.26 58 127.26
25 132.57 59 121.96
26 137.87 60 116.66
27 143.17 61 111.36
28 148.47 62 106.05
29 153.78 63 100.75
30 159.08 64 95.45
31 164.38 65 90.15
32 169.69 66 84.84
- 33 174.99 67 79.54
34 180.29 68 74.24
24
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:22 PM
Hyd. No. 9
— 2A
Hydrograph type = Rational Peak discharge = 14.66 cfs
Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 3.8 ac Runoff coeff. = 0.58
Intensity = 6.649 in/hr Tc by User = 12 min
IDF Curve = WELD.IDF Asc/Rec limb fact = 1/1
Hydrograph Volume=10,552 cult
Hydrograph Discharge Table (Pm'edva1 "'%otOp)
Time —Outflow
(min cfs)
1 1.22
2 2.44
3 3.66
4 4.89
5 6.11
6 7.33
7 8.55
8 9.77
9 10.99
10 12.21
r` 11 13.43
12 14.66«
13 13.43
14 12.21
15 10.99
16 9.77
17 8.55
18 7.33
19 6.11
20 4.89
21 3.66
22 2.44
23 1.22
25
Hydrograph Report
Hydrafow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:22 PM
Hyd. No. 10
OS-1
Hydrograph type = Rational Peak discharge = 48.06 cfs
Storm frequency = 100 yrs Time interval = 1 min
Drainage area = 13.9 ac Runoff coeff. = 0.52
Intensity = 6.649 in/hr Tc by User = 12 min
IDF Curve = WELD.IDF Asc./Rec limb fact = 1/1
Hydrograph Volume=34,605 cuft
Hydrograph Discharge Table Minted values>� %dQp)
Time —Outflow
(min cfs)
1 4.01
2 8.01
3 12.02
4 16.02
5 20.03
6 24.03
7 28.04
8 32.04
9 36.05
10 40.05
11 44.06
12 48.06«
13 44.06
14 40.05
15 36.05
16 32.04
17 28.04
18 24.03
19 20.03
20 16.02
21 12.02
22 8.01
23 4.01
26
Hydrograph Report
Hydraflow Hydrographs by Intelisolve Wednesday,Sep 28 2005,6:22 PM
r
Hyd. No. 11
TOTAL FLOW OFF-SITE
Hydrograph type = Combine Peak discharge = 91.61 cfs
- Storm frequency = 100 yrs Time interval = 1 min
Inflow hyds. = 7, 9, 10
- Hydrograph Volume=417,582 cult
Hydrograph Discharge Table (Rimed raiues).-1%map)
Time Hyd. 7+ Hyd.9+ Hyd. 10= Outflow
(min) (efs) (cfs) (cfs) (cfs)
1 0.00 1.22 4.01 5.23
- 2 0.01 2.44 8.01 10.46
3 0.03 3.66 12.02 15.71
4 0.07 4.89 16.02 20.97
5 0.13 6.11 20.03 26.26
- 6 0.19 7.33 24.03 31.55
7 0.27 8.55 28.04 36.86
8 0.39 9.77 32.04 42.20
9 0.54 10.99 36.05 47.58
- 10 0.70 12.21 40.05 52.97
11 0.89 13.43 44.06 58.39
12 1.24 14.66« 48.06« 63.96
13 3.19 13.43 44.06 60.68
14 7.24 12.21 40.05 59.51
15 12.72 10.99 36.05 59.76
16 19.41 9.77 32.04 61.22
- 17 26.71 8.55 28.04 63.30
18 33.99 7.33 24.03 65.35
19 41.46 6.11 20.03 67.59
20 48.89 4.89 16.02 69.80
- 21 56.19 3.66 12.02 71.87
22 63.16 2.44 8.01 73.61
23 69.39 1.22 4.01 74.62
24 74.84 0.00 0.00 74.84
- 25 79.53 0.00 0.00 79.53
26 83.33 0.00 0.00 83.33
27 86.30 0.00 0.00 86.30
28 88.59 0.00 0.00 88.59
- 29 90.24 0.00 0.00 90.24
30 91.21 0.00 0.00 91.21
31 91.61 « 0.00 0.00 91.61 «
_ 32 91.52 0.00 0.00 91.52
33 90.97 0.00 0.00 90.97
34 89.96 0.00 0.00 89.96
35 88.64 0.00 0.00 88.64
- 36 87.17 0.00 0.00 87.17
37 85.54 0.00 0.00 85.54
38 83.74 0.00 0.00 83.74
- Continues on next page...
POND 1
Kiteley Ranch at Foster Lake
Pond 1 Calculations
Date: 8/23/2005
Project#: 4190
Designer: BEC
DESIGN CRITERIA
Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001
DESIGN
- Detention Volume (pond volume calculated using the prismoidal formula):
VOLUME CUMULATIVE CUMULATIVE
CONTOUR(FT) AREA(F7) VOLUME(ACRE
(FT3) VOLUME(FT) FT)
_ 4956.24 89312 0 0 0
4957 97678.0 71032.5 71032.5 1.631 (Ai +Az + A,A;)Depth
4958 108651.0 103115.8 174148.3 3.998 V= 3
4959 119311.0 113939.4 288087.8 6.614
4960 129487.0 124364.3 412452.1 9.469
REQUIRED POND 1 WATER QUALITY STORAGE VOLUME
�—. Design Criteria:
Urban Storm Drainage Criteria Manual; Urban Drainage and Flood Control District,June 2001
Water Quality Volume
Vwq=(WQCV/12)x Area x 1.2
Assumptions:
(1)Additional 20%for sedimentation per city of Aurora
(2)WQCV-.17 inches(From UDFCD,Table SQ-2)
(2)WQCV=a*(.91'I^3-1.19^2+.78i)
where 6hr drain time a=.7
where 12hr drain time a=.8
where 24hr drain time a=.9
where 40hr drain time a=1.0
Impervious(I) 0.4
a 1
Area 105.1 acres
WQCV 0.17984 inches
Sedimentation 1.2
Vwq 1.89 acre-ft
—
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
8.0 CONSTRUCTED WETLANDS BASIN (CWB)- SEDIMENTATION FACILITY
411
wC `^ iii;•‘
yf a ddp.� {' d e&ptt
8.1 Descrip"on
A constructed wetlands basin (CWB) is a shallow retention pond (RP) which requires a perennial base
flow to permit the growth of rushes, willows, cattails, and reeds to slow down runoff and allow time for
sedimentation, filtering, and biological uptake. It is a sedimentation basin and a form of a treatment
plant.
A CWB differ from "natural"wetlands as they are totally human artifacts that are built to enhance
stormwater quality. Sometimes small wetlands that exist along ephemeral drainageways on Colorado's
high plains could be enlarged and incorporated into the constructed wetland system. Such action,
however, requires the approval of federal and state regulators.
Current (1999) regulations intended to protect natural wetlands recognize a separate classification of
_ wetlands constructed for a water quality treatment. Such wetlands generally are not allowed on receiving
waters and cannot be used to mitigate the loss of natural wetlands but are allowed to be disturbed by
maintenance activities. Therefore, the legal and regulatory status of maintaining a wetland constructed
forte primary purpose of water quality treatment, such as the CWB, is separate from the disturbance of
a natural wetland. Nevertheless, the U.S. Army Corps of Engineers has established maximum areas that
can be maintained under a nationwide permit. Thus, any activity that disturbs a constructed wetland
should be first cleared through the U.S. Army Corps of Engineers to ensure it is covered by some form of
an individual, general, or nationwide 404 permit.
8.2 General Application
A CWB can be used as a followup structural BMP in a watershed, or as a stand-alone onsite facility if the
owner provides sufficient water to sustain the wetland. Flood control storage can be provided above the
CWB6 water quality capture volume (WQCV) pool to act as a multiuse facility.
9-1.99 S-53
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
CWB requires a net influx of water to maintain its vegetation and microorganisms. A complete water
budget analysis is necessary to ensure the adequacy of the base flow.
8.3 Advantages/Disadvantages
8.3.1 General.A CWB offers several potential advantages, such as natural aesthetic qualities, wildlife
habitat, erosion control, and pollutant removal. It can also provide an effective followup treatment to
_ onsite and source control BMPs that rely upon settling of larger sediment particles. In other words, it
offers yet another effective structural BMP for larger tributary catchments.
The primary drawback of the CWB is the need for a continuous base flow to ensure viable wetland
growth. In addition, silt and scum can accumulate and unless properly designed and built, can be flushed
out during larger storms. in addition, in order to maintain a healthy wetland growth, the surcharge depth
for WQCV above the permanent water surface cannot exceed 2 feet.
_ Along with routine good housekeeping maintenance, occasional Ynucking out"will be required when
sediment accumulations become too large and affect performance. Periodic sediment removal is also
needed for proper distribution of growth zones and of water movement within the wetland.
8.3.2 Physical Site Suitability. A perennial base flow is needed to sustain a wetland, and should be
determined using a water budget analysis. Loamy soils are needed in a wetland bottom to permit plants
to take root. Exfiltration through a wetland bottom cannot be relied upon because the bottom is either
covered by soils of low permeability or because the groundwater is higher than the wetland's bottom.
Also, wetland basins require a near-zero longitudinal slope, which can be provided using embankments.
8.3.3 Pollutant Removal. See Table SQ-6 for estimated ranges in pollutant removals. Reported
removal efficiencies of constructed wetlands vary significantly. Primary variables influencing removal
efficiencies include design, influent concentrations, hydrology, soils, climate, and maintenance. With
periodic sediment removal and routine maintenance, removal efficiencies for sediments, organic matter,
and metals can be moderate to high; for phosphorous, low to high; and for nitrogen, zero to moderate.
Pollutants are removed primarily through sedimentation and entrapment, with some of the removal
occurring through biological uptake by vegetation and microorganisms. Without a continuous dry-weather
base flow, salts and algae can concentrate in the water column and can be released into the receiving
water in higher levels at the beginning of a storm event as they are washed out.
_ Researchers still do not agree whether routine aquatic plant harvesting affects pollutant removals
significantly. Until research demonstrates and quantifies these effects, periodic harvesting for the general
upkeep of wetland, and not routine harvesting of aquatic plants, is recommended.
S-54 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
8.4 Design Considerations
Figure CWB-1 illustrates an idealized CWB. An analysis of the water budget is needed to show the net
inflow of water is sufficient to meet all the projected losses (such as evaporation, evapotranspiration, and
seepage for each season of operation). Insufficient inflow can cause the wetland to become saline or to
die off.
8.5 Design Procedure and Criteria
The following steps outline the design procedure for a CWB.
1. Basin Surcharge Provide a surcharge storage volume equal to the WQCV based on a
Storage Volume 24-hour drain time, above the lowest outlet(i.e., perforation) in the
basin.
A. Determine the WQCV using the tributary catchments percent
imperviousness. Account for the effects of DCIA, if any, on Effective
Imperviousness. Using Figure ND-1, determine the reduction in
impervious area to use with WQCV calculations.
B. Find the Required Storage Surcharge Volume (watershed inches of
runoff) above the permanent pool level.
Determine the Required Storage (watershed inches of runoff) using
Figure CWB-2, based on the constructed wetland basin 24hour
drain time.
Calculate the Surcharge Volume in acre-feet as follows:
WQCV
Design Surcharge Volume =I I*Area
12 J
In which:
Area =The tributary drainage area tributary to the CWB (Acres).
2. Wetland Pond Depth The volume of the permanent wetland pool shall be no less than 75%
and Volume of the WQCV found in Step 1.
Proper distribution of wetland habitat is needed to establish a diverse
ecology. Distribute pond area in accordance with the following:
TABLE 1
_ Percent of Permanent Water Design
Components Pool Surface Area Depth
Forebay, outlet and 30% to 50% 2 to 4 feet deep
free water surface
areas
Wetland zones with 50% to 70% 6 to 12 inches
emergent vegetation deep'
`One-third to one-half of this zone should be 6 inches deep.
3. Depth of Surcharge The surcharge depth of the WQCV above he permanent poo5 water
WQCV surface shall not exceed 2.0 feet.
9-1-99 S-55
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
4. Outlet Works Provide outlet works that limit WQCV depth to 2 feet or less. Use a
water quality outlet that is capable of releasing the WQCV in no less
than a 24-hour period. Refer to the Water Quality Structure Details
section for schematics pertaining to structure geometry; grates, trash
racks, and screens; outlet type: orifice plate or perforated riser pipe;
cutoff collar size and location; and all other necessary components.
For a perforated outlet, use Figure CWB-3 to calculate the required area
per row based on WQCV and the depth of perforations at the outlet. See
•
the Water Quality Structure Details section to determine the appropriate
perforation geometry and number of rows (The lowest perforations
should be set at the water surface elevation of the outlet pool). The total
outlet area can then be calculated by multiplying the the area per row by
the number of rows.
5. Trash Rack Provide a trash rack of sufficient size to prevent clogging of the primary
water quality outlet. Size the rack so as not to interfere with the hydraulic
capacity of the outlet. Using the total outlet area and the selected
perforation diameter(or height), Figures 6, 6a or 7 in the Water Qaulity
Structure Details section will help to detemrine the minimum open area
required for the trash rack. If a perforated vertical plate or riser is used
as suggested in the Manual, use one-half of the total outlet area to
calculate the trash racld size. This accounts for the variable inundation
of the outlet orifices. Figures 6 and 6a were developed as suggested
standardized outlet designs for smaller sites.
_ 6. Basin Use Determine if flood storage or other uses will be provided for above the , -
wetland surcharge storage or in an upstream facility. Design for
combined uses when they are to be provided for.
7. Basin Shape Shape the pond with a gradual expansion from the inlet and a gradual
contraction to the outlet, thereby limiting short circuiting. The basin
length to width ratio between the inlet and outlet should be 2:1 to 4:1
_ with 3:1 recommended. It may be necessary to modify the inlet and
outlet point through the use of pipes, swales, or channels, to accomplish
this.
8. Basin Side Slopes Basin side slopes are to be stable and gentle to facilitate maintenance
and access needs. Side slopes should be no steeper than 4:1, preferably
5:1 or flatter.
9. Base Flow A net influx of water must be available throughout the year that exceeds
all of the losses. The following equation and parameters can be used to
estimate the net quantity of base flow available at a site:
Q..,
Where:
QNrr = Net quantity of base flow (acre-fUyear)
Qinf,,,„ = Estimated base flow (acre-ft/year) (Estimate by
seasonal measurements and/or comparison to similar
watersheds)
= Loss attributed to evaporation less the precipitation
(acre-ft/year) (Computed for average water surface)
S-56 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
Qscepag,. = Loss (or gain) attributed to seepage to groundwater
(acre-ft/year)
QE 7- = Loss attributed to plant evapotranspiration (computed
for average plant area above water surface, not
including the water surface)
10. Inlet/Outlet Protection Provide a means to dissipate flow energy entering the basin to limit
sediment resuspension. Inlets should correspond to UDFCD drop-
- structure criteria. Outlets should be placed in an offbay that is at least 3
feet deep. The outlet should be protected from clogging by a skimmer
shield that starts at the bottom of the permanent pool and extends above
_ the maximum capture volume depth. Provide for a trash rack also.
11. Forebay Design Provide the opportunity for larger particles to settle out in an area that
has a solid driving surface bottom for vehicles to facilitate sediment
removal. The forebay volume of the permanent pool should be 5 to 10
percent of the design water quality capture volume.
12. Vegetation Cattails, sedges, reeds, and wetland grasses should be plaited in the
weti3nd bottom. Berms and side-sloping areas should be planted Wth
native or irrigated turf-forming grasses. Initial establishment of the
wetlands requires control of the water depth. After planting wetland
species, the permanent pool should be kept at 3 to 4 inches to allow
growth and to help establish the plants, after which the pool should be
raised to its final operating level.
— 13. Maintenance Access Provide vehicle access to the forebay and outlet area for maintenance
and removal of bottom sediments. Maximum grades should not exceed
10 percent, and a stabilized, all-weather driving surface needs to be
provided.
8.6 Design Example
Design forms that provide a means of documenting the design procedure are included in the Design
Forms section. A completed form follows as a design example.
9-1-99 S-57
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL(V.3)
Side Slopes No
Steeper Side Slope No Steeper than 3:1
Than 5:1 -
Forebay � •. Embankment
I,,*
Outlet Works
.' At Ac
Ae � � w Spillway
Maintenance Access
PLAN
NOT TO SCALE
Depth Variation Legend
Innundated 6" below permanent pool
• Innundated to 12"below permanent pool
Inundated 2'to 4'below permanent pool
Permanent Row Baffle
WS. Structure Spillway Crest je/Flow
\� Outlet Works
210 4' 6• 12'
V
1 Cutoff Collar
o0
PROFILE Provide Bottom
NOT TO SCALE Drain
FIGURE CWB-1
Plan and Profile of a Constructed Wetland Basin Sedimentation Facility
S-58
9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
0.50
0.45
Extended Detention Basin
0.40 40-hour Drain Time
u, 0.35 I !Constructed Wetland Basin
24-hour Drain Time
0.30 wocvlRvn.or3-I 1912+n7 i)
V
.c
i 0.255 6-hr drain time a=0.7
12-hr drain time a=0.8
_ 3 24-hr drain time a=0.9
0.20 40-hr drain time a=1.0
cr
3 0.15
Retention Pond,Porous Pavement
0.10 Detention and Porous
Landscape Detention
0.05 12-hour Drain Time
0.00
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Total Imperviousness Ratio(1=/„91100)
FIGURE CWB-2
Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
9-1-99
Urban Drainage and Flood Control District S-59
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL(V.3)
-
10.00 - . Iii
/ 4 4 .
I i
- EXAMPLE: D WQ=2.0 ft 1 I i I {
WQCV=3.2 ACRE - FEET l , ! I I
SOLUTION: REQUIRED AREA PER ROW I
= 13 IN .
—
J r
r I _ .....___ .....
w 1.00 _ _ A i -
® ��
I
J
— co
o 111111 .5,0�
Lr . ,
m 4
r .
el
P ''.
4.
= o
Q
1
3 0.10 _ - EQUATION:
a= WQCV
K24
IN WHICH,
K =0.012DwQ2+0.14DwQ-0.06
r •i
NOTE: DwQ<_2.0 FT FORA CONSTRUCTED WETLAND
-
e.. BASIN (CWB)
I
0.01 ` I r
_ 0.1 1 10 100
Required Area per Row,a(in.2)
Source:Douglas County Storm Drainage and Technical Criteria, 1986.
FIGURE CWB-3
Water Quality Outlet Sizing: Constructed Wetland Basin
With a 24-Hour Drain Time of the Capture Volume
—
S-60 9-1-99
Urban Drainage and Flood Control District
_
POND 2
Kiteley Ranch at Foster Lake
Pond 2 Calculations
Date: 8/23/2005
- Project#: 4190
Designer: BEC
- DESIGN CRITERIA
- Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, June 2001
DESIGN
-Detention Volume (pond volume calculated using the prismoidal formula):
VOLUME CUMULATIVE CUMULA(TNE
CONTOUR(FT) AREA(FT') (Fla) VOLUME(FT') VOLUME(ACRE
4956.78 0 0 0 0
4957 500.0 36.7 36.7 0.001 (A: +A. +JA,A,)Depth
4958 3400.0 1734.6 1771.3 0.041 V =
4959 7750.0 5427.7 7199.0 0.165 3
4960 12020.0 9807.2 17006.2 0.390
4961 14431.0 13207.1 30213.4 0.694
REQUIRED POND 2 WATER QUALITY STORAGE VOLUME
.,-.. Design Criteria:
Urban Storm Drainage Criteria Manual; Urban Drainage and Flood Control District,June 2001
Water Quality Volume
Vwq=(WQCV/12)x Area x 1.2
Assumptions:
(1)Additional 20%for sedimentation per city of Aurora
(2)WQCV-.17 inches(From UDFCD,Table SQ-2)
(2)WQCV=a*(.91*I^3-1.19^2+.78i)
where 6hr drain time a=.7
where 12hr drain time a=.8
where 24hr drain time a=.9
where 401w drain time a=1.0
Impervious(I) 0.4
a 1
Area 3.8 acres
WQCV 0.17984 inches
Sedimentation 1.2
Vwq 0.07 acre-ft
-
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
6.0 EXTENDED DETENTION BASIN (EDB)- SEDIMENTATION FACILITY
V t r " r iI s4
t pd .f
6.1 Description
An extended detention basin (EDB) is a sedimentation basin designed to totally drain dry sometime after
stormwater runoff ends. It is an adaptation of a detention basin used for flood control. The primary
difference is in the outlet design. The EDB uses a much smaller outlet that extends the emptying time of
the more frequently occurring runoff events to facilitate pollutant removal. The EDBS drain time for the
brim-full water quality capture volume (i.e., time to fully evacuate the design capture volume) of 40 hours
is recommended to remove a significant portion of fine particulate pollutants found in urban stormwater
runoff. Soluble pollutant removal can be somewhat enhanced by providing a small wetland marsh or
_ ponding area in the basin's bottom to promote biological uptake. The basins are considered to be"dry"
because they are designed not to have a significant permanent pool of water remaining between storm
runoff events. However, EDB may develop wetland vegetation and sometimes shallow pools in the
bottom portions of the facilities.
_ 6.2 General Application
An EDB can be used to enhance stormwater runoff quality and reduce peak stormwater runoff ra'es. If
_ these basins are constructed early in the development cycle, they can also be used to trap sediment
from construction activities within the tributary drainage area. The accumulated sediment, however, will
need to be removed after upstream land disturbances cease and before the basin is placed into final
long-term use. Also, an EDB can sometimes be retrofitted into existing flood control detention basins.
_ EDBs can be used to improve the quality of urban runoff from roads, parking lots, residential
neighborhoods, commercial areas, and industrial sites and are generally used for regional or follow-up
treatment. They can also be used as an onsite BMP and work well in conjunction with other BMPs, such
as upstream onsite source controls and downstream infiltration/filtration basins or wetland channels. If
S-35
9-1-99
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
desired, a flood routing detention volume can be provided above the water quality capture volume
(WQCV) of the basin.
6.3 Advantages/Disadvantages
6.3.1 General. An EDB can be designed to provide other benefits such as recreation and open space
opportunities in addition to reducing peak runoff rates and improving water quality. They are effective in
removing particulate matter and the associate heavy metals and other pollutants. As with other BMPs,
safety issues need to be addressed through proper design.
6.3.2 Physical Site Suitability. Normally, the land required for an EDB is approximately 0.5 to
2.0 percent of the total tributary development area. In high groundwater areas, consider the use of
_ retention ponds(RP) instead in order to avoid many of the problems that can occur when the EDEt
bottom is located below the seasonal high water table. Soil maps should be consulted, and soil borings
may be needed to establish design geotechnical parameters.
6.3.3 Pollutant Removal. The pollutant removal range of an EDB was presented in Table SQ-6 in the
Storm water Quality Management chapter of this volume. Removal of suspended solids and metals can
be moderate to high, and removal of nutrients is low to moderate. The removal of nutrients can be
improved when a small shallow pool or wetland is included as part of the basin's bottom or the basin is
followed by BMPs more efficient at removing soluble pollutants, such as a filtration system, constructed
wetlands or wetland channels.
The major factor controlling the degree of pollutant removal is the emptying time provided by the outlet.
The rate and degree of removal will also depend on influent particle sizes. Metals, oil and grease, and
some nutrients have a close affinity for suspended sediment and will be removed partially through
sedimentation.
6.3.4 Aesthetics and Multiple Uses. Since an EDB is designed to drain very slowly, its bottom and
lower portions will be inundated frequently for extended periods of time. Grasses in this frequently
inundated zone will tend to die off,with only the species that can survive the specific environment at
each site eventually prevailing. In addition, the bottom will be the depository of all the sediment that
_ settles out in the basin. As a result, the bottom can be muddy and may have an undesirable appearance
to some. To reduce this problem and to improve the basin's availability for other uses (such as open
space habitat passive recreation), it is suggested that the designer provide a lower-stage basin as
suggested in the Two Stage Design procedure.As an alternative, a retention pond (RP) could be used, in
which the settling occurs primarily within the permanent pool.
S-36 9-1-99
Urban Drainage and Flood Control Distract
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
6.4 Design Considerations
Whenever desirable and feasible, incorporate the EDB within a larger flood control basin. Also, whenever
possible try to provide within the basin for other urban uses such as passive recreation, and wildlife
habitat. If multiple uses are being contemplated, consider the multiple-stage detention basin to limit
inundation of passive recreational areas to one or two occurrences a year. Generally, the area within the
_ WQCV is not well suited for active recreation facilities such as ballparks, playing fields, and picnic areas.
These are best located above the WQCV pool level.
Figure EDB-1 shows a representative layout of an EDB. Although flood control storage can be
accomplished by providing a storage volume above the water quality storage, how best to accomplish
this is not included in this discussion. Whether or not flood storage is provided, all embankments should
be protected from catastrophic failure when runoff exceeds the design event. The State Engineer's
regulatory requirements for larger dam embankments and storage volumes must be followed whenever
regulatory height and/or volume thresholds are exceeded. Below those thresholds, the engineer should
design the embankment-spillway-outlet system so that catastrophic failure will not occur.
Perforated outlet and trash rack configurations are illustrated in the typical details section. Figure EDP-3
equates the WQCV that needs to be emptied over 40 hours, to the total required area of perforations per
row for the standard configurations shown in that section. The chart is based on the rows being equally
spaced vertically at 4-inch centers. This total area of perforations per row is then used to determine the
number of uniformly sized holes per row (see detail in the typical details section). One or more
perforated columns on a perforated orifice plate integrated into the front of the outlet can be used. Other
_ types of outlets may also be used, provided they control the release of the WQCV in a manner consistent
with the drain time requirements and are approved in advance by the District.
Although the soil types beneath the pond seldom prevent the use of this BMP, they should be considered
during design. Any potential exfiltration capacity should be considered a short-term characteristic and
ignored in the design of the WQCV because exfiltration will decrease over time as the soils clog with fine
sediment and as the groundwater beneath the basin develops a mound that surfaces into the basin.
High groundwater should not preclude the use of an EDB. Groundwater, however, should to be
considered during design and construction, and the outlet design must account for any upstream base
flows that enter the basin or that may result from groundwater surfacing within the basin itself.
Stable, all weather access to critical elements of the pond, such as the inlet, outlet, spillway, and
sediment collection areas must be provided for maintenance purposes.
9-1-99 S-37
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
6.5 Design Procedure and Criteria
The following steps outline the design procedure and criteria for an EDB.
1. Basin Storage Volume Provide a storage volume equal to 120 percent of the WQCV based on
a 40-hour drain time, above the lowest outlet(i.e., perforation) in the
basin. The additional 20 percent of storage volume provides for
sediment accumulation and the resultant loss in storage volume.
A. Determine the WQCV tributary catchment percent imperviousness.
Account for the effects of DCIA, if any, on Effective Imperviousness.
Using Figure ND-1, determine the reduction in impervious area to
use with WQCV calculations.
B. Find the required storage volume (watershed inches of runoff):
Determine the Required WQCV (watershed inches of runoff) using
Figure EDB-2, based on the ECM 40 -hour drain time.
Calculate the Design Volume in acre-feet as follows:
Design Volume=r WQCV l*Area*1.2
2
In which: Ill J
Area = The watershed area tributary to the extended
detention pond
1.2 factor = Multiplier of 1.2 to account for the additional
20% of required storage for sediment
accumulation
2. Outlet Works The Outlet Works are to be designed to release the WQCV(i.e., not the
Design Volume) over a 40-hour period, with no more than 50 percent
of the WQCV being released in 12 hours. Refer to the Water Quality
Structure Details section for schematics pertaining to structure
geometry; grates, trash racks, and screens; outlet type: orifice plate or
perforated riser pipe; cutoff collar size and location; and all other
necessary components.
For a perforated outlet, use Figure EDB-3 to calculate the required area
per row based on WQCV and the depth of perforations at the outlet. See
the Water Quality Structure Details section to determine the appropriate
perforation geometry and number of rows (The lowest perforations
should be set at the water surface elevation of the outlet micropool). The
total outlet area can then be calculated by multiplying the the area per
row by the number of rows.
S-38 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V. 3) STRUCTURAL BEST MANAGEMENT PRACTICES
3. Trash Rack Provide a trash rack of sufficient size to prevent clogging of the primary
water quality outlet. Size the rack so as not to interfere with the hydraulic
capacity of the outlet. Using the total outlet area and the selected
perforation diameter (or height), Figures 6, 6a or 7 in the Water Quality
Structure Details section will help to detemrine the minimum open area
_ required for the trash rack. If a perforated vertical plate or riser is used
as suggested in the Manual, use one-half of the total outlet area to
calculate the trash rack's size. This accounts for the variable inundation
of the outlet orifices. Figures 6 and 6a were developed as suggested
standardized outlet designs for smaller sites.
4. Basin Shape Shape the pond whenever possible with a gradual expansion from the
inlet and a gradual contraction toward the outlet, thereby minimizing
short circuiting. The basin length to width ratio between the inlet and the
outlet should be between 2:1 to 3:1, with the larger being preferred. It
may be necessary to modify the inlet and outlet points through the use
of pipes, swales or channels to accomplish this.
5. Two-Stage Design A two-stage design with a pool that fills often with frequently occurring
runoff minimizes standing water and sediment deposition in the
remainder of the oasin. The two stages are as follows:
A. Top Stage: The top stage should be 2 or more feet deep with its
bottom sloped at 2 percent toward the low flow channel.
B. Bottom Stage: The active storage basin of the bottom stage should
be 1.5 to 3 feet deeper than the top stage and store 5 to 15 percent
of the WQCV. Provide a micro-pool below the bottom active storage
volume of the lower stage at the outlet point. The pool should be 'A
the depth of the upper WQCV depth or 2.5 feet, whichever is the
larger.
6. Low-Flow Channel Conveys low flows from the forebay to the bottom stage. Erosion
protection should be provided where the low-flow channel enters bottom
stage. Lining the low flow channel with concrete is recommended.
Otherwise line its sides with VL Type riprap and bottom with concrete.
Make it at least 9 inches deep; at a minimum provide capacity equal to
twice the release capacity at the upstream forebay outlet.
7. Basin Side Slopes Basin side slopes should be stable and gentle to facilitate maintenance
and access. Side slopes should be no steeper than 4:1, the flatter, the
better and safer.
8. Dam Embankment The embankment should be designed not to fail during a 100-year and
larger storms. Embankment slopes should be no steeper than 3:1,
preferably 4:1 or flatter, and planted with turf forming grasses. Poorly
compacted native soils should be excavated and replaced. Embankment
soils should be compacted to at least 95 percent of their maximum
density according to ASTM D 698-70 (Modified Proctor). Spillway
structures and overflows should be designed in accordance with local
drainage criteria and should consider UDFCD drop-structure design
guidelines.
9. Vegetation Bottom vegetation provides erosion control and sediment entrapment.
Pond bottom, berms, and side sloping areas may be planted with native
grasses or with irrigated turf, depending on the local setting.
9-1-99
S-39
Urban Drainage and Flood Control District
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
-- 10. Access All weather stable access to the bottom, forebay, and outlet works area
shall be provided for maintenance vehicles. Maximum grades should be
10 percent, and a solid driving surface of gravel, rock, concrete, or
gravel-stabilized turf should be provided.
11. Inlet Dissipate flow energy at pond's inflow point(s) to limit erosion and
promote particle sedimentation. Inlets should be designed in accordance
with UDFCD drop structure criteria or as another type of an energy
dissipating structure.
12. Forebay Design Provide the opportunity for larger particles to settle out in the inlet in an
area that has a solid surface bottom to facilitate mechanical sediment
removal. A rock berm should be constructed between the forebay and
the main EDB. The forebay volume of the permanent pool should be 5
to 10 percent of the design water quality capture volume. A pipe
throughout the berm to convey water the EDB should be offset from the
inflow streamline to prevent short circuiting and should be sized to drain
the forebay volume in 5 minutes.
13. Flood Storage Combining the water quality facility with a flood control facility is
_ recommended. The 10-year, 100-year, or other floods may be detained
above the WQCV. See Section 1.5.5 of the BMP Planning For New
Development and Significant Redevelopmentchapter of this volume for
further guidance.
14. Multiple Uses Whenever desirable and feasible, incorporate the EDB within a larger
flood control basin. Also, whenever possible try to provide for other
urban uses such as active or passive recreation, and wildlife habitat. If
—
multiple uses are being contemplated, use the multiple-stage detention
basin to limit inundation of passive recreational areas to one or two
occurrences a year. Generally, the area within the WQCV is not well
suited for active recreation facilities such as ballparks, playing fields,
and picnic areas. These are best located above the EDB level.
6.6 Design Example
Design forms that provide a means of documenting the design procedure are included in the Design
Forms section. A completed form follows as a design example.
S-40 9-1-99
Urban Drainage and Flood Control Distnct
Y STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL(V.3)
Side Slopes No Steeper than 4:1 Embankment Side Slope
No Steeper than 3:1
Presedimentation _/— Top Stage �'. Embankment
— Forebay / I 2%Slope Floor Drainage
Ft „L,
y- 1 Bottom S Access to Outlet
A A / AStage �\ Outlet wlTrash Rack
C .y.— ry w
'� Channel
J 1
t I
y- . r� Spillway
Maintenance Access
- -•rte
—
PLAN
NOT TO SCALE
,— �...
Emergency Spillway Flood
Water Quality Capture Level
Frequent volume level(including @ Spillway Crest
— Runoff Pool 20%additional volume (e.g. 100-yr,SPF,PMF,etc.)
10%to 25%of WOCV for sediment storage)
Inflow Presedementation Secondary Berm /Spillway Crest
— Forebay f
Top of Low Cutoff Collar
Flow Channel D AEmbankment
Flow wo DBs
— Dispersing Size Outlet& J� s.,. Outflow
OutFlow
Inlet i n Drain Forebay / .�
Volume in 45 R
Minutes Invert of S=0.0%t \Outlet Works
Flow (see detail)
Driving Low
Surface Channel
DMp≥z Dwo(2'Min)
• Could tre Impact Basin,GS8 Drop.Concrete
Rundown.other Hardened Rundown
wet
SECTION
NOT TO SCALE
FIGURE EDB-1
Plan and Section of an Extended Detention Basin Sedimentation Facility
9-1-99
Urban Drainage and Flood Control District S-41
STRUCTURAL BEST MANAGEMENT PRACTICES DRAINAGE CRITERIA MANUAL (V. 3)
0.50
0.45
Extended Detention Basin
40-hour Drain Time
0.40 I I
Constructed Wetland Basin
w 0.35 24-hour Drain Time
0
6-hr drain time a=0.7
Su0.30 — 12-hr drain time a=0.8 Mil
O 24-hr drain time a=0.9
• 0.25 — do hr drain time a=t.o
0.20
U
0.15
0.10 Retention Pond.Porous Pavement
Detention and Porous
_ 0.05 Landscape Detention
12-lour Drain Time
0.00
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Total Imperviousness Ratio(i=1„0100) •
FIGURE EDB-2
Water Quality Capture Volume (WQCV), 80th Percentile Runoff Event
•
S-42 9-1-99
Urban Drainage and Flood Control District
DRAINAGE CRITERIA MANUAL (V.3) STRUCTURAL BEST MANAGEMENT PRACTICES
10.0
6.0
EXAMPLE: DWO= 4.5 ft
WOCV = 2.1 acre-feet
4.0 SOLUTION: Required Area per
Row = 1.75 in?
2.0
_ EQUATION:
WQCV
a= K40
_ 1.0 in which,
K40 =0.013DWQ+0.22DWQ -0.10
— m 0.60
as
^O— .
m 0.40
E O.C�O
cp�
2 OJ �
0.20 elq rbSc
0
ry�l ��
O N.
3 0.10 ^-
0.06
I
0.04 Qr
Oe
0.02
0.01 4.0 6.0
0.02 0.04 0.06 0.10 0.20 0.40 0.60 1.0 2.0
Required Area per Row,a (in.2 )
_ FIGURE EDB-3
Water Quality Outlet Sizing:
Dry Extended Detention Basin With a 40-Hour Drain Time of the Capture Volume
9-1-99 S-43
Urban Drainage and Flood Control District
LEVEL SPREADER
Designing Level Spreaders to Treat Stormwater Runoff
W.F. Hunt', D.E. Line', R.A. McLaughlin2,N.B. Rajbhandari2, R.E. Sheffield'
North Carolina State University
What are Level Spreaders & Why Use Them?
Level spreaders are structures that are designed to uniformly distribute
concentrated flow over a large area. Level spreaders come in many forms, depending on
the peak rate of inflow,the duration of use, the type of pollutant, and the site conditions.
All designs follow the same principle:
1. Concentrated flow enters the spreader through a pipe, ditch or swale.
2. The flow is retarded, energy is dissipated.
3. The flow is distributed throughout a long linear shallow trench or behind a low berm.
_ 4. Water then flows over the berm/ditch, theoretically, uniformly along the entire
length.
_ The use of level spreaders is expected to grow as riparian buffer rules become
widespread throughout North Carolina. Riparian buffers are stream-side vegetated zones.
Buffer requirements state that a minimum of 50' of vegetation must be preserved
_ alongside streams from the top of stream bank.There are many rules regarding riparian
buffers employed across much of central and eastern North Carolina. Another important
component of riparian buffer rules currently adopted in the Neuse and Tar-Pamlico River
Basins is the elimination of concentrated flow of stormwater runoff through a riparian
buffer. The rule specifically states:
"Concentrated runoff from new ditches or manmade conveyances shall be converted to
diffuse flow before the runoff enters the riparian buffer." {Tar-Pamlico Rules (I5A
NCAC 2B .0259 (5) (a)))
The most efficient way of creating diffuse flow is by employing level spreaders.
The pollution removal effectiveness of riparian buffers and vegetated filter strips has
been demonstrated rather extensively. Assuming appropriate widths and hydrology, these
vegetated strips of land remove high percentages of sediment, total nitrogen, and total
phosphorus. if flow through buffers and strips is not concentrated in channels. Level
spreaders help reduce concentrated flow thereby increasing the effectiveness of buffers
and strips.
Types of Level Spreaders & How They are Constructed
All designs follow the same premise: spread concentrated flow out and"release"
the flow simultaneously across the same elevation. Figure I is a small schematic
illustrating the function of level spreaders. Five types of level spreaders are discussed
below.
Department of Biological&Agricultural Engineering
2 Department of Soil Science
N.C. DOT Level Spreader Workshop
February 19,2001 —Raleigh, NC
Figure 1. Purpose and Function of Level Spreader
, , Concentrated Flow
Spread Flow
Across Grade
M `the
reafnwa-
i t s rSc - . ` a
i
Receiving Stream ,16a Y
I. Rock lined Channel
One of the simpler designs, rock-lined channels operate under the assumption that
the lower(downslope) lip of the channel is the same elevation. The channel must be dug
along an elevation contour,which helps make the downstream lip "level." Rock-lined
channel depths and widths tend to be small (6-12") and are flow dependent. The channel
does not serve as a detention device. Standard ABC stone (crusher run) can be used.
Geofabric can be used to underlay the channel and protect the downslope lip, as shown in
— Figure 2. A disadvantage of this type of channel is that it is very hard to get the lip truly
level and keep it that way. The crusher run can prevent uniform flow.
Figure 2. Cross-section of Rock-lined channel with geo-fabric underlay.
Geo-fabric
ow of Water
Typicay 6''
2. Treated Lumber
_ Another simple design is laying treated lumber end-on-end to create a downslope
lip, as shown in Figure 3. Each piece of wood can be easily set to grade. Sometimes the
boards are installed in a trench and serve as the downstream lip so that water can flow out
_ of the level spreader more uniformly. The boards are often supported by rebar driven
into the ground. This effectively marries options I and 2. While 2X6 pretreated lumber
has been most frequently used, other board sizes can work. Joints between boards can be
N . DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
constructed by wrapping cloth around both ends of the board. Maintenance on this
option is very important as tree roots can cause some boards to heave. This option may be
the most aesthetically pleasing and could potentially have a life of 5-10 years.
Figure 3. Installing a Pretreated Lumber Level Spreader
5t '
-a. r
� .
. .t-x 't
;;; : att
3. Concrete Troughs& %3 Pipe
_ A more expensive option is to pour a concrete trough. Standard depths of the
trough will range from 4"to 12."The troughs will be comparably wide. A similar option
is to have the troughs be one-half sections of pipe.Neither option is particularly
aesthetically pleasing, but both are structurally sound.
There are two prime advantages to using a concrete level spreader. The concrete
trough is easy to maintain. If there is a sediment or debris accumulation, the extra
material can be easily shoveled out. Also, this design is the most permanent. While other
level spreader designs may be able to effectively function for a period of 5-10 years,
concrete level spreaders could conceivably have lives as long as 20 years. Accordingly,
long term maintenance should be very low if installed properly.
4. PVC-Silt Fence
One option that has proven particularly effective for removing TSS and reducing
turbidity in runoff from construction areas is a level spreader constructed like a low silt
fence—except in a sturdier fashion. An advantage of this spreader is that it allows water
to seep through the silt fence in addition to having runoff flow over the top. A cross
section of this level spreader is shown in Figure 4.
Rebar is driven into the ground on two feet intervals and capped with a 1.5" PVC
pipe.This pipe is easily made level. Over the pipe sediment control fabric, silt fence
material, is draped over the top of the pipe. This fabric can be backfilled, or trenched into
the ground on the upstream side.
If desired. it is possible to put washed, 57 or 47, stone on either side of the fabric.
No trench is dug with this type of level spreader. The PVC-Silt Fence type of level
spreader may be best used for shorter term purposes, such as during and immediately
after construction projects. This type of level spreader has yet to be tested for long term
usage; so. there is a concern as to the longevity of silt fence material when exposed to
N.C. DOT Level Spreader Workshop
February 19,2001 — Raleigh, NC
direct sunlight. It should be placed away from potential foot traffic, as it can easily be
made unlevel by stepping on it.
Figure 4. Level Spreader Cross-Section and Profile using rebar, silt fence, and PVC.
Sediment control
fabri
Backfill 1.5-in �I f 3-5
PVC pipe in.
2'ft,lylvir rebar
— h s
i
f,.
II e�rS
Helpful Construction Tips
There are several common mistakes during construction that need to be averted.
1. Level Spreaders must be LEVEL. By allowing small variations in height on the
downstream lip of gravel-lined trench, height in lumber boards, concrete channel or
PVC cap, small rivulets will quickly reform. Experience suggests that variations of
more than 0.25 inches will in time cause water to quickly reconcentrate and
potentially erode downstream of the level spreader. It is imperative that the site
selected for level spreader installment be nearly level before construction. A change
in ground elevation of more than 4" across the entire length of the level spreader can
begin to make `level" construction difficult.
2. The downslope side of the level spreader should be clear of debris. Often after
construction, debris such as earth,wood, and other organic matter will accumulate
immediately downstream of the level spreader. This effectively blocks water as it
tries to flow out of the level spreader, forcing it to quickly re-concentrate.
3. Avoid constructing upstream of disturbed area. If a level spreader is installed above a
disturbed area without a good vegetative stand, such as grass or trees, or other ground
cover such as mulch or construction matting, erosion rills will quickly form. Even
sheet flow can initially cause significant downstream erosion on disturbed areas.
4. Do not construct level spreaders in newly deposited fill dirt. Virgin earth is much
more resistant to erosion than fill. Even with what appears to be a good young stand
N . DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
of grass over fill dirt, erosion is likely to occur. Site level spreaders away from newly
_ deposited earth.
5. Except for the PVC-Silt Fence and concrete trough forms of level spreaders, do not
use spreaders to remove sediment. They are not made for removing sand and larger
—
size sediment. Significant sediment deposition in the spreader can render it
ineffective.
Level Spreader System Configuration
Level spreaders are part of a treatment system. This level spreader system consists
of three main parts:. 1. Preliminary treatment, 2. Principal treatment, and 3. Emergency
treatment. Wet ponds, stormwater wetlands, and sand filters each have the same
treatment path as level spreaders. A schematic of the level spreader system configuration
is shown in Figure 5.
Figure 5. Level Spreader System consists of pre-treatment(forebay), principal treatemnt
— (level spreader with grassed buffer), and emergency treatment(reinforced grassy swale
downslope of spreader).
- Level
Spreader Forebay�
• �4
�vv�yt}
l?, ' 4r
.y�y{..<•\.0 , ��► rl' / Reinforced
a
i
y x•,,41 _
- • !,,, , rassy
/ N'�� r�l fin./i.�( h
t7 ' � r
, f,f rf ` ,'I,
,I�t t/�1NI Ii
i "i r r
t
reek ,, .1k,t ,
I. Preliminary treatment. A forebay is commonly used in other practices to drop out
heavy sediment before it enters the main body of the BMP. A stilling area such as a
forebay is particularly useful because flows entering the level spreader should not
—
approach with high energy. There are several procedures for sizing a stilling
basin/forebay. They are included in NC DENR documents such as the Erosion and
N.C. DOT Level Spreader Workshop
February 19, 2001 — Raleigh, NC
Sediment Control Planning and Design Manual and the Stormwater Best
Management Practices Manual.
One simple way of sizing a forebay for a level spreader is to calculate the size a wet
pond would need to be to treat the amount of runoff that would enter the level
spreader.This is typically 1-2% of the watershed area. Were the wet pond to be
constructed, the forebay would account for 5-10% of the pond surface area. Using
these guidelines, the surface area of the level spreader forebay(or series of forebays)
_ would be between 1/2000 to 1/500 the size of the watershed area. Forebay depth
would be relatively shallow (up to 2 feet). The forebay will fill with sediment
periodically and it will need to be cleaned out to continue to function.
2. Principal treatment. Principal treatment tends to be the distinguishing feature of best
_ management practices. For sand filters it is the bed of sand through which water must
infiltrate; whereas, for stormwater wetlands,the principal treatment is the constructed
wetland. The level spreader's principal treatment is the level spreader and the buffer
_ immediately downslope. The sizing of this principal treatment mechanism is the focus
of the second half of this document.
3. Emergency treatment. It is not realistic to expect the level spreader to handle all flows
all the time.There is a limit to the amount of flow a level spreader can reasonably
transport. Once this limit is reached it will be necessary to bypass the excess flow.
This can be done using environmentally sensitive means such as grass swales
— constructed with turf reinforcement mats. Swale design is found in N.C. DENR's
Stormwater Best Management Practice Manual.
The overflow or bypass swale is essential. If all flow from large runoff events were
forced through the level spreader, then new swales or ditches may be eroded by the
concentrated and excess water after it flows over the level spreader. Once these
channels have formed downslope of the level spreader, it will be easier for dispersed
flow to reconcentrate even if the runoff event is relatively small. At that point the
level spreader would lose its design goal: keep overland flow dispersed.
Maximum Flows
The maximum allowable flow,which the level spreader effectively distributes, is
a function of 1. the ability to still inflow before it flows over a level spreader and 2. the
length of the level spreader. If the"stilling" basin in front of a level spreader is a small
stormwater pond and the level spreader is several hundred feet long then the maximum
flow allowed to spill over a level spreader is considerably high. However, normal usage
of level spreaders to disperse parking lot or road runoff does not require a drastic energy
dissipator and excessive lengths.
Design storms
Like any other stormwater quality BMP, level spreaders should be constructed to
treat the water quality storm. This is often the first flush event,which ranges from 0.5" to
1.5" of rain depending on land use and geographic location. A standard 1.0"storm is
most often considered to be the first flush event. For a level spreader to"adequately treat"
N.C. DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
an event, it must be able to disperse a concentrated flow so that no erosion occurs
downslope. In other words a level spreader would fail if any storm event less than a water
quality rainfall (first flush) event creates erosion. It is imperative that other, larger storms
be bypassed without creating additional erosion. This will be discussed later.
_ The length of the level spreader is determined by peak flow. To determine peak
flow from small watersheds, the rational method is typically used. The rational method is
described by the following equation:
Qp = C •I • A
Where Qp is peak flow (in cfs),
C is the Rational Runoff Coefficient(the higher the number the more runoff—as
shown in Table 1),
I is rainfall intensity measured in terms of inches/hour;
A is watershed size in acres.
Assuming a 1.0" event is the design storm, a suggested rainfall intensity(I) is
1"/hour. This describes a 1.0" storm with a one-hour duration that rains at a constant rate.
There are other methods that could be used to calculate the peak flow entering the level
spreader. An example of the method described is shown below:
Table 1. Selection of Rational Coefficients per Land Use. (taken from Malcom, 1997,
and Lindeburg, 1999)
Land Use Runoff Peak Flow per Acre
Coefficient(C) (First Flush=1.0")
Street, Driveway, Sidewalk, Rooftop 0.95 0.95 cfs
Parking Lot 0.90 0.9 cfs
Commercial 0.85 0.85 cfs
Apartments, Schools, Churches 0.60 0.6 cfs
Light Industrial 0.50-0.80 0.5-0.8 cfs
Heavy Industrial 0.60-0.90 0.6-0.9 cfs
Single Family Residential 0.30-0.50 0.3-0.5 cfs
Playground, Lawn w/dense soil & steep slope 0.25-0.35 0.25-0.35 cfs
Park. Cemetery 0.25 0.25 cfs
Lawn on Clay Soil, moderate to flat slope 0.13-0.22 0.13-0.22 cfs
Lawn on Sandy Soil 0.10-0.20 0.1-0.2 cfs
Wooded 0.10-0.20 0.1-0.2 cfs
N . DOT Level Spreader Workshop
February 19,2001 — Raleigh, NC
Example I:
_ Given: 6 acre Watershed comprised of apartments.
Find: Peak flow (Qp) entering the level spreader system
_ 1. From Table 1, the rational coefficient is 0.6 (C=0.6)
2. Assume a first flush event of 1.0"with an intensity of 1"/hour(I=1.0)
3. Multiply C • I • A (with area=6 acres)
Qp=0.6 . 1.0 . 6
4. Peak Flow to be managed by level spreader is 3.6 cfs
Qp= 3.6cfs
Flow Bypass
Most municipalities require stormwater devices such as a level spreader to
_ adequately pass a 10-year storm event. Once the first flush flow has been diverted to the
level spreader, higher runoff rates will bypass the level spreader to avoid overloading the
device. A typical bypass is a grassed swale often employing turf reinforcement matting.
This swale should be designed to carry the 10-year (or other specified) storm event.
There may be particularly sensitive areas where precipitation events with less frequent
return intervals, or greater rainfall amounts, need to be carried.An example would be a
25-year storm. The 10-year peak flow event is calculated similarly to the first flush flow.
The only difference being a change in rainfall intensity. A typical 10-year rainfall
intensity for Raleigh,NC, is 6 in/hour. A flow splitter will need to be constructed to
allow the level spreader to only treat flows resulting from the first flush event. The
splitter will bypass portions of heavier runoff events.
Design to Avoid Downstream Erosion
In determining allowable flows over a level spreader, downstream conditions are
considered. In particular, what is the soil covering: grass, mulch, or something else in
between such as a thicket. The length of level spreader is determined by what's on the
downstream side.
Allowable Velocities
Different ground coverings have different allowable velocities,which is the
maximum velocity of water before it causes erosion. The maximum allowable velocities
for downstream soil covers are shown in Table 2. Please note that tree and shrub riparian
buffer is assumed to have a mulch groundcover.
Table 2. Allowable velocities for downstream covers for channeled flows.
Ground Cover Allowable Velocity
Grass 4 feet per second (fps)
Gravel 5 fps
Mulch 1-2 fps
The level spreader length needs to be designed so that velocities are not exceeded. It is
important to include in the design the following fact: water will recollect as it flows down
N.C. DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
slope. Studies have shown that water that has been distributed across the grade may
recollect in as little as 10-12 feet. Recollection is inevitable. How much recollection is
allowable until flow can no longer be considered sheet flow? It is suggested that once
water is using only 33%of available land (as shown in Figure 6), sheet flow becomes
_ concentrated flow. The distance down slope of the level spreader where only 33%of
available land is used can be described as the level spreader's Effective Distance, or Ed.
Flow beyond the level spreader's effective distance would be considered to be
concentrated, not dispersed.
Figure 6. Concentration of Flow Downslope of Level Spreader Level Spreader
,
I F
o
ytl P
8 q ^Fa^N
Effective �, c t
^E ,
Distance, Ed, fgj
�.4� t^"fy
1
,
4,A A Flow uses only of available la
_ Level spreaders must be designed,therefore, to ensure non-erosive velocities not only at
the time water passes over the level spreader(when flow is theoretically completely
dispersed), but at the time water has reached the effective distance. The more limiting
parameter is the latter. Level spreaders must be designed so that non-erosive velocities
are not exceeded once the flow has traveled the effective distance down slope.
Velocities allowed as water flows over the level spreader must be 33%of the erosive
velocity experienced at the effective distance down slope. So, if a mulch ground covering
is able to withstand velocities as high as 2 feet per second (fps)the design velocity over
the level spreader needs to be 0.67 fps, or 1/3 of the erosive velocity.
Calculating Level Spreader Length
The designer's main goal with level spreader design is to ensure an appropriate length of
a level spreader—a length that does not allow for erosive velocities down slope.
Allowable velocities over a level spreader are summarized in Table 3.
N . DOT Level Spreader Workshop
February 19,2001 — Raleigh,NC
Table 3. Maximum Velocities of Flow Across Level Spreader
_ Down Slope Ground Cover Velocity at Level Spreader "Equivalent"Water Height over
Level Spreader,X
Grass 1.33 fps 0.058 ft
_ Gravel l.5 fps 0.074 ft
Thicket(Shrubs, Grass) 1.33 fps 0.058 ft
Mulch (Trees/Shrubs) 0.67 fps 0.015 ft
Using Allowable Velocities to Establish Level Spreader Length
With an allowable velocity determined based upon down slope ground cover, it is now
possible to calculate the necessary level spreader length.The calculation is based on two
_ equations: 1.the Weir Equation and 2. the Continuity Equation. They are described
below.
_ Weir Equation:
It is assumed that the level spreader functions as a long weir. Flow over a weir is
described by the following equation and graphically shown in Figure 7.
Q = Cw • L • H3/2
Where Q=Flow
L=Length of Level Spreader
Cy,=Weir Coefficient(set to 3)
H = Driving Head (shown in Figure 7)
Flow over the level spreader is a function of its length and the height of water up slope.
Increasing the length reduces the height of water, as they are directly related. This is
important because the height and length of water flow dictates the velocity of flow over
the level spreader. This relationship is shown in the second equation, the continuity
equation.
Continuity Equation:
Q = V •A
_ Where, Q =Flow
V =Velocity
A = Cross-Sectional Area of Flow= (L • 2/3 H)
The allowable velocity is determined by down slope cover(grass, gravel, mulch). This
then dictates the cross-sectional area, L • 2/3H. Combining the two equations lead to the
following relationship:
N.C. DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
V = 1.5 • CW • H ��Z
In this way the height of water flow over the weir is determined for the three down slope
_ cover conditions(grass: 0.09'; gravel: 0.11'; mulch: 0.02'). By inserting this height back
into either the weir equation or continuity equation, it is possible to calculate the length of
level spreader needed to distribute a given flow. An example is shown below and a more
complete list in Table 4 shows required level spreader lengths as a function of flow and
down slope cover.
Figure 7. Weir Equation Inputs Shown during Storm
H H* = 2/3 H
L-444 4 =-44461140,
it yt1410 41,
'T
5 a
Level .
Spreader
r,
f
. sal
9 11 4: " .5.-
J"1
y4
.,a...., , .Y._._.._.,_..s..�.
Example 2: Determine length of level spreader with mulch down slope and an incoming
flow of I cfs.
Use Continuity Equation. Q= V •A =V • 2/3 H • L.
As listed above, Q= l cfs. Cw is set to 3, allowable velocity for mulch down slope (from
Table 3) is 0.67 fps and H = 0.02'. Inserting these known parameters into the continuity
equation gives:
1 cfs= 0.67 fps • 0.02 ft • 2/3 • L
L= I cfs= (0.67 fps • 0.02ft • 2/3)
L= 112 ft
V.C. DOT Level Spreader Workshop
February 19, 2001 —Raleigh, NC
mai
Simple Level Spreader Length Equation:
By combining the equations discussed above a simple equation can be used to calculate
the required length of the j level spreader.
L = Q -- (X • )
Where X="Equivalent" Water Height over Level Spreader(from Table 3, page 9)
V = 1.33 for grass and thicket, 0.67 for mulch, and 1.5 for gravel
Table 4. Level Spreader Lengths as a function of flow and cover down slope
Flow Down slope Cover Length of Level Spreader
(cfs) (feet)
1 Grass 13
2 Grass 26
3 Grass 39
5 Grass 65
_ 10 Grass 130
1 Gravel 9
2 Gravel 18
3 Gravel 27
5 Gravel 45
_ 10 Gravel 90
1 Thicket(Shrubs/Grass) 13
2 Thicket(Shrubs/Grass) 26
3 Thicket(Shrubs/Grass) 39
5 Thicket(Shrubs/Grass) 65
10 Thicket(Shrubs/Grass) 130
1 Mulch (Trees/Shrubs) 100
2 Mulch (Trees/Shrubs) 200
3 Mulch (Trees/Shrubs) 300
5 Mulch (Trees/Shrubs) N/A
10 Mulch (Trees/Shrubs) N/A
Effective Distance
Level Spreaders have a"zone" of influence downstream. As described above,
water eventually congregates into new mini-channels that quickly flow through the
riparian buffer, bypassing the desired function. How quickly water re-congregates is
dependent upon two factors, the ground cover over which water is flowing and how steep
the slope is below the level spreader. Water will recollect more quickly when flowing
N.C. DOT Level Spreader Workshop
February 19,2001 — Raleigh,NC
msm
through a wooded buffer than when flowing over a grassed buffer. Water will typically
_ regroup faster if it flows over steep slopes than over gentle slopes. Effective distances
based upon observed flow recollection are shown below in Table 5.
Table 5. Effective Distance of Level Spreaders
Ground Cover Slope from Level Spreader Effective Distance
to Top of Stream Bank (feet)
Trees/ Shrubs 0-6% 50'
Trees/ Shrubs 6-15% 25'
Trees/ Shrubs >15% 17'
_ Thicket 0-8% 50'
Thicket 8-25% 25'
Thicket >25% 17'
_ Grass 0-8% 50'
Grass 8-25% 25'
Grass >25% 17'
Putting Level Spreaders in Series
_ The outcome of effective distance is that level spreaders may need to be placed in
series, particularly on steeped sloped sites. If a level spreader were installed in a
tree/shrub area 50' from a stream bank with a standard slope of 15%, three level
spreaders in series would be needed to maintain a degree of sheet flow throughout the
riparian buffer. For a quick calculation of the number of level spreaders in series needed
throughout a riparian buffer use the following equation:
Ns = W + Ed
Where: Np=Number of Level Spreaders in Series
W = Width of Riparian Buffer through which flow is spread
Ed=Effective Distance Flow is Sheet Flow (from Table 5)
Example Calculation
A complete level spreader design is reviewed below:
Problem Statement:
A road in a residential development on the western shores of Lake Norman will encroach
within 75 feet of the lake. A 50' foot wooded buffer has just been required along the
Catawba River in Lincoln County. No concentrated flow is allowed through the buffer.
The drainage area (all road runoff) collecting at a point 75' from the lake is 1.2 acres. The
average slope from the roadway to the Lake Norman waterline is 7%. This slope is
continuous. The existing condition is shown in Figure 8.
N.C. DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
S
Figure S. Development Before Level Spreader Installment
Roadway
• Concentrated
unoff
Wooded
50 ft ► Slope @ 7%
alb
Lake Norman
A designer wishes to know the required length and number of level spreaders to keep
flow in the final 50 feet of the buffer dispersed.
I. Find Design Storm
A 1.0 inch first flush storm is decided upon. A rainfall intensity of 1.0 in/hr is
used. Using the Rational Method, the following inputs are needed to calculate
peak flow to be dispersed over the level spreader.
I. Drainage Area (known to be 1.2 acres)
2. Runoff Coefficient(0.90 standard for roadway)
3. Rainfall Intensity(I in/hour)
These parameters are inputs for calculating peak flow using the equation,
Qp = C • I • A,
Where Qp = Peak Flow (cfs), C =Runoff Coefficient, I= Rainfall Intensity
(inches/hour) , and A=Area(acres).
Qp=0.90 • I . 1.20
Qp = I cfs
11. Determine Length of Level Spreader
A. Quick Design:
Both flow and downstream cover are known (l cfs, mulch). From Table 4, the
length of level spreader is found to be 100 feet.
B. Long Design:
I. From Table 3,the maximum velocity allowed over the level spreader
when the down slope condition is tree/shrub is 0.5 fps.
N . DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
ft
Inserting this velocity into the following equation calculates the associated
_ height of water up slope of the level spreader:
V= Cw • H /2
Where, V = 1 fps and Cw is 3. H is found as:
H=(V=Cw)2 = (0.5-3) 2= 0.03
As shown in Figure 7, the height of water as it flows over the level
spreader is 2/3 H. Leaving the following as the height of water directly
over the level spreader(H*) during the peak storm event:
H* = 2/3 H= 0.02
_ 2. Insert H*, Flow, Allowable Velocity into Continuity Equation (or weir
equation)
Q=V • L • H*
L=Q (V • H*)
L= 1 cfs_(0.5 fps • 0.02 ft)
L= 100 feet
_ III. Determine Number of Level Spreaders
Down slope conditions include mulch covering and an average slope of 7%. A
level spreader's effective distance through the buffer can be determined from
Table 5 and is shown to be 25 feet. The riparian buffer width is 50 feet. Using the
following equation the number of level spreaders in series is determined:
N5= W=Ed
_ Inserting W= 50 ft and Ed=25 ft, the Number of Level Spreaders in series needed
to keep flow dispersed is shown as,
N5= 50' =25'
N5= 2
The design is now complete: 2 level spreaders constructed in series that are each 100'
feet long will adequately disperse flow through a 50 feet wide wooded buffer. The buffer
is on land with a slope of 7%. The final design is shown in Figure 9.
N . DOT Level Spreader Workshop
February 19,2001 —Raleigh,NC
Figure 9. Level Spreaders in Series to disperse overland flow into Lake Norman.
Roadway
oncentrated
..:
Runoff
— Level 0o'
Sprea' - x
5' Wooded
Slope @ 7%
25'
Lake Norman
Other Design Factors
Level spreader design described previously was a hydraulic design.There are
other ways of determining level spreader spacing and length. The most closely related to
— - the design presented here is to determine critical shear stress and make sure this stress is
not exceeded.
Level spreaders can be designed so that infiltration rates down slope are met. That
is, flow can be spread out so that water that flows over a level spreader during a first
flush event (such as 1.0"rainfall) is able to infiltrate into the soil down slope.
A third design factor that could be included is riparian buffer effectiveness. Level
spreaders should be designed so that they utilize the minimum width of riparian buffer
found to have a desired pollutant material. For example, studies may indicate that a
grassed buffer on 0-8% slopes is able to remove 90%of TSS within the first 25 feet. If
90%TSS removal is required at a given site, then a level spreader must be sized and
spaced so that at least 25' of buffer down slope is used.
_ Maintenance & Costs
Level spreaders, like any other Best Management Practice (BMP) do require
regular maintenance. This is particularly true of the less structurally sound level spreaders
_ such as PVC-Silt Fence design. Maintenance concerns include cleaning debris that may
accumulate immediately up slope of the level spreader. This prevents long-term clogging.
Debris accumulation could be significant if the level spreader is constructed down slope
of a construction site. As mentioned in the construction tips section, debris can also
gather immediately down slope of the level spreader causing localized damming, forcing
the level spreader to have concentrated flow.
With the exception of the concrete construction, level spreaders must be
occasionally checked to make sure they are still level. Animals, falling limbs, and
differential settling can cause the level spreaders to have low areas on the down slope
N . DOT Level Spreader Workshop
February 19,2001 — Raleigh,NC
end, rendering level spreaders no longer level. Livestock should be fenced out. Often
_ simple visual inspection is adequate. The frequency of inspection is dependant upon site
conditions, including local traffic (by people and other animals) and weather.
Perhaps the best time to inspect is immediately after a large precipitation event. Is
there evidence that flow has congregated sooner than expected?
Level spreaders are a preferred BMP because they are simple to construct and
relatively inexpensive. A two-person crew can construct a 50 feet long wooden or PVC-
silt fence level spreader in a few hours. Per foot material and equipment cost will range
from $3-$10 depending upon the type of level spreader,with the exception of concrete
trough level spreaders,which are substantially more expensive. A sample cost estimation
is shown in Table 6.Note that by comparison, if a sand filter were needed to treat a
comparable amount of runoff, construction costs would range from 10-15 times higher
than level spreader costs shown below.
Table 6. Calculating a Level Spreader Construction Cost for a 100 feet long channel with
wooden 2X6" lower"lip"
Activity Unit Cost Total Cost
(if labor—per hour @ $30/hour
for 2 person crew)
Site Selection & 1 hour- $30 $30
Clearing Location/Path
Trench Excavation 2 hours - $60 $60
Equipment Rental $65/hour $130
2X6 Purchase $2/linear foot $200
Geo-Fabric Purchase $1/ linear foot $100
Geo-Fabric, Wood 3 hours- $90 $90
Installation
TOTAL $600
References
Lindeberg, M. R. 1999. Civil Engineering Reference Manual. Belmont, CA: Professional
Publications, Inc. p 22-10.
Malcom, H. R. 1997. Elements of Stormwater Design, Raleigh,NC;North Carolina State
University- Industrial Extension Service, 85 pp.
N.C. DENR. 1988. Erosion and Sediment Control Planning and Design Manual.
Raleigh,NC: North Carolina Department of Environment and Natural Resources.
N.C. DENR. 1997. Stormwater Best Management Practices Manual. Raleigh,NC: North
Carolina Department of Environment and Environmental Resources—Division of Water
Quality. 85 pp.
N.C. DOT Level Spreader Workshop
February 19, 2001 —Raleigh,NC
Final Drainage and
Erosion Control Report
contains oversized
maps (5 sheets)
Please see original File
Hello