HomeMy WebLinkAbout20001730.tiff PARK ENGINEERING
C,
P CONSULTANTS
SKETCH PLAN STORM DRAINAGE REPORT
FOR
PETERSBURG MINOR SUBDIVISION
Attachment E
Ecsierr
2000-1730
420 21st Ave. Suite 101 • Longmont, CO 80501 • (303) 651-6626 • FAX (303) 651-0331
SKETCH PLAN STORM DRAINAGE REPORT
FOR
PETERSBURG MINOR SUBDIVISION
Prepared for:
Grant& Grant, LLP
Colorado National Bank Building
436 Coffman Street, Suite 200
P.O. Box 908
(303)541-9300
Prepared By:
Park Engineering Consultants
420 21st Avenue, Suite 101
Longmont, Colorado 80501
(303)651-6626
July 9, 1998
PEC Job#221-3
SKETCH PLAN STORM DRAINAGE REPORT
FOR
PETERSBURG MINOR SUBDIVISION
"I hereby certify that this sketch plan drainage report for the Petersburg Minor Subdivision in
Weld County, Colorado was prepared by me(or under my direct supervision)in accordance with
the provisions of the Weld County storm drainage criteria for the owners thereof"
Registered Professional F,P. . perState of Colorado
Tr. -`-0:
SKETCH PLAN STORM DRAINAGE REPORT
FOR
PETERSBURG MINOR SUBDIVISION
GENERAL SITE LOCATION AND DESCRIPTION
The site contains approximately 44.4 acres and is located in the SE 1/4 of Section 9, Township I
North, Range 68 West of the 6th P.M., Weld County, Colorado. More specifically,the site lies
adjacent to and north of Weld County Road 10, approximately 1/2 mile east of Weld County
Road 5, adjacent to and south of the Union Pacific Railroad, and approximately 1/4 mile west of
Weld County Road 7. Community Ditch bounds the southwestern portion of the site and then
flows through the northwestern corner of the site.
Access to the site is from Weld County Road 10. The site consists of pasture and farmed ground,
with three residences and several barns, stalls, and small storage buildings.
TOPOGRAPHY
Pasture and cropland, along with residences on large lots, bound the site on all four sides. There
are approximately five residences located between the site and WCR 7, and approximately 10
residences located between the site and WCR 5.
Located northeast of the center of the site is a dry man-made pond surrounded with trees. There
are very few other trees on the site. The west side of th.e site is located at the top of a gentle ridge,
with the remainder of the site sloping generally to the northeast with slopes ranging from one to
seven percent. A few irrigation laterals from Community ditch provide service to the site. Other
than Community Ditch, there are no other drainageways passing through the site.
GENERAL EXISTING DRAINAGE DESCRIPTION
Approximately 7.8 acres of the site drain to the dry pond,while the remaining 36.6 acres drain
generally northward into the Union Pacific Railroad Right-Of-Way. Some of these flows which
travel northward to the railroad will first flow through neighboring properties to the east and west.
The railroad is depressed below the surrounding ground in this area Flows which enter the
railroad cut travel both eastward and westward,with some flows entering the Community Ditch.
The dry pond is large enough that it retains all of the 100-year runoff.
Located east of the site,the land of the adjacent pasture forms a very broad,undefined
drainageway. There is a manmade pond in this drainageway that contains water and that has no
defined drainage channel leaving it. Overland flows travel northward in this undefined
drainageway to the railroad. There is no culvert under this low point of the railroad bed and it is •
assumed that in a very major storm event the runoff would flow over the tracks and northward
through adjacent pasture.
Since the site is located at the top of a ridge, there is no offsite drainage onto the site except for
Community Ditch. Because the ditch is located along the ridge line it is unlikely that it would be a
major source of offsite storm flows to the site. In the unlikely event that Community Ditch did
overflow its banks within the site, excess water would sheet flow in the patterns described above.
Calculations of historic runoff from the site as well as for the retention capacity of the dry pond
are included in the appendix.
Criteria used for the analysis includes the Urban Drainage and Flood Control District manuals as
well as the Boulder County Storm Drainage Criteria Manual. Retention calculations were
performed using"Intellisolve Hydrosolve Hydrographs" software.
PROPOSED CONDITIONS
The site is to be divided into five lots ranging in size from three to eighteen acres. Three of these
lots will each contain one of the existing three residences. The other two lots will each contain
one residence. Access to the existing and proposed residences will be from WCR 10.
Because this subdivision filing consists of adding two residences into an area of 44.4 acres, the
imperviousness of the site will increase by less than one percent. The proposed building
envelopes are located in an area with slopes from two to four percent. Runoff from the proposed
homes will enter into pasture land and return to a sheet flow pattern similar to the historical
pattern.
On the basis of the large size of the site relative to the size of the proposed improvements, the
proposed drainage conditions will be essentially unchanged from historic conditions and thus have
very little or no drainage impact on neighboring properties. As such,no detention or other
drainage facilities are proposed. _
It is recommended that the residences be elevated at least one foot above surrounding ground to
prevent flooding from irrigation or stormwater runoff.
CONCLUSIONS
On the basis of the large size of the site relative to the size of the proposed improvements,the
proposed drainage conditions will be essentially unchanged from historic conditions and thus have
very little or no drainage impact on neighboring properties. As such,no detention or other
drainage facilities are proposed.
EXHIBIT"A"
Name of Subdivision: tr.
Filing:
Location:
Intending to be legally bound, the undersigned Applicant hereby agrees to provide throughout this
subdivision and as shown on the subdivision final plat County dated , 19
recorded on 19 , in Book _ , Page No. Reception Nc:.
,the following improvements.
(Leave spaces blank where they do not apply)
Estimated
Improvements Unit Cost Construction Cost
Street grading ?.
Street base , < <`r
1
Street paving
Curbs, gutters. &culverts
Sidewalk
Storm sewer facilities
Retention ponds
Ditch improvements
Subsurface drainage
Sanitary sewers
Sanitary sewers
Trunk&forced lines
Mains
Laterals(house connected)
On-site sewage facilities
On-site water supply& storage
Water mains-Includes Bore
Fire hydrants
Survey & street monuments&boxes
Street lighting
Street name signs
Fencing requirements L. 1 .!L
Landscaping
Park improvements
Road Culvert
Grass Lined Swale
Telephone
Gas
Electric
Water Transfer
SUB-TOTAL
9 Revised !2/9
Engineering and Supervision Costs
(testing, inspection, as-built plans and work in addition to preliminary and final plat; supervision of actual
construction by contractors)
TOTAL ESTIMATED COST OF IMPROVEMENTS AND SUPERVISION $ ..5 '/1'
The above improvements shall be constructed in accordance with all County requirements and specifications.
and conformance with this provision shall be determined solely by Weld County,or its duly authorized agent
Said ifroven nts shall be completed according to the construction schedule set out in Exhibit "B".
,
, :a 1
(In corporation, to be signed by President and attested to by Secretary,together with corporate seal.)
Date: r i ,, 'r; .
10 Revised 12/9'
EXHIBIT "B"
Name of Subdivision: rt. II/
e
Filing.:
Location:
Intending to be legally bound. the undersigned Applicant hereby agrees to construct the
improvementsshown on the final subdivision plat of Subdivision.
dated , 19 , Recorded on , 19 , in Book
. Page No. ,Reception No. , the following schedule.
All improvements shall be completed within years from the date of approval of the
final plat.
Construction of the improvements listed in Exhibit"A" shall be completed as follows:
(Leave spaces blank where they do not apply.)
improvements Time for Completion
Site grading •
Street base �i`i c(uca , `f `f 1_.i ! i<. 7 ' �" " •
Street paving f
Curbs, gutters. and culverts
Sidewalk
Storm sewer facilities
Retention ponds
Ditch improvements
Subsurface drainage _
Sanitary sewers
Trunk and forced lines
Mains
Laterals (house connected)
On-site sewage facilities
On-site water supply and storage
Water mains
Fire hydrants
Survey& street monuments& boxes
Street lighting
Street name signs
Fencing requirements ' Z -. rerr 'a t• '`'`
Landscaping /
Park improvements
Telephone
Gas
Electric
Water Transfer
Sub-Total
11 Revised i2!9.;
The County, a,its option, and upun.the request by the Applicant, may grant a,extension of time for
completion for any particular improvements shown above, upon a showing by the Applicant that the
above scltule,cannot be met.
(7,/
(If corporation,to be signed by President and attested to by Secretary,together with corporate seal.)
Date: �i .Z. .
m'.\ronmaprivate.db
12 Revised 12.91
C'
APPENDIX
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UUULDER COUNTY
STORM RAINAGE CRITERIA MAN. ",L ' FIGURE 601
RAINFALL ZONES
•
SCALE '
10 5 0 IOMILES
I:500,000
p \\
• 1 LARIMER x
COUNTY i S
b
LYONS
::::::•I V.;.:.v.:C:;:::. ••7 .}:'{'I'}:}::: I I.NGM•
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o GILPIN ` r
COUNTY JEFFERSON �f"
COUNTY S'
•
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WRC ENG. REFERENCE:
Base map from USGS map for State of Colorado,' Rev 1980
BOULDER COUNTY
. STORM .,RAINAGE CRITERIA MAN ...XL ' FIGURE 602
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WRC .ENG. REFERENCE: WRC TM-1 NOV. 1983
DRAINAGE CRITERIA MAhuAL RUNOFF
TABLE 3-1 (42)
RECOMMENDED•RUNOFF COEFFICIENTS AND PERCENT IMPERVIOUS
LAND USE OR PERCENT FREQUENCY
SURFACE CHARACTERISTICS IMPERVIOUS 2 5 10 100
Business:
Commercial Areas 95 .87 .87 .88 .89
Neighborhood Areas 70 .60 .65 . 70 .80
Residential :
Single-Family * .40 .45 .50 . 60
Multi-Unit (detached) 50 .45 .50 .60 .70
Multi-Unit (attached) 70 .60 .65 .70 .80
1/2 Acre Lot or Larger * .30 .35 .40 .60
Apartments 70 .65 .70 .70 .80
Industrial :
Light Areas 80 .71 .72 .76 .82
Heavy Acres 90 .80 .80 .85 .90
Parks , Cemetaries: 7 . 10 . 18 .25 .45
Playgrounds: 13 . 15 .20 .30 .50
Schools: 50 .45 .50 .60 .70
Railroad Yard Areas 20 .20 .25 .35 .45
Undeveloped Areas :
Historic Flow Analysis- 2 (See "Lawns")
Greenbelts, Agricultural
Offsite Flow Analysis 45 .43 .47 .55 .65
(when land use not defined)
Streets:
Paved 100 .87 .88 .90 .93
Gravel (Packed) 40 .40 .45 .50 .60
Drive and Walks: 96 .87 .87 .88 .89
Roofs: 90 .80 .85 .90 .90
Lawns , Sandy Soil 0 .00 .01 .05 .20
Lawns , Clayey Soil 0 .05 .15 .25 .50
NOTE: These Rational Formula coefficients may not be valid for large basins.
*See Figure 2-1 for percent impervious.
11-1-90 ;
URBAN DRAINAGE AND FLOOD CONTROL DISTRICT
DRAINAGE CRITERIA MANUAL RUNOFF
50
30 -- --_ _
I- 20 ,./o
o
Z 4
W p #
i
O 'N' tiw U1O z VA
Ac�r 'i O ° ��N ? „ a 4r--'O 3 o A.
s
o
W 2 y Q, ----
4CY
1 414
QPP
.5 I I "■
1 .2 .3 .5 1 2 3 5 10 20
VELOCITY IN FEET PER SECOND
FIGURE 3-2. ESTIMATE OF AVERAGE FLOW VELOCITY FOR
USE WITH THE RATIONAL FORMULA.
f MOST FREQUENTLY OCCURRING "UNDEVELOPED"
LAND SURFACES IN THE DENVER REGION.
REFERENCE: "Urban Hydrology For Small Watersheds" Technical
Release No. 55, USDA, SCS Jan. 1975.
5 .1-84
URBAN DRAINAGE & FLOOD CONTROL DISTRICT
TCHIS 1.XLS
TIME OF CONCENTRATION WORKSHEET
PETERSBURG MINOR SUBDIVISION
HISTORIC FLOW ANALYSIS
sub-basin initial/overland time, Ti travel time, Tt1 total time
name length slope C5*"" Ti` length swale type slope velocity" TV" Tc=Ti+Tt1+Tt2
(ft) (%) (min) (ft) (%) (f/s) (min) (min)
A 500 1.9 0.08 33.1 200 grass 2.5 2.5 1.3 34.5
B 500 1.9 0.08 33.1 730 grass 2.5 2.5 4.9 38.0
'Ti from equation 3-3 of Urban Drainage and Flood Control manual
"From figure 3-2 of Urban Drainage and Flood Control manual
"*Tt = travel length/travel velocity
""'From Table 3-1 of UDFCD Manual: assume c-value for"undeveloped Areas:
Historic Flow Analysis- Greenbelts, Agricultural" = lawns of mixed clay and silty soils.
SF3H100.XLS
PROJECT: PETERSBURG MINOR SUBDIVISION
HISTORIC FLOW ANALYSIS
STANDARD FORM SF-3 (RUNOFF)
STORM DRAINAGE SYSTEM DESIGN
(RATIONAL METHOD PROCEDURE)
design event area runoff Tc C x A I•' Q
area (acres) coeff.' (min) (acres) (in/hr) (cfs)
Basin A 100-year historic 7.8 0.35 35 2.73 3.95 10.8
Basin A 10-year historic 7.8 0.15 35 1.17 2.50 2.9
Basin A 5-year historic 7.8 0.08 35 0.62 2.05 1.3
Basin B 100 year historic 36.6 0.35 38 12.81 3.75 48.0
Basin B 10-year historic 36.6 0.15 38 5.49 2.35 12.9
Basin B 5-year historic 36.6 0.08 38 2.93 1.95 5.7
'From Table 3-1 of UDFCD Manual: assume c-value for"undeveloped Areas:
Historic Flow Analysis-Greenbelts, Agricultural" = lawns of mixed clay and silty soils.
"From Figure 502 of Boulder County Storm Drainage Criteria Manual -Zone I
nyus uyrapn summary Report
Rage 1
I ________.
Hyd• Hydroyraph Peek Time Time to Volume Return Inflow
No. type flow IntervalMavto Maximum Hydrograph
peak period hyd(s) elevation storage
( (�9in) (eh) (min) (min) (�) (Yrs) (n) (acft) description
1 Rational 10.9 1 34 0.66 100
--- Dry Pond Reten
2 Reservoir 0.0 1 10 0.02 100 1 5114.57 0.67
•
,4 file: DRYPOND.GPW IDF file: BCZONEI.IDF Run date: 06-29-1998
1 - Rational - 100 Yr - Qp = 10.85 cfs
15
10
Q cfs ,
5 ► / Out
0
0.0 0.5 1.0 1.5 2.0
Time(Ms)
&SEA O Po,J
Zou DER GouNTY
�oNE T z - D - cuRvEs
(DRY n,4b) Stage / Storage
C s
4- -
3-
Stage(ft)
2 -
1
0
0.0 0.5 1.0 1.5 2.0
Storage(acft)
r
2 leservoir - 100 Yr - Max. El. = 14.57 ft
5115.0
5114.2
5113.4 _
Elev(ft)
5112.6
5111.81
5111.0
0 5 10 15 20 25
Time(hrs)
Dg PoND ST0RA6E 2TENTielk) 1) ErrN
f
s
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