HomeMy WebLinkAbout20123232.tiff RECEIVED
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WELD COUNTY
8120 Gage Street • Frederick, CO 80516 COMMISSIONERS
Bus.: (303) 666-6657 • Fax: (303) 666-6743
November 9, 2012
Weld County Clerk to the Board
915 10" Street, 3`d Floor
Greeley, Colorado 80632
Subject: Varra Companies, Inc. —Western Sugar Reclamation Land Development Project
Technical Revision Application —Permit M2010-049
Materials submitted to the Colorado Division of Reclamation Mining and Safety (CRMS) —
Office of Mined Land Reclamation (OMLR):
ATTACHMENTS:
• Proof of Placement— Weld County Clerk to the Board
• Technical Revision Letter
• Flood Analysis
• Riprap Design Memo
• Riprap Design Spreadsheet Calculations
• Technical Revision - Map
Your signature below acknowledges receipt of the above referenced material, as attached. The
material should he added to the above referenced Application, as originally submitted to the
Weld County Clerk to the Board, and made accessible for public review.
Received On \-112012
By: (711q4
Office of the Weld County Clerk to the Board of County Commissioners
�I1 1(✓ &U1ct CL'.`��� �ld 2012-3232
I k
8120 Gage Street• Frederick, CO 80516
Bus.: (303) 666-6657 • Fax: (303) 666-6743
November 9, 2012
Colorado Office of Mined Land Reclamation
Division of Reclamation Mining and Safety
ATTN: Peter Hays, Environmental Protection Specialist
1313 Sherman Street, Room 215
Denver, Colorado 80203
Subject: Technical Revision—Varra Companies, Inc.
Western Sugar Reclamation Land Development Project - DRMS File No. M-
2010-049
ATTACHMENTS:
• Technical Revision Submittal Fee—Check#: 32391 in the Amount of$216.00.
• Proof of Placement—Weld County Clerk to the Board
• Flood Analysis
• Riprap Design Memo
• Riprap Design Spreadsheet Calculations
• Technical Revision—Map
This Technical Revision (TR) is intended to satisfy the concerns expressed in the September 21,
2012 meeting and now withdrawn TR-01. Two copies of the TR are included along with the
required fee and proof of placement with the Weld County Clerk to the Board, and related
attachments (see above).
As part of this Technical Revision, we will be bonding for the replacement of
embankment material should a flood event occur that would erode the pit walls during the course
of mining. The enclosed riprap design will be the final mitigation for erosion of pit walls post
mining, and will be installed as a part of the final reclamation.
Embankment material required for erosion event during mining
Dimensions taken from Best Case in table 1 in Western Sugar Reclamation Land Development
Project Flood Analysis
Material - (155 ft. wide x 100 ft. long x 45 ft. deep)/2 = 13,000 cy acres —total soil volume
We trust our reply adequately addresses the concerns of the Office. Naturally, should you
require further clarification or additional information, we look forward to working with you.
Thank-you again for your cooperation and kind assistance.
Respectfully,
Varr�panies, Inc.
Brad J es
Civil Engineer
cc. Christopher L. Varra, President
Garrett Varra, Vice President
Varra Companies, Inc.
•
WESTERN SUGAR RECLAMATION LAND DEVELOPMENT PROJECT
FLOOD ANALYSIS
October 8,2012
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))) Vertu Companies, Inc
inns / 8120 Gage Street
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!I� _ Frederick,Colorado 80518
r _ Phone:303-686-8657
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Prepared byr
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XI µr.�. Hydrology
�'�' P.O.Box 6100
Hydraulics Breckenridge,CO 80424
7eellnGlogies Phone:970.5473823
Water Resources www_Oowtechnologies.blz
Project No.: FT121(1
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TABLE OF CONTENTS
Executive Summary 3
I. Introduction 4
II. Methodology 4
III. Project Description and Potential for Site Flooding 5
IV. Headcut Modeling and Berm Width Analysis 5
V. Pit Fill Time 10
VI. Flood Warning Time 10
VII. Tract D 11
VIII. Flood Recession Back into the River vs. Bank Erosion 11
IX. Hard Armoring as an Extra Level of Protection Against Capturing the River 11
X. Discussion and Concluding Remarks 12
References 14
Appendix 15
LIST OF TABLES
Table 1. WinDAM B Results Summary for 100-Foot-Wide Berm—Without 8
Considering Pit Tailwater
Table 2. WinDAM B Results Summary for 100-Foot-Wide Berm—Considering Pit 10
Tailwater
FIGURE
Figure 1. WinDAM B Predicted Headcutting Rate vs. Tract C Fill Time 9
Western Sugar Reclamation Land Development Project
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Technologies
EXECUTIVE SUMMARY
This report discusses a presentation pertaining to flood analysis for the Western Sugar Land
Development Project given by Mr. Douglas J. Trieste, P.H. of Flow Technologies, LLC at a
meeting between the Department of Reclamation, Mining, and Safety and Varra Companies,
Inc. on September 21, 2012. Mr. Trieste is a consultant to Varra Companies, Inc.
The presentation was a follow-up from a July 21, 2012 meeting between DRMS and Varra
Companies, LLC where Mr. Trieste suggested a method for using a dam breach erosion model to
estimate headcutting and erosion from flood flows into a gravel pit. Information presented in this
study adds a high degree of confidence that headcutting due to a 100-yr flood event will not
capture the river; key points are summarized as follows:
• Erosion modeling indicates that a 100-foot berm will not likely erode back to the river.
And being that the Tract C pit rim will be at least 200 ft from the river at the breakout
area (west side of Tract C just upstream from the Oglivy Ditch diversion dam), analysis
considering a 100-ft berm width adds a margin of safety to the results. Note that although
a berm width of 100 ft is referred to with respect to erosion modeling analyses, but in
actuality the berm width for Tract C at the river breakout location will be 200 ft.
• Direction of extraction will be from southwest to northeast on Tract C which means that
extraction begins hundreds of feet from the river. And, it will be approximately 2 to 10
years before the rim of the pit reaches a minimum distance of 200 ft from the river on the
west side of Tract. Thus, due to the longer operation time with a wide berm (greater than
the 200-ft minimum) exposed to the 100-yr flood, that that operation time greatly reduces
the probability of erosion and headcuting back to the river.
• The largest peak discharge on record (107 years of record) at the Cache LaPoudre River
at Greeley stream gage (Colorado Department of Natural Resources ) is 6,090 cfs as
compared to the FEMA Base Flood(100-yr flood) of 10,600 cfs. Thus, the FEMA Base
Flood appears to be high. In any case, the above headcuting and erosion analysis was
performed with the larger FEMA 100-yr discharge which adds conservatism to the
analysis.Note that if the FEMA Base Flood was lower,the Site may not even flood
during a 100-yr event.
• When the ultimate pit is achieved, it will be allowed to fill—and remain full - creating a
reservoir and thereby eliminate headcutting.
In addition, a flood mitigation plan was discussed and solutions agreed upon to minimize risk of
headcutting in the gravel pits that may capture the Cache LaPoudre River(CLPR) should a large
flood occur. That flood mitigation plan will be discussed in a separate document provided by
Varra Companies, Inc.
pg.3
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WESTERN SUGAR RECLAMATION LAND DEVELOPMENT PROJECT
(FILE NO. M-2010-049)
FLOOD ANALYSIS
October 8, 2012
I. INTRODUCTION
As part of a September 21, 2012 meeting with the Colorado Division of Mining, Reclamation,
and Safety(DRMS) and Varra Companies, Inc, a PowerPoint presentation was made by Flow
Technologies, LLC, consultant to Varra Companies, Inc regarding the impacts of the 100-yr
flood on the proposed Western Sugar Land Reclamation Project (Site). In addition, a flood
mitigation plan was discussed and solutions agreed upon to minimize risk of headcutting in the
gravel pits that may capture the Cache LaPoudre River(CLPR) should a large flood occur.
This report discusses flood analysis—in addition to headcutting and erosion analysis - and
findings by Flow Technologies, LLC as discussed in the PowerPoint presentation during the
September 21, 2012 meeting. A flood mitigation plan will be discussed in a separate document
provided by Varra Companies, Inc.
Note that much of the material presented is intended to satisfy the comments and concerns
expressed by DRMS in their letter to, Mr. Chris Varra,Varra Companies, Inc. dated February 27,
2012, Re: Varra Companies, Inc.; Western Sugar Reclamation Land Development Project File
No. M-2010-049; Technical Revision No. 1 (TR-01)Adequacy Review—although not discussed
on an item-by-item basis.
The methodology discussed below was performed for Tract C. However, it also applies to Tract
D because Tract D would receive the same flood discharge as Tract C, and also has basically the
same soil composition.
H. METHODOLOGY
The analysis is three-fold: (1) determine if headcutting back to river is possible using a state-of-
the-art dam breach erosion model, (2) determine if Tract C pit will fill via shutting pumps
allowing ground water inflow before erosion back to river occurs (it is assumed that once pit is
full, no more erosion can occur), and (3) compare pit fill time to flood warning time. That is if
ample warning can be obtained allowing the pit to fill consequently stopping headcutting and
erosion to river, then the river will not be captured by a large flood entering the pit.
pg.4
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III. PROJECT DESCRIPTION AND POTENTIAL FOR SITE FLOODING
3.1 Project Description
The project has been previously described via past submittals to DRMS, and thus won't be
discussed in this report. However, some project drawings are included in the Appendix for
reference.
3.2 Potential for Site Flooding
It is important to note that all flood data and information are based on the FEMA Effective Flood
Insurance Study(FEMA, 1999), and the most recent US Army Corps of Engineers HEC-RAS
study(USACE, 2008). Because this information is the approved FEMA Effective Flood
Insurance Study(FIS), no further flood analysis was performed as such would be contradictory
to the Effective study and not approved by FEMA.
The 100-year flood (Q= 7,080 at the site) does not break out of the right bank of the CLPR in
the vicinity of the Site until entering a reach between Ash Avenue and the Ogilvy Ditch
Diversion Dam. This flow would move from west to east through the Site. There are no detailed
HEC-RAS cross-sections in that reach to substantiate the flooding in detail (Appendix I). The
HEC-RAS water surface profile through the reach is actually below the channel bank grade. But
again, the data and information used is from the FEMA Effective FIS and thus is adopted for the
purpose of this study. Any additional flood study would need to be approved by FEMA before
adopted—a very expensive and time-consuming process.
River Station 26048 (See Appendix) does not indicate right overbank flooding (which would
enter the Site). However, RS 24159 (See Appendix)—which is the approximate center of Tract C
- does indicate right overbank flooding. Such flooding is questionable because a berm runs along
the right channel bank (See Appendix)that is higher than the 100-yr water surface elevation
(WSEL). Thus, it is important to note that flows may not spill overbank in that reach.. Thus, this
flood impact analysis is considered conservative because further detailed HEC-RAS study may
indicate no or minimal flooding onto the Site.
One-hundred year discharge onto the site is based on right overbank flow from RS 24159 (See
Appendix)which is about 900 cfs. Such discharge is the basis for flood analysis in this study.
IV. HEADCUT MODELING AND BERM WIDTH ANALYSIS
4.1 Methodology
A special study was performed to evaluate headcutting and berm width for site-specific
conditions on Tract C. More specifically, the berm will be treated as an earthen dam crest and the
pit side wall the face of a dam. Thus, the berm will be evaluated as an"earthen dam" such that
breach computer modeling technology can be applied. Such modeling will use site-specific soil
physical parameters, flood inflow hydrograph, and state-of-the-art methodology to evaluate
headcutting in the pit and scour over the berm.
pg.5
Western Sugar Reclamation Land Development Project
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Such analysis - as with any computer modeling of natural processes - is not an exact science but
will provide a"sanity check" and relative comparisons of potential for headcutting and erosion.
Such analysis is valuable for determining extent of certain erosion scenarios such as berm width,
tailwater elevation in the pit, time to headcut back to the river, etc.
The dam-breach model being considered is the National Resource Conservation Service (NRCS)
WinDam B (Windows Dam Analysis Modules) (National Resource Conservation Service, 2011.)
WinDam B is a modular software application for the analysis of overtopped earth embankments
(berms in this case) and internal erosion. The model addresses routing of a flood over the dam
and evaluation of the potential for vegetation or riprap to delay or prevent failure of the
embankment (berm in this case). In addition, the model includes erosional failure of an
embankment (berm) through overtopping.
The three-phase erosion model was jointly developed by the Agricultural Research Service
(ARS) and the NRCS. Those three phases are:
1) Phase one of the erosion or failure process is failure of the vegetal cover and development of
concentrated flow.
2) Phase two is downward erosion in the area of concentrated flow, resulting in headcut
formation.
3) Phase three is downward and upstream movement of the headcut, potentially breaching the
dam (or, berm with regard to gravel mines).
Each phase is described by a set of threshold-rate relationships based on the process mechanics.
A headcut erodibility index describes the resistance of the exposed geologic materials to erosive
attack during the third phase of the process.
For a complete erosion estimate, the geotechnical composition must be characterized. Typical
parameters are representative particle size, percent clay fraction, plasticity index, total unit
weight, undrained shear strength, and critical shear stress. Specific to WinDAM B software, the
headcut erodibility index and detachment coefficient also need to be estimated.
4.2 WinDAM B Parameters
4.2.1 Key Parameters
Model parameters are listed in the Appendix. Berm width (dam crest) of 100 ft was applied for
three different scenarios. The scenarios, Weakest, Best, and Strongest involved changing a key
parameter which would result in the model to predict weakest(most) erosion potential, strongest
(least) erosion potential, and best which is in-between weakest and strongest. All parameters
remained constant for the three scenarios except for the erodibility factor, Kd which is the most
sensitive parameter. For this study, Kd had a range of two orders of magnitude from 10 for
Weakest, to 0.1 for Strongest. Such a range of magnitude was chosen to cover a very large range
pg.6
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of erosion possibilities due to the many uncertainties of such modeling with the intent that the
actual values would fall somewhere within the range of model results.
4.2.2 Hydrograph Development
The model is driven by an inflow flood hydrograph based on the right bank overtopping 100-yr
peak discharge of 900 cfs as previously mentioned. The hydrograph was developed by selecting
the largest historic thunderstorm flood, and proportioning the amount of time that it flowed
overbank. A thunderstorm (vs, snowmelt)was the flood of choice because it would have less
warning time to make for a conservative argument that Tract C pit would fill if ample flood
warning (due to shutting pumping and allowing groundwater inflow) is received by Varra
Companies, Inc. before flood flows enter the pit.
Discharge records exist for the Cache LaPoudre River near Greeley, Colorado stream gage
(Cache LaPoudre, 2011) from 1903 to 2011 (see Appendix). Review of those records indicates
that the largest thunderstorm occurred during June, 1947 (see Appendix) . That flood hydrograph
was adjusted by linearly proportioning the ordinates to a ratio of the FEMA Effective 100-yr
discharge to the June 1947 peak discharge (see Appendix ). The purpose of such was to estimate
a flood hydrograph for use in WinDAM B that would have the same peak discharge as the
FEMA Effective 100-yr flood at the site (7,080 cfs). It is important to note that the FEMA Base
Flood (100-yr flood)just upstream from the site is 10,600 cfs which splits to the north leaving
7,080 cfs at the Site. The largest historial peak discharge based on the 107 years of the Cache
LaPoudre River near Greeley streamflow gage is only 6,090 cfs (WY1983)—far short of 10,600
cfs. Thus,the discharge hvdrograph used in this analysis—based on the 100-vr flood-may be
conservative and the FEMA Base Flood is questionable.
After developing a daily peak 100-year hydrograph, another hydrograph was developed that just
considered overbank flow onto Tract C (see Appendix). That was done by subtracting the
difference between the 900 cfs overbank flow (discussed above) and the adjusted 100-yr
hydrograph. Peak discharge is enough to flow overbank for 3 days only- from June 23 to June
25. Because the Greeley gage data are daily peak discharges, the peak was assumed to occur at
12 hours from midnight June 23 and decay through June 25 with all ordinates linearly
proportioned until zero flow occurs (see Appendix ). This is an approximation of an actual
hydrograph (hydrographs are not available),but sufficient for the purpose of this study and the
WinDAM B model. Different hydrograph ordinates would make little difference in the final
model results. The most important factors are the discharge peaks and amount of time that
overtopping is occurring.
4.3. WinDAM B Modeling Results
A summary of headcutting and erosion results is presented below with two different scenarios.
4.3.1. Conservative Scenario -No Pit Tailwater
The first scenario is the most conservative (worst-case)because it is based on the ultimate pit not
being evacuated(i.e., pumps not shut down). That is, it assumes that Tract C has no water and
pg 7
R»?,:!(:_ i Western Sugar Reclamation Laud Development Woject
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remains empty during the flood.Note that this is extremely conservative because,(1)it is highly
unlikely that the pit will be ultimate due to the long time period of extraction(2 to 10 years)
needed to reach that point,and(2)it is highly unlikely that the pit will be empty.This scenario is
included for the purpose of predicting headcutting and erosion in the unlikely event that the pit is
empty.
Results for this scenario are summarized in Table 1 which indicate that it is possible for Tract C
pit to erode across the berm and back to the river for the weakest and best parameter case.
However for the strongest parameter case,results indicate that there will not be erosion back to
the river.
Table 1.WInDAM B Results Summary for I00-foot-Wide Berm-Without Considering Pit
1'aitwater
Timeto- UltimatePlt Max Max Max
Headcut- Warning Fill Time Headcut Headcut Headcut
to-River Time (hrs) " Width length Depth
(hrs) (days)0) (ft) at Top of ((t)
Berm
(D)
Weakest 9 5-7 15 215 100 45
Rest 30 5-7 15 155 lee 45
Strongest v/a 5-7 15 20 20 al 12
(1)Discussed below.
(2)Doesn't erode to river.
4,3,2.Realistic Scenario—Includes Pit Tatlwater
The second scenario is most realistic in that it considers that the pit will be filling due to pro-
actively stopping pumping by Vats Companies,Inc,and also filling of the pit due to overbank
flood flow.Due to such,a"tailwater."hcadcutting will not have the opportunity to erode down
the full depth of the pit.In addition and more importantly,the pit tailwater elevation will
eventually meet that of the foodplain WSEL much sooner than the first scenario and
conseµuently,less time is available for headcutting and erosion.
This scenario is still conservative in that it considers the ultimate pit.In reality,it will be 2 to I0
years before the ultimate pit is achieved decreasing the likelihood of having such available to
hcadcut back to the river(from the 100-yr flood)because direction of extraction will be from
p9.a
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Western Sugar Reclamation Land Development Project
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southwest to northeast. Thus, berm width through most of life of project will be much greater
than 100 ft. Also when the ultimate pit is achieved, it will be allowed to fill—and remain full -
creating a reservoir and thereby eliminate headcutting.
Note that although a berm width of 100 ft is discussed, in actuality the berm width for Tract C at
the river breakout location discussed above will be 200 ft. That width adds more conservatism to
this analysis.
For this scenario, WinDAM B modeling was performed for"Best"parameter input only. This
was because the Weakest Parameter Case is ultra conservative. And if there is no headcutting for
the Best parameter case, there would also be no headcutting for the Strongest Parameter Case. In
addition, the three parameter cases would be confusing on Figure 1 (explained below).
Figure 1 illustrates headcutting rate vs. pit fill time. In approximately 10 hours, the headcutting
elevation meets that of the pit tailwater elevation and headcutting stops.
g
Ape lax• P,r F,1( lime
u670r Tor •f pit
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Figure 1. WinDAM B Predicted Headcutting Rate vs. Tract C Fill Time
pg.9
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Results for this scenario are summarized in Table 2 which indicates that only minimal
headcutting and erosion will occur before the pit tailwater elevation meets that of the floodplain
elevation whereby headcutting and erosion will not occur.
Table 2.WInDA.M B Results Summary for 100-foot-Wide Berm—Considering Mt
Tailwater
Parameter Time to Time to Max Deaden* .,MU r Tidal
Case Headcut to Max Length at Top Headeut Hearleut
River fleadeut of Berm Width Depth
(hrs) (hrs) (ft) (ft) (ft)
•S
Weakest ----
Best N/A 10 20. 20 15
Strongest ------ -- ----.
V.PIT FILL TIME
Tract C pit fill time is based on a combination of groundwater inflow rate with no pumping plus
flood flow due to overbank flow from a 100-yr flood-into the pit.This information is
presented in the Appendix.
Note that the calculations were based on average groundwater inflow and ultimate pit volume
(for conservatism).If a detailed reservoir routing were performed that considers inflow and pit
volume at various time increments,the pit fill time would be less.
VI.FLOOD WARNING TIME
The Colorado Flood Threat Portal(htto:+www.coloradopoodthreat.conu issued by the Colorado
Water Conservation Board(CWCB)includes a daily statewide flood threat bulletin and map,7-
15 day flood threat outlook,and statewide 24-hr precipitation map.
Should a large flood be imminent,appropriate flood threats will be issued by CWCB.As an
example,should a storm similar to the 1947 thunderstorm discussed above occur,there would be
approximately 5-7 days(June 17-June 23)to issue a flood threat as the flood hydrograph
begins rising(around June 17i°).In addition,from June 8—16,there is an antecedent flood
D9 40
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Western Sugar Reclamation Land Development Project
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typical of large storm events. With such an occurrence, it is likely that flood threats would be
issued well in advance of flows that have the potential to flood the Site.
Once flood threats are issued, Varra Companies, Inc. will shut down dewatering pumps for Tract
C allowing the pit to fill. Even with no flood inflow, the pit would fill in approximately 3.5 days
due to groundwater inflow. And once the pit is full, headcutting and erosion would not occur
because of minimal water surface elevation difference between the floodplain and the pit-
eventually the two will be equal.
VII. TRACT D
Per the September 21, 2012 meeting between Varra Companies, Inc and DBMS, it was agreed
that due to the relatively small volume of Tract D, it would fill prior to possibility of headcutting
back to the river. The WinDAM B model results for Tract C berm width also apply to Tract D,
and being that those results indicate that headcutting from a 100-ft berm is unlikely for Tract C,
it would be unlikely for Tract D also—especially considering a much shorter fill time for Tract
D.
VIII. FLOOD RECESSION BACK INTO THE RIVER AND BANK EROSION
Headcutting and bank erosion as the flood recedes is not a concern. This includes flows from the
dewatering ditch that runs between Tracts C and D. As the flood recedes, the river and floodplain
water surface elevations will decrease at the same rate because they are essentially a"pool."
Thus, an elevation gradient will not exist between the floodplain and river which would be
necessary for headcutting and bank erosion.
IX. HARD AMORING AS AN EXTRA LEVEL OF PROTECTION AGAINST
CAPTURING THE RIVER
Analyses such as above can not conclusively predict that the pit will erode back to the river. —it
is impossible to truly predict natural events occurring in nature. However, the results do add a
high degree of confidence that headcutting will not occur back to the river and thereby capture
it.
Because of uncertainties, an extra level of protection will be added to the Site post mining as
agreed upon during the 9/21/2012 meeting between Varra Companies, Inc and DRMS. That
protection will include lining a section of Tract C between the pit rim and river with overtopping
protection (as would be done for an embankment dam) at the breakaway section between Oglivy
Ditch Diversion Dam and Ash Avenue. Such protection will extend from the pit rim to the
normal high water mark of the pit reservoir. Overbank hard armoring protection will be
discussed in detail in a separate document provided by Varra Companies, Inc.
Also, hard armoring protection will be placed around the gas battery in the northeast corner of
Tract C. This design will be discussed in detail in another document provided by Varra
Companies, Inc.
pg. 11
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X. DISSCUSSION AND CONCLUDING REMARKS
Study results indicate that for a major rainfall/runoff event, it is possible to have ample flood
warning time for dewatering pumps to be stopped allowing the ultimate pit(for conservatism) to
fill before headcutting can reach the river.
In addition, in the unlikely event that there is no flood warning and flooding occurs on the Site,
and if rising water surface level - due to inflow from both the river and groundwater(pumps
stopped when flooding is noticed) - in the pit is considered, there will be less time for
headcutting to occur and likely not have sufficient time to erode to the river.
In a situation like Great Western Sugar Reclamation Site (and all others), we can't predict the
future but we can make some reasonable evaluations and assumptions as to flood consequences
and mitigating measures.
The direction of extraction for Tract C will be from southwest to north east. Thus, the berm
width at the western edge of the Site (breakout area just upstream from Oglivy Ditch Diversion
Dam; refer to Appendix, Plate 1, Site Conditions)will be hundreds of feet for many years
(approximately 2 to 10)thereby decreasing the probability of a flood occurring when the project
reaches the ultimate pit. That is, during the majority of the life of the project, the berm width will
be hundreds of feet, with the narrowest berm width being 200 ft.
WinDAM B erosion modeling is not an exact science, but the results appear reasonable and
within the realm of possibility.
Analyses and discussion such as above can not conclusively predict that the pit will erode back
to the river. —it is impossible to truly predict natural events. However, information presented in
this study adds a high degree of confidence that headcutting due to a 100-yr flood event will not
capture the river; key points are summarized as follows:
• Erosion modeling indicates that a 100-foot berm will not likely erode back to the river.
And being that the Tract C pit rim will be at least 200 ft from the river at the breakout
area (west side of Tract C just upstream from the Oglivy Ditch diversion dam), analysis
considering a 100-ft berm width adds a margin of safety to the results.Note that although
a berm width of 100 ft is referred to with respect to erosion modeling analyses, but in
actuality the berm width for Tract C at the river breakout location will be 200 ft. Refer to
the Appendix, Plate 1, Site Conditions for a depiction of setbacks and berm widths for the
Site.
• Direction of extraction will be from southwest to northeast on Tract C which means that
extraction begins hundreds of feet from the river. And, it will be approximately 2 to 10
years before the rim of the pit reaches a minimum distance of 200 ft from the river on the
west side of Tract. Thus, due to the longer operation time with a wide berm (greater than
the 200-ft minimum) exposed to the 100-yr flood, that that operation time greatly reduces
the probability of erosion and headcuting back to the river.
pg. 12
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• The largest peak discharge on record(107 years of record) at the Cache LaPoudre River
at Greeley stream gage (Colorado Department of Natural Resources ) is 6,090 cfs as
compared to the FEMA Base (100-yr) flood of 10,600 cfs. Thus, the FEMA Regulatory
flood appears to be high. In any case, the above headcuting and erosion analysis was
performed with the larger FEMA 100-yr discharge which adds conservatism to the
analysis.Note that if the FEMA Regulatory flood was lower, the Site may not even flood
during a 100-yr event.
• When the ultimate pit is achieved, it will be allowed to fill—and remain full - creating a
reservoir and thereby eliminate headcutting.
pg. 13
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REFERENCES
Cache LaPoudre River near Greeley(1903-01-01 to 2011-12-31), Colorado Department of
Natural Resources, Time Series Identifier 06752500, Reported July 19, 2012
FEMA Flood Insurance Study, Weld County, Colorado Unincorporated Areas, Community
Number 080266, Revised September 22, 1999.
National Resource Conservation Service, WinDAM B Integrated Development Environment
Version 1.0 (http://go.usa.gov/8Oq), Developed by USDA and USACE in cooperation with
Kansas State University(KSU), Copyright (2011)by USDA, USACE, KSU, and SNL.
US Army Corps of Engineers, HEC-RAS Model (2008) obtained from Mr. Derek Glosson,
P.E., CFM, Engineering Development Manager, City of Greeley
pg. 14
1 �
Western Sugar Reclamation Land Development Project
:IOW ... ......
Flood Analysis
7echnolo9ies
APPENDIX
pg. 15
Western Sugar Reclamation Land Development Project
:LOW ... _...
Flood Analysis
Technologies
OVERVIEW OF WESTERN SUGAR
RECLAMATION LAND DEVELOPMENT
PROJECT
pg. 16
i.11'al'•••91 Wuuem Sugar Reclamation Land Development Project
`II ow i4:::::.;"4:-
Flood Amlysie
?ethnologicc
SITE CONDITIONS
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•
I
•I Western Sugar Reclamation Land Development Prq
�AOW •
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Flood Analysts
7eebnologiws
FLOODPLAIN
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1•low L'ie`'�'l Western Sugar Reclamation Land Ikveloptnent Project
Mood Analysis
7crhnologies
FEMA EFFECTIVE FIS RSs(USACE 2003)
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Plats 2-H •rauliC Cross Sections t'�" '+i -1 yr, `- v-. I .n I ,
L
{re 19
•
Western Sugar Reclamation Land Development Project
flOW
Flood Analysis
Technologies
OVERBANK FLOW INTO TRACT C
pg.20
--- Western Sugar Reclamation Land 1)avclaptmcm Project
flow F:„C•
W.:.•.::
Flood Analysis
7achnotogics.
RIVER STATION 26048 (JUST D/S ASH AVE)
a.—.,a.:s•.C$nsu.. Fiat.a2+sInv tomboy na«fl .vaou
a. Jam ra+ nn VD ISM
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p9.21
Western Sugar Reclamation Land Development Project
Flood Analysis
?rchnolooir5
RIVER STATION 24159 (APROX CENTER OF TRACT C)
urnc.rvLamaism Ilia plenaC d l.a arr CG•AC
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'� Western Sugar Reclamation Land Development Project
v IOW ... ......,.
.. .... .... ..
Flood Analysis
7eehnologies
RIVER STATION 24159 (APROX CENTER OF TRACT C)
HEC-RAS HYDRAULIC OUTPUT
Pair pmv=FIST Cfll la POesa WS RS:24159 Palle:/Oar PIS
E.C.en(q 4627.11 Bat In 011 anfl a
vu tNM MI(q GAO 111 WA. 0440 aide 0405
W s.emit) 462171 Read la pg 1400.00 imam 131¢00
anti 0) Re Ana pqq 7a.W 112117 1055.31
Ea Slpapq 11=11011 me pyq 26110 112117 1315/1
a TiS 70es// me n.24610666 M71 4-
TepfYOi p 16833 TOpWS0) 257.17 131.69 1251.8
wings pey as Mgwa pis) 015 au 612
tang opt pq 1111 Met.MOM 0.116 as OM
Can ROI pSq 2227142 Can(d) 24191 1920611 212221
leerVil pq toots wiles Pc pl) 5442 13115 1151.16
1111098() 461¢60 Sep9II) Oa 051 106
216 !bon Par ars) 0.06 171 1M
rain lass 222 On venae MINA L19 15132 O976
Cl E MOM am Cam M s3 2571 1159 116.57
pg.23
•
Western Sugar Reclamation Land Development Project
low ... ...... .
.. .... .... ..
Flood Analysis
7echnotogies
OVERBANK FLOW
HYDROGRAPH DEVELOPMENT
FOR WINDAM B MODEL
pg.24
Weston Sugar Reclamation land Development Frojccl
lose ....
Flood Analysis
.'vt I,rlolo31 es
CACHE LAPOUDRE R. NEAR GREELEY DAILY STREAMFLOW
1903 TO 2011
MSS sea flow Tine Sams Graph Pp I aft
ro:y atcanrw
tar
mp
u:)
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ro: s a a P n a q all
w F L s 5 1 i P al ;x F F s n
nfl fn osnn-wi •nu..e.weua aim r+nawvv,.V x+u
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pa.25
1 •
Western Sugar Reclamation Land Development Project
flow ... . ......
Flood Analysis
Technologies
LARGEST HISTORIC PEAK DISCHARGE
- SNOWMELT HYDROGRAPH WY 1983
Sue d Cdoacb 93.048aIe
D4olplon; CACHE LA MORE RIVER NEAR GREELEY,CO.
in.kiln iduwflc 047S23WDWRA9 aiWkt .47 Oda 391491: DWR
LOoded in Wier[Nike,Dletln: 3.1 Itainen9411 Toe; Saab
WAS MCady,Sn WELD,CO DWIntivost Dally
Loedldln6WC: 101/0607 Dahl UIt RCS
Wide,lanyla0a 40.417786 4044341
Ulu L UTa Y—13 NA3431: 53034.7 44I41142
EWatae lhil: 4410
The hen bate Mabry.
Mal4144DaC 1103 T02010
Sdeced in.bits f font 17034 To 241942
Wa*Year 1963 pen 982 b Sep11983J
Dor Oct Nov Doc Jan Feb Not As Nov Am Ai Me Sc
1 151 124 185 160 110 147' 344 2040 3C 4040 840 173
2 161 117 180 140 i4 131 370 1W0 3820 3700 93 105
3 151 131 186 170 280 118 292 1754 4230 3350 421 167
4 146 115 203 175 135 123 301 1600 6500 3790 201 207
5 144 123 210 185 112 207 301 ISO BA 3170 421 236
6 159 110 210 187 I09 222 24 1551 424 1850 759 225
7 153 111 48 191 106 162 219 1450 4WD 1120 874 195
8 101 113 421 182 103 148 348 1390 4740 MO 306 175
9 138 113 310 175 100 155 355 1410 4520 2010 240 166
10 135 114 217 173 97 157 346 1420 444 2340 210 191
11 135 121 210 182 96 119 424 1380 4580 2700 189 212
12 140 119 2)3 178 98 108 4W 1300 5110 1780 191 203
13 144 105 300 173 97 113 386 1480 6030 1150 478 180
14 140 98 491 171 113 131 385 19)0 8090 715 515 207
15 147 97 318 187 111 47 355 1430 5360 47 435 230
16 135 103 212 116 110 169 340 1370 49%1 853 320 310
17 133 108 2)3 106 14 176 379 1770 4624 30 193 271
IS 138 103 193 108 116 173 385 161 0 4940 588 185 221
19 144 102 186 105 123 NI 3.79 t$0 9010 618 175 196
20 142 103 193 106 14 155 432 1740 5400 809 240 151
21 138 102 193 111 121 155 me 1870 5000 765 335 140
22 133 1W 191 111 121 254 977 2070 WAD 140 304 133
23 133 102 193 108 121 307 2610 230 4070 1810 222 131
24 128 98 180 108 130 227 2385 2350 474 1856 193 149
25 126 97 153 113 140 332 2136 2444 420 CO 18.1 183
28 130 97 191 113 149 328 216 2C0 430 432 155 155
27 133 97 235 165 140 38 270 260 4205 320 210 14
28 133 97 227 173 151 288 193 2440 4256 429 289 140
29 121 100 180 114 — 313 1880 2810 43* 770 257 ISO
30 128 151 140 110 — 342 2720 330 1210 235 130
31 123 — 180 110 — 32 — 3680 — 1260 175 —
1An 123 98 140 105 93 418 216 138 393 30 155 130
Max 181 152 491 191 281 32 2100 3630 9633 440 840 310
042 111/7 VM97 Tx Pt 1.414 17141 78714 Mc 47 19p71 174 went 11016 isnot
pg.26
Western Sugar Reclamation Land Development Project
:IOW ..... _.......
.... .... ..
Flood Analysis
7eehnologies
LARGEST HISTORIC THUNDERSTORM PEAK DISCHARGE
WY 1947
Stele d[dent HydrHaee
OnepBee: CACHE LA P0U0RE RIVER NEAR G EELEY.W.
79,4 Bombs lder,Wbr. 08752780DYYREBwMbr.O Iy Oda Suer. D9YR
Lagoa In Wass taNabq 940kt: 3.1 IYawnaNrtW.: 90.48."
LOONS In Catty.Mai* WELD.CO DMe Senn: Daly
LOUIS I12IC: 1919297 Data Unit CFI
LASS,Lonolludt 40.117759.104N8901
07Y X.WY Y(zone 131411 831: 530544.7,4741882
Ereeaton(Sd): 410
Moo SeMCtedon Nbtoty.
Ayes.Date 1903112016
Seeabd tb.SAN From 19(0-0 t.3131642
War Yew 1947 pc t119469991911917)
b 9e911917)
Dr. Oct Noy Dec Jan Foe Ns As Nay Am A4 Ault So
1 3 22 112 88 88 59 Se 35 11 49 15 43
2 09 40 107 81 4 58 S 29 15 218 15 40
3 0S S 105 72 0 58 S 29 II 106 18 35
4 8 a 108 75 59 62 Q 241 5 79 20 32
5 88 49 105 78 a 68 0 2e 3.4 76 18 31
6 11 45 105 74 53 81 59 15 4 81 19 3t
7 29 51 107 88 51 65 58 37 85 80 17 a
8 32 95 103 64 50 70 58 22 4 48 20 2B
9 19 0 ea 58 4 77 S 22 12 52 20 32
10 27 78 95 58 4 79 2 22 12 62 19 a
11 12 2 91 91 48 4 0 12 2 51 23 34
12 IS S 91 64 4 95 S 402 3S 52 23 32
13 22 S a8 4 a 103 S DO 1S 49 24 29
14 27 112 102 55 a *5 Q 39 149 43 25 23
15 32 120 108 58 S 93 42 27 378 24 27 E
18 33 115 104 48 51 92 4 25 177 18 29 22
17 40 12 93 54 6 154 2 24 54 25 38 21
18 37 10 82 63 51 109 65 19 255 31 37 20
19 30 w 87 72 SI 107 72 9 875 31 35 24
20 25 95 94 87 52 103 65 75 925 30 38 25
21 30 91 90 64 2 93 Q 3 1 1330 24 40 24
22 25 S 89 65 2 4 0 22 2540 21 39 22
23 21 91 91 4 2 88 90 4 9%70 41 59 22
24 18 95 93 70 2 4 A 65 360 79 59 22
25 25 w 4 62 SI 80 35 10 X10 41 02 25
26 24 92 4 62 52 77 94 25 2410 28 59 a
27 21 94 88 83 50 70 34 34 1070 23 53 25
28 27 10 90 65 54 67 35 54 170 19 37 20
29 30 106 73 64 - 4 11 111 1840 10 39 20
30 25 110 74 50 — 80 30 44 1020 15 44 17
31 19 — 78 54 — 59 — 16 — 14 41 —
1An 08 22 73 48 4 58 3) 22 14 10 15 17
l as 40 110 112 68 66 154 72 402 3970 49 62 43
ties 2142 BSA 423 6441 5225 8155 53A 42S5 0t21 63 3258 26.9
Nate:
Yews sewn a rata"years.
A"star yes spry OS of tea prrNara 1r a Wes year b 949trnt r of the cant olrWv year(S Attire the hWmted serer year).
Annual teems and Rata em computed a*on tern-mlaan0 dee.
NC Indicates meta[sine Y not compared beouas of missing data or M data tabs leaf Is meting
8800 Beta 2112-07-19 Page 45 41(9 hammer Rare Dab.2012-01138
pg.27
r Western Sugar Reclamation Land Development Project
" IOW 1::::::• :::•:E
Flood Analysis
Technologies
WY 1947 T-STORM HYDROGRAPH
ADJUSTED TO FEMA Q100 AT SITE
Date DWR Q Adjusted Q Tract C
(June 1947) (cfs) (cfs) O/B Q
17 54 93 0
18 255 441 0
19 875 1514 0
20 925 1600 0
21 1330 2301 0
22 2540 4394 0
23 3970 6868 897*
24 3580 6193 222 *
25 2880 4982 0
26 2410 4169 0
27 2470 4273 0
28 1780 3079 0
29 1640 2837 0
30 1020 1765 0
pg.28
Western Sugar Reclamation Land Development Project
IOW l.c..... ..... .... .....
..
Flood Analysis
Technologies
DEVELOPED HYDROGRAPH FOR WINDAM MODEL
JUNE 23 - 25, 1947
June 23 June 24 June 25
0 0
1 75 25 653 48 222
2 150 26 635 49 213
3 224 27 616 50 204
4 299 28 597 51 194
5 374 29 578 52 185
6 449 30 560 53 176
7 523 31 541 54 167
8 598 32 522 55 157
9 673 33 503 56 148
10 748 34 485 57 139
11 822 35 466 58 130
12 897* 36 447 59 120
13 878 37 428 60 111
14 860 38 410 61 102
15 841 39 391 62 93
16 822 40 372 63 83
17 803 41 353 64 74
18 785 42 335 65 65
19 766 43 316 66 56
20 747 44 297 67 46
21 728 45 278 68 37
22 710 46 260 69 28
23 691 47 241 70 19
24 672 71 9
72 0
*June 23 Qp. Assume flood peaks in 12 hrs.
Western Sugar Reclamation Land Development Project
.. .... .... ..
Flood Analysis
7cchnologles
FLOOD WARNING TIME VS PIT FILL TIME
pg.30
•
•
Weslem Sugar Reclamation Land Development Project
Flood Analcsi..
•
7eeh1,olofgie5
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pp.31
. . a
Wcutcm SV W Reclercwtinn Dlard Development l4ejCCt
Flood Analysis
7ec lrn o l 0.)icti
TRACT C FILL TIME
ESTIMATES
6W Inflow lisle• River Inflow River Inflow Total Inflow Pit nil Time
Ave
Pit Vol((o
45 ft depth)
( 0 (af/day) (e6) (af/day) (aflday) (day*)
712 207.6 0 0 207.6 3.43
712 207.6 100 198 405.6 1.76
712 207.6 200 396 603.6 1.18
712 207.6 300 594 801.6 0.89 _
712 207.6 400 792 999.6 b.71
712 207.6 500 990 1197.6 .59
712 207.6 600 1188 13956 0.51
712 207.6 700 1386 1593.6 0.45
712 207.6 800 1584 1791.6 0.40
712 2074 900 1782 1989.6 0.36
•
P9.32
• a
-Clow Wcatern Sugar Rcclammion I.and Dcvclopuxur Project
........... Flood Analysis
''echno1o9ies
WinDAM B Input Parameters
RUN NUMBER RUN NUMBER RUN NUMBER
PARAMETER 2a 2b 2c
Strongest
Weakest Estimate Best Estimate Estimate
User Specified Discharge Coefficient 3.1 3.1 3.1
Simple Dam Cross-section Template no no no
Earth(Vegetated)0/S Slope
Riprap 0/S Slope
Bare Soli D/S Slope Yes Yes Yes
Perform Breach Analysis Yes Yes Yes
No Breach Analysis
Temple/Hanson
Hanson/Robinson Yes Yes Yes
Total Unit Weight(Ib/ft"3) 115 115 115
Erodibl lity(Kd)(ft/h)/(Ib/ft"2) 10 1 0.1
Undrained Shear Strength(lb/f02) 0 0 0
Critical Shear Shear Stress(Ib/ft"2) 0 0 0
Slope(H/V) 2.0 2.0 2.0
Retardance Curve Index(or,n) 10 10 10
Darn Crest Width(ft) 100 100 100
Retardance Curve Index(or,n) 2.88 2.88 2.88
Vegetal Cover Factor(Bare Soli) 0 0 0
Vegetal Cover Factor(Vegetation) 0.9 0.9 0.9
pa.33
Weston Sugar Reclamation[And Development Pmjcxt
`s Avis
Flood Analysis
�iclmo looits
Plasticity Index 14 14 14
Scope(H/V) 1.5 1.5 1.5
Maintenance Code 2 2 2
Particle Diameter(In) 0.98 0.98 0.98
Retardance Curve Index 0.035 0.035 0.035
Station(ft) 0 0 0
Elev(R) 4630 4630 4630
Station(ft) 500 500 500
Elev(ft) 4630 4630 4630
N/A N/A N/A
Principle Spvn/Rating&Reservoir
Stage Storage
Elevation(ft) 4630 4630 4630
Discharge(cfs) 0 0 0
Reservoir Storage(af) 10 10 10
Reservoir Surface Area(ac) 4 4 4
Start Routing(ft) 4630 4630 4630
Dam Base Elevation(ft) 4585 4585 4585
Tdie QI00 RF HG Q100 RF HG Q100 RF HG
Start Time(hrs) 0 0 0
O100 HG(cfs) see Excel SS see Excel 55 see Excel 55
Time Increment(hr) 1 1 1
Constant Time Increment(hrs) 1 1 1
Variable Time Increment(hrs) n/a n/a n/a
Anal Time Increment his) n/a n/a n/a
Automatically Ad ust durin run No No No
n/a n/a n/a
Taihvater Elevation(ft) 4581 4581 4581
Reservoir Outflow 0 0 0
Number of Auxiliary Spillways 0 0 0
P9.34
Western Sugar Reclamation Land Development Project
Flood Analysis
Technologies
•
pg.35
1
8120 Gage Street• Frederick, CO 80516
Bus.: (303) 666-6657 • Fax: (303) 666-6743
Memo
To: Peter Hays, Environmental Protection Specialist
CC: Tim Cazier, P.E., Environmental Protection Specialist
From: Brad Jones, P.E.
Date: November 9, 2012
RE: Western Sugar Reclamation Land Development Project - DRMS File No. M-2010-049
Per our meeting on September 21, 2012, as well as the request within the (now
withdrawn) February 27, 2012 Technical Revision No. 1 Adequacy Review letter, we have
prepared the following riprap design for the western and eastern edges of Tract C, as well as the
western edge of Tract D adjacent to Tract C. Additionally, we have decided to cut what is
essentially a one foot deep by three hundred foot long broad crest weir between Tract C and
Tract D. This weir will help facilitate a controlled direction of flow of the flood waters, while
also reducing the need for costly, extensive riprap placement along the entire rim of the pit. This
riprap design is intended to be put in place post mining, and concurrent with site reclamation.
These riprap measures are intended to prevent river capture from an outward direction only
(starting internally from Tract C or Tract D), and are not intended to prevent river bank erosion.
Likewise, this riprap is not intended to control flows or prevent any other onsite erosion due to
flood.
The riprap design method used for this project is the "Simplified Design Guidelines for
Riprap Subjected to Overtopping Flow" as prepared by Kathleen H. Frizell, James F. Ruff, and
Subhendu Mishra. This procedure was provided to me by Tim Cazier, P.E. Further, I
corresponded with Tony Wahl, P.E., Hydraulic Engineer at the U.S. Bureau of Reclamation,
regarding some of the input parameters that go into the calculations contained within this design
guideline, as he has experience with this procedure and knows its authors.
Tony has prepared a spreadsheet which summarizes this design guideline and
incorporates the calculations necessary to complete the design exercise. This spreadsheet was
used for the design of the riprap selected, and is attached for your review. The inputs that went
into this design are the following:
•
Overtopping discharge C1 25.49 m3/s (900 cfs)
Embankment length L 91.44 m (300 ft)
Overtopping unit discharge q 0.279 m3/s/m (3 cfs/ft)
Angle of repose of stone $ 42°
Embankment crest width W 4.6 m 15 ft
Discharge coefficient Cd 1.57 m1/2/s
Embankment slope (V:H) S 33%
Embankment slope a 18.3°
Coefficient of uniformity, D6o/Dio Cu 1.75
Porosity p 0.45
Specific gravity of riprap G, 2.65
Specific gravity of water Gw 1
acceleration due to gravity g 9.806 m/s'
Manning equation constant 1
Unfortunately this design guideline was prepared using metric units and thus the inputs had to be
converted prior to their usage. Likewise, the outputs are metric units and must be converted to
English units afterwards.
Regarding the above inputs:
The overtopping discharge of 900 cfs was taken from the "Western Sugar Reclamation
Land Development Project Flood Analysis" that was prepared for us by Flow Technologies,
LLC. This value represents what was expected to overflow on the right bank of the river into the
site. The embankment length of 300 feet is the length of the broad crest weir between Tract C
and Tract D, likewise it represents the length of riprap to be placed on the western bank of Tract
C. All other inputs are physical parameters taken from the site, or are inputs that were
recommended by the graduate student's (Subhendu Mishra) dissertation supporting the
methodology presented in the design guideline.
Outcomes and design:
After inserting the aforementioned inputs into the spread sheet, the D50 size riprap that
satisfies the requirements of the procedure is 0.416 m, or about 16.5 inches average diameter.
Per the guidelines, this riprap will be placed at twice the D50 diameter, which is about 33 inches
deep. Additionally, riprap will be placed over the weir crest (or to rim edge) and down to 5 feet
below static water level. The riprap will be placed over a bedding thickness which will be 12
inches deep. Riprap bedding gradation and design will be in accordance with the U.S.B.R.
Design Standards No. 13 (Embankment Dams), Chapter 7 Riprap Slope Protection. These
bedding requirements are those mentioned in the design guidelines and also confirmed with
Tony Wahl.
Lastly, an approximate 1 foot deep by 300 feet wide cut will be made into the west bank
of Tract C. This cut will then be "feathered" back into the surrounding existing topography at an
approximate two percent grade. The cut will not be a weir, rather its' purpose is to subtly help
direct flow to the riprap portion of the pit and mitigate erosion.
For further details regarding the riprap calculations, please see the attached spreadsheet.
Additional information regarding the methodology used in sizing the riprap can be found in the
"Simplified Design Guidelines for Riprap Subjected to Overtopping Flow", likewise additional
information regarding the bedding requirements can be found in the U.S.B.R. Design Standards
No. 13 (Embankment Dams), Chapter 7 Riprap Slope Protection.
Please feel free to contact us with any other concerns, questions, or requirements.
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LARGE MAP AVAILABLE
FOR VIEWING
AT
THE CLERK TO THE
BOARD ' S OFFICE ,
IN THE
PUBLIC REVIEW FILE .
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