HomeMy WebLinkAboutWPO201100071 Correspondence 2012-02-14 OUNTY OF ALBEMARI
Department of Community Development
REVISED APPLICATION SUBMITTAL
This form must be returned with your revisions to ensure proper tracking and
distribution. County staff has indicated below what they think will be required as a
resubmission of revi ons. If you need to submit additional information please explain on
this form for the b efit of the intake staff. All plans must be collated and folded to fit
into legal size flu , in order to be accepted for submittal.
TO: 71-I DATE: 2/19/1Z
PROJECT N E: 5��EY � A -t7
Submittal Type Requiring Revisions()indicates Submittal Code County Project dumber #Copies
Erosion& Sediment Control Plan(E&S) —20��co U i Z_.__
Mitigation Plan(MP)
Waiver Request(WR) 'i
Stormwater Management Plan(SWMP)
Road Plan(RP)
Private Road Request,with private/public comparison
(PRR)
Private Road Request—Development Area(PRR-DA)
Preliminary Site Plan(PSP)
Final Site Plan(or amendment)(FSP)
Final Plat(FP)
Preliminary Plat(PP)
Easement Plat(EP)
Boundary Adjustment Plat(BAP)
Rezoning Plan(REZ)
Special Use Permit Concept Plan(SP-CP)
Reduced Concept Plan(R-CP)
Proffers(P)
Bond Estimate Request(BER)
Draft Groundwater Management Plan(D-GWMP)
Final Groundwater Management Plan(F-GWMP)
Aquifer Testing Work Plan(ATWP)
Groundwater Assessment Report(GWAR)
Architectural Review Board(ARB)
Other: Please explain:
(For staff use only)
Submittal # Distribute To: Submittal # Distribute To:
Code Copies Code Copies
*Unassigned(in County Project Column)—Intake to assign a new Application Number
NP Engineering
February 13, 2012
County of Albemarle
Department of Community Development
401 McIntire Road
Charlottesville, VA 22901
Re: SWM Plan comments
Restore'n Station (WPO-2011-00071)
Mr. Phil Custer:
I am writing to address the Storm Water Management (SWM) Plan comments provided in your
letter dated November 7, 2011 for the Restore'n Station site plan. I have addressed each
comment individually and listed the comment and intended response for clarity.
1. Please provide an approval letter from Filterra that the current layout and grading plan is
acceptable to them. I have concerns with the grading plan not allowing any water to
some of the structures. For instance, the contours are pitched away from the curb that
F4 is placed on.
RESPONSE:The review letter from Filterra is attached.
2. Please provide an approval letter from ACF Environmental that the current layout is
acceptable for the use of the modular Raintank system.
RESPONSE: The SWM structure has been revised and will be provided by Contech. Their review
letter of the design is attached.
3. This application will require that a Stormwater Management Facility Maintenance
Agreement be recorded. Please complete this form and submit it to Ana Kilmer with a
$17 recordation fee after reading the instructions online. Please include all parcels
contained in this site plan on this agreement.
RESPONSE: The SWM maintenance agreement has been submitted under separate cover.
4. The modified simple spreadsheet must analyze the watersheds for each stormwater
quality facility proposed on site and should not analyze a watershed including offsite
water. By doing so, you are obligating yourself to treating that offsite water to that
removal rate,which the current plan is not doing and is also not desirable. Please
update the modified simple spreadsheet for only the drainage areas to the detention
facility and to the cistern.
RESPONSE: The modified simple spreadsheet is attached.
5. If removal credit is desired for the cistern, the four pages of the state's Cistern Design
Spreadsheet in Appendix C should be included in the Stormwater report in full so it can
be evaluated. Page 4 is impossible to read and the first three pages are very difficult to
680 Ivy FARM DRIVE•CHARLOTTESVILLE,VIRGINIA 22901
•PHONE:(434)531-7387•
Restore'n Station-WPO Currlments (WPO-201 1-0007 1)
Page 2
February 13, 2012
read. Please indicate in the stormwater report what the removal rate of the cistern is
and provide justification in the calculations. If the removal rate of the cistern does not
meet the required rate after the modified simple spreadsheet is amended per comment
4, the cistern must become larger, toilets in the gas station must use water from the
cistern, or another BMP facility (upstream or downstream) must be provided.
RESPONSE: Removal credit is not desired for the cistern. For information, the design calculations
have been attached.
6. Please provide pre-treatment and screening for the drainage system upstream of the
cistern per VA DCR Stormwater Design Specification No. 6.
RESPONSE: The pre-treatment and screening is incorporated into the design of the system by
Contech-please refer to Contech's review letter.
7. The proximity of the Raintank 2 and one of the drainfields is a concern of the county. I'm
not certain that the two systems are far enough apart not to affect each other and I
have contacted the Virginia Health Department regarding this issue. An impervious liner
may be required on this system to make sure septic effluent does not find its way into the
detention system and that the detention system does not affect the efficiency of the
drainfield.
RESPONSE: Previously addressed in your email dated 1 1/16/1 1 from the Virginia Department of
Health.
8. Detention requirements have been met: the 2 and 10 year discharges for the 1.49 acre
post-development watershed has been reduced to the pre-development rates. For all
other projects submitted to this county, the updated IDF curves found in the Design
Manual must be used. For this project, you do not need to use the updated IDF curves
because the routings are acceptable.
RESPONSE: No response required.
9. The control structures for the detention system must be accessible for inspection and
maintenance. The current design of the facility has the potential for clogging at the inlet
end of the pipe inside the facility where maintenance would be difficult. The control
structure must have a trashrack placed overtop of it that meets state minimum
standards. I also recommend placing some sort of screening or filter upstream of the
detention system to prolong the life of the facility. This last suggestion is not a
requirement.
RESPONSE: The storm water detention facility has been revised as provided by Contech.
Inspection and maintenance of this system will be less problematic than the previously designed
system.
10. Please use a minimum of 15" diameter pipes in the stormwater facility to decrease the
likelihood of clogging.
RESPONSE: The pipe size has been changed to 15"diameter.
11. An analysis of the downstream channel per Minimum Standard 19 was not provided with
the SWM or ESC plan. Please refer to page 7 (of 35) of the County's Design Manual and
the Virginia Erosion and Sediment Control Handbook for what the county expects for an
analysis of downstream channels. Per state law, this analysis must be performed using
the 24-hour storm. According to DCR's Technical Bulletin #1, detention does not
constitute compliance with MS-19 because total volume of runoff is increased and poses
a potential threat to downstream properties.
RESPONSE: MS-19 requirements have been addressed through the hydraulic calculations of the
680 IVY FARM DRIVE•CHARLOTTESVILLE,VIRGINIA 22901
•PHONE:(434)531-7387•
Restore'n Station-WPO Corrlments (WPO-2011-00071)
Page 3
February 13, 2012
storm water detention facility. It is impossible to gain access to the downstream channel for
analysis.
12. To receive a bond estimate, please provide a completed Bond Estimate Request Form to
the County Engineer after all comments have been addressed.
RESPONSE: The bond estimate request is attached as noted above.
I trust that the above comments are adequately addressed for preliminary site plan approval.
Should you have questions regarding the revisions, please call me at (434) 531-7387.
Sincerely,
Nat Perkins, P.E.
680 IVY FARM DRIVE•CHARLOTTESVILLE,VIRGINIA 22901
•PHoNE:(434)531-7387•
NP Engineering
February 13, 2012
County of Albemarle
Department of Community Development
401 McIntire Road
Charlottesville, VA 22901
Re: ESC Plan comments
Restore'n Station (WPO-2011-00071)
Mr. Phil Custer:
I am writing to address the Erosion and Sediment Control Plan comments provided in your letter
dated October 15, 2011 for the Restore'n Station site plan. I have addressed each comment
individually and listed the comment and intended response for clarity.
1. It appears that the ESC Plans were all printed at 30 scale, not 40. If this is correct, please
replace all references to 40 scale with 30 scale.
RESPONSE: The plans are 30 scale and all reference to 40 scale have been removed.
2. On all three phases, please clearly show and label the limits of disturbance boundary.
RESPONSE: The disturbance boundary has been clearly identified.
3. Please show all proposed grading on Phase 2 and Phase 3. It is difficult to evaluate the
adequacy of these phases without proposed contours. Additional comments may be
necessary because the plan was not able to be fully evaluated.
RESPONSE: Phase 2 and 3 grading have been shown as well as the items to be completed in each
phase.
4. Related to the previous comment, the sediment basin and sediment trap should be sized
for the largest watershed each facility will likely experience as the site is filled in. For
instance, the site will likely be tipped towards the sediment basin, since the stormwater
facility is located in the vicinity, so its drainage area will increase as the earthwork
progresses.
RESPONSE: The sediment basin has been designed for a total of 4.68 acres (sum of the 3.83 acres
in drainage area 1 and 0.85 acres in drainage area 2). Revised sediment basin calculation sheets
are attached.
5. Silt fence is frequently proposed perpendicular to contour lines in this plan which is not
allowed per state guidelines. In these instances, water will not travel through the fence
but will be redirected downhill, like a diversion. Please replace the silt fence on the east
side of the property line with a diversion from the northeast corner to the sediment trap.
On the west end of the property, please simply remove the silt fence. If a visual
boundary is desired by the applicant, I recommend a type of safety fence.
680IVY FARM DRIVE•CHARLOITESVILLE,VIRGINIA 22901
•PHONE:(434)531-7387•
Restore'n Station-WPO C -nents-EC Plan (WPO-2011-00071)
Page 2
February 13, 2012
RESPONSE: Revisions to the silt fence have been made as noted above.
6. Please remove the silt fence from directly below the outlet of both settling facilities. Silt
fence cannot receive concentrated flow.
RESPONSE: Silt fence has been removed from the plan as noted above.
7. During the review of the preliminary site plan, the Chief of Current Development, Bill Fritz,
approved the disturbance of a 20ft wide section of the undisturbed buffer to the south.
Please show the area of the buffer that was approved for disturbance. It appears that
the area shown on this submittal does match the area approved by Bill. If the area
proposed for disturbance is, in fact, different, another waiver of this disturbance may
need to be processed.
RESPONSE: The undisturbed buffer is shown per prior approval. No revisions are necessary.
8. The embankment of the sediment basin ties into existing grade within the undisturbed
buffer (see where the 676 contour line would be). Please modify the plan to make sure
no disturbance to the undisturbed buffer occurs,other than the area previously
authorized.
RESPONSE: The sediment basin has been shifted north to prevent disturbance to the buffer area.
9. In plan view, please draw the sediment basin bottom as 671.
RESPONSE: Sediment basin bottom has been noted as 671 on the plan as noted above.
10. Please show Permanent Seeding (PS) symbols throughout the plan where necessary.
RESPONSE: Permanent seeding symbols have been added to the plan as noted above.
11. Please include the county's paved wash rack detail in this sheet set. This detail can be
found in the county's design manual on page 28 of 35.
RESPONSE: Paved wash rack detail has been added to the plan as noted above.
12. The county has updated its standard ESC Note set. Please use the latest version found in
the county's design manual.
RESPONSE: The ESC note set has been updated on the plan as noted above.
13. An analysis of the downstream channel per Minimum Standard 19 was not provided with
the ESC plan. Please refer to page 7 (of 35) of the County's Design Manual and the
Virginia Erosion and Sediment Control Handbook for what the county expects for an
analysis of downstream channels. Per state law, this analysis must be performed using
the 24-hour storm.
RESPONSE: The calculations for the MS-19 are included in the SWM plan and calculations.
14. Please provide the cross-sections and calculations (2-year velocity and 10-year
capacity) for the new VDOT ditch. Please specify any liner, if necessary.
RESPONSE: North arrows have been added to the site plan.
15. To receive a bond estimate, please provide a completed Bond Estimate Request Form to
the County Engineer after all comments have been addressed. All owners of properties
disturbed with this application must sign this document and be party to the bond unless
all offsite easements are recorded. The easements must be written in a manner that
allows the county and its assigns to the construction site.
RESPONSE: The bond estimate request is attached as noted above.
680 IVY FARM DRIVE•CHARLOTTESVILLE.VIRGINIA 22901
•PHONE:(434)531-7387•
Restore'n Station-WPO C enents-EC Plan (WPO-201 1-00071)
Page 3
February 13, 2012
I trust that the above comments are adequately addressed for preliminary site plan approval.
Should you have questions regarding the revisions, please call me at (434) 531-7387.
Sincer
Nat erkins, P.E.
680 IVY FARM DRIVE•CHARLOTTESVILLE,VIRGINIA 22901
•PHONE:(434)531-7387•
AauTCAt,• 605 Global Way,Suite 113
Linthicum,MD 21090
II*411, ` ` www.contech-cpi.com
CONSTRUCTION PRODUCTS INC.
Nat Perkins, P.E. January 23rd, 2012
NP Engineering
680 Ivy Farm Drive
Charlottesville,VA 22901
RE: Review of stormwater management design for Re-Store'N Station,Albemarle County,Virginia
The purpose of this letter is to document for Albemarle County and VA DCR our review of the plans and the
proposed application of the water quality treatment structures at this site as you have requested.
CONTECH has reviewed stormwater management designs for both the rainwater harvesting system and the
underground detention pond.
Rainwater Harvesting System
Based on the catchment area of 7,300 sf (gas station canopy) and irrigation requirements, CONTECH
recommends a 48" diameter SPRE cistern with a total length of 74If. This tank will provide a storage volume
of approximately 15,000 gallons and a runoff reduction of 78%. The system is designed to irrigate 18,000 sf
from April to October with an average depth of 0.785" per week(varies by month). When the cistern empties
out, city makeup water will be pulled to fill the tank. Additionally, CONTECH recommends hydrodynamic
separation for pretreatment to the system. The CDS Model CDS2015-4 was selected to trap sediment and
debris from entering the cistern.The CDS2015-4 can treat up to 0.70 cfs before internal bypass occurs.
Underground Detention System
Perforated 72" diameter CMP was selected to minimize the overall footprint. The dimensions of the system
are 44'x86' including a 1'stone perimeter.
In summary, both the rainwater harvesting system and underground detention system are expected to
operate in accordance with CONTECH Construction Products' design intent.
Please feel free to contact me if you have any questions or concerns.
Sincerely,,/
Aaron M. Lowell
Design Engineer—Stormwater Products
CONTECH Construction Products Inc.
Iowella@contech-cpi.com
www. contechstormwater. corn
1 r' "°"""""""" 9"„" ,VorteChs• I CON I SPAN'
CMP DETENTION C StormFiltelDETENTION SYSTEMS
Nat Perkins
NP Engineering
Ivy Farm Drive
Charlottesville, VA.22901
fjfilterra
September 13,2011 A Graving Idea in Stomiwater Filtration.
Plan Review of Filterra®
Re-Store'n Station, Albemarle County, VA
Dear Sirs
Thank you for submitting the revised plans on 09 September 2011 for our review of the
Re-Store'n Station project.
Filterra®structures Fl (8x4), F2 (8x4), F3 (6x4),F4 (6x4), F5 (6x4), F6 (6x4), F7 (8x4)
and F8 (8x4)were studied for;
•Planned Filterra®box size
•Filterra®contributing drainage area meeting project's regional sizing specification
•Filterrao invert elevations are higher than effluent invert elevations
•The bypass is lower than the Filterra®elevation(spot elevations)
•The grading pattern encourages cross linear flow and not head-on flow
•The Filterra®outlet drain pipe is sized correctly and exits perpendicular to the wall
•For any conflicting structures such as storm drain pipes below Filterra®
•For most efficient placement of Filterra®units
The plan review concluded that the Filterra® structures listed above is sited and sized
appropriately to treat stormwater to our published specifications.
Operational consistency with these specifications is contingent upon the stormwater unit
being installed correctly and according to the plans,as well as regular maintenance being
performed. Installation Help documents will be forwarded to the Buyer at time of order.
The Filterra®Installation,Operation and Maintenance Manual will be made available
upon request.
Yours sincerely
Loti
Duane Vincent
Engineer Support
Filterra®Bioretention Systems
Manufactured by Americast T:(804)798-6068 A M E R I C A S T
11352 Virginia Precast Road F:(804)798-8400 not just concrete.concrete solutions.
Ashland,VA 23005 E:design@filterra.com www.filterra.com
Philip Custer
From: Kirtley, Joshua (VDH) [Joshua.Kirtley@vdh.virginia.gov]
Sent: Wednesday, November 16, 2011 2:08 PM
To: Philip Custer
Cc: McDaniel, Jeff (VDH)
Subject: Re-Store'N Station Setback Question
Phil:
I wanted to summarize our previous conversations as they pertain to the Re-Store'N Station, specifically the storm water
management plan that you are reviewing. I understand your concern about any required setbacks to a potential septic
system and I appreciate you giving me a heads up about the situation.
After reviewing my notes and our files here at the Health Department,it appears that the lower storm water collection area
will reside at least fifty feet(50')of a proposed septic reserve area and over one hundred(100')to the actually septic field
itself. I also note that the storm water collection will be down slope of the nearby reserve area.
I have talked it over with my manager,and we both agree that there is no specific setback in the current Sewage and
Disposal Regulations. However,there are other setbacks for similar entities that could be interpreted to apply. For
instance, if we classified the drainage area as a LGMI(Lateral Ground Water Movement Interceptor,i.e. "French
drain"),then we could be as close as fifty feet(50')if the"french drain"was sited down slope of the proposed septic
system. The same setback of fifty feet(50')also applies if we classified the storm water area as a drainage ditch,a
stream,or a pond. If I understand you correctly,the area would normally be dry and would only contain water after
storm events long enough for it to be released back into the environment. One could argue that the storm water
management area is very similar to each of these setbacks contained in the Sewage and Disposal Regulations with the
common denominator being a fifty foot(50') setback.
I also spoke to Michael Craun of Old Dominion Engineering and I expressed my concern regarding the distance between
one of the unlined"rain tank"storm water units and a proposed septic reserve area. Mr. Craun explained that he was
aware of the storm water collection area and that he factored that into his septic design. Mr. Craun explained that Virginia
did not have guidelines as they pertain to setbacks between storm water areas and septic systems and that he looked at
other States for guidance. Mr. Craun went on to state that a fifty foot(50')setback between a storm water collection area
and a sewage disposal system was"best management practice". I would also like to add that the Regulations governing
Alternative Systems indicate a horizontal septic setback of twenty feet(20')between a septic system that disperses treated
effluent and a drainage trench.The effluent distributed for this septic system will be treated per the Engineer's report.
Please let me know if you have any questions or concerns regarding my comments as they pertain to this project.
Josh
Josh Kirtley
Environmental Health Specialist Senior
Thomas Jefferson Health District
1138 Rose Hill Drive
Charlottesville,Virginia 22906
(434) 972-6288
1
Short Version BMP Computations i-yr Worksheets 2 -6
Albemarle County Water Protection Ordinance: Modified Simple Method
Plan: Re-Store'n Station Water Resources Area: Rural Area
Preparer: NP Date: 13-Feb-12
Project Drainage Area Designation DA A
L storm pollutant export in pounds, L=[P(Pj)Rv/12][C(A)2.72]
Rv mean runoff coefficient, Rv=0.05+0.009(1)
Pj small storm correction factor,0.9
I percent imperviousness
P annual precipitation,43"in Albemarle
A project area in acres in subject drainage area, A= 1.49
C pollutant concentration,mg/I or ppm target phosphorus
f factor applied to RR
✓ required treatment volume in cy,0.5"over imperv.area= A(1)43560(0.5/12)/27
RR required removal, L(post)-f x L(pre)
%RR removal efficiency, RR100/L(post)
Impervious Cover Computation(values in feet&square feet)
Item
pre-development Area post-development Area
Roads Length Width subtotal Length Width subtotal
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0
0 0 0 0
Driveways Length Width no. subtotal Length Width no subtotal
and walks 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0
Parking Lots 1 2 3 4 1 2 3 4
0 0 58153.99 0 58153.99
Gravel areas Area Area
0 x 0.70= 0 0 x 0.70= 0
Structures Area no. subtotal Area no. subtotal
0 0 0 2775 1 2775
0 0 0 3495.41 1 3495.41
480 1 480
0 0 0 0 6750.41 6750.41
Actively-grazed pasture& Area Area
yards and cultivated turf 64904.4 x 0 08= 5192.352 0 x 0.08= 0
Active crop land Area Area
x0.25= 0 x0.25= 0
Other Impervious Areas
0 0
Impervious Cover 8% 100%
l(pre) (post)
Rv(post) V
0.95 100.2
New Development(For Development Areas,existing impervious cover<=20%)
C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type
0.70 1.00 20% 0.23 2.10 8.69 6.59 76% Development Area
0.35 1.00 0% 0.12 0.56 4.34 3.79 87% Drinking Water Watersheds
0.40 1.00 1% 0.12 0.64 4.97 4.33 87% Other Rural Land
*min.values
Redevelopment(For Development Areas,existing impervious cover>20%)
C f I(pre)* Rv(pre) L(pre) L(post) RR %RR Area Type
0.70 0.90 20% 0.23 2.10 8.69 6.80 78% Development Area
0.35 0.85 0% 0.12 0.56 4.34 3.87 89% Drinking Water Watersheds
0.40 0.85 1% 0.12 0.64 4.97 4.42 89% Other Rural Land
Interim Manual,Page 70 rev. 16 Feb 1998 GEB
.vtSE�t) 2.J13/IL._.
1992 3.14
TEMPORARY SEDIMENT BASIN DESIGN DATA SHEET
(with or without an emergency spillway)
Project IZEST-Gr-4V.—Ikk S'1117k �J
Basin # S8 1 Location Sa7,^7%.1 wEST
Total area draining to basin: 4.tag acres.
Basin Volume Design
Wet Storage:
1. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x 4.,g acres = 313.5 b cu. yds.
2. Available basin volume =357. a. cu. yds. at elevation 675% 1 . (From
storage - elevation curve)
3. Excavate cu. yds. to obtain required volumes.
* Elevation corresponding to required volume = invert of the dewatering
orifice.
4. Available volume before cleanout required.
33 cu. yds. x 4.L$ acres = 154.4 cu. yds.
5. Elevation corresponding to cleanout level = (.71 Z•17
(From Storage - Elevation Curve)
6. Distance from invert of the dewatering orifice to cleanout level =Z.2.3 ft.
(Min. = 1.0 ft.)
Dry Storage:
7. Minimum required volume = 67 cu. yds. x Total Drainage Area (acres).
67 cu. yds. x 4.LS acres = 313 •Ste,cu. yds.
III - 112
1992 3.14
8. Total available basin volume at crest of riser* = GDZB cu. yds. at
elevation (. 7B. 4 . (From Storage - Elevation Curve)
* Minimum = 134 cu. yds./acre of total drainage area.
9. Diameter of dewatering orifice = 3 in.
10. Diameter of flexible tubing = (p in.(diameter of dewatering orifice
plus 2 inches).
Preliminary Design Elevations
11. Crest of Riser = (0-18.11
Top of Dam = tB1
Design High Water = ((gp
Upstream Toe of Dam = C--1
Basin Shape -33�9 k(e' 4...72-
12. Length of Flow = ?,�. S
Effective Width We 41•7z
If > 2, baffles are not required —
If < 2, baffles are required ye s
Runoff g''' 5 41 L3 8-t.93, 1-hae = 2.28
13. Q2 = 7.5 cfs (From Chapter 5)
14. Q25 = 12.- D cfs (From Chapter 5)
Principal Spillway Design
15. With emergency spillway, required spillway capacity Qp = 02 = 7.S cfs.
(riser and barrel)
Without emergency spillway,required spillway capacity Qp = Q2 - 4/4 cfs.
(riser and barrel)
III - 113
1992 3.14
16. With emergency spillway:
Assumed available head (h) = t.O ft. (Using Q2)
h = Crest of Emergency Spillway Elevation - Crest of Riser Elevation
&big.y. -- 4.78.4 t. o
Without emergency spillway:
Assumed available head (h) = .4.)A ft. (Using Q25)
h = Design High Water Elevation - Crest of Riser Elevation
17. Riser diameter (Di) = 3 3 in. Actual head (h) = 0.45 ft.
(From Plate 3.14-8.)
Note: Avoid orifice flow conditions."
18. Barrel length (1) = 43.17 ft.
Head (H) on barrel through embankment = 8.4 ft.
(From Plate 3.14-7).
19. Barrel diameter = t5 in.
(From Plate 3.14-B [concrete pipe] or Plate 3.14-A\[corrugated
20. Trash rack and anti-vortex device
Diameter = 54 inches.
Height = 1-7 inches.
(From Table 3.14-D).
Emergency Spillway Design
12.-7s
21. Required spillway capacity Qe = 025 - Op = c c•
22. Bottom width (b) = S. ft.; the slope of the exit channel (s) =
-?,.9 ft./foot; and the minimum length of the exit channel (x) =
-3Z ft.
(From Table 3.14-C).
III - 114
1992
3.14
Anti-Seep Collar Design
23. Depth of water at principal spillway crest (Y) = 7.�} ft. ( .4-L1%
Slope of upstream face of embankment (Z) = 2 :1.
Slope of principal spillway barrel (Sb) = 1.52- %
Length of barrel in saturated zone (Ls) = So ft.
24. Number of collars required = Z dimensions = S'
(from Plate 3.14-12).
Final Design Elevations
25. Top of Dam = G.B\
Design High Water = (.. o
Emergency Spillway Crest = 4
Principal Spillway Crest = (,`(t.q•
Dewatering Orifice Invert = (.-75-• 1
Cleanout Elevation = (.iZ. S1
Elevation of Upstream Toe of Dam
or Excavated Bottom of "Wet Storage
Area" (if excavation was performed) = 4,7 l
III - 115