SW4210704_Plansheet - SCM Detail_20211210

BEFORE YOU DIG!
CALL 811
N.C. ONE -CALL CENTER
IT'S THE LAW!
.•
CUT-OFF COLLAR
NOT TO SCALE
ALUMINUM BAPS
O 4~ 0.i
ANTI -VORTEX PLATES
NOTE:
C.A.P. =CORRUGATED ALUMINUM PIPE 12' TOP WIDTH
_ _ 54" TRASH RACK TOP OF DAM EL. = 732.5
_ - - - (SEE DETAIL) (MAX. OF 10:1 SLOPE) FINAL GRADE
APPROXIMATE - - _ FINAL GRADE (98% COMPACTION) SEEDING ON ALL
EXISTING GRADE EMERGENCY POND SLOPES SHALL
�ILCWTY = 3U_5- - - 3 TURF
NON -CLUMPING
- - - 1 TURF GRASS
100 YR. N.W.L. L. = 730.9 TOP OF RISER FILL - - - �__. - - - I
10 YR. H.W.L. EL. = 730.0 EL. = 729.0 _� 1 MATERIAL ¢
1 YR. HAL_EE = 729.2 3 IN. 98% COMPACTION) � -
(l (-
TEMP. 3" (W/3" HEAD) FAIRCLOTH SKIMMER
W/ 4" SCHD 40 PVC BARREL 4" SKIMMER
FLEXIBLE HOSE AND 4" STEEL NIPPLE HOSE
(TO BE REMOVED UPON CONVERSION TO
PERM POND (SEE SEQUENCE) 36"
__.� 1 C.A.P
12" STUBBED OUT OF �_ --- �_ FLANGED JOINT
RISER 12" AT ELEV 720.0 WITH SMALL POOL 0 ` "' '
4" THREADED HOLE TO
PERM. ORIFICE WITH GASKET
RECEIVE THE 4" NIPPLE PREFABRICATED BARREL TO RISER
TO BE CAPPED WITH 1 5/8" BOTTOM POND=720t (WATERTIGHT CONNECTION)
OR FINV. EL = 720.0
IICE HOLE AT COMPLETION
NOTE:
OWNER SHALL PROVIDE SOILS ENGINEER TO
APPROVE SUBGRADE AND KEYWAY PRIOR TO
ANY FILL MATERIAL BEING PLACED. ALL 6,7 (W)x 6. )'((W))x 2 '(H)= 90 CF
FILL MATERIAL AND COMPACTION WILL ALSO 3000 PSI CONCRETE POURED IN
BE MONITORED BY SOILS ENGINEER TO BE AND AROUND BASE SECTION
PROVIDED BY OWNER.
GENERAL NOTES
1. THE OWNER IS RESPONSIBLE FOR MAINTAINING THE COMPLETED
PERMANENT DRY DETENTION POND AS DIRECTED BY THE GOVERNMENTAL
OFFICE HAVING JURISDICTION FOR WATERSHED PROTECTION, IN CONFORMANCE
WITH THE APPROVED MAINTENANCE PLAN.
2. THE PERMANENT DRY DETENTION POND SHALL HAVE FULL DESIGN VOLUME
AVAILABLE PRIOR TO ANY ISSUANCE OF CERTIFICATES OF OCCUPANCY FOR THE
SITE AND/OR PRIOR TO ANY PLAT RECORDATION FOR THE SITE. THIS MAY
REQUIRE THE CLEANOUT AND DISPOSAL OF SEDIMENT FROM THE POND.
3. FINAL APPROVAL OF INSTALLED RUNOFF CONTROL STRUCTURES WILL BE
REQUIRED AT FINALIZATION OF THE GRADING PERMIT OR AT ISSUANCE OF THE
FINAL BUILDING CERTIFICATE OF OCCUPANCY (COMPLIANCE), WHICHEVER COMES
LATER. ENGINEERING CERTIFICATION OF COMPLETION SHALL BE REQUIRED
PRIOR TO FINAL APPROVAL BY THE ENFORCEMENT OFFICER.
4. THE GOVERNMENT OFFICE HAVING JURISDICTION FOR STORMWATER DEVICES
AND THEIR ASSIGNS HAVE RIGHT OF ACCESS TO THE PERMANENT DRY DETENTION
POND(S) FOR INSPECTIONS AND MAINTENANCE ENFORCEMENT.
SITE DATA
EXISTING ZONING: MX-R
PROP. LAND USE: SINGLE FAMILY
TOTAL No. LOTS PROPOSED: 119
TOTAL SITE AREA: 77.73 AC.
L.F. STREETS: 4710 L.F.
SEWER: CITY OF LEXINGTON
WATER: CITY OF LEXINGTON
SOIL TYPE: CeD2, CcB, PaE, SfB, ChA,
PaD, EnD
AVERAGE SLOPE: 8% t
DISTANCE TO FLOODWAY: 50 LF
DISTURBED AREA: 44.3 AC,
PHASE 1: 21.0 Ac.t
PHASE 2: 23.3 Ac.f
PARCEL ID: 67216-01-36-0231
DEED REF: 1584-1466
RIVER BASIN: YADKIN/PEE-DEE
LAT/LONG: 35.8466/-80.2766
IMPERVIOUS SURFACE AREA:
ROADS: 2.44 AC.f
LOTS: 10.93 AC.f
TOTAL: 13.37 AC.f (17.37o)
OPEN SPACE: 39.2 Ac.f (507.)
EST. START DATE: JUNE, 2020
EST. END DATE: DECEMBER, 2022
CUT-OFF COLLAR
(SEE DETAIL)
IT SHALL BE THE RESPONSIBILITY OF THE
CONTRACTOR TO COORDINATE ALL CONSTRUCTION
ACTIVITIES WITH THE SOILS ENGINEER PROVIDED BY
THE OWNER. NO CONSTRUCTION ACTIVITIES SHALL
BE INITIATED UNTIL WHICH TIME A SITE MEETING
HAS OCCURRED TO ESTABLISH/COORDINATE A
SCHEDULE AND BASIS OF COMMUNICATION.
(MIN)
-:1 1-•- 4'(MIN) NEW INV IN=718. 0
KEYWAY
(SEE NOTE)
- 117 L.F. OF 24" C.A.P.
® 1.20%
DRY DETENTION POND TYPICAL SECTION
NOT TO SCALE
NO TREES OR SHRUBS SHOULD BE PLANTED WITHIN
10 FEET OF INLET OR OUTLET PIPES, SPILLWAYS OR
FLOW SPREADERS, OR, ON ANY DAM AREAS.
MAINTFNANrF RF0111RFMFNTS
24" RCP
- POND SITE DATA
WATERSHED: YADKIN
BASIN: YADKIN
ON -SITE DRAINAGE AREA = 13.00 AC.
OFF -SITE DRAINAGE AREA = 0.00 AC.
TOTAL DRAINAGE AREA TO POND = 13.00 AC.
PROPOSED IMPERVIOUS SURFACE
HOUSES, DRIVES = 4.41 AC.
PAVEMENT, CBU = 0.95 AC.
TOTAL = 5.36 AC.
DESCRIPTION
FREQUENCY
MAINTENANCE REQUIRED
Mow maintain buffer vegetation
Quarterly
As needed
Inspect bank embankment for erosion
Quarterly
Repair as needed
Inspect pipe inlet and outlet areas for undercuttin erosion
Quarterly
Repair as needed
Inspect trash rack principal and emergency spillways for trash blockage
After large storms
Remove trash as necessary
Inspect structural integrity of outflow device
Annually
Repair as needed
Inspect sediment accumulation
Annually
I Remove when 50% of foreboy capacity lost
54~ DIA. CORR. `
ALUM. TRASH RACK
STAINLESS STEEL STRAP - ~
\4
12" �
SLOTS IN ANTI -VORTEX PLATES \
36" C.A.P. RISER ARE USED TO POSITION THE TRASH
RACK ON THE RISER PIPE
TRASH RACK DETAIL
BOUYANCY CALCULATIONS NOT To SCALE \
2 � RISER.
V_ 2 1 = 63.6 FT3 FORCE OF H2O = (110.7 F ) (62.4 lb./FT3) 6907 Ib.
BARREL 3 6
CONCRETE = 7 907 = 79 FT 3 USE 90 CF
(15.0,)(24211iT =47.1 FT. = 3.4 C.Y.
F, = 110.7 F13
3 3
20'
TOP DAM = 732.5
SYNTHETIC EROSION MATRIX
SECTION EMERGENCY SPILLWAY
NOT TO SCALE
THIS IS NOT A SURVEY. NOT FOR RECORD, SALES, OR CONVEYANCE.
1 ' '
1
..... . ....
0
30' 20' 10' 0 30' 60'
SCALE: 1 " = 30'
ROUTINE MAINTENANCE - To be provided by the Property Owner at the designated frequencies for each of the
following items that apply.
A) MOWING - Quarterly - Grass vegetation is an effective way to prevent erosion of the embankment surfaces.
While not necessary for embankment stabilization, mowing the area surrounding a pond helps eliminate problems
from animal pests and provides a more aesthetically appealing area. Grass shall be mowed when the uniform
height exceends six (6) inches.
B) DEBRIS REMOVAL - Many permanent runoff control structures have pipe and riser spillways with low flow
orifices. Any of these that become plugged with trash or debris will reduce the spillway capacity. As a result, the
emergency spillway will operate more frequently and there is a greater potential for overtopping the dam. Trash racks
are normally installed to prevent clogging and debris must be removed from these devices periodically. For these
reasons, it is recommended to inspect the trash racks monthly and/or after major storm events and to remove debris as
necessary.
C) MINOR SLOPE FAILURES - Minor slope failures should be repaired by seeding or sodding as soon as they are
discovered to prevent major damage or sediment build-up in the pond. Re -occurring slope failures may be an
indication of a more serious problem and should be brought to the attention of the governmental office having
jurisdiction for watershed protection.
D) PERIODIC INSPECTIONS - After storm inspections should be done after major storm events (more than 2 inches
of rainfall in 24 hours) or after extended periods of rainy weather (more than 2 or three days). Major items to look for
are damage to spillways or channels, excessive debris build-up on trash guards, and eroded or slumped embankments.
E) VALVES AND GATES - The reservoir drain should always be operable so that the permanent pool can be drawn
down in case of an emergency, for repairs, or for clean -out of sediment. Reservoir drain valves that have not been
operated for a long time are often a problem in that the valve may not open. Also it may not close after opening which
will drain the impoundment. All valves should be operated from the fully closed to the fully open position at least
twice a year.
F) TREES AND BRUSH - Trees and brush should not be permitted on embankment surfaces or in vegetated
spillways. Brush and trees provide a haven for burrowing animals (like muskrats and groundhogs) and extensive root
systems can weaken an earth fill dam or provide a pathway for excessive water flow through the dams. Tree growth
adjacent to concrete walls and structures will eventually cause damage to footings creating cracks and possible
structure failure.
G) MISCELLANEOUS ITEMS - Excessive plant growth, algae blooms, odors, discoloration, perceived animal pests,
etc. should be addressed with the governmental office leaving jurisdiction for watershed protection on an as needed
basis. Solutions to these types of problems should be non -chemical and deemed safe for drinking water supply
reservoir application.
H) ANNUAL INSPECTIONS - Annual maintenance inspections will be performed by the owner. Documentation of
inspections and maintenance must be submitted to the Stormwater Engineer annually upon the anniversary of the
as -built plan set approval by the City. The "Wet Detention Basin Operation and Maintenance Manual" is available
on the City of Greensboro website. This form shall be utilized for the annual inspection.
NON -ROUTINE MAINTENANCE - To be provided by the Property Owner at the designated frequencies for each of
the following items. These maintenance items will require a registered professional engineer to prepare a plan and/or
detail(s) and to certify completion of the maintenance in accordance with the plan and/or detail(s). All revisions and
repairs to permanent runoff control structures shall be done in accordance with City of Winston-Salem guidelines and
specifications.
A) SEDIMENT CLEAN -OUT - Water quality measures like wet detention ponds and retention ponds trap sediment
as an inherent part of their function. With time, the volume allocated to sediment will become filled and they must be
cleaned out to remain effective.
Sediment removal from the pool, sediment foreba (s) or rip -rap baffles shall be detailed to indicate finish elevations
(relative to riser), removal and disposal method(s)y, stabilization of disturbed areas, erosion control, and stabilization of
spoil areas. Engineering detail and certifications for rip -rap baffle clean -out only, may be waived on a case -by -case
basis depending upon the extent of the work involved and whether the baffle is damaged.
B) CHANNEL STABILIZATION - Grassed waterways will filter out sediment (when there is a sediment load) and
they will in time aggrade to the point that they no longer have the capacity to handle the required flow. This is a major
maintenance problem. Another problem is erosion of the channel bottom, particularly before the grass can become
established.
Both situations require repair, possibly regrading. Small rills can be repaired by sodding, the preferred approach.
However, waterways, which have lost much of their capacity due to sedimentation, will require reshaping and
revegetating.
Waterways need to be mowed a minimum of three times a year to prevent tree growth and excessively high
vegetation.
Rip -rap channels need to be maintained to prohibit tree growth on the banks and bottom as necessary to maintain the
required capacity. Where rip -rap is used, the channel should be inspected after major storms to see if it is damaged. If
so, rip -rap will need to be replaced in the damaged areas.
C) PRINCIPAL SPILLWAY CONDUITS - Most water quality ponds have a pipe or conduit that serves as a principal
spillway. These carry normal stream flow and small flood flows safely past the dam throughout the life of the
structure. Pipes through embankments can be extremely dangerous to the embankment if problems develop after
construction.
Frequent inspection is necessary to ensure the spillway conduit is functioning properly. All conduits should be
inspected for improper alignment, elongation and displacement of joints, cracks, leaks, loss of protective coating,
corrosion, and blockage.
Problems with conduits occur most frequently at joints. Open joints can cause erosion of embankment materials or
cause leakage of water. The outlet should be checked for signs of water seeping along the exterior of the pipe. A
depression in the soil surface may be a sign the joint is no longer watertight and that soil is being removed from
around the pipe. Metal pipe spillways will have to be replaced when they become so corroded that they are no longer
watertight.
Principal spillway replacement shall be detailed, approved, constructed, and certified in accordance with Guilford
County guidelines.
D) EMERGENCY SPILLWAYS - Channel and structure repair or replacement shall be detailed, approved,
constructed, and certified in accordance with these guidelines.
E) DAM FAILURE - Which endangers the structural integrity or watertightness of the dam shall have a plan and
detail(s) prepared to repair said damage.
F) SEEPAGE - At most dams, some water will seep from the reservoir through the foundation. The need for remedial
seepage control will depend on the quantity and location of the seepage. As a general rule, seepage control measures
(after construction is complete) will not be necessary unless seepage is threatening the safety of the dam. Remedial
measures to control seepage will be required if the safety of the dam is threatened. All methods to control seepage
must be designed and constructed under the supervision of and certified by a professional engineer experienced with
dams.
[)AM [DESIGN EDATA SUMMARY
BOTTOM ELEV.
= 720f
TOP OF RISER ELEVATION
= 729.0
EMER. SPILLWAY ELEVATION
= 730.5
TOP OF DAM
= 732.5
1 YEAR H.W.L.
= 729.2
10 YEAR H.W.L.
= 730.0
100 YEAR H.W.L.
= 730.9
WQV REQUIRED
= 19,857 C.F.
WQV PROVIDED
= 28,381 C.F.
DESIGN DATA
DRAINAGE AREA (DA) = 13.00 ACRES
IMPERVIOUS SURFACE (I) = 5,36 AC (41.27.)
DESIGN RAINFALL (P) = 1 INCH
Rv = 0.05 + 0.009(I) = 0.42
WQV = P*Rv*DA*43560 / 12 = 19,857 C.F.
WQV PROYD = 28,381 CF
DURING CONSTRUCTION, THE POND WILL FUNCTION AS A
TEMPORARY SEDIMENT BASIN FOR EROSION CONTROL. THE
FAIRCLOTH SKIMMER (OR APPROVED EQUAL) SHALL BE USED
TO DECANT/DRAIN THE BASIN TO THE ELEVATION OF THE
BARREL INVERT. UPON STABILIZATION OF THE SITE, ALL
SEDIMENT SHALL BE REMOVED FROM THE BASIN AND
THE SKIMMER SHALL BE REMOVED. THE CONTRACTOR
SHALL COMPLETE CONSTRUCTION OF THE POND
(SEE POND CONSTRUCTION SEQUENCE).
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