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OPERATIONS & MAINTENANCE MANUAL
STORMWATER CONTROL STRUCTURE
WET DETENTION POND
Owner(s): Town of Fuquay Varina Public Service Center
Address: 1415 Holland Road, Fuquay-Varina, NC 27526
Phone Number: 919-552-1402
Site/Subdivision Plan # N/A
Prepared by: TOFV Engineering Department
Receiving Water Course: UT to Neuse
Date: 8/29/16
Date Constructed: August 2016, updated December 2019
OPERATIONS AND MAINTENANCE MANUAL
PROJECT NAME: TOFV Public Service Center
Wet Detention Pond
This manual establishes procedures for maintenance and operation of the TOFV Public Service
Center Wet Detention Pond (s) in accordance with the Town of Fuquay-Varina's Land
Development Ordinance as set forth in Section 9-1405(e)(8) MAINTENANCE.
I. Maintenance of Embankments
A. Vegetation
The embankment has a ground cover of fescue, which if properly maintained will
prevent erosion of the embankment and provide an easy surface for inspection. The
grass will be most difficult to obtain in the area subject to water level fluctuation
below the top of the riser.
♦ Re -Seeding — periodically re -seeding may be required to establish grass on areas
where seek did not take or has been destroyed. Before seeding, fertilizer (12-12-
12) should be applied at a minimum rate of 12 to 15 pounds per 1,000 SF. The seed
should be evenly sewn at a rate of three pounds per 1,000 SF. The seed should be
covered with soil to the depth of approximately 1/4". Immediately following the
planting, the area should be mulched with straw.
♦ Trees & Shrubs —trees, shrubs, and other landscape vegetation should be permitted
only as shown on the approved planting plan.
♦ Mowing — grass mowing, brush cutting and removal of weed vegetation will be
necessary for the proper maintenance of the embankment. All embankment slopes
and vegetation of spillways should be mowed when the grass exceeds 8" in height.
Acceptable methods include the use of weed whips or power brush cutters and
mowers.
B. Erosion
Erosion occurs when the water concentrates causing failure of the vegetation or when
vegetation dies and sets up the environment for rill erosion and eventually gullies
from the stormwater runoff. The dam should be inspected for these areas. Proper
care of vegetative areas that develop erosion is required to prevent more serious
damage to the embankment. Rills and gullies should be filled with suitable soil
compacted and then seeded. Methods described in Section I -A, on vegetation, should
be used to properly establish the grass surface. Where eroded areas are detected, the
cause of the erosion should be addressed to prevent a continued maintenance
problem. Frequently problems result from the concentration of runoff to one point of
the embankment crest instead of a uniform distribution of runoff. This can be
corrected by reshaping the crest to more evenly distribute the runoff to areas, which
are not experiencing erosion problems. The top of the dam should not be allowed to
be used for pedestrian or bicycle traffic.
♦ Abutment Areas — the abutment is the line formed where the embankment fill
comes into contact with the existing slope. Runoff from rainfall concentrates in
these gutter areas and can reach erosive velocities because of the steep slopes. If a
normal stand of grass cannot be maintained on the abutments, additional measures
may be needed such as jute matting to provide for the establishment of a good
ground cover.
♦ Upstream Embankment Slope — Erosion problems can develop on the upstream
face of the dam due to the fluctuation of water level in the pond. This is a result of
a combination of wave actions and ground saturation, which occurs from the
elevated water levels. The erosion generally occurs as the water level falls and the
saturated ground becomes subjected to the wave action. If erosion becomes a
problem, it may necessitate the installation of a stone armoring along the zone
subject to fluctuating water level. This would consist of 18" of NCDOT Class B
stone for erosion control underlain with Mirifi 140 geotextile fabric. It should be
centered at the point of the erosion problem and covering an area 2' above and
below the approximate center of the eroded area.
C. Seepage
♦ Detection - Seepage should not be expected on the downstream slope of the
embankment. However, a cursory inspection of the road embankment should be
made for completeness of the inspection. Seepage may vary in appearance from a
soft wet area to a flowing spring. It may show up first as only an area where the
vegetation is lusher and darker green. Cattails, reeds, mosses and other marsh
vegetation often become established in a seepage area. The downstream abutment
areas where the embankment fill and natural ground interface are very common
locations for seepage. Also the contact between the embankment and the spillway
conduit is a very common location which is generally attributed to poor compaction
around the conduit. Due to the way in which conduits are put in, this is generally
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most evident on the underside of the conduit. Slides may result from excessively
saturated embankment slopes. The natural foundation area immediately
downstream of the dam abutment should also be inspected to ensure that "piping"
is not occurring underneath the embankment. "Piping" may appear as a "boil"
evident as spring carries soil. The soil usually deposits around the boil area and is
evident by the sedimentary deposits accompanying it. Seepage can also occur into
the spillway conduit through cracks in the pipe or improperly sealed joints. These
can be seen by observing the conduit when the water level is high. The movement
of the water itself is not dangerous, but if soil particles are being carried with it,
then it can create a shortcut for the piping of soil. This might show up on the
upstream face of the embankment roughly along the line of the conduit itself.
D. Cracks, Slides, Sloughing, and Settlement
♦ Cracks — the entire embankment should be inspected for cracks. Short, isolated
cracks are usually not significant, but larger cracks (wider than 1/4"); well defined
cracks indicate a serious problem. There are two types of cracks: transverse and
longitudinal.
Traverse cracks appear crossing the embankment and indicated difference of
settlement within the embankment. These cracks provide avenues for seepage
and piping could develop.
Longitudinal cracks run parallel to the embankment and may signal the early stages
of a slide. In recently built structures, these cracks may be indicative of poor
compaction or poor foundation preparation resulting in consolidation after
construction.
♦ Slides — Slides and slumps are serious threats to the safety of an embankment.
Slides can be detected easily unless obscured by vegetation. Arch shaped cracks
are indications that slides are slipping or beginning to slip. These cracks soon
develop into large scarps in the slope at the top of the slide.
♦ Settlement — settlement occurs both during construction and after the embankment
has been completed and places in service. To a certain degree this is normal and
should be experienced. It is usually the most pronounced at the location of
maximum foundation depth or embankment height. Excessive settlement will
reduce the free board (difference in elevation between the water surface and the top
of the dam). Any area of excessive settlement should be restored to original
elevation and condition to reduce the risk of overtopping. A relatively large amount
of settlement (more than 6") within a small area could indicate serious problems in
the foundation or perhaps the lower part of the embankment. Settlement
accompanied by cracking often precedes failure.
♦ What to do if seepage, cracks, slides or settlement are detected: If any of the above
items are detected there may be signs of significant problems, which could lead, to
the failure of the structure. A geotechnical or civil engineer should be consulted
regarding the origin of these problems and for the assessment of the appropriate
solutions for correcting them. If the professional is not immediately able to inspect
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the dam, then the bottom drain should be opened and the water level lowered to
remove the risk of failure until a professional can observe these problems.
E. Rodent Control
Generally in this urban environment, rodents are not a problem. Rodents such as
ground hogs, muskrats, and beavers are attracted to dams and reservoirs and can be
quite dangerous to structural integrity and proper performance of the embankment
and spillway. Groundhog and muskrats thrive on burrowing in the manmade earth
embankments, which become pathways for seepage. In the event that burrows are
detected within the dam, then the rodents should be dealt with by removal.
II. MAINTENANCE OF SPILLWAYS & CONTROL STRUCTURES
A. Inspection of Spillway Conduits
Conduits should be inspected thoroughly once a year. Conduits should be visually
inspected by actually entering the conduit a sufficient distance between the riser
structure and the outlet to check all the joints. Because the outlet works tie into the
street storm sewer system, catch basins and pipes. Conduit should be inspected for
proper alignment (sagging), elongation and displacement at joints, cracks, leaks,
surface water, surface wear, loss of protective coating, corrosion and blocking.
Problems with conduits most often occurs at joints and special attention should be
given to them during inspection. Joints should be checked for gaps caused by
elongation or settlement and loss of joint filler material. Open joints can permit
erosion of the embankment material and possibly the piping of soil material through
the joints. Catch basin should be checked for signs of water seeping along the
exterior surface of the pipe where it enters the catch basin. A depression in the soil
surface over the pipe may be signs that soil is being removed from around the pipe.
♦ What to do if problems are detected with the spillway: Retain the assistance of a
civil engineer or geotechnical engineer qualified in the design of embankments to
perform an inspection of the dam. If in doubt, lower the water surface elevation of
the pond until such time as an inspection can be performed by a qualified
professional.
B. Trashracks on Pipe Spillways
The spillway riser for this dam is the only spillway structure. The intake structure has
been fitted with a trashrack to prevent debris from entering the spillway structure.
Most of the runoff entering the pond comes in through grated inlets, which have
essentially provided filtration of the runoff and should limit the size of the debris that
enters the basin to floating debris which will most likely pass through the trashrack.
The opening between the trashrack and riser is smaller than the opening of the outlet
pipe. The intent is that any debris, which passes through the trashrack, will be easily
passed by the pipe outlet.
Maintenance should include periodically checking the rack for rusted or broken
sections and repairing as needed. The trashrack should be checked frequently during
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and after storm events to ensure that it is properly functioning and to remove
accumulated debris.
III. OPERATION
A. Lake Drains
Lake drains should always be operable so that the pool level can be drawn down in
case of an emergency or for repairs or maintenance. Lake drain valves or gates that
have not been operated for a long time present a special problem. Generally, when
draining the pond, it should be drained slowly. Open the drain until a good flow of
water is present but not a torrent, so that the water level can be drained over a period
of 48 hours or more. Rapidly lowering the water level in the pond can cause
permanent damage to the embankment and must be avoided. The gate valve
controlling the lake drain should be operated from fully closed to fully opened
position at least twice a year.
B. Record Keeping
Operation of a dam should include recording of the following:
a. Annual Inspection Reports — a collection of written inspection report should be kept
on record. Inspections should be conducted annually. Copies should be provided
to the Town of Fuquay-Varina's Engineering Department on the Town of Fuquay-
Varina's form.
b. Observations — all observations should be recorded. Where periodic inspections
are performed following significant rainfall events, these inspections should be
logged into the Periodic Inspection report.
c. Maintenance — written records of maintenance and/or repairs should be recorded
on the Periodic Inspection report.
d. Other Operation Procedures — the owner should maintain a complete and up-to-date
set of plans (as -built drawings) and all changes made to the dam over time should
be recorded on the as-builts.
C. Sedimentation & Dredging
Sedimentation from establishing areas tributary to the pond will eventually result in
the reduction of the retention pool and eventually will have to be removed. The
frequency of this sediment removal can be reduced by ensuring that the site areas
around the building be stabilized with a vegetative ground cover such that it restrains
erosion. This would include a periodic application of fertilizer and other treatments
necessary to promote a stable groundcover and minimize sedimentation to the pond.
The maintenance on this pond requires that when the sediment level (as measured
from the top of the riser to the sediment pool) is within 75% of the top of the riser that
the sediment must be removed and the original pond restored. For aesthetic purposes
it may be desirable to maintain it prior to this point. Generally, the dredging process
begins with the removal of as much water as possible from the deposited silt and so
the material can be excavated with conventional equipment for trucking offsite. The
removed material should be hauled offsite to a suitable landfill site or mounded
somewhere on site and stabilized with a groundcover sufficient to restrain erosion.
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IV. INSPECTION, OPERATION & MAINTENANCE CHECKLISTS
POND INSPECTION CHECKLIST
(Project Name):
Date:
Time:
Wet Detention Pond #
SPILLWAYS — DRAINS — OUTLETS
Check/Circle Observations Action Action Action
Condition Noted I Repair I Monitor Investigative
Principal Spillway Type:
Trashracks/Debris
Cracks/Deterioration
Joint Deterioration
Improper Alignment
Cracks/Deterioration
Joint Deterioration
Seepage/Piping
Undercutting
Erosion
Lake Drain/Other Type:
Outlets
GatesNalves
Operability
General Comments, Sketches & Field Measurements
POND INSPECTION CHECKLIST
Date:
Time:
(Project Name): Wet Detention Pond #
EMBANKMENT -- POOL
Check/Circle Observations Action Action Action
Condition Noted Repair Monitor Investi ative
U/S Sloe
Type:
Ve etation/Ri ra
Beaching/slides/cracks
Undermining/erosion
Rodent burrows
Crest
Type:
Ruts/erosion
Cracks/settlement
Poor alignment
D/S Sloe
Type:
Vegetation/erosion
Rodent burrows
Sloughs/slides/cracks
Seepage/wetness
Pool
Type:
Erosion/ground cover
Sedimentation
Water quality
Abutment
Type:
Vegetation/erosion
Slough/slides/cracks
Seepage/wetness
General Comments, Sketches & Field Measurements
PERODIC INSPECTION, OPERATION & MAINTENANCE RECORDS
(Project Name):
Wet Detention Pond #
Date
e
Rain "
Pool Level
Weather
General
Recorded
IF7
Conditions
Observations or
By
Comments
Date Maintenance Performed Comments Recorded
B
Date Equipment Operated Comments Recorded
B