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Detention Basin Inspection and Maintenance Guide
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Executive Summary
This document provides guidelines for the inspection and maintenance of stormwater management detention basins within Bethlehem Township, Hunterdon County, New Jersey. It is intended to be a practical tool to aid in maintaining stormwater management facilities. The manual addresses the types of stormwater management basins existing in the Township at the time of its writing and includes inspection checklists and recommendations for routine and emergency maintenance, vegetative maintenance, trash and debris removal, and mechanical/structural component maintenance. Inspections are crucial to ensure continued proper functioning of basins, and should occur monthly for general site conditions, annually for structural/mechanical components and earthwork, biannually for vegetation, and after every major storm event for trash racks and grates.
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Document Text
--- Document: Detention Basin Inspection and Maintenance Guide Document ---
Paul Muir
Mayor
Gregory Glazer
Deputy Mayor
Steve Keefe
Committeeman
Walter Baumgarten
Committeeman
Jose Medeiros
Committeeman
September 16, 2016
PREPARED BY:
32 Brower Road
Hillsborough, New Jersey 08844
(908) 359-8291
Detention Basin
Inspection and Maintenance
Guidelines
TOWNSHIP OF BETHLEHEM
HUNTERDON COUNTY, NEW JERSEY
Purpose
This manual is intended to be a practical tool to aid in the inspection and
maintenance of stormwater management facilities within a development. Do to
the number of developments within Bethlehem Township, site specific guidelines
are not feasible. Homeowner Associations or individuals responsible for
maintaining stormwater management facilities may need to engage the services
of a licensed professional engineer for additional site specific guidance. This
manual has been prepared to address the types of stormwater management
basins existing in Bethlehem Township at the time of its writing.
Stormwater Runoff Control
During precipitation or snow melt, portions of the water soak into the ground,
evaporate or flow over land. The part that flows over land is called stormwater
runoff. In natural settings, water from storm events is slowed by vegetation and
other obstacles as it flows over land. Depending on soil types, most of the
stormwater infiltrates into the soil.
In developed areas, much of the land is covered by hard surfaces such as
buildings and pavement. These hard surfaces, due to their impervious nature,
allow little to no infiltration. This results in an increase in the stormwater runoff
quantity and the ability for the runoff to convey various pollutants to the natural
waterways. Pollutants may include oil, antifreeze, salt, cigarette butts, paper and
other trash. Soil and organic material can also be transported as the runoff
flows from hard surfaces and erodes less stable surfaces.
Residential and commercial developments within Bethlehem Township were
required by State, County and Municipal regulations to attenuate the additional
runoff such that the post-developed runoff rates to adjacent properties and
waterways did not exceed the pre-developed condition. Over time the
regulations evolved to require specific reductions in runoff from various storm
events. For example, the 100 year storm event needed to be reduced to 80% of
the pre-developed condition.
To address the regulations, developments incorporated detention basins in their
design. These basins, with a system of control devices are generally designed to
slow down or hold the water for a short time and remove pollutants before it is
released to a stream. Stormwater controls are widely referred to as best
management practices or BMPs. All of the residential developments within
Bethlehem Township for which this manual is applicable have generally the same
features.
Inspection
Stormwater controls must be routinely inspected and maintained to ensure they
continually function as designed. If proper maintenance is not provided, adverse
environmental impacts such as the discharge of pollutants into ground and
surface waters may occur. In extreme cases, the structural integrity of the
detention basin berm or control structures can be compromised resulting in
failure and flooding of downstream areas.
Stormwater management facilities must be routinely inspected and have the
necessary maintenance performed on them to be certain that they continually
function as designed. An inspection checklist is provided in Appendix “A” of this
report. The following is a list of problems that may be encountered during an
inspection.
General Site Conditions
Trash and debris
Evidence that water remains in the basin longer than 5 days. Cattails and
other wetland vegetation are good indicators that water is remaining in the
basin longer than intended. If this is the case, try to determine the cause of
the standing water.
Animal burrows
Vandalism
Structural/Mechanical
Obstructions of the inlet or outlet devices by trash, debris, and vegetative
growth
Cracks and deterioration of inlets, outlet structures, pipes, and catch basins
Damaged or missing trash racks
Outlet protection buried with silt and sediment
Damaged or sediment laden low flow channels
Water seepage or ponding
Vegetation
Bare ground void of vegetation
Weeds and woody vegetation
Invasive plant species
Trees and other woody vegetation on the berm
Earthwork
Excessive erosion or sedimentation, particularly in emergency spillways and
swales.
Cracks or settling in the embankment or berms
Deterioration of downstream channels
Frequency of Inspection
Regularly conducted inspections are crucial to ensure effective performance.
Inspection frequency varies based on the stormwater management feature. As a
guideline, the following should be followed at a minimum. Significant storm
events may necessitate more frequent inspections.
• General Site Conditions - Monthly
• Structural/Mechanical Components – Annually
• Earthwork - Annually
• Vegetation – Biannually
• Trash Racks and Grates – After every major storm event for clogging.
Safety Considerations
Safety considerations must be a constant focus during stormwater control
inspections. Prior to conducting the inspection, anticipate any potential hazards
based on recent or current conditions (i.e., flooding after a heavy rain). Always
avoid hazardous conditions and document them on the inspection checklist.
Common safety concerns when performing stormwater control inspections
include:
• Never conduct inspections of confined spaces alone, without proper training.
• Take precautions around standing water; depths are likely unknown and the
ground may be unstable.
• Park in areas that provide safe entrance and exit of work area; do not create
potential conflicts with other vehicles/equipment operating in the work area;
and provide maximum protection for workers entering and exiting the vehicle
along roadways.
• Always wear protective clothing, boots, and safety vests.
• Be cognizant of the hunting seasons.
• Be aware of large vertical drops and avoid standing on retaining walls or other
structures that present a fall hazard. Make a note of hazard areas on the
inspection form.
• If toxic, hazardous or unknown substances are discovered in the area, leave
the vicinity and report the findings by contacting 911.
• Be aware of loose material (such as riprap), excavation drop-off, tripping
hazards, uneven ground, and other obstructions.
• Be aware of poisonous plants, insects, and wildlife.
Reporting and Record Keeping
Observations made at the time of inspection pertaining to the status of the
stormwater control shall be documented. All inspection findings and
maintenance activities should be noted on the appropriate inspection form in
Appendix A. Completed inspection forms are to be retained by the entity
responsible for maintaining the stormwater management system with copies
provided to the Bethlehem Township Clerk and an annual basis.
Overall Maintenance
Stormwater management controls require two basic types of maintenance: (1)
routine maintenance and (2) emergency maintenance. All routine maintenance
and/or emergency repair needs found at the time of inspection should be
identified and reported. Visual observations, contacts made, maintenance
performed, and any maintenance recommended at the time of inspection must be
documented.
If emergency maintenance needs are found, the inspector should either take
immediate action to correct the problem(s) or alert the responsible parties of
maintenance and/or repair needs. A follow-up inspection should be made to
ensure that corrective actions have been satisfactorily completed and normal
operation has been restored. All correspondence and corrective actions shall be
documented.
Routine Maintenance
Routine maintenance is any procedure performed on a regular basis to maintain
the proper working order of a stormwater control. Tasks associated with routine
maintenance include, but are not limited to, the following:
• Periodic maintenance of grasses, trees, shrubs, and other desirable plant
species
• Removal of undesirable plant species
• Removal of trash and debris
Upkeep of mechanical/structural components
Routine maintenance predominately involves some type of vegetation
management practice. Care should be taken to avoid using equipment that can
cause soil compaction in or around stormwater controls. Heavy equipment with
narrow tracks or narrow tires, rubber tires with large lugs, or high-pressure tires
can cause excessive compaction resulting in reduced infiltration and damage to
underdrain systems. When mowing in or around a stormwater control, use riding
mowers or tractor mowers with turf-type tires, push mowers and/or weed eaters.
Emergency Maintenance
Emergency maintenance is a non-routine repair performed to correct a problem
and restore a stormwater control to its proper working order. Tasks associated
with emergency maintenance include, but are not limited to:
• Sediment removal
• Structural repair
• Erosion repair/bank stabilization
Since emergency maintenance needs (i.e., berm failure) often require both
structural repair and soil stabilization work, it is anticipated that most emergency
repairs will performed under the guidance of a licensed professional engineer.
If emergency maintenance needs are found, the inspector should either take
immediate action to correct the problem(s) or alert the responsible parties of
maintenance and/or repair needs.
Vegetative Maintenance
Desirable vegetation is an important component of many stormwater controls.
Basins currently within Bethlehem Township are designed to be stabilized with
turf-type grasses along the bottom, side slopes and berms. The grass is to help
control erosion, provide structural stability and remove pollutants from
stormwater runoff. Some have native/ornamental grasses, trees, shrubs, and
herbaceous plants around their outside perimeter. Desirable vegetation can also
enhance the aesthetic appeal of stormwater controls and enable them to blend
into the landscape.
Periodic maintenance of desirable vegetation is required to ensure that it remains
healthy and established. Climatic conditions, lack of proper maintenance, storm
events, vehicular/equipment traffic, and vandalism can have a detrimental effect
on plant material. Provisions may be needed to supplement or replant some
vegetated areas due to plant loss. Supplemental and replacement planting
should occur during the appropriate planting season for the particular plant
species being utilized. These new plantings will require additional care until they
are established.
Turf-Type Grasses
Turf-type grasses are common to most stormwater controls. They can be the
major component in a stormwater control’s makeup or simply used to stabilize
the areas surrounding a stormwater control. Turf-type grasses provide soil
stability, reduce water flow velocities, and help maintain the structural integrity of
stormwater controls. They serve as pretreatment for stormwater controls by
slowing the overland runoff and filtering out sediment and pollutants. If
maintained properly, turf-type grasses can also improve access to stormwater
controls, making inspection and maintenance tasks easier.
Provisions should be made to reestablish a uniform cover of turf-type grass on
those areas damaged by sediment accumulation, stormwater flow, and/or
vehicular/equipment traffic. Failure to maintain a uniform turf-grass cover could
result in structural failure and sediment loss. Any turf found not in a healthy
growing state should be evaluated to determine the maintenance needs (i.e.,
fertilization, repair seeding, sodding).
Mowing should be tailored to the specific site conditions, turf-grass type, and
seasonal variations. Ideally, turf-type grasses should be mowed at a frequency
to maintain a maximum height of 4 inches for warm-season grasses and 6 inches
for cool-season grasses. Mowing activities should include trimming grass around
fences and structures. All clippings discharged from mowers or string trimmers
should be directed away from the stormwater device so they do not add nutrients
to the water.
Herbaceous Plants and Native/Ornamental Grasses
Existing stormwater management basins within Bethlehem Township are not
designed to have herbaceous plants or native ornamental grasses within the
storage area of the basin or on its berms. Current regulations permit basins to
be designed with herbaceous and native/ornamental grasses to provide
additional water quality treatment and reduce routine maintenance. However the
basins within Bethlehem Township predate these regulations and would require a
retrofit design prepared by a licensed professional engineer. (See Appendix “B”
for Rutgers Cooperative Extension document on Detention Basin Refits and
Maintenance.) Therefore basin maintenance will require the removal and
replacement of these plants with turf type grasses.
Trees and Shrubs
Existing stormwater management basins within Bethlehem Township are not
designed to have trees or shrubs within the storage area of the basin or on its
berms. Current regulations permit basins to be designed within the bottom of the
basin. However the basins within Bethlehem Township predate these
regulations and would require a retrofit design prepared by a licensed
professional engineer. Therefore basin maintenance will require the removal and
replacement of trees and shrubs with turf type grasses. In all cases berms
should be kept free of trees, shrubs and woody plants. Root structures
associated with these plants can compromise the stability and promote
capillary movement of water through the berm.
Fertilization
Fertilizer should only be used when necessary and not as a routine seasonal
practice. Spread fertilizer uniformly over the targeted area; during application,
use extreme care to prevent the fertilizer from contaminating the stormwater
control or adjacent streams, ponds, lakes, or other bodies of water. Immediately
incorporate fertilizers into the soil when seeding. Do not apply topdressing
fertilizers to grass swales, filter strips, or buffer areas that drain to nutrient
sensitive water bodies.
Undesirable Vegetation Removal
If proper maintenance is not provided, undesirable vegetation such as weeds,
grasses, and woody plants (trees and shrubs) will invade the vegetated areas of
stormwater controls. In time, this vegetation can inhibit the ability of a stormwater
control to store, treat, and/or convey water. .
Invasive plant species should be eliminated within all areas of the basin. New
Jersey invasive species can be readily identified on smartphones by downloading
an APP from NJDEP at http://www.njisst.org/NRCSGrant.htm or from lists
provided at http://www.invasivespeciesinfo.gov/unitedstates/nj.shtml#thr.
Remove undesirable vegetation before it becomes established. Once
established, this plant material can have an adverse effect on the survivability of
desirable plants and the aesthetic appeal of stormwater controls. The best time
to do this is during routine mowing or plant maintenance activities. Undesirable
plants can be removed by physical, mechanical, and/or herbicidal practices.
Dispose of the trimmed plant material properly; do not discard into waterways
because the material could clog the waterways and add nutrients to the water or
reestablish elsewhere.
Undesirable Woody Vegetation Removal
Although plant roots are important for soil stabilization, they can present
problems if volunteer trees and shrubs are allowed to mature in locations they
are not wanted. Mature trees and shrubs can impede and redirect water flow in
inlet and outlet ditches. As trees and shrubs mature, their root systems can
penetrate deep into the basin and clog the underdrain system. Decaying plant
roots can create voids in the dams and embankments when mature trees die or
are cut. This can result in structural failure if the situation is not addressed.
Woody vegetation not removed can also impede access to basin control
structures.
Remove undesirable woody vegetation when found and dispose of it off-site.
Any void created by removal activities should be completely filled in and properly
compacted using an appropriate earthen material. Reestablish desirable
vegetation to stabilize the area and prevent erosion.
Trash and Debris Removal
Trash and other debris can pollute surface waters and damage stormwater
control devices. The removal of floating trash and other debris will not only
improve water quality, it will reduce the potential for outlet clogging during storm
events and improve the overall aesthetic appeal of a stormwater management
basin. Trash should be removed on a routine basis as part of the maintenance
activities. Remove trash and debris from outlet orifices, trash racks, basin and
swale floors and side slopes, and other components, as well as from the area
surrounding the basin.
Mechanical and Structural Component Maintenance
Mechanical/structural components need to be maintained regularly to ensure that
they remain functional at all times. All mechanical components, including valves,
sluice gates, pumps, fences, gates, trash racks, and access hatches, should be
operated during each inspection to ensure that they function properly. Check
security components such as fences, gates, and locks for soundness. Repair
any fence, gate, or lock found damaged in a timely manner in order to restore
site security and safety.
Mechanical/structural repairs should be made promptly by qualified personnel.
Equipment, materials, and personnel should be readily available to perform
repairs on short notice. The following conditions could lead to structure failure
and may necessitate an emergency repair: a broken sluice gate; cracks in
concrete outlet structures; settling, scouring, cracking, sloughing, or furrowing on
embankments; or seepage around an outflow pipe.
Outlet Control Structure
The outlet control structure is used to drain the dry detention basin. Outlet
control structures can have several components, including a trash rack, a trash
screen, one or more drawdown orifices, and an outlet pipe. The drawdown
orifice(s) is located at the bottom of the outlet control structure and slowly drains
the basin, reducing peak flow and allowing solids to settle. Typically, the outlet
control structure has a second, larger opening that allows flow from large rainfall
events to escape without overtopping the basin. Usually, this is in the form of an
open-top outlet structure. All outlet controls should have a trash rack installed at
their inlet.
Standing water in the basin may conceal parts of the outlet structure. If access to
submerged components is needed, the basin can be drained or pumped out;
however, the water must first be visually inspected for obvious signs of
pollutants. Check for an oily sheen or excessive suspended solids. If either of
these is present, do not drain the basin and contact the appropriate authority for
guidance.
Treated water should be allowed to flow freely upon entering the outlet control
structure. Inspect the outlet control structure thoroughly for any signs of damage
such as cracking, holes, or leakage. Verify that the outlet box remains covered
with a trash rack. Repair any damaged areas of the outlet control structure, and
remove sediment and debris if it is accessible. If the outlet is clogged or blocked
and standing water prevents access to the structure, hip waders or a small boat
may be needed to make the necessary repairs. Ensure that proper safety
procedures are followed when working in or around standing water.
Trash Racks
Positioned atop the outlet control structure (box) and in front of any weir or
orifice, the trash rack protects the flow through the outlet structure from becoming
clogged with debris. Inspect the trash rack for debris and excessive corrosion.
Remove trash and debris. Replace the trash rack if it is corroded or otherwise
damaged. The replacement trash rack should be consistent with the original
design specifications.
Outlet Drainage System
The outlet drainage system conveys water from the outlet control structure
through the embankment to a swale or other open channel. Inspect the inside of
the outlet box and pipe(s) for sediment and debris. Inspect the ground surface
above buried pipes and structures for depressions or other signs that might
indicate pipe breakage or separation. Inspect ditches for signs of erosion and
undesirable vegetation.
Remove any sediment or debris that is accessible. Repair eroded areas and
damaged pipes. Replace outlet protection materials (i.e., riprap) as necessary.
Emergency Spillway
The emergency spillway serves as an overflow structure that is typically
constructed as a channel in natural ground. The emergency spillway is
necessary to minimize the potential for overtopping the basin, which can damage
the embankment and lead to failure and downstream flooding.
The emergency spillway should remain free of trash and debris. Emergency
spillways are typically covered with grass, but concrete and riprap are also used.
For grass channels, verify that grass is maintained as previously described.
Inspect concrete to verify that it is in good condition, or verify that adequate
riprap is present. Note all erosion and undesirable vegetation.
Emergency spillways must be free of trash, debris, and undesirable vegetation to
maintain their functionality. Remove these if present. Grass should be carefully
maintained as previously described. If applicable, repair concrete or replace
riprap as necessary. Repair areas of erosion.
Sediment Removal
Sediment will eventually accumulate in every type of stormwater control. The
degree to which it accumulates will depend on the upstream sediment source,
rainfall intensity, and the amount of runoff that a basin receives. Any sediment
found blocking the inlet or outlet of a stormwater control should be removed. If
sediment buildups are allowed to block inlets or outlets, stormwater may be
diverted to areas of the basin not designed for concentrated water flow and
cause these areas to erode.
Conduit outlet protection areas of rip rap or gabions are most prone to collection
of sediment. When clogged with sediment, these features no longer dissipate
the water energy discharged from the pipe resulting in potential downstream
erosion. Similarly low flow channels may collect sediment over time impeding
the full and complete drainage of the basin creating ponding conditions. Ponding
conditions are known to promote mosquito breeding.
Sediment that has accumulated and is inhibiting the function of a basin must be
removed. Sediment can be flushed from the outlet protection with the use of a
high pressure hose. The dredged or removed sediment must be transferred to a
waste pile or area that is protected from stormwater run-on. Make sure the
removed sediment is not left in the vicinity of the basin where stormwater could
come into contact with it and transport it back to the basin or nearby receiving
waters.
Erosion Repair & Soil Stabilization
It is necessary that a uniform vegetative cover be maintained to prevent soil loss,
to maintain structural integrity, and to enhance the pollutant removal benefits of a
stormwater management basin. Failure to maintain a uniform vegetative cover
could result in structural failure and sediment loss.
Take corrective actions when erosion is found. Repair activities should be
tailored to the specific site conditions, grass type, and seasonal variations.
Repair may include the use of one or a combination of the following measures:
erosion control blankets, riprap, matting, sodding, and/or seeding and mulching.
Animal Burrow Repair
Voids created by animal burrows can weaken dams and embankments, and
result in structure failure. Animal burrows found in the dams, berms, and
embankments of stormwater management basins should be filled in as soon as
possible. Burrows should be completely filled in and properly compacted using
an appropriate earthen material. Reestablish desirable vegetation to stabilize the
area and prevent erosion. If burrowing problems persist, local wildlife officials
should be consulted for information regarding preventive tactics or animal
removal.
Glossary
Attenuate
The reduction of flow in volume and/or force
Berm
Elevated earthen embankment that impounds stormwater
runoff within the stormwater management basin. Berms
typically have a minimum top width of 10 feet.
Best Management Practice
(BMP)
A general term most often used to describe methods that
are the most effective and practical means of preventing or
minimizing pollution. The term BMP is often used to
describe the structures that are built to reduce stormwater
pollution.
Channelization
The process by which concentrated flow erodes a channel
through areas in or around a stormwater control that can lead
to compromised performance of the control or even failure.
Concentrated Flow
Water that is flowing in a channel or pipe, or that has
otherwise collected and is flowing in a manner not consistent
with sheet flow.
Confined Space
A space that (1) is large enough and so configured that an
employee can bodily enter and perform assigned work; (2) has
limited or restricted means for entry or exit (for example, tanks,
vessels, inlets, manholes, and pits); and (3) is not designed for
continuous employee occupancy.
Embankment
An earthen berm, constructed from fill material, used to store
runoff in basins.
Emergency Spillway
A level, depressed area along the top of berm over which
stormwater is discharged during storm events exceeding the
100 year storm event or due to blockage of the primary outlet
structure.
Detention Basin
A stormwater control that reduces peak stormwater flows,
promotes the settling of suspended pollutants, and minimizes
erosive velocities downstream of the outlet structure.
Erosion
The process by which a surface is worn away. In the context
of this manual, erosion refers to the process by which runoff
washes away soil.
Gabion
Wire mesh baskets filled with Rip-Rap stone installed to
prevent erosion from higher velocity runoff conditions.
Impervious Surface
A land cover through which water cannot infiltrate; examples
include concrete, asphalt, rooftops.
Infiltration
The act of water soaking through the surface of the soil.
Low Flow Channel
A relatively flat 3 to 6 inch deep channel constructed along the
bottom of a detention basin typically constructed of concrete
or bituminous asphalt. Used to provide positive drainage of
runoff remaining after a storm event and prevent ponding of
water.
Orifice
Positioned near the base of the outlet control structure, the
drawdown orifice is a restricting device that allows stormwater
to slowly enter the outlet box. In most cases, the drawdown
orifice consists of either one or more 3-inch holes drilled
directly into the side of the box or a predrilled steel plate
attached to the side of the outlet control structure covering a
manufactured outlet opening
Outlet Control Structure
Typically a concrete structure within the basin that
incorporates weirs and orifices to regulate the discharge of
stormwater through the stormwater management basin.
Outlet Protection
Rip rap or gabions installed at a storm sewer discharge
location
Percolation
The act of water traveling downward through the soil.
Permanent Soil
Reinforcement Matting
A material used to hold soil in place so that vegetation can
take root and prevent erosion; commonly used in areas with
steep slopes or other erosive conditions.
Rip-Rap
Large quarry processed rock that can vary in size from 3
inches to 24 inches installed at the discharge of a storm sewer
pipe discharge or along a channel to prevent erosion
Runoff
Precipitation on land that eventually reaches streams and
rivers.
Sediment
Soil that has been eroded and deposited elsewhere; typically
contains pollutants and has a negative impact on aquatic
environments.
Seepage
The slow discharge or escape of water.
Sheet Flow
A shallow layer of water flowing over land at a low
velocity, enabling pollutants to settle out.
Storm Event
Rainfall events categorized by their frequency. For example a
10 year storm event has a likelihood of occurring once every
10 years or a 10 percent chance each year. Similarly a 100
year storm event has a likelihood of occurring once every 100
years or a 1 percent chance each year.
Stormwater
A term used to describe water that originates from
precipitation; often used interchangeably with the term runoff.
Suspended Solids
Small particles carried in stormwater as a result of erosion;
regarded as an indicator of water quality.
Swale
A vegetated channel that conveys stormwater runoff.
Toe (of embankment)
The bottom of the embankment where it meets the natural
ground.
Trash Rack
A stainless steel or aluminum grid applied to the upstream
portion of an outlet structure to prevent trash and debris from
clogging the control devices.
Weir
A control feature of an outlet control structure which is a
rectangular or triangular notch that regulates the flow of
stormwater through the structure
Appendix “A”
Inspection and Maintenance Checklist
Extended Detention Basin
Inspection and Maintenance Checklist
Property Address:
Property Owner:
Treatment Measure No.:
Date of Inspection:
Type of Inspection: Monthly Pre-Wet Season
After heavy runoff (1” or greater)
End of Wet Season
Inspector(s):
Other:
Defect
Conditions When
Maintenance Is Needed
Maintenance
Needed? (Y/N)
Comments (Describe maintenance
completed and if any needed maintenance was
not conducted, note when it will be done.)
Results Expected When Maintenance Is Performed
General
Trash &
Debris
• Trash and debris
accumulated in basin.
• Visual evidence of
dumping.
Trash and debris cleared from site and disposed of
properly.
Undesirable
Vegetation
Weeds, invasive vegetation
and woody plants
Vegetation treated with herbicides or physically
removed and disposed of properly.
Contaminants
and Pollution
Any evidence of oil,
gasoline, contaminants or
other pollutants.
No contaminants or pollutants present.
Animal
Burrows
If facility acts as a dam or
berm, any evidence of
rodent holes, or any
evidence of water piping
through dam or berm via
rodent holes.
The design specifications are not compromised by
holes.
Any rodent control activities are in accordance with
applicable laws and do not affect any protected
species.
Insects
Insects such as wasps and
hornets interfere with
maintenance activities.
Insects do not interfere with maintenance activities.
Tree/Brush
Growth and
Hazard Trees
• Growth does not allow
maintenance access or
interferes with
maintenance activity.
• Dead, diseased, or dying
trees.
• Trees do not hinder maintenance activities.
• Remove hazard trees. (Use a certified Arborist to
determine health of tree or removal
requirements).
Extended Detention Basin Inspection and Maintenance Checklist
Date of Inspection:
Property Address:
Treatment Measure No.:
Defect
Conditions When
Maintenance Is Needed
Maintenance
Needed? (Y/N)
Comments (Describe maintenance
completed and if any needed maintenance was
not conducted, note when it will be done.)
Results Expected When Maintenance Is Performed
Drainage time
Standing water remains in
basin more than five days
after a storm event.
Correct any circumstances that restrict the flow of water
from the system. Restore drainage to design condition.
If the problem cannot be corrected and problems with
standing water recur, then mosquitoes should be
controlled by a licensed pesticide applicator.
Outfall
structure
Debris or silt build-up
obstructs an outfall structure.
Remove debris and/or silt build-up and dispose of
properly.
Side Slopes
Erosion
• Eroded where cause of
damage is still present or
where there is potential for
continued erosion.
• Any erosion on a
compacted berm
embankment.
Cause of erosion is managed appropriately. Side
slopes or berm are restored to design specifications, as
needed.
Storage Area
Sediment
Accumulated sediment
affecting inflow or outflow of
the facility
Sediment cleaned out to designed basin shape and
depth; basin reseeded if necessary to control erosion.
Sediment disposed of properly.
Emergency Overflow/ Spillway and Berms
Settlement
Berm settlement lower than
the design elevation.
Dike is built back to the design elevation.
Tree Growth
Tree growth on berms or
emergency spillway.
• Trees should be removed. If root system is small
the root system may be left in place. Otherwise the
roots should be removed and the berm restored.
• A licensed professional engineer should be
consulted for proper berm/spillway restoration.
Emergency
Overflow/
Spillway
Rock is missing and soil is
exposed at top of spillway or
outside slope.
Rocks and pad depth are restored to design standards.
Extended Detention Basin Inspection and Maintenance Checklist
Date of Inspection:
Property Address:
Treatment Measure No.:
Debris Barriers (e.g., Trash Racks)
Trash and
Debris
Trash or debris is plugging
openings in the barrier.
Trash or debris is removed and disposed of properly.
Damaged/
Missing Bars
Bars are missing, loose, bent
out of shape, or deteriorating
due to excessive rust.
Bars are repaired or replaced to allow proper
functioning of trash rack.
Inlet/Outlet
Pipe
Debris barrier is missing or
not attached to pipe.
Debris barrier is repaired or replaced to allow proper
functioning of trash rack. There are to be no barriers
present at pipe discharges.
Fencing and Gates
Missing or
broken parts
Any defect in or damage to
the fence or gate that
permits easy entry to a
facility.
Fencing and gate are restored to design specifications.
Deteriorating
Paint or
Protective
Coating
Part or parts that have a
rusting or scaling condition
that has affected structural
adequacy.
Paint or protective coating is sufficient to protect
structural adequacy of fence or gate.
Miscellaneous
Miscellan-
ous
Any condition not covered
above that needs attention
to restore extended
detention basin to design
conditions.
Meets the design specifications.
Appendix “B”
Detention Basin Retrofits and Maintenance
by
Rutgers Cooperative Extension Water Resource Program
http://water.rutgers.edu/Projects/Sussex/Detention%20Basin%20Retrofits%20and%20Maintenance.pdf
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First Discovered
Apr 1, 2026
Last Info Update
Apr 1, 2026
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