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Facilities - Detention pond

Detention Pond

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Good: A well maintained detention pond. Detention ponds are dry between storms.
Detention Pond with water
Good: A well-maintained detention pond draining slowly after a storm.

A stormwater detention pond is an open basin built by excavating below ground or constructing above-ground berms or embankments. The detention pond temporarily stores stormwater runoff and slowly releases it through a specially designed outlet or control structure. Detention ponds typically are designed to drain completely within a few hours or days. Some detention ponds include other types of facilities such as biofiltration swales

Detention ponds can vary greatly, from appearing well-manicured to more natural. Sometimes, more natural-appearing vegetation is preferred for reduced maintenance and enhanced wildlife habitat. Some facilities are designed to appear as natural water bodies or park-like areas. Vegetation requirements can vary between jurisdictions, so make sure to check in with your local stormwater professionals.

Virtual tour

Click on the image below to get inside a detention pond and learn about common components and maintenance tasks.

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Maintenance needs commonly associated with detention ponds

Man tripping vegetation in swale.


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Control structure 

a field inlet

Field inlet 

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Pet waste 

inlet of a stormwater facility

Inlets and outlets 

combined stormdrain catch basin and curb inlet.

Catch basin 

Maintenance is needed if you see these signs

Problem Detention Pond sediment
Problem: This detention pond has a sedimentation problem.
Problem Detention Pond
Problem: This detention pond is overgrown with vegetation.

Bare, exposed soil

Slopes that are deteriorating

Sediment that restricts flow or clogs inlet and outlet pipes

Sediment buildup; the facility is not draining or conveying runoff

Unhealthy or dead vegetation

Blackberries or other problem weeds

Overgrown vegetation     

Holes in berms or slopes

Leaves, trash and other debris

Water surface is discolored or has a sheen

Water stands in infiltration basin or detention ponds longer than 72 hours after rain stops

Bottom of slopes show signs of seepage and leaking

Trees, often alders, growing on the slopes


Tips for fixing problems and general maintenance


Remove weeds such as blackberries and English ivy, then check for them on a regular basis and remove new vines.  Contact Clark County Vegetation Management for questions about controlling weeds at (360) 397-6140 or email 

Remove cattails before they start to dominate a facility.

Remove all unplanned trees or saplings that block parts of the facility or hinder maintenance.

Make sure banks, slopes and areas designed for vegetation are planted with native or easy-to maintain species. Avoid trees near the pond and on berms.

Plant at appropriate times during the year so vegetation can get established.

Replace vegetation damaged or removed during maintenance.

Check access roads and fencing, if the facility has them. They should be free of overgrown vegetation and other materials so that the facility is easily accessible for maintenance.


Control erosion by reseeding areas where soil is exposed, especially on slopes around a facility.

Fill in eroded areas and cover them with sod, mulch or other erosion control materials.


Removing sediment is best done in July and August before winter rains set in.


Pick up leaves before rains begin.

Inspect and remove debris regularly, particularly after storms.

Remove any material clogging drains, outfalls and channels.

Avoid using fertilizers, herbicides or pesticides in or near the facility. Chemicals pollute the water and can cause unwanted plant growth.

Identify sources of leaks or spills and contain them as quickly as possible.


Check inlets and any open or confined standing water for mosquito larvae (see photos below). If mosquitoes are a concern, contact Clark County Mosquito Control District for information. The 24-hour service request line is 360.574.7906.

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Check roads and fencing in the facility. They should be maintained to allow easy access.