Wetpond

Wetpond
Good: Well-maintained wetpond

Wetpond
A two-pool wetpond.

A wetpond, or wetpool, is an open basin that has a pool of water year-round. The volume of the wetpond allows sediment to settle out as stormwater runs in. Wetland vegetation is typically planted to provide additional treatment by removing nutrients such as phosphorus and nitrogen.

Typically, there are two pools. Stormwater flows into the first pool, where sediment settles before moving into the second pool. The water is then discharged to streams and groundwater.

Wetponds also have additional temporary storage above the permanent water level to detain and slowly release stormwater. They often are fenced for safety. 

 

 

 

Maintenance sheet

Wetpond
Field inlet
Flow control structure / flow restrictor
Debris and access barrier

Maintenance is needed if you see these signs  

Bare, exposed soil

ProblemDetentionPond 300x197.jpg
Problem: The detention pond above is over-
grown with vegetation. 

Slopes that are deteriorating

Sediment that restricts flow or clogs inlet and outlet pipes

Sediment buildup, especially on base of pond

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 an oil sheen

First cell/pond is empty and doesn't hold water

Berm dividing cells should be level so water flows evenly over entire length of berm

Trees, often alders, growing on the slopes

Tips for fixing problems and general maintenance

Completely 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 vegetation.management@clark.wa.gov 

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) 397-8430.

mosquito larve.jpg     mosquito larve1.jpg

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

 

Additional wetpond elements

Field inletField-inlet.jpg

A field inlet is a concrete structure that collects stormwater and routes it through underground pipes. Fitted with a slanted, slotted grate, it often traps sediment and debris. Regular maintenance is important. Keep the opening clear of obstructions. A field inlet is usually cleaned by a truck with a  vacuum hose but sometimes can be cleaned with hand tools.

Flow control structure / flow restrictorFlowControl.jpg

Underground flow control structures and flow restrictors direct or restrict flow in or out of facilities. They slowly release stormwater at a specific rate. It is important to make sure they do not become plugged or damaged because the facility could release water too quickly or too slowly and overflow. They are usually found in manholes.

Debris and access barrierDebrisBarrier.jpg

A debris or access barrier is a bar grate over the open end of a pipe larger than 18 inches in diameter that prevents large material, people or animals from entering. They typically are located on the outlet pipe from a detention pond to the control structure.

For safety purposes, only qualified personnel should remove debris from the barrier when water is flowing through the pipe.