Dry Detention Basin Typical Maintenance Requirements

Reporting Requirements

An initial installation certification (as-built) stamped by a Professional Engineer (P.E.) registered in the state of Wisconsin shall be submitted to the City Engineer upon completion of construction.  The as-built shall be of sufficient detail to show the system was constructed and is functioning as designed. It shall include a statement by the certifying P.E. along with a marked-up drawing (if applicable), infiltration observation, and photograph(s). 

An annual report shall be submitted via email to City Stormwater Management staff. The report shall include records of all inspections and maintenance performed for the year. Inspections shall be done every calendar year, with reports being submitted by June 1 of the following year.

Maintenance Provisions

The Owner shall maintain records of inspections, mowings, and survey data, all in accordance with Chapter 37 of the Madison General Ordinances.

Owner shall install and maintain dry detention basin in accordance with plans approved by City Engineer and in accordance with WDNR Conservation Practice Standard #1011 Vegetated Dry Detention Basin. Any alterations to approved bioretention system shall be approved by the City Engineer.

At a minimum annually, visually inspect the basin, outfalls and outlet structure for deterioration or damage, erosion, obstructions, sediment build up, and general operation (including emergency drawdown & overflow devices if present). Check the condition at the receiving area/channels at the outlet and downstream from the release structures for stability and signs of erosion damage or sparse vegetation.

No structures of any kind are permitted within the detention basin area, without prior written approval of the City Engineer.

A topographic survey of the detention basin shall be taken once every three (3) years.  The survey shall be of sufficient detail so as to ensure maintenance of basin and outlet structure design and integrity of outfall structures. Survey data shall be sealed by a registered land surveyor and submitted to City Engineer for review. 

Siltation in the basin, as identified by the topographic survey, shall be removed and disposed of offsite in accordance with WDNR 347. 

Maintenance shall be required when the system shows standing water beyond 72 hours of rain event.  Visually inspect and record observation of system within 72 hours after a rain event greater than 0.5 inches. Include photos and copy of rain event data in report. If standing water is still present, maintenance is required. Add compost to the soil surface and rototill it into the soil as deep as possible to improve infiltration.  If basin is still not draining, remove two (2) foot undercut, undercut replacement with material consisting of 15% compost and 85% sand and restoration in-kind.

Infiltration Observation After Rain Event

Vegetation Management

Areas restored with native vegetation shall be mowed a maximum of twice annually (Spring and Fall) to promote sediment filtration and retention.

Areas restored with turf grass shall be mowed to a minimum grass height of 6 to 8 inches.  All undesirable vegetation and volunteer tree growth shall be removed, including close proximity to any outfall and the outlet structure.