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Post Construction Stormwater Management
As development occurs, be it residential, commercial or industrial, previously impervious and uncompacted soils are graded, compacted and mostly converted to impervious surfaces such as roads, driveways, parking lots and buildings. The ability for those uncompacted and impervious surfaces to infiltrate stormwater has been reduced or eliminated, which leads to large increases in stormwater runoff. That stormwater runoff is also a significant source of water pollution.
To mitigate those impacts, new developments are required to implement Best Management Practices (BMPs) as part of their projects. A BMP is a technique or practice that is used to manage the quantity and quality of stormwater runoff. The goal of these is to remove pollutants and improve water quality, prevent downstream streambank and channel erosion, reduce downstream overbank flooding and safely convey and reduce runoff from extreme storm events. Common BMPs include rain gardens, bioswales, permeable pavement and stormwater detention.
Detention Basins
Detention basins are the most common BMP found in new developments. They help mitigate the increased stormwater runoff by collecting all runoff generated by a new development and then releasing it a controlled rate. Current standards require the 100-year developed runoff to be detained and then released at the same release rate as a 5-year undeveloped condition. Additionally, the City requires the most common and frequent rainfall events (referred to as the Water Quality Volume which is equivalent to 1.25 inches of rain) to be captured and treated, as well as the Channel Protection Volume (equivalent to 2.60 inches of rain) to be detained for an extended period of time to reduce erosive velocities and protect downstream creeks and streams. More information can be found in the City of Bettendorf Stormwater Design Standards Manual
Construction Site Erosion and Sediment Control
Rain events, melting snow, and high winds can cause erosion of sediment from construction sites into the storm sewer system and adjacent creeks and streams. Sediment entering stormwater degrades water quality and can cause the storm intakes and pipes to clog and cause localized flooding.
For these reasons, the Iowa Department of Natural Resources (IDNR) NPDES General Permit No. 2 and the City of Bettendorf's MS4 permit require that all construction activity over one acre develop a Stormwater Pollution Prevention Plan (SWPPP) in order to minimize the amount of erosion that occurs. Additionally, the City requires that a COSESCO permit be obtained for all land disturbing activities.
The City is also mandated by their MS4 permit to routinely inspect all construction sites to ensure that they are in compliance with all local, NPDES and other state regulations. Maintaining on-site erosion controls in good working order is key to decreasing stormwater pollution. The City does have the authority to stop work on construction sites if erosion controls are missing or are not maintained.
- COSESCO Permit
- COSESCO Termination Form
- City Code - Construction Site Erosion and Sediment Control (COSESCO)
Anyone seeking additional information on erosion and sediment control should email Rob DePover, Erosion & Sediment Control Technician, or call him at (563) 344-4056.