Storm water drain plan by Erich Tietze and Associates
Figure details (lot 1)
Figure details (lots 2, 3, and 4)
Do all downspout splash block locations have the required 50 ft. of vegetated flowpath before reaching wetlands or streams, particularly for lot 1? Is it possible to place storm water drainage that meet all the requirements?
The City of Lake Forest Park's Municipal Code 16.06.080 specifies a number of conditions that need to be met for the design of the storm drainage system.
In addition, a Washington State Dept. of Ecology senior wetlands specialist's letter states that storm water system cannot be located within the wetlands and their buffers, and that the mitigation plan must be approved by the Dept. of Ecology.
Studies have found that changing hydrology "can have significant impacts on the livelihood of the whole range of wetland flora, from bacteria to the higher plants" (Azous & Horner, 1997, p.6)** Even if the annual average flow into the wetlands is unchanged, the increased variation in flow quantity due to impervious surfaces such as roof and driveway (e.g., greater flow in winter, diminished flow in summer) can result in the loss of plant species, as studies found that while "dominating species were found in a wider range of conditions of drought to inundation and water level fluctuation", "less common and less dominant species were almost always found in narrow ranges of hydrologic conditions" (Cooke & Azous, 1997, p.169).***
*: The term, "BMPs" mentioned on page 1, we believe, refers to "Best Management Practices"
**: Azous, A. L., & Horner, R. R. (1997). Wetlands and Urbanization: Implications for the future. Final report of the Puget Sound Wetlands and Stormwater Management Research Program. Washington State Dept. of Ecology, King County Walter and Land Resources Division, and the University of Washington.
***: Cooke, S. S., & Zaous, A. L. (1997). The hydrologic requirements of common pacific northwest wetland plant species. In A. L. Azous, & R. R. Horner (Eds.), Wetlands and Urbanization: Implications for the future (see above). pp.154-169.
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