BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

Left: Dripline erosion below a deck needs at least 3 inches of gravel to protect the soil.Right: Riprap protecting the toe of a cut slope down to an A/C curb prevents soil fromsloughing onto the parking lot.3.5.3 HYDROLOGIC SOURCE CONTROLIn most cases, the baseline design storm used for calculating the size ofinfiltration BMPs on these scale sites is the 20-yr/1-hr storm, approximately1”/hr. Using the BMP Calculation Spreadsheet may be adequate for driplinetrenches and small impervious areas within the project to design this storagecapacity. However, other calculation techniques for designing storage andconveyance may be more appropriate. Refer to Chapter 1, Urban Hydrologyfor further discussion of the BMP Calculation Spreadsheet and other usefulstormwater tools.Where project proponents are required to document an Environmental ImpactStatement or similar, the environmental analysis and mitigation maynecessitate an updated or unique design storm.See Table 3-8 for appropriate infiltration techniques that provide hydrologicsource control for stormwater runoff from driveways, parking lots, and rooftops.Figure 3-b shows an example of an infiltration basin collecting runoff between twoparking areas.TRPA BMP HandbookCHAPTER 3: Permanent BMP Planning and Selection2012 Page 3-21