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Last modified
1/25/2010 6:47:45 PM
Creation date
10/5/2006 1:08:03 AM
Metadata
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Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Storm Water Management for Constructed Activities
Date
9/1/1992
Prepared By
EPA
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />- <br />I <br />I <br />I <br />I <br />I <br /> <br />Chapter 2-Storm Water Pollution Prevention Plan <br /> <br />5. The last step is to divide the number of square feet on the site by 43,560 square feet per <br />acre to see how many acres there are. The result is an estimate of the site area in acres. <br />Repeat this method using the outline of the disturbed area to find the estimated acreage of <br />soil disturbing activities. <br /> <br />Example: <br /> <br />The site plan pictured below (Figure 2.2) is drawn to a 1 inch equals 200 feet scale /1":200'). <br />After tracing the boundary and counting the number of squares, the result is 620 1/4-inch <br />squares. <br /> <br />Divide 620 by the number of 1/4-inch squares per square inch, which in this case is 16 (the <br />number of 1/4-inch squares in a square inch is 16). The result is 38.75 one-inch squares. <br /> <br />Multiply 38.75 square inches by the number of square feet per square inch, 40,000 square <br />feet per square inch (based on the scale of this drawing that would be 200' times 200'). The <br />result is 1,550,000 square feet. <br /> <br />The final step is to convert the estimated area from square feet to acres by dividing by 43,560 <br />square feet per acre into the total number of square feet. The final result is 35.6 acres. <br /> <br />The area should be expressed in acres to the nearest tenth of an acre, e.g., 5.5 acres total site <br />area and 3.5 acres disturbed area. <br /> <br />The first measurerrent which you should make is to determine the total area of the site. The total <br />area of the site should include the area inside the project's property boundaries, easements and/or <br />right-of-ways. The total area includes both the disturbed and undisturbed areas. The second <br />measurement which you should make is the area which will be disturbed by the construction <br />project. This area can be determined by measuring the area enclosed by the limit of disturbance <br />drawn in on the site map (see Section 2.1.2) and subtracting from this value the area of any <br />undisturbed "islands" within the limit of disturbance. The disturbed area should always be less <br />than or equal to the total site area. <br /> <br />2.2.2 Determine the Drainage Areas <br /> <br />The final areas which you should measure are the size of each drainage basins for each point where <br />concentrated flow will leave the site. Although you do not need to put this information into the <br />pollution prevention plan, you will need this data to help you select and design the sediment control <br />and storm water management measures for your project. <br /> <br />For design of the sediment control measures, you will need to know the area of the portion of each <br />drainage basin which will be disturbed. The disturbed areas of the drainage basins should be <br />measured using the methods suggested above to estimate the area enclosed by the limit of <br />disturbance and/or the drainage boundary (whichever boundary gives the smaller area). <br /> <br />For the design of the storm water management controls and for the calculation of the runoff <br />coefficient. you should measure the total area of each drainage basin and the areas of each land <br />use which will occur in the basin after the construction is complete. Be sure to include offsite <br />water draining onto your site when determining the total size of the drainage basin. See Table 2.1 <br />for a listing of different types of land uses. The area of each land use in the drainage basins should <br />be measured using the methods suggested above to estimate the area enclosed by the land use <br />boundary and/or the drainage boundary (whichever boundary gives the smaller area). Topographic <br />maps are helpful tools to use in determining drainage boundaries. <br /> <br />September 1992 <br /> <br />2-9 <br />
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