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KRAUS ANDERSON - MOUNDS VIEW SCOTTLAND GREEN POND - ANALYSIS OF EXISTING CONDITIONS EXISTING LAND USE Following is a breakdown of present land use in the 266 acre drainage area tributary to Scottland Green Pond. The area of the pond is presently undeveloped, is partially marshy, with the remainder being idle upland in grasses and trees. The following table breaks down land use for the watershed. Percent Total Area Area. Land Use Impervious Area Imp . _ Perv. . Open Space 10 136.3 13.6 122.7 Single Family Res. 27 51.7 14.0 37.7 Multiple Residential 55 21.7 11.9 9.8 Commercial 80 12.1 9.7 2.4 T.H. 10 ROW 40 26.0 10.4 15.6 City Hall Property 40 18.2 7.3 10.9 Totals 266.0 66.9 199.1 Note that all areas are in acres. It is assumed that approximately 5 acres of the 199.1 acres of pervious area will be pond. -or open water area and as such will have 100 percent runoff potential. On an overall drainage area basis, the existing conditions percent- age impervious is 66.9/266.0 = 0.25 or 25 percent. INFILTRATION IN TURFED AREAS Soil types in the area are sands having high infiltration rates. Such soils are common all over the City. A major control to infiltra- tion is depth to water table. Where the pre -storm water table is shallow infiltration will be limited by the capacity of the soil. On the Kraus Anderson property (the major pervious area), the water table is normally more than six feet in depth. Infiltration is estimated in two ways: a. SCS Curve Number: From the SCS Hydrology manual, curves are given that relate rainfall and runoff for various soil types. We assumed that the pervious area soils would be Zimmerman Soils (Class A). From the SCS tables for fair pasture land (should be reasonably equivelant to lawns), we should use curve number 49. Use CN = 50. For Cn = 50 and a 100 year-24 hour rainfall of 5.9 inches, runoff should be approximately 1.1 inches.