Laserfiche WebLink
<br />, <br /> <br />Ii <br /> <br />II <br />J <br />.. <br />.;a <br />J <br />J <br />J <br />J <br />J <br />, <br /> <br /> <br />II <br />-.j <br />~.. ,: <br />.-.. !. ~ ' <br />,- . <br /> <br />:.t <br />'j <br />J <br />11 <br />.j <br />'j <br />j <br />.1. <br />.. <br />. <br /> <br />ill <br /> <br />The impervious part is the area that does not readily allow water to infiltrate <br /> <br /> <br />into the ground. such as paved areas, sidewalks, and buildings. As urbani. <br /> <br /> <br />zation occurs, the per cent of impervious area increases and the rainfall- <br /> <br /> <br />runoff ratio changes. In this report, only the land use as given by the <br /> <br /> <br />Planning Department, and as ultimately developed, was considered. The area <br /> <br /> <br />presen'Uy undeveloped, but to be developed, was assumed to be 60 per cent <br /> <br /> <br />pervious. The areas west of Overland Trail Road in Drainage Areas 24, 25, <br /> <br /> <br />26, 27, 32, and 40 and the eastern half of Drainage Area 18 were assumed <br /> <br /> <br />60 per cent pervious. All other areas west of Overland Trail Road were <br /> <br /> <br />assumed to be 90 per cent pervious. <br /> <br />Rainfall collected and retained in small depressions does not become <br /> <br /> <br />runoff and is called depression storage. This water evaporates or eventually <br /> <br /> <br />infiltrates. Depression losses include water intercepted by trees and bushes. <br /> <br /> <br />The parameters used for these abstractions were: <br /> <br />Impervious storage <br />Pervious storage <br /> <br />0.10 inch <br />0.50 inch <br /> <br />These figures do not include any planned ponding areas such as con- <br />, <br />trolled roof and parking lot ponding or larger detention basins or reservoirs. <br /> <br />Infiltration is the flow of water through the soil surface. In urban areas <br /> <br /> <br />much of the infiltration occurs on grass-covered areas. Soil type is the most <br /> <br /> <br />important factor in determining the infiltration rate. Infiltration can be <br /> <br /> <br />greater during the early part of a storm when the top layer of soil is <br /> <br /> <br />unsaturated, but will taper off to the true infiltration ability of the saturated <br /> <br /> <br />soil. The Soil Conservation Service in Fort Colhns was consulted in determin- <br /> <br /> <br />ing an average soil lyre and infiltration factor for the service area. Based on <br /> <br /> <br />consultation with the SCS personnel relative to soil type, the following <br /> <br /> <br />infiltration parameters were selected and used: <br /> <br />2-year storm <br /> <br />7.; inch per hour for first half hour <br />1, inch per hour thereafter <br /> <br />1, inch per hour <br /> <br />SO-year storm <br /> <br />17 <br />