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<br />::: <br /> <br /> <br />CONTOUR LINES <br /> <br />DIRECTION <br />OF FLOW <br /> <br /> <br />o <br />... <br />~ <br /> <br />'{ RIDGE LINE <br />OR <br />DRAINAGE DIVIDE <br /> <br />Exhibit 16. A drainage area is defined by drainage divides or lines <br />that connect the high points or follow the ridge lines <br />around the area served by the culvert. <br /> <br />a. Climatic Factors--C1imatic factors which may influence the amount of <br />runoff include rainfall intensity, storm duration, rainfall distribution <br />within the drainage area, soil moisture, snow melt, rain-on-snow, rain-hail, <br />and other factors. <br /> <br />b. Topographic Factors--Topographic factors which may influence runoff <br />include the land use within the drainage area; the size, shape, and slope of <br />the drainage area; and other factors such as the type of soil, elevation, and <br />orientation of the area. <br /> <br />(1) Land use is the most likely characteristic to change significantly <br />during the service life of a culvert. Changes in land use may have a <br />considerable effect on the amount and type of runoff. Some surface <br />types wi 11 permit more infiltration than other surface types. <br />Practically all of the rain falling on paved surfaces will drain off <br />while much less runoff will result from undeveloped land. If changes <br />in land use were not planned during the design of a culvert, <br />increased runoff may exceed the capacity of an existing culvert when <br />the land use does change. <br /> <br />27 <br />