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~ ~ ( - 34 - . ~ Discharge-damage curves were constructed for each kind of damage in the three main evaluation reaches fram the above data. The hydrologist constructed discharge-frequency curves for each damage evaluation area under present conditions and with the proposed structural program installed. Average annual damages and benefits were then computed by developing the damage-frequency curves for each type of damage and measuring the area under the curves. ~ Damages to residential and commercial property were adjusted to t~ce account of the expected urbanization and commercialization of the present agricultural lands in the overflow area of Indian Wash proper by the 25th year of the evaluation year. It is estimated that damageable values in this area will be approximately 150 percent of present values by the 25th year and that they ~till !emain at abQut that level for the remainder of the 50-year evaluation period. The increase in damages was discounted to allow for lag in accrual. Additional benefits that were not evaluated are the possible savings in the size of the culvert for the proposed new Interstate Highvrey 1-70 crossing of the Indian Wash. The proposed route crosses Indian Wash about 700 feet above the High Line Canal. ~ ( In addition to direct-floodwater d~nages, there are indirect da~mages such as loss of business, depreciation of property in the flooded areas, interruption of travel during flooding, extra travel due to road and bridge damage, and interruption of railroad traffic. For this evaluation indirect damages were estimated at 10 percent of direct agricultural damages, 15 percent of direct residential property damages, and 20 percent of commercial property, road, bridge and railroad damages. . Engineering Investigations Field investigations to detennine structural measure needs were conducted on the entire Indian Wash drainage above the High Line Canal. These investigations resulted in the selection of one site, IVl-l, for a floodwater-retarding structure. The site is located on the main tributary of the Indian Wash drainage in Section 29, Township I N., Range 1 E., of the Ute Principal Meridian approximately 1 1/2 miles north of the High Line Canal. Factors included in the selection of this~ructure site included: (1) maximum control of floodwater, (2) topography, (3) site conditions, and (4) existing facilities including Walker Airfield, proposed Interstate High,~y, a power tranmission line, and the High Line Canal. A detailed topographic map of the dam site and reservoir area was obtained by planetable survey. L .