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<br />9-11. Infiltration values selected to determine the outflow hydro- <br />graphs for the subareas varied from 0.70 inch per hour for cultivated <br />land to 0.50 inch per hour for urban areas. The I-hour 25-year recur- <br />rence interval rainfall was used to determine the volume of outflow <br />from each subarea. Studies of substantial rainfall coincident with <br />flood stages in the Arkansas River indicate about a 45 percent chance <br />of occurrence. Triangular-shaped runoff hydro graphs were constructed <br />for each subarea. The runoff hydrographs were routed to key points. for <br />design of the collection system to convey the runoff to about levee <br />station 472+00 on the right bank levee and to about levee station 37+50 <br />on the left bank levee. Details of the interior drainage computations <br />are given in table 15. <br /> <br />9-12. <br />tion ditch <br />follows: <br /> <br />Design flows for the right bank interior drainage collec- <br />at locations where inflows will be intercepted are as <br /> <br />Location <br />(Levee Station) <br /> <br />Discharge <br />(c.f.s.) <br /> <br />290+00 0 <br />310+00 50 <br />350+00 67 <br />353+75 1'3 <br />354.00 tU.S. Highway 50 133 <br />354+25 133 <br />390+50 'tRailway 230 <br />458+00 325 <br />472+00 325 <br /> <br />9-13. ponding areas. - The required ponding storage for subarea <br />A would be 27 acre-feet. This amounts to 1.20 inches of runoff from <br />an area of 271 acres. The required ponding storage for subarea B <br />would result from 1.20 inches of runoff from 687 acres and would <br />amount to 69 acre-feet. The required ponding volume at about right- <br />bank levee station 472+00 would comprise the runoff from subareas Cl, <br />C2, C3, D, E, and F and would amount to 119 acre-feet. The required <br />ponding storage at about left-bank levee station 37+50 would comprise <br />the runoff from subarea G, H, and J and would amount to 30 acre-feet. <br />Data pertinent to the collection system and required ponding volume <br />design are given in table 15. The locations of the significant items <br />pertaining to interior drainage are shown on plates 18 and 19. <br /> <br />9-14. Sediment from intel'ior drainage,- The sediment contribu- <br />tion from the 2,134 acres contributing to interior drainage behind the <br />right-bank (south) levee and the 300 ~cres contributing to interior <br />drainage behind the left-bank (north) levee would be negligible. This <br /> <br />31 <br /> <br />