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<br />Reply Attention: 752 <br /> <br />':.' ,. .",' <br /> <br />copy <br /> <br />C,opy <br /> <br />To: <br /> <br />Director, Project Planning Division, Washington, D. C. <br />Attention: 737 <br /> <br />Subject: <br /> <br />Chief,Hydrology Branch, Project llLanntng Division <br /> <br />Review of Survey Report--Fountain River Watershed, <br />Colorado, Department of Agriculture ' ' <br /> <br />From: <br /> <br />By copy of Assistant Director E. E.Tomlinson's letter of December 17, 1951, <br />to Regional Director, Denver, Colorado, subject as above, we were furnished a <br />copy of the subject report and comments were requested by January 15, 1952. The <br />report has been reviewed in detail by engineers of this Branch and their comment" <br />are summarized ,in a memorandum to me dated lJahuary 10, 1952, two copies of which <br />are transmitted for your reference. <br /> <br />In evaluatiryg the effectiveness of the proposed program upon the reduction of <br />floods, the repOrt has presented a theoretical hydrologic analysis based on data <br />from infiltrometer tests on areas representing present and improved vegetal cover <br />conditions. No firm data of flood runoff from water studies comparable to the plains <br />areas of the Fountain River Watershed are included in the report for both present <br />and improved cover conditions. We question that the i1Jheoretical hydrologic analysis <br />based on infiltrometer data provides a, realistic estimate of the reductions in flood <br />flow which would result from the proposed program. We believe that proper analysis <br />of these data would result in considerable reduction of the percentage spread between <br />runoff jrom present and improved conditions. <br /> <br />Also, the Survey Report predicts major re&xrlion in flood volume and flood peak <br />as a result of the 2,800 small detention dams included in the proposed program. <br />Experience over the past two decades proves that such structures do not provide <br />, firm and lasting flood reduction due to the necessity for careful and continued <br />maintenance, to their fr~quentfailure under localized centers of high precip~tation <br />and to their rapid filling With sediment. <br /> <br />The over-all average annual reduction in sediment load of the Fountain River <br />, and its tributaries resulting from the proposed program is claimed to be about 50 <br />percent. Our review indicates that this claimed reduction is not fully substantiated <br />"eitherbyadequate field data or by proper analysis of these data. Furthermore, the <br />predicted reduction in sediment transportation and yield of Fountain River is largely <br />dependent upon (1) the land treatment and complementary structural measures proposed <br />in the report attaining their full effectiveness, (2) the actual effeytiveness of <br />. these measures in producing the flood peak reduction which we question, and (3) the <br />continued and effective maintenance of qetention dams, bank stabilization measures, <br />and other structural treatment. In view of the above, we believe that '~he anticipated <br />58 per cent reduction in sediment yield of Fountain River by the proposed program is <br />highly optimistic. <br /> <br />The SUrvey Report states that ,the effect of the proposed program on the <br />availability of water for irrigation in the Arkansas River Basin has been considered <br />and evaluated. However, our review of the report has revealed no substantiation of <br />this statement. The attached memorandum discusses this matter in some detail. <br />Particularly, it is noted that: <br /> <br />,.-" <br /> <br />. ',,-fo~ '.'O.C--'_ <br /> <br />