Laserfiche WebLink
In 2(105, the Office of the State Engineer embarked on the Hydrologic Basin Response Study <br />with Tierra Grande International, Inc. Two previous reports were submitted for that study: <br />Phase I, June 2005, included an assessment of the state-of-the-practice, relevant literature, <br />data sources and selection of study watersheds in Colorado. Phase II-A, January 2006, was <br />a pilot program wherein two watersheds were selected and hydrologic response parameters <br />estimated. Verification of the procedures were performed using the best available <br />information. Those two pilot program watersheds were the La Plata River near Hesperus, <br />Colorado and Pawnee Creek in Logan and Weld Counties. <br />Scoue of the C~urrent Studv <br />Phase II-B is the preparation of guidelines for estimating rainfall loss and unit hydrograph <br />para.meters for the performance of inflow design flood (IDF) hydrologic studies for dam <br />safet.y and dam design in Colorado. <br />Proa~dures for estimating rainfall loss parameters are presented for the Green and Ampt <br />infiltration equation and the Initial loss plus Uniform Loss Rate Method. <br />Dime~nsionless unit hydrographs and S-graphs are recommended for use with natural <br />watersheds in Colorado. The Clark unit hydrograph is recommended for use with urban and <br />agric.ultural watersheds. The Clark unit hydrograph is an acceptable alternative for natural <br />wate~rsheds when its use results in verifiable or more reasonable results than use of <br />dime;nsionless unit hydrographs or S-graphs. Procedures are provided for calculating the <br />dime;nsionless unit hydrograph and S-graph lag. Recommendations are provided for <br />estimating K~ in the lag equation. Equations and procedures are provided for calculating the <br />CIarN: unit hydrograph parameters. <br />A~plicability and Limitations of the Guidelines <br />The intent of these guidelines is to promote public safety and welfare consistent <br />with the state-of-the-practice for the design, operation, maintenance and periodic <br />safety inspection of dams in Colorado. <br />19 March 2007 3 <br />