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I' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 <C) (0') N ~ 0') ~j RECEIVED AUG 1 1 1997 HELTON & WILLIAMSEN, P.C. CONSULTING ENGINEERS IN WATER RESOURCES 384 INVERNESS DRIVE SOUTH, SUITE 115 ENGLEWOOD, COLORADO 80112 PHONE (303) 792-2161 FAX (303) 792-2165 DIV:St(;i~ ~: ;,_::;\:i.:r.:.H ~L~j~.(:,. (,JLO!Yl.DO August 8, 1997 Mr. Steven J. Witte Colorado Division of Water Resources 310 E. Abriendo. Suite B Pueblo, Colorado 81004 Subject: Supplemental Information for Replacement Plan Amendment _ Lower Arkansas Water Management Association Dear Mr. Witte: This letter supplements the information concerning the historical use of LAWMA's interests in the Highland Irrigation Company. Our earlier correspondence. dated July 10.1997. requested that the Highland Canal water be included as a replacement source for LAWMA's 1997 plan. We submitted an amendment to the replacement plan on August 1 in which we agreed to present an analysis of the historical use of the Highland Canal consistent with the algorithm and parameters used in Kansas' H-I model. This letter presents the results of that analysis. I conferred with Dewayne Schroeder about the data and procedures used in the H-I model. The Highland Canal was not included in Kansas' analyses of Colorado irrigation ditches. so the parameters used in this analysis are based on information for similar ditches included in the H-I model. In general, the H-I model performs a water budget analysis in which irrigation deliveries are inflow to the root zone and crop consumptive use, tail water and deep percolation are outflow. The soil acts as a reservoir, and when the root zone is full. excess applications are assigned to deep percolation. The model also accounts for canal and lateral seepage. The canal seepage rate is based on the canal length. For the Highland Canal. the seepage rate is calculated to be about 10 percent of the diversion. The lateral seepage has off- farm and on-farm components. The lateral seepage rate used for all Colorado ditches was 7 percent. One-half of this rate. or 3.5 percent. is applied to the canal diversion volume and one- half, 3.5 percent. is applied to the farm delivery. Tail water for all ditches is calculated as 10 percent of the farm delivery less on-farm lateral losses. In the recent H-I model version. the maximum irrigation efficiency for Colorado ditches was limited to 65 percent except for the Lamar/Manvel and Colorado Canals which were set at 70 percent. The irrigation efficiency includes on-farm lateral seepage, tail water and deep percolation losses. Using a maximum efficiency of 65 percent, the minimum deep perCOlation rate works out to be about 22.6 percent of the farm delivery less on-farm lateral losses. The H-I model also calculates "secondary evaporation" (SEV) on the canal seepage. off- farm and on-farm lateral seepage and tail water. Following are the monthly SEV rates: