Laserfiche WebLink
Canal lengths and soil description for ditch systems were extracted from the ArcView <br />canal and soils coverage developed for the RGDSS project. The canal GIS coverage did <br />not have information for 75 explicitly modeled ditch systems. These 75 structures, along <br />with the 44 aggregated surface water structures represented in the model, were assigned a <br />conveyance efficiency of 80 percent. It is estimated that the missing ditches are smaller <br />and irrigate within a short distance from the river. <br />Table 4 shows the results of this analysis and the number of ditches that are represented <br />in each efficiency category. <br />Table 4 <br />Conveyance Efficiencies and Corres ondin Number of Ditches <br />Efficient Number of Ditches <br />>90% 15 <br />80 to 90% 61 <br />70 to 80 % 257 <br />60 to 70 % 47 <br />< 60% 27 <br />Total 407 <br />There has not been a trend towards improving or lining canals and laterals in an attempt <br />to decrease conveyance losses in the San Luis Valley. Canal losses, and the resulting <br />aquifer recharge, are considered beneficial by most of the ditch systems, since many <br />irrigators depend on ground water to meet crop requirements. Therefore, the <br />recommended conveyance efficiencies are appropriate for the period considered in the <br />RGDSS project. In addition, the range of conveyance efficiencies is consistent with our <br />knowledge of conveyance efficiencies in areas outside of the Rio Grande basin. <br />Results -Maximum Application Efficiencies <br />As mentioned in the introduction, application efficiencies are dependent on irrigation <br />methods, which may vary with crop type. In addition, irrigation methods have changed <br />considerably during the period considered in the RGDSS project. <br />A conference call was held with Kirk Thompson and Leroy Salazar of Agro Engineering, <br />Inc. to discuss application efficiency studies and general knowledge of on-farm <br />efficiencies within the San Luis Valley. Specific information included irrigation methods <br />for the large ditch systems and by water district, estimated on-farm efficiencies for each <br />method, and, if applicable, timing of installation of sprinkler systems. They indicated <br />that "flood" irrigated lands within the basin include uncontrolled, overland flood <br />irrigation as well as border irrigation systems. <br />The user interview memorandums were reviewed for the local water commissioners' <br />estimates of irrigation methods used in their districts, and estimates of application <br />efficiencies. According to Agro Engineering, efficiency estimates can vary both by <br />irrigation methods and by crop types. Agro Engineering suggested a range of likely <br />appendB_cropcu_6-2004.doc B-15 of B-19 12/13/00 <br />