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Conveyance System Efficiencies <br />A commonly used methodology for estimating conveyance efficiency was published by <br />the SCS in the National En~ineerin~ Handbook 15-2, (Part 623-2), Irrigation Water <br />Requirements, 1993. This methodology predicts conveyance efficiency when the <br />following information is available or can be estimated: <br />• Soil type (or soil permeability) <br />• Ditch length <br />• Wetted perimeter <br />• Number of days water is in the ditch <br />• Diversion flow rate <br />Several other methods have been developed that use the same basic information. These <br />methods are appropriate for estimating monthly or annual efficiencies for an individual <br />ditch system when the above information is known. However, this methodology is not <br />appropriate for use in the RGDSS basin-wide analysis because ditch configuration, <br />required for wetted perimeter, is not known. The data-centered approach used for the <br />historic crop consumptive use analysis requires information to be developed or estimated <br />basin-wide using available data from GIS coverages or Hydrobase. <br />There is limited efficiency information available for the large canal systems in the San <br />Luis Valley. This available information was used to develop a simplified approach to <br />estimating likely efficiencies for other ditch systems using available GIS coverages and <br />data stored in HydroBase, as follows: <br />1. Develop a list of questions relating to system efficiencies for the Surface Water <br />Contractor to use in their interviews with water administrators and ditch companies. <br />Extract the following information from the resulting User Interview Notes: <br />- Conveyance Loss information from the large ditch companies <br />- Corresponding main canal lengths <br />2. Measure main canal lengths not available from the User Interview Notes or from the <br />ArcView GIS canal coverage developed for the RGDSS project <br />3. Obtain main canal capacities from Hydrobase <br />4. Estimate an average available soil moisture content (AWC) and soil type to represent <br />each main canal from the Soil AWC GIS layer prepared for the RGDSS project <br />5. Investigate relationships between percent canal loss and canal length <br />6. Investigate relationships between percent canal loss and soil characteristics <br />7. Investigate relationships between percent canal loss and canal capacity <br />8. Use appropriate relationships, if they exist, to estimate canal losses by soil type, ditch <br />size, or proximity to the river <br />Maximum Application Efficiencies <br />1. Develop a list of questions relating to irrigation practices for the Surface Water <br />Contractor to use in their interviews with water administrators and ditch companies. <br />2. Extract the following information from the resulting User Interview Notes: <br />appendB_cropcu_6-2004.doc B-2 of B-19 June 2004 <br />