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<br />. <br /> <br />OUiHl <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />i <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />of shortage acreages and cutoff dates for consumptive use on the shortage acreages are <br />two such procedures. The backup engineering for these two procedure has been <br />misplaced or lost according to USBR personnel; therefore, the basis for these procedures <br />could not be reviewed. Shortage areas are irrigated acreages of alfalfa and pasture grass <br />which received less than a full supply of water. In the affected hydrology unit, an irrigation <br />cutoff date for alfalfa and lor pasture grass is defined. The amount of consumptive use in <br />shortage acreages is assumed to be 100% of NIR prior to the cutoff date and zero (0) after <br />the cutoff date. For each hydrologic unit, the cutoff date for each year is based upon <br />gauged streamflow in the recession portion of the annual stream hydro graph as measured <br />at specific gaging stations. The cutoff date is identified as the date the streamflow falls <br />below a specific flow rate. <br /> <br />Recommended Chanaes. Based upon a review of the available documents, the <br />following changes are recommended for the USBR procedures. <br /> <br />~ 1. <br /> <br />Update engineering procedures utilized to determine crop <br />evapotranspiration. <br /> <br />~ 2. <br /> <br />If SCS-BC is used, it should be locally calibrated. <br /> <br />3. <br /> <br />Verify or correct procedure used to calculate ET on alfalfa-short or pasture- <br />short areas. <br /> <br />4. Pasture grass coefficients should not be used for irrigated meadow grass. <br /> <br />5. Improve estimation procedure for effective precipitation. <br /> <br />6. The contribution to crop evapotranspiration from stored soil moisture should <br />be included. <br /> <br />7. Improve method of calculation effectiveness of precipitation. <br /> <br />8. <br /> <br />Check weather station sites for representativeness. <br /> <br />UDdate of Procedures. Martin et al. reported that the SCS was updating its <br />techniques for estimating water requirements because of advancements made in methods <br />used to predict crop water use. They reported that since 1970, when TR-21 was <br /> <br />5 <br />