WSP01376 - Laserfiche WebLink

Home Browse Search

., .t 2~:::O been irrigated each year with no water transferred out of the Model right and with all winter storage charged to the Model right. Under Case 3, the com- putation shows the difference in the actual inflow as compared to what would have occurred had the same acreage as was actually irrigated in 1979-84 been irrigated, but with no water transferred out of the Model right and with all winter water storage charged to the Model right. , .. The computations used in all three cases were patterned after those used in the 1961 and 1964 studies and utilized the computer model developed for this review. In order to use the computer model, the depletion at the Alfalfa gauge under the actual conditions was calculated using the following formula (same formula as used in the 1961 and 1964 studies): Depletion at Alfalfa = Headgate requirement + excess diversion - irrigation release shortage + Trinidad Reservoir inflow - Trinidad Reservoir releases - return flow. Actual Trinidad Reservoir inflow and release were used in all three cases. Case 1 computations used irrigated acreages as shown in the Colorado Agricultural Statistics (except 18,386 acres in 19841/)and actual headgate diversions to determine excess irrigation and shortages, whereas Cases 2 and 3 assumed ideal headgate diversion. Cases 2 and 3 were computed under the assumption that the actual diversions were equa 1 to the headgate requi rement. Table 2 shows the computa t i on of headgate requirement, actual headgate diversion, excess diversion, return flow and deple- tion at the Alfalfa Gauge used in Case 1. Table 3 shows the actual headgate diversion, return flow and depletion at the Alfalfa Gauge used in Case 2 and 3. The values for the depletion at the Alfalfa gauge under Cases 1, 2 and 3 were entered into the computer model. The model calculated the depletion that would have occurred at the Alfalfa gauge had the transfer from the Model right not taken place and had the winter storage been charged to the Model right. The difference in the depletion at the Alfalfa gauge was then run through the channel loss part of the model to determine the impact at John Martin Reservoir. The annual impacts on the inflow to John Martin Reservoir for Cases 1, 2 and 3 are shown in Table 4. Monthly summary of results and more detai 1 on the computations are contained in Appendix II. During the review period, transmountain water was delivered down the Arkansas River to John Martin Reservoir in exchange for "out of priority" storage of inflow to Trinidad Reservoir (see Chapter IV.H.). Since the com- putat ions for Cases 1, 2 and 3 used actua 1 Tri n i dad Reservoi r i nfl ow, the impact on the inflow to John Martin Reservoir must be adjusted for the exchange. These adjustments are also shown in Table 4. liThe Colorado agricultural statistics on irrigated land include some lands out- side the project area. These statistics reported 21,400 acres irrigated in 1984 whereas Bureau of Reclamation field survey found the maximum project lands irrigated during the review period to be 18,386 acres (see Chapter IV.D.1.). 13 ., .."