Efficiency in irrigation
the conjunctive use of surface and groundwater resources
Bibliographic details
Additional authors
O'Mara, Gerald T.
Summary
To be useful simulation must almost always be based upon some prototype. The results are closely tied to a particular real system. This problem is inherent in using simulation as tool for optimization. We believe that the results of our analysis of the South Platte system provide an understanding of the economics of other similar systems; however, one can only infer this from our reslts. Nevertheless, the methodology presented has wide application As indicated in earlier studies, using the groundwater aquifer as a reservoir in a conjunctive water system such as that typified by the South platee in Colorado greatly increases the economic benefits to be derived from the system. As pumping capacity is installed in the system the expected net nenefit is increased greatly depending upon availability of surface water that is, surface water rights. For an area typified by our area 2, the expected net income is increased thirteen times from the situation in which it depends only on surface water to that in which it cam pump suffiecient groundwater to meet its need. Our results suffest that under the current economic condition existing in the South Platte Valley in Colorado, the most reasonable groundwater capacity is total capacity capable of irrigating all the available acreage with groundwater. Our usggest that the additional cost of pumping groundwater are not significant. The best strategy is to discount surface water entierly when considering wheat pumping capacity to install if of course, one can augment streaflow to the downstream to the downstream users in periods of low flow. Installing sufficient pumping capacity to irrigate all available acreage has two benefits: it maximizes the expected net benefit, and it reduces the variance in expected income to nearly zero. Given these results, it is understandable that the actual installed capacity in the South Platte system is capable of supplying approximately 2.5. feet of water the avaialbale acreage. Our results suggest that the present Colorado plan of 5 percent flow augmentation may be small in rellay dry years. We expect that an augmentation capacity approaching 10 percent may be necessary in such dry years as occurred from 1953 to 1956. An augmentation of 5 percent is, however adequate much of the time. As pumping capacity is installed in conjuctive use system the value of flow forecasts diminishes. Poor forecasts are compensated for by pumping from the wells. it si questionable in sytems such as the South Platte with a larege installed well capacity for most of the area that one should spend much effort on improving flow forecasts for water supply purposes.