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The Closed Basin Project consists of a series of wells, canals, and pipelines that is used to extract water from the shallow aquifer within the Project boundaries without significantly affecting water levels in the unconfined and confined aquifers outside the Project boundaries. The Project was completed in 1992, but is experiencing difficulty with well yields due to an unusual bacterium causing clogging of the well screens. This problem is being addressed by the Bureau of Reclamation and must be resolved before the RGWCD accepts the Project from the Bureau of Reclamation. Currently the Project is yielding a maximum of about 40,000 acre-feet per year. For additional information regarding the Closed Basin Project, see the memorandum titled Closed Basin Proiect Interview. Historical Agricultural Practices In 1963 or 1964, center-pivot sprinkler systems were introduced to the San Luis Valley. Prior to this time the primary irrigation methods were sub-irrigation and flood irrigation, using surface water supplies to recharge the shallow groundwater to the extent that the water levels were raised to the root zone of the crops. Sub-irrigation saturated the soils and caused waterlogging, and some lands in the central portion of the Closed Basin went out of production. Therefore, several drainage districts were established to create to large drainage systems to drain the lands by lowering the water levels. Following the advent of the center pivot sprinkler technology in the Valley, irrigators became much more efficient with their use of water, and the use of sub-irrigation became less and less prevalent. Currently, the general practice of irrigators north of the Rio Grande is to use center- pivot sprinkler systems fed directly by pumping from shallow wells. These wells pump shallow groundwater that is recharged each year from existing surface water diversions. South of the River the general practice is to use center-pivot sprinkler systems fed from on-farm ponds. These ponds are filled either by surface water diversions when available or groundwater pumping. Much of the land south of the River is still flood irrigated. Wild flooding occurs on irrigated meadows and pasture lands in the Basin. Because of the rapid growth in the use of center pivot sprinkler systems the water users in the Closed Basin, in 1981, asked the State Engineer to stop issuing new well permits for the unconfined aquifer within the Closed Basin. In order to keep the water level in the unconfined aquifer at an economic pumping level, the ditch companies' encourage their shareholders to use their surface water for artificial recharge purposes. This is accomplished by constructing recharge pits on the center pivot corners, diking the corners or using the existing drain ditches. Recharge also occurs because of leaky canals and laterals. One would initially think that the loss of acreage in the corners of center pivots would affect crop yields. However, the lost acreage is more than offset by the efficiency and precision of application that center pivot irrigation affords the farmers. In fact, the precise application of irrigation water and pesticides that center pivot technology provides has caused yields to nearly double for many of the locally grown crops (including alfalfa, potatoes, etc.) despite the loss of some irrigated acreage on the corners. At the present time fifteen to twenty additional center pivot sprinklers are being installed each year in the Valley on previously irrigated ground. There are currently about 2,200 center pivot systems in use representing 45 to 55 percent of the irrigated acres in the Valley. The use of center pivot sprinklers started in the 1960's but really accelerated in the 1970's until the State restricted the installation of new wells in the unconfined aquifer. C:Acdss\RGWCD.doc Rio Grande Water Conservation District Interview May 10 -Page 3 of 4