Arkansas River Channel Capacity and Riparian Habitat Planning Study

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16 B66,1973 :50 -53, 1985:15; Nadler 1978:89,113, 126; Nadler and Schumm 1981:104, 109, 113). John Martin Reservoir supplies water to irrigation users as far downstream as Garden City, those for agricultural irrigation diversion to their canal delivery systems, to off - channel reservoirs, or to John Martin Reservoir (USACE 1997b:2/1, 3/1; USGS 1998; Mueller et al, 1991 :8, Figures 1 & 2; Milenski 1990:131 -133). Similarly, flows that originate in the Purgatoire ' River basin above the Corps' Trinidad Lake Project:may be temporarily stored at Trinidad Lake for subsequent delivery to specific downstream irrigation users or to John Martin Reservoir. The Purgatoire River flows do not affect the study area with the exception of Channel Problem Area No. 3 at the confluence of the Purgatoire River with`the Arkansas River. However, flows that derive from the other tributaries such as Timpas, Horse, and Adobe Creeks have affected and continue to affect the Arkansas River channel (Sharps 1969; USACE 1965:23, 1970:B27, B65- , B66,1973 :50 -53, 1985:15; Nadler 1978:89,113, 126; Nadler and Schumm 1981:104, 109, 113). John Martin Reservoir supplies water to irrigation users as far downstream as Garden City, Kansas. Current reservoir operations for conservation storage and release follow the plan adopted by the Arkansas River Compact Administration in 1980, as amended. Releases for irrigation and delivery normally are made between April 1 and October 31 of each year. Inflow ' is stored in November through March except for releases required for flood control. Flood control operations begin when John Martin Reservoir storage exceeds an elevation of 3,851 feet; that is water temporarily stored above the elevation of the top of the conservation pool. The current operational channel capacity of the Arkansas River is approximately 3,000 cubic feet per second (cfs) at Coolidge, Kansas. Actual release from the dam may exceed 3,000 cfs when flows are expected to diminish before reaching Coolidge - due to irrigation withdrawal or transit , loss. While some of the preceding information regarding John Martin Reservoir and water releases from the dam is more specific to areas downstream, it is important to understand that the administration of water according to the Compact's 1980 conservation storage plan not only has significant effects on the amount of water stored at John Martin Reservoir but also affects the timing of releases at John Martin Reservoir as well those at Pueblo Reservoir and Trinidad Lake and the amount of water that flows through the Arkansas Valley and the study area, whether by the river channel or via irrigation canal systems. Prior to the Compact's 1980 agreement, irrigation users called for and used practically all of the stored irrigation water at John Martin Reservoir during the irrigating season. As a result, there were many years where the irrigation water supply was used prior to the end of the irrigating season and also many years when John Martin Reservoir was completely dry for most of the year. The Compact's 1980 agreement instituted a more conservation minded approach to water delivery and management. Since 1980, water users call for water as necessary, and although: storage has been low during some years, John Martin Reservoir has always had stored water. Although the exact relationships between surface and ground water within and flowing r through the valley are not fully understood and are the subject of increasing study, concerns regarding flood and related water resources problems such as increasing serious flood threat, heavy plant growth, decreasing channel capacities, aggradation, and bank erosion were raised by t local citizens and officials at public hearings as far back as the 1940s and 1950s. Local officials also voiced concerns about the potential for backwater flooding at Las Animas from flood water storage at John Martin Reservoir, and some believed that storage at John Martin Reservoir was f affecting and thereby creating problems with high ground water in areas as far upstream as La 6