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I I I I I I I I I I I I I I I I I I I the amount of sediment reaching the main body of the reservoir" (USACE 1999d:l). The Corps attributes this change in the sediment deposition pattern from the reservoir body to the head of the reservoir to salt-cedars that are acting as a sediment trap and to higher pool elevations that have occurred in recent years. In the spring of 1999 flooding and high overwinter reservoir storage established a new record storage elevation for John Martin Reservoir on May 9, 1999, at an elevation of 3860.45 feet (US ACE 1999b:24). At this record reservoir storage elevation, the reservoir pool reached up the Arkansas River to the Purgatoire Rivers' confluence. That area is also this study's Channel Problem Area No.3. Sediment problems in this area have been causing serious concerns for several years and examples include the fact that the wasteway for the interior drain at the eastern end of the Las Animas levee had to be realigned from draining to the Arkansas River to draining to a point at the Purgatoire River confluence. As reported, salt- cedar are restricting river flows in this marshy area of the floodplain and a small amount of river flow is now flowing/draining to the wasteway. Another example near Las Animas is that a landside return drain structure on the north levee no longer functions properly. Sediment deposition in the river channel in the vicinity of the Colorado State Highway 50 Bridge north of Las Animas is estimated to be about 5 to 6 feet in depth and has nearly covered the return structure. Soil conservation efforts were initiated during the 1930s drought and, especially with modem tillage methods and range management techniques, have reduced wind and water erosion of the highly erodible southeastern Colorado soils, although overgrazing continues in many areas. The Natural Resources Conservation Service (NRCS; formerly the Soil Conservation Service), under their Watershed Protection and Flood Prevention Program (Public Law 83-566), are currently planning two studies in upland areas that are adjacent to the area of this planning study. These NRCS projects include the Bent's Fort and the Patterson Hollow Watershed Projects, and these studies will provide structural and ma!1agement recommendations for .. irrigation methods, salinity, groundwater, and water quality problems, and for floodwater control, respectively (NRCS 2000a; 2000b). If recommendations for these projects were implemented, they would assist in minimizing problems along the river. Other NRCS conservation efforts include education regarding the revegetation, rather than abandonment, of irrigated cropland from which the irrigation water has been sold (Sutherland et al. 1990). As noted above, the management of river flows arid operation of John Martin Dam and Reservoir officially began on March 11, 1943 (USACE 1943: 25, 1948:3-4, 1999:2; Nadler and Schumm 1981:104) and Pueblo Dam and Reservoir began operations on January 9,1974 (US ACE 1977b:3/1; USGS 1998; Abbott 1985; Mi1enski 1990:143). While the storage of agricultural water in these reservoirs allows for the management and the beneficial use of the water, as administered through the Arkansas River Compact signed in 1948, as amended, (US ACE 1983a:B I-B 10), the construction of these major dams has contributed significantly to changes induced by irrigation diversions along the Arkansas River by controlling flood waters, regulating the timing of flows, and by retaining sediment. By controlling flood water and the timing and size of river flows which work to control the size of a river's active channel, dams across the west, including those on the Arkansas River, have in effect allowed for encroachment on river channels by vegetation and by the expansion of agricultural fields nearer to the river channel and have contributed to the loss of riparian cottonwoods (Nadler and Schumm 1981; USACE 1999a:21-22, Figure 7; Snyder and Miller 1991:173-174; Rood and Mahoney 1990; 21