Arkansas River Channel Capacity and Riparian Habitat Planning Study

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McDonald and Sidle 1992; Johnson 1994). Subsequent to agricultural diversions and the construction of dams, active channel widths have decreased, channel sinuosity has increased, and wavelength has decreased in the area of Bent's Old Fort (Nadler 1978:111 -117). Since sediment is retained by reservoirs, clear waters are being released. Historically, the silt -laden river water diverted for irrigation prevented significant seepage from the canals. Clear ' water has a substantial capacity to scour (pickup sediments), whether the scouring occurs in the river channel or in a canal. The scouring is causing some erosion problems and major seepage problems for downstream irrigation canals (Milenski 1990:86, 99). Increased seepage from ' canals in turn may be intensifying ground water problems such as those in the La Junta area (Bossong 2000; Watts and Lindner - Lunsford 1992).. In summary, the Arkansas River has a complicated mix of problems. Both the timing of historic river flows and its attendant sediment transport capabilities have been altered, reduced, and managed for agricultural use, flood control, municipal and industrial supply, fish and wildlife ' enhancement, and recreation. An increase in ground water occurred subsequent to irrigation diversions and resulted in an increase in floodplain vegetation. The river changed from being an intermittent to a perennial flow. Grazing of the floodplain and significant droughts provided the opportunity for the exotic salt -cedar to establish itself along the river channel, in old meanders, and on sand bars. The construction of two major dams on the Arkansas River and other upland reservoirs provided for the more efficient management of irrigation water storage and use as well as flood control. The river channel has degraded in some areas while aggradation occurred in other portions. The river, in most reaches, has changed from a rather straight and wide braided channel to a meandering incised channel with increased sinuosity and descreased wavelength. Numerous areas in the Arkansas River Valley are continuing to experience ground water problems although pumping from wells has localized effects on problem areas (Bossong 2000). Modern management of the river does not provide the necessary active - channel nursery sites or the flooding occasions for significant cottonwood gdrmination and therefore salt -cedar dominates in many areas. Significant flooding still occurs occasionally in the study area, however, and the flooding may be intensified by sedimentation problems in the valley. Over time, with reduced flows and reduced threat of flood, more and more floodplain lands were converted to farmland and encroachment on the river channel occurred. Researchers such as Nadler and Schumm (1981:109) report that "Perennial flows, droughts, and especially dense salt -cedar growth were ' major factors leading to the [Arkansas Rivers'] metamorphosis." In other words, diversion of irrigation water and sediment, the construction of the dams, the expansion of the invasive salt - cedar, high groundwater and pumping, and encroachment on the river channel are the leading factors that have led to changes in the hydrologic character and created the problems of the Arkansas River. Attendant with these riverine problems are growing water quality concerns (USACE 1965:22-24-,1983a:4-9; Cain 1987; Muelldr 1991; Zielinski 1995; MRCS 2000a). Nadler (1978:133) also notes that channel analysis 4 the Arkansas River in his study reaches at Bent's Old Fort and near Carlton indicates that "these reaches are unstable with respect to channel pattern, and may shift quickly from one pattern to another [from braided to meandering or vise - versa]." J 11 22 1