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I I I I I I I I I I I I I I I I I I I 29 179:1 inigate thousands of acres. During the irrigation season, the river was becoming what is now' generally tenned "a gaining ri ver" as ground water percolated from the irrigated upland areas back to the river {Bittinger and Stringham 1963:3-4; Watts and Lindner-Lunsford 1992: 11) and because of this groundwater return flow, the river changed as Nadler and Schumm (1981:97) report: "the major hydrologic change was from [an] intermittent to [a] perennial stream flow" (Nadler 1978:111). The famous Dust Bowl of the 1930s and the droughts of the 1950s had major effects on the region and on how the population utilized the valley's resources (USACE.1965:23). During and after these drought years, domestic, municipal, industrial, and agricultural interests focused on the importance of ground and transmountain water. Developments to gain access to these resources were intensified as numerous ground water wells were drilled and water diversions constructed (Abbott 1985:9; Bittinger and Stringham 1963:3; Nadler 1978:60-63; MiJenski 1990:157). Ground water was primarily used to supplement agricultural irrigation and locally, in the immediate area of the WellB, diminished the return flow to the river {Bittinger and Stringham 1963:3-4). Along with changes in the hydrologic character of the river, caused by diversions and increasing ground water, "there were [also] changes in the types and amounts of floodplain vegetation" (Nadler and Schumm 1981:97, 104-105). The earliest account of salt-(:edar (Tamarix) occurring in the Arkansas River Valley is reported in 1913, near Lamar (Lindauer 1970:4-5; Lindauer and Ward 1968:3-4). This phreatophyte "is a highly wateHonsuming naturalizing shrub" that is known to be very aggressive in the way it has spread across most of the arid and semi-arid areas of the west (Robinson 1965:1). "...it has not only invaded but has entirely replaced the native vegetation in many areas" (Robinson 1965:1). Turner (1974, in Nadler 1978:87) "credited the success of salt-cedar in competing with the native vegetation to its prolific seed production, its effective seed dissemination, its rapid growth, and its early maturation." "The [general] time of awareness of salt-(:edar in the Southwest" is considered to be in the 1920s and salt-cedar was reported in local accounts to have been spread in the Arkansas River floodplain by the floods of 1.921 and 1937 (Robinson 1965:4-6; Lindauer and Ward 1968:3). During the 1930s, the drought created a situation that allowed salt-cedar to encroach on the river channel and in old meanders, establish itself below the high water levels of the channel, and stabilize the point bars (Nadler and Schumm 1981:109). The primary' concerns regarding the spread of and increased density of salt-cedar are related to the effects of the plant encroachment on the river channel. In establishing itself, salt-cedar constricted channel widths and increased bank roughness thereby slowing river flows and increasing sediment deposition especially in overbank areas (Robinson 1965:10; Nadler 1978: 87; Nadler and Schumm 1981:98, 105, 111; Snyder and Miller 1991:173). . Studies also indicate that salt-cedar consumes a.significant amount of ground water (Robinson 1965; Bittenger and Stringham 1963), enough so thBt this is of great concern and which Robinson (1965: 1,8-10) refers to as "consumptive waste." Bittenger and Stringham (1963:4) conducted a vegetative and consumptive use study in the Arkansas River Valley and determined that for the study years between 1940 and 1961 there was a significant decrease in average annual river gain between 1949 through 1961. They attributed the reduction in river gain to increases in floodplain vegetation and estimated for the area between La Junta and Las 19