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<br />DESCRIPTION OF STUDY AREAS <br /> <br />Backwaters A-7 and A-I0 are located adjacent to the main chan- <br /> <br />nel of the Lower Colorado River. A-7 (lat 33034' N. and long 114032.5' <br /> <br />W.) and A-IO (lat 33010' N. and long 114033' W.) are on the Arizona <br /> <br />- <br />side of the river (Figures 1 and 2) 1.1 and 10.5 km, respectively, down- <br /> <br />stream from the Ehrenberg bridge. This area is in the Palo Verde Irrigation <br /> <br />Division of the river. The dredging of A-7 began June 25, 1969 and was <br /> <br />completed November 14, 1969. A-I0 was dredged from April 10, 1970 <br /> <br />through May 27, 1970. <br /> <br />A-7 and A-I0 are similar in design. Each has a main channel <br /> <br />with numerous" fingers." In most physical aspects, A-7 is the larger of <br /> <br />the two (Table 1). These backwaters are not typical of either lake or <br /> <br />river environments. The main channels of each contain flowing waters. <br /> <br />The currents are generally sluggish as compared to those of the river. <br /> <br />On the other hand, the fingers and those areas where the width of the <br /> <br />main channel is expanded are quiescent. The slopes of the bottoms <br /> <br />throughout these two backwaters are generally steep. However, a few <br /> <br />areas have gradual slopes forming shoals. <br /> <br />Both of these backwaters are directly connected to the river. <br /> <br />Water from the river enters through culverts into A-7 at two locations. <br /> <br />At the northernmost inlet, water first flows into a desilting basin and <br /> <br />then into the upper end of the backwater. At the second inlet, located <br /> <br />1.5 km downstream from the first, water flows directly into the back- <br /> <br />water. Water returns to the river through an open channel at the southern <br /> <br />2 <br />