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<br />~ <br />~ <br />c <br />~ <br /> <br />~ <br /> <br />EXISTING PROTECTIVE MEASURES <br /> <br />This section describes the riverworks along the Lower Colorado <br />River established by the Bureau of Reclamation to prevent <br />flooding, control stream meandering and sediment deposition, <br />salvage water, enhance fish and wildlife habitats, and improve <br />recreation opportunities. <br /> <br />The Colorado River below Davis Darn has been divided into 10 <br />divisions: <br /> <br />* Mohave Valley Division (Davis Darn to Topock) <br />* Topock Gorge ,Division (Topock to Lake Havasu) <br />* Havasu Division (Upper Lake Havasu to Headgate Rock Darn) <br />* Parker Division (Headgate Rock Darn to Palo Verde Diver- <br />sion Darn) <br />* Palo Verde Division (palo Verde Diversion Darn to <br />Taylor Ferry) <br />* Cibola Division (Taylor Ferry to Imperial Ruins) <br />* Imperial Division (Adobe Ruins to Adobe Darn) <br />* Laguna Division (Imperial Darn to Laguna Darn) <br />* Yuma Division (Laguna Darn to Morelos Darn) <br />* Limitrophe Division (Morelos Darn to Southern Arizona <br />Border) <br /> <br />Mohave Valley Division (Davis Darn to Topock) <br /> <br />Scouring of the river channel below Hoover Darn by bed load <br />free clear water released from the reservoir, along with subse- <br />quent deposition of the eroded sediment in the backwater zone <br />above Parker Darn creating severe aggradation in the lower Mohave <br />Valley. Prior to 1946, aggradation of the channel in the lower <br />valley caused a rise in average water levels until serious <br />flooding occurred near Needles. Channel stabilization was <br />begun in 1949 with initial work consisting of dredging an <br />improved channel between Needles and Topock. Subsequently, <br />channel dredging, levee construction, and associated work was <br />completed upstream from Needles to a point 10 miles below Davis <br />Darn, reducing the pick up and transport of sediment. A settling <br />basin was built in the river above Topock trapping sediment <br />arriving from upstream sources and preventing deposition in <br />Topock Gorge. A hydraulic suction dredge, used in the basin <br />to remove sediment, achieved the needed stability of the <br />channel, bringing water levels at Needles under control. <br /> <br />Recently adjacent lands have experienced rapid development and <br />may need the protection of additional levees. Topock marsh, <br />created by the closure of Parker Darn and filling of Lake Havasu <br />in 1938, has been encompassed with a dike to maintain water <br />levels at elevation 455 feel above mean sea level. At this level, <br />approximately 4000 acres of open water are available for fisher- <br />ies and wildlife management. In addition, inlet and outlet <br /> <br />APPENDIX D <br />