APPENDIX A 

 CASE STUDY OF OAHE RESERVOIR 



Oahe Dam is a 9,300-£oot-long (2.83 kilometers), 230-foot-high (70.1 

 meters) earthfill dam located on the Missouri River in central South 

 Dakota (Fig. A-1) . 



LOCATION MAP 



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Figure A-1. Oahe Dam. 



The reservoir behind Oahe Dam, filled in 1962, is about 190 miles 

 (360 kilometers) long and 5 to 10 miles (8 to 16.1 kilometers) wide. 

 About 100 miles (161 kilometers) upstream from the dam, a railroad 

 crosses the reservoir near the town of Mobridge, South Dakota. The rail- 

 road crossing is made by a 4,500-foot-long (1.37 kilometers) earth embank- 

 ment reveted by riprap and a 2,000-foot-long (610 meters) bridge. Figure 

 A-2 is a project map showing the railroad embankment and the reservoir 

 segment near the embankment. 



The embankment core is dredge- fill material with 1 on 3 side slopes. 

 Both upstream and downstream slopes are reveted with a 6-inch- thick bed 

 of gravel, 6-inch-thick layer of spalls, and a 24-inch-thick (61 centi- 

 meters) layer of riprap armor. This riprap revetment has a top elevation 

 of 1,627 feet (496 meters) mean sea level (MSL) on both upstream and 

 downstream sides. The toe elevation of the upstream side is 1,543 feet 

 (470 meters) MSL and 1,588 feet (484 meters) MSL on the downstream side. 

 The reservoir operating levels (U.S. Army Engineer District, Omaha, 1969) 

 in feet above MSL are: 



Maximum operating pool 1,620 



Maximum normal operating pool 1,617 



Minimum flood control pool 1,607.5 



Limit of drawdown 1,540 



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