which are separated by Bradford Island. The 

 spillway spans the Columbia River north of the 

 island, and the powerhouse spans the south 

 channel. The spillway has eighteen 15.2-m.-wide 

 gates that release water not needed for power 

 generation. To attract fish to the adjacent ladder 

 entrances, the gate at each end of the spillway 

 discharges water (except during very high or very 

 low flows). The gates are the vertical-lift type, 

 and water is released under them at a maximum 

 forebay depth of about 17.8 m. (fig. 2). The spill- 

 way extends downstream from the gates to form 

 two rows of concrete baffles that partially dissi- 

 pate the energy of the water rushing under the 

 gates. The flow through the spillway varies from 

 a few cubic meters per second to several thousand. 

 Bonneville Dam has little water storage capac- 

 ity. Differences in the water level between the 

 forebay and the tail water range from 12.1 to 

 18.3 m., depending on riverflow and power genera- 

 tion requirements. The powerhouse contains 10 

 Kaplan turbines, each with a maximum discharge 

 capacity of 410 c.m.s. Flow through the power- 

 house is nearly constant throughout the year, 

 but flow through the spillway varies greatly. 



Facilities for passage of adult salmon upstream 

 over the dam are extensive and complex. Most 

 fish go up two gravity-flow ladders, which have 

 slopes of 0.3 m. in 6 m. The Washington shore 

 (north) ladder has a single entrance adjacent to 

 the north end of the spillway and exits into the 

 forebay about 120 m. upstream from the dam. 

 The Bradford Island (south) ladder has three 

 entrances and a single exit into the forebay about 

 120 m. above the powerhouse on the south side of 

 Bradford Island. One entrance of the Bradford 

 Island ladder is adjacent to the south end of the 

 spillway; another is at the north end of the power- 

 house; and the third, consisting of many small 

 entrances, is across the powerhouse above the 

 draft tubes. 



Information on dead fish below Bonneville Dam 

 comes from several sources. The principal sources 

 are Federal and State agencies: the BCF (Bureau 

 of Commercial Fisheries), U.S. Army Corps of 

 Engineers, Oregon Fish Commission, and Wash- 

 ington Department of Fisheries. Some information 

 is also provided by commercial fishermen, who 

 spend much time on the river during the major 

 fish migrations; salmon sport fishermen; and 



CARCASS RELEASE POINT-1954 



L 



SPILLWAY GATE 



^ M A XIMUM POOL -H 2 5 

 ; NORMAL POOL-I- 22 



FOREBAY 



OGEE CREST 7 



SEA LEVEL 



J/-"- ; ? ' ' ■> ! r ! -'.^''m'. ' .«".-.- .'. * - ' ■* ' • ' I !' . ' A ' -- 



BEDROCK 



IIIIIIIIUIIIIIiiiiii 



Figure 2. — Bonneville Dam spillway construction and flow cross-sectional diagram (from U.S. Army Corps of Engineers 



drawing). Elevations are in meters above mean sea level. 



CHINOOK SALMON MORTALITY IN COLUMBIA RIVER NEAR BONNEVILLE DAM 



463 



