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- River engineering 192
- Northwest, Pacific 175
- Bodies of water 133
- West (U.S.) 125
- Rivers--Oregon 99
- United States. Congress--Records and correspondence 95
- Dams 68
- River surveys 59
- Rivers 56
- United States--Appropriations and expenditures 47
- Railroad engineering 46
- Water--Pollution 36
- Flood control 32
- Dams--Design and construction 27
- Canals--Design and construction--Costs 26
- Transportation 26
- Fishes--Conservation 25
- Lectures and lecturing 25
- Salmon 25
- River channels 23