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- Northwest, Pacific 14
- Rivers 13
- River engineering 12
- Photography 8
- Bodies of water 7
- Canals--Design and construction--Costs 5
- Dams--Design and construction 5
- Jetties 5
- Transportation 5
- United States--Appropriations and expenditures 5
- River surveys 4
- West (U.S.) 4
- Locks (Hydraulic engineering) 3
- Water resources development 3
- Mountains 2
- Nature 2
- Railroad engineering 2
- Riparian areas 2
- River channels 2
- Scenic byways 2