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Topic
- Flood control 50
- Dams 36
- Rivers--Oregon 33
- Irrigation 22
- Fishes--Conservation 12
- Salmon 11
- Agriculture 9
- Economics 7
- Groundwater 5
- Hydrology 5
- Demography 4
- Inland water transportation 4
- Water-power 4
- Water-supply 4
- Watersheds 4
- Contamination of environment 3
- Lectures and lecturing 3
- Precipitation (Meteorology) 3
- Water quality 3
- Water--Pollution 3