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Topic
- Dams 47
- Irrigation 17
- Building 14
- Hydrology 11
- Politics and government 10
- Rivers--Oregon 9
- Canals 8
- Water diversion 8
- Agriculture 6
- Groundwater 6
- Resource allocation 6
- Water-power 6
- Rivers 5
- Finance 4
- Water--Storage 4
- Aerial photographs 3
- Bodies of water 3
- Climate 3
- Dams--Design and construction 3
- Demography 3
