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Understanding Geomorphic Effects of Dams on River Systems

This research delves into the impact of dams on rivers, examining changes in flow, sediment regime, channel response, and geological influences. It explores the complex interplay between hydrology, sediment transport, and river morphology resulting from dam construction.

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Understanding Geomorphic Effects of Dams on River Systems

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  1. Geomorphic Effects of Dams on Rivers Gordon Grant

  2. Hydrologic Regime • The hydrologic “regime” • Geology • Climate • Topography • Changes in flow (Q) due to manipulation • Direct = dams, diversions • Indirect = climate shift, forest practices • Flows are influenced in magnitude, duration, frequency and time • There are consequences for manipulation

  3. Hydrograph – McKenzie River, OR Flood control dams

  4. Run of the River Dam-No Flood Control Capacity

  5. Sediment Regime • Much harder to get sediment data than hydrologic data • Use reservoir sedimentation rates – Japan surveys once a year • Influenced by other dams • Landuse history • Ratio of sediment supply above and below dam • Sediment budgets

  6. Channel Response • Incision occurs immediately downstream of dam • Bed incises to equilibrium then stops • Channel narrowing in which peak flows are affected • Loss of secondary channel • Colonization of bars by vegetation (traps sediment) • Alluvial fans stabilize

  7. How to bring hydrologic and sediment transport effects together? • How is the dam affecting the river? • Channel response • Flow and sediment

  8. Geologic Influence • Geology plays a major role in hydrology • High Cascades vs. Western Cascades streams

  9. Dam Effects • High cascades • Very little sediment derived • Little sediment accumulated behind dams • W. Cascades • Deeply dissected • More sediment accumulation

  10. Summary • Dams alter… • Sediment regime • Hydrologic regime • River morphology

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