Geomorphic Effects of Dams on Rivers Gordon Grant.

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Presentation transcript:

Geomorphic Effects of Dams on Rivers Gordon Grant

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

Hydrograph – McKenzie River, OR Flood control dams

Run of the River Dam-No Flood Control Capacity

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

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

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

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

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

Summary  Dams alter… Sediment regime Sediment regime Hydrologic regime Hydrologic regime River morphology River morphology