Geomorphic Effects of


22 Φεβ 2014 (πριν από 4 χρόνια και 2 μήνες)

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Geomorphic Effects of
Dams on Rivers

Gordon Grant

Hydrologic Regime

The hydrologic “regime”




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


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

surveys once a year

Influenced by other dams

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

Alluvial fans stabilize

How to bring hydrologic and
sediment transport effects

How is the dam affecting the river?

Channel response

Flow and sediment

Geologic Influence

Geology plays a major role in hydrology

High Cascades vs. Western Cascades

Dam Effects

High cascades

Very little sediment derived

Little sediment accumulated behind dams

W. Cascades

Deeply dissected

More sediment accumulation


Dams alter…

Sediment regime

Hydrologic regime

River morphology