Geomorphic Effects of

coriandercultureMechanics

Feb 22, 2014 (3 years and 3 months ago)

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Geomorphic Effects of
Dams on Rivers

Gordon Grant

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

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


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


Flow and sediment

Geologic Influence


Geology plays a major role in hydrology


High Cascades vs. Western Cascades
streams


Dam Effects


High cascades


Very little sediment derived


Little sediment accumulated behind dams



W. Cascades


Deeply dissected


More sediment accumulation

Summary


Dams alter…


Sediment regime


Hydrologic regime


River morphology