Transcript Going With The Flow… Or Not. - Geo

Going With The Flow…
Or Not.
One Dam’s March For Freedom
Why?
• Hydroelectricity
• Allocating water to other resources, such
as farming
• Control flooding of inhabited areas
What Happens After?
• Sediment starved downstream, sometimes 90-100%
• River banks become easily eroded, beaches disappear
• River bed becomes “armoured” with rocks, this means no gravel for
spawning of fish or other benthic organisms.
• Typically eroded several meters within a decade of first closing in a
dam, after the Hoover Dam was built, the sediment starved water
washed away more than 110 million cubic meters of material,
lowering the river more than 4 meters
Riverbed Deepening
• Riverbed deepening also lowers the groundwater table along a river,
this causes a drop in the level of water in wells on the floodplain,
and threatens to dry out local vegetation
• Impacts agriculture by loss of nutrient rich sediment being deposited
downstream
• Sediment starvation also affects the coastlines, since the 1920’s,
dams have reduced 4/5ths the sediment reaching the coast of
Southern California. This leads to cliff collapse…
Water Quality
• The chemical, thermal and physical changes that flowing
water undergoes when it is stilled can seriously
contaminate a reservoir and the river downstream
• Temperature changes affect life cycles of aquatic
animals that rely on season changes in temperature
• Reservoirs can become oxygen depleted due to detritus
build up, the bacteria that feed on the build up of dead
organic matter can transform inorganic mercury found in
the plants into methylmercury, a neurotoxin which is then
moved up the food chain.
• Salt concentrations can also build up on reservoirs due
to increased evaporation