human impacts Flashcards
flood forecasting and warning
flood forecasting is the estimation of future water levels or flowsn at a single
or multiple sites of a river system for a different lead times.
Deforestation
will reduce the interception of
rainwater and increase the possibility of surface
runoff and increase rates of soil erosion.
Water will reach river channels more quickly,
reducing lag times, and eroded soil will infili river
channels, reducing their channel capacity and
increase the potential number and size of floods.
Deforestation will not simply affect interception
but it will also have an effect on infiltration,
overland flow, groundwater flow and the degree of
evapotranspiration.
Afforestation
can have the opposite effect by
increasing interception, protecting the soil from
erosion and increasing lag times
Urbanisation
can increase flows into a river
channel by the construction of impermeable
surfaces of concrete and tarmac and the
construction of storm drains to remove water
from buildings and roads which often stops or
reduces the infiltration of rainwater and reduces
the amount of water available as baseflow.
This will therefore increase both the amount of
quick flow discharge and the speed of overland
flow. In urban areas, as in Los Angeles, USA,
river channels are often canalised to produce
more rapid river flow and remove potential flood
water quickly. Flood prevention methods such as
artificial levees and embankments, flood walls,
dredging and channel straightening are also used
to increase channel capacity and efficiency.
Water Abstraction
As water is removed from aquifers, it causes
a drop in water tables, which then reduces the
river discharge, increasing the rate of sediment
deposition.
Water Storage
Water storage involves building dams
and creating reservoirs. Projects such as the
Three Gorges Dam on the Yangtze River in China
have significant and widespread impacts on river
flow, velocity and types of flow as far down as the
Shanghai urban area. Dams provide an interruption
to the flow of water throug~1 the systern. Surface
storage is increased due to the reservoir behind
the dam at the expense of river channel flow
Dam building
clear water
erosion. This is where the river has more energy
than before the building of the dam as it no longer
has to use much of its energy to transport its load
- which has been deposited in the lake behind the
dam. This means that it is more powerful and will
increase the erosion of its channel bed and sides
below the dam.
Grazing
decline in infiltration due to compaction of soil
Advantages of dams
Flood and drought control-good crops in dry years
-irrigation- 60% of Aswan High DAM ON nile usd for irrigation up to 4000km irrigated
-hydro electric power
-improved navigation
-tourisim
Disadvantages of dams
water losses - less than half the water expected is provided
salinisation-crop yields have been reduced to 1 third of the area
groundwater changes- increased levels may lead to increased salinisation
-displacement- indigenous ppl removed
-seismic stress- as water levels in dam increase so tdoes seismic activity
- eroision of delta -2.5 cm each year
Areas vulnerable to flooding
low lying areas of floodplain
small basins subject to flash floods- common in arid regions
- unsafe dams
-low lying inland shorelines
Causes of Floods
Excessive input of precipitation
coastal storm surges
dam failure
snow melt
urbanisation
changes in vegetation cover
climate change
Loss sharing
Disaster aid and insurance
Disaster aid
money equipment techinical assistance staff given to a community after a disaster
Insurance
a means of protection from financial loss in which, in exchage for a
fee, a party agrees to compensate another party in the event of a certain loss,
damage or injury
