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Causes & Impacts of Low River Flows
1. Causes
& Impacts
Case study1: River
Colorado, USA
Case study2:
River Wylye,
Wiltshire
2. What are low flows?
Fall in the level of
water tables with
the resultant drop
in river levels.
3. Causes:
Drought conditions
Dam construction which regulates downstream
river discharge and the regime of the river,
affects the migratory routes of some fish
increase in salts & pollutants
E.g. in the Russian Federation, dams have
reduced natural discharge from the Dnestr,
Dnepr & Don rivers by 50-60% accumulation
of salts & pollutants in the Black sea
4.
5. Causes:
Over abstraction which can lead to:
water shortages
Deteriorating water quality
Increased sedimentation
Ecological changes
6.
7. Case Study: Colorado river,
USA
E.g. River Colorado basin area, USA , growing
demand for water due to:
The aridity of many areas within the catchment
Extraction of water to irrigate agricultural areas
in the central valley of California
Expansion of urban areas and the demand for
water supplies such as in the ‘Sansan’
megalopolis area
8.
9.
10.
11. Result:
Little flow by the time the river reaches the
Gulf of Mexico
Increase salinity (up to 3000 ppm) due to water
loss through evaporation during the irrigation
process
Mexico has been forced to spend $200m on a
desalination plant
Water quotas have been introduced for the use
of water from river, California currently uses
around 59% of the water.
12.
13. Case Study 2: River Wylye,
Wiltshire
Between 1988 -1992:
River Wylye & its tributaries registered
particularly low flows.
People became concerned about the
state of fish stocks in the river ( river
well-known for trout fishery) as well as
aquatic environment in general
17. Causes…
Abstraction of
groundwater
Climatic –
the amt of precipitation & movement
of water through the drainage basin
18.
19. Impact of abstraction…
Groundwater abstraction, despite being within its
licensed limit, was having a detrimental effect on
low flows
Harmful effects on fish stocks
Growth of algae caused by nutrients from
fertilisers being washed into streams, reduction in
oxygen
Most serious affected area, the upper Wylye,
abstraction reduced typical summer flows by
50-60%
20.
21.
22. Strategies:
Sink two new boreholes to augment flows in
Chitterne Brook & the River Till
Increase river augmentation at Brixton Deveril
Aim for more constant level of abstraction
Monitor the effects of abstraction on river
flows esp on the quality of the aquatic
environment
23. Noting activities…
1. What are ‘low flows’?
2.Why do you think people are concerned
about low flows in rivers?
3. Outline two main causes of low flows.
4. What are the impacts of water
abstractions, provide examples to your
explanation.