low flows issues
DESCRIPTION
TRANSCRIPT
LOW FLOWS ISSUES
Causes
& Impacts
Case study1: River Colorado, USA
Case study2:
River Wylye, Wiltshire
What are low flows?
Fall in the level of water tables with the resultant drop in river levels.
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
Causes: Over abstraction which can lead to:
water shortagesDeteriorating water qualityIncreased sedimentationEcological changes
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
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.
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
WILTSHIRE
Causes…
Abstraction of groundwater
Climatic – the amt of precipitation & movement of water through the drainage basin
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%
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
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.