Agriculture Reference
In-Depth Information
Environmental flow is the water regime provided within a river, wetland or coastal
zone to maintain ecosystems and their benefits where there are competing water
uses and where flows are regulated.
Key concepts in environmental flow assessment are:
- river systems can be maintained at different levels of health
- different flows play different roles in maintaining river systems
- ecological and social consequences of flow manipulation can be predicted
- complexity and variability are vital to ecosystem health
5.2.4.2 Methods of Environmental Flow Assessment
Generally the following two methods are used to assess environmental flow:
(i) Building block method
(ii) Drift method
Drift Method
It is a scenario based method. Scenario is used to identify tradeoffs that can be used
in negotiations between water users to balance needs of the ecosystem with other
needs. A set of scenarios (produced as output from different water levels) or options
for a river is used in decision and policy making.
Building Block Method
It is an objective based method. In this method, a specific ecological status of a river
is maintained. The future desired condition of the river is identified. Environmental
flow regime is then constructed based on premise that riverine species rely on basic
elements of flow regime (building block). The main phases of building block method
(BBM) are
a. Comprehensive information gathering on river system, normally undertaken by
a team of experts.
b. Exchange opinion among agency representative, water managers, engineers and
scientific experts to identify flow regimes; usually through a workshop.
c. Linking the environmental flow consideration with engineering considerations
Information gathering involves:
- identification of study area
- present condition of river for overall riverine habitat
- determination of importance of study area at local, regional and international
scale.
- assessment of water quality
- biological surveys at selected points
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