Civil Insight: A Technical Magazine Volume 2 | Page 30

30
TEACHERS’ SECTION
CIVIL INSIGHT 2018
Figure 1: Impact due to
obstruction in river
With the facts presented above, it seems obvious that the construction and operation of dams and weirs can
cause myriad changes to river ecosystems, river health and usage. Increasing demands and withdrawal of water
are responsible for large reduction in natural fl ows. Since fl owing water is one of the important determinants
of the health of the river, a large reduction of fl ow can cause many adverse impacts including degradation
of the river ecosystem, livelihood based on the river system and even the sustainability of the river. However,
many of these impacts can be avoided, minimized or mitigated through proper planning and management of
the infrastructures, thereby limiting the disruption of ecosystem services and loss of biodiversity.
Alternatively, to overcome environmental and social concerns involved in building or operating a dam, it is
particularly important to maintain adequate environmental fl ow conditions downstream of dams. The term
environmental fl ow (e-fl ow) refers to a variable water fl ow regime that has been designed and implemented
such as through the intentional release of water from a dam into a downstream reach of a river in an effort
to support desired ecological conditions and ecosystem services. Environmental fl ow is one of the tools in
managing the impacts of hydropower dams on the river health and socio-economic dependency.
g
Figure 2: Elements of Building Block
Methodology for EFA
y
p
p j
Figure 3: Representative fl ow requirements
for different parameters
As the concept of e-fl ows has evolved, there has been signifi cant development of approaches to their
assessment; from the narrow purpose of describing fl ows for maintaining ecosystems of a river to their
present use as a tool in holistic catchment management. The fi gure 2 above shows the elements of Building
Block Methodology (BBM) for environmental fl ow assessment. The underlying principle that drives initiatives
on e-fl ows is that it is a multidimensional approach and the assessment is both a social and technical process,
with social choices at its core. Social, as it depends on what the society views as the functions of the river in