Explain the effect of the construction of Weir or Barrage on the regime of the river?
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Normally weirs and barrages are constructed to enable a continuous supply of water into an off taking canal. We will understand the effect on the regime of river in two parts:
Since the velocity of flow reduces upstream, silt carrying capacity reduces and leads to deposition of silt on river bed creating shoals and islands.
The water travels downstream with increased velocity of flow with high demand for silt carrying capacity which is met by erosion on the downstream bed of river causing lowering of bed in downstream side also known as retrogression.
Weir is a barrier built-in river to change the depth of flow. It is a barrier that alters the floor height of the river. It is also used to control the velocity of flow during high discharge.
weir is also called a small-dam to store water in a small area.
Effects of wier on the regime of the river:
Following are some types of the wier
Effect of Weir construction on the regime of the river:
Weir is a solid obstruction which is put across a river to raise the water level.
It’s very necessary to avoid any adverse effect on the environment of construction of weir on the environment, to study the fallout of.
The effect of the construction of Weir or Barrage on the regime of the river are given below,
that a weir is constructed across the river at a certain location
(A). The immediate effect is an increase in water levels upstream
(B). This increase is not uniform but varies from place to place.
As a consequence, flow velocities differ from place to place too. The variations in flow velocity and, hence, the variations in the capacity to transport sediment give rise to a pattern of initial erosion and sedimentation along the river . Sedimentation over a relatively long distance occurs upstream of the intervention, whereas punctuated local erosion occurs downstream. This erosion advances downstream as a rarefaction wave.
Eventually, in the long run, the river reaches a new morphological equilibrium without further trends of erosion or sedimentation . Upstream bed and water levels have become higher than at the start of the intervention. Downstream, the river resumes its original shape by sedimentation after an intermediate period of erosion.
The longitudinal profiles in the diagrams provide a simplified picture. They do not include the response of channel width, bed sediment composition or vegetation. Nonetheless, they offer the key to understanding the relation between local pressures or measures and their effects far upstream and downstream
The affect of the construction of weir or barrage on the regime of the river are as follows :-
– The velocity of flow of water reduces.
– Sedimentation can be occured which makes the height of the flow constant.
– Fishes and other water animals migrations can be restricted.
– Increases the flow height for a short duration.
– Because of the barrier the particles settle down near it.