'Desiltation can improve only a river's hydraulic performance'

Indiscriminate desiltation work can cause "more harm" to a river's ecology, a high-level panel formed to prepare guidelines for desilting work of 2525-km Ganga river has said.
Countering the popular perception that desiltation improves river's ecology and its e-flow (environment flow), it has argued that if carried out properly, at best, it could only improve the hydraulic performance of the river.
In its draft report submitted to the Union Water Resources Ministry, the Madhav Chitale-led committee has recommended the government to make institutional arrangement to appraise any proposal for desiltation works by forming a national-level technical agency.
The four-member committee has advocated such institute to conduct sediment budgeting, morphological and flood routing studies that would substantiate necessity of desilting a river stretch concerned.

In the case of Ganga, it has suggested the government to entrust Ganga Flood Control Commission (GFCC), whose main job is to work out plans for controlling inundation in the river basin, with additional mandate to carry out such studies.
Among other, the committee, formed under the Centre's ambitious 'Namami Gange' programme, has urged avoiding encroachment on the river's flood plain areas, "generally avoid dredging" in Ganga and pitched for providing the river with sufficient flood plain areas.

The panel has also insisted on encouraging agricultural practices along flood plains in a way that it does not disturb passage of flood by increasing resistance to flow causing aggradation.

"The Committee has the opinion that desiltation works can at best improve hydraulic performance of the river and have no direct role in improving ecology and/or environment flow in the river.
"On the other hand, indiscriminate desilting or sand mining would cause adverse impacts on river ecology and/or environment flow," said the panel's report, accessed by PTI.
Underscoring the need for realising value of sediment and viewing it "as an asset", the panel has argued that gravel in a river has a role to play in providing spawning habitat for fish, aerating water with oxygen by increasing local roughness and inducing turbulent flows.

"De-silting/dredging may restrict over bank flow, thereby reducing ground water recharge and flood detention in adjoining low-lying areas, and consequently, reduction in base flow," the panel has warned.
Insisting the government to undertake in a comprehensive way river catchment area treatment, it said watershed development and river bank protection works to reduce silt inflow in Ganga.
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In its Ganga-specific desiltation guidelines, the panel has stressed desilting proposals involving the river should contain "environmentally acceptable, practically possible" silt disposal plan.
It has stressed that river gravels/sands/silts could be used "gainfully" in construction works, including housing, roads, embankment and reclamation works.

"Under no circumstances, disposal should create any contamination of the water bodies, harmful to the flora and fauna existing adjacent to the disposal sites or disposed material should come back into the river again," it has said.
The panel has also warned that any effort to diminish Ganga's width of the corridor (floodway) and curb the river's freedom to meander would prove "counterproductive".
Stating erosion, movement and deposition of sediment in a river are its natural regulating functions, the committee has observed that a stable river is able to constantly transport the flow of sediments.
"Instead of 'keeping the silts away', strategy to 'giving the silts way' should be adopted," it has urged.

Proposed de-silting of any of the river's stretches must first clear inundation in the river was caused due to siltation.
"Desilting of confluence points, especially with huge silt carrying tributaries, such as Ghagra, Sone, etc., maybe necessary to make confluence hydraulically efficient," the report said.
The committee has advised that reservoirs in main river Ganga and its tributaries, particularly in upper reaches, should be operated in such a manner that first floods, having high silt load, are allowed to pass through without storage.
"(Instead) the river flows in later phases of the monsoon are only stored for use during non-monsoon season. This would require quantitative long term forecast with decision support system to be established for optimum reservoir operations," it said.