Chitale committee on
Desiltation of Ganga has recommended a slew of measures which include study of
reach wise sediment transport processes along with establishing annual sediment
budgets to guide de-silting activities, Preparation of annual reports (Sand
registry) describing the previous de-silting/ dredging activity and a technical
institute may be entrusted to conduct the sediment budget, morphological and
flood routing studies that would examine and confirm the necessity of the
de-silting of the reach under consideration.
The committee was constituted
in July 2016 by the Ministry of Water Resources River Development and Ganga
Rejuvenation to prepare guidelines for desiltation of river Ganga from
Bhimgauda (Uttarakhand) to Farakka (West Bengal). Shri Madhav Chitale (Expert
Member, NGRBA) was appointed as Chairman of the committee. The other members of
the committee were: Secretary, Ministry of Water Resources, River Development
& Ganga Rejuvenation, Secretary, Ministry of Environment, Forests &
Climate Change and Dr. Mukesh Sinha, Director, Central Water and Power Research
Station, Pune. The committee was asked to establish difference between
desilting and sand mining and also to establish need for desilting for ecology
and e-flow of the river Ganga.
The committee in its
report says erosion, sediment transport and siltation are very complex
phenomena. It is impossible to apply a “one-size-fits-all‟ approach to
sediment management and control, because the issues involved are frequently
very regionally-specific. Local factors such as topography, river control
structures, soil and water conservation measures, tree cover, and riparian
land-use or land disturbance (for example agriculture, mining, etc.) can have a
large impact on sediment loads in rivers. River control structures (such as
reservoirs), soil conservation measures and sediment control programmes can
cause downstream sediment loads to decrease, while factors such as land
disturbance (clearing of vegetation, for example) or agricultural practices can
cause increased sediment loads. At the same time, indiscriminate de-siltation
works may result into more harm to ecology and environment flow. Thus, there is
a need to evolve Guidelines, better broad principles, which should be kept in
mind while planning and implementing de-silting works.
According to the report
erosion, sediment transport and siltation in large rivers like Ganga are very
complex phenomena and their estimation has inherent limitations and
uncertainties. A reconnaissance of Main River Ganga on Google earth map reveal
that different reaches are in a dynamic equilibrium phase. Sedimentation is
mainly seen downstream of Bhimgauda barrage and near the confluences of
tributary rivers with Ganga. The discharge congestion, large scale sediment
deposition and its negative effects are mainly seen downstream of the
confluence of Ghagra and beyond. The river flood plain drastically
widens beyond the confluence of Ghagra and is estimated to be around 12 to 15
kms.
The committee says though
de-siltation works can improve hydraulic performance of the river and this
itself can justify undertaking de-siltation, these have no direct role in
improving environment flow in the river. On the other hand, indiscriminate
de-silting or sand mining would cause adverse impacts on river e-flow.
Recognizing the importance of sediment transport in rivers, following basic
principles of siltation in rivers should be kept in mind while considering
de-siltation works:
·
Catchment
Area Treatment and Watershed Development works, along with good agricultural
practices and river bank protection/anti-erosion works, are necessary to reduce
silt inflow into the river system and must be undertaken in a comprehensive
way.
·
Erosion,
movement and deposition of sediment are natural regulating functions of river
and Sediment equilibrium of river should be maintained.
·
Rivers
should be provided with sufficient flood plains (lateral connectivity) without
any hindrance to the flow.
·
Instead
of “keeping the silt away”, strategy to “giving the silt way” should be
adopted.
In specific reference
to de-siltation works in river Ganga, in addition to MoEF&CC Sand Mining
Guidelines, which are statutory in nature, and the GSI Guidelines, the
committee has suggested following Guidelines;
1. River
Ganga tends to achieve equilibrium on its own given the hydrology, sediment and
natural bed and bank disposition. It is necessary to provide the river
sufficient areas of flood plain and lakes along the river to moderate the flood
level. Any encroachment of flood plain, reclamation of lakes or disconnection
of lakes from river should be avoided; rather adjoining lakes/depressions may
be de-silted to increase their storage capacities. The de-silting of lakes,
etc., should be in such a manner that the sediment continuity is maintained and
should not lead to head cut that creates safety issues for the river crossings,
water intakes or river training works locally, downstream or upstream.
2. Upstream
reaches of natural constriction works, like barrages/bridges, etc., tend to get
silted leading to wandering of river. Possibly river training, cut-off
developments and provision of extra water way near the constrictions could be
tried after proper assessment without impacting the morphology of river
elsewhere. The area freed from the development in the form of oxbow lakes
should be used for flood moderation rather than reclaiming it for other
purposes.
3. In
case where constriction is causing large scale siltation, de-siltation along
the preselected channel to deepen and attract the flow could be tried to guide
the main course of flow. The dredged material may be dumped along the alternate
channel which was to be closed to avoid bank erosion. Care shall be taken to
develop stable channel which do not affect the flow either on upstream or
downstream. Efforts should be made to provide silt continuity along the weirs
and barrages.
4. Embankments,
spurs and river training measures provided to protect the banks should not
encroach upon the flood plains and delink the lakes, flood plains and other
riverine environment from the river.
5. The
proposed de-silting of any river reach need to be justified bringing out
clearly the flooding caused due to siltation along with technical comparisons
of the alternative flood mitigation measures with “do nothing” or “proposed
de-silting/ dredging” being other options. It should invariably be associated
with sediment flux studies and morphological studies to confirm no significant
adverse effect on downstream or upstream reach of the river including the
safety and effectiveness of river crossings, water intakes, existing river bank
/ flood protection measures etc.
6. De-silting
of the confluence points, especially with huge silt carrying tributaries, such
as Ghagra, Sone, etc., may be necessary to make confluence hydraulically
efficient.
7. 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 and 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.
8. Agricultural
practices along the river flood plains should be such that it does not disturb
the passage of flood by increasing the resistance to flow causing aggradations.
9. River
morphological studies should be carried out to initiate in-stream channel
improvement works. It shall be ensured that the head cut induced upstream
should automatically de-silt the reach. The headcut induced should progress
upstream slowly so that the flora and fauna will have sufficient time to
re-adjust its habitat.
10. The
proposal should also contain environmentally acceptable and practically
feasible silt disposal plan. 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. It should also be ensured that disposed material should not come back
into the river again.
11. In
view of specific issues being raised about siltation in front of the Farakka
Barrage, it is suggested that the shoals formed may be de-silted/dredged by
taking care of the river training works around it. The sediment removed may be
used for re-grading the Farakka Feeder Canal or may be used for strengthening
the existing embankments around the barrage pond. Sediment sluicing may be
incorporated to maintain sediment continuity from upstream to downstream
reaches after carrying out necessary studies. The de-silting / dredging works
of the barrage pond shall not cause any structural problem to the barrage by
excessive erosion on the downstream. In view of this the dredging shall be
restricted only up to original bed level or higher.
12. Feasibility
of introducing an arrangement need to be studied to pass the incoming sediment
safely to downstream of the dams/ barrage structures to maintain the sediment
equilibrium. It shall also be ensured that the concentrated sediment flux
passed downstream will not create any major morphological changes on the
downstream reaches.
13. Any
bridges across River Ganga which are causing large afflux (more than 1% of
normal depth) should be modified to reduce the afflux, which in turn will also
reduce the sediment deposition and erosion of banks on the upstream.
14.
The
dredging/de-siltation/mining activities may result into some adverse impacts,
i.e., (a) River bed degradation; (b) Bank erosion; (c) Channel widening; (d)
lowering of water surface elevations in the river channel; (e) lowering of
water table elevations adjacent to the river; (f) a reduction in the structural
integrity of bridges, pipelines, jetties, barrages, weirs, foundations
supporting high tension lines, existing bank protection works and other manmade
structures; and (g) a loss of environmental values resulting from (a) through
(e). Restrictions as presented in Appendix IV of this Report need to be
enforced before planning and executing any dredging/ de-silting / mining
activities. These restrictions may be modified only after proper study and
monitoring the effects of dredging / de-silting / mining.
15.
The Ganga Flood Control Commission, a
sub-ordinate office of Ministry of Water Resources, River Development and Ganga
Rejuvenation and secretariat and executive wing of Ganga Flood Control Board,
headed by Union Minister of Water Resources, River Development and Ganga
Rejuvenation with the Chief Ministers of Ganga river basin States and Member,
NITI Ayog (erstwhile Planning Commission) may be entrusted with additional
mandate to carry out necessary studies with regard to sediment management in
river Ganga and incorporate sediment management strategies in their
comprehensive plans prepared for all sub-basins of river Ganga. These
integrated plans could serve as base documents for Central, State and District
Level Authorities for considering proposals for environment clearances for
works related to river Ganga.
Samir/JKD/jk