Special Note – II on ‘Odisha Floods 2011’ from Water
Initiatives Odisha (WIO)
24th September, 2011
Different Designs, Same Management
‘Did we manage the
Rengali dam the way we managed Hirakud?’ asks Water Initiatives Odisha, as it
brings a special note on this issue in response to the latest spell of the
flood disaster in northern Odisha Rivers.
The
latest spectre of floods over Brahmani and Baitarani has once again brought the
Dam Operations and Management systems of the state into question. This time the focus goes to the Rengali
dam. Before going further to the
discussion, we would like to bring to your notice the water storage level that
was maintained in the Rengali dam on select dates as against the recommended
Rule Curve for that dam.
|
Select Date
|
Recommended Maximum Reservoir and Minimum Limits (by Rule Curve)
|
Level at which the Reservoir was
kept
|
|
1st July
|
109.72 M / 109.72 M
|
114.84 M
|
|
1st August
|
115.85 M/ 115.85 M
|
114.91 M
|
|
1st September
|
122.50 M/ 121.95 M
|
122.36 M
|
|
7th September
|
122.50 M/ 121.95 M
|
122.87 M
|
|
14th September
|
122.50 M/ 121.95 M
|
123.54 M
|
|
20th September
|
122.50 M/ 121.95 M
|
123.66 M
|
|
21st September
|
122.50 M/ 121.95 M
|
123.55 M
|
|
22nd September
|
122.50 M/ 121.95 M
|
123.56 M
|
|
23rd September
|
122.50 M/ 121.95 M
|
123.56 M
|
|
24th September
|
122.50 M/ 121.95 M
|
124.39 M
|
As
can be observed from the above, even as warnings of depression/low pressure
were coming in (and in fact that has historically brought rain at this time of
the year over Brahmani and Baitarani river basins), the Reservoir was kept
consistently at a higher level. On 23rd September, when we sent
out our 8th Flood Update for this year, the Govt. of Odisha’s Water
Resources Department’s website shown the Rengali Reservoir Level at 124.15 M,
that’s 0.65 M above the recommended FRL, which was 105.4%! Even though Rengali,
unlike Hirakud, is touted as a dam whose design has a specific space devoted
above the designed water level for the project, the multi-functionality of the
project makes it controversial each time floods have come. Further, the incomplete canals have also
added to the woes as water from the reservoir could not be drained out faster
than envisaged. At the crux of it, the
dam authorities should never have allowed so much of water to stay in the
reservoir till the last moment. This is
how we managed our reservoir and let the flood devastate about half a million
people by design. Another thing that
comes to light with this is when we note that , on 23rd September,
the OHPC site, which has been quoted in the above table, shows a lower actual
reservoir level than what the WR department records. This shows how effective is the coordination
among various departments and institutions responsible for flood management in
our river basins.
Flood is a regular phenomenon in Brahmani and
Baitarani as heavy inundations take place causing severe damage. Documents from govt. departments tell us that
floodings can be reduced by temporary storage of water behind Rengali dam on
Brahmaniriver, which controls roughly some 50% of the total catchment area
draining to the delta. To use the dam for flood mitigation, floods are being
forecasted based on real-time information of rainfall and discharge in the two
basins. The lead-times for forecasting at present are limited as only the
contributions of the basins in Orissa are covered by the forecasting system.
This includes the entire Baitarani basin and Brahmani river below Panposh.
Upstream of Panposh, the Koel and Sankh rivers drain, which constitute over 75%
of the catchment area controlled by the Rengali dam. Experts have been viewing
that by expanding the flood forecasting system to the upper reaches of the
Brahmani basin lead times can be extended and knowledge about the flood volumes
to be temporarily stored at Rengali can be improved considerably. We really don’t know what is being done in
that regard by the government. Time
the government releases a White Paper on the flood management to clear all the
doubts of the citizens of the state.
From
a document of the CWC we found out that the shortfalls of the present system
were realised long time back. In August 1992 the Central Planning Unit,
Irrigation Department, Orissa finalised a feasibility study on “Telemetry
System for Rengali Dam Project”. In this study it proposed a communication system
for real-time collection of hydro-meteorological data in the Brahmani basin
which could cover such an expansion to improve the flood forecasting. This was
further taken up in World Bank’s Staff Appraisal Report (SAR) of the Hydrology Project
(July, 1995). In the SAR activities related to the improvement of flood
forecasting in Brahmani basin were covered under the heading: “Improvement to
Real-Time Water Resources Management”, with a total budget of Rs.24.7 million. It’s
also time that the Government tells us what happened to this study and its
recommendations?
Coming
back to the Rengali dam on river Brahmani, it is a multipurpose dam to store
water for irrigation and for the production of hydro-electric energy and to
mitigate floods. This dam is a gravity masonry type of dam with a length of
1,040 m. It has a 464 m long overflow section with an Ogee type spillway
consisting of 24 gates. The spillway capacity is nearly 47,000 m3/s at a
maximum reservoir level of 125.4 m. The installed hydropower capacity is 5x50
MW. The dam controls a catchment area of over 25,000 km2.
As
per the Central Planning Unit 1992 guidelines, the Rengali reservoir is guided
by the following two considerations:
1.
Dam safe condition: in no case the safety of the dam should be allowed to be threatened.
There should always be ample space in the reservoir for moderation of the
incoming flood. Releases from the reservoir should be designed accurately.
2.
Safe flood condition: an attempt should be made to restrict the release to safe
flood conditions in the downstream area (i.e. a total inflow to the delta of
less than 8,000m3/s); this should be done only if the dam safe condition so
permits.
As
per a document of the CWC, the first condition requires a reliable forecast of
the maximum inflow volume to the reservoir, so that under all conditions the
reservoir level can be kept below an MRL of 125.4 m. Both conditions benefit
most from a low initial reservoir level. This conflicts however with the other two
objectives of the multipurpose dam: storage of water for irrigation and
hydropower.
Therefore,
pre-releases from the reservoir to create extra storage capacity for flood
mitigation will only be acceptable if the rule curve levels will at least be
attained again after the passage of the flood. This requires thus a reliable
forecast of a guaranteed minimum inflow volume to the reservoir. The safe flood
condition requires also a reliable forecast of the total inflow from the
uncontrolled catchments, i.e. of the Brahmani downstream of Rengali and of the
entire Baitarani. It is noted that effective manipulation of the gates
atRengali require proper information about the flow conditions well in advance.
The travel time of Rengali releases to the delta is about 20 hours. This is
almost equal to the basin lag (= time between centroids of net rainfall and
runoff) of the Brahmani basin draining downstream of Rengali (about 24 hours)
and only slightly less than the basin lag of Baitarani(approximately 30
hours). However, we don’t seem to be
having any reliable systems of inflow forecasting in place as yet. This needs to be looked into with utmost
urgency now.
The
government cannot say that it was not warned of these issues earlier. The CWC document had already pointed out the
following weak points of the Rengali dam project and its flood control
mechanisms, as follows:
•
The system produces insufficient lead time for the flow at Rengali. It does not
account for the Brahmani basin upstream of Panposh, which comprises about 75%
of the basin area controlled by Rengali dam. The lag time between rainfall in
this area and its contribution to the Brahmani flow at Rengali is about 30 hrs
for Koel and 24hrs for Sankh river.
•
Contributions of the sub-basins below Panposh and in the Baitarani catchment
are difficult to estimate, though rainfall is to some extent considered in the
correlation technique used to produce the forecasts.
•
The lead times are also small because neither rainfall-runoff modelling is
considered nor are quantitative precipitation forecasts taken into account.
•
The inflow to the delta, contributions by the delta area itself and the water
levels at sea determine the flood stages in the delta. The present system does
not provide any means to translate the boundary conditions into flood levels.
The
report had also noted that effective flood mitigation through Rengali dam requires
proper information about the flow conditions upstream as well as downstream of
the dam well in advance. The Rengali releases travel in about 20 hrs to the
delta, which is only slightly less than the basin lags of the uncontrolled
areas (respectively about 24 and 30hours for Brahmani d/s of Rengali and
Baitarani).
Time
the government looks into all these suggestions and opens up its Flood
Management policies to public of the state and come up with a Flood Management
Policy for the state which is not only technically advanced (including
integration of climate change scenarios) but also transparent and involves all
sections of the society through proper river basin management, reservoir
operations and flood plain management activities. Below, we put forth some
specific suggestions:
1.
The first thing we need to understand is that we have to live with floods. All
the mechanisms of better flood management practices, flood control measures,
flood preparedness activities and flood forecasting practices depend on a
reliable data transmission and telemetry system. Time has come, Government
should catch up with the scientific practices for better flood forecasting,
flood control and flood mitigation measures.
2.
Regular and continuous study of river morphology, hydrology and necessary
changes due to climate change and other phenomenon to keep updating the flood
management practices The upper as well as lower catchments should have well
defined stations for recording river discharge and water levels.
3.
Having interstate agreements for all interstate rivers to have a proper
mechanism of flood information sharing.
4.
Flood inundation area demarcation in the whole state.
5.
Flood Plain zoning regulation be
implemented.
Or
else, the floods will continue to be man-made and devastations will increase by
the floods.
Ranjan K Panda
Convenor, Water Initiatives Odisha
Water Initiatives Odisha: Fighting
water woes, combating climate change... more
than two decades now!
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Sambalpur
768 004, Odisha, INDIA
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Email: ranjanpanda@gmail.com, ranjanpanda@yahoo.com
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===========
Water Initiatives Odisha (WIO) is a state level
coalition of civil society organisations, farmers, academia, media and other
concerned, which has been working on water, environment and climate change
issues in the state for more than two decades now.
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