Orissa: Civil Society calls for Revisit of Hirakud Rule Curve
Sunday, September 11, 2011
Orissa: Civil Society calls for Revisit of Hirakud Rule Curve

By Pranab Ranjan Choudhury
Mighty Mahanadi is once again on its mightiest spate and the flood has already affected 19 districts, with millions marooned and an increasing toll on communication, life and property. All eyes are now concentrated on the operation of the Hirakud reservoir with questions being raised about the reservoir operation and fingers pointed at the Rule Curve. This is the time to concentrate on flood management and relief and to gather efforts to minimize the losses and not to spend energy on engage in debates. However, such situations also make it difficult to completely ignore critical analysis of the causes, rather reiterate the need of research and analysis to contribute to informed dialogue and evidence-based decision making.

As a first step towards this, Odisha Water Forum and Baitarani Initiative have tried to analyze the ‘Rule Curve’ – based reservoir operation of Hirakud, to see whether the violations in rule curve prescriptions add to flood severity and woes, or the ‘Rule Curve’ itself needs modification with changing circumstances and situations in the dam’s catchment and the reservoir capacity. Based on a rapid analysis of rainfall, runoff, siltation, reservoir level data over about 50 years (1957-2009) and this flood’s daily observations along with post-Hirakud water-resources development trends in Chhatishgarh, which contributes to 85% of dam’s catchment, we make a strong appeal for revisit of the ‘Rule Curve’ developed in 1988 to make it more adaptive to changing climatic and development context and also the need of exploring a formal arrangement with Chhatisgarh over management of water and water-information on Mahanadi basin. We also suggest the state to ensure active participation of civil society, primarily the representatives of the affected stakeholders of the basin, both in the Hirakud-downstream and delta, in these two processes, for developing a more inclusive, effective and adaptive system for flood management.


What is Rule Curve?

A Committee appointed by Central Water Commission in 1988 had developed Rule for managing reservoir levels for flood control during monsoon and maintenance of reservoir function (irrigation and power production) post-monsoon.  Rule curve prescribes reservoir level in dam to be between 590 to 595 feet during 1st July to 1st August, which is near to the dead storage. This is to facilitate flood cushioning. In case there is heavy inflow into reservoir, water can be retained and discharged in regulative manner. From 1st of August reservoir level would be raised till 1st of October, when reservoir will be filled up to FRL (Full Reservoir Level).

It was also recommended that during rising water levels at the end of monsoon the dam authorities should consider, general long term metrological forecast issued by I.M.D. on the trend of monsoon and base flow into the reservoir in monsoon. There should be formation of pre-depletion plan for reservoir from following information

·         Satellite image of cloud formation,

·         I.M.D. forecast of current and predicted situations of storms, troughs, speed storms, translation velocity strength of circulation and its location.

·         I.M.D. prediction of quantitative precipitation

·         Average rainfall calculated from daily/ 3 hourly rainfall records of 40 stations in upper catchment and 31 stations of lower catchment.

·         The runoff records from gauzing stations in upper catchment give inflow records though approximate, 48 hours in advance of reaching the dam site.

·         The release from upstream reservoirs, if intimated in advance will further help the reservoir operations.


a.       Analysis of Rule Curve

      
Analysis of Rule Curve

The rule curve is premised on higher rainfall and inflow in July and Aug (at dead storage level in July and Aug) and lesser rainfall in September (619-627 ft on 1st Sep). The rule curve committee has indicated that during the period of 30 years before rule curve (1957-88), there were only 3 instances of deviations of upper limit. However, of late there seems to be more such deviations and more regular deviations. As can be seen in subsequent analysis (section on rainfall and runoff) we find there is a clear shift towards more rainfall and runoff in the month of September. Probably the existing rule curve is unable to accommodate cushion to September inflows. Lack of appreciation of this shift and accommodation of this into the Rule Curve along with reduction in live storage capacity and unpredicted release from dams in Chhatisgarh, is decreasing the flood cushioning ability of the Hirakud dam.

The actual management of reservoir operations against rule curve in 2008 and 2009 was different. Reservoir water level was kept high than prescribed water levels during June to August.

b.      Situation this year

This year, during 2nd September to 10th of September reservoir levels were within the limit of prescribed rule curve, though towards upper limit during 5th to 10th Sept. Due to this there was absence of any flood water retaining capacity in reservoir. When inflow, jumped up to 11 lakh cusecs at 10.00 hours on 10th September, dam authorities were forced to release of more than 9 lakh cusecs of water, which increased threat of flood in the delta.

The inflow into reservoir was in normal situation up to 5th of September, at the same time out flow from dam was kept accordingly same as there was absence of heavy rainfall in downstream. On 6th Sept catchment area started to get heavy rainfall with steadily increase inflow into the reservoir. However inflow in reservoir at 12:00 on same day was 3.98 lakh cusecs and outflow from dam was 2.12 lakh cusecs, through opening of 13 sluice gates. After this there was steadily increase in water inflow and outflow from reservoir due to heavy rainfall in upper catchment and also due to sudden release from dams in upstream.

Inflow and Outflow in Hirakud during 1st - 10th Sep, 2011

Flow in cusecs at 12 hours

A very simple analysis of reservoir capacity at different water levels on 5th, 7th and 8th of September shows that the storage space available to accommodate the inflow is not adequate and hence the flood moderating capacity of the reservoir has failed up to some extent.

Reservoir Capacity analysis at different water levels on 5th, 7th and 8th September, 2011

Date

Reservoir Level

Inflow (cusec)

Outflow (cusec)

Reservoir capacity in cft at these water levels  (2007 data)

Change in storage (inflow-Outflow) in cft

Storage capacity available after accommodating the change in storage (MAF)

5

624.23

313253

379533

3887413.97

-5726592000.00

0.13

7

626.31

543840

482907

4199200.03

5264611200.00

-0.12

8

627.27

950630

709215

4350412.51

20858256000.00

-0.48

 

 

 

 

 

c.       Changing Rainfall pattern: More rain in September in post-Rule Curve Period

There seems to be a trend of shift in the rainfall pattern in upper catchment of Hirakud with respect to Aug and Sep rainfall, which have a great bearing on the Rule Curve-based reservoir operation being in place for Hirakud since 1988.

A comparison of rainfall pattern in the months of August and September between pre-rule curve (1957-88) and post-rule curve (1989-2009) years, indicate that there is a 10% fall in monthly average rainfall in August (379mm to 333 mm), while average monthly rainfall has reduced by only 1% in September (195 mm to 193 mm). While the average monsoonal rainfall has reduced from 1155mm to 1065mm during these periods, share of August rainfall (to total monsoonal rains) has reduced from 33% to 32%, while share of Sept rainfall has gone up from 16% to 18%. In terms of variations, while for more number of years (50%) August month was experiencing more rainfall than average during pre-rule curve period, the % of years experiencing the same have been lesser (45%) during post-rule curve period. But, the trend has reversed for the month of September, which has contributed more rainfall than average for 45% number of years during post-rule curve, whereas only 33% of the years had more than average during pre-rule curve years.

Rainfall (mm) in Pre-Rule Curve (57-88)

 

50% of the years had more rainfall than monthly Avg

 

33% of the years had more rainfall than monthly Avg

 

Post-Rule Curve(89-09)

10% fall in average rainfall in Aug

45% of years had more than monthly avg

1% fall in average rainfall in Sep

45% of years had more than monthly Avg

 

 

 

d.      Runoff Trend: More runoff in September in post-rule curve period

Runoff pattern into the reservoir also seems to have been undergoing a shift with respect to Aug and Sep runoff, which have a great bearing on the Rule Curve-based reservoir operation being in place for Hirakud since 1988.

A comparison of runoff pattern in the months of August and September between pre-rule curve (1957-88) and post-rule curve (1989-2009) years, indicate that there is a 20% fall in monthly average rainfall in August (10.61 MAF to 8.44 MAF), while average monthly runoff has reduced by only 7% in September (6.83 MAF to 6.37 MAF). While the average monsoonal runoff has reduced from 26.5 MAF to 23.4 MAF during these periods, share of August runoff (to total monsoonal runoff) has reduced from 43% to 38%, while share of Sept runoff has gone up from 25% to 29%. In terms of variations, while for more number of years (52%) August month was experiencing more runoff into the reservoir than average during pre-rule curve period, the % of years experiencing the same have been lesser (45%) during post-rule curve period. But, the trend has reversed for the month of September, which has contributed more runoff than average for 45% number of years during post-rule curve, whereas only 42% of the years had more than average during pre-rule curve years.

e.       Reducing storage including live storage, less space to accommodate inflow peaks

As per the DPR, the live storage is 8% of annual run off of river at Hirakud. There was decision that total silt deposition in dam should not exceed beyond 8% of annual silt yield. The silt reserve that is dead storage is having capacity of 1.20 MAF. Provisions of deep sluice gates (set at height of 580 R. L. ) were there with flood discharge capacity of  7 lakh cusecs of water which was expected to remove entire suspended silt and to large extent coarse silt.

Though there have been conflicting reports on sedimentation of live storage in Hirakud, there is enough evidence and consensus around considerable reduction in storage space than was estimated. There has been a reservoir capacity loss of                5.32ha-m/100sqkm/year, in comparison to estimated 2.5 ha-m/100sq Km/year, which is almost double the rate. (Remote sensing study, 2007) Sedimentation study, 1986  (through Hydrographic method) reported that, 49% (0.6 MAF) of total sediment deposited into live storage of dam (R. L. 590 feet to 630 feet) causing about 12% loss in live storage (loss @ 0.44% per year). Remote sensing study of sedimentation (1988) reported a loss of 24% in the live storage. Jaysheelan committee report (2007), quoting Remote sensing sedimentation study, 1995 reported loss of live storage in 50 years to be 20%, with live storage capacity in 2007 as 3.77 MAF. However, Remote sensing Sedimentation study of reservoir in 2007, reported a loss of 11% in live storage and a capacity in 2007 of 4.18 MAF.

Though the monsoonal runoff has now reduced by 12% (from 26.5 MAF to 23.4 MAF from pre Rule Curve to Post-Rule Curve Period), the reservoir capacity has also reduced. There has been a reduction of 28% storage (1.82 MAF. 6.6 MAF to 4.8 MAF) at 630 ft  RL to 52% (1.01 MAF; 1.88 MAF to 0.87 MAF) at 590 ft  RL due to siltation.

 

f.        Changing pattern on Inflow from Chhatisgarh

Over 90 per cent of Hirakud's catchment area lies in Chhattisgarh. It has constructed five major and medium dams and about 150 small dams on the Mahanadi and its tributaries upstream of the Hirakud reservoir in the past 50 years.  Though concerns have been shown regarding reduction in inflow (@ 5% per decade), the appreciation of the impact of changed inflow pattern due to the reservoir operation of these dams on the reservoir operation of Hirakud has not been very forthcoming. Through construction of dams and reservoirs in Chattisgrah now there is interception of 24% (16,845 sq km catchment out of 83,400 sq km) of total catchment of Hirakud reservoir. The total capacity of reservoir constructed in Chattisgarh is 6401 MCuM, out of which on 9th of September there was 90.96 % of total capacity was filled. Sudden release from these dams owing to heavy rainfall in Chhatisgarh leads to peaking of inflow in Hirakud, which was probably not expected. For example, Bango Dam suddenly increased to 1.5 lakh cusecs in River Hasdeo in Chattisgarh at 16:00 hours on 8th of September, allegedly without any information to Hirakud.

In inter-state and dammed rivers, dams in upstream are required to share information about water release with downstream dams to enable them control their reservoir operations. Since the Rule Curve is developed in 1988, many dams have come up in Chhatisgarh along with massive catchment treatments and increased storage capacity. It is obvious that they have got considerable influence on the way inflow peaks and pace are generated. While lack of accommodation of the same into ‘rule curve’ operation is  a matter of serious concern, need of having a formal arrangement between two states and involvement of civil society and basin-stakeholders in such process is also highly imperative.

 

Compilation and Analysis: Pranab Ranjan Choudhury, Jinda Sandbhor & Padma Kesharee Sahoo

Baitarani Initiative, Forum for Policy Dialogue on Water Conflicts in India & Odisha Water Forum

Bhubaneswar, Orissa, India

baitarani@gmail.com

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