Every time there is a huge flood in India with massive loss of lives and extensive physical damage, there is a hue and cry. Especially if this takes place in an area not normally prone to such floods. Assam and Bihar for instance are regularly laid waste by floods and so there is not much agitation over that anymore. But when there were sudden unprecedented floods in Uttarakhand, Kashmir, Chennai and Mumbai a few years back and now recently in Kerala, there is a massive outpouring of wrath and a severe blame game begins. In the instance of Kerala, one particular allegation has been that the many dams that are there in the state were almost full to capacity before the torrential rains began in late August and so they did not have much of a flood cushion to absorb the higher runoff coming into them and had to release this excess water downstream creating havoc. Stung to the quick by this allegation that began to be repeatedly made, the usually secretive Central Water Commission (CWC) did what it normally does not do - opened its mouth and revealed its data even if partially!!
The Central Water Commission has published a report in which it has analysed the data regarding the various river basins of Kerala and the impact of the dams on the floods there. The crucial data that needs to be understood is that regarding the river flows at the major dams and at the hydrological stations in the plains close to the sea where the floods mostly had devastating effect in the urban areas. However, the CWC has given this data only for the biggest river Periyar which also has 47 percent of the live storage capacity of all the dams in Kerala. Even though there is data regarding the total runoff and the total flow in the river along with the amounts impounded in the dams, for all the basins that have been analysed by the CWC, this does not give us an understanding as to the force of the floods at their peak. Therefore, the CWC's report is still deficient in this respect.
The Periyar basin has three major dams, the Mulla Periyar followed by the Idukki on the main stem of the river and another on the Idamalayar tributary. The peak flood discharge in the river at the Neeleshwaram measuring site of the CWC in the plains near the sea during the height of the flood was 8800 cubic meters per second (cumecs). The outflow at the Idukki dam then was 1500 cumecs. The flood cushion that was there in the dam resulted in about 1000 cumecs being absorbed. However, if a greater flood cushion had been created by releasing water from the dam in phases earlier in the month, then another 1000 cumecs could have been absorbed. The Idamalayar dam on the tributary of the Periyar released another 1500 cumec at its peak despite being a smaller dam as it had very little flood cushion. Being a smaller dam it could have absorbed another 500 cumecs if there had been more free live storage space in the dam. In other words the flood flow at Neeleshwaram would have been 7300 cumecs if these dams had been properly operated. This is more or less the case with the other smaller basins also as even if they had kept a flood cushion, given their much smaller live storage capacity as compared to the huge runoffs coming into them, they would not have been able to absorb much of this. The CWC of course goes overboard with this data and says that the lack of a designed flood cushion resulted in only a "miniscule" increase in the flood impact even though the increase is actually about 20 per cent which is quite significant.
The important conclusion that comes from this analysis is that the dams in general have limited flood protection capacities, especially when faced with rainfall that is of such huge proportions ranging from 100 to 250 percent more than the normal for the month occurring in just three days. Even though proper operation of the dams by following the rule curve which prescribes the level of water to be kept at the reservoir at different times of the year so as to provide a flood cushion, would have reduced the flood impact a little but that would not have averted the disaster. Actually, the imperative of producing hydropower, which is the primary aim of the biggest Idukki dam and most other dams in Kerala, led the dam operators to err on the side of keeping the reservoir levels high and failing to provide a substantial flood cushion.
The main reason for the floods in Kerala having been so devastating, is the huge deforestation that has taken place in the Western Ghats along with quarrying for stones and minerals as is evident from the graphic below.
This has been compounded by construction in paddy fields whose area has gone down from 8.5 lakh hectares earlier to just 2 lakh hectares now. The wetlands and the floodplains of rivers have also been encroached on. All this has together increased the runoff and also decreased the water holding capacity of the hills and the plains. The Vembanad Lake, which is a protected Ramsar site, into which several rivers drain has been encroached and its capacity to hold water has been drastically reduced because of the huge urbanisation that has taken place around it. Consequently it did not have the capacity to hold the huge runoff coming into it and overflowed and submerged the urban areas around it.
This massive deforestation and mining combined with indiscriminate construction in floodplains and fields is indeed the reason for floods in the Himalayas and their foothills and plains also from Kashmir to Arunachal Pradesh whenever there is an extreme weather event resulting in concentrated precipitation in a short period of time.
Flood control, not only in Kerala but throughout the country, thus, has to be brought about by greater soil and water conservation measures to increase artificial recharge and stabilisation of steep hill slopes and afforestation to increase natural recharge and reduce runoff. This will also have the benefit of sequestering carbon and preventing global warming and increase the availability of groundwater. Indeed in the aftermath of the floods Kerala is facing a drinking water crisis because many of the wells and tubewells have been packed with mud and debris. Even though repeated floods over the past few years in various places have shown that business as usual will not do, yet we do not seem to learn. The Madhav Gadgil headed Western Ghats Ecology Expert Panel had specifically said that the Western Ghats and especially the steeper section in Kerala and Tamil Nadu should be conserved as an ecologically sensitive zone by banning construction activity all of four years ago. Their recommendations were vehemently opposed by all and sundry and the report was consigned to the wastepaper basket and the consequences are there for all to see.
The CWC in its report typically concentrates only on the dams. While exonerating these dams by saying that they even by design did not have the capacity to mitigate floods resulting from such a heavy downpour, it takes the blinkered approach of suggesting that some more dams should be built solely for the purpose of flood control and completely ignores the need for augmenting artificial and natural recharge as it has in other areas also. For instance in the Brahmaputra basin, the flow from the Tsangpo in China contributes only 5 per cent of the total flow in the basin and so if intensive soil and water conservation measures and afforestation are undertaken in the catchments of the Indian Rivers of the basin then flood control, maintenance of environmental flow and drought proofing can easily be done. However, the CWC once again advocates only dams and creates the false bogey of China either withholding and diverting or releasing excess water from the Tsangpo to create droughts and floods in India. Massive decentralised soil, water and afforestation programmes conducted through the local governance bodies will also provide huge employment and create a flourishing natural resource base for sustainable development.
The Central Water Commission has published a report in which it has analysed the data regarding the various river basins of Kerala and the impact of the dams on the floods there. The crucial data that needs to be understood is that regarding the river flows at the major dams and at the hydrological stations in the plains close to the sea where the floods mostly had devastating effect in the urban areas. However, the CWC has given this data only for the biggest river Periyar which also has 47 percent of the live storage capacity of all the dams in Kerala. Even though there is data regarding the total runoff and the total flow in the river along with the amounts impounded in the dams, for all the basins that have been analysed by the CWC, this does not give us an understanding as to the force of the floods at their peak. Therefore, the CWC's report is still deficient in this respect.
The Periyar basin has three major dams, the Mulla Periyar followed by the Idukki on the main stem of the river and another on the Idamalayar tributary. The peak flood discharge in the river at the Neeleshwaram measuring site of the CWC in the plains near the sea during the height of the flood was 8800 cubic meters per second (cumecs). The outflow at the Idukki dam then was 1500 cumecs. The flood cushion that was there in the dam resulted in about 1000 cumecs being absorbed. However, if a greater flood cushion had been created by releasing water from the dam in phases earlier in the month, then another 1000 cumecs could have been absorbed. The Idamalayar dam on the tributary of the Periyar released another 1500 cumec at its peak despite being a smaller dam as it had very little flood cushion. Being a smaller dam it could have absorbed another 500 cumecs if there had been more free live storage space in the dam. In other words the flood flow at Neeleshwaram would have been 7300 cumecs if these dams had been properly operated. This is more or less the case with the other smaller basins also as even if they had kept a flood cushion, given their much smaller live storage capacity as compared to the huge runoffs coming into them, they would not have been able to absorb much of this. The CWC of course goes overboard with this data and says that the lack of a designed flood cushion resulted in only a "miniscule" increase in the flood impact even though the increase is actually about 20 per cent which is quite significant.
The important conclusion that comes from this analysis is that the dams in general have limited flood protection capacities, especially when faced with rainfall that is of such huge proportions ranging from 100 to 250 percent more than the normal for the month occurring in just three days. Even though proper operation of the dams by following the rule curve which prescribes the level of water to be kept at the reservoir at different times of the year so as to provide a flood cushion, would have reduced the flood impact a little but that would not have averted the disaster. Actually, the imperative of producing hydropower, which is the primary aim of the biggest Idukki dam and most other dams in Kerala, led the dam operators to err on the side of keeping the reservoir levels high and failing to provide a substantial flood cushion.
The main reason for the floods in Kerala having been so devastating, is the huge deforestation that has taken place in the Western Ghats along with quarrying for stones and minerals as is evident from the graphic below.
This has been compounded by construction in paddy fields whose area has gone down from 8.5 lakh hectares earlier to just 2 lakh hectares now. The wetlands and the floodplains of rivers have also been encroached on. All this has together increased the runoff and also decreased the water holding capacity of the hills and the plains. The Vembanad Lake, which is a protected Ramsar site, into which several rivers drain has been encroached and its capacity to hold water has been drastically reduced because of the huge urbanisation that has taken place around it. Consequently it did not have the capacity to hold the huge runoff coming into it and overflowed and submerged the urban areas around it.
This massive deforestation and mining combined with indiscriminate construction in floodplains and fields is indeed the reason for floods in the Himalayas and their foothills and plains also from Kashmir to Arunachal Pradesh whenever there is an extreme weather event resulting in concentrated precipitation in a short period of time.
Flood control, not only in Kerala but throughout the country, thus, has to be brought about by greater soil and water conservation measures to increase artificial recharge and stabilisation of steep hill slopes and afforestation to increase natural recharge and reduce runoff. This will also have the benefit of sequestering carbon and preventing global warming and increase the availability of groundwater. Indeed in the aftermath of the floods Kerala is facing a drinking water crisis because many of the wells and tubewells have been packed with mud and debris. Even though repeated floods over the past few years in various places have shown that business as usual will not do, yet we do not seem to learn. The Madhav Gadgil headed Western Ghats Ecology Expert Panel had specifically said that the Western Ghats and especially the steeper section in Kerala and Tamil Nadu should be conserved as an ecologically sensitive zone by banning construction activity all of four years ago. Their recommendations were vehemently opposed by all and sundry and the report was consigned to the wastepaper basket and the consequences are there for all to see.
The CWC in its report typically concentrates only on the dams. While exonerating these dams by saying that they even by design did not have the capacity to mitigate floods resulting from such a heavy downpour, it takes the blinkered approach of suggesting that some more dams should be built solely for the purpose of flood control and completely ignores the need for augmenting artificial and natural recharge as it has in other areas also. For instance in the Brahmaputra basin, the flow from the Tsangpo in China contributes only 5 per cent of the total flow in the basin and so if intensive soil and water conservation measures and afforestation are undertaken in the catchments of the Indian Rivers of the basin then flood control, maintenance of environmental flow and drought proofing can easily be done. However, the CWC once again advocates only dams and creates the false bogey of China either withholding and diverting or releasing excess water from the Tsangpo to create droughts and floods in India. Massive decentralised soil, water and afforestation programmes conducted through the local governance bodies will also provide huge employment and create a flourishing natural resource base for sustainable development.
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