By Rajiv Shah
The new environment impact assessment report proposed for the development of Dholera special investment region, being planned as a “dream city” by the Gujarat government, admits that the area where the new industrial township is being planned is flat, low lying and is prone to flood, and things may aggravate in case of urbanization.
The new draft report, “Environmental Impact Assessment (EIA) of Dholera Special Investment Region (DSIR) in Gujarat”, prepared by SENES Consultants India Pvt Ltd, for the Delhi Mumbai Industrial Corridor Development Corporation, New Delhi, for environmental public hearing slated on January 3, 2013, has identified “flooding from inundation by the sea and from seasonal monsoon rains” as one of two most important problems to be reckoned with while developing the area. The other problem is that of seismicity. The DSIR is to be developed south of Ahmedabad city on a 900 square kilometer area as a modern industrial township with a population of 20 lakh in three decades. Giving reason for being flood prone, the report frankly admits, “The terrain profile of DSIR is flat and low lying.”
The report has warned, “This problem (of flooding) could be directly enhanced by urbanization, resulting in increase in the area of impervious surfaces and indirectly by global warming and consequent sea level rises.” Hence, it has stressed on the need for “planning for the risk of flooding” so that the impact of a natural calamity is minimized on “life and property of neighboring communities.” One of the steps required for flood management of rivers in the DSIR, it says, would have ensure that they are “dredged and de‐silted to ensure rapid dispersal of flood waters.” Further, it would necessary to “construct bunds which will be connected to river channels”, which would “prevent the flood water from destroying crops and property, whether flooding is from seasonal rains or from the sea water inundation.”
Pointing towards the importance of such a study, the report says, “During high magnitude flood, the water level rises in river channel and overtops the low river banks inundating the surrounding lower area. This causes flood hazard to those areas which may be developed or being developed. There is spread of flood water in the area meant for DSIR development. This is not acceptable for DSIR development, hence it is necessary to carry out flood mitigation measures such that inundation of the area even during the highest flood is averted to safeguard the properties, i.e. industries, business centers, etc. or if it is flooded, it is within the tolerable limits.“
Already, the report says, plans are being worked out to mitigate flooding. “The mitigation activities required for flood hazard are currently being planned and broadly involve bunding and interlinking of the streams passing through DSIR region along with training of these streams… DSIR is in the delta portion of five rivers starting from River Sukhbhadar in the North to Lilka, Utavli, Padalio and River Keri at extreme south and local Khadi (creek) namely Bhadhar creek, Vankol creek, Bavaliyari creek and Sonrai creek of Gulf of Cambay. The flood water of these rivers outflanks the low river banks and spreads on this entire area in form of sheet flow submerging vast land area. For this purpose, the Gujarat State Disaster Management Authority (GSDMA) along with WAPCOS, is assessing flood hazard risk, extent of vulnerability, identify the least hazard affected area, provide mitigation plan toward disaster management.”
The overall flood mitigation, the report says, is being planned through a detailed hydrological and hydrodynamic modeling study, “using commercially available MIKE FLOOD software. One of the alternatives for calculating the flood discharge is by observed rainfall and spillway overflow.” The same is being done by using MIKE 11. “The rivers traversing the DSIR area are rain-fed rivers and hence water flow in river is only during the rainy season or till rain water precipitated is disposed off. The floods generated in rivers are dependent to the intensity, duration and spread of the rain storm and also the hydraulics of the river”, it adds.
The report gives special importance to “storm water drainage planning in DSIR is to drain the storm run- off during rainfall and manage the storm water entering into the region from other areas, to manage the quantity of surface storm-water drained into the system on account of urbanisation, and monitor its quality to reduce downstream environmental impacts.” Storm water management system would have to include:
• Flood control measures such as the formation of small check dams at desired locations based on contours;
• Augmentation and maintenance of natural streams and rivers by de-silting, increasing the depth or width based on the volume of water flow;
• Formation of embankments and guide bunds for flood control with the available soil and embankment pitching with stones and boulders;
• Canalizing smaller streams towards main streams and connecting with the main streams;
• Development of green spaces along the entire course of stream to provide recreational space and flood storage areas;
• Proposing water reservoirs to store the upstream water to avoid flooding of the DSIR during periods of high tide and heavy rain fall. Water retained in the channels may be utilized as part of the city water supply after appropriate treatment; and
• Provision of weirs across the rivers to act as barriers to stop sea ingress and the entry of silt and to raise the water level in the rivers for recreational and aesthetic purposes.
The report further says, “The proposed storm water drainage system is conceptualized to cater for surface runoff within the project area by gravity flow. Trunk storm water drains are proposed on both the sides of the roads and lateral and main drains are proposed on one side of the roads. The surface runoff collected from the catchment areas would be discharged by major outfalls into the natural streams, rivers and creeks and open land lying in the coastal regulatory zone (CRZ) along the DSIR development area boundary. To avoid flooding in the area, sluice gates and boosting system will be provided at the outlets of the drains.”
It underlines, “When the natural streams and nallahs are full and cannot flow by gravity from drains, the water may need to be pumped out. Outfalls lying in the CRZ area will be planned and designed such that water discharging from the drain does not erode the land and spread in the form of sheet flooding. In order to determine the hydraulic grade line due to backwater impact under high tide conditions coinciding with downpours, the invert levels for outfalls should be kept such that the DSIR should not be submerged during high tides coinciding with heavy monsoon rainfall.” Hence, the formation level of the DSIR will have to be planned in such a way that “it can be protected from any kind of flooding or submergence.”
Considering the flood hazard at DSIR area, the report says, “the only techno economical solution for flood mitigation is to provide bunding, such that the flood water are confined within the banks of river passing through DSIR area and the sheet flow formed on upstream side is diverted into the river channel for disposal into sea.” It adds, already, “river hydraulic for post-DSIR development is computed for whole study area. The local area storm water is assumed to be disposed of into sea by storm water disposal network system of the DSIR area, which is independent system and is unaffected due to river flood. If this is not done it will require raising of the DSIR development area.”
The report says, “For flood mitigation purpose, the river training from state highway (SH)-36, Valbhipur canal, DSIR area up to sea are proposed to be connected with the river bank embankments.” The topography of the area is such that “the river training work is required up to SH-36 for all the rivers.” It adds, “Along with this the tributaries are also to be considered. For safe disposal of local drainage it is proposed to connect the nallas and tributaries with ponds coming in drainage path and further connecting the outfall channel to other pond or to the tributary leading to river provided with river training.”
Pointing out that all this is necessary because “the terrain profile of Dholera SIR region is flat and low lying”, the report underlines, “It is in the delta of five rivers starting from river Sukhbhadar in the North to Lilka, Utavli, Padalio and Keri river at extreme south and local Khadi (creek) namely Bhadhar creek, Vankol creek, Bavaliyari creek and Sonrai creek. These rivers are east flowing rivers, discharging into the Gulf of Khambhat through Dholera SIR area. During heavy monsoon and tidal activity the water of these rivers outflanks the low river banks and spreads on this entire area in form of sheet flow submerging vast land area.”
The study suggest, “For flood management rivers in the DSIR will be dredged and de‐silted to ensure rapid dispersal of flood waters. It is proposed to construct bunds which will be connected to river channels. This will prevent the flood water from destroying crops and property, whether flooding is from seasonal rains or from the sea water inundation. Since the ground water aquifer is saline, no recharging is proposed. Interventions proposed for surface water streams as part of flood protection measures will contribute to recharging of aquifers.”
The new draft report, “Environmental Impact Assessment (EIA) of Dholera Special Investment Region (DSIR) in Gujarat”, prepared by SENES Consultants India Pvt Ltd, for the Delhi Mumbai Industrial Corridor Development Corporation, New Delhi, for environmental public hearing slated on January 3, 2013, has identified “flooding from inundation by the sea and from seasonal monsoon rains” as one of two most important problems to be reckoned with while developing the area. The other problem is that of seismicity. The DSIR is to be developed south of Ahmedabad city on a 900 square kilometer area as a modern industrial township with a population of 20 lakh in three decades. Giving reason for being flood prone, the report frankly admits, “The terrain profile of DSIR is flat and low lying.”
The report has warned, “This problem (of flooding) could be directly enhanced by urbanization, resulting in increase in the area of impervious surfaces and indirectly by global warming and consequent sea level rises.” Hence, it has stressed on the need for “planning for the risk of flooding” so that the impact of a natural calamity is minimized on “life and property of neighboring communities.” One of the steps required for flood management of rivers in the DSIR, it says, would have ensure that they are “dredged and de‐silted to ensure rapid dispersal of flood waters.” Further, it would necessary to “construct bunds which will be connected to river channels”, which would “prevent the flood water from destroying crops and property, whether flooding is from seasonal rains or from the sea water inundation.”
Pointing towards the importance of such a study, the report says, “During high magnitude flood, the water level rises in river channel and overtops the low river banks inundating the surrounding lower area. This causes flood hazard to those areas which may be developed or being developed. There is spread of flood water in the area meant for DSIR development. This is not acceptable for DSIR development, hence it is necessary to carry out flood mitigation measures such that inundation of the area even during the highest flood is averted to safeguard the properties, i.e. industries, business centers, etc. or if it is flooded, it is within the tolerable limits.“
Already, the report says, plans are being worked out to mitigate flooding. “The mitigation activities required for flood hazard are currently being planned and broadly involve bunding and interlinking of the streams passing through DSIR region along with training of these streams… DSIR is in the delta portion of five rivers starting from River Sukhbhadar in the North to Lilka, Utavli, Padalio and River Keri at extreme south and local Khadi (creek) namely Bhadhar creek, Vankol creek, Bavaliyari creek and Sonrai creek of Gulf of Cambay. The flood water of these rivers outflanks the low river banks and spreads on this entire area in form of sheet flow submerging vast land area. For this purpose, the Gujarat State Disaster Management Authority (GSDMA) along with WAPCOS, is assessing flood hazard risk, extent of vulnerability, identify the least hazard affected area, provide mitigation plan toward disaster management.”
The overall flood mitigation, the report says, is being planned through a detailed hydrological and hydrodynamic modeling study, “using commercially available MIKE FLOOD software. One of the alternatives for calculating the flood discharge is by observed rainfall and spillway overflow.” The same is being done by using MIKE 11. “The rivers traversing the DSIR area are rain-fed rivers and hence water flow in river is only during the rainy season or till rain water precipitated is disposed off. The floods generated in rivers are dependent to the intensity, duration and spread of the rain storm and also the hydraulics of the river”, it adds.
• Flood control measures such as the formation of small check dams at desired locations based on contours;
• Augmentation and maintenance of natural streams and rivers by de-silting, increasing the depth or width based on the volume of water flow;
• Formation of embankments and guide bunds for flood control with the available soil and embankment pitching with stones and boulders;
• Canalizing smaller streams towards main streams and connecting with the main streams;
• Development of green spaces along the entire course of stream to provide recreational space and flood storage areas;
• Proposing water reservoirs to store the upstream water to avoid flooding of the DSIR during periods of high tide and heavy rain fall. Water retained in the channels may be utilized as part of the city water supply after appropriate treatment; and
• Provision of weirs across the rivers to act as barriers to stop sea ingress and the entry of silt and to raise the water level in the rivers for recreational and aesthetic purposes.
The report further says, “The proposed storm water drainage system is conceptualized to cater for surface runoff within the project area by gravity flow. Trunk storm water drains are proposed on both the sides of the roads and lateral and main drains are proposed on one side of the roads. The surface runoff collected from the catchment areas would be discharged by major outfalls into the natural streams, rivers and creeks and open land lying in the coastal regulatory zone (CRZ) along the DSIR development area boundary. To avoid flooding in the area, sluice gates and boosting system will be provided at the outlets of the drains.”
It underlines, “When the natural streams and nallahs are full and cannot flow by gravity from drains, the water may need to be pumped out. Outfalls lying in the CRZ area will be planned and designed such that water discharging from the drain does not erode the land and spread in the form of sheet flooding. In order to determine the hydraulic grade line due to backwater impact under high tide conditions coinciding with downpours, the invert levels for outfalls should be kept such that the DSIR should not be submerged during high tides coinciding with heavy monsoon rainfall.” Hence, the formation level of the DSIR will have to be planned in such a way that “it can be protected from any kind of flooding or submergence.”
Considering the flood hazard at DSIR area, the report says, “the only techno economical solution for flood mitigation is to provide bunding, such that the flood water are confined within the banks of river passing through DSIR area and the sheet flow formed on upstream side is diverted into the river channel for disposal into sea.” It adds, already, “river hydraulic for post-DSIR development is computed for whole study area. The local area storm water is assumed to be disposed of into sea by storm water disposal network system of the DSIR area, which is independent system and is unaffected due to river flood. If this is not done it will require raising of the DSIR development area.”
The report says, “For flood mitigation purpose, the river training from state highway (SH)-36, Valbhipur canal, DSIR area up to sea are proposed to be connected with the river bank embankments.” The topography of the area is such that “the river training work is required up to SH-36 for all the rivers.” It adds, “Along with this the tributaries are also to be considered. For safe disposal of local drainage it is proposed to connect the nallas and tributaries with ponds coming in drainage path and further connecting the outfall channel to other pond or to the tributary leading to river provided with river training.”
Pointing out that all this is necessary because “the terrain profile of Dholera SIR region is flat and low lying”, the report underlines, “It is in the delta of five rivers starting from river Sukhbhadar in the North to Lilka, Utavli, Padalio and Keri river at extreme south and local Khadi (creek) namely Bhadhar creek, Vankol creek, Bavaliyari creek and Sonrai creek. These rivers are east flowing rivers, discharging into the Gulf of Khambhat through Dholera SIR area. During heavy monsoon and tidal activity the water of these rivers outflanks the low river banks and spreads on this entire area in form of sheet flow submerging vast land area.”
The study suggest, “For flood management rivers in the DSIR will be dredged and de‐silted to ensure rapid dispersal of flood waters. It is proposed to construct bunds which will be connected to river channels. This will prevent the flood water from destroying crops and property, whether flooding is from seasonal rains or from the sea water inundation. Since the ground water aquifer is saline, no recharging is proposed. Interventions proposed for surface water streams as part of flood protection measures will contribute to recharging of aquifers.”
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