A study by Anna University and Indian Institute of Technology Madras (IIT-M) recommends regular diversion of water from Chembarambakkam reservoir to abandoned quarries near the city to conserve a considerable amount of water lost in evaporation, and improve water supply to the urban areas.
Titled ‘Innovative Water Management Using Abandoned Quarries for Urban Water Supply and Flood Mitigation’, the study, which was published in the Environment, Development and Sustainability journal, says the combined capacity of the abandoned quarries in Sikkarayapuram and Erumaiyur is enough to store 1,000 million cubic feet.
The study was taken up under different scenarios such as excess, normal, and deficit rainfall. It was found out that increased use of quarries delayed peak flow in Adyar river, and reduced the impact of floods.
The approach tested four diversion strategies from Chembarambakkam reservoir, taking into account factors such as rainfall and water storage, and found out that diversion of water to quarries would reduce evaporation loss, and increase the water supply.
L. Elango, the author of the study and visiting faculty at IIT-M, said that, instead of focusing on filling up main reservoirs, the storage capacity at abandoned quarries, which have less surface area, could be built up initially to reduce evaporation loss, especially during summer
.The amount of water lost in evaporation is reduced to a minimum of 604 mcft per year during excess rainfall years; 82 mcft per year during normal rainfall years, and eight mcft during rain deficit years.
The effect of the proposed interventions was studied using mike 11 NAM model, which simulated rainfall process in the study area, to arrive at the efficiency of diversion and water supply – either from the reservoir or from quarries.
M. Rinisha Kartheeshwari, one of the authors, said scenarios such as diversion of 150 cubic feet per second of water from Chembarambakkam reservoir to quarries, prioritising drawing water supply from reservoir or quarries, and the diversion of 400 cusecs with options of supply from either the reservoir or quarries were studied. The impact on water supply, evaporation loss, and surplus flow into Adyar river were assessed for these strategies.
The study found that diversion of water to quarries through a channel would mean a substantial improvement in the domestic water supply irrespective of excess or rain deficit year. For instance, water supply would improve to a minimum of 3,218 mcft/year compared to 1,985 mcft/year without any such interventions during excess rainfall. Even during deficit rainfall years, the amount of water available would be marginally higher, she said.
Ligy Philip, professor, Department of Civil Engineering, IIT-M, coordinated the study, which included Kaveri S. and P.V.Razi Sadath.
The intervention to divert 400 cusecs to quarry and draw supply from the reservoir was found to be the best measure in terms of better water supply, lesser evaporation loss and reduced surplus water. However, the study has suggested diverting 150 cusecs to quarries and prioritising water supply from reservoir as ideal after considering construction and operation cost of infrastructure, Mr. Elango said.
Transferring water to quarries first during heavy rains would also help conserve 2% to 38% of water that is otherwise released as surplus from Chembarambakkam reservoir, he added.