This study was undertaken to assess the quantum of water available in the region to meet the domestic demand. The study brings out that there is sufficient water available in the region, but fails to understand the inability or ineffectiveness of the local administrators to sustainably manage the water resources in the region. Sufficient water is available to meet everyone’s requirement, provided (i) water harvesting is undertaken through surface water bodies; this requires rejuvenation of lakes and reestablishment of interconnectivity; harvesting of rainwater (at decentralized levels), treatment; (ii) treatment and reuse of sewage. However, the success of sustainable water path depends on the political will, bureaucracy shedding their colonial style of functioning and more importantly citizen’s assertion for their right for equal quantity and quality of water.
Average annual rainfall in Bangalore is about 787 mm with 75% dependability and return period of 5 years. Catchment wise water yield analysis indicates about 49.5% (7.32 TMC) of water yield in the Vrishabhavathi valley (including Arkavathi and Suvarnamukhi), followed by 35.2% (5.2 TMC) in Koramangala Challaghatta valley and 15.3% (4.2 TMC) in Hebbal valley and the total annual water yield in Bengaluru is about 14.80 TMC. Domestic demand of water (at 150 lpcd) is 20.05 TMC per year (1573 MLD). This means about 73% of Bangalore’s water demand can be met by efficient harvesting of rain water. Quantification of sewage generated shows that about 16.04 TMC (1258 MLD) of sewage is generated in the city.
Sewage treatment with complete removal of nutrients and chemical contaminants can be achieved by adopting decentralized treatment plants similar to the success model (secondary treatment plant integrated with constructed wetlands and algae pond) at Jakkur lake. In addition to this, water available with efficient rainwater harvesting is about 14.8 TMC. This accounts to total of 30.85 TMC of water that is available annually would cater the demand of 20.05 TMC, provided the city administration opts for decentralized optimal water management through (i) rainwater harvesting by rejuvenating lakes - the best option to harvest rain water is through interconnected lake systems, (ii) treatment of sewage generated in households in each locality (opting the model functional since 2010 at Jakkur lake – STP (Sewage Treatment Plant) integrated with constructed wetlands and algal pond; (iii) conservation of water by avoiding the pilferages (due to faulty distribution system); (iv) ensuring water supply 24x7 and (v) ensuring all sections of the society get equal quantity and quality of water. Rejuvenating lakes in the region helps in retaining the rain water. Treating sewage and options to recycle and reuse would minimize the demand for water from outside the region.
However, this model of decentralised harvesting of water and reuse of treated sewage is not an attractive proposition for the current breed of decision makers with the colonial style of functioning/mind-set. The financial gain is much higher in the case of mega projects (such as water diversion) compared to these decentralised models. This is the sole reason for the local administrators to degrade decentralised water harvesting structures and alienating local community. The main reason for deliberate inefficient management of water resources is to maximise the net return for the ruling class themselves than the overall growth of the region with water security. The analysis illustrates that the city has at least 30 TMC (Bangalore city) of water, which is higher than the existing demand (20.08 TMC, at 150 lpcd and 2016 population), if the city adopts 5R’s (Rejuvenate, Retain, Recycle - Reuse, and Responsible citizens’ active participation with good governance).
Scope for decentralized rainwater harvesting: During 1800, the storage capacity of Bangalore was 35 TMC. In 70’s, lakes covered an area of nearly 3180 hectares and now the spatial extent of lakes cover an area of 2792 hectares. The current capacity of lakes is about 5 TMC and due to siltation, the current storage capacity of the lakes is just about 1.2 TMC, i.e., nearly 387 hectares of water bodies disappeared besides reduction in the storage capacity by 60%. Bangalore being located on the ridge, forms three watersheds – Koramangala Challagatta valley, Vrishbhavathi Valley and Hebbal Nagavara Valley. Earlier rulers of the region, created interconnected lake systems taking advantage of undulating terrain. Number of lakes in the Koramangala Challaghatta Valley is about 81, followed by the Vrishabhavathi Valley (56) and the Hebbal Nagavara Valley (46).
Land use analysis in Bangalore City shows 1005% increase in urban (built-up) area between 1973 and 2016 i.e., from 8.0% (in 1973) to 77% (in 2016). Land use prediction using Agent Based Model showed that built up area would increase to 93.3% by 2020, and the landscape is almost at the verge of saturation.
In order to enhance the water retaining capability in the catchment, it is essential to rejuvenate lakes and undertake large scale watershed programme (soil and water conservation). Lakes are the optimal means of rainwater harvesting at community level. This entails
(i) Reestablishing interconnectivity among lakes (requires removal of all encroachments without any consideration, as the water security of a region is vital than the vested interests, who have unauthorisedly occupied without respecting future generation’s food and water security). This would also reduce the frequency of floods and consequent damage to life and property,
(ii) removal of all encroachments of lakes and lake bed, and maintaining buffer region with the good riparian vegetation cover (without any artifacts),
(iii) rejuvenation and regular maintenance of water bodies. This involves de-silting of lakes to (a) enhance the storage capacity to retain rainwater, (b) increase the recharge potential – will improve groundwater table, (c) ensure recharging without any contamination,
(iv) allowing only treated sewage (removal of chemical and biological contaminants) through adoption of integrated wetlands ecosystem (Jakkur lake model),
(v) creation of wetlands with native vegetation and regular harvesting of macrophytes; food and fodder, which supports local people’s livelihood, and
(vi) maintaining at least 33% green cover with native vegetation (grass, trees, shrubs) in the catchment and planting riparian vegetation in the buffer region. This would help infiltration of water and retain this water.
Figures - uploaded by T V Ramachandra
All figure content in this area was uploaded by T V Ramachandra
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