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This study examines the status of water bodies, drainage network, and water management in and around Bangalore. It includes three case studies and provides insights on the importance of using tanks for drinking water supply to save Bangalore in the future.
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Status of Water bodies, Drainage Network and Water Management in and around Bangalore Dr.T.J. Renuka Prasad, Professor of Geology, Bangalore University, Bangalore 560056 Chandan G.S, Research Scholar, Dept.of Geology, Bangalore University, Bangalore 560056 Krishna Murthy.B. N, Research Scholar, Dept.of Geology, Bangalore University, Bangalore 560056
One individual Sri Yele Mallappa Shetty, who was leading an ordinary life as a beetle leaf vendor could able to build a tank successfully with a great vision. Probably he has done a wonderful survey and got a feel of water flow in that area and acted as a water resources engineer. Water was supplied to military camps from this tank for many years. Making use of tanks for drinking purpose is the solution to save Bangalore in the days to come. Therefore a study of water resources is very important Three case studies: • Yele Mallappa Sheetty Kere Water shed • Seven tanks around Bangalore • Arkavathi Basin study
Yele Mallappa Shetty Kere Watershed • The Watershed area of the YMSK expands upto 286 sq kms. The series of flow tanks of Yele Mallappa Shetty Kere (YMSK) begins with MattiKere tank in the NorthEast and Singanayakanahalli Kere (AmmaniKere) in the North of Bangalore. • Drainage Net work and tanks studied using 1:50,000 toposheets It is a Fifth Order catchment I Order cum length – 170 km II Order Cum length – 74 km III Order Cum length – 28 km IV Order Cum length – 14 km V Order Cum length – 15 km
Water bodies: Surface water bodies has been delineated using both 1:50000 & 1:25000 Scale toposheet. • 86 Water bodies and 195 Water bodies are noticed. • 40 Minor tanks maintained by MI • 45 small tanks maintained by ZP & TDB • 110 tiny water bodies (identified with the help of 1:25000 toposheet ) • 45 tiny water bodies vanished (Remote sensing studies)
Study of Water Bodies Number of Tanks shown in 1:50000: • YMSK consists of 86 WB in 286 sqkm • BMP consists of 584 WB- 1253 sqkm • Arkavathi basin consists of1775 – 4043 sqkm • BMRDA consists of 3154 Number of Tanks shown in 1:25000: • YMSK 195 WB (1:25000 & RS) Necessary to study in detail status of WB using smaller scale toposheets/Remote Sensing.
Already one minor tank and 35 tiny water bodies vanished due to urbanization. • It is astonish to note 44 tiny water bodies are still exist in the valley yielding approximately 287MLtrs along with 24010 MLtrs from Major and 1368 MLtrs from Minor Tanks. • Assuming 150ltr/day per capita, taking into account 70% of water from Major & Minor water bodies, it is possible to cater water for 328139 persons. • The tiny water bodies may be maintained from the point of recharging the ground water.
Similarly a digital elevation model has been developed and identified 250 locations for creating tiny water bodies in YMSK area. • This envisages scope for increase of the water table level from water bodies in the study area enormously. • The existing tiny water bodies may be definitely used for recharging by harvesting rainwater efficiently. I • It is very necessary to maintain the drainage network as Storm water drainages. • Instead of letting effluent to major water tanks, it may be checked at point source before polluting the I & II order drainages. Ground water flow direction may be detected to check the contamination of ground water.
Jnana Baharathi campus Bangalore University has increased 1.5 m of water table. • Developing additional 18 water bodies (in 1000 acres) is in the pipe line. • One water body per month Jnanabharathi campus
HYDROGEOLOGICAL STUDY OF SELECTED WATERSHEDS AROUND BANGALORE USING REMOTE SENSING & GIS • A detailed study of hydrogeological setup has been carried out on seven watershed basins. The seven watersheds are: 1. Doddabommasandra 2. Narasipura 3. Tindlu tank 4. Chikkabanavara 5. Kammagondanahalli 6. Mallasandra 7. Bagalakunte A comparison of present and earlier status has been attempted in the present study. Change detection study also has been carried out.
The drainage detail of each watershed has been studied. • The table shows the 1st, 2nd and 3rd order streams lengths as in toposheet and as seen in satellite imagery and also difference between them. • The study reveals that the streams have been shortened in length. Majority of 1st order streams vanished due to development activities like layout formation and construction on the drainage lines. • The water spread area also reduced in majority of the cases. • As a consequence of shortening of the streams, the rate of infiltration has been drastically decreased and resulted in depletion of ground water level. • The water spread area also increased at some places indicating blockage of drains causing spread over of water in the nearby vicinity.
The shortening of the stream length varies from 8% to 100%. This indicates development of new layouts and slums on the drainage lines. Encroachment of “RajaKaluve” (Feeder channel) has become the order of the day. • Both surface water and groundwater problems increased enormously. • Surface water during rainy season gave rise to flash floods. • Ground water level touched nearly thousand feet below the surface. • Creation of artificial recharge sites in these watersheds is possible against good storage of surface water. • Maintenance of these tanks (desilting etc..) and taking care of drainage lines along with developmental activities is very essential as this is going to be the “Life Lines” of society.
Importance may be given to Under Ground Drainage (UGD) in place of septic tanks so that the ground water will not be contaminated. • Continuous field verification is necessary to monitor the water bodies with the help of private Public Participation (PPP). This automatically brings awareness about the importance of water & there by protection to the water bodies. • GIS data base may be made available consisting of Land use/ Land cover map, Contour survey, Geology, Geomorphology, Lineaments, Soil, Infiltration studies, Well Inventory, Pump Tests, Resistivity Survey. A case study of Arkavathi basin has been taken up and an action plan has been evolved.
Action Plan for Arkavathi Basin • Arkavathi Basin: River Arkavathi is a tributary to river Cauvery. It spread over in the three districts, Bangalore Urban, Rural and Ramanagarm. It is the southern part of the Karnataka Plateau and characterized by undulating terrain with broad based valleys. The basin area is 4043 sq.km; Maximum length is 125.5 km; Maximum width is 47.5 km; Perimter of the basin is 360km. • Different thematic maps (19 layers) have been generated to understand the complex nature of hard rock terrain (Table 1).The basin is comprises of various rocks like schists, peninsular gneisses, closepet granites, amphibolites and dolerite dykes intrusions. The bed rock thickness is very shallow at some places measuring only 4m and it will be more than 18m at some places. Bedrock resistivity also varies between 92 to 4600 ohmm. The fracture density varies between 1 and 3.
Morphometric details of length and area of different stream segments are derived (Table 2). The drainage density of major sub-basins have been worked out. It is less than 0.1km/sqkm and reaches around 1.38 km/sqkm. The birfucation ratio, length ratio and area ratio have been obtained. Lineament length varies between 0.1 to 0.68 km/sqkm. Number of lineaments varies between 1 to 7 per every 5 sqkm. • Red loamy and red sandy soil predominates with few patches of lateritic soil. Soil thickness varies between 0.4m to 2m. The resistivity of soil varies between 0.5 and 1000 ohmm. • Different land forms like Water bodies, Valley fills, Pediplains, Pediments, Pediments inselbergs and Residual hills are seen in the basin. The weathered zone thickness is between 3 and 18m and its resistivity varies between 0.5 and 1000ohmm.
The basin encompasses wetlands, grasslands, forest, agricultural, wastelands and settlements. Least slope of 0% and maximum slope of 50% is visible. Rainfall varies between 750 and 950mm. Depth to Water levels of pre-monsoon and post-monsoon also brought to the GIS environment. • Analysis: A GIS model has been developed to delineate the Artificial Recharge Zones. • Suitable weights have been assigned to different thematic layers and and integrated using ArcGIS package to achieve the objective. The total weights derived have been regrouped to obtain different categories of Artificial Recharge Zones. • Poor, Moderate, Good, Very Good and Excellent zones for artificial recharge have been derived. The Zonal areas have been computed and used in the action plan. The same has been validated using the yield data of bore wells.
The GIS model shows that there exists a good matching to nearly matching (81%); moderate matching (10%) and a meager 10% of the zones are not matching. Hence, the model is working with minor variations. GIS model may be used in similar hydro-geological set-up to delineate artificial recharge zones before implementation.
Action Plan • The very purpose of the study to rise the water table in Arkavathi basin.Keepin this in mind a blue print has been designed. The suitable Recharge Structures have been worked out (Table 7). There is scope for additional 2020 check dams, 1421 point recharge structures and 216 percolations tanks may be implemented in the area. Apart from these designated artificial recharge structures, 6650 dry dug wells, 1574 dry bore wells, 710 tiny water bodies and 871 minor irrigation tanks (both maintained by Minor Irrigation and Zilla Parishat) are also may be used. In addition to this, Approximately, 60 sqkm roof top area may be available for rainwater harvesting. The quantum of recharge from all the designed structures is around 1363 MCM (Table 8). Considering the hydrogeologicl properties of hard rock aquifers, a rise of 3-5m of groundwater table may be achieved annually. As a part of management strategy, groundwater draft may be monitored with the participation of governmental, non governmental agencies along with public to get the back the water table near to the surface.
Thematic layers and their weights to delineate Artificial recharge zones.
Recommended Artificial recharge Structures with expected Quantum of recharge
Conclusions • Conjunctive use of surface water available in and around Bangalore along with groundwater is very essential. • There are 51 major tanks; 28 medium tanks; 44 tiny water bodies in YeleMallappaShettyKere watershed and more than 1700 water bodies in Arkavathi basin. • The available surface water is 25665 Mltrs in the YeleMallappaShettyKere watershed and it is possible to supply potable water to approximately 3 lakhs persons annually. • Already 35 tiny water bodies vanished in the YMSK watershed due to urbanization.
The shortening of the stream length varies from 8% to 100% is observed in the water sheds due to urbanization, leading to shortage of flow to water bodies and aquifers. • Importance may be given to maintain small order streams to improve flow to water bodies and recharge to groundwater bodies. • Artificial recharge plays an important role to augment the ground water resources. • It is desirable to adopt an integrated and scientific approach of development of ground water resources. • A proper blending of the controlling parameters such as slope, soil, resistivity of soil, weathered zone and bed rock, Thickness of soil, weathered zone, landforms, landuse/landcover geology, rainfall, depth to bed rock & water levels, drainage density, fracture density, lineament length and density, transmissivity and well density are important in delineating the areas for artificial recharge.
Artificial Recharge Zones like Excellent, Very good, Good, Moderate and Poor may be delineated. • The spatial distribution of the AR Zones are used for developing an action plan to suggest different artificial recharge structures. Accordingly, 2020 check dams, 1421 point recharge structures and 216 percolations tanks may be constructed in the area. • Dried up 6650 dry dug wells and 1574 dry bore wells also may be used for Artificial recharge.
Out of 1581 tanks in the basin, a quantum of 10 % of water available 871 minor irrigation tanks (maintained by MI and ZP) may be reserved for Artificial Recharge. • The remaining 710 tiny water bodies of the basin may be maintained for the Artificial recharge purpose only. • The proposed plan of action yields approximately 1363 MCM of recharge to the groundwater and a rise of 3-5m of groundwater table may be achieved annually. • The GIS model developed may be used in the similar hydrogeological set up to delineate zones of artificial recharge.
