Groundwater vulnerability assessment of highly urbanized Chennai City, India

Transcription

1 Groundwater vulnerability assessment of highly urbanized Chennai City, India M.Sc. Tim Wolters M.Sc. Mahdi Rahimian Prof. Dr. rer. nat. Manfred Koch University of Kassel - Department of Geohydraulics and Engineering Hydrology

2 Chennai City - Overview Chennai Metropolitan Area / 3 main districts Chennai, Tamil Nadu, India YEAR Population (in million) Density [people/km²] Area [km²]

3 Methodology Vulnerability Likelihood for contaminants to reach a specified position in the groundwater system after introduction at some location above the uppermost aquifer (FOCAZIO ET AL., 2002) Liggett & Talwar (2009) Research Goal Design and application of a suitable groundwater vulnerability assessment approach for urbanized Chennai City 3

4 Vulnerability Assessment Method Index/Parametric/Overlay method DRASTIC (ALLER ET AL., 1987) SINTACS (CIVITA, 1994) Mediterranean Conditions 7 Parameters, 10 rating values, 5 weighting factors, 5 vulnerability classes Empirically based on field studies of different natural, hydrogeological settings LIGGETT & TALWAR (2009) Pro: Widely used Modifiable Inexpensive SINTACS Weighting system Recharge Contra: Empirical Intrinsic Urban conditions 4

5 DRASTIC Vulnerability Assessment D - Depth to Water Table R - Groundwater Recharge A - Aquifer Media + Impact of Vadose Zone S - Soil Media / Land Cover T - Topography C Hydraulic Conductivity 5

6 DRASTIC - Depth to Water Table Depth to water table [m] < > 6.75 Vulnerability Score

7 [mm] KEA [mm] [mm] DRASTIC - Groundwater Recharge Chennai City - Rainfall Season Dry Season Summer Southwest-monsoon Northeast-monsoon Station Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Mean 17,6 11,9 5,8 15,4 42,1 50,9 96,1 139,1 138,3 248,9 283,9 132,9 1182,9 Median 8,8 1,9 0,3 6,4 21,2 47,3 84,6 136,3 123,6 214,5 267,3 98,0 1010,1 Mean 20,3 16,4 36,7 10,3 44,9 76,2 106,8 133,5 131, ,5 167,7 1433,9 Median ,0 KEA Rain days ,0 Rain intensity [mm/event] 19,1 15,3 16,7 18,8 27,9 34,8 33,5 500 mean median mean median Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 7

8 DRASTIC - Groundwater Recharge Recharge [mm/a] < > 700 Score

9 DRASTIC Aquifer Media + Impact of Vadose Zone Geology Medium Sand Clayey Sand / Sand Sandy Clay / Silt Weath. hard rock Score

10 DRASTIC Soil Media+Land Cover Soil Groups (USDA, 1986) Soil Type Soil Group Sand A Coarse loam B Clayey Sand B Sandy Clay C Clay D 10 Modified scoring scheme based on Nobre et al. (2007) Land Cover + Soil Group Lakes Marsh Non- Urban + A Non- Urban + B Non- Urban + C/D Urban + A Urban + B Urban + C/D Rivers / Canals Score

11 DRASTIC Topography Isolines from Ganapathy (2011) Slope [%] < 1.5 > 1.5 Score

12 DRASTIC Hydraulic Conductivity K [m/d] < Score

13 DRASTIC Final Map Score Weight V = D S x D W + R S x R W + AI S x AI W + S S x S W + T S x T W + C S x C W V = D S x 5 + R S x 3 + AI S x 6 + S S x 3 + T S x 2 + C S x 1 13

14 DRASTIC Fuzzy Logic Approach Crisp Thresholds: Aquifer Media/Unsaturated Zone (A) + Soil Media/Land Cover (S) not suitable for Fuzzy logic Continous data series: Depth to Water Table (D) + Groundwater Recharge (R) + Topography (T) + Hydraulic Conductivity (C) suitable for Fuzzy logic 1. Membership Functions Π-shape (D, R, C) Gaussian (T) 2. Weighting 3. Defuzzification 4. Combination with two remaining, weighted layers 14

15 DRASTIC Results 15

16 Risk Terms Risk Intensity Total Risk Risk Sensitivity Simplified contaminant transport from the surface via unsaturated zone to aquifer and well (Liggett & Talwar, 2009) 16

17 Risk Assessment 17

18 Conclusion Result: Criticism: Vulnerability maps as potential tools to provide information for groundwater management and land use planning The aquifer pollution vulnerability concept: aid or impediment in promoting groundwater protection? (FOSTER ET AL., 2013) Simplified models uncertainties As simple as possible, as complex as absolutely neccessary First step, not Last word Outlook: I. Hydrogeological investigation (Pumping tests, Sampling, ) Statistical analysis a) Map removal sensitivity/single parameter Sensitivity b) Contaminant occurence Pollution probability Specific Vulnerability, Hazard, Consequences Risk Process-Based- and numerical modelling II. Awareness rising Enforcing laws (Pollution penalties, rain water harvesting, maintainance/development of infrastructure, etc.) 18

19 References Aller, L., Lehr, J. H., Petty, R., Bennett, T., Hackett, G. (1987). DRASTIC: A Standardized System to Evaluate Ground Water Pollution Potential Using Hydrogeologic Settings. US Environmental Protection Agency. Civita, M. (1994). Le carte della vulnerabilità degli acquiferi all inquinamento. Studi sulla vulnerabilità degli acquiferi. Teoria & Pratica. Pitagora Editrice. Bologna. CMWSSB (2012). Chennai Metro Water Supply and Sewerage Board. Geological map of Chennai City. Hydrogeological Section. Tondiarpet, Chennai. March Focazio, M. J., Reilly, T. E., Rupert, M. G., Helsel, D. R. (2002). Assessing Ground-Water Vulnerability to Contamination: Providing Scientifically Defensible Information for Decision Makers. USGS Circular Foster, S., Hirata, R., Andreo, B. (2013). The aquifer pollution vulnerability concept: aid or impediment in promoting groundwater protection?. Hydrogeology Journal (21), Ganapathy, G. (2011). First level seismic microzonation map of Chennai city - a GIS approach. Natural Hazards and Earth System Sciences (11), Liggett, J., Talwar, S. (2009). Groundwater Vulnerability Assessments and Integrated Water Resource Management. Watershed Management Bulletin Vol. 13/No. 1, Nobre, R., Rotunno Filho, O., Mansur, W., Nobre, M., Consenza, C. (2007). Groundwater vulnerability and risk mapping using GIS, modeling and a fuzzy logic tool. Journal of Contaminant Hydrology (94), SGSWRDC. (2005). Groundwater Persepectives - A Profile of Chennai District - Tamil Nadu. Chennai: State Ground and Surface water Resources Data Centre. USDA (1986). Urban Hydrology for Small Watersheds - Technical Release 55. Natural Resources Conservation Centre Conservation Engineering Division. US Department of Agriculture. Thank you for your attention! 19