Estimation of Groundwater Vulnerability using Remote Sensing and GIS Techniques

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1 IJIRST International Journal for Innovative Research in Science & Technology Volume 1 Issue 9 February 2015 ISSN (online): Estimation of Groundwater Vulnerability using Remote Sensing and GIS Techniques C.Ashokraj PG Student Department of Civil Engineering Regional Office Anna University Chennai, Tirunelveli M.Kirubakaran PG Student Department of Civil Engineering Regional Office Anna University Chennai, Tirunelveli J.Colins Johnny Assistant Professor Department of Civil Engineering Regional Office Anna University Chennai, Tirunelveli Abstract Groundwater is a good source for human water requirement because it has low susceptibility to pollution and its natural availability is good when compared to surface water. Groundwater is primarily used for domestic, agriculture and industrial activities. Groundwater is a nonrenewable source and at same time over exploitation and pollution of groundwater is spoiling the groundwater. So developments of groundwater resource and prevention of contamination are prominent task in the groundwater management. The primary objective of the study is to map groundwater vulnerability of Palayamkottai taluk in Tirunelveli district Tamil Nadu by applying SINTACS model. This model uses the input from remote sensing and geographical information system (GIS) techniques. SINTACS model is based on overlay index methodology. The SINTACS model comprising of seven hydro geological parameters namely water table depth, net Recharge, unsaturated zone, soil media, aquifer media, hydraulic conductivity and slope. These parameters are integrated to delineate the area that is more susceptible to pollution. The SINTACS model classified the Palayamkottai taluk into low (108.1 km2) and moderate (191.9 km2) vulnerable area. Keywords: SINTACS, vulnerability, GIS, hydraulic conductivity, unsaturated zone I. INTRODUCTION Groundwater contributes about two third of fresh water resources in the world. Rain water percolates below the soil stratum and enters into voids of rocks and joins aquifer media which is called groundwater. In the world scenario the availability of groundwater is reducing because of excessive usage groundwater rather than surface water. In India, groundwater is primary source for all purpose of water requirements; it plays an important role in economic development of country. Due to the unbalancing equilibrium between infiltration and groundwater exploitation is leading to decline in groundwater level. The contamination of groundwater is prime environmental problem which degrades the quality of groundwater. It is essential to protect the groundwater from contamination. The vulnerability mapping will be helpful in identifying the region that is in danger. Proper groundwater resource management is essential to protect groundwater vulnerability. Theory of groundwater vulnerability was first introduced in 1960s in France to create alertness of groundwater contamination (Vrba and Zaraporozec et al. 1994). The term intrinsic vulnerability has risk of groundwater being exposed to the loading pollutants from source, impact of many pollutants according to their interaction and chemical properties. Monitoring of groundwater is consuming enormous time and cost to adequately define the geographical extent of contamination at a regional scale. In recent few decades the use of geographic information system (GIS) has grown rapidly in groundwater management studies. Many researches such as S.M.Shiraz (2002), K.Srinivasamoorthy (2000), J.P.Loboferrira (2003), Dhundiraj (2008) used the DRASCTIC method to determine the groundwater vulnerability. The SINTACS method which used to determine groundwater vulnerability and the following researchers, such as MCivitamaimo (2004), G.Cusimano(2004), Daniela ducii(2010),s.kumar(2012), Babiker (2005) used the SINTACS model to evaluate intrinsic vulnerability of groundwater. However, the main dis-advantage in assigning numerical values to descriptive entities and relative weights for different attributes was discussed by S.Kumar et al. (2012). Overlay and index methods combine factors controlling the mobility of pollutants from ground surface into vadose zone resulting in vulnerability indices at different locations. The primary objective of the study to map groundwater vulnerability by applying SINTACS model the input for The model is acquired from remote sensing and geographical information system (GIS) techniques. All rights reserved by 118

2 II. STUDY AREA The study area is Palayamkottai Taluk of Tirunelveli district is situated in southern part of Tamil Nadu, India. In Tirunelveli district there are eleven taluks among those taluks Palayamkottai and Tirunelveli taluks with high population density. The study area has coverage of 300 square kilometers. The geographical location of study area lies in longitudes and latitudes of and it comprises the following survey of India to posheets numbers 58h/9,58h/10,58h/14.The study area located in eastern bank of Thamirabarani river with a relative humidity of percent. According to 2011 census the taluk of Palayamkottai has the population of 91,174and with literacy rate of 75.25percent. III. MATERIALS AND METHODOLOGY The groundwater contamination vulnerability evaluation system has numerous overlay index methods. Among those methods SINTACS method is preferred for the study due to different considerations such as low cost, depending on data sets availability, geology and hydrological environment. SINTACS model is an updated model of US DRASTIC. SINTACS model shows vulnerability index of study area using the seven hydrological parameters such as 1) water table depth, 2) net recharge, 3) vadosezone, 4) soil media, 5) aquifer media, 6) hydraulic conductivity, and slope SINTACS vulnerability index is computed using following equation. Where P i - The ratings of each of seven parameters W i - The relative weight of each parameter A. Preparation of Parameter Maps: 1) Water Table Depth(S): Depth-to- water table is about the depth from the ground level to the water table or the distance between the ground surface to water level. Depth to water table parameter is arrived from water level data of 23observation wells (including bore well and dug well) of the Public Works Department (PWD). The well location vector layer was prepared based on the GPS survey and the spatial distribution map of water table was obtained through IDW interpolation technique which was in terms of raster image. 2) Recharge (I): Recharge required for the study area to find the total recharge estimated by using water table fluctuation method (WFD).This most preferable field based method for estimating amount of infiltration. The general water table fluctuation equation as follows: Recharge =change in water level (D h ) Specific yield (y). The water level fluctuation of the corresponding well was estimated with aid of graphical approach. This method gives the water level variation information of wells. Based on the point data the spatial variation map for effective infiltration was prepared. 3) Unsaturated Zone(N): The zone present below the soil and above the water table which is called unsaturated zone or discontinuously saturated zone. Unsaturated zone is one of the important parameter in vulnerability assessment and hence a higher weightage is assigned to unsaturated zone. The unsaturated zone map for the study area was prepared from the well lithology data acquired from Public Work Department (PWD). 4) Soil Media (T): The soil media has an important role in assessing intrinsic vulnerability of groundwater. Soil has ability to restrict the vertical flow of contamination in to the subsurface. The textural characteristic ofsoil has capacity to control intrinsic vulnerability of groundwater. The soil map is generated by onscreen digitization technique from digital map of European Digital Archive of Soil Maps. The soil classification is done based on USDA soil taxonomy. The ratings are assigned to soil layer as per the infiltration capacity. 5) Aquifer Media (A): This is the area that has the potential for storage of water. The rocks of consolidated and unconsolidated (gravel, sand, or silt) form can act as a aquifer media. In the presence of fractures or openings in rocks the permeable value differs. If the impermeable area, overlays the aquifer is called confined aquifer. Aquifer detail are obtained from the subsurface geology map which was prepared from geological map of Geological survey of India and ratings are assigned as per the consideration of primary, secondary porosity in the aquifer media. All rights reserved by 119

3 6) Hydraulic Conductivity(C): The term hydraulic conductivity is the property of aquifer materials to broadcast water. This controls the rate at which groundwater will flow under a given hydraulic gradient. Aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another. This is because of ability of the plume to be travelled easily through the aquifer this layer was prepared from the field pumping test result of 6 wells which in the study area. 7) Slope (S): Slope map is prepared from SRTM DEM data using the topographic modeling tool of ENVI Software. Slope of terrain is expressed in degree and it refers to steepness. Increase in slope leads to increase in run off and decrease in infiltration. The slope determines the extent of runoff of the pollutant and degree of settling time for sufficient infiltration. IV. RESULTS AND DISCUSSION The current study describes assessment of groundwater vulnerability in Palayamkottaitaluk using SINTACS model. The seven parameters which are used in SINTACS model are depth to water table, effective infiltration, unsaturated zone, soil media, aquifer media, hydraulic conductivity, and slope. The characterization and influence of SINTACS model in parameters are discussed below. A. Depth to Water Table: Depth to water level is important parameter in groundwater contamination assessment. The increase in depth leads to decrease in vulnerability to contamination or vice versa. The depth to water level layer of the palayamkottaitaluk was prepared based on 23 PWD observation (21 dugwells, 2 bore wells) well data. The wells which are located in and around the study area (7 wells within study area and 16 wells around the study area). Depth to water table in the study area ranges from m. Among those wells, well number has the maximum depth of 13.09mwhich is located in Sivanthipatti village. Depth to water table is generated using IDW techniques in the GIS environment. High ratings are assigned to low depth to water table and low rating values assign to high depth to water table in the consideration of infiltration capacity. Depth to water table parameter are shown infig.-2 B. Recharge: Recharge is the rate of water per unit area of land which penetrates the ground surface and reaches the water table. The greater recharge can have the maximum potential for groundwater pollution. The change in water level Dh computed in the graphical approach as ratio between peak value of water level during recharge and decline water table when recharge not occurred. The water level fluctuation of Palayamkottaitaluk varies 2.3 to 6.4m. The specific yield value of this wells assigned based on the well lithological unit, most of the aquifers in Palayamkottaitaluk was underlined with weathered gneiss formations. So the specific yield for the study area varies from to 1.5 percentages. Net recharge value of Palayamkottaitaluk is about range from 5-96mm.Gongathanparai and Sivanthipatti has the maximum recharge rate and rest of the taluk has moderate recharge rate. Reclassified layer of net recharge of study are shown in Fig.-3. C. Unsaturated Zone: Unsaturated zone has prominent role in assessment of ground water vulnerability. The zone act as protection of aquifer from the pollutant. The processes of physical and chemical operation are done within the unsaturated zone for diluting the contamination. The unsaturated zone materials in this study area are Silt/clay and Sandstone complexes. Ratings of unsaturated zone are done based on permeability capacity. Unsaturated zone of the study areaare shown in Fig.-4. D. Soil: Soil has important role in evaluation of groundwater vulnerability. Groundwater vulnerability is controlled by the textural properties of soil. The soil types in the study area are AIFISOLS (51.64 Km 2 ), ENTISOLS (79.92Km 2 ), VERTISOLS (19.79Km 2 ), INCEPTISOL (148.1Km 2 ) and unclassified reserve forest. On the basis soils textural and permeability behavior, the ratings of soils were assigned. Soil map for the study area is shown in Fig.-5. E. Aquifer Media: Aquifer media of the study comprise instructive rocks and crystalline rocks. Aquifer may occur at various depths. In the study area aquifer media contains gneiss materials namely granite gneiss and biotite gneiss. Granite gneiss ( Km 2 ) covers lager extent compared to biotite gneiss (14.12 Km 2 ). The ratings of the aquifer media is based on the infiltration capacity. Aquifer media are represented as map layer with ratings are shown in Fig.-6. All rights reserved by 120

4 F. Hydraulic Conductivity: Hydraulic conductivity of clay or non-porous rocks is low and its denoted as K. Hydraulic conductivity is arrived from field pumping test result of 6 wells in the study region. The computed hydraulic value of the Palayamkottaitalukranges from 0-2.8mm/day. The spatial distribution map of hydraulic conductivity is generated from point value of the hydraulic conductivity using IDW techniques in GIS environment. The reclassification of prepared layer was done based on the previous literatures. The reclassified layer of hydraulic conductivity is shown in Fig.-7. G. Slope: The slope map study area is generated using SRTM DEM data. The slope of the study area is 0-17 degree. The study shows that the maximum area covered by very gentle slope which permits less runoff and has a good potential for recharge. But in the SINTACS model will provide the minimum weight for slope so it could not affect the vulnerability result. Slope of the study are classified in to moderate slope, moderate to steep slope, steep slope, very steep slope. If slope value increase the treat to contamination is reduced. Slope of the study are represented in the Fig.-8. H. Vulnerability Index: Vulnerability index map was prepared based on the overlay process using reclassified input parameters with desired weights in the Raster calculator tool of GIS. Vulnerability index of the study area is in the range of This resultant index shows that the study area is in the range of low to medium vulnerability condition as per SINTACS method. Vulnerability map shows that south west and north east of the study has maximum of vulnerability. Vulnerability index map is useful aid measure or predict the nature of groundwater. The degree of intrinsic vulnerability is assigned based on the Table-2.Vulnerability map of the study area is shown in Fig.-9. V. CONCLUSION The vulnerability map that is produced from the SINTACS method is similar to DRASTIC method. The weightage characteristics are the only difference, which makes SINTACS superior than DRASTIC. The vulnerability map required for Palayamkottai has considered depth to water table, recharge, unsaturated zone, soil, aquifer media, hydraulic conductivity and slope as parameter which decides the vulnerability index. In this seven parameters depth to water table, vadose zone, recharge and soil media carries a higher weight whereas slope has a lower weight. The vulnerability index map prepared in this study has low to moderate class. This shows that the Palayamkottai taluk is a safer zone when considered for contamination. However the absence of hazardous effluent discharging industries was not present in the study area which reforms the safety of the region. ACKNOWLEDGEMENT The Authors wish to express sincere thanks to Dr.G.Sakthinathan, Dean, Regional Center of Anna University, Tirunelveli for providing all necessary institutional support also Agricultural Engineering Department and PWD, Government of Tamil Nadu for providing necessary data. REFERENCES [1] Insaf S. Baibiker, Mohamed A.A Mohamed, Tetsuya Hiyama, Kikuokato(2005). A gis based DRASTIC model for assessing aquifer vulnerability in kakamigahara heights, gifu prefecture, central Japan. Science of total environment, Vol 345,pp [2] Jose A, Ramos Leal, Felipe O, Tapia Silva(2011). Analysis of aquifer vulnerability and water quality using SINTACS and geographic weighted regression, environ earth science, Vol.66,pp [3] Aminrezaneshat, BisajeetPradhan, Mohan Dadras(2014) Groundwater vulnerability assessment using an improved DRASTIC method in GIS. 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5 Fig. 1: Study Area Fig. 2: Depth to groundwater rating map Fig. 3: Recharge rating map All rights reserved by 122

6 Fig. 4: Impact of vadose zone rating map Fig. 5: Soil media rating map Fig. 6: Aquifer media rating map All rights reserved by 123

7 Fig. 7: Hydraulic conductivity rating map Fig. 8: Topography rating map Fig. 9: Groundwater vulnerability map All rights reserved by 124

8 Table - 1 SINTACS rating and weighting values for the various hydrogeological parameter settings for the study area S.No Parameters Interval/Classes Area (mm 2 ) Rank Weight 1 Water table depth (m) Recharge (mm) Aquifer media Granite gneiss Biotite gneiss Alfisol Soil media Entisol Inceptisol Vertisol Topography (% slope) > Silt / Clay Vadose zone Shale Sandstone Sand gravel with silt Hydraulic conductivity(m/day) > Table - 2 Classes of intrinsic Vulnerability SINTACS Vulnerability Index Degree of Vulnerability Very low Low Medium High Very high Extreme All rights reserved by 125