Appl Water Sci (2015) 5:137–151 DOI 10.1007/s13201-014-0168-8 ORIGINAL ARTICLE Geomorphology and its implication in urban groundwater environment: case study from Mumbai, India V. R. Rani • H. S. Pandalai • K. S. Sajinkumar • A. P. Pradeepkumar Received: 26 September 2013 / Accepted: 20 February 2014 / Published online: 14 March 2014 Ó The Author(s) 2014. This article is published with open access at Springerlink.com Abstract Landforms of Mumbai Island have been largely and it proved that geomorphology corroborates with modified by the urban sprawl and the demand for groundwater chemistry and subsurface geology. groundwater will increase exponentially in the future. Quality and quantity of groundwater occurrence in island Keywords Mumbai Á Groundwater Á Geomorphology Á are highly influenced by the geomorphic units. As this Sea water incursion Á Hydrogeochemistry metropolis receives heavy rainfall, the area rarely faces the issue of water scarcity, nevertheless, quality always remains a question. The landforms of Mumbai Island have Introduction been shaped by a combination of fluvial, denudational and marine processes. These landforms are categorized into Mumbai Island is one of the most intensely urbanized and two broad zones on the basis of its influence in ground- industrialized regions of the world. It is included in the water occurrence. Denudational landforms are categorized United Nations (UN) list of ‘megacities’ (UN redefined a as runoff zones whereas the other two are categorized as ‘megacity’ as a city with a population of at least ten million storage zones. This classification is on the basis of occur- people; Brockeroff 2000). The population of Mumbai has rence and storage of groundwater. Mumbai Island is also gradually increased to become the fourth highest in the exposed to frequent sea water incursion and groundwater world—20.04 million (United Nations 2010). The island of quality has deteriorated. The varied hydrogeological con- Mumbai usually experiences greater demand for high- ditions prevalent in this area prevent rapid infiltration. This quality groundwater than other areas due to this increasing combined with the overextraction of groundwater resources population and because of the industrial boom along the for agriculture and industry has caused serious concern coastal belt as well as due to the demands of agriculture in about the continued availability of potable water. This the flat fertile areas (Rani 2004). Moreover, groundwater study aims at validating the geomorphic classification of resources assume considerable importance in this area the landforms with hydrogeochemistry and borehole data because the monsoonal rainfall is limited to a four-month period (Limaye 2010), while the water demand for the rest of the year is met by the groundwater. In Mumbai, frequent V. R. Rani Á H. S. Pandalai Department of Earth Sciences, Indian Institute of Technology, water shortages are the result of a combination of issues: Mumbai 400 076, India altered seasonality of rainfall, floods, salt water intrusion and the contamination due to the poor drainage and & K. S. Sajinkumar ( ) Á A. P. Pradeepkumar wastewater systems (Murthy et al. 2001; Nair 2009). Department of Geology, University of Kerala, Thiruvananthapuram 695 581, India Ground and surface waters in Mumbai are polluted due to e-mail: [email protected] the dumping of sewage and industrial effluents (Gupta 2009). Groundwater quality in the deeper regions of the Present Address: aquifer is brackish to slightly saline in Colaba, Dharavi, V. R. Rani Central Ground Water Board, Thiruvananthapuram 695 004, and Khar which could be attributed to seawater incursion India (MPCB 2011). High concentrations of pollutants exist in 123 138 Appl Water Sci (2015) 5:137–151 many places near the creek area (Haque et al. 2012) and its from the mainland. Besides the Thane and Vasai creeks, content has exceeded the prescribed limits. In addition, Manori and Malad creeks are other smaller creeks on the various alkali and dye industries are responsible for mer- east of Mumbai Islands. The creeks are the sites where six cury pollution in Thane Creek. Moreover, various effluents major streams which traverse the length and breadth of from oil refineries and reactors, as well as fertilizer resi- Mumbai Island debouch. The area is densely populated dues have polluted the groundwater (Sabnis 1984; Zingde and highly urbanized and is characterized by industrial, and Sabnis 1989). commercial and residential land uses. Vast regions of the The urban sprawl together with rapid industrialization Mumbai Island are also covered by dense forests. Hilly around this coastal city has modified the landforms to a areas are characterized by moderate to thick vegetation great extent, which in turn has profound effect on and many such areas have been designated as reserve groundwater systems. Landforms are the base for human forests. Three large reservoirs occur in this island like activity and they are continuously modified. Understanding Tulsi, Vihar and Powai. Agriculture and fishing are the the geomorphic processes and the landscape helps us to major occupations. Salt panning is another important plan land development and management in a better way. activity. The majority of ‘‘hotspots’’ of groundwater depletion due to the overextraction were found in the areas of coastal megacities in the developing countries like Mumbai (Se- Methodology kovski et al. 2012), though there exists a framework for groundwater extraction mentioned by the Government of The present study focuses on the study of role of geo- Maharashtra Act (1993). The effect of urbanization on morphology on groundwater occurrence. A macro-analysis groundwater systems is dependent on the geological and of geomorphology was carried out through field studies hydrogeological setting (Barron et al. 2012) apart from the supplemented with Survey of India (SOI) topographic geomorphic setting. sheets on 1:50,000 scale and remotely sensed data (IRS— A study about the geomorphic set up of an area, par- 1C LISS III digital data). The geomorphic features iden- ticularly a reclaimed and amalgamated island like Mumbai tified were classified on the basis of hydrogeomorphic which has become the hub for all the developmental characteristics. These categorized zones are further vali- activities, has paramount importance as the majority of the dated through hydrogeochemistry of groundwater (analysis population depends upon groundwater. The study aims at carried out as per APHA 1998) collected from both dug delineating the different geomorphic landforms on the well and bore wells and sampled from different geomor- basis of its hydrogeomorphic characteristics. These delin- phic terrains. Further, this was validated with the subsur- eated landforms are further characterized by their hydrog- face geology. The study, on a whole, proved that the eochemistry and subsurface geology. A number of studies geomorphic classification of landforms by field studies on on the hydrogeochemistry of Mumbai have been conducted the basis of groundwater occurrence was well validated (cf. Naik et al. 2007; Tirumalesh et al. 2010; Kamble and with hydrogeochemistry and subsurface geology. The Vijay 2011) and the use of GIS in such studies explored geomorphology not only tells the tale of the quantity but (Anbazhagan and Nair 2004; Shankar and Mohan 2006). also the quality of groundwater occurrence. But a study, melding hydrogeomorphology, hydrogeo- chemistry and subsurface geology, has not been attempted so far and the present study may be a first of its kind. This Geological setup study also proves the need for a macro-analysis of geo- morphology for better management of groundwater Mumbai Island forms a part of Deccan Volcanic Province resources. (DVP). DVP represents the remnants of one of the largest volcanic events on earth and is one of the best studied continental flood basalt provinces of the world. It originally Study area covered an area of 1.5 million sq. km. (Krishnan 1982) with a total erupted volume of 2 9 106 km3 (Krishnan Mumbai Island is located on the western coast of India 1960; Pascoe 1964; Rao et al. 1978). The geological for- (Fig 1) and experiences a tropical climate with copious mations found in Mumbai include the Deccan Basalts and rainfall. Geographically it lies between North latitudes its acid variants, volcanic tuffs, intertrappean sediments, 18°500 and 19°180 and East longitudes 72°450 and 73°030. dykes, laterite and alluvium. The geology of Mumbai The study area is bounded by Vasai creek to the north, Island is rather unusual compared to that of the main Thane creek to the east and Arabian Sea to the south and Deccan flood basalt province, particularly the Western west. The creeks of Thane and Vasai separate this island Ghats in several aspects (Sukeshwala and Poldervaart 123 Appl Water Sci (2015) 5:137–151 139 Fig. 1 Location map of the study area 1958; Sethna 1981, 1999; Sheth et al. 2001). Important respectively. The Madh and Gorai Islands in the west were differences include. separated from the Salsette Island by the Malad and Manori Creek. (1) The common occurrence of sedimentary intertrappe- The Mumbai Island has ridges along its western and ans, red boles and weathering profiles eastern sides running north–south, with broad intervening (2) Sub-aqueous nature of the lava flows indicated by lowlands between the ridges. The eastern ridge exposes pillow structures, spilitic petrography and the pre- amygdaloidal basalt which in places is albitized and shows sence of hyaloclastics