Chapter 3 Geology of the Area Chapter 3 Geology of the Area

In order to understand the lithologic input to the soils, knowledge on bedrock geology is most essential. This chapter therefore deals with the regional to local geology of the study area (Fig. 3.1). The study area essentially lies in the regional extent of the Deccan traps covering almost entire state of and the west central part of . It lies between N latitudes 15"45': 22"0', and E longitudes 43"()": SO^SQ' and can be physiographically divides as below: 1. The Maharashtra Plateau 2. The Western 3. The Coastal of

3.1. The Maharashtra Plateau It extends from the eastern border of the state, through and upto the Ghats covering about 75% of the state. The region is more or less an upland plain and is traversed by almost east-west or northwest to southwest trending river valleys and hill ranges with more or less similar trends (Fig. 3.1). The eastern region covering , , districts is occupied by narrow alluvial plains of Painganga and Wardha rivers with the maximum altitude of 300 m. The alluvials of Tapi River valley, with east-west trend and maximum altitude of 300 m above MSL occupies the northern part of the - and districts of . The remaining part of Plateau is occupied by the valleys of the Godavari, Bhima and Krishna rivers. The altitude of these plains ranges from 300 to 600 m above MSL. In general the altitudes of the plateau increases from east to west. There are some hill ranges in this area which are connected to the on the west. Their altitude ranges between 600 to 900 m above MSL.

3.2. The Western Ghats These constitute the ranges of Sahyadri Mountains. Trending almost north-south they arc parallel to the west coast of India along the entire western border of Maharashtra. They

26 4= H

cS o u s-< Cu u M c3 ^O t/i ^o Lo. 5 o ^o c o ? <+- 0 o c;

nS u X! "3 S' o '3) s% L> e* ^^/a c •? nj 4o3 CO CS ts 43 «cd ^ 4= cS

O o

s are about 1600 km in length with average elevation between 1000-1300 m. Among all the ranges is the highest peak in the Sahyadri mountains with the maximum elessvation of 1650m. The Sahyadri is an area of spatial elevation having been formed by tectonic processes of the western margin further modified by the differential weathering and erosion. The ranges are composed of piled one over the other with individual flows varying in thickness from a few meters to upto 36m. Some major rivers of Maharashtra have their source in the Sahyadri whereas some of the tributaries of these rivers originate in the east-west trending ranges.

3.3. The Coastal Region of Maharashtra The narrow strips of land west of Sahyadri upto the or the west coast of India is the coastal region or the Konkan coast. There are small and narrow plateaus at different elevations in this region at places covered by the laterites. The coastal region display various geomorphic features including the rocky and sandy beaches, wave cut platforms, uplifted terraces, dunes, creeks and mangroves swamp.

Drainage The drainage system of Maharashtra can be divided into three parts viz. Konkan, Central Maharashtra and eastern Maharashtra systems. The Sahayadri forms the major divide for the drainage system in the Konkan and Central Maharashtra regions. The rivers in the Konkan region flow in the west direction whereas the rivers in the central Maharashtra flow in the eastern direction towards the Bay of Bengal (e.g., Godavari, Bhima and Krishna rivers). Godavari is the largest and longest river in the Indian Peninsula, with a total length of 1500 km, about 500km of which lies in the Maharashtra. The originates from the Bhimashankar in Sahyadri. Bhima basin lies between the Mahadeva hills in south and Balaghat range in the north. The rises in Sahyadri near Mahabalcshwar and it occupies the southern triangular portion of the state. In contrast to these major rivers, the Tapi River, which flows in the east-west trending basin occupy the north central part of the state and debouch in the Arabian Sea. The rivers in

27 the eastern part oF Maharashtra have their courses in ahnost N-S direction. The major river in this area is Vainganga.

Climate Weather conditions in the Maharashtra are variable. Three distinct seasons are recognized viz. summer, rainy and winter. In the summer the highest temperature ranges between 40" and 48° C over the greater part of state. In the Konkan region the weather is hot and humid. In Ghats, temperature is comparatively low. In the region east to the Ghats, weather is mostly hot and dry in the Vidarbha region and at some places like Akola, Nagpur and maximum temperature reaches upto 48" C. In the rainy season from June to October, the state receives rainfall from SW . The rainfall in the state varies from 500 mm in the central semi-arid part to over 6000 mm in the Western Ghats. The coastal region receives 2000-3000 mm annual rainfall, the Western Ghats zone receives 4000-6000 mm, the central arid part receives 450-550 mm and the Vidarbha region receives 1200-1500 mm. The central zone has been identified as the drought-prone areas in the state. In the winter the weather is generally pleasant with the maximum temperature reaching upto 30"C and the minimum temperature of 4"-5"C.

Soils Major part of the Maharashtra, right from the Western Ghats up to Nagpur, is covered with the black soil or "Regur' which is the ultimate product of the weathering and erosion of the Deccan Traps. It is black in colour, porous and swells when water is added and on drying contracts producing cracks. In Konkan region and the Western Ghats, soil is mainly lateritic. It is produced from laterite which is the alteration product of . In the eastern part of Vidarbha region the soil is usually reddish generally formed by the alteration of granitic, gneissic, and other metamorphic rocks underlying this region. Apart from this, adjoining the Tapi River, a thick sequence of Late Quaternary alluvium is observed. The borehole data indicate that the thickness of this soil is more than 200m. Bank failure and gulling in the alluvium track is common during large floods and this has given rise to "Badland" topography.

28 3.4. Regional Stratigraphic Distribution The oldest rocks having an age of about 3500 Ma are mostly biotite gneisses. These form the basement over which the younger sediments were deposited and metamorphosed. They were involved in several orogenic cycles and hence are intensely deformed and mixed up. The unclassified basement gneisses are overlain by the meta-sediments belonging to Amgaon, Sakoli and Sausar groups (Table 3.1). They are represented by different types of schists, gneisses, marbles, amphibolites and hornblende schist's with intercalated bands of iron and manganese ore. All these rock fonnations are then intruded by the doleritic dykes. After the intrusive activity there was a long period of quiescence during which the Archean rocks were subjected to weathering. This period is recognized as Eparchaean unconformity or period of no sedimentation. In Maharashtra, Proterozoic rocks are exposed in , Chandrapur, Gadchiroli and districts in the fonn of isolated outcrops. During the period between Cambrian and upper Carboniferous (ca. 300 Ma) there is no record of any sedimentation in the southern India, this may be because this part of Indian Peninsula was concealed below ice cover, being the part of the giant continental mass called Gondwanaland. After the cessation of sedimentation of the basin around 200 m.y. ago a marine incursion marked by the deposition of Bagh and Lamela beds occurred in parts of Nagpur and Chandrapur districts. The major event after this was during the upper Cretaceous duuring which there was voluminious outpouring of lava through extensive fissures. The eruption was mostly silent, not of explosive type and the lava spread over extensive areas in the form of horizontal (lows of varying thickness. Hundreds of such flows are found piled one above the other and some individual flows can be traced for several hundred kilometers. The flows occupy almost the entire area of Maharashtra expecting some parts of Nagpur, Vidarbha region, and Ratnagari and Sindhudurg districts of Konkan. The lava flows of Deccan traps are intruded by the number of dolerite dykes which shows almost N-S trend parallel to the western coast. The last episode in the geological history of the state was the formation of the laterite and the older and younger alluvia in , , , Kolaba and district and some districts of eastern Maharashtra. A concise sequence of the stratigraphy in the Maharashtra region is given in Table 3.

Table 3.1. Stratigraphic sequence in the Maharashtra region (Deshpande, 1998) Age Stratigraphic Representative in ml Geographic Distribution Sequence Rock-Formation years Younger and older alluvium in Nagpur, Bhandara, Chandrapur, Wardha, Yavatmal, Alluvium, Akola, Thane, Kolhapur, Satara, Sangli Pleistocene- Latcrite, <2.5 districts. River terraces of Vainganga and Recent Sand, Soils. Painganga rivers, raised beaches along west coast. Miocene- Tertiary sediments, 2.5-23.5 Ratnagari and . Pliocene lignite, shales. Basalt flows cover most of the state from the Nagpur upto the Arabian sea coast Dcccan trap basalt ilows excepting in the eastern parts of Nagpur, Eocene-Upper with intertrappeans and Bhandara, and Ratnagari districts. 34-135 Cretaceous infratrappeans (Lamctas, Intertrappeans occur in Nagpur, Yavatmal Bagh beds) & Chandrapur. Infratrappeans occur Nagpur & Chandrapur & Bagh beds in Dhulc. Jurassic-Upper Limestone Chikiala and 135-350 Gondwana Kota Formation Clays & sandstone Sironcha Tahsil, Gadchiroli district and Triassic 205-245 Pachmari & ' Maleri Achalpur Tahsil, Formation Sandstone and Shales (Magli Forination) Sandstone and shale Permian 245-295 Nagpur, Yavatmal & Chandrapur districts. (Kamthi Fonnataion) Sandstone, shales and coal (Barakar formation.

30 Upper 295-360 Talchir Fonnation Nagpur, Yavatmal & Chandrapur districts. Carboniferous Limestone, shales and Yavatmal & Chandrapur districts sandstone (Vindhyan Supergroup) Penganga beds, (jadchiroli district Proterozoic 540-2500 Limestone & shales (Pakhal Group) Conglomerate, Ratnagari and Sindhudurg district. sandstone and shales, (Kaladgi)

Sausar Group, Nagpur, Yavatmal & Chandrapur, Nandgoan Group, Sakoli Ratnagari and Sindhudurg district. Group, Bailadila Group, Archcan 2500-3500

Amgoan Group .

Unclassified Gneisses Nagpur, Yavatmal & Chandrapur, Ratnagari and Sindhudurg district.

3,5. Dcccan Trap Deccan Traps is one of the most spectacular continental flood basalt (CFB) provinces of the world. Although, they cover an area of approximately 500,000 sq. km in the western, southern and central part of India in the states of Maharashtra, , Madhya Pradesh, Andhra Pradesh and Kamataka, originally they must have spread over a still larger area (up to 1,500,000 sq. km) including those extensions which lie hidden beneath the Arabian sea and the eroded portions leaving some detached outcrops far away from the main mass, for example the one near Rajamundri towards the eastern coast of India (Krishnan, 1956). The Deccan Trap volcanism is believed to have been initiated when the Indian sub-

31 separated away from the rest of the Gondwanaland fragments and moved towards north during the Cretaceous - Tertiary period (65±5m.y.). These basaU, popularly known as Deccan Trap constitutes predominant formations. They are generally characterized by step-like terraces formed by successive layers of basalt flows. The Deccan Trap sequence essentially comprises of more or less horizontal tholeiitic basalt flows, varying in thickness from nearly 1500 m in the west in the vicinity of the Western escarpment to few tens of meters along the eastern fringe areas. The lava flows are intruded by a number of dykes and sills. The lava flows are generally considered horizontal in character, but detailed field observation demonstrates gentle dips ranging from 1.2 to 3.3 in/km (Raja Rao, 1982). The basaltic flows in the area are genetically classified into two prominent types viz. the Pahoehoe and the AA flow. Macdonald (1953), on the other hand, developed the classification scheme for the basaltic lava flows using Hawaiian flows as an example and recognized two types viz. 1) Pahoehoe and 2) aa. The Deccan lavas in general exhibits the characteristics of the 'Pahoehoe' and 'aa' types of lava flows typical of the Hawaiian Islands. Nichols (1936) and Walker (1972) classified basaltic lava flows into two classes namely - 1) Compound flows: Compound lava flows are those lavas, which are divisible into flow units, have a shield like form and are thought to develop when rate of extrusion is relatively low. 2) Simple flows: Simple lava flows are not divisible into flow units and are thought to form when the rate of extrusion is relatively high. According to Walker, (1972) Pahoehoe flows are always compound whereas the aa flows arc always simple. The Pahoehoe flows are compound in nature and consist of several flow units, varying in thickness from less than a meter to over several meters indicating episodic eruption. Single unit in vertical section describes a basal segment constituting vertical pipe vesicles, filled with secondary minerals like zeolites, agate, chalcedony etc. The middle part of the unit comprises of hard and compact rock. The top portion is full of spherical vesicles packed with zeolites, chert, or quartz. The Pahoehoe flow is generally altered and shows grey, purple or red colour. In some thick units, the middle section comprises of dark dense unaltered basalt. The uppermost surface of the Pahoehoe unit is reddish in colour, glassy and shows rope like curved or twisted stmcture. Several units comprise the formation of a flow,

32 which is hummocky on the top. Lava tunnels are encountered at many places. Typical topography with smooth hill slopes, flat table lands called as mesa, broad valleys and conical peaks, is attributed to the Pahoehoe flows as these flows weather easily. The aa flows differ in its characteristics from the Pahoehoe flows. The basal piece of the aa flow comprises of grayish clinker, showing blocks of dense glassy trap cemented by glass, zeolites and very fine grained basaltic material. The core section of the flow encompasses dark grey dense fresh basalt overlain by a flow of breccia. They range in thickness from a few centimeters to over half the thickness of the flow. Such flows are constituted of sub rounded to angular blocks of vesicular trap cemented by glass or zeolites or very fine grained altered basalt. Upper parts of the aa flow commonly show presence of rough surface called as clinkary top. Thin red clay like altered glassy substances referred as red bole is seen at various places. The aa flows comprise of two sections, which show differential resistances to weathering. The brecciated part of the flow is more prone to weathering and hence breaks down easily while the basal rock being dense is resistant to weathering leading to accumulation of large boulders at the base of the hills. Formation of cliffs, terraces and benches is a common phenomenon. Valleys with broad bottoms formed even at high levels along the hill ranges is one of the characteristic feature. The aa flows are predominantly know for columnar joints and structure. Striking presence of large number of dyke intrusions in both simple and compound flows is seen in the northern and western part of the Province. Deshmukh and Sehgal (1988) have grouped these dykes into two on the basis of their trends. 1) The West Coast dykes trending N-S and 2) Narmada - Tapi area dykes trending E-W. The area extending from Bombay-Daman coast inland to and occupying about one quarter of the Deccan Trap can be defined by the abundance of compound flows. In the rest of the Deccan, all of its southern, eastern and northern parts, simple lava flows predominate. Over vast regions of the Deccan Province the lava flows are nearly horizontal, with dips of 1" or less (e.g. West, 1959; Raja Rao et al. 1978). The weathering and erosion pattern of both the lava flow types are different and therefore presents distinctly different geomorphic expressions. Pahoehoe flows weather more easily and give rise to conical hills with smooth hill tops, whereas the dense lower and

33 middle part of aa flow stands up as prominent cliff sections. Spheroidal weathering is seen in both aa and Pahoehoe flows. In areas of heavy rain fall such as Konkan plains and neighboring Western Ghat escarpments, the Deccan located due south of 18"N latitude show alteration to laterite.

3.6. Paieomagnetic Classification The Paieomagnetic work on Deccan Volcanic Province (DVP) was started in 1959 by Deutsch and co-workers that was continued for more than four decades by different workers. Sahasrabuddhc (1963) divided the Deccan Basalts into Upper and Lower divisions with Lower traps recording "Reversed polarity" and upper traps being "Nomial". Pal and Bhimashankaram (1971) on the other hand classified the Deccan Basalts into four groups A, B, C, D, and suggested that the Deccan lava extruded in at least four pulses. Later on many workers continued to developed magnetostratigraphy at various sections of the Deccan traps.

3.7. Stratigrapliy Pascoe, (1965) was the first to record stratigraphic classification based on broad lithologic features such as existence of intertrappean ash beds and fossiliferous zones. The Deccan trap was divided into Lower, Middle and Upper formations. The eastern part was considered to represent the older formations amid the younger formations occurring in the western part. On the basis of gross lithology, Konda (1985) classified the DVP into two parts as follows: 1) Plateau Sub-province: Composed of simple and compound type basaltic flows occurring in and regions of Maharashtra. 2) Graben Sub-province: Constituting of variety of volcanic rocks including andesites, rhyolites, trachj^es and dacites. Intrusive rocks like gabbros, lamprophyres, dolerites, trachytes, nepheline-syenites and carbonatites are predominantly present in graben sub-province.

A multidisciplinary approach using field characters, geochemical signatures and paleomagnetism to classify the western parts of the Deccan basalt province was adopted by a number of workers in last two decades of the 20''^ century. Najafi et al. (1981) studied

34 area and made a beginning of this new approach. This was followed by Beane et al. (1983), Bodas et al. (1985), Cox & Hawkesworth (1985), Beane et al. (1986), Devey and Lightfoot (1986), Bodas et al. (1988), Khadri et al. (1988), Mitchell and Widdowson (1991), Bilgrami (1999). Subbarao and Hopper (1988) gave the reconnaissance geological map of western Deccan Basaltic Province. Geological Survey of India mapped the Deccan trap province either systematically or on the basis of photo geological studies. Initially (pre-mid 1960s) the individual lava flows were not mapped but in post-mid 1960's period the Deccan basalts were divided in individual lava flows. Ghodke et al. (1985), and Godbole ct al. (1996) summarized the results of the stupendous efforts in the western parts of DVP (see table 3.1). Whereas, Nair and Bhusari (2001) gave classification of the Central Deccan. Geological maps showing geochemical sub-divisions of the DVP from the Western Ghats were first published by Beane et al. (1986), Devey, and Lightfoot (1986). Deccan volcanics have been grouped into three Sub-groups and twelve formations based on the geochemical (Cox and Hawkesworth, 1985; Beane et al. 1986; Subbarao and Hooper, 1988; Khadri et al. 1988, Mitchell and Widdowson, 1991, Subbarao et al. 1994). Three major sub-groups of DVP are • Kalsubai Sub-group as oldest and covering whole of Kalsubai mountain range and adjoining areas in the north. This subgroup is divisible into five different formations from older to younger as Jawahar, . Neral, Thakurwadi and Bhimashankar. A volcanic shield centered on Kalsubai - area at the northern end of DVP has been recognized (Subbarao and Hooper, 1988). • Subgroup comprises of and Bushe fonnation that overlie the Kalsubai subgroup. • Wai Sub-group designated as the younger flows is exposed in south and includes Poladpur, Ambenali, Mahabaleshwar, Panhala and Desur formations (Table 3.1).

35 Table 3.2. Simplified chemostratigraphic classification of the Deccan Volcanic Province (After Cox and Hawkesworth, 1985; Beane et al. 1986; Bodas et al. 1988; Subbarao and Hooper, 1988; Khadri et al. 1988;Sethna, 1999). Sub Group Formation

Manori (Trachytes and Basalt intrusion)

D Salsctte Madh-Utan (Rhyolite lava flows) E Island (Hyaloclastite, spilite basalt and shale) C Desur C Panhala A Wai Mahabaleshwar N Ambenali Poladpur

B Bushc A Lonavala Khandala S Bhimashankar A Thakurwadi I. Kalasubai Ncral 1 Igatpuri Jawahar

3.8. Chemostratigraphic classification of flows Knowledge about the chemical compositions of lava flows from DVP has contributed immensely to establish their chemostratigraphy. The composition of rocks and minerals is important in ascertaining the chemical composition of soils in general and heavy metals in particular. This is because the soil is subjected to chemical interaction with groundwater to a considerable extent and hence information about the chemostratigraphic classification of lava flows is essential. Chemostratigraphically the Western Ghats have been Stratigraphically divided into three subgroups and twelve formations (Cox and Hawkesworth, 1985, Beane et al 1986, Subbarao et al. 1994 Bodas et al. 1985).

36 3.9. Geology of the Mumbai Metropolitan Region In order to understand the lithologic input to the soils, the bedrock geology is most essential. Geologically, the region falls in the Deccan Volcanic Provience. The Deccan trap lava flows shows horizontal bedded relationship with the dip of 0.5" in more or less radial pattern. (Bodas et al., 1988; Cox, 1989). Whereas in Mumbai (Bombay) the lava flows distinctly shows the westward dip of lO" to 20" which has been described by various workers (Buist, 1851; Carter, 1852; Wynne, 1886; Sukeshwala, 1953; and Sukeshwala and Podlervaart, 1958; Merchant, 1977) The Mumbai lavas are believed to represent much younger phase of emption in the Deccan volcanic province. Sethna, (1999) has proposed to classify these lavas into the new Salsette Subgroup. The basic dykes and lopoliths were marked by Tolia and Sethna, (1990) in . The rhyolite flows were observed by Tolia and Sethna, (1990) at Madh and Utan-Dongri in Mumbai. The excavation of tunnel shows the fossiliferous carboniferous shale marked out between the Malbar Hill and Worli Hills depicting the intertrappeans in the basaltic flows. Based on the stratigraphy compiled by Subbarao and Hooper (1988), the Salsette Subgroup is further classified by Sethna, (1999) into Mumbai Island formation composing hyaloclastite, spilites, tholeiitic basalt and shale beds older than rhyolitic lava flows of Madh-Utan and further followed by intrusive phase of contemporaneous basalts and trachytes (See Table 3.2). The Deccan basalt in the region is well accompanied by much of felsic lava (rhyolite, trachyte) and the pyroclastic material (tuff, breccias), as well as sub-aqueous volcanism (spilite, tachylite, hyaloclastite). Many dykes cut the lavas and pyroclastic rocks. The geology of Mumbai thus differs from that of the rest of the Region. The types of rocks found in Mumbai are - Various types of basalts. Volcanic breccias. Ash beds Diorites Inter - trappean beds Trachyte Rhyolite

37 Some dark coloured fossiliferous shales attaining a thickness of about 2 m are exposed at the foot of the Worli hills. Being deposited during a period of quiescence and overlain by a later flow, these beds are known as ' intertrappean beds'. In addition, a number of basic dykes and aplitic veins also occur. The dykes have a general north-south trend and appear to be limited to the eastern margin of the main ridge from west of Mulund, and the eastern banks of the Vihar lake to Vikhroli. Some of these dykes extend further south towards Mankhurd, Chembur and Nanole in the Trombay Island. In Thane area acid differentiates, namely Rhyolytes and Trachytes do not occur. The area is chiefly made up of basalt volcanic breccias and tachylitic basalts. These have been intruded by numerous basaltic and doleritic dykes. In the southern part of the region, namely in the areas of Panvcl and Uran both compact and amygdaloidal basalt predominates. They are intruded by a number of dykes. In some places in this area, the soil over burden is found to be 5 to 8 meters deep. A feature of geological importance in the region is the hot springs at Vajreshwari, Ganeshpuri and Akloli in the northern part. The temperature of water ranges between 42" celcius to 55"celcius and gas with slightly sulphur smell rises from the waters. The waters are mainly saline containing mostly sodium, calcium, chloride and sulphates.

Important Geological Structures in MMR

• The Gilbert Hill in Andheri with hexagonal basaltic columns of about 40 meters height, most of which is now quarried but similar features at Oshiwara quarry can still be seen; • Sewri - Another rare site with pillow lavas • Worli Hills with frog beds (intra-trappcan beds of great scientific value) • Dongri - Monzonite dyke cutting rhyolitic tuff • SGNP - Boxwork pattern formed by the network of veins intruding the basic volcanic rock showing the network polygons and various shapes and size. • - Sea cliffs and wave cut platforms.

38 3.10. Mutnbai at a Glance 3.10.1. Growth of MMR The present island was formerly made up of several smaller islands, which were joined together during the 19th and early 20th centuries to form a single island^The Mumbai Metropolitan Region (MMR) is the largest city in the India and the sixth largest metropolis in the world. It is the major business and commercial center of India. After independence the Mumbai became a hub of industries and which took it to the fast pace growth in industrialization, transportation and urbanization by widening its outer extremities. From the last 50-60 years Mumbai shows somehow steady and drastic change in the form of growth and development. Being the economic capital of India and the capital of the state of Maharashtra, Mumbai faces the overburden of mass migrating from all over the India and hence remain un-balanced all the time in all respect. The uncontrolled growing population in Mumbai and its struggle for sustainance and adjustment is and will remain the matter of concern all the time, j

3.10.2. Physiography oj MMR The study area is consisting of coastal landfomis mostly, having the sandy beaches at Marine Drive, and Juhu, Rocky beaches at Haji Ali, Worli and Bandra and Mud Island and Malad. The study area is also encroached by three creeks. One is from western side called creek, one is from the south side called and another small creek from the west side but in the southern part of the study area at called Panvel creek. Most of the rivers and small tributaries originating in the Western Ghat are merging into the Arabian sea through creeks. One of the river called is originating in Ghat and reaching to Kalyan after meandering through the hilly tracks and mountainous terrain covering 100 km of distance. After Kalyan it meanders through coastal plains to reach Arabian sea at Vasai creek (Bhosale and Sahu, 1991). The outlet of the river touches the head of the Thane creek south of Mumbra (Fcmandes and Nayak, 2010). Physiographically the area exhibits a highly rugged and mountainous topography manifested by the north south trending Sahyadri mountain ranges with steep scarp on the western side and a gently undulating terrain known as Konkan plain bordering the Arabian

39 sea. The area is drained by the Mithi, Dahisar, Ulhas and Vaitama rivers and their tributaries and other streams. The Deccan basaU flows in the study area are classified into 'pahoehoe' and 'aa' and are normally phyric to feldspar phyric. At places, some of the feldspar phyric flows are very highly porphyritic containing giant sized phenocryst of plagioclase feldspar. These megacryst flows are quite extensive and serve as reliable regional markers for grouping the flows onto various fonnations. The basaltic pile of the area is profusely intruded by the rocks of Borivali formation which includes doleritic and basaltic dykes, tuffs and agglomerates. The frequency of dykes is very conspicuous. Dykes trending in NW-SE, NE-SW and E-W are also observed. Frequency of dykes becomes relatively in the south eastern part. At places triangular and rectilinear dyke patterns are nolicei Laterite of Cainozoic age occur as small isolated cappings on the top of the hills.

Rivers Ulhas River and its tributaries, Bhatsai^d Kalu, in the northern part of the Region, Panvel River in the Central Area; and Patalganga, Amba, Balganga, Bhogcshwari and Bhogwati in the south are the main rivers draining the Region. Tansa in the north forms the northern limit of the Region. The details of the important rivers in the region are as follows: Ulhas River, about 135 km long, rises in the rainy ravines of the and bound by the steep scarps of the Sahyadri and ridge. It flows northwards after leaping over a depth of 90 meters in two waterfalls one below the other. The valley opens out steadily as the river flows past towards the north. Near Badlapur, the river is dammed and used for a drinking water reservoir. It supplies drinking water to Badlapur, Ambemath and Kalyan. After its confluence with Kalu and Bhatsai, east of Kalyan, the river turns west and flows through Mumbra ridge. Later it turns northwards to flow for about 10 km through a picturesquely forest-clad hill country and then turning west again to develop an estuary. After 3 km it joins the sea south of Vasai. An island, namely Panju Island, just east of the estuary on the river is used by the Western Railway for a bridge to connect Salsette with Vasai. The river is distinctly tidal as far as Kalyan, which is reported by historians as a port during the historic past. Tansa River raises in the Shahapur uplands beyond the limits of the region and has a westward flow till it cuts through hills. Thereafter, it turns north

40 and joins Vaitama River before the latter develops its estuary. Panvel River is a small stream rising in the northern parts of the Matheran hills and flowing through the Panvel flats before joining the Thane Creek west of Panvel. Patalganga River rises in the steep western scarps of the Matheran uplands where it branches off from the main ridge near and maintains a general westward flow till it joins the Creek with a wide estuary. The tail-waters of the Khopoli power project are let into the river near Khopoli. Amba, Bhogeshwari, Bhogwati, and Balganga rivers traverse the southern part of the region. A portion of Amba River up to Nagothane is navigable but it gets frequently silted and requires dredging. Bhogwati is also useful for navigational purpose for a small portion of its length from Dharamtar creek. There are also small rivulets which rise in the central Alibag hills and drain into the Arabian Sea.

Coastline The entire north-south coast line along the mainland presents many interesting features. All along the coast, there are many small creeks, the main ones being Versova, Manori and Vasai Creeks, besides the larger Thane Creek. What is known as Vasai Creek is in reality Ulhas estuary. Panvel Creek has also a similar opening through which Panvel River drains into Thane Creek. Dharamtar Creek is the main creek in the southern part of the Region. The coastal belt between Vasai and Amala in the north is marked by beautiful beaches and plantations all along the coast. This 2 to 3 km wide belt along this coast is famous for its rich horticultural development consisting of coconut and banana plantations, flower gardens and vegetation. In the south main ones among the beaches are Gorai and Juhu in Salsette, Dadar and Chowpaty beaches along the western shores of Mumbai Island. Amongst the bays, the salient ones are; the Backbay in the south and the Mahim Bay in the north which have both been carved out in relatively soft rock

Climate The climate of Mumbai is tropical humid type and is fairly equable since seasonal fluctuations of temperature are not significantly large. The moderating effects of the nearby sea and the fairly high amount of relative humidity in the atmosphere have restricted the

41 variability. The seasonal variations of temperature follow closely the course of the sun. January is invariably the coldest month and May the warmest. With the onset of in early June there is a reversal of the temperature curve, and the temperature during the period of monsoon remains very nearly uniform at about 27^ Celsius. The slight rise in temperature in October falls gradually till it reaches the coldest month in January. The prevailing direction of the normal seasonal wind during the year is west- northwest. The mean wind direction in December oscillates between west-north-west to east- north-east and in June south-west is the dominant wind direction. Though the direction is subjected to considerable diurnal and seasonal variations, there is little fluctuation in the velocity during the dry season. The winds are generally light and variable about 8 km/h. During the wet season, however the velocity gradually increases reaching the peak of value about 13 km/h in the month of July with the direction in the meantime having veered round to west-south-west. In the southern part of the region, namely Alibag, wind velocities are higher with average value of 10 km/h and peak velocities of about 25 km/h in July, in the month of June the wind is greatly affected by the irregular and abnormal disturbance from the south-east associated with the first break of monsoon. The weather is often squally and associated with gusty winds during the monsoon. After July the reverse movement commences and by September it gradually moves to west reducing in velocity, till it reaches the other limit of north-north-east in December. The monsoon - generally sets in around the second week of June and continues till late September. July and August are the wettest months all over the Region. There is hardly a day without rain, particularly in the hills and the Ghats in these two months. Towards the later part of the season there are breaks in between, when the oppressive hot weather is associated with high humidity along the coast. The average rainfall in the Region is over 2,000 mm. The coastal areas in general receive the first onslaught of the squally winds and rains but record much less rains than the interior. Even the plain stations, like Kalyan, Bhiwandi located closer to the hills receive more copious rains than the coastal areas like Mumbai (Colaba), Uran, Vasai and Alibag, Kurla (Santacruz) and Panvel. This is due to local relief conditions.

42 3.10.3. Geographic and Geomorphic Setting Mumbai Island is surrounded by Arabian Sea in the West and South, and Thane creek to the East (Fig 3.2). The MMR region is spread over an area of ~ 4500 sq km. Along the coast, the area extends to about ~ 75 km with highly sinuous stretch showing arch shaped bays with skewed length measuring to > 130 km N-S from Amala fort in Virar (W) to Colaba south end (Navy Nagar). The E-W lateral extension from Arabian Sea to Badalapur is ~ 50 km. The study area is confined in latitude and longitude of N 19^33' - E 72^45' to N 19*^33' - E 73"l8' and N 18"54'- E 72^^45' to N 18''54' - E 73"l8'. The exposed basalt is horizontally bedded and occurs as eroded / isolated cliffs and hills. The uplifted basaltic landforms include the flat mesas and escarpments in the New Bombay region. In the coastal region the landforms include sandy and rocky beaches, mud flats, creeks and mangrove swamps on the western and harbour parts. The city is longitudinally dissected by the remnant hills and ridges and majority of the rivers flow towards the coast with sinuous turns due to presence of these eroded cliffs. The use of Digital Elevation Model (DEM) (Fig 3.3) is important to derive the landscape attributes that are utilized inland forms characterization (Brough 1986; Dobos et al. 2000) and hence to understand the regional setup of the study region and to identify the geomorphic control over the geophysical agents DEM for MMR is generated which broadly depicts that the MMR has linear N-S directed remnant ridges along the western and eastern sides running parallel to sub-parallel to the coast. Major and older part of the city is built on the central low lying area and on the western slopes of the ridges parallel to the sea coast. Overall the slopes of the region merge to the west (in Arabian Sea) and in the southern part while to east in the tidal swamp areas of Thane creek entering in central region. One of the ridge called Central ridge (includes harbour part of the MMR) is running parallel to the Thane creek, sloping gently towards east (in undulating regions up to Badalapur) and towards west in the tidal swamp area of Thane creek (Fig. 3.2 and 3.3). The contour map of the region (Fig. 3.4) also illustrates highest contour (600 m) rests in the north and in the east part of the study region. The closed space contour lines follows N-S trend suggest the steep slope merging in low lying region in the east and west direction. This indicates the higher surface runoff and hence higher redistribution of the surface soil in the study region. Sea enters into the land from NW side by Vasai creek and from SW side by Thane creek. There are three major lakes

43 Mumbai Metropolitan Region

I—IMMR Aol Mumb_SRTM.imgHI 713.01-885 • MMRLocations ^ -38 - 317 |^ 885.01 - 1.528 Kilometers Mumb Roads CH 317.01-590 Hi MMRBoundary iBMMR^Water I—I 590.01-713

Figure 3.2. Map of the study area showing geographic setup and the soil sampling locations, water bodies and road network of MMR Region. I I I o u I ^

^ o o ts .-•

t: id o ti oa •t-» 03

C

•^ 3 o 0) (50 C3

6 (fU s i Pi !/3

O en 3 ^ C

c 00 s

T3 i o 3 O in I Q ^—/ o "w •a o S CI o >

'5b 5

S MMR Contour Map

MMR_Cntr100 MumbSRTM.img ^ 713.01-885 I 1 MMR Aol I—I -38-317 » 885.01 - 1,528 Kilometers • MMRLocations ^1 317.01-590 |H MMRBoundary m MMR Water !• 590.01-713

Figure 3.4, MMR Contour Map of 100 m contour interval showing highest contour resting in east and north part of study area, created by using SRTM image and ArcGIS 9.3 version. present in the city viz; Powai, Vihar and Tulsi. All these lakes are elongated in NS direction and are located on the eastern flank of the Western ridge. Two of these lakes, Tulsi and Vihar fall on the periphery of the Sanjay Gandhi National Park (SGNP) in Borivali region which is one of the largest national parks in located within the urban land. This Island city receives extensive rainfall during June to September from SW monsoon and occasionally during (April-May) as pre-monsoon and the post-monsoon (July-November) rains accompanied with thunderstorm activity. The typical coastal warm and humid climates accelerate the chemical weathering of rocks to fonn predominantly medium to deep black and reddish colored soils. The soils in MMR are sandy-swampy types and are of the order Entisols with majority of the coastal peripheral areas and creek locations showing the suborder aquents. While the other areas show variation from arents to psaments in the Soil Survey Staff (1999) classification. Majority of these soils are also described as alluvial and loamy soils (e.g., Sehgal et al. 1996). The hill tops show mostly the lateritic soils (oxisols). The pediments show brown to black soil (Regur type) that is also popularly known as black cotton soils (BCS) over the entire Deccan plateau region. The BCS is porous soil, exhibits high smectite percentage, having hard clods (a mixture of sand, silt and clay) and is contlned to the areas of forest land and areas which have lesser density of settlement, that includes SGNP on the western hitch, Harbour part in the New Bombay region, some areas in the eastern side of the Thane creek and parts of Badalapur under the . The reddish brown soil marking the high chemical weathering is particularly noted in the areas like Goregaon (Arrey Milk Colony) and at Malad in the Western express highway road cuttings. Overall the vegetation is average including trees in gardens of each small area in pockets, shrubs on the hills and mangroves in the coastal and creek areas. The vegetation density is more on the western side and near Thane due to SGNP. While the areas on eastern side of the Harbour ridge are barren, swampy and flat with scanty vegetation and small shrubs with mangroves at places (see Fig. 3.2 and 3.3).

44 3.10.4. Change in Land use The spatial growth in urban part of MMR is specifically noticed in the three periods 1968, 1983 and 1987. The growth in 1968-1975 is remarkable, occupying the low lying areas along Mahim creek, Malad creek, Thane creek, Chembur, Ghatkopar, Sakinaka. After 1975 the growth occurred with transportation that is towards, Bhiwandi, Mumbra, Kalyan, Badalapur and a large part of agricultural land was brought under urbanization. After 1983 the growth was mainly focused in the , Thane and Panvel region. The population of MMR was 14.5 million as per 1991 census and is projected to increase to 22.4 million by the year 2011.

45