CHAPTER 2 GEOLOGY AND GEOMORPHOLOGY

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1 CHAPTER 2 GEOLOGY AND GEOMORPHOLOGY 2.1 Introduction Groundwater is one among the most precious natural resources. The occurrence and movement of groundwater is directly controlled by the local geological formations. Major volume of water is located in oceans, glaciers and in deeper subsurface openings (Ralph, 1983). The knowledge about the geological structures, aquifer systems, and spatial distribution of landforms and quality of groundwater is necessary to implement best management practices of water resources in adverse conditions. Many of the hydrological parameters are related to the geology and geomorphology of the terrain. The agricultural practices of south India are dependent on the occurrence of groundwater. The unconfined aquifers are mainly recharged with rainfall in these places. An aquifer is basically a rock unit or geological formation, which can yield considerable quantities of water (Todd, 1986). Confining bed is referred as a rock unit having very low hydraulic conductivity that restricts the movement of groundwater. Groundwater occurs in aquifers with different conditions, which are described as unconfining and confining units. Water in unconfined conditions partially contains the aquifer wherein the upper surface of the saturated zone is not stable. Unconfined aquifers are also referred to as water-table aquifers which fluctuate with varying hydrogeologic conditions. In situations, wherein the water completely fills an aquifer that is overlain by a confining bed, the aquifer is said to be confined or artesian aquifer. The nature of these aquifer conditions are controlled by the prevailing geological setup. 2.2 Geology of Kerala The geology of Kerala is a part of the south Indian Precambrian terrain, which is composed of granulites, gneisses, granites and greenstones. The granulites and associated gneisses belong to the Precambrian in Kerala state. The younger Meso-Cenozoic dykes and pegmatites are found to intrude late Precambrian rocks. The tertiary sedimentary formations of 13

2 the land belong to Neogene period only (Soman, 2002). The geology map of Kerala state is shown as Figure 2.1. The Charnockites and charnockitic gneisses are the oldest rock complex units of Kerala state. Charnockitic gneisses, gneisses and the pyroxene-bearing granulites occupy the major parts of the Western Ghats and the midland regions located within Kerala state. The granuliticgneisses are very well spatially connected with lineaments and faults in Kerala state (Soman, 2002). Khondalites are yet another major rock formation of south Kerala and are associated with garnet-biotite gneiss and garnetiferous quartzofeldspathic gneiss. The presence of intrusives especially, the dykes, have hydrogeological role to find good zones of water bearing fractures. Intrusive formation dykes of Lower-Middle Proterozoic age, pegmatites of Middle Proterozoic age, host of younger granites (Late Precambrian-early Palaeozoic age) and later dolerite dykes, contemporaneous with Cretaceous-Paleocene Deccan Basalt magmatism, are the common elements seen in granulitic terrain of this state. The western parts of the State consists of sedimentary formations of Neogene period and quaternary period having four distinct beds viz. Alleppey, Vaikom, Quilon and Warkali. In midland regions, the Tertiary and crystalline formations are found as lateritized units which act as good aquifer. Along the coastal regions, alluvial deposits of Recent origin are found. 2.3 Groundwater Occurrence in Geologic Formations of Kerala Hydrological parameters of Kerala state is closely controlled by the geological formations. Hydrogeological map of Kerala is given as Figure 2.2. The Vaikom and Warkali beds act as the most potential aquifers within the Tertiary group of formations. The bore holes drilled in the coastal tract of Alappuzha district revealed that Alleppey beds from the deeper strata were saline ingressed (CGWB, 2011). Warkali aquifer development is good enough to provide water into coastal area between Kollam and Cherthala of the state. The presence of intrusive, especially the dykes, have hydrogeological importance to locate potential zones of water bearing fractures. In case of hard rock terrains, comprising weathered crystallines and laterites, groundwater occurs under phreatic conditions, wherein the shallow fractures are hydraulically connected. The situation is under semi-confined to confined 14

$conditions in the case of deep fracture zones. There are many artesian wells reported from Kerala.$

3 conditions in the case of deep fracture zones. There are many artesian wells reported from Kerala. When the water level from the confining bed intersects with the ground surface, the artesian wells are resulted. Figure 2.1 Geological Map of Kerala (After Soman, 2002) 15

4 Figure 2.2 Hydrogeological Map of Kerala (GEC, 2011) 2.4 Geology of Lower Ponnani River Basin Major part of lower basin of Bharathapuzha is underlain by rocks of Archaean metamorphic complex which include the granulite group, gneisses and schists. Laterite and alluvium are the formation which overlies the granulite formations. Intrusives of pegmatites and quartz veins are indicative of the structural disturbances of the terrain. The younger intrusives are the good indicators of fractures in locating the good potential zones. The River basin of Ponnani River covers three districts, namely, Palakkad, Thrissur and Malappuram. Many drinking water projects confined on the banks of Ponnani river are showing 16

5 the implications of this river basin. Overviews of the details of three districts are provided in Tables 2.1, 2.2 and 2.3. The geological and geomorphological features differ in many aspects from place to place. Palakkad (Palghat) is the land of Palm trees and Paddy fields. It is also known as the Gateway of Kerala which connects different parts of India with the state. The unique physiographical feature, the Palakkad gap, acts as green belt in the massive Western Ghats. Over development of groundwater structures by domestic, irrigation and industrial users of the district are major reasons of lowering water table, and experiences water scarcity especially along the eastern parts of the district. Many workers have studied hydrogological features of Palakkad, Malappuram and Thrissur districts (CGWB, 2007, 2008, 2009). SIDA projects activities during and have revealed the subsurface features of the area (CGWB report, 2007). Thrissur district, which is also known as cultural capital of Kerala, has an area of about 3032 sq.km and is located in the central part of the State. It covers an area of about 7.8% of the area of the state. The bore wells constructed along the fracture and lineaments are highly productive nature and are used dominantly for irrigation purposes in Thrissur district. Malappuram district of Kerala State was came into existence in Laterite was first identified near to Angadippuram Railway Station by Francis Buchanan from this district. The Ponnani river (Bharathapuzha), the second longest river of Kerala, originates from the Anamalai Hills in the Western Ghats. The river course at the point of the confluence of Bharathapuzha and Gayathripuzha is called as Ponnani River (CGWB, 2009) that later in lower reaches joins Arabian sea at Ponnani. The Ponnani river is the fifth order stream. The drainage pattern of Ponnani river basin dendritic pattern. The geology map of lower basin of Ponnani River is adapted from Geological Survey of India (GSI) map, in the year Figure 2.3 shows the geology map of study area. The midland area of Pattambi and Ottapalam blocks are composed of hard rock of Charnockites, which is underlain by weathered soil of thickness more than 10m. The borewells located in these areas are productive when they are drilled along NW-SE and E-W fractures. Charnockites and charnockitic gneisses are the dominant rock type of the area. Migmatite complex are the other major rock type, which is followed by gneiss and Khondalites. Migmatites and khondalites are seen in eastern side of the area. The laterites intercalated with charnockites are seen in south west side of the area which are highly productive for large diameter dugwells as in Chalissery, Parudur and Thrithala. Even though the thickness of laterite bed is high, the borewells are not 17

6 high yielding in Mannarkkad area. This situation is due to the massive nature of the bedrock formations. The wells that are drilled in valley fills along valley portion of hills and river banks are good zones for tapping groundwater. The coastal tract of the area at western part is composed by sand and silt. The clay bed which is followed by sand and silt in the sedimentary terrain is also a factor which affects the recharge capabilities of the area. Geology map of the study area is depicted in Figure 2.3. Figure 2.3 Geology Map of Study area 18

7 Table: 2.1 List of General Information of Palakkad District SI.No General Items Statistics 1 Geographical area (sq.km) 2 Tehsils Revenue villages Development Blocks 13 5 Municipalities 4 6 Panchayaths 90 7 Geomorphology Major Units Major drainage Physiographic Mid Land and High Land Bharathapuzha basin and Bhavani Puzha basin. The northern highland region (Attapady Block), remarkable for highly undulated nature, is noticed for moderate groundwater potential. Such area are composed by crystalline rocks but are fractured along NW-SE and NE-SW direction and borewells tapping from semi confined to confined aquifers. The crystalline rocks in Ambalapara and Ananganady are not fractured enough to support good yielding borewells and the development of groundwater extraction structures are not feasible in this region. 19

8 Table: 2.2 List of General Information of Thrissur District SI.No General Items Statistics 1 Geographical area (sq.km) Tehsils 5 3 Development Blocks 17 4 Municipalities 7 5 Panchayaths 97 6 Geomorphology Major Physiographic Units Major drainage Low Land, Mid Land and High Land Parts of Ponnani basin, Keecheri & Karuvannur basins (Kole lands) and part of Chalakudy basin. Table: 2.3 List of General Information of Malappuram District SI.No General Items Statistics 1 Geographical area 3550 (sq.km) 2 Tehsils 6 3 Revenue villages Development Blocks 14 5 Municipalities 5 6 Panchayaths Geomorphology Major Physiographic Units Major drainage Low Land, Mid Land and High Land Bharatha Puzha, Kadalundipuzha and Chaliyarpuzha basins 20

9 2.5 Geomorphology Physiographically the area can be divided into three parts viz, low land ( 8m - 60amsl) mid land (60m 600m amsl) and highland (above 600m amsl). The study area shows a slope towards the west direction. The elevation of the landforms varies from less than one meter to 2386 m amsl in the study area. Ponnani Taluk is a part of coastal plain and sandy alluvium is the major geologic formation of the area. Heavy sand deposits are formed at Ponnani sea mouth by the riverine action which causes lots of development in this region. Coastal dynamics of Ponnani is very active which influence the rate of erosion and accretion. The area between the coastal plain in the west and the high ranges in the east is occupied by midlands. This is the most prominent physiographic unit of this basin, which are important for locating groundwater. Flat topped hillock and valleys (filled with weathered soil and ridges) are the unique characterestics of those land forms. The valley region forms potential area for many types of agriculture crops like arecanut, paddy, vegetable, banana and coconut. Ottapalam and Pattambi Talukas are the good example for mid land region. Valley flats and laterite formations are the geomorphological features of midland area (Subin et al, 2012). Infilled valleys are composed of lateritic soil and alluvial sediments. The hill range of Silent Valley is unique for its geomorphologic set up. The structural cum denudational hills and plantation surface with escarpments are the landforms of north east side. The Anginda peak (2386 m) is the most elevated area of the region. Figure 2.4 shows the geomorphology of the area. 21

10 Figure 2.4. Geomorphology of the study area 22

CHAPTER 9 SUMMARY AND CONCLUSIONS

CHAPTER 9 SUMMARY AND CONCLUSIONS The following are the important conclusions and salient features of the present study. 1. The evaluation of groundwater potential is a prerequisite for any kind of planning