P. Seralathan

Application of remote sensing and GIS for the demarcation of groundwater potential zones of a river basin in Kerala, southwest coast of India

An integrated hydrogeological investigation has been made to delineate the groundwater‐potential zones of the Muvattupuzha river basin, Kerala, along the southwest coast of India. The basin is characterized by charnockites and gneisses of Archean age covering more than 80% of the area and the remaining by Pleistocene laterites and Miocene formation. The basin receives high rainfall, measuring 3100 mm/year. However, acute water shortage occurs during the premonsoon season and hence, a number of dug wells are made to tap the groundwater. Seasonal rainfall during NE and SW monsoons is the major source of groundwater recharge. Further, hydrogeomorphology, geology, fracture systems and the slope of the terrain also play a significant role on the movement and behaviour of the groundwater of this basin. The integration of conventional and remote sensing data has been made through geographic information system (GIS) and it is found that about 50% of the area can be identified as very good or good potential zones, whereas the remaining area falls under moderate and poor categories. Most of the Muvattupuzha sub‐basin and the western part of the Kothamangalam and Kaliyar sub‐basins are classified as good groundwater‐potential zones, although the eastern upstream part of the basin has poor groundwater potential.

Change Detection Studies of Sagar Island, India, using Indian Remote Sensing Satellite 1C Linear Imaging Self-Scan Sensor III Data

Abstract The coastal zone of Sagar Island, India, is subjected to various cyclic and random processes that continuously modify the region. The shoreline and land-use/land cover changes have been studied using Indian Remote Sensing Satellite 1C (IRS IC) linear imaging self-scan sensor (LISS) III satellite data from 1998 and 1999. A comparison between a topomap of 1967 and satellite data of 1999 established that during these years about 29.8 km of coastline was eroded, whereas the accretion is only 6.03 km2. A comparison of satellite data from 1998 and 1999 showed that the island had undergone severe erosion of about 3.26 km2, while the accretion was just about 0.08 km2. Change detection studies based on land-use patterns of the region revealed that the areal extent of mangrove vegetation of the island during 1998 and 1999 was 2.1 km2 and 1.3 km2, respectively. The areal extent of agricultural fields during these periods was 130.4 km2 and 118.6 km2, respectively. These results can be used to develop an index for temporal land-use changes in the region as an aid to quantify the extent and nature of the development change and to understand the surrounding environment, which in turn may help the planning agencies to develop sound and sustainable land-use practices.

Identification of groundwater prospective zones using irs-id liss iii and pump test methods

The role of hydrogeomorphological units and lineaments in the storage of groundwater from the Muvattupuzha river basin has been investigated using IRS ID LISS III data. Other than the usual water bodies such as river course, reservoirs and ponds, the major hydrogeomorphological units identified in this basin in the descending order of their groundwater potential are: valley fills, moderately dissected plateau, pediments, residual mounts, residual mount complex, linear ridges, residual hills and structural hills. Majority of the lineaments trends in NW-SE and WNW-ESE directions. Even though the eastern part of the basin is characterised by moderate to high lineament density, the above area is found to be poor to moderate groundwater prospect zone because of high gradient and structural hills. The pump test analyses of dug wells from different hydrogeomorphic units also confirm that valley fills are the most promising unit for groundwater prospecting than the rest.

Hydrochemistry and dissolved nutrient flux of two small catchment rivers, south-western India

This paper deals with the water chemistry and dissolved nutrient flux of two small mountainous and heavily dammed rivers—Periyar and Chalakudy—of Kerala on the south-west coast of India. The lower reaches of these rivers are affected by sea-water ingression from the Arabian Sea during the non-monsoon season. Human interference through agriculture, urbanization, and industrialization in the lower and middle stretches of the river basins induces marked concentration variations in the hydro-chemical parameters. Except for N & P, all other chemical constituents exhibit high values during the non-monsoon season. Industrial contaminants in specific locations of the Periyar river reduce the pH to lower levels. Nutrients in the two rivers reveal marked seasonal and regional concentration variations. During the monsoon season, dissolved inorganic nitrogen (DIN) predominates over dissolved organic nitrogen (DON), but the reverse trend is observed during the non-monsoon season. The Periyar river shows higher average concentrations of DIN (monsoon 801 μg l−1 and non-monsoon 292 μg l−1) than Chalakudy river (monsoon 478 μg l−1 and non-monsoon 130 μg l−1). Dissolved inorganic phosphorus (DIP) has lower average values in the monsoon season (Periyar river, 38 μg l−1; Chalakudy river, 42 μg l−1) than dissolved organic phosphorus (DOP) values (Periyar river, 107 μg l−1; Chalakudy, 62 μg l−1). The rivers show a marked difference in nutrient flux due to its difference in water discharge/basin characteristics and point/non-point sources of contaminants. The flux rates of DIN, DIP, and DOP during the monsoon are higher than during the non-monsoon season, while those of dissolved silicon (DSi), dissolved Fe (DFe), and DON are lower. On average, the Periyar river discharges 4953 t y−1 of DIN and 1626 t y−1 of DON to the coastal waters, and the corres-ponding values of the Chalakudy river are 772 t y−1 and 596 t y−1. The Periyar and Chalakudy rivers discharge 245 t y −1 and 70.8 t y−1 of DIP, respectively. The total flux of DOP is considerably higher (Periyar river 703 t y−1 and Chalakudy river 101 t y−1). The discharge of DSi into the Periyar river (40 193 t y−1) is nearly five times higher than that in the Chalakudy river (8275 t y−1). The discharges of DFe through the Periyar and Chalakudy rivers are 257 t y−1 and 36.7 t y−1, respectively. To sum up, this study addresses the water quality and nutrient flux of two tropical rivers and discusses the impact of urbanization and industrialization on river-water quality.

Geochemistry of Fe and Mn in surficial sediments of a tropical river and estuary, India—a granulometric approach

Geochemical characteristics of Fe and Mn in sand, silt, and clay fractions as well as in bulk sediments of the tropical perennial Muvattupuzha river and the Central Vembanad estuary of the southwest coast of India have been studied and discussed. The results of a physical fractionation study of Fe and Mn indicated a substantial increase in the content of these metals in silt and clay fractions above that in sand. The riverine silt and clay fractions account for two to three times the enrichment of Fe and Mn than the corresponding sand fraction; the estuarine counterparts indicate four to eight times the enrichment. The observed enrichment of Fe and Mn towards the more finer size grades is mainly due to the increased surface area of the finer clastics, which in turn increase the absorptive ability. However, the mineralogical diversities of the three size fractions also influence the enrichment of Fe and Mn. The spatial distribution of Fe and Mn indicates a marked decrease in the content of the latter than the former towards the high saline zones of the river and the estuary. This variation could be due to the higher solubility of Mn towards the high saline zones of the aquatic environment where reducing condition prevails most of the year.

Seasonal Variations in Groundwater Chemistry of a Phreatic Coastal and Crystalline Terrain of Central Kerala, India

This article investigates the seasonal variation in geochemical characteristics of groundwater in phreatic aquifers of the coastal plain and crystalline terrain of central Kerala, India. Within the coastal plain, the western barrier island area shows values of electrical conductivity (EC, > 3 times), Na+, K+, Cl− (four times), Mg2+ (10 times), Ca2+ (two times), and HCO3 −+ CO3 2− (approximately two times) higher than those of the eastern coastal plain during both seasons. In contrast, pH and SO4 2− concentrations showed little variation. The alkaline nature and high EC of groundwater in the western barrier island–coastal plain is found to result from the intrusion of saltwater from the adjacent Vembanad estuary. In contrast, groundwater of the crystalline terrain is found to be slightly acidic with low EC. Within the crystalline terrain, the area east of Muvattupuzha River showed high EC values during both seasons while other parameters showed marginal variation. The trilinear diagram reveals that most of the groundwater samples from the crystalline terrain, which is of type IV (Ca2+–Mg2+–Cl−–SO4 2−) during the premonsoon period, changed character to type II (Na+–K+–Ca2+–HCO3 −) during the postmonsoon period. This shift is possibly caused by the addition of Na+ and HCO3 through the leaching of the country rock. Results for the western barrier island reveals that most of the samples are affected by the saline water incursion. Fecal contamination is found to be comparatively high in the groundwater of the coastal plain versus that of the crystalline terrain. This study indicates that the groundwater from the crystalline terrain is of higher quality than that of the coastal plain. The study further reveals the need for seasonal or multi-seasonal sampling when a geochemical characterization is performed and the recognition of physical events, such as heavy precipitation or droughts, when interpreting the geochemical characteristics of an aquifer.

VERTICAL ELECTRICAL SOUNDINGS FOR DELINEATION OF GROUNDWATER PROSPECT ZONE IN A CRYSTALLINE TERRAINS OF THE MUVATTUPUZHA RIVER BASIN, KERALA, INDIA

ABSTRACT The Muvattupuzha basin is characterised by lateritic capping followed by weathered/fractured rock and hard bedrock consisting of Pre-Cambrian and Archean gneisses. Groundwater in the Muvattupuzha river basin occurs under water table conditions in latentes and semi-confined to confined conditions in fractured crystalline. Vertical Electrical Soundings (VES) were conducted in the four sub basins of the Muvattupuzha (Muvattupuzha, Kothamangalam, Kaliyar and Thodupuzha) and the results were analysed qualitatively and quantitatively using both geological and hydrogeological information so as to demarcate potential groundwater zone in the phreatic aquifer and a few promising zone for putting medium to deep bore wells. It is found that among four sub basins, a large area of the Muvattupuzha sub basin is characterised by good to moderate phreatic groundwater potential zone while the rest of the basin fall under the category of poor to moderate. Certain promising sounding stations are identified in the basin for tapping groundwater from the third and fourth layers by putting medium to deep bore wells.

Assessment of groundwater quality in Kavaratti Island in the Lakshadweep Archipelagos, India

This study attempts to address the processes controlling the chemical composition of the Kavaratti aquifer system of Lakshadweep Island in India. Major ions and other physico-chemical parameters were determined for the premonsoon period in the Kavaratti of the Lakshadweep Island system. The trilinear diagram confirms the ingress of sea water into the shallow lens of freshwater in the islands by the changing water types. The abundance of major cations varied in the order Na>Ca>Mg>K and anions in the order Cl>HCO3>SO4. The ionic relations suggest that the higher concentration Na and Cl are the results of ion exchange and evaporation. The plots of data on the Gibbs diagram suggest that chemical weathering of rock-forming minerals and evaporation are the dominant factors controlling groundwater chemistry in the area. The hydrochemistry concept was deduced by the multivariate analysis for better understanding on the dynamic and complexity of the groundwater chemical processes. By the multivariate analytical techniques, the samples were grouped into two: one with saline water dominance and the other with freshwater characteristics. Thus proper management of these aquifers should be assured to retain their freshwater yield in the future.