Sabu Joseph

Morphometrical analysis of two tropical mountain river basins of contrasting environmental settings, the southern Western Ghats, India

The morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale. A morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining, mountain river basins of the southern Western Ghats, India, Muthirapuzha River Basin (MRB) in the western slopes and Pambar River Basin (PRB) in the eastern slopes. The basins, forming a part of the Proterozoic, high-grade, Southern Granulite Terrain of the Peninsular India, are carved out of a terrain dominantly made of granite- and hornblende-biotite gneisses. The Western Ghats, forming the basin divide, significantly influences the regional climate (i.e., humid climate in MRB, while semi-arid in PRB). The Survey of India topographic maps (1:50,000) and Shuttle Radar Topographic Mission digital elevation data were used as the base for delineation and analysis. Both river basins are of 6th order and comparable in basin geometry. The drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements. The Rb of either basins failed to highlight the structural controls on drainage organization, which might be a result of the elongated basin shape. The irregular trends in Rb between various stream orders suggest the influence of geology and relief on drainage branching. The Dd values designate the basins as moderate- to well-drained with lower infiltration rates. The overall increasing trend of Rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic Ihyp values. The Re values imply an elongate shape for both MRB and PRB and subsequently lower vulnerability to flash floods and hence, easier flood management. The relatively higher Rr of PRB is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes. Further, the derivatives of digital elevation data (slope, aspect, topographic wetness index, and stream power index), showing significant differences between MRB and PRB, are useful in soil conservation plans. The study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate.

Environmental status of a tropical lake system

Eutrophication has become a serious threat to the lake systems all over the world. This is mainly due to the pollution caused by anthropogenic activities. Carlson trophic state index (CTSI) is commonly used for the classification of trophic conditions of surface waters. The study is conducted to assess the trophic status of a tropical lake (Akkulam–Veli lake, Kerala, India) using CTSI based on Secchi disc depth (SD), total phosphorus (TP) and chlorophyll-a. The TSI values based on SD and TP are high (>70), indicating the hypereutrophic state which needs urgent action for the restoration of the fragile ecosystem. The higher TP in both lakes, and the lower value of chlorophyll-a in the Akkulam part, warrant explanation, are discussed here. The influence of other biochemical parameters in both the Akkulam and the Veli part of the lake has been assessed. Correlation analysis is conducted to study the effect of various water quality parameters. The variation in the water quality before and after the opening of sand bar is studied using paired t test. As almost all the lakes in the world are experiencing similar situation of extinction, this study is helpful to have an insight in the hydrochemistry of the lake as well as to identify the worst affected areas of the lakes.

Trophic state index of a lake system using IRS (P6-LISS III) satellite imagery

Water pollution has now become a major threat to the existence of living beings and water quality monitoring is an effective step towards the restoration of water quality. Lakes are versatile ecosystems and their eutrophication is a serious problem. Carlson Trophic State Index (CTSI) provides an insight into the trophic condition of a lake. CTSI has been modified for the study area and is used in this study. Satellite imagery analysis now plays a prominent role in the quick assessment of water quality in a vast area. This study is an attempt to assess the trophic state index based on secchi disk depth and chlorophyll a of a lake system (Akkulam–Veli lake, Kerala, India) using Indian Remote Sensing (IRS) P6 LISS III imagery. Field data were collected on the date of the overpass of the satellite. Multiple regression equation is found to yield superior results than the simple regression equations using spectral ratios and radiance from the individual bands, for the prediction of trophic state index from satellite imagery. The trophic state index based on secchi disk depth, derived from the satellite imagery, provides an accurate prediction of the trophic status of the lake. IRS P6-LISS III imagery can be effectively used for the assessment of the trophic condition of a lake system.

Morphometric aspects of a small tropical mountain river system, the southern Western Ghats, India

Abstract The Muthirapuzha watershed (MW) is one among the major tributaries of Periyar – the longest west flowing river in Kerala, India. A morphometric analysis was carried out to determine the spatial variations in the drainage characteristics of MW and its 14 fourth order sub-watersheds (SW1–SW14) using Survey of India topographic maps and Landsat ETM+ imagery. The study revealed that the watershed includes a sixth order stream and lower order streams dominate the basin. Results did indicate that rainfall has a significant role in the drainage development whereas structure and relief of rocks dictate the drainage pattern. The asymmetry in the drainage distribution is correlated with the tectonic history of the Munnar plateau in the late Paleocene age. The watershed is moderate to well-drained and exhibited a geomorphic maturity in its physiographic development. The shape parameters revealed the elongated nature of MW and drainage network development in the watershed. Further, the analysis provided significant insight into the terrain characteristics. This study strongly brings to light, (a) the tendency of the watershed to soil loss and (b) the hydrological makeup of the sub-watersheds, which combined helped to formulate a comprehensive watershed management plan.

Influence of lake morphology on water quality

Lakes are seriously affected due to urban pollution. The study of the morphological features of a lake system helps to identify its environmental status. The objective of the present study is to analyse the influence of morphometry on water quality in a lake (Akkulam–Veli Lake, Thiruvananthapuram, Kerala). The morphological features namely mean depth, surface area, volume, shoreline length, shoreline development and index of basin permanence have been evaluated. Correlation analysis has been conducted to determine the relationship between morphological features and water quality. Regression analysis has been conducted to find out the extent of influence of morphometric features on water quality. The study revealed that the lake is less affected by wind-induced wave action due to various reasons. The depth and volume have significant role in the water quality. The nitrogen fixation of blue green algae can be observed from the morphological features. The morphology has greater role in the water quality of a lake system.

Computation of physical characteristics of a lake system using IRS P6 (LISS-III) imagery

Abstract Lakes are versatile ecosystems and they are under the threat of eutrophication and siltation. The physical characteristics of a lake provide some insight into the status of the lake. Satellite imagery analysis now plays a prominent role in the quick assessment of characteristics of a lake system in a vast area. This study is an attempt to assess the water temperature, depth, and turbidity level of a lake system (Akkulam–Veli lake, Kerala, India) using IRS P6–LISS-III imagery. Field data were collected on the date of the overpass of the satellite. For the assessment of water temperature from satellite imagery, regression equation using spectral ratio (green/red bands) is found to yield superior results than the simple regression equation and multiple regression equation. For predicting the water depth, radiance in green and red bands can be used whereas that for turbidity, radiance in green and SWIR can be used. IRS P6–LISS-III imagery can be effectively used for the assessment of the physical characteristics of a lake system at a low cost.

Land use and land cover changes over a century (1914–2007) in the Neyyar River Basin, Kerala: a remote sensing and GIS approach

Abstract Land use and land cover change, perhaps the most significant anthropogenic disturbance to the environment, mainly due to rapid urbanization/industrialization and large scale agricultural activities. In this paper, an attempt has been made to appraise land use/land cover changes over a century (1914–2007) in the Neyyar River Basin (L=56 km; Area = 483.4 km2) in southern Kerala – a biodiversity hot spot in Peninsular India. In this study, digital remote sensing data of the Indian Remote Sensing satellite series I-D (LISS III, 2006–2007) on 1:50,000 scale, Survey of India (SOI) toposheet of 1914 (1:63,360) and 1967 (1:50,000) have been utilized to map various land use/land cover changes. Maps of different periods have been registered and resampled to similar geographic coordinates using ERDAS Imagine 9.0. The most notable changes include decreases in areas of paddy cultivation, mixed crops, scrub lands and evergreen forests, and increases in built-up areas, rubber plantations, dense mixed forests, and water bodies. Further, large scale exploitation of flood plain mud and river sand have reached menacing proportions leading to bank caving and cut offs at channel bends. Conservation of land and water resources forms an important aspect of ecosystem management in the basin.

Discriminant analysis for characterization of hydrochemistry of two mountain river basins of contrasting climates in the southern Western Ghats, India

Discriminant analysis (DA) was performed on river hydrochemistry data for three seasons (i.e., monsoon (MON), post-monsoon (POM), and pre-monsoon (PRM)) to examine the spatio-temporal hydrochemical variability of two mountain river basins (Muthirapuzha River Basin (MRB) and Pambar River Basin (PRB)) of the southern Western Ghats, India. Although the river basins drain tropical mountainous terrain, climate and degree of anthropogenic disturbances show significant differences (i.e., humid, more disturbed MRB vs semiarid, less disturbed PRB). In MRB, TDS, Na+, pH, Mg2+, and K+ are the attributes responsible for significant hydrochemical variations between the seasons, while Cl−, TH, and Na+ are the predictors in PRB. The temporal discriminant models imply the importance of rainfall pattern, relative contribution of groundwater toward stream discharge and farming activities in hydrochemistry between the seasons. Inclusion of hydrochemical attributes (in the temporal discriminant functions) that can be derived from both natural and anthropogenic sources suggests that ionic enrichment strongly depends on the seasons, and is mainly due to the variability in the intensity of anthropogenic activities as well as fluctuations in river discharge. In spatial discriminant models, Cl− is the only variable responsible for hydrochemical variations between the basins (during MON), whereas Si discriminates during POM and PRM, implying the role of atmospheric supply, anthropogenic modifications as well as intensity of weathering. In the spatial discrimination models, misclassification of hydrochemistry data between MRB and PRB can be attributed to the overlapping effect of humid climate of MRB extending toward the upstream of (semiarid) PRB. This study underscores the versatility of DA in deciphering the significance of climatic controls on hydrochemical composition of tropical mountain rivers.

Hydrogeochemical Drivers and Processes Controlling Solute Chemistry of Two Mountain River Basins of Contrasting Climates in the Southern Western Ghats, India

Water samples were collected from two mountain rivers of contrasting climates, viz., humid, Muthirapuzha River Basin (MRB) and semi-arid, Pambar River Basin (PRB) during monsoon (MON), post-monsoon (POM) and pre-monsoon (PRM) seasons, and were analyzed to understand the spatio-temporal variability as well as the sources and processes controlling hydrogeochemistry. In MRB and PRB, Ca2+ and Mg2+ dominate the cations, while Cl− dominates the anions in MRB and HCO3 − dominates the anions in PRB. PRB shows an elevated level of ionic abundance and higher degree of mineralization, due to multiple factors such as semi-aridity, discharge dominated by groundwater, lithological variations and the influences of carbonates and soil evaporites. However, K+, Cl− and H4SiO4 are relatively higher in MRB, implying significance of both anthropogenic activities and intense silicate weathering. The Ca2+ + Mg2+/HCO3 − ratios in MRB are also relatively larger than PRB, suggesting high intensity of anthropogenic influences in MRB. Downstream variation of hydrogeochemistry implies a general decreasing trend in MRB, which is attributed to dilution due to high discharge, whereas hydrogeochemistry of PRB shows an increasing downstream trend, by which, the significance of semi-arid climate of the downstream tracts of the basin is implied. Both MRB and PRB show temporal variability in hydrogeochemical attributes implying the role of monsoon rainfall determining stream water composition. The Na+-normalized Ca2+ versus Na+-normalized HCO3 − plots suggest the control exercised by mixing between silicate and carbonate end members in both the basins. However, in PRB, dissolution of soil evaporites during MON and POM is evident by relatively lower Ca2+/Na+ ratios. The Ca2+ + Mg2+/Na+ + K+ ratios in MRB and PRB during MON (mean = 1.96 and 2.23 in MRB and PRB respectively), POM (mean = 3.29 and 2.41) and PRM (mean = 5.74 and 4.40) also suggest sources other than silicate weathering. Relative enrichment of Cl− (with respect to Na+) indicates multiple sources for Cl− (i.e., anthropogenic as well as atmospheric). Even though there are significant differences in water types between MRB and PRB, most of the waters of both the basins are considered to be “transitional”. Relatively higher pCO2 in stream waters (compared to atmosphere) is observed and the phenomenon is attributed to the influent nature of the stream discharge (i.e., contributed by groundwater which is significantly enriched in CO2) and the slower rate of re-equilibration (i.e., solubility vs. release of CO2) with atmosphere. Hence, evidently the hydrogeochemical composition of MRB and PRB is jointly controlled by weathering of silicate and carbonate minerals as well as anthropogenic activities and is influenced by climatic seasonality. The spatio-temporal variability of hydrogeochemical attributes of MRB and PRB is mainly due to the variations in climate, lithology, hydrologic pathways and degree of various anthropogenic activities.

Assessment of soil erosion in a monsoon-dominated mountain river basin in India using RUSLE-SDR and AHP

ABSTRACT The long-term average annual soil loss (A) and sediment yield (SY) in a tropical monsoon-dominated river basin in the southern Western Ghats, India (Muthirapuzha River Basin, MRB; area: 271.75 km2), were predicted by coupling the Revised Universal Soil Loss Equation (RUSLE) and sediment delivery ratio (SDR) models. Moreover, the study also delineated soil erosion risk zones based on the soil erosion potential index (SEPI) using the analytic hierarchy process (AHP) technique. Mean A of the basin is 14.36 t ha−1 year−1, while mean SY is only 3.65 t ha−1 year−1. Although the land use/land cover types with human interference show relatively lower A compared to natural vegetation, their higher SDR values reflect the significance of anthropogenic activities in accelerated soil erosion. The soil erosion risk in the MRB is strongly controlled by slope, land use/land cover and relative relief, compared to geomorphology, drainage density, stream frequency and lineament frequency.