Natural radioactivity distribution studies in Trivandrum district,Kerala, India

The distribution pattern of radioactive minerals in Trivandrum district of Kerala has been investigated. The surface radioactivity was measured employing a jeep-mounted four-channel gamma-ray spectrometer coupled to a high volume Na I (T1) crystal detector. The distribution of radioactivity has been correlated with the corresponding litho-units and major structures of the study area. The total countrate from sedimentaries including beach sands and pegmatite rich zones (～ 3,500 CPS) are significantly higher than that of the laterites and gneisses which are substantiated by laboratory studies.     

Estimating surface sensible heat flux using sodar and surface temperature measurements in the evolving convective boundary layer

A simple method is described for estimating the sensible heat flux by using a Doppler sodar system and a thermal probe. This method, which can be applied to a convective boundary layer in morning hours, is based on knowing the zero heat flux level from the reflectivity and the vertical wind speed.     

Geochemical characterization of groundwater from an arid region in India

A study on the geochemical processes in arid region of western India (Kachchh district) was carried out using major, minor, trace metal data and isotopic composition (δ²H, δ¹⁸O) of groundwaters. Results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments, dissolution of salts in root zone and incongruent dissolution of carbonate minerals. Common inorganic contaminants such as fluoride, nitrate and phosphate are within drinking water permissible limits. However, most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose. Trace metal data indicates no contamination from toxic elements such as arsenic and lead. An increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources. The chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition. Environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge. The processes responsible for observed brackishness are identified using chemical and isotope indicators, which are in agreement with subsurface lithology and hydrochemistry. These data though represent hydrochemical scenario of 2001 can still be used for understanding the long-term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models.     

Terrain characteristics and longitudinal,land use and land cover profiles behavior—a case study from Vamanapuram river basin,southern Kerala,India

The morphology of Vamanapuram river basin (VRB), southern Kerala, India has been studied by preparing longitudinal profiles from the source of VRB at Chemmunji Mottai (1,717 m) to its mouth at Muthalapallipozhy (Lakshadweep Sea). Survey of India topographical maps, Geocoded Satellite Imageries, Microsoft Excel and GIS software ILWIS 2.1 are used in this study. The morphometric analysis reveals that there are 1,489, 347, 79, 21, 6, 2 and 1 first-, second-, third-, fourth-, fifth-, sixth- and seventh-order streams, respectively, in VRB, which are responsible for the present-day landform genesis. The mean bifurcation value of VRB is 3.49. The Ponmudi hills receive the highest rainfall in VRB in the Western Ghats Region and Attingal, the lowest in the Coastal Strand Plain. The six land use and land cover profile sections show the distribution of land use–land cover with respect to elevation and depth to water level. The study reveals that mid and high lands generally occupy lower order streams up to fourth order and generally originate from linear ridge, hill crest, rocky slope (scarp face), side slope (S3)/slope 10–15° and hilly terrain.     

Geochemistry of Vellayani lake sediments: Indicators of weathering and provenance

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO₂, MnO, CaO, MgO, Na₂O, K₂O, and P₂O₅ content while TiO₂, Fe₂O₃ and Al₂O₃ are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO₂ is high in coarse fractions while Al₂O₃ is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area.     

On the structure of sea-breeze fronts observed near the coastline of Thumba,India

An investigation has been made of the structure of sea-breeze fronts observed at Thumba mostly during the months of December to April using data from a Doppler SODAR and in situ measurements of wind components, humidity and temperature. The study shows that the vertical wind structure observed in the SODAR height range provides a distinct signature of the passage of a front and that the intensity of the front is decided by the intensity and direction of the prevailing winds as well as the amount of rotation of the wind vector during the onset of the sea-breeze. Spectral analyses of vertical winds during the passage of the front reveal a dominant periodicity of about 6 min for strong sea-breeze fronts.