• ELANGO L

      Articles written in Journal of Earth System Science

    • Hydrogeochemical modelling to understand the surface water–groundwater interaction around a proposed uranium mining site

      Manoj S Thirumurugan M Elango L

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      The interaction between surface water and groundwater is a complex process and is considered as an important component for controlling the mining activities. The objective of this study is to understand the interaction between surface water and groundwater around a proposed uranium mining site by geochemical modelling. Surface water and groundwater samples along the groundwater flow path were collected from September 2013 to June 2016 across the uranium mineralised region located near Gogi, Karnataka, India. Collected water samples were analysed for major ion and uranium concentrations. This hydrochemical data was used as input in the geochemical modelling code PHREEQC to calculate the uranium speciation and saturation indices. Inverse geochemical modelling was performed along the flow direction by considering the mineralogical composition of host rock. Measurement of surface water and groundwater level indicates that the recharge and discharge of this region were primarily controlled by rainfall. Relation between the temporal variation of rainfall and saturation index of mineral reveals the various scenarios of interaction between surface water and groundwater around the mineralised region. Silicate/carbonate weathering, irrigation return flow and dissolution of evaporites are the major processes indicated by inverse geochemical modelling, which controls the hydrogeochemical evolution of water in this region. Geochemical modelling was effectively used to understand the temporal changes in the interaction between surface water and the groundwater in a uranium mineralised region.

    • Spatio-temporal analysis of rainfall, meteorological drought and response from a water supply reservoir in the megacity of Chennai, India

      ANANDHARUBAN P ELANGO L

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      Assessment of rainfall variability and drought is essential to address the existing water crisis and water resources management. This study was carried out to assess the rainfall variability, meteorological drought and relative response of a water supply reservoir located in Chennai Metropolitan, India. Spatial and temporal variation of rainfall and drought across the river basin was assessed using historical rainfall records from 1978 to 2016. A significant number of rainfall stations show increasing trends in post-monsoon and northeast monsoon. The annual rainfall is concentrated for less than six months and shows an irregular to strongly irregular distribution. The degree of variability in monthly rainfall reveals markedly seasonal with long dry periods. Three different drought indices such as rainfall deviation method, Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) were used and compared to identify the meteorological droughts. The duration of meteorological drought events in this region ranged from 3 to 9 months. Identified drought events reveal that the rainfall deficiency in the northeast monsoon causes most of the meteorological drought. The reservoir system has higher response and coherence with SPI at a higher time scale. So, SPI can be used to represent the hydrological drought in higher time scales. Hence, SPI is recommended as more appropriate for drought assessments for this region. The large scale atmospheric circulations have moderate impacts on drought events in this region. The outcomes of this study could be useful for better drought and water resources management.

      $\bf{Highlights}$

      $\bullet$ Chennai region has higher interannual rainfall variability and susceptible to droughts once in about four years.

      $\bullet$ About 44.44% of droughts in this region when India witnessed drought indicating large scale atmospheric circulations.

      $\bullet$ Deficiency in rainfall during both southwest and northeast monsoon increase the gap between water demand and supply.

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