Hydrogeologically controlled freshwater dynamics in the coastal sand dune aquifer of Ongole coast (AP), India

Abstract

A sand dune area,~50 km 2 in size, the only source of freshwater in the coastal zone of Prakasham district, Andhra Pradesh, India, is bounded by marine sediments in the northwest, and the Bay of Bengal in the southeast. Measurements of groundwater level, hydrochemistry and stable isotopes for three years facilitated the identification of the aquifer response to drought and intense cyclonic storms. There was no major change in hydrochemistry and isotope values between drought and highly saturated conditions, except in a few wells in the northwest. During drought, the groundwater remained fresh, although the levels dipped to 2-5 m b.m.s.l., signifying no saline water ingression (no measurable bromide). Based on the field observations, resistivity soundings, electrical conductivity and groundwater level change due to pumping, the existence of impermeable boundaries in the northwest and southeast are hypothesized. Thus, the existing hydrogeological settings appear to be inhibiting the movement of the freshwater-saline water interface into the freshwater zone.

Hydrogeochemical processes as a conditioner of freshwater lenses associated with coastal deposits

“…Recharge by rainwater infiltration generates a response in the phreatic aquifer evidenced by a rise in levels after rainfall (Carretero & Kruse, 2012; Reddy, 2013; Reddy et al, 2014; Rupert & Plummer, 2004). This phenomenon was recorded in sensors installed in the Coast‐D and BRs where water table rises (WT) occur immediately after precipitation (Figure 3a).…”

“…However, these fluctuations have also contributed to the formation of positive littoral geoforms, such as beach ridges generally with superimposed sand dunes (Kokot, 2010; Otvos, 2000; Tamura, 2012; Violante et al, 2001). These geoforms, due to their high permeability, facilitate the local rainwater infiltration (Greggio et al, 2018; Reddy et al, 2014; Stuyfzand, 2017; Zhang et al, 2020) leading to the development of freshwater lenses (Carol et al, 2021; Carol, García, & Borzi, 2015; Eeman et al, 2012). The development of freshwater lenses in coastal—marine environments also may be associated to island geoforms (White & Falkland, 2010) showing, in both cases (littoral and island), similar hydrogeological behaviour (Chesnaux & Allen, 2008).…”

Sustainable Land-Use Planning to Improve the Coastal Resilience of the Social-Ecological Landscape

“…Accordingly, it is anticipated that the structure of the agricultural industry area will collapse before the salinity of the groundwater begins to decrease (Figure 4, B4). resulting from reinforcing loops R4 and R5 increased the amount of water available for agricultural use while decreasing the amount of groundwater [54]. Such a continual decrease in the groundwater level will increase the salinity of the groundwater over the long run and will eventually create an inadequate environment for growing crops [55,56].…”