Distributed groundwater recharge potentials assessment based on GIS model and its dynamics in the crystalline rocks of South India

Extensive change in land use, climate, and over-exploitation of groundwater has increased pressure on aquifers, especially in the case of crystalline rocks throughout the world. To support sustainability in groundwater management require proper understating of groundwater dynamics and recharge potential. GIS based studies have gained immense popularity in groundwater exploration in recent years because they are fast and provide recent information on the resource for future growth. Thus, the present study utilized a GIS-based Weighted Overlay Index (WOI) model to identify the potential recharge zones and to gain deep knowledge of groundwater dynamics. The in situ infiltration tests have been carried out, which is the key process in groundwater recharge and is neglected in many cases for WOI. In the WOI, ten thematic layers from the parameters influencing and involved in the recharge process are considered to identify potential recharge zones. The results suggested a significant underestimation of recharge potential without considering site-specific infiltration rates that one needs to be considered. The present WOI model considered in situ infiltration information and classified the entire area into four recharge zones, good, moderate, poor, and very poor. The final integrated map compared with the real-time field data like water level fluctuation and infiltration to analyse occurrence and quantification of recharge. The estimated average groundwater draft is 21.9 mcm, while annual renewable recharge is only 5.7 mcm that causing a continuous fall of the groundwater table. The study is useful in selecting regions with more focussed recharge studies and suggested the need of reducing groundwater demand by changing cropping patterns through a predictive decision support tool.

Barrier island groundwater dynamics

Nearly 1.5 million people inhabit barrier islands along the U.S. Atlantic and Gulf Coasts and coastal groundwater dynamics influence the availability of freshwater, ecosystem health, pollutant transport, and flooding in these densely populated communities. However, groundwater dynamics, including the aquifer head distribution and subsurface salinity structure, in coastal aquifers are affected by multiple environmental forcings, such as waves, tides, storm surges, and precipitation that act on a variety of spatial and temporal scales, making coastal groundwater dynamics complex and difficult to predict. Here, measurements of groundwater heads, salinities, and temperatures collected for 3 years across a 550-m-wide barrier island are used in conjunction with observations of ocean tides, surge, waves, sound level, and rainfall to characterize the dynamics of the surface aquifer. Infiltration from surge, tides, and waves during storms caused up to 2 m increases in the groundwater level under the dune. The head gradients owing to these storm-induced groundwater bulges suggest flows become inland directed on the ocean-side of the island during storms. An upper saline plume (20-30 PSU) was observed above fresher (10 PSU) water up to 30 m inland of the dune face, which was the maximum wave runup location. Differences in inland propagation between tidal- and storm-induced groundwater head fluctuations are explained using analytical theories for intermediate depth aquifers. Additionally, a separate analytical water-table evolution model driven with estimated ocean shoreline water levels (based on the 36-hr-averaged offshore tide, surge, and wave height) and measured precipitation is validated by citizen-science flood reports and predicts the maximum water-table height within 0.1 m of the observed levels across the barrier island.