Approximately 40% of the world's population faces water shortage. The situation is particularly challenging in subtropical karst areas with a pronounced dry season, where the lack of surface storage capacity and the difficulty of accessing groundwater cause serious seasonal supply shortages. Additionally, water resources in karst regions are highly vulnerable to contamination due to rapid infiltration and transport in the conduit network. Innovative and locally-adapted water resource protection strategies are therefore required in these regions.
Defining adequate water resource protection zones requires considering many hydrogeological factors. In large emphasized textand geologically heterogeneous catchments, large amounts of data are required. In remote and socio-economically weak regions, the necessary data is usually not available. To address these problems, we demonstrate a simplified approach to develop a pragmatic, sustainable drinking water supply protection plan for a karst catchment in the Dong Van region of Vietnam. This effort is part of the KaWaTech Solutions water resources project.
First, the catchment area was delineated by tracer tests. Next, we characterized microbiological contamination with faecal bacteria, and measured the particle-size distribution (PSD) at several sampling sites in the catchment. Based on these preliminary investigations, we selected a subset of locations – springs, swallow holes and surface runoff – to carry out high-resolution measurement campaigns to further characterize PSD, turbidity, total organic carbon (TOC), colored dissolved organic matter (CDOM) and E. coli concentration. Using these data, we determined flow velocities and were able to localize and characterize contamination hotspots in the catchment area. The results show three types of temporal water-quality variations: (i) seasonal variations, i.e. higher fecal bacteria levels in the rainy season than in the dry season; (ii) event-related variations caused by precipitation events; (iii) diurnal fluctuations in water quality at the principal drinking water abstraction site due to the release of untreated wastewater, especially in the morning and evening hours. The fluctuations of PSD, turbidity and TOC are correlated with each other. However, influx in the catchment area from homogeneously flowing springs with constant hydrochemical conditions minimizes and dampens the fluctuations.
Based on our investigations, we developed a plan to improve drinking water quality at the water pumping system. We focus on delineating catchment areas relevant for drinking water protection, and on building a hydrogeological model that can be used to develop a sustainable protection plan. Plans for future drinking water treatment and an early-warning system for spring water contamination will rely on our characterization of the highly variable particle load, as well as the microbial and hydrochemical water quality in the catchment and in the immediate inflow to the water pumping system.