A Cost-Effective Probe for High-Resolution Monitoring of Hyporheic Zone Dynamics

Surface water (SW) and groundwater (GW) interact with each other in almost all types of landscapes forming a hydrological continuum known as a hyporheic zone. Interest in these water exchanges has increased due to their impact on both resources. With changing climate and population growth, managing and understanding these exchanges becomes important as these have been strongly advocated to improve water quality.

Despite its importance, more standardized methods are needed. Traditional methods using chemical tracers or seepage meters are labour-intensive labor-intensive. Hence in recent times dependency on temperature as a tracer has gained significant attention. Different techniques and instruments have been developed to use temperature to detect these exchanges, which can collect sub-hourly data without human intervention. Whereas, these off-the-shelve instruments become expensive in the developing world context.  

Hence, to have repeated observations catering to the socio-economic conditions of a region. We sought to develop a cost-effective probe for determining flux rates in the hyporheic zone using open source system, which can be deployed with high spatiotemporal coverage (amounts to ~100$ (that includes a data-logger, waterproof sensors (as many are required), Real-time clock, etc.). The hybrid probe developed can measure Vertical Hydraulic Gradient (VHG) values and temperature values at required depths. The probe is designed in such a way that, depending on the site of installation and depth of interest the sensor on the probe could be customized.

The probe has been tested with HOBO Tidbit sensors (off-the-shelve) at an upwelling location of a meander bend section at a headwater stream in the mountainous region of the Indian Himalayas. The values from the developed instrumentation had a strong correlation (>0.85) with those from the HOBO Tidbit sensor, indicating the reliability and accuracy of the newly developed probe.

Additionally, the flux values derived from the probe data provide us with valuable insights into GW-SW interactions, especially in the unexplored Himalayan headwater catchments. The probe’s low cost enables micro-monitoring of field sites with additional instrumentation, allowing for the collection of spatially and temporally robust data, thereby enhancing our physical understanding of GW-SW interfaces.