Vertically Integrated Hydraulic Conductivity: A New Parameter for Groundwater-Surface Water Analysis

Numerical modeling of groundwater-surface water interactions provides vital information necessary for determining the extent of nutrient transport, quantifying water budgets, and delineating zones of ecological support. The hydrologic data that drive these models are often collected at disparate scales and subsequently incorporated into numerical models through upscaling techniques such as piecewise constancy or geostatistical methods. However, these techniques either use basic interpolation methods, which often simplifies the system of interest, or utilize complex statistical methods that are computationally expensive, time consuming, and generate complex subsurface configurations. We propose a bulk parameter termed “vertically integrated hydraulic conductivity” (K_V), and defined as the depth-integrated resistance to fluid flow sensed at the groundwater-surface water interface, as an alternative to hydraulic conductivity when investigating vertical fluxes across the groundwater-surface water interface. This bulk parameter replaces complex subsurface configurations in situations dominated by vertical fluxes and where heterogeneity is not of primary importance. To demonstrate the utility of K_V, we extracted synthetic temperature time series data from a forward numerical model under a variety of scenarios and used those data to quantify vertical fluxes using the amplitude ratio method. These quantified vertical fluxes and the applied hydraulic head gradient were subsequently input into Darcy's Law and used to quantify K_V. This K_V was then directly compared to the equivalent hydraulic conductivity (K_T) assuming an infinitely extending layer. Vertically integrated hydraulic conductivity allows for more accurate and robust flow modeling across the groundwater-surface water interface in instances where complex heterogeneities are not of primary concern.     

Quantifying groundwater–surface water interactions in a proglacial valley,Cordillera Blanca,Peru

A myriad of downstream communities and industries rely on streams fed by both groundwater discharge and glacier meltwater draining the Cordillera Blanca, Northern Peruvian Andes, which contains the highest density of glaciers in the tropics. During the dry season, approximately half the discharge in the region's proglacial streams comes from groundwater. However, because of the remote and difficult access to the region, there are few field methods that are effective at the reach scale to identify the spatial distribution of groundwater discharge. An energy balance model, Rhodamine WT dye tracing, and high‐definition kite‐borne imagery were used to determine gross and net groundwater inputs to a 4‐km reach of the Quilcay River in Huascaran National Park, Peru. The HFLUX computer programme ( http://hydrology.syr.edu/hflux.html ) was used to simulate the Quilcay River's energy balance using stream temperature observations, meteorological measurements, and kite‐borne areal photography. Inference from the model indicates 29% of stream discharge at the reach outlet was contributed by groundwater discharge over the study section. Rhodamine WT dye tracing results, coupled with the energy balance, show that approximately 49% of stream water is exchanged (no net gain) with the subsurface as gross gains and losses. The results suggest that gross gains from groundwater are largest in a moraine subreach but because of large gross losses, net gains are larger in the meadow subreaches. These insights into pathways of groundwater–surface water interaction can be applied to improve hydrological modelling in proglacial catchments throughout South America. Copyright © 2016 John Wiley & Sons, Ltd.