Quantifying Groundwater-Surface Water Interactions with a Stream Energy Balance, Cordillera Blanca, Peru

English Abstract:

Communities and industries in the Cordillera Blanca mountain range, Northern Peruvian Andes, rely extensively on streams fed by both groundwater and glacier meltwater for water during the dry season. It is hypothesized that groundwater baseflow accounts for at least half of the overall stream discharge during the dry season. Heat tracing (energy balance) was used to determine groundwater advection to the stream. Data was collected along a 4 km reach of the Quilcayhuanca River, including meteorological observations, stream discharge, stream dimensions, groundwater temperature, shading and view to sky observations. Stream temperature was also recorded using thermochrons at 39 points along the stream for 4.9 days. Field data was used to determine boundary conditions for a numerical stream temperature model, HFLUX (http://hydrology.syr.edu/hflux.html). The model calculates all energy fluxes entering and leaving the stream, including solar radiation, advection of groundwater, evaporative heat flux, sensible heat flux, and streambed conduction. The model, which calculates a stream temperature profile through time, was calibrated to measured temperatures. A groundwater baseflow profile for the stream is derived from the calibrated model. It is observed that groundwater baseflow dampens diurnal temperature fluctuations and that, during most of the day, the groundwater temperature is warmer than the stream temperature. Model sensitivity analysis showed that the simulations were, in decreasing order, most sensitive to solar radiation, groundwater baseflow volume, and groundwater temperature. These results suggest that groundwater-surface water interactions in the Cordillera Blanca have a significant impact on the stream thermal regime system and that the stream energy balance may be a viable way to quantify groundwater contributions.