The impact of heterogeneity at various spatial locations on dune-induced hyporheic exchange

Abstract

The hyporheic exchange is not evenly influenced by heterogeneous hydraulic conductivity (K) values throughout the streambed. Few studies have investigated the impact of K heterogeneity in different regions of the streambed on the hyporheic exchange. This study employed a first-order stochastic analysis and a dislocation superposition method to examine the cross-correlation between hyporheic exchange flux (HEF) and K anywhere in synthetic, heterogeneous, 2-D cross-sectional streambed models. Results show that hyporheic exchange flux positively correlates with K heterogeneity in every part of the streambeds. This relationship provides a mechanistic explanation for the impact of high/low K zones on the HEF in the hyporheic zone. The effect of K impact on the HEF intensifies in streambeds when 1) upwelling groundwater flux increases, 2) the dunes are steep and asymmetric, or 3) the streambed is stratified. This study develops an empirical linear formula based on dune height and stoss length for estimating the high cross-correlation zone (HCZ) locations, potentially guiding the sampling scheme of hydraulic conductivities for evaluating the HEF in practical fieldwork.