Estimation of hyporheic zone depth based on advective heat transfer and characterization of the surface water-groundwater mixing zone

Abstract

Surface water and groundwater can affect each other if they share a hyporheic zone, to either degrade or improve the water quality. Thehyporheic zone is a region where the mixing and exchange of surface water and groundwater occur actively due to the large chemical, biological, and hydraulic gradients. Therefore, various processes such as contaminant transport, degradation and transformation occur in the hyporheic zone.Due to the complexity and diversity of the underground medium, the delineation of the hyporheic zone isof vital importance for an integrated management of groundwater and surface water resources. Hyporheic zone is the region where mixing if surface water and groundwater occurs. In this study, it is defined as the section from streambed to the depth where the vertical component of fluid flux becomes zero. The depth of hyporheic zone was determined with numerical analysis using time series of temperatures below the streambed.This study introduced a new concept of streambed hyporheic zone velocity models. Based on this concept, this study delineated the hyporheic zone depth more quantitative than the existing research results. The methods of this study and the obtained results are sequentially focused on hydrological, biological, and chemical approaches to verify theproposed method.

1. Though the tracer test is somewhat challenging to determine the hyporheic zone depth using this best-fit, the hyporheic zone depth can be thought to be in the range of 2 and 30 cm, which is fairly comparable with the range (9-15 cm) of hyporheic zone depth from the proposed method using temperature analysis.The proposed method gives moreprecise range of the hyporheic zone depth. 2. The hyporheic zone was verified through biological approach. The effect of the flow direction of hyporheic flux determined from the proposed method on the bacterial community is examined. 3. Influence of hyporheic exchange patterns within the delineated hyporheic zone on bacterial diversity was estimated. Quantitative changes and characteristics of the hyporheic zone were analyzed to have an effect on the resident bacterial communities. 4. The hyporheiczone was verified through chemical approach. The chemical compositionsof groundwater, stream water, paddy water and hyporheic water areexamined.The chemical compositions of the hyporheic water reflect the history related to the recharge and discharge of the waters.