Influence of bank slope on sinuosity-driven hyporheic exchange flow and residence time distribution during a dynamic flood event
Abstract. This study uses a reduced-order two-dimensional (2-D) horizontal model to investigate the influence of riverbank slope on the bank storage and sinuosity-driven hyporheic exchange flux (HEF) along sloping alluvial riverbanks during a transient flood event. The Deformed Geometry Method (DGM) is applied to quantify the displacement of the sediment-water interface (SWI) along the sloping riverbank during river stage fluctuation. This new model approach serves as the initial step to consider complicated floodplain morphologies in physics-based models for better predictions of HEF. Several controlling factors, including sinuosity, alluvial valley slope, and river flow advective forcing and duration of flow are incorporated in the model to investigate the effects of bank slope in aquifers of variable hydraulic transmissivity. Compared to simulations of a vertical riverbank, sloping riverbanks were found to increase the HEF. For sloping riverbanks, the hyporheic zone (HZ) encompassed a larger area and penetrated deeper into the alluvial aquifer, especially in aquifers with smaller transmissivity (i.e., larger aquifer hydraulic conductivity or smaller specific yield). Furthermore, consideration of sloping banks as compared to a vertical river bank can lead to both underestimation or overestimation of the pore water residence time. The impact of bank slope on residence time was more pronounced during a flood event for high transmissivity aquifer conditions, while it had a long-lasting influence after the flood event in lower transmissivity aquifers. Consequently, this decreases the residence time of HEF relative to the base flow condition. These findings highlight the need for (re)consideration of the importance of more complex riverbank morphology as control of hyporheic exchange in alluvial aquifers. The results have potential implications for river management and restoration and the management of river and groundwater pollution.
Yiming Li et al.
Status: open (extended)
- RC1: 'Comment on hess-2023-29', Anonymous Referee #1, 29 May 2023 reply
Yiming Li et al.
Yiming Li et al.
Viewed (geographical distribution)
The authors present an interesting modelling exercise on hyporheic exchange between river water and groundwater as function of river bank slope. This is an overlooked variable but highly relevant in the outer world. I made many remarks in the manuscript itself that are major to minor. My major overall concern is that the RESULTS chapter is a very, very hard read. It repeatedly took me two times reading to understand the meaning of sentences or text parts. This is largely due to the fact that the authors use the symbols and abbreviations instead of the hydrological terms. I therefore ask for a complete rewriting of this chapter where the features observed are explained in terms of hydrological processes. Attention should also be paid to the related figures and their captions as these are hard to grasp, too. I did make less small remarks in this chapter for this reason.
The DISCUSSION chapter is meagre. The authors do not convince that slope is an important attribute when it comes to associated biogeochemical processes. The authors should provide some examples to illustrate this. They may also realise that many drinking water abstractions are situated in alluvial valleys of hilly or mountainous catchments. What does this mean and what is the impact of an abstraction? This is worth to be discussed under this chapter.
Another topic is whether the authors deal with phreatic or confined aquifers when it comes to propagation of hydraulic pressure. This makes a big difference and is relevant in the field but not addressed at all. I also ask them to discuss the other case in the DISCUSSION chapter (in terms of differences and similarities).