Event-Driven Hyporheic Exchange during Single and Seasonal Rainfall in a Gaining Stream
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Event-Driven Hyporheic Exchange during Single and Seasonal Rainfall in a Gaining Stream Chengpeng Lu 1 & Keyan Ji 1 & Yong Zhang 2 & Jan H. Fleckenstein 3 & Chunmiao Zheng 4 & Kate Salsky 2 Received: 2 April 2020 / Accepted: 17 September 2020/ # Springer Nature B.V. 2020
Abstract
This study combined a reach-scale field survey and numerical modelling analysis to reveal the pattern of transient hyporheic exchange driven by rainfall events in the Zhongtian River, Southeast China. Field observations revealed hydrodynamic properties and flux variations in surface water (SW)/ groundwater (GW), suggesting that the regional groundwater recharged the study reach. A two-step numerical modelling procedure, including a hydraulic surface flow model and a groundwater flow model, was then used to interpret the transient hyporheic flow system. The hyporheic exchange exhibited strong temporal evolution in the study reach, as indicated by the rainfall event-driven hyporheic exchange. The reversal of the hydraulic gradient and transient hyporheic exchange were simulated using numerical simulation. Anisotropic hydraulic conductivity is the key to generating transient hyporheic exchange. A revised conceptual model was used to interpret the observed temporal patterns in hyporheic exchange. The seasonal rainfall events generate transient hyporheic exchange, and the pattern of transient hyporheic exchange indicates that transient hyporheic exchange appears only after an increased phase of the river stage but does not last long. The temporal pattern of hyporheic exchange can significantly affect the hydrodynamic exchange and the evolution of hydrology in the hyporheic zone for a gaining stream, and these results have important guiding significance for the comprehensive management of surface water and groundwater quantity and quality. Keywords Hyporheic exchange . Rainfall . Transient process . Hydraulic gradient reversal . Gaining stream
* Chengpeng Lu [email protected] * Yong Zhang [email protected] Extended author information available on the last page of the article
Lu C. et al.
1 Introduction Hyporheic exchange (HE), referring to the water from a stream that enters the hyporheic zone (HZ) and then returns to the stream, is driven by hydraulic gradients at the streambed surface, which evolve from the interplay between streambed pressure distributions caused by the interactions among surface water (SW) hydraulics, streambed morphology, and ambient groundwater (GW) heads (Cardenas and Wilson 2007; Trauth et al. 2013). Here, HE is broadly defined as any kind of flow in the HZ affected by the dynamic interplay between SW and GW (Han and Endreny 2014). Moreover, hyporheic flow dynamics and flow paths may be affected by stage variations (Gerecht et al. 2011), wood addition in the channel (Sawyer and Cardenas 2012), and hydraulic jumps (Endreny et al. 2011a, b; Trauth et al. 2013). There has been a recent focus on understanding spatial variability in HE across different morphological units, mainly under steady baseflow conditions (Bu
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