Modelling hyporheic processes for regulated rivers under transient hydrological and hydrogeological conditions

Abstract

Abstract. Understanding the effects of major hydrogeological controls on hyporheic exchange and bank storage is essential for river water management, groundwater abstraction, restoration and ecosystem sustainability. Analytical models cannot adequately represent complex settings with, for example, transient boundary conditions, varying geometry of surface water-groundwater interface, unsaturated and overland flow, etc. To understand the influence of parameters such as (1) sloping river banks, (2) varying hydraulic conductivity of the riverbed and (3) different river discharge wave scenarios on hyporheic exchange characteristics such as (a) bank storage, (b) return flows and (c) residence time, a 2-D hydrogeological conceptual model and, subsequently, an adequate numerical model were developed. The numerical model was calibrated against observations in the aquifer adjacent to the hydropower-regulated Lule River, northern Sweden, which has predominantly diurnal discharge fluctuations during summer and long-lasting discharge peaks during autumn and winter. Modelling results revealed that bank storage increased with river wave amplitude, wave duration and smaller slope of the river bank, while maximum exchange flux decreased with wave duration. When a homogeneous clogging layer covered the entire river-aquifer interface, hydraulic conductivity positively affected bank storage. The presence of a clogging layer with hydraulic conductivity < 0.001 m d −1 significantly reduced the exchange flows and virtually eliminated bank storage. The bank storage return/fill time ratio was positively related to wave amplitude and the hydraulic conductivity of the interface and negatively to wave duration and bank slope. Discharge oscillations with short duration and small amplitude decreased bank storage and, therefore, the hyporheic exchange, which has implications for solute fluxes, redox conditions and the potential of riverbeds as fish-spawning locations. Based on these results, river regulation strategies can be improved by considering the effect of certain wave event configurations on hyporheic exchange to ensure harmonious hydrogeochemical functioning of the river-aquifer interfaces and related ecosystems.

Groundwater flow, nutrient, and stable isotope dynamics in the parafluvial-hyporheic zone of the regulated Lower Colorado River (Texas, USA) over the course of a small flood

“…Gu et al (2012) showed that recurring floods with durations much longer than at the LCR, may introduce nitrate into the banks that eventually is denitrified. Their results are somewhat consistent with modeling studies showing that water and solutes may take a long time to get flushed from the PHZ, especially after higher amplitude and longer duration floods (Doble et al 2012;Siergieiev et al 2015). However, the results suggest that during the low-flow and small-pulse regime at the LCR, there is little mixing and that the water in the PHZ is mostly groundwater; any left-over river water that may have infiltrated from previous floods is no longer distinguishable beyond 2 m from the river.…”

Solute dynamics across the stream‐to‐riparian continuum under different flood waves

“…The width and height of the model were 200 and 20 m, respectively, with a 5‐m incised stream channel. Preliminary simulations indicated that the effect of water level variations on groundwater level was negligible at a distance of 200 m from the stream (Siergieiev et al, ; Welch et al, ). The aquifer was assumed to be homogeneous and isotropic in effective porosity and hydraulic conductivity.…”

“…The hyporheic process within a riparian zone is influenced by numerous factors, such as river water fluctuation (e.g., Siergieiev et al, ), aquifer properties (e.g., Chen & Chen, ), direction of ambient groundwater flow (e.g., Welch et al, ), and morphology features of the river–aquifer interface (e.g., Doble et al, ), in which the fluctuation of the river stage plays a critical role. Transient river stage fluctuation is widespread in natural river systems, and it is caused by diel snowmelt (e.g., Loheide & Lundquist, ), storms and storm events (e.g., Dudley‐Southern & Binley, ; Vidon et al, ), tides (e.g., Lenkopane et al, ), reservoir operations (Gerecht et al, ; Sawyer et al, ), and mountain floods (Constantz, ; Wondzell & Swanson, ).…”

“…Many numerical simulations have indicated that river water fluctuations increase the bank storage and infiltration distance of water particles (Chen & Chen, ; Doble et al, ; Gu et al, ; Maier & Howard, ; Welch et al, ; Welch, Cook, Harrington, & Robinson, ) and enable the retention of water particles within the aquifer for a long time (Diem et al, ; McCallum & Shanafield, ). The characteristics of hyporheic exchange in riparian zone under different flood conditions have also been investigated (e.g., Siergieiev et al, ; Welch et al, ). For example, Siergieiev et al () indicated that bank storage increases with wave amplitude and duration, and the return/fill time ratio (fill time is the time required for the bank storage to reach its maximum, whereas return time is the time between the maximum and zero bank storage on the falling limb) of a water particle is positively and negatively related to amplitude and duration, respectively.…”

“…The characteristics of hyporheic exchange in riparian zone under different flood conditions have also been investigated (e.g., Siergieiev et al, ; Welch et al, ). For example, Siergieiev et al () indicated that bank storage increases with wave amplitude and duration, and the return/fill time ratio (fill time is the time required for the bank storage to reach its maximum, whereas return time is the time between the maximum and zero bank storage on the falling limb) of a water particle is positively and negatively related to amplitude and duration, respectively.…”