The effect of streamflow, ambient groundwater, and sediment anisotropy on hyporheic zone characteristics in alternate bars

The hyporheic exchange is the main driver for the biogeochemical transformations of nutrients within a river bed. The current study addresses the variations in hyporheic zone (HZ) characteristics in alternate bars due to different streamflow, ambient groundwater, and sediment anisotropy. Several simulations, using a sequentially coupled surface water‐groundwater model of a synthetic reach with fully developed alternate bars morphology, were performed. Two HZs exist within the streambed; a shallow zone that is more linked to surface water, and a deep one that is more influenced by the groundwater variations. Increasing streamflow, and therefore bar submergence, decreases the hyporheic flow. The residence times distribution is bimodal, which implies the existence of two HZs . This bimodality is enhanced by anisotropic sediment conditions, while it is much milder in isotropic ones. The shallow zone residence times increase when streamflow value rises, while the residence times in the deep HZ are less affected. The mean and median residence times decrease by increasing streamflow in partially submerged case, and they are larger in fully submerged case. The hyporheic flow, area, residence times, and extent decrease by increasing groundwater fluxes. The deep zone is the most affected by the groundwater fluxes. Hyporheic flow and extent values are significantly larger in isotropic conditions than in anisotropic ones. The change in residence times values is different between the deep and shallow zones. A predictive model is driven to predict the hyporheic flux, residence times, and hyporheic depths dependence on bar submergence, ambient groundwater, and sediment anisotropy

Effect of Combined Subsurface Structures and Steps on Hyporheic Exchange

The deployment of artificial structures in streambeds has been proposed as a way to enhance hyporheic exchange, and numerical models can be used to quantify their effects. In this study, combinations of different structures—that is, boxes, steps and a new type of subsurface structure (L-shaped structure)—were considered to evaluate their potential applicability on river restoration. Flow-3D and COMSOL were applied to simulate surface and subsurface flow, respectively. The performance of the structures was evaluated on the basis of hyporheic flow and residence time distributions. For the structure sizes here considered, results showed for steps (single step, combination of two steps) and L-shaped structures (single L-shaped structure, combination of two L-shaped structures) most hyporheic flowpaths return to the stream after 5 and 2.5 hr, respectively. Instead, shorter residence times (<0.25 hr) were found for boxes (single box, combination of two boxes). For combinations of steps and permeable boxes, the values of hyporheic flow per unit width are higher (0.35 and 0.3 m2/hr, respectively) than for the combination of L-shaped (0.06 m 2/hr). As a result, the combinations of steps and boxes are more effective in increasing hyporheic flow. However, when subsurface structures are combined with steps the resulting hyporheic exchange is dominated by the steps. Therefore, the combined use of in-stream and subsurface structures separately may increase their benefits for hyporheic exchange, but when steps are the other subsurface structures provide minor advantages

Role of the hyporheic zone in increasing the resilience of mountain streams facing intermittency

5openInternationalItalian coauthor/editorWe investigated the impact of intermittence in previously-perennial Alpine stream reaches, targeting the role of the hyporheic zone in increasing the resilience of these aquatic systems. We selected a perennial and an intermittent site in a reach of the Po River (North-Western Italy). We installed piezometers reaching −1 m (permanent and intermittent site), and −3 m (intermittent site) and monitored three supraseasonal droughts over a period of three years. We classified the hyporheic fauna into three categories of increasing affinity to life in the hyporheic (stygoxene, stygophile, stygobite), and used communities composition, abundance, beta-diversity and functional groups: (1) to compare assemblages at the same depth but with different hydrological characteristics, as well as assemblages from two depths at the intermittent site, and (2) to assess how the connection with surface water and the direction of the vertical aquifer flow determined the faunistic assemblages. Different taxonomic groups responded differently to intermittence, the hyporheic zone acted as a refuge increasing the resilience of the system, but resilience decreased with increasing degree of affinity to hyporheic life. Disentangling the effects of intermittence on the different faunistic component in the hyporheic zone can help guiding effective protection and restoration measures of river systems with temporary reaches.openBruno, M.C.; Doretto, A.; Boano, F.; Ridolfi, L.; Fenoglio, S.Bruno, M.C.; Doretto, A.; Boano, F.; Ridolfi, L.; Fenoglio, S

Role of the hyporheic zone in increasing the resilience of mountain streams facing intermittency

We investigated the impact of intermittence in previously-perennial Alpine stream reaches, targeting the role of the hyporheic zone in increasing the resilience of these aquatic systems. We selected a perennial and an intermittent site in a reach of the Po River (North-Western Italy). We installed piezometers reaching -1 m (permanent and intermittent site), and -3 m (intermittent site) and monitored three supraseasonal droughts over a period of three years. We classified the hyporheic fauna into three categories of increasing affinity to life in the hyporheic (stygoxene, stygophile, stygobite), and used communities composition, abundance, beta-diversity and functional groups: (1) to compare assemblages at the same depth but with different hydrological characteristics, as well as assemblages from two depths at the intermittent site, and (2) to assess how the connection with surface water and the direction of the vertical aquifer flow determined the faunistic assemblages. Different taxonomic groups responded differently to intermittence, the hyporheic zone acted as a refuge increasing the resilience of the system, but resilience decreased with increasing degree of affinity to hyporheic life. Disentangling the effects of intermittence on the different faunistic component in the hyporheic zone can help guiding effective protection and restoration measures of river systems with temporary reaches

Role of the hyporheic zone in increasing the resilience of mountain streams facing intermittency

We investigated the impact of intermittence in previously-perennial Alpine stream reaches, targeting the role of the hyporheic zone in increasing the resilience of these aquatic systems. We selected a perennial and an intermittent site in a reach of the Po River (North-Western Italy). We installed piezometers reaching ??1 m (permanent and intermittent site), and ??3 m (intermittent site) and monitored three supraseasonal droughts over a period of three years. We classified the hyporheic fauna into three categories of increasing affinity to life in the hyporheic (stygoxene, stygophile, stygobite), and used communities composition, abundance, beta-diversity and functional groups: (1) to compare assemblages at the same depth but with different hydrological characteristics, as well as assemblages from two depths at the intermittent site, and (2) to assess how the connection with surface water and the direction of the vertical aquifer flow determined the faunistic assemblages. Different taxonomic groups responded differently to intermittence, the hyporheic zone acted as a refuge increasing the resilience of the system, but resilience decreased with increasing degree of affinity to hyporheic life. Disentangling the effects of intermittence on the different faunistic component in the hyporheic zone can help guiding effective protection and restoration measures of river systems with temporary reaches