Controls on Interactions Between Surface Water, Groundwater, and Riverine Vegetation Along Intermittent Rivers and Ephemeral Streams in Arid Regions

Abstract

Intermittent rivers and ephemeral streams (IRES) make up the majority of waterways in arid and semi‐arid regions. While the physical underpinnings of surface water‐groundwater (SW‐GW) flow systems are well understood, how ephemerality, hydraulic properties and vegetation interact along IRES is not clear, posing severe challenges to their sustainable management. This study sought to identify the controls for SW‐GW‐vegetation interactions along IRES. To this end, numerical experiments on a quasi‐hypothetical IRES cross‐section with an integrated surface‐subsurface hydrological model were undertaken. The influence of different degrees of ephemerality on infiltration and riverine transpiration was tested by varying the duration of no‐flow periods. The influence of hydraulic conductivity (K), moisture retention capacity, root density, and local rainfall was also explored. Experiments showed that infiltration is controlled by ephemerality and K, with infiltration decreasing rapidly with increasing ephemerality and decreasing K. Transpiration is influenced by a complex interplay between ephemerality, hydraulic properties, and vegetation. While transpiration is strongly controlled by the degree of ephemerality, the capacity of the subsurface to maintain variably saturated conditions can strongly attenuate the effects of ephemerality. A large moisture retention capacity of the subsurface can partly compensate for the reduced infiltration under increasing ephemerality. Transpiration can be as large under ephemeral as under perennial conditions, especially where water table fluctuations exhibit large amplitudes within the zone of high root density. Overall, the results provide important insights into the complex dynamics of IRES and highlight how changes in flow dynamics can have significant impacts beyond instream processes.

A Framework for Untangling Transient Groundwater Mixing and Travel Times

“…Although these changes will profoundly influence groundwater recharge and discharge in mountainous environments (Hayashi, 2019), they have largely been ignored so far (Somers et al., 2019). Since surface water and groundwater resources are closely coupled, an improved understanding of surface water‐groundwater interactions is highly relevant for a sustainable water governance as well as for water‐dependent ecosystems in mountainous regions (e.g., Holman, 2006; Krause et al., 2014; Schilling et al., 2020).…”

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Although these changes will profoundly influence groundwater recharge and discharge in mountainous environments (Hayashi, 2019), they have largely been ignored so far (Somers et al, 2019). Since surface water and groundwater resources are closely coupled, an improved understanding of surface water-groundwater interactions is highly relevant for a sustainable water governance as well as for water-dependent ecosystems in mountainous regions (e.g., Holman, 2006;Krause et al, 2014;Schilling et al, 2020).Within the last two decades, studies on river-aquifer exchange dynamics have substantially improved the understanding of the drivers (e.g., river discharge) and controls (e.g., riverbed hydraulic conductivity) of water exchange patterns and their impact on biogeochemical cycling of solutes (e.g., reviews by Boano et al, 2014;Brunner et al, 2017; Lewandowski et al, 2019 and references therein). Particularly, the continued recognition and investigation of riverbed dynamics as key controls on river-aquifer exchange have brought substantial scientific progress in the field of surface water-groundwater interactions (e.g., Mutiti & Levy, 2010;Tang et al, 2018).

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A parametric sensitivity analysis for prioritizing regolith knowledge needs for modeling water transfers in the West African critical zone

“…We can conclude that the fine‐scale heterogeneity of K s in H2, notably the distribution of clay in this layer together with the vegetation type, is the first‐order target to represent HP in CZMs for the study area (deep‐weathered tropical soil overlying a hard‐rock basement and ∼1,000–1,500 mm annual rainfall and P ∼ ET). This is a crucial step before using scenario modeling as a tool to understand the complex interplay among SW, GW bodies, vegetation, and subsurface properties during no flow or streamflow intermittency events (Schilling et al., 2020). Although our results show that large‐scale spatial variability in K s in the saprolite (H3 and H4) is not important for modeling water transfers, it may be important on the smaller scale.…”

Non‐Darcy Flow Through a Natural Streambed in a Disconnected Stream

“…Thus, significant exchanges of mass and momentum across the streambed‐stream water interface must occur in a disconnected system and may have important ecological implications (Bhaskar et al., 2012; Boano et al., 2014). These exchanges are intertwined with many important environmental and engineering issues, including water budget (Brunner, Cook, et al., 2009; Brunner et al., 2011), solute and pollutant transport (Roche et al., 2018; Schilling, Gerber, et al., 2017), the quality of riparian conditions (Schilling et al., 2021; Z. Wang et al., 2021), and the functioning of stream ecosystems (Bhaskar et al., 2012; Zhao et al., 2021). A detailed understanding of streambed seepage mechanisms is thus crucial for both water balance and water quality studies in arid areas.…”