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Abstract Hyporheic exchange has the potential to significantly influence river temperatures in regions of continuous permafrost under low‐flow conditions given the strong thermal gradients that exist in river bed sediments. However, there is limited understanding of the impacts of hyporheic exchange on Arctic river temperatures. To address this knowledge gap, heat fluxes associated with hyporheic exchange were estimated in a fourth‐order Arctic river using field observations coupled with a river temperature model that accounts for hyporheic exchange influences. Temperature time series and tracer study solute breakthrough curves were measured in the main channel and river bed at multiple locations and depths to characterize hyporheic exchange and provide parameter bounds for model calibration. Model results for low‐flow periods from 3 years indicated that hyporheic exchange contributed up to 27% of the total river energy balance, reduced the main channel diel temperature range by up to 1.7 °C, and reduced mean daily temperatures by up to 0.21 °C over a 13.1‐km study reach. These influences are due to main channel heat loss during the day and gain at night via hyporheic exchange and heat loss from the hyporheic zone to the ground below via conduction. Main channel temperatures were found to be sensitive to simulated changes in ground temperatures due to changes in hyporheic exchange heat flux and deeper ground conduction. These results suggest that the moderating influence of hyporheic exchange could be reduced if ground temperatures warm in response to projected increases in permafrost thaw below rivers.
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GW / SW‐MST : A Groundwater/ Surface‐Water Method Selection Tool
Abstract Groundwater/surface‐water (GW/SW) exchange and hyporheic processes are topics receiving increasing attention from the hydrologic community. Hydraulic, chemical, temperature, geophysical, and remote sensing methods are used to achieve various goals (e.g., inference of GW/SW exchange, mapping of bed materials, etc.), but the application of these methods is constrained by site conditions such as water depth, specific conductance, bed material, and other factors. Researchers and environmental professionals working on GW/SW problems come from diverse fields and rarely have expertise in all available field methods; hence there is a need for guidance to design field campaigns and select methods that both contribute to study goals and are likely to work under site‐specific conditions. Here, we present the spreadsheet‐based GW/SW‐Method Selection Tool (GW/SW‐MST) to help practitioners identify methods for use in GW/SW and hyporheic studies. The GW/SW‐MST is a Microsoft Excel‐based decision support tool in which the user selects answers to questions about GW/SW‐related study goals and site parameters and characteristics. Based on user input, the tool indicates which methods from a toolbox of 32 methods could potentially contribute to achieving the specified goals at the site described.
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- Award ID(s):
- 1824820
- PAR ID:
- 10478252
- Publisher / Repository:
- NGWA
- Date Published:
- Journal Name:
- Groundwater
- Volume:
- 60
- Issue:
- 6
- ISSN:
- 0017-467X
- Page Range / eLocation ID:
- 784 to 791
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Driven by the need for integrated management of groundwater (GW) and surface water (SW), quantification of GW–SW interactions and associated contaminant transport has become increasingly important. This is due to their substantial impact on water quantity and quality. In this review, we provide an overview of the methods developed over the past several decades to investigate GW–SW interactions. These methods include geophysical, hydrometric, and tracer techniques, as well as various modeling approaches. Different methods reveal valuable information on GW–SW interactions at different scales with their respective advantages and limitations. Interpreting data from these techniques can be challenging due to factors like scale effects, heterogeneous hydrogeological conditions, sediment variability, and complex spatiotemporal connections between GW and SW. To facilitate the selection of appropriate methods for specific sites, we discuss the strengths, weaknesses, and challenges of each technique, and we offer perspectives on knowledge gaps in the current science.more » « less
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Abstract Field studies of hyporheic exchange in mountain systems are often conducted using short study reaches and a limited number of observations. It is common practice to assume these study reaches represent hyporheic exchange at larger scales or different sites and to infer general relationships among potential causal mechanisms from the limited number of observations. However, these assumptions of representativeness are rarely tested. In this study, we develop numerical models from four segments of mountain streams in different geomorphologic settings and extract shorter reaches to test how representative exchange metrics are in shorter reaches compared to their reference segments. We also map the locations of the representative reaches to determine if a pattern exists based on location. Finally, we compare variance of these shorter within‐site reaches to 29 additional reaches across the same basin to understand the impacts of inferring causal mechanisms, for example, the expectation that wide and narrow valley bottoms will yield different hyporheic exchange patterns. Our results show that the location and length strategy of the study reach must be considered before assuming an exchange metric to be representative of anything other than the exact segment studied. Further, it is necessary to quantify within and between site variations before making causal inferences based on observable characteristics, such as valley width or stream morphology. Our findings have implications for future field practices and how those practices are translated into models.more » « less
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Abstract Hyporheic zones are commonly regarded as resilient and enduring interfaces between groundwater and surface water in river corridors. In particular, bedform‐induced advective pumping hyporheic exchange (bedform‐induced exchange) is often perceived as a relatively persistent mechanism in natural river systems driving water, solutes, and energy exchanges between the channel and its surrounding streambed sediments. Numerous studies have been based on this presumption. To evaluate the persistence of hyporheic zones under varying hydrologic conditions, we use a multi‐physics framework to model advective pumping bedform‐induced hyporheic exchange in response to a series of seasonal‐ and event‐scale groundwater table fluctuation scenarios, which lead to episodic river‐aquifer disconnections and reconnections. Our results suggest that hyporheic exchange is not as ubiquitous as generally assumed. Instead, the bedform‐induced hyporheic exchange is restricted to a narrow range of conditions characterized by minor river‐groundwater head differences, is intermittent, and can be easily obliterated by minor losing groundwater conditions. These findings shed light on the fragility of bedform‐induced hyporheic exchange and have important implications for biogeochemical transformations along river corridors.more » « less
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Abstract Streambed biogeochemical processes strongly influence riverine water quality and gaseous emissions. These processes depend largely on flow paths through the hyporheic zone (HZ), the streambed volume saturated with stream water. Boulders and other macroroughness elements are known to induce hyporheic flows in gravel‐bed streams. However, data quantifying the impact of these elements on hyporheic chemistry are lacking. We demonstrate that, in gravel‐bed rivers, the amount of dissolved oxygen (DO) in the bed depends chiefly on changes in bed shape, or morphology, such as the formation of scour and depositional areas, caused by the boulders, among other factors. The study was conducted by comparing DO distributions across different bed states and hydraulic conditions. Our experimental facility replicates conditions observed in natural gravel‐bed streams. We instrumented a section in the bed with DO sensors. Results generally indicate that boulder placement on planar beds has some effects, which are significant at high base flows, on increasing hyporheic oxygen amount compared to the planar case without boulders. Conversely, boulder‐induced morphological changes noticeably and significantly increase the amount of oxygen in the HZ, with the increase depending on sediment inputs during flood flows able to mobilize the sediment. Therefore, streambeds of natural, plane‐bed streams may have deeper oxic zones than previously thought because the presence of boulders and the occurrence of flood flows with varying sediment inputs induce streambed variations among these elements.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/gwat.13194
