Subsurface Water Exchange Research Articles

Current and future roles of meltwater–groundwater dynamics in a proglacial Alpine outwash plain

Abstract. Glacierized alpine catchments are rapidly evolving due to glacier retreat and consequent geomorphological and ecological changes. As more terrain becomes ice-free, reworking of exposed terrain by the river as well as thawing of the top layer may lead to an increase in surface and subsurface water exchanges, leading to potential changes in water storage and release, which in turn may impact ecological, geomorphological and hydrological processes. In this study, we aim to understand the current and future hydrological functioning of a typical outwash plain in a Swiss Alpine catchment. As with many other fluvial aquifers in alpine environments, this outwash plain is located at the valley bottom, where catchment-wide water and sediment fluxes tend to gather from multiple sources, may store water and provide specific habitats for alpine ecosystems. Their dynamics are however rarely studied in post Little Ice Age proglacial zones. Based on geophysical investigations as well as year-round stream and groundwater observations, we developed a simplified physically based 3D MODFLOW model and performed an optimized automatic calibration using PEST HP. We highlight the strong interactions between the upstream river and the aquifer, with stream infiltration being the dominant process of recharge. Groundwater exfiltration occurs in the lower half of the outwash plain, balancing out the amount of river infiltration at a daily timescale. We show that hillslope contributions from rain and snowmelt have little impact on groundwater levels. We also show that the outwash plain acts as a bedrock-dammed aquifer and can maintain groundwater levels close to the surface during dry periods lasting months, even in the absence of glacier meltwater, but may in turn provide only limited baseflow to the stream. Finally, we explore how new outwash plains may form in the future in this catchment due to glacier recession and discuss from a hydrological perspective which cascading impacts the presence of multiple outwash plains may have. For this case study, we estimate the total dynamic storage of future outwash plains to be about 20 mm, and we demonstrate their limited capacity to provide more stream water than that which they infiltrate upstream, except for very low river flows (<150 to 200 L s−1). Below this limit, they can provide limited baseflow on timescales of weeks, thus maintaining moisture conditions that may be beneficial for proglacial ecosystems. Their role in attenuating floods also appears limited, as less than 0.5 m3 s−1 of river water can be infiltrated. The studied outwash plain appears therefore to play an important role for alpine ecosystems but has a marginal hydrological effect on downstream river discharge.

Impact of increasing vegetation coverage on gaining and losing streams in an arid endorheic river watershed

AbstractTo improve the ecology in northern China, the Chinese government has launched a series of revegetation projects. However, the impact of increasing vegetation coverage on gaining and losing streams remains largely unexplored, particularly in arid endorheic watersheds with frequent exchanges of water and other materials between surface water and groundwater. To address this, we modified the vegetation growth module of the soil and water assessment tool (SWAT) to simulate the vegetation coverage change proposed for the middle and lower reaches of the Bayin River. We then coupled the modified SWAT to a modular finite‐difference groundwater flow model to simulate the surface and subsurface water exchange. Hydrological, meteorological, and hydrogeological observation data were then used to build and calibrate the coupled model for the period 2001–2019. We set two vegetation coverage scenarios (non‐revegetation and vegetation) and two irrigation variants (non‐irrigation and irrigation) to investigate the impact of changes in vegetation coverage and the related irrigation variant on gaining and losing streams. The results showed that the vegetated land area and annual leaf area index both increased significantly between 2019 and 2001. The groundwater discharge to the gaining streams was more strongly affected by revegetation and related irrigation than the groundwater recharge from the losing streams. Irrigation related to revegetation emphasizes the effect of revegetation on streamflow. We suggest that in arid endorheic river basins, because of the related irrigation, revegetation has a substantial impact on groundwater level and streamflow, which is mainly composed of baseflow. Therefore, the irrigation efficiency of newly planted vegetation must be improved to stabilize the groundwater level and related ecological conditions.

Time-Lapse Seismic and Electrical Monitoring of the Vadose Zone during a Controlled Infiltration Experiment at the Ploemeur Hydrological Observatory, France

The vadose zone is the main host of surface and subsurface water exchange and has important implications for ecosystems functioning, climate sciences, geotechnical engineering, and water availability issues. Geophysics provides a means for investigating the subsurface in a non-invasive way and at larger spatial scales than conventional hydrological sensors. Time-lapse hydrogeophysical applications are especially useful for monitoring flow and water content dynamics. Largely dominated by electrical and electromagnetic methods, such applications increasingly rely on seismic methods as a complementary approach to describe the structure and behavior of the vadose zone. To further explore the applicability of active seismics to retrieve quantitative information about dynamic processes in near-surface time-lapse settings, we designed a controlled water infiltration experiment at the Ploemeur Hydrological Observatory (France) during which successive periods of infiltration were followed by surface-based seismic and electrical resistivity acquisitions. Water content was monitored throughout the experiment by means of sensors at different depths to relate the derived seismic and electrical properties to water saturation changes. We observe comparable trends in the electrical and seismic responses during the experiment, highlighting the utility of the seismic method to monitor hydrological processes and unsaturated flow. Moreover, petrophysical relationships seem promising in providing quantitative results.

Assessing the effect of flood restoration on surface–subsurface interactions in Rohrschollen Island (Upper Rhine river – France) using integrated hydrological modeling and thermal infrared imaging

Abstract. Rohrschollen Island is an artificial island of the large Upper Rhine river whose geometry and hydrological dynamics are the result of engineering works during the 19th and 20th centuries. Before its channelization, the Rhine river was characterized by an intense hydromorphological activity which maintained a high level of biodiversity along the fluvial corridor. This functionality considerably decreased during the two last centuries. In 2012, a restoration project was launched to reactivate typical alluvial processes, including bedload transport, lateral channel dynamics, and surface–subsurface water exchanges. An integrated hydrological model has been applied to the area of Rohrschollen Island to assess the efficiency of the restoration regarding surface and subsurface flows. This model is calibrated using measured piezometric heads. Simulated patterns of water exchanges between the surface and subsurface compartments of the island are checked against the information derived from thermal infrared (TIR) imaging. The simulated results are then used to better understand the evolutions of the infiltration–exfiltration zones over time and space and to determine the physical controls of surface–subsurface interactions on the hydrographic network of Rohrschollen Island. The use of integrated hydrological modeling has proven to be an efficient approach to assess the efficiency of restoration actions regarding surface and subsurface flows.

Thermal and isotopic evidence for surface and subsurface water contributions to baseflow in a high Arctic river

AbstractSeven longitudinal water temperature tow surveys were conducted to attempt to identify the location of surface and subsurface river water exchanges along the length of the West River at the Cape Bounty Arctic Watershed Observatory, Melville Island, Nunavut, Canada (74°55′ N, 109°35′ W). Water temperature data were collected using a calibrated thermistor with an accuracy of ±0.002 °C (resolution <0.00005 °C) along the river during July 2014 in conjunction with stable water isotope sampling to support the thermal data and to determine the extent of surface water mixing from different sources such as precipitation, snowmelt, and surface/subsurface water contributions to the river. Atmospheric conditions were found to be the main contributor to seasonal temperature variance in the river, whereas tributary inflows and residual channel snow also had important thermal effects to river temperatures. Residual channel snow was a sustained source of cold water during much of the 2014 summer season (June–August) and substantially offset downstream warming. The longitudinal temperature profiles indicate notable changes to the thermal state of the river, which are interpreted to be indicative of subsurface and surface water exchange through inputs of relatively cold or warm water. Broadly, surface inflows were found to provide warmer water relative to the West River, and contributed to downstream warming of the river, along with downstream enrichment of δD and δ18O. Subsurface inflows provided cooler water relative to the river, and contributed to downstream depletion of δD and δ18O and downstream cooling of river temperatures. These results demonstrate that localized changes in river temperature, in conjunction with isotopic tracers, can be used to track channel–slope water interactions in Arctic hydrological systems, work previously limited to alpine and temperate settings.

Reviving the Ganges Water Machine: potential

Abstract. The Ganges River basin faces severe water challenges related to a mismatch between supply and demand. Although the basin has abundant surface water and groundwater resources, the seasonal monsoon causes a mismatch between supply and demand as well as flooding. Water availability and flood potential is high during the 3–4 months (June–September) of the monsoon season. Yet, the highest demands occur during the 8–9 months (October–May) of the non-monsoon period. Addressing this mismatch, which is likely to increase with increasing demand, requires substantial additional storage for both flood reduction and improvements in water supply. Due to hydrogeological, environmental, and social constraints, expansion of surface storage in the Ganges River basin is problematic. A range of interventions that focus more on the use of subsurface storage (SSS), and on the acceleration of surface–subsurface water exchange, has long been known as the Ganges Water Machine (GWM). The approach of the GWM for providing such SSS is through additional pumping and depleting of the groundwater resources prior to the onset of the monsoon season and recharging the SSS through monsoon surface runoff. An important condition for creating such SSS is the degree of unmet water demand. The paper shows that the potential unmet water demand ranging from 59 to 124 Bm3 year−1 exists under two different irrigation water use scenarios: (i) to increase irrigation in the Rabi (November–March) and hot weather (April–May) seasons in India, and the Aman (July–November) and Boro (December–May) seasons in Bangladesh, to the entire irrigable area, and (ii) to provide irrigation to Rabi and the hot weather season in India and the Aman and Boro seasons in Bangladesh to the entire cropped area. However, the potential for realizing the unmet irrigation demand is high only in 7 sub-basins in the northern and eastern parts, is moderate to low in 11 sub-basins in the middle, and has little or no potential in 4 sub-basins in the western part of the Ganges basin. Overall, a revived GWM plan has the potential to meet 45–84 Bm3year−1 of unmet water demand.

Improved simulation of river water and groundwater exchange in an alluvial plain using the SWAT model

Hydrological interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The soil and water assessment tool (SWAT) model is a semi-distributed model that has been successfully applied around the world. However, it has not been able to simulate the two-way exchanges between surface water and groundwater. In this study, the SWAT-landscape unit (LU) model – based on a catena method that routes flow across three LUs (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT-LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water-level simulation during flooding periods was modified, and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT-LUD was compared with the output of a two-dimensional distributed model, surface–subsurface water exchange model. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT-LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface–groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river; water that flowed in this direction accounted for 65% of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the surface–subsurface water exchange process; it accounted for 69% of total water that flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale.

The effects of discharge and slope on hyporheic flow in step‐pool morphologies

AbstractThis paper focuses on surface–subsurface water exchange in a steep coarse‐bedded stream with a step‐pool morphology. We use both flume experiments and numerical modelling to investigate the influence of stream discharge, channel slope and sediment hydraulic conductivity on hyporheic exchange. The model step‐pool reach, whose topography is scaled from a natural river, consists of three step‐pool units with 0.1‐m step heights, discharges ranging between base and over‐bankfull flows (scaled values of 0.3–4.5 l/s) and slopes of 4% and 8%. Results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges. In contrast to findings in a pool‐riffle morphology, those in this study show that steep slopes cause deeper surface–subsurface exchanges than gentle slopes. Numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity. These experiments and numerical simulations emphasize the importance of topography, sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange. Our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool‐riffle bed forms. Copyright © 2014 John Wiley & Sons, Ltd.

Modification of the National Weather Service Distributed Hydrologic Model for subsurface water exchanges between grids

To account for spatial variability of precipitation, as well as basin physiographic properties, the National Weather Service (NWS) has developed a distributed version of its hydrologic component, termed the Hydrology Laboratory‐Research Distributed Hydrologic Model (HL‐RDHM). Because channels are the only source of water exchange between neighboring computational elements, the absence of such exchange has been identified as a weakness in the model. The primary objective of this paper is to modify the model structure to account for subsurface water exchanges without dramatically altering the conceptual framework of the water balance module. The subsurface exchanges are established by partitioning the slow response components released from the lower layer storages into two parts: the first part involves the grid's conceptual channel, while the second is added to the lower layer storages of the downstream pixel. Realizing the deficiency of the water balance module to locate the lower zone layers in sufficient depths, a complementary study is conducted to test the feasibility of further improvement in the modified model by equally shifting downward the lower zone layers of all pixels over the basin. The Baron Fork at Eldon, Oklahoma, is chosen as the test basin. Ten years of grid‐based multisensor precipitation data are used to investigate the effects of the modification, plus shifting the lower zone layers on model performance. The results show that the modified‐shifted HL‐RDHM can markedly improve the streamflow simulations at the interior point, as well as very high peak‐flow simulations at the basin's outlet.

Surface–subsurface water exchange rates along alluvial river reaches control the thermal patterns in an Alpine river network

Summary1. Water temperature is a key characteristic of stream ecosystems that is gaining scientific and managerial relevance as maximum temperatures in aquatic ecosystems increase worldwide.2. To assess the effect of surface–subsurface water exchange on stream water temperature patterns, four alluvial reaches in the Tagliamento River basin (NE Italy), constrained by geomorphic knickpoints at the upper and lower end, and two to four hyporheic flowpaths within each reach, were continuously studied during summer 2007 and winter 2007–08. Water temperature was continuously monitored at the upstream and downstream knickpoints of the floodplains, as well as at discrete upwelling areas within each reach. Discharge and vertical hydraulic gradient were measured along the alluvial reaches, and the residence time and chemistry of upwelling water were assessed four times during the study.3. Discharge variation along the study reaches revealed that massive hyporheic exchange occurred in all sites, ranging from 21% in reach 2–52% in reach 1. End member mixing analysis showed little influence of ground water, as almost all upwelling water was freshly infiltrated hyporheic water. Importantly, hyporheic exchange flows shaped surface temperature at the upwelling locations in all study reaches, providing potential thermal refugia for aquatic biota. At sites with highest hyporheic flow rates, net temperature change was also reflected at the floodplain scale.4. The magnitude of the thermal change along a hyporheic flowpath was not related to the flowpath length but to the estimated 222Rn water age. Reduction in the diel thermal amplitude by hyporheic flows rather than net temperature change, reduced temperature extremes. Therefore, restoration activities to create thermal refugia should consider the role of hyporheic flows and enhance the exchange between surface and hyporheic waters.

Modeling the effects of lowland stream restoration projects on stream–subsurface water exchange

The relative effect of individual elements of restoration projects on stream–subsurface water exchange was studied by identifying elements that were most effective in increasing downwelling stream water (DSW) into subsurface environments using groundwater flow modeling. Several restoration projects studied in lowland streams involved riffle-pool construction, lateral gravel bar construction and channel re-meandering. Simulations using a homogeneous field of mean hydraulic conductivity that removed heterogeneity showed a large decline in DSW in the four restoration projects studied, suggesting that use of coarse sediments in construction initially increases stream–subsurface water exchange, but the effects may not persist in streams where fine sediments clog streambeds. In two riffle-pool construction projects studied, modification of the channel gradient showed a greater effect on DSW than the alteration of substrate texture. In the gravel bar construction site, modeling results indicated that the construction of a riffle-pool sequence along the bar had a greater effect than the construction of the gravel bar itself. In contrast in the channel re-meandering site, the combination of a greater sinuosity and a lower hydraulic head along the small riffles resulted in re-meandering having a greater effect than the associated riffle-pool construction. A simulation in which the floodplain sediments of low saturated hydraulic conductivity at the re-meandered site were replaced with sandy gravels increased DSW by 10 times. This modeling suggests that the addition of coarse sediments in combination with re-meandering would be required to significantly enhance stream–subsurface water exchange in reaches with fine-grained floodplain sediments. Designing the size and type of morphologic features constructed in restoration projects is somewhat flexible, and the use of modeling to simulate stream–groundwater interactions may help to enhance the hydrologic link with a stream and the subsurface environment in restored stream reaches.

Instream restoration: its effects on lateral stream–subsurface water exchange in urban and agricultural streams in Southern Ontario

AbstractInstream restoration strategies do not generally consider the subsurface environment. The study of recently restored stream reaches can provide an opportunity to assess the impacts of restoration on surface–subsurface exchange. In this study, lateral hyporheic zones occurring in a constructed gravel bar and re‐meandered stream reach were examined, using hydrometric data in combination with differences in background conservative ion and tracer injection experiments. Both the constructed gravel bar and the meander bends induced lateral hyporheic exchange flow. In the gravel bar, lateral hyporheic exchange increased after a riffle‐pool sequence was constructed in the channel adjacent to the bar. The substrate in the meander bends had low saturated hydraulic conductivity, and the stream–subsurface exchange was limited despite the large change in channel configuration. These results suggest that to enhance and maintain stream–subsurface water exchanges, restoration projects that modify horizontal geometry should involve construction of vertical morphologic features, and where floodplain sediments are fine‐grained, the addition of coarse sediments should also be incorporated in the design. Copyright © 2007 John Wiley & Sons, Ltd.

Comparative analysis of groundwater formation in arid and super-arid deserts (with examples from Central Asia and northeastern Arabian Peninsula)

Groundwater formation within arid and super-arid deserts is discussed through comparative analysis. Although fresh groundwater is being formed in both types of deserts, mainly from infiltrated surface runoff, in arid deserts, infiltration is currently taking place, whereas in super-arid areas, it occurred mainly in the Pleistocene pluvial epoch. Groundwater discharge conditions are also different. In arid deserts, the discharge occurs mainly through transpiration by phreatophytes, which form phyto-hydrogeological ecosystems where the dominant factor is an interaction between groundwater and vegetation, with transpiration reaching over hundreds of mm/year and the thickness of the groundwater evaporation zone extending over 10 m. Active subsurface water exchange does not favor the preservation of Pleistocene fossil groundwater. Super-arid deserts, however, have an extremely scarce vegetative cover (low, if any), physical evaporation, a thin zone of evaporation influence, and slow water outflow. Favorable conditions therefore exist for the preservation of relict low-mineralized waters. Furthermore, arid and super-arid deserts differ by types of groundwater accumulation and horizontal and vertical zonalities. In arid deserts, hydrogeological problems are connected with the anthropogenic influence upon groundwater, and with control on rational use of surface water and groundwater. In super-arid deserts, the basic problem is depletion of fossil groundwater.

Early Holocene water budget of the Nakuru-Elmenteita basin, Central Kenya Rift

The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange.

River regulation, decline of ecological resources, and potential for restoration in a semi-arid lands river in the western USA

Societal needs for power generation, water management/use, and land uses (e.g., urban and agricultural) have often resulted in a significant departure from the natural processes of hydrologic regimes and material transport and deposition throughout most of the rivers flowing through arid and semi-arid landscapes of the western USA. We examine the compromised ecosystem integrity of one such river, the upper Snake River in eastern Idaho, below a large irrigation and power dam that has altered hydrologic regimes and reduced channel sediment supply. We review the ecological structure and function of gravel-bed rivers as they vary across a hierarchy of landscape scales with different spatial and temporal dimensions. Major linkages within the large, alluvial river systems of the western USA include exchange of water and materials along longitudinal connections from streams to rivers, lateral connections between river and floodplain systems, and vertical surface and subsurface (hyporheic) water exchanges. Longitudinal linkages dominate confined (canyon) river reaches while unconfined (floodplain) reaches show strong affinities for lateral and vertical exchange. Hydrogeomorphic processes, driven by river power and cut and fill alluviation, produce a dynamic landscape in floodplain reaches, which we refer to as a Shifting Habitat Mosaic (SHM). The SHM fosters high physical and ecological diversity of habitats, biotic communities, and ecosystem complexity. In this case study, we examine the dynamics of a series of floodplains along a 90 km river landscape, employing an airborne spectrophotometer, producing georeferenced hyperspectral imagery, coupled with ground truth measures of river hydraulics, river depth, riparian vegetation and other surface characteristics. From these data we derived estimates of the hydraulics and hydrographic regimes necessary to mobilize channel and riparian sediments, thus reestablishing the dynamics of the river SHM. We also evaluated subsequent variation in aquatic and riparian habitat characteristics. Evaluation of these factors, which affect interactions between the river channel and the surrounding river–riparian corridor, permitted us to develop a restoration strategy focused on normative variation among the various physical and biotic processes contributing to ecosystem integrity.

Riparian Trees and Flow Paths between the Hyporheic Zone and Groundwater in the Oberer Seebach, Austria

AbstractWe investigated lateral subsurface water exchange in a 2nd order mountain stream with a piezometer method. At both banks the stream hyporheic zone lost water to the riparian groundwater zone. Independently, the hydraulic heads at three sites in the streambed and in the riparian zone exhibited periodic, diurnal fluctuations. We attributed them to water consumption by the riparian trees, as solar radiation explained part of this additional variation.Our results demonstrate that subsurface water exchanges take place between the hyporheic zone and lateral riparian groundwater in spatially defined small‐scale flow paths. These small‐scale interactions occur within the context of large‐scale patterns of loss and gain of channel water.

Lacunal allocation and gas transport capacity in the salt marsh grass Spartina alterniflora.

Lacunal allocation as the fraction of the total cross sectional area of leaves, stem bases, rhizomes, and roots was determined in both tall and short growth forms of Spartina alterniflora collected from natural monospecific stands. The results indicate that in both growth forms lacunal allocation is greater in stem bases and rhizomes than in leaves and roots and that tall form plants allocate more of their stem and rhizome to lacunae than short form plants.Measurements made in natural stands of Spartina alterniflora suggest that total lacunal area of the stem base increases with increasing stem diameter and that stem diameter increases with increasing plant height and above-ground biomass. However, the fraction of cross section allocated to lacunae was relatively constant and increased only with the formation of a central lacuna.Experimental manipulations of surface and subsurface water exchange were carried out to test the influence of flooding regime on aerenchyma formation. No significant differences in lacunal allocation were detected between plants grown in flooded (reduced) and drained (oxidized) sediments in either laboratory or field experiments. While aerenchyma formation in Spartina alterniflora may be an adaptation to soil waterlogging/anoxia, our results suggest that lacunal formation is maximized as a normal part of development with allocation constrained structurally by the size of plants in highly organic New England and Mid-Atlantic marshes.The cross sectional area of aerenchyma for gas transport was found to be related to the growth of Spartina alterniflora with stands of short form Spartina alterniflora exhibiting a lower specific gas transport capacity (lacunal area per unit below ground biomass) than tall form plants despite having a similar below-ground biomass supported by a 10 fold higher culm density. The increased specific gas transport capacity in tall vs. short plants may provide a new mechanism to explain the better aeration, higher nutrient uptake rates and lower frequency of anaerobic respiration in roots of tall vs. short Spartina alterniflora.