In this study, both laboratory experiments and numerical simulations were conducted to investigate the effect of density-driven flow on the transport of high-concentration pollutants in the hyporheic zone. The results show that the density gradient can change the flow of pore water and the strong density-driven flow can lead to an unstable flow, which increases the effect of preferential flow and thus causes the appearance of solute fingers in the hyporheic zone. Notably, these solute fingers become more obvious with the increase of depth. The appearance of solute fingers depends on the relative strength of the pumping exchange and density gradient, which are represented by the dimensionless number M* and N* respectively. Finger flows appear near the interface when M* is less than 0.5 N*. This study may contribute to better understanding the transport and destination of solutes and thus may provide some insights into the assessment on pollution incidents.

Water temperature is an important habitat factor in river ecosystems that exhibits the characteristics of continuous change. Dam construction disrupts the continuity of the water temperature and reset it, thus exerting range reduction and hysteresis effects on the characteristics of water temperature change. The effect of a dam on river continuity is directly related to the dam size. To explain this relationship, two rivers in China were selected: one river without reservoirs and one river with cascade reservoirs. Through the analysis of the longitudinal change of water temperature in free-flowing rivers, we found that water temperature changes continuously and uniformly in the longitudinal direction. Based on this, a temperature trend hypothesis in river was proposed, and the discontinuity of the water temperature in the reservoir section was evaluated. The result is as follows: (1) In mixed reservoirs, river water temperature remained as continuous as free-flowing rivers. However, the river water temperature had a large discontinuity in the stratified reservoir; (2) Water residence time was used as an indicator of the continuity of reservoir water temperature; (3) Selective withdrawal of stratified reservoirs in January could not remove the discontinuity caused by itself, but it worked in June.

There is increased interest in the potential of tree planting to help mitigate flooding using nature-based solutions or natural flood management. However, many publications based upon catchment studies conclude that, as flood magnitude increases, benefit from forest cover declines and is insignificant for extreme flood events. These conclusions conflict with estimates of evaporation loss from forest plot observations of gross rainfall, throughfall and stem flow. This study explores data from existing studies to assess the magnitudes of evaporation and attempts to identify the meteorological conditions under which they would be supported. This is achieved using rainfall event data collated from publications and data archives from studies undertaken in temperate environments around the world. The meteorological conditions required to drive the observed evaporation losses are explored theoretically using the Penman-Monteith equation. The results of this theoretical analysis are compared with the prevailing meteorological conditions during large and extreme rainfall events in mountainous regions of the UK to assess the likely significance of wet canopy evaporation loss. The collated dataset showed that Ewc losses between approximately 2 and 38% of gross rainfall (1.5 to 39.4 mm d-1) have been observed during large rainfall events (up to 118 mm d-1) and limited data for extreme events (> 150 mm d-1). Event data greater than 150 mm, where duration was not reported, showed similarly high percentage evaporation losses. Theoretical estimates of wet-canopy evaporation indicated that, to reproduce these high losses, relative humidity and the aerodynamic resistance for vapour transport needed to be within an envelope of approximately 90 to 97.5% and 0.5 to 2 s m-1 respectively. Surface meteorological data during large and extreme rainfall events in the UK suggest that conditions favourable for high wet-canopy evaporation are not uncommon and indicate that significant evaporation losses during large and extreme events are possible but not for all events and not at all locations. Thus the disparity with the results from catchment studies remains.

We present, by using previous results on extended Petri Nets, the relations of various hydrological dynamical systems ($\mathtt{HDSys}$) derived from the water budget ($\mathtt{DynWB}$). Once $\mathtt{DynWB}$ has been implemented, there exist a consistent way to get the equations for backward travel time distributions ($\mathtt{DynTT}$), for the forward response time distribution ($\mathtt{DynRTD}$) and for the concentration for a solute or a tracer ($\mathtt{DynC}$). We show that the $\mathtt{DynWB}$ has a correspondence one to many with the $\mathtt{DynTT}$. In fact to any one of the $\mathtt{DynWB}$ equation correspond as many equation as the input precipitation events times. The $\mathtt{DynTT}$ is related to $\mathtt{DynRTD}$ by the Niemi’s relationship and, in presence of multiple, $n$ outputs, by the specification of $n-1$ partition functions, which determine which fraction of water volume, injected in the control volume at a specific time $t_{in}$, goes asymptotically into a specific output. The $\mathtt{DynC}$, given $\mathtt{DynTT}$, depends further on the solute/tracer concentration in inputs. The paper clarifies the complicate set of relations above by using an example from literature. Upon the introduction of the appropriate information, it is also shown how these ($\mathtt{HDSys}$) can be solved simultaneously without duplicating calculations. It is also shown that these systems can be solved exactly, under the hypothesis of uniform mixing of water ages inside each reservoir within the system.

The Hammond Hill Research Catchment (HH) is a small (120 ha), temperate, second order tributary to Six Mile Creek, Cayuga Lake, and the Great Lakes (42.42°, -76.32°). The HH has been monitored since January 2017 for the purpose of understanding how recent infiltration mixes with antecedent soil water on hillslope forest floors and the spatial and temporal patterns of Root Water Uptake (RWU) by temperate northeastern US tree species (eastern hemlock [Tsuga canadensis], American beech [Fagus grandifolia], and sugar maple [Acer saccharum]). These data are informing us about the hydrologic consequences of anticipated tree species composition change and supporting the development of more refined ecohydrological models. The glaciated catchment is underlain by a shallow confining siltstone layer (1 – 1.5 m depth) and dense with a regrowth (approximately 60 years old) mixed species forest of hemlock, beech, and other deciduous tree species common to the northeastern US. Current datasets from the HH include fixed-internal precipitation snow water equivalent, and discharge, and associated isotopic water compositions (2H & 18O). Frequent (<1 month) measurements of shallow (top 10 cm) soil water content and bulk soil water and hemlock and beech xylem isotopic compositions are made at six locations across a topographic wetness gradient. The near-term role of the HH is to support an understanding of the environmental and ecological drivers of plant RWU competition and ecohydrologic education.

A document by Keith Beven. Click on the document to view its contents.

A document by Tricia A. Stadnyk. Click on the document to view its contents.

A document by Ali Aldrees. Click on the document to view its contents.

The effect of climate change on water resources has been an area of continued research, especially in Australia. Previous studies have suggested significant trends in rainfall, and these are amplified causing larger changes in streamflow. However, most of the previous analysis was based on annual time scales or modelled data and did not account for changes in land cover, which could interact with changes in climate. Climate data and streamflow data sourced from 13 fully forested small catchments (<250 km2) was analysed for trends. Non-parametric Mann-Kendall trend analysis, generalised additive mixed modelling and rainfall-runoff modelling were combined for the analysis. This indicates consistent increases in maximum temperature and varied decreases in rainfall. Limited to a small number of catchments in south eastern Australia there were small, but significantly amplified, decreases in streamflow. In general, overall decreases are much smaller than predicted in earlier research.

Predicting the behavior of overland flow with analytical solutions to the kinematic wave equation is appealing due to its relative ease of implementation. Such simple solutions, however, have largely been constrained to applications on simple planar hillslopes. This study presents analytical solutions to the kinematic wave equation for hillslopes with modest topographic curvature that causes divergence or convergence of runoff flowpaths. The solution averages flow depths along changing hillslope contours whose lengths vary according hillslope width function, and results in a one-dimensional approximation to the two-dimensional flow field. The solutions are tested against both two-dimensional numerical solutions to the kinematic wave equation (in ParFlow) and against experiments that use rainfall simulation on machined hillslopes with defined curvature properties. Excellent agreement between numerical, experimental and analytical solutions is found in all cases. The solutions show that curvature drives large changes in maximum flow rate qmax and time of concentration tc, predictions frequently used in engineering hydrologic design and analysis.

As the global population continues to shift into cities, urban hydrologic systems are becoming increasingly important drivers of overall water quality. Engineered waterways and impervious surfaces strongly influence baseline flow, peak flow, and the transport of pollutants in the urban environment. Between May 2016 -- May 2019, we systematically measured water temperature, pH, dissolved oxygen, biochemical oxygen demand, and the concentrations of nitrate-N, ammonia-N, and orthophosphate in the South Platte River in the Denver metropolitan area, Colorado, USA. We found that the overall water quality of the river decreased through the study area. In addition, there appear to be several hotspots with consistently poor water quality. While it is beyond the scope of this paper to determine the specific sources of the hotspots, it seems likely that wastewater treatment facilities contribute to elevated pollution levels. We also found that water quality was strongly influenced by season. Decreased natural flows during the late fall and winter lead to higher concentrations of nutrients and lower dissolved oxygen levels. Most of the samples collected in this study had nutrient levels that were out of compliance with state regulations for nitrogen and phosphorus concentrations while dissolved oxygen and temperature levels were better than threshold values. Urban hydrologic systems are complex and improving water-quality may be difficult. However, tightening of water-quality standards could result in positive changes to this system.

While evapotranspiration (ET) is normally measured as one hydrologic component, evaporation (E) and transpiration (T) result from different physical-biological processes. In the two-source model, a trapezoidal framework has been widely applied in recent years. The key to applying the trapezoidal framework is the determination of the dry/wet boundaries of the land surface temperature-vegetation coverage trapezoid (LST-fc). Although algorithms have been developed to characterize the two boundaries, , there still, however, exists a significant uncertainty near the wet boundary which scatters in a discrete and uneven manner. It thus is difficult to precisely locate the wet boundary. To tackle the problem, a Wet Boundary Algorithm (WBA) was developed in this study and the algorithm was applied in the region of Huang-Huai-Hai plain of China by using Pixel Component Arranging and Comparing Algorithm (PCACA) to retrieve ET from MODIS Data. The latent heat flux (LE) observed by eddy covariance (EC) measurements from China FLUXNET was used to verify the modified model where the coefficient of determination (R2) was found to 0.81 and the root-mean-square-error (RMSE) was 22.8 W/m2. The ratio of transpiration to evapotranspiration (T/ET) varied between 0.5-0.75 over the region of Huang-Huai-Hai plain. The spatial and temporal distribution of ET revealed that agriculture practices had a great influence on the hydrological cycle.

Environmental dating tracers (3H, 3He, 4He, CFC-12, CFC-11, SF6) and the natural response of spring (hydrochemistry, water temperature, and hydrodynamics) were jointly used to asses mixing processes and to characterize groundwater flow in a relatively small carbonate aquifer with complex geology in South Spain. Results evidence a marked karst behavior of some temporary outlets, while some perennial springs show buffer and delayed responses to recharge events. There is also a general geochemical evolution pattern, from higher to lower altitudes, in which mineralization and the relation Mg/Ca rises, evidencing longer water-rock interaction. The large SF6 concentrations in groundwater suggest terrigenic production, while CFC-11 values are affected by sorption or degradation. The groundwater age in the perennial springs deduced from CFC-12 and 3H/3He point out to mean residence times of several decades, although the difference between both methods and the large amount of radiogenic 4He in the samples indicates a contribution of old groundwater (free of 3H and CFC-12). Lumped Parameter Models and Shape-Free Models were created based on 3H, tritiogenic 3He, CFC-12, and radiogenic 4He data in order to interpret the age distribution of the samples. The resulting groundwater-age distributions evidence the existence of two mixing components, with an old fraction ranging between 160 and 220 years. Some dating parameters derived from the mixing models and their correlation to physicochemical parameters permits to explain the hydrogeochemical processes occurring within the system. All these results prove that large time residence times are possible in small alpine systems with a clear karst behavior when the geological setting is complex, and they highlight the importance of applying different approaches, including groundwater dating techniques, to completely understand the groundwater flow regime within this type of media.

Mine reclamation in the Athabasca oil sands region Canada, is required by law where companies must reconstruct disturbed landscapes into functioning ecosystems such as forests, wetlands and lakes that existed in the Boreal landscape prior to mining. Winter is a major hydrological factor in this region as snow covers the landscape for 5 to 6 months and is ~25% of the annual precipitation, yet few studies have explored the influence of winter processes on the hydrology of constructed watersheds. One year (2017-2018) of intensive snow hydrology measurements are supplemented with six years (2013-2018) of meteorological measurements from the constructed Sandhill Fen Watershed to: 1) understand snow accumulation and redistribution, snowmelt timing, rate and partitioning, 2) apply a physically-based model for simulating winter processes on hillslopes and 3) evaluate the impact of soil prescriptions and climate change projections on winter processes in reclaimed systems. The 2017-2018 snow season was between November and April and SWE ranged between 40-140 mm. Snow distribution was primarily influenced by topography with little influence of snow trapping from developing vegetation. Snow accumulation was most variable on hillslopes and redistribution was driven by slope position, with SWE greatest at the base of slopes and decreased towards crests. Snowmelt on hillslopes was controlled by slope aspect, as snow declined rapidly on west and south-facing slopes, compared to east and north-facing slopes. Unlike results previously reported on constructed uplands, snowmelt runoff from uplands was much less (~30%), highlighting the influence of different construction materials. Model simulations indicate that antecedent soil moisture and soil temperature have a large influence on partitioning snowmelt over a range of observed conditions. Under a warmer and wetter climate, average annual peak SWE and snow season duration could decline up to 52 % and up to 61 days, respectively while snowmelt runoff ceases completely under the warmest scenarios. Results suggest considerable future variability in snowmelt runoff from hillslopes, yet soil properties can be used to enhance vertical or lateral flows.

The Arctic is warming at an unprecedented rate. One relatively under researched process is how seasonally frozen soils and changes thereof affect the water cycle. As frozen soils thaw, flow pathways within a watershed open, allowing for enhanced hydrologic connectivity between groundwater and rivers. As the connectivity of flow paths increase, the storage-discharge relationship of a watershed changes. The objective of this study is to quantify trends and spatio-temporal differences in the degree of linearity in the storage-discharge relationships for sixteen watersheds within Northern Sweden throughout the years of 1950 and 2018. We demonstrate a clear increase in non-linearity of the storage-discharge relationship over time for all catchments with twelve out of sixteen watersheds (75%) having a statistically significant increase in non-linearity. Springs have significantly more linear storage-discharge relationships than summer for twelve watersheds (75%), which supports the idea that seasonally frozen soil with a low degree of hydrological connectivity have a linear storage-discharge relationship. For the period considered, spring showed the greater change in storage-discharge relationship trends than summer, signifying changes in recessions are occurring during the thawing period. Separate storage-discharge analyses combined with preceding winter conditions demonstrated that especially cold winters with little snow yield springs and summers with more linear storage-discharge relationships. We show that streamflow recession analysis shows ongoing hydrological change of an arctic landscape as well as offers new metrics for tracking the change across arctic and sub-arctic landscapes.

The páramos, a neotropical alpine grassland-peatland dominated biome of the northern Andes and Central America, play an essential role in regional and global cycles of water, carbon, and nutrients. They act as water towers, delivering water and ecosystem services mainly from the continental water divide at the Andean highland down to the Pacific and Amazon regions. The anthropogenic influence in form of the climate crisis exerts enormous pressures on these identified “hotspot” ecosystems and increases the vulnerability of nearby populations undermining the socio-economic and human development. Further, increasing pressures reduce the resilience to face climate shocks, and dramatically alters the hydro-climatic regime and shifts the páramos from long-term carbon sinks towards carbon sources. Despite their importance and vulnerability, only three decades ago, páramos, were globally among the least studied ecosystems. However, researchers have since identified them as ideal targets for solving water scarcity issues and to offset carbon emissions. Increasing awareness of the need for hydrological evidence to guide sustainable management of the páramos prompted action for generating data and to fill long-standing knowledge gaps. This has led to a remarkably successful community-research-policy effort to generate this knowledge. The combination of well-established and innovative approaches was used to data collection, processing and knowledge extraction. In this review, we provide a short overview of the state of knowledge of the hydrometeorology, flux dynamics, anthropogenic and the influence of extreme events in the regional páramos. Then, we present emerging technologies for hydrology and water resources research and management applied to páramos. Lastly, we discuss how converging science and policy efforts have leveraged traditional and new observational techniques to generate an evidence base that can support the sustainable management of the páramos. We conclude that this co-evolution of science policy was able to cover different spatial and temporal scales. Finally, we outline future research directions to showcase how sustainable long-term data collection can be sustained for the responsible development of páramo water towers.

Crowd-based hydrological observations can supplement existing monitoring networks and allow data collection in regions where otherwise no data would be available. In the citizen science project CrowdWater, repeated water level observations using a virtual staff gauge approach result in time series of water level classes. To investigate the quality of these observations, we compared the water level class data for a number of locations where water levels were also measured and assessed when these observations were submitted. We analysed data for nine locations where citizen scientists reported multiple observations using a smartphone app and stream level data were also available. At twelve other locations, signposts were set up to ask citizens to record observations on a form that could be left in a letterbox. The results indicate that the quality of the data collected with the app was higher than for the forms. A possible explanation is that for each app location, most contributions were made by a single person, whereas at the locations of the forms almost every observation was made by a new contributor. On average, more contributions were made between May and September than during the other months. Observations were submitted for a range of flow conditions, with a higher fraction of high flow observations for the data collected with the app. Overall, the results are encouraging for citizen science approaches in hydrology and demonstrate that the smartphone application with its virtual staff gauge is a promising approach for crowd-based water level class observations.

Gully erosion is a significant source of fine suspended sediment (<63µm) and associated nutrient pollution to freshwater and marine waterways. Researchers, government agencies, and monitoring groups are currently using monitoring methods designed for streams and rivers (e.g., autosamplers, rising stage samplers, and turbidity loggers) to evaluate suspended sediment in gullies. This is potentially problematic because gullies have unique hydrological and operational challenges that differ to those of streams and rivers. Here we present a laboratory and field-based assessment of the performance of common suspended sediment monitoring techniques applied to gullies. We also evaluate a recently-described method; the pumped active suspended sediment (PASS) sampler, which has been modified for monitoring suspended sediment in gully systems. Discrete autosampling provided data at high temporal resolution, but had considerable uncertainty associated with the poor collection efficiency (25 ± 10%) of heavier sediment particles (i.e., sand). Rising stage sampling, while robust and cost-effective, suffered from large amounts of condensation under field conditions (25-35% of sampler volume), thereby diluting sample concentrations and introducing additional measurement uncertainty. The turbidity logger exhibited low uncertainty (< 10%) when calibrated with suspended sediment concentration data from physically collected samples, however, this calibration approach needs to be performed on a site-specific basis to overcome the error associated with the impact of different particle size distributions on the turbidity measurement. The modified PASS sampler proved to be a reliable and representative measurement method for gully sediment water quality, however, the time-integrated nature of the method limits its temporal resolution compared to the other monitoring methods. We recommend monitoring suspended sediment in alluvial gully systems using a combination of complementary techniques (e.g., PASS and RS samplers) to account for the limitations associated with individual methods.