Stream Discharge Research Articles

Linking Snow, Soil, and Stream During Snowmelt and Rain‐On‐Snow Events: Storage and Transport of Ions in an Acid‐Sensitive Alpine Catchment (Tatra Mountains, Poland)

AbstractThe purpose of the study was to examine the storage and transport of ions through snowpack, soils, and stream water in an acid‐sensitive alpine catchment (Tatra Mountains, Poland) during snowmelt and rain‐on‐snow events. Samples of snowpack layers, near‐surface soil horizons, and stream water were collected in the winter and snowmelt seasons of 2019. A laboratory experiment was conducted to determine the effect of temperature on the rate of soil nitrogen mineralization and nitrification. Our study has shown that snowpack is an important source of ions in the catchment. As the snow melts, the release of ions from snowpack occurs. A gradual and slow melting of snow starts even before the first snowmelt‐induced increase in stream discharge. ions eluted from available snowpack are temporarily stored in soil, which is shown by a large increase in the concentration of water‐soluble in the soil at that time. ions are washed out of soils and supplied to streams during the first snowmelt event. This is demonstrated by a large increase in the stream water concentration, termed an “ pulse.” The ion is a key acid anion responsible for the acidification of the studied stream during snowmelt season, as the pulse coincides with a decrease in bicarbonate alkalinity. Our field research and laboratory experiment have shown a minor role of mineralization and nitrification in production in soils in the winter and pulse formation in stream water during the early stages of the snowmelt season.

Effects of population density and environmental conditions on life-history prevalence in a migratory fish.

Individual variation in life-history traits can have important implications for the ability of populations to respond to environmental variability and change. In migratory animals, flexibility in the timing of life-history events, such as juvenile emigration from natal areas, can influence the effects of population density and environmental conditions on habitat use and population dynamics. We evaluated the functional relationships between population density and environmental covariates and the abundance of juveniles expressing different life-history pathways in a migratory fish, Chinook salmon (Oncorhynchus tshawytscha), in the Wenatchee River basin in Washington State, USA. We found that the abundance of younger emigrants from natal streams was best described by an accelerating or near-linear function of spawners, whereas the abundance of older emigrants was best described by a decelerating function of spawners. This supports the hypothesis that emigration timing varies in response to density in natal areas, with younger-emigrating life-history pathways comprising a larger proportion of emigrants when densities of conspecifics are high. We also observed positive relationships between winter stream discharge and abundance of younger emigrants, supporting the hypothesis that habitat conditions can also influence the prevalence of different life-history pathways. Our results suggest that early emigration, and a resultant increase in the use of downstream rearing habitats, may increase at higher population densities and with greater winter precipitation. Winter precipitation is projected to increase in this system due to climate warming. Characterizing relationships between life-history prevalence and environmental conditions may improve our understanding of species habitat requirements and is a first step in understanding the dynamics of species with diverse life-history strategies. As environmental conditions change-due to climate change, management, or other factors-resultant life-history changes are likely to have important demographic implications that will be challenging to predict when life-history diversity is not accounted for in population models.

Reducing chromium discharge in tanning: The salt-free chrome tanning process

Nowadays, there is increasing concern about environmental protection in global industrial activities. The sustainable leather industry is currently focusing on cleaner processing methods to promote a greener environment. However, the discharge of waste streams containing several pollutants poses a significant social threat to the leather sector. The conventional pickling and chrome tanning process is particularly problematic due to the enormous amounts of chlorides and chromium emissions, which have been a longstanding issue that has not been satisfactorily resolved. In order to minimize the emissions of chromium and chloride integrately, a salt-free and high exhaustion chromium tanning method was designed and optimized. The study's results demonstrated that the chrome tanning process could be improved by conducting it in a salt-free environment, resulting in a smooth process and a chromium absorption rate increase to 99% compared to 75% in the conventional process. Moreover, the dosage of Chrome required was minimized from 1.5% to 0.8%, resulting in a significant reduction of residual Chromium concentration in the spent liquor from above 1150 mg/L to 40 mg/L. The novel chrome tanning process significantly decreases the amount of chromium-containing sludge generated and facilitates the disposal of spent liquor with a reduced amount of chrome and chloride. The novel process effectively addresses long-standing problems and meets the requirements of the modern sustainable leather industry.

An integrated watershed-scale framework to model nitrogen transport and transformations

Excess nitrogen in water bodies is associated with a number of environmental problems, including hypoxia and eutrophication. Originating from anthropogenic activities such as fertilizer application, and influenced by watershed characteristics such as the structure of the drainage network, stream discharge, temperature, and soil moisture, factors influencing nitrogen transport and transformation are many and interconnected. This paper describes the development and application of a process-oriented nitrogen model based on the modeling framework of PAWS (Process-based Adaptive Watershed Simulator) that can describe coupled hydrologic, thermal and nutrient processes. The integrated model was tested for an agricultural watershed with complex land use, namely the Kalamazoo River watershed in Michigan, USA. Nitrogen transport and transformations on the landscape were modeled by representing multiple sources and processes (fertilizer/manure application, point sources, atmospheric deposition, nitrogen retention and removal in wetlands and other lowland storage, etc.) across multiple hydrologic domains (streams, groundwater, soil water). The coupled model provides a tool to examine nitrogen budgets and to quantify the impacts of human activities and agricultural practices on the riverine export of nitrogen species. Model results indicate that the river network removed approximately 5.96 % of the total anthropogenic nitrogen input to the watershed, and that the riverine export of nitrogen accounted for 29.22 % of the total anthropogenic inputs during 2004–2009 while the groundwater contribution of nitrogen to the rivers during the same period was found to be 18.53 % highlighting the important role of groundwater within the watershed.

Prospects for the Implementation of an Intense Source of Ultraviolet Radiation Based on a Gas-Discharge Plasma in a Quasi-Optical Cavity Excited by a Pulse of Terahertz Radiation

An electrodynamic system is described that provides the creation of an electromagnetic wave field of high intensity at a frequency of 1 THz due to a combination of accumulation in time and compression in space of a wave pulse coming from an electron cyclotron maser (gyrotron). This system is based on the use of a three-mirror cavity consisting of two focusing mirrors and one flat corrugated Bragg-type photonic structure providing coupling between the gyrotron wave pulse and the operating wave of the cavity. The aim of this work is to use a “spot” of the intense terahertz field inside the cavity to provide a point-like plasma discharge in a gas stream injected into this spot; such a discharge can be a source of extreme ultraviolet radiation.

Water availability and seasonality shape elemental stoichiometry across space and time.

The interaction of climate change and increasing anthropogenic water withdrawals is anticipated to alter surface water availability and the transport of carbon (C), nitrogen (N), and phosphorus (P) in river networks. But how changes to river flow will alter the balance, or stoichiometry, of these fluxes is unknown. The Lower Flint River Basin (LFRB) is part of an interstate watershed relied upon by several million people for diverse ecosystem services, including seasonal crop irrigation, municipal drinking water access, and public recreation. Recently, increased water demand compounded with intensified droughts have caused historically perennial streams in the LFRB to cease flowing, increasing ecosystem vulnerability. Our objectives were to quantify how riverine dissolved C: N: P varies spatially and seasonally and determine how monthly stoichiometric fluxes varied with overall water availability in a major tributary of LFRB. We used a long-term record (21-29 years) of solute water chemistry (dissolved organic carbon, nitrate/nitrite, ammonia, and soluble reactive phosphorus) paired with long-term stream discharge data across six sites within a single LFRB watershed. We found spatial and seasonal differences in soluble nutrient concentrations and stoichiometry attributable to groundwater connections, the presence of a major floodplain wetland, and flow conditions. Further, we showed that water availability, as indicated by the Palmer Drought Severity Index (PDSI), strongly predicted stoichiometry with generally lower C:N and C:P and higher N:P fluxes during periods of low water availability (PDSI < -4). These patterns suggest there may be long term and significant changes to stream ecosystem function as water availability is being dramatically altered by human demand with consequential impacts to solute transport, in-stream processing, and stoichiometric ratios. This article is protected by copyright. All rights reserved.

A Framework for Assessment of Flood Conditions Using Hydrological and Hydrodynamic Modeling Approach

River flooding has been triggering significant damage to lives and infrastructure and is a major worry all around the globe. To lessen these losses, proper planning and management methods need to be deployed. The purpose of this research is to fill a knowledge gap on the effects of reservoirs operation of the Idukki and Idamalyar to Periyar River Basin massive flooding. The proposed methodology is implemented on the Periyar River Basin located in Kerala, India, where severe flooding occurred during monsoon season in the year 2018. In this study, modelling technique has been used in two-step: (1) development of 1D physically based, distributed-parameter model (Soil and Water Assessment Tool, SWAT) to compute the stream flow and estimate the stream discharge at different outlet points; and (2) hybrid model is developed by linking SWAT with a well-known 2D hydrodynamic model (International River Interface Cooperative, iRIC) to display flood scenarios and to identify the flood-prone areas. The ArcSWAT user interface employed in the ArcGIS software was utilized to delineate the river basin. The SWAT model was calibrated and validated on daily and monthly basis at two gauge discharge stations, i.e., Neeleeswaram and Kalady. The statistical coefficients result obtained from SWAT model was in good agreement with the measured values for calibration and validation. The hybrid model simulation results compared with observed flood depth and remote sensing data demonstrated good capability of the model. Agreeable performances of computed results were observed in both flow fields and flood propagations. The result was compared with 2018 flood to check model accuracy and found to be satisfactory. The proposed framework can be utilized as an effective tool for efficient planning and management of natural disasters, such as flash floods.

Spatiotemporal Variability Comparisons of Water Quality and Escherichia coli in an Oklahoma Stream

AbstractFecal indicator bacteria, Escherichia coli, for primary body contact recreation (PBCR) in Oklahoma waterbodies, is defined as the geometric mean of 10 samples from the recreation season, May 1 to September 30, with an impairment threshold of 126 colony forming units (cfu) per 100 mL. However, the water quality standards provide limited guidance on spatiotemporal and environmental factors that could influence samples collected and analyzed. In this study, two stream cross sections under baseflow conditions in a central Oklahoma urban perennial stream, Spring Creek, were densely sampled to investigate temporal and spatial variability of E. coli concentrations and water quality parameters across the stream channel. Water quality parameters (specific conductivity, temperature, dissolved oxygen, pH, turbidity, and total suspended solids (TSS)), stream discharge, and bacteria samples were collected simultaneously at equal intervals across the two cross sections in the morning and afternoon during one summer day with sunny, dry, and hot weather conditions. Results indicate a significant difference between time‐of‐day samples and water quality parameters and E. coli concentrations. Strong correlations between temperature, dissolved oxygen, and time versus E. coli concentrations were observed, while location, turbidity, and TSS were not significant or correlated to measured values. Furthermore, E. coli concentrations were highly variable spatially across each stream cross section, regardless of time of day or location. Results from this study provide an initial indication that stream water quality, spatial cross section sample location, and diurnal variations may be influencing factors on bacteria concentrations.

Real‐Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge

AbstractGroundwater discharge along channels can affect stream discharge, chemistry, and ecological communities. Although the spatial distribution of groundwater springs along wide rivers can be investigated by areal thermal infrared (TIR) remote sensing, this technique is difficult to apply to mapping at a high spatial resolution and under riparian tree canopies. We present a real‐time monitoring and postprocessing method of ground‐based TIR video for determining groundwater discharge sampling points and mapping the surface water temperature. We applied this method to mapping two headwater streams in Hokkaido, Japan, in the summer. The first site was a 1.3‐km‐long reach underlain by Pleistocene andesite lava. Almost all of the springs were colder and had a different chemistry compared to that of the stream water, which supports the usefulness of TIR monitoring for determining groundwater discharge zones. Video postprocessing showed that cold groundwater springs were spaced every ∼100 m, and their distribution did not follow the topography. At the second site, cold and warm springs were underlain by Holocene volcanic ash. The cold springs mainly seeped from hyporheic and riparian zones downstream, while warm springs were at the footslope. Some cold springs had much higher solute concentrations than the stream and warm springs, which suggests that the water temperature is useful for inferring sources of groundwater discharge. At this site, the video postprocessing could map not only the locations of the cold springs but also the spatial heterogeneity of the stream temperature associated with groundwater inputs.

Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal.

Riparian zones and the streams they border provide vital habitat for organisms, water quality protection, and other important ecosystem services. These areas are under pressure from local (land use/land cover change) to global (climate change) processes. Woody vegetation is expanding in grassland riparian zones worldwide. Here we report on a decade-long watershed-scale mechanical removal of woody riparian vegetation along 4.5 km of stream channel in a before-after control impact experiment. Prior to this removal, woody plants had expanded into grassy riparian areas, associated with a decline in streamflow, loss of grassy plant species, and other ecosystem-scale impacts. We confirmed some expected responses, including rapid increases in stream nutrients and sediments, disappearance of stream mosses, and decreased organic inputs to streams via riparian leaves. We were surprised that nutrient and sediment increases were transient for 3 years, that there was no recovery of stream discharge, and that areas with woody removal did not shift back to a grassland state, even when reseeded with grassland species. Rapid expansion of shrubs (Cornus drummondii, Prunus americana) in the areas where trees were removed allowed woody vegetation to remain dominant despite repeating the cutting every 2 years. Our results suggest woody expansion can fundamentally alter terrestrial and aquatic habitat connections in grasslands, resulting in inexorable movement toward a new ecosystem state. Human pressures, such as climate change, atmospheric CO2 increases, and elevated atmospheric nitrogen deposition, could continue to push the ecosystem along a trajectory that is difficult to change. Our results suggest that predicting relationships between riparian zones and the streams they border could be difficult in the face of global change in all biomes, even in well-studied sites.

Climate change impacts on native cutthroat trout habitat in Colorado streams

AbstractHeadwater streams support vital aquatic habitat yet are vulnerable to changing climate due to their high elevation and small size. Coldwater fish are especially sensitive to the altered streamflow and water temperature regimes during summer low flow periods. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect habitat availability for various native cutthroat trout species, suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) native to headwater regions of Colorado, USA. Thus, this study used field data collected from selected headwater streams across the current distribution of GBCT to construct one‐dimensional hydraulic models to evaluate streamflow and physical habitat under four future climate projections. Results illustrate reductions in both predicted streamflow and physical habitat for all future climate projections across study sites. The projected mean summer streamflow shows greater decline (−52% on average) compared to the projected decline in mean August flow (−21% on average). Moreover, sites located at a relative higher elevation with larger substrate and steeper slope were projected to experience more reductions in physical habitat due to streamflow reductions. Specifically, streams with step‐pool morphologies may experience grater changes in available habitat compared to pool‐riffle streams. Future climate change studies related to coldwater fish that examine spatial variation in flow alteration could provide novel data to complement the existing literature on the thermal characteristics. Tailoring reintroduction and management efforts for GBCT to the individual headwater stream with adequate on‐site monitoring could provide a more holistic conservation approach.

HeadwaterstreamSNevada: Data on riparian vegetation and water parameters of headwater streams in Sierra Nevada, Spain.

Providing historical data on riparian plant biodiversity and physico-chemical parameters of stream water in Mediterranean mountains helps to assess the effects of climate change and other human stressors on these sensitive and critical ecosystems. This database collects data from the main natural headwater streams of the Sierra Nevada (southeastern Spain), a high mountain (up to 3479 m above sea level [m asl]) recognized as a biodiversity super hotspot in the Mediterranean basin. On this mountain, rivers and landscapes depend on snowmelt water, representing an excellent scenario for evaluating global change's impacts. This dataset covers first- to third-order headwater streams at 41 sites from 832 to 1997 m asl, collected from December 2006 to July 2007. Our goal is to supply information on the vegetation associated with streambanks, the essential physico-chemical parameters of stream water, and the physiographic features of the subwatersheds. Riparian vegetation data correspond to six plots sampled at each site, including total canopy, individual number, height and DBH (diameter at breast height) in woody species, and cover percentage for herbs. Physico-chemical parameters were measured in situ (electric conductivity, pH, dissolved O2 concentration, stream discharge) and determined in the laboratory (alkalinity, soluble reactive phosphate-phosphorus [SRP], total phosphorus [TP], nitrate-nitrogen [ -N], ammonium-nitrogen [ -N], total nitrogen [TN]). Watershed physiographic variables comprise drainage area, minimum altitude, maximum altitude, mean slope, orientation, stream order, stream length, and land cover surface percentage. We recorded 197 plant taxa (67 species, 28 subspecies, and 2 hybrids), representing 8.4% of the Sierra Nevada vascular flora. Due to the botanical nomenclature used, the database can be linked to FloraSNevada database, contributing to Sierra Nevada (Spain) as a laboratory of global processes. This data set can be freely used for non-commercial purposes. Users of these data should cite this data paper in any publications resulting from its use.

Changes in the stream discharge in the forest-steppe zone in the XXI century under the environmental regime (based on the research of the dynamics of the length of the channel network of elementary watercourses on the territory of the “Sengileevskie Mountains” National Park Ulyanovsk region, Russia))

The article presents the results of researching changes in the stream discharge in the forest-steppe zone in the XXI century in the conditions of the environmental regime. Due to the lack of data on the stream discharge within the researched area in previous years, the length of the channel network is considered as an indicator of water content – an indicator that generally correlates with the value of the length of the channel network. Elementary watercourses are taken as the object of research, since in short periods they are able to show high variability under the influence of external conditions, especially if it is necessary to establish the influence of specific local factors. The research was conducted on the territory of the “Sengileevskie Mountains” National Park, which lies within the Volga landscape region and the Low Volga region in the forest-steppe zone. This territory exists in the conditions of the nature protection regime and has a high forest cover. The research was based on the materials of the expedition work carried out in the summer of 2022. and the results of geoinformation analysis of topographic maps reflecting the position of the sources of elementary watercourses in 2001. As a result of the expedition work, the length of the channels of elementary watercourses as of 2022 has been established, the indicator of the change in the length of their channels in the XXI century – from 2001 to 2022 has been calculated. The fact of the multidirectional dynamics of the length of the channel network of elementary watercourses is established. In the conditions of the nature protection regime established at the beginning of the XXI century, against the background of the restoration of the landscapes of the researched territory, there is an increase in the length of the channel network of elementary watercourses, which has a correlation with the areal indicators of the restoration of natural plant communities – forests and meadows.

Estimating the Role of Bank Flow to Stream Discharge Using a Combination of Baseflow Separation and Geochemistry

This study investigated the role of bank return flow to two medium size rivers in southeast Queensland using a combination of hydrograph separation techniques and geochemical baseflow separations. The main aims were to provide a case study to demonstrate spatial and temporal variability in groundwater contributions to two river systems in Southeast Victoria; the Avon River and the Mitchell River. The two rivers show large spatial and temporal variations in groundwater contributions with higher percentages during low flow periods and more surface runoff during wet years. At the end of the Australian millennium drought, groundwater discharge accounted for 60% of the total flow for the Avon River and 42% for the Michell River, whereas groundwater discharge only had a minor component to the total discharge in wetter years, ∼15% for the Avon River and only 3% for the Mitchell River. Radon and chloride were used for the geochemical baseflow separation and provide a means to separate regional groundwater discharge to the rivers from bank return flow. Bank return flow accounts for 2 to 5 times higher fluxes in certain areas. Geochemistry in combination with physical hydrogeology enhances the overall understanding of groundwater connected river systems over the river length.

Protracted dynamicity of microplastics in the coastal sediment of the Southeast Black Sea

This study provided the first evaluation of microplastic abundance, features, risk assessment, and decade-changing status in sediment along the southeastern Black Sea coast. Sediment samples were collected from thirteen stations in the Southeast Black Sea in 2012 and 2022. >70 % of the detected microplastics had a length of up to 2.5 mm and consisted of fragments and fibers in shape. The average microplastic abundance in the sediment samples was 108 MP/kg. The composition in the sediment (particles/kg) was dominated by polyethylene (PE) (44.9 %), polyethylene terephthalate (PET) (27.2 %), and polypropylene PP (15.2 %). Remarkable results for contamination factors, polymeric risk assessment and contamination risk indices. The sharp rise in MPS highlighted the heavily populated stations and stream discharge locations. The data shed light on anthropogenic and basal microplastic pollution in the Southeast Black Sea, assisting in developing effective policies for preserving and managing the Black Sea environment.

User-focused evaluation of National Ecological Observatory Network streamflow estimates

Accurately estimating stream discharge is crucial for many ecological, biogeochemical, and hydrologic analyses. As of September 2022, The National Ecological Observatory Network (NEON) provided up to 5 years of continuous discharge estimates at 28 streams across the United States. NEON created rating curves at each site in a Bayesian framework, parameterized using hydraulic controls and manual measurements of discharge. Here we evaluate the reliability of these discharge estimates with three approaches. We (1) compared predicted to observed discharge, (2) compared predicted to observed stage, and (3) calculated the proportion of discharge estimates extrapolated beyond field measurements. We considered 1,523 site-months of continuous streamflow predictions published by NEON. Of these, 39% met our highest quality criteria, 11% fell into an intermediate classification, and 50% of site-months were classified as unreliable. We provided diagnostic metrics and categorical evaluations of continuous discharge and stage estimates by month for each site, enabling users to rapidly query for suitable NEON data.

Elevation-dependent warming of streams in mountainous regions: implications for temperature modeling and headwater climate refugia

Climate change is warming stream temperatures with significant implications for species that require cold temperatures to persist. These species often rely on headwater habitats in mountainous regions where elevation gradients in hydroclimatic conditions may induce differential patterns of long-term warming that affect the resistance of refugia. Forecasts from mechanistic and statistical stream temperature models diverge regarding whether this elevation dependence will cause above- or below-average warming in headwaters during warm summer periods, so we examined monitoring records for stream temperature (n = 271), air temperature (n = 690), and stream discharge (n = 131) across broad elevation gradients in a mountainous region of western North America to better understand potential future trends. Over a 40-year period characterized by rapid climate change from 1976–2015, air temperature stations exhibited below-average warming rates at high elevations while stream discharge declined at above average rates. Between climatically extreme years that involved summer air temperature increases >5 °C and discharge declines >70%, temperatures in high-elevation streams exhibited below average increases but otherwise showed negligible elevation dependence during intermediate climate years. In a subsequent example, it was demonstrated that elevation dependent stream warming has a minor effect on the amount of thermal habitat loss relative to the average water temperature increase within a mountain river network. We conclude that predictions of above average warming effects on headwater organisms for this region may be overly pessimistic and discuss reasons why different types of temperature models make divergent forecasts. Several research areas warrant greater attention, including descriptions of elevation-dependent patterns in other regions for comparative purposes, examination of long-term stream temperature records to understand how sensitivity to climate forcing may be evolving, use of new data sources to better represent key processes in temperature models across broad areas, and development of hybrid models that integrate the best attributes of mechanistic and statistical approaches.

Responses of Extreme Discharge to Changes in Surface-Air and Dewpoint Temperatures in Utah: Seasonality and Mechanisms

The changes in stream discharge extremes due to temperature and seasonality are key metrics in assessing the effects of climate change on the hydrological cycle. While scaling is commonly applied to temperature and precipitation due to the physical connections between temperature and moisture (i.e., Clausius–Clapeyron), the scaling rate of stream discharge extremes to air and dewpoint temperatures has not been evaluated. To address this challenge, we assess the scaling rates between stream discharge and air temperature and between stream discharge and dewpoint temperature in Utah using a well-designed statistical framework. While there are deviations from the Clausius–Clapeyron (CC) relationship in Utah using discharge data based on stream gauges and gridded climate data, we identify positive scaling rates of extreme discharge to temperatures across most of the state. Further diagnosis of extreme discharge events reveals that regional factors combined with topography are responsible for the marked seasonality of scaling, with most areas of Utah driven by spring snowmelt tied to high temperatures. The exception is far southwestern areas, being largely driven by winter rain-on-snow events. Our research highlights a measurable portion of stream discharge extremes associated with higher temperatures and dewpoints, suggesting that climate change could facilitate more extreme discharge events despite reductions to mean flows.

Glacier contribution to lowland streamflow: A multi-year, daily geochemical hydrograph separation study in subarctic Alaska

Glacier melt water is a critical fresh water contribution of stream discharge for many regions and in high latitudes glacier extent is decreasing with climate warming. However, characteristics of glacierized contributions to subarctic watershed-scale geochemistry and runoff have attracted limited attention. Tracer studies of glacier dominated watersheds are also commonly limited to a few days. We conducted a six-year geochemical hydrograph separation study of melt season daily streamflow in a glacierized watershed in Interior Alaska to estimate glacier, rain, snow, and baseflow contributions. Bulk streamflow water samples were collected daily from the lowlands of Jarvis Creek (634 km2, 3.3% glacier cover) throughout the flow season (late April through September) during 2011–2016. Synoptic sampling of source waters included rain, snow, headwater late-winter streamflow and late-summer glacier terminus discharge. All 1227 source water and bulk streamflow samples were analyzed for stable water isotopes (δ18O and δD) and dissolved ion concentrations (SO42−:Cl− ratio). Bulk streamflow water samples exhibited large seasonal and inter-annual geochemical variation. Considerable inter-annual differences in stable water isotopes within each source water (δ18O values of −15.8 to −20.9‰ for rain, for example) emphasize the importance of informing the mixing model with source waters sampled during the same season as bulk streamflow collection. We estimated glacier discharge to be the largest seasonal contributor to total warm season lowland streamflow (average 35%, ranging from 20% in year 2016 to 44% in 2012) with daily variability from 2 (June 2, 2011) to 80% (September 10, 2013). If the glacier contribution were to cease completely, total warm season bulk stream discharge would be reduced by between 22 and 48% during an above or below average total seasonal rainfall, respectively, with up to an 80% reduction in peak flows. Results from this study suggest that high variability in source contribution of glacierized watersheds, extending across intra- and interannual timescales, challenge any generalization of hydrologic function derived from short-term studies.

Effects of Within-Storm Variability on Allochthonous Flash Flooding: A Synthetic Study

Rainfall is a spatiotemporally variated process and one of the key elements to accurately capture both catchment runoff response and floodplain extents. Flash floods are the result of intense rainfall, typically associated to highly variable rain in both space and time, such as convective storms. In this work, the extent within-storm variability affects runoff and flooding is explored. The Kan catchment (Tehran, Iran) is used as base topography for the simulations. The allochthonous nature of floods in the catchment and how they interact with the effects of storm variability are further investigated. For this, 300 synthetic rainfall signals with different hyetograph variabilities are generated and imposed on a 1D/2D hydrodynamic model. Additionally, a set of simulations with different levels of spatial variability are performed. The results suggest that temporal and spatial variability affect the runoff response in different degrees. Peak discharge and hydrograph shapes, as well as flooded areas, are affected. The effect of storm temporal variability is shown to be significantly higher than storm spatial variability and storm properties such as return period, duration, and volume. Further on the influence of storm spatiotemporal variability on stream discharge and flood response is seen to be strongly dependent on the location within the drainage network at which it is assessed.