Stream Discharge Research Articles

Stability in headwater chemical signatures across a dynamic flow regime in a highly urbanized Piedmont catchment

AbstractUrbanization has substantially altered low‐order streams, which show systematic degradation in water quality. Studying the spatiotemporal character of catchment scale solute dynamics is a crucial part of understanding the hydrology of urban catchments. The objectives of our study were to characterize spatial and temporal variability of solutes in headwater streams of the Upper South River, Atlanta, GA, and to examine relationships between solute concentrations and stream discharge during storm events across the watershed. Synoptic sampling was performed at 18 nested sites in the watershed during summer and fall 2020. Storm samples were also collected at three of these sites, all collocated with USGS stream gages. Samples were analysed for major ions including Ca2+, Mg2+, Na+, K+, Cl−, SO42−, and NO3−. Synoptic sampling showed an unexpectedly high level of spatial stability over time at all first‐order sites, meaning that the relative ranks of concentrations among headwater sites remain consistent over time. This is even more unexpected considering the extremely flashy and dynamic nature of the highly urbanized watershed. Contrary to stormflow studies in other settings, examination of concentration‐discharge relationships showed a homogeneous response among storms, sites, and solutes, with most hysteresis loops exhibiting a dilutive response with clockwise rotation. This indicates source‐limited behaviour for solutes in this system, where groundwater represents the highest‐concentration component of stormflow. Taken together, baseflow and stormflow solute data show that this system retains consistent headwater signals across a highly dynamic flow regime. Furthermore, such stability drives a consistent solute signature at the watershed outlet. This type of information may prove useful for understanding sources and flow paths that drive urban stream geochemistry, particularly where budget constraints limit the number of locations where instrumentation may be installed.

Identification, Abundance, and Distribution of Microplastics in Surface Water Collected from Luruaco Lake, Low Basin Magdalena River, Colombia

There are few studies on microplastic (MP) contamination in Colombia, and little is known about its impacts on continental aquatic ecosystems. This study evaluated, for the first time, the identification, abundance, and distribution of MP particles in the surface water of Luruaco Lake, in the low basin of the Magdalena River, Colombia, included in national programs in marine sciences and hydrobiological resources. Six stations and four samplings were established in the dry and rainy seasons. A total of 72 water samples were collected for microplastic extraction using hydrogen peroxide (H2O2) digestion, density separation with sodium chloride solution (NaCl), and filtration. The abundance of MPs ranged from 0 to 3.83 MPs·L−1, with an average of 1.90 MPs·L−1 in the rainy season and 0.25 MPs·L−1 in the dry season. According to the calculated coefficient of microplastics impact, the contamination in the surface water of Luruaco Lake is “maximum” to “extreme” for fibers with an average length of 2.05 mm and “minimum” to “average” for fragments that are 0.35 mm in size on average. Polyester (PES, 57.9%), polystyrene (PS, 47.0%), and polyethylene terephthalate (PET, 35.3%) polymers were more abundant in surface water. The temporal variation of the MPs indicates contamination related to the discharges of the tributary streams to the lake in the rainy season.

Influence of a cattle access point on temporal changes in stream turbidity

Unrestricted cattle access can have negative impacts on aquatic systems, including increases in stream water turbidity and suspended sediment levels. Many agri-environmental policies require the exclusion of livestock from waterbodies; however, data that quantify these impacts are scarce. This study used sensors measuring turbidity, a proxy for suspended sediment, together with motion-detecting cameras, to examine the influence of cattle in-stream activity on water quality in north-east Ireland. Two nephelometers, which automatically measured and logged turbidity, were placed upstream and downstream of a cattle access point in July 2017, while cameras were used to record cattle behaviour. A second deployment was made during February 2018 when cattle were absent. During low flows, frequent short-lived increases in turbidity were recorded at the downstream nephelometer only. These coincided with cattle accessing the water. There was a significant positive relationship between the longitudinal differences (downstream − upstream) in turbidity and the total number of cattle accessing the stream. There was no relationship between turbidity and stream discharge in July (when cattle were present), although that period was dominated by lower flow levels, with only 2 days in which discharge increased above baseflow. In contrast, there were no similar short-lived increases in turbidity in February 2018 when cattle were absent from the field, but there was a strong significant positive relationship between stream discharge and turbidity. These results highlight the consequences of cattle access for water column turbidity levels, particularly during periods of low streamflow, and therefore inform future agri-environmental policy in Ireland.

Estimation of Runoff and Sediment Yield in Response to Temporal Land Cover Change in Kentucky, USA

Land cover change is prevalent in the eastern Kentucky Appalachian region, mainly due to increased surface mining activities. This study explored the potential change in land cover and its relationship with stream discharge and sediment yield in a watershed of the Cumberland River near Harlan, Kentucky, between 2001 and 2016, using the Soil and Water Assessment Tool (SWAT). Two land cover scenarios for the years 2001 and 2016 were used separately to simulate the surface runoff and sediment yield at the outlet of the Cumberland River near Harlan. Land cover datasets from the National Land Cover Database (NLCD) were used to reclassify the land cover type into the following classes: water, developed, forest, barren, shrubland, and pasture/grassland. Evaluation of the relationship between the land cover change on discharge and sediment was performed by comparing the average annual basin values of streamflow and sediment from each of the land cover scenarios. The SWAT model output was evaluated based on several statistical parameters, including the Nash–Sutcliffe efficiency coefficient (NSE), RMSE-observations standard deviation ratio (RSR), percent bias (PBIAS), and the coefficient of determination (R²). Moreover, P-factor and R-factor indices were used to measure prediction uncertainty. The model showed an acceptable range of agreement for both calibration and validation between observed and simulated values. The temporal land cover change showed a decrease in forest area by 2.42% and an increase in developed, barren, shrubland, and grassland by 0.11%, 0.34%, 0.53%, and 1.44%, respectively. The discharge increased from 92.34 mm/year to 104.7 mm/year, and sediment increased from 0.83 t/ha to 1.63 t/ha from 2001 to 2016, respectively. Based on results from the model, this study concluded that the conversion of forest land into other land types could contribute to increased surface runoff and sediment transport detached from the soil along with runoff water. The research provides a robust approach to evaluating the effect of temporal land cover change on Appalachian streams and rivers. Such information can be useful for designing land management practices to conserve water and control soil erosion in the Appalachian region of eastern Kentucky.

Environmental predictors of the life history of the flag tetra Hyphessobrycon heterorhabdus (Characiformes: Characidae) in streams of the Eastern Amazon

Abstract This study aimed to characterize the reproductive biology of Hyphessobrycon heterorhabdus, and its response to environmental variations in the Eastern Amazon streams. We sampled specimens every two months, between March 2019 and January 2020. The population was evaluated for sex ratio, reproductive activity, growth pattern, condition factor, size at the first sexual maturation, spawning type, and fecundity. We analyzed 180 specimens, which showed a sex ratio of 1.6 males for each female across the whole period, with 2.3 males for each female during the period of greatest reproductive activity. The peak of reproductive activity coincided with higher precipitation periods and was partially predicted by factors such as water temperature, stream discharge, dissolved oxygen, substrate complexity, and electrical conductivity. The length where 50% and 100% of population to reach sexual maturity was 18.0 and 22.0 mm for males and 19.7 and 27.0 mm for females. The oocyte diameters showed a bimodal frequency, with at least two batches of oocytes. The average fecundity of 197 oocytes. The results indicate that this species presents an opportunistic strategy, and the tactics that make up this strategy depend on variations in both the physical structure of the habitat and physicochemical aspects of the water.

The effect of stream power in the instability and morphological changes of Haji Arab River, Buin Zahra (Qazvin Province, Iran)

The stream power is one of the important river variables which is used in morphological analysis. Therefore, the stream power determines both erosion and deposition. This research examines the stream power, instability and morphometric changes of the channel using the annual geomorphic energy (AGE) in Haji Arab River in Buin Zahra (Qazvin Province). The AGE is calculated by integrating the relationship between the excess specific stream power and discharge using a flow duration curve. The AGE values for each reach should be either positive or negative. Therefore, according to the differentials in AGE values, depositional and erosional reach are determined. In this paper, the results of the AGE method were compared with the rapid geomorphic assessments (RGA), including the channel stability indicators (CSI) model and OSEPI index. Also, the RHS method based on the field works was used to identify depositional and erosional geomorphic landforms. Comparing the results of the AGE with rapid RGA indices, shows that results of the OSEPI are more consistent with the erosional and depositional status of the reaches, based on the AGE. Spatial variations in lithology and structure, when combined with the course of the Haji Arab River indicate that channel morphometry locally reflects geological factors that have caused slope differences in different reaches. The calculated AGE values at different cross-sections have significant variability, reflecting characteristic local variation in bed slope, cross-section geometry and bed-sediment composition.

Rainfall-Runoff Time Lags from Saltwater Interface Interactions in Atlantic Coastal Plain Basins

The dynamic behavior of the freshwater-saltwater interface (FSI) in coastal aquifers can introduce unexpected lags between recharge and stream discharge, especially when recharge is forced by long-term cyclical precipitation patterns. This work seeks to assess these FSI impacts at the watershed scale. Recharge-discharge time lags were evaluated in 68 watersheds overlying the Floridan Aquifer System in the coastal region of the southeastern United States (Florida, Georgia, and South Carolina). Utilizing the strength of the Atlantic multidecadal oscillation (AMO) signal in this region, 10–20 year averaged recharge and discharge time series were used for the selected watersheds. Lags of 10–25 years between recharge and discharge were found in 16% of the basins considered, possibly induced by a dynamic FSI which responded slowly to the AMO-scale recharge signal. Freshwater storage coefficients (S) were estimated from time series of change-in-storage and groundwater level, with 11 basins showing S>1.5 indicating water storage well above that expected for unconfined aquifers. These 11 basins with both multidecadal recharge-discharge time lags and high S values showed a positive linear relationship between time lag and FSI depth with slope 0.016 yr/m (R-squared = 0.30). These large time lags may be directly impacting the management of these basins as they obscure water and solute mass balances in the southeastern US.

Spatial Heterogeneity and Temporal Stability of Baseflow Stream Chemistry in an Urban Watershed

AbstractSynoptic sampling of streams is an inexpensive way to gain insight into the spatial distribution of dissolved constituents in the subsurface critical zone. Few spatial synoptics have focused on urban watersheds although this approach is useful in urban areas where monitoring wells are uncommon. Baseflow stream sampling was used to quantify spatial variability of water chemistry in a highly developed Piedmont watershed in suburban Baltimore, MD having no permitted point discharges. Six synoptic surveys were conducted from 2014 to 2016 after an average of 10 days of no rain, when stream discharge was composed of baseflow from groundwater. Samples collected every 50 m over 5 km were analyzed for nitrate, sulfate, chloride, fluoride, and water stable isotopes. Longitudinal spatial patterns differed across constituents for each survey, but the pattern for each constituent varied little across synoptics. Results suggest a spatially heterogeneous, three‐dimensional pattern of localized groundwater contaminant zones steadily contributing solutes to the stream network, where high concentrations result from current and legacy land use practices. By contrast, observations from 35 point piezometers indicate that sparse groundwater measurements are not a good predictor of baseflow stream chemistry in this geologic setting. Cross‐covariance analysis of stream solute concentrations with groundwater model/backward particle tracking results suggest that spatial changes in base‐flow solute concentrations are associated with urban features such as impervious surface area, fill, and leaking potable water and sanitary sewer pipes. Predicted subsurface residence times suggest that legacy solute sources drive baseflow stream chemistry in the urban critical zone.

Invasion of natural grasslands by exotic trees increases flood risks in mountainous landscapes in South India

Invasive trees in catchments around the world are a source of concern due to their hydrological and ecological impacts. A large number of studies have focused on their impact on dry-season stream discharge due to enhanced transpiration. The impact of invasive trees on stream discharge and flood risk during extreme rain events, which are becoming more frequent due to climate change, has not been addressed adequately. We examined the influence of land-cover, canopy cover, and other catchment morphological characteristics on stream discharges in hilly catchments during light, heavy, and extreme rain events. Three years of rainfall-runoff observations, between January 2014 and December 2016, were collected in eleven neighbouring mountainous catchments in Nilgiris, South India. Each catchment had a distinct land cover, namely shola forests, montane grasslands, and catchments invaded by wattle (Acacia mearnsii). Hourly rain intensities between the percentiles 25–90, 90–95 and over 95 were categorised as light, heavy and extreme respectively, and were used to study hourly peak stream discharge responses. We compared discharge between native grassland catchments and grassland catchments invaded by wattle. Discharge rates were corrected for the catchment area. We found that land cover and canopy-cover influenced the hydrologic response to extreme rain events. Regression models with flood event as the response variable suggested an increase in rainfall-runoff response with an increase in canopy cover. The maximum hourly discharge observed in the reference grassland catchment (0.00098 mm s−1) was lower than the maximum discharge observed in low density (0.00529 mm s−1) and high density (0.00497 mm s−1) wattle catchments. At higher discharges, the flood magnitude in wattle invaded catchments was much greater than that in the grassland catchment for a given flood frequency – indicating a higher risk of severe flooding in wattle-dominated catchments. We attribute the enhanced flood discharges to the effects of spreading wattle roots on the enhancement of rapid, shallow sub-surface flows in invaded catchments. Catchments dominated by shallow sub-surface flows are known to have reduced water retention times in response to high rain intensities. Antecedent moisture conditions and drainage density were other factors that influenced the local rainfall-runoff relationships. In the Western Ghats and other parts of India grasslands have been planted with exotic woody trees, and some have become invasive. Our study indicates that replacing grasslands with woody plants at landscape scales, could affect hydrological processes and could increase flood risks during the monsoon, especially in mountainous regions. Management of invaded catchments by regulation of wattle and restoration of semi-natural grassland, combined with the installation of early warning systems in these impacted areas will help reduce flood risk during extreme rain under climate change.

Seasonal variation of transit time distribution and associated hydrological processes in a Moso bamboo watershed under the East Asian monsoon climate

Understanding seasonal variation of the transit time distribution of stream discharge and evapotranspiration is crucial in exploring the flow pathways and the rainfall-storage-streamflow processes in a watershed of interest . Here, both time-variant and time-invariant StorAge Selection (SAS) functions were adopted to estimate the transit time distribution in a Moso bamboo watershed under the East Asian monsoon climate. Daily stable isotopic compositions (δ18O, δ2H) of precipitation and streamflow at the watershed outlet from 1 October 2017 to 31 December 2020 were measured to calibrate the model parameters. The time-variant SAS method considering watershed wetness performs slightly better than the time-invariant SAS method, implying adding a watershed wetness indicator in the time-variant model results in only a minor improvement. Young water fraction and median age as two streamflow age measures were derived from the time-variant SAS model. The median age decreases abruptly within several days at three periods (one is in January 2020, and the other two periods are in Meiyu season) with larger uncertainty, while the estimated young water fraction varies gradually with much smaller uncertainty. The young water fraction derived from the time-variant SAS method appears to be more reliable than that estimated by the tracer cycle damping method. For stream discharge, the storage preferentially releases younger water to discharge under wetter conditions in the East Asian summer monsoon (EASM; June-September) period, while this phenomenon does not occur in the East Asian winter monsoon (EAWM; October-May) period. The larger hourly rainfall intensity for the whole EASM period (mean intensity 2.08 mm/h) likely enhances direct contribution of event water to streamflow than that in the EAWM period (mean intensity 0.75 mm/h). The evapotranspiration is estimated to extract older water than stream discharge in both the EAWM period and the EASM period. That is likely related to the occurrence of ecohydrological separation, and root water uptake below the soil-bedrock interface.

Understanding the anthropogenic development impacts on long-term flow regimes in a tropical river basin, Central Vietnam

ABSTRACT The Vu Gia Thu Bon (VGTB) basin constitutes the primary water supply in Central Vietnam. While climate change disturbs stream discharges and affects flood extremes, upstream dam development may intensify or mitigate such impacts. Therefore, this study provides a quantitative evaluation of long-term alterations in the flow regimes of the VGTB rivers from 1977 to 2020 resulting from the impacts of upstream anthropogenic developments. The datasets are divided into two periods, pre-2000 (1977–2000) and post-2000 (2001–2020), using different indices and analytical methods. The analyses show that since 2011, reservoir operations have reduced the maximum and high-flow discharges downstream in excess of climate change and land-use effects. However, due to the impact of water transfer by the Dak Mi 4 hydropower dam from the Vu Gia River to the Thu Bon River through a diversion channel, the minimum and low-flow discharges decreased in the pre-dam period and increased in the post-dam period.

Resolving streamflow diel fluctuations in a small agricultural catchment with an integrated surface‐subsurface hydrological model

AbstractDuring dry periods, stream discharge in vegetated catchments can naturally fluctuate up to 10% daily. Despite intensive efforts put in observing and interpreting diel fluctuations of stream discharge across a range of instrumented natural catchments worldwide, the capability of state‐of‐the‐art hydrological models to reproduce and explain such processes has rarely been tested. Here, we used CATHY, a physics‐based integrated surface‐subsurface hydrological model (ISSHM), to simulate the stream discharge in a small tile‐drained agricultural catchment in Switzerland, where streamflow diel fluctuations appeared in dry periods. The model was able to satisfactorily reproduce the measured stream discharge, including the observed diel fluctuations. Next, we designed and simulated a series of modelling scenarios aimed to disentangle the processes contributing to the diel fluctuations in stream discharge. These scenarios revealed the predominant role of evapotranspiration (ET) in the establishment of diel fluctuations in stream discharge. Irrigation sustained the baseflow in dry periods and caused short‐living streamflow peaks, which did not directly cause, but superposed to, diel patterns. Vegetation rooting depths and response to oxygen stress in the root zone slightly affected the amplitude of the streamflow diel fluctuations, while changes in the saturated hydraulic conductivity driven by diel soil temperature fluctuations caused an amplitude of the streamflow diel signal 10 times smaller compared to the one caused by ET. Our study demonstrates that ISSHMs such as CATHY can provide high‐fidelity spatially‐distributed dynamic simulations of evapotranspiration and irrigation fluxes, as well as soil moisture and groundwater flows, enhancing our understanding of the role of these hydrological processes during dry periods and thus making these models useful tools for a more sustainable management of agricultural catchments.

Characterizing seasonal differences in hydrological flow paths and source water contributions to alpine tundra streamflow

AbstractAlpine headwaters collect larger volumes of precipitation per unit area than neighbouring lowlands, recharge regional aquifers, and generate a greater proportion of river discharge than their limited extent would suggest. Despite the importance of alpine headwaters, field observations and assessments of source water contributions to streamflow in alpine tundra settings are sparse throughout the subarctic and absent in the Taiga Cordillera ecozone specifically. As such, it remains uncertain how changes to seasonally specific hydrological processes control discharge of the larger rivers to which these alpine headwaters contribute. This study quantified variability in source water contributions and flow paths during the 2019 open water season within a Mackenzie Mountain alpine tundra basin based on measurements of stable water isotopes, specific conductivity (SPC), and water volumes during runoff generating events. During the freshet, large daily snowmelt volumes resulted in the greatest volume of streamflow, which was composed mainly of pre‐event water (~92%). As the summer progressed, evapotranspiration increased, and groundwater flow paths extended, resulting in reduced event water fractions and hydrograph amplitude, and an extended duration of streamflow response. A headwater subbasin within the larger study basin was both hydrologically and isotopically unresponsive to summer rains, and instead was characterized by a delayed hydrograph response and reduced event water fraction. Results indicate this portion of the catchment was regulated by discharge from groundwater springs capable of sustaining streamflow before snowmelt commenced and during the dry summer months. As climate change continues, greater precipitation volumes and a longer open water season will likely result in reduced runoff and stream discharge from alpine basins as greater evapotranspiration and channel bed infiltration occur. This study provides a valuable data set and observations of seasonally distinct runoff generation processes to inform prediction of changes in northern alpine tundra hydrology in response to a warming climate.

Effects of deforestation on dissolved organic carbon and nitrate in catchment stream water revealed by wavelet analysis

Deforestation can lead to an increase in the availability of nutrients in the soil and, in turn, have an impact on the quality of water in receiving water bodies. This study assesses the impact of deforestation by evaluating the in-stream concentrations of dissolved organic carbon (DOC) and nitrate, their internal relationship, and those with stream discharge in the Wüstebach headwater catchment (Germany). This catchment has monitored stream water and associated environmental parameters for over a decade as part of the TERENO initiative. Additionally, there is a paired undisturbed forested catchment that serves as a reference stream. Our approach included a more advanced correlation analysis, namely wavelet analysis, that assists in determining changes in the correlation and lag time between the variables of interest over different time scales. This study found that after deforestation, there was an immediate increase in in-stream DOC concentrations, followed by an increase in nitrate ~1 year later. Overall, the mean DOC concentration increased, and mean nitrate concentration decreased across the catchment post-deforestation. Elevated stream water nutrient levels peaked around 2 to 3 years after the clear-cutting, and returned to pre-deforestation levels after ~5 years. The deforestation had no influence on the anti-correlation between DOC and nitrate. However, the correlation between both compounds and discharge was likely altered due to the increased soil nutrients availability as a result of deforestation. Wavelet coherence analysis revealed the “underlying” changing strengths and directions of the main correlations between DOC, nitrate and discharge on different time scales resulting from severe forest management interventions (here deforestation). This information provides new valuable impact insights for decision making into such forest management interventions.

Examining spatial variation in soil solutes and flowpaths in a semi-arid, montane catchment

Biogeochemical properties of soils play a crucial role in soil and stream chemistry throughout a watershed. How water interacts with soils during subsurface flow can have impacts on water quality, thus, it is fundamental to understand where and how certain soil water chemical processes occur within a catchment. In this study, ~200 soil samples were evaluated throughout a small catchment in the Front Range of Colorado, USA to examine spatial and vertical patterns in major soil solutes among different landscape units: riparian areas, alluvial/colluvial fans, and steep hillslopes. Solutes were extracted from the soil samples in the laboratory and analyzed for major cation (Li, K, Mg, Br, and Ca) and anion (F, Cl, NO2, NO3, PO4, and SO4) concentrations using ion chromatography. Concentrations of most solutes were greater in near surface soils (10 cm) than in deeper soils (100 cm) across all landscape units, except for F which increased with depth, suggestive of surface accumulation processes such as dust deposition or enrichment due to biotic cycling. Potassium had the highest variation between depths, ranging from 1.04 mg/l (100 cm) to 3.13 mg/l (10 cm) sampled from riparian landscape units. Nearly every solute was found to be enriched in riparian areas where vegetation was visibly denser, with higher mean concentrations than the hillslopes and fans, except for NO3 which had higher concentrations in the fans. Br, NO2, and PO4 concentrations were often below the detectable limit, and Li and Na were not variable between depths or landscape units. Ratioed stream water concentrations (K:Na, Ca:Mg, and NO3:Cl) vs. discharge relationships compared to the soil solute ratios indicated a hydraulic disconnection between the shallow soils (<100 cm) and the stream. Based on the comparisons among depths and landscape units, our findings suggest that K, Ca, F, and NO3 solutes may serve as valuable tracers to identify subsurface flowpaths as they are distinct among landscape units and depth within this catchment. However, interflow and/or shallow groundwater flow likely have little direct connection to streamflow generation.

Reduced complexity models for regional aquatic habitat suitability assessment

AbstractGeneralizable methods that identify suitable aquatic habitat across large river basins and regions are needed to inform resource management. Habitat suitability models intersect environmental variables to predict species occurrence, but are often data intensive and thus are typically developed at small spatial scales. This study estimated mean monthly aquatic habitat suitability throughout Utah (USA) for Bonneville Cutthroat Trout (Oncorhynchus clarkii utah) and Bluehead Sucker (Catostomus discobolus) with publicly available, geospatial datasets. We evaluated 15 habitat suitability models using unique combinations of percent of mean annual discharge, velocity, gradient, and stream temperature. Environmental variables were validated with observed conditions and species presence observations to verify habitat suitability estimates. Stream temperature, gradient, and discharge best predicted Bonneville Cutthroat Trout presence, and gradient and discharge best predicted Bluehead Sucker presence. Simple aquatic habitat suitability models outperformed models that used only streamflow to estimate habitat for both species, and are useful for conservation planning and water resources decision‐making. This modeling approach could enable resource managers to prioritize stream restoration across vast regions within their management domain, and is potentially compatible with water management modeling to improve ecological objectives in management models.

Regional Drivers of Stream Chemical Behavior: Leveraging Lithology, Land Use, and Climate Gradients Across the Colorado River, Texas USA

AbstractUnderstanding relationships between stream chemistry and watershed factors: land use/land cover, climate, and lithology are crucial to improving our knowledge of critical zone processes that influence water quality. We compiled major ion data from >100 monitoring stations collected over 60 years (1958–2018) across the Colorado River Watershed in Texas (103,000 km2). We paired this river chemistry data with complementary lithology, land use, climate, and stream discharge information. Machine learning techniques were used to produce new insights on controls of stream water chemical behavior, which were validated using traditional multivariate analyses. Studies on stream flow and chemistry in the American west and globally have shown strong relationships between major ion chemical composition, climate, and lithology which hold true for the Colorado River basin in this study. Reactive minerals, including carbonates and evaporites, dominate major ion chemistry across the upper, low‐precipitation regions of the watershed. Upstream and middle reaches of the Colorado River showed shifts from Na‐Cl‐SO4 dominated water from multiple sources including dissolution of gypsum and halite in shallow groundwater, and agricultural activities, to Ca‐HCO3 water types controlled by carbonate dissolution. In the lower portion of the watershed multiple analyses demonstrate that stream chemistry is more influenced by greater precipitation and the presence of silicate minerals than the middle and upstream reaches. This study demonstrates the power of applying machine learning approaches to publicly available long term water chemistry data sets to improve the understanding of watershed interactions with surficial lithology, salinity sources, and anthropogenic influences of water quality.

Assessment on Methodology for Predicting Flood Discharges in Creeks

As the small public facilities established in the early stages of economic development are at increased risk of disasters due to aging, the Ministry of the Interior and Safety established the “Law of Safety Management on Small Public Facilities” and provided guidelines for reducing vulnerabilities and damages. In this study, the applicability of the Clark unit hydrograph method and a rational formula, which are methods suggested in the guidelines for predicting flood discharges, are evaluated. For the evaluation, three creek basins located in urban, agricultural, and mountainous areas are selected as test watersheds, and the measured flow discharges of small streams downstream of the creeks are determined using the area ratio flow method. The evaluation results show that, for all three creeks, the peak flood discharges predicted using both the Clark unit hydrograph method and the rational formula are greater than those determined using the area ratio flow method ; therefore, the first two methods can be used to predict flood discharges in creeks to ensure safety. However, for a more precise verification of flood discharges and for selecting optimal methods, continuous investigations are required for measuring the hydrological and hydraulics data of the creek and obtaining characteristic information regarding watersheds and channels.

How much water is stolen by sewers? Estimating watershed-level inflow and infiltration throughout a metropolitan area

Human activities can have substantial impacts on watersheds, yet a major but understudied impact on many urban watersheds is the inflow and infiltration (I&I) of water into sewage infrastructure. I&I is important, because it is a major cause of sewer overflows, increases wastewater treatment plant costs, and reduces base flows of urban streams. Unfortunately, I&I information is deficient at the watershed scale. Therefore, this study uses a water-budget approach to quantify the magnitude of I&I for 90 watersheds in the Atlanta, Georgia USA region during 2013–2020. I&I for each watershed is calculated by subtracting outflows (i.e., stream discharge, water withdrawn by public water systems, and actual evapotranspiration (AET)) from inflows (i.e., precipitation, water-supply pipe leakage, and non-I&I effluent from wastewater treatment plants). Included in the AET estimates is irrigation water from public water systems and water withdrawals for agriculture. Results show that I&I is a major contributor to the total outflow in urban watersheds. The mean annual I&I total for the 15 most urbanized watersheds is 138 mm, constituting 25% of stream discharge. The mean annual I&I total from the watersheds with the five highest totals is 216 mm, which is 40% of stream discharge. These annual I&I totals align well with totals calculated for urban catchments in Europe, where most of the previous research has been conducted. Regression analyses show that the density of older housing, which is a proxy for deteriorating sewage infrastructure, is the most important predictor of I&I across the Atlanta region. Despite the uncertainties in estimating annual totals for all components, especially AET for urban watersheds, of the water budget, we conclude that estimating I&I using the water-budget approach is a useful initial approach to estimating I&I throughout a region.

Numerical Modeling in Membrane Processes

Membrane processes have demonstrated their enormous potential for water treatment, either by removing organic and mineral contaminants before permeating stream discharge, or by concentrating high added-value compounds in retentate stream [...].