River Flow Variability Research Articles

A Practical Approach for Environmental Flow Calculation to Support Ecosystem Management in Wujiang River, China.

To promote ecosystem protection in the Wujiang River, this paper proposes a practical approach for calculating the environmental flow. The proposed approach combines the idea of the “guarantee rate” of the flow duration curve (FDC) method and the grading idea of the Tennant method. A daily flow series of the Wujiang River was compiled from 1956 to 2019 and used to compare the effect of the proposed approach versus the traditional approaches in four selected sections along the river. The results show that the environmental flow of the Wujiang River can be divided into five levels by the T-FDC method, with a level-by-level disparity, and all levels can capture the temporal and spatial variability of river flow. Additionally, the calculated basic environmental flow process ranges between the historical minimum and second minimum monthly average flow, and the threshold width of the optimal flow is more reasonable than the Tennant method. The T-FDC method can provide technical support for Wujiang River ecosystem management and sustainable development.

Effects of climate and anthropogenic changes on current and future variability in flows in the So'o River Basin (south of Cameroon)

Abstract Due to climate and environmental changes, sub-Saharan Africa (SSA) has experienced several drought and flood events in recent decades with serious consequences on the economy of the sub-region. In this context, the region needs to enhance its capacity in water resources management, based on both good knowledge of contemporary variations in river flows and reliable forecasts. The objective of this article was to study the evolution of current and future (near (2022–2060) and distant (2061–2100)) flows in the So'o River Basin (SRB) in Cameroon. To achieve this, the Pettitt and modified Mann–Kendall tests were used to analyze hydrometeorological time series in the basin. The Soil and Water Assessment Tool (SWAT) model was used to simulate the future flows in the SRB. The results obtained show that for the current period, the flows of the So'o decrease due to the decrease in precipitation. For future periods, a change in precipitation in line with the predictions of the CCCma model will lead to a decrease in river discharge in the basin, except under the RCP8.5 scenario during the second period (2061–2100), where we note an increase compared to the historical period of approximately +4%. Results from the RCA4 model project an increase in precipitation which will lead to an increase in river discharge by more than +50%, regardless of the period and the scenario considered. An increase in discharges was noted in some cases despite a drop in rainfall, particularly in the case of discharges simulated for the second period (2061–2100) from the outputs of the CCCma model. This seems to be a consequence of the increase in impervious spaces, all the more the runoff increases during this period according to the model. Results from this study could be used to enhance water resources management in the basin investigated and the region.

Dynamic High Resolution Hydrological Status Monitoring in Real-Time: The UK Water Resources Portal

Understanding the current hydro-meteorological situation is critical to manage extreme events and water resources. The United Kingdom Water Resources Portal (UKWRP) has been developed to enable dynamic, interactive access to hydro-meteorological data across the United Kingdom, including catchment daily rainfall (near), real-time daily mean river flows, groundwater levels, real-time soil moisture data, and standardised climate indices. The UKWRP offers a way of exploring the full range of river flow and rainfall variability, including comparing current conditions to those in the past, from droughts to floods. A variety of different plotting capabilities mean users can view and explore data in different ways depending on their requirements. Here we discuss the mechanisms and the engagement undertaken to develop the UKWRP, in addition to the technical issues and solutions of bringing multiple data sources and types together, how the data are processed, stored and published to deliver an integrated tool for water resources management. The UKWRP enables all water users–from farmers, to water companies to members of the general public–to view and explore the data used by regulators to manage water supplies. We demonstrate how the UKWRP can be used to monitor the hydrological situation, using recent examples of both floods and droughts, and enables consistent messaging and universal access to data and information. Finally, we discuss the decisions the information provided in the UKWRP can support, and possible future developments. The UKWRP is aimed at the United Kingdom water research and management community, but we envisage that the Portal (and the development pathway and technical solutions reported here) could provide a useful exemplar for similar systems in other international settings.

Development History of the Numerical Simulation of Tides in the East Asian Marginal Seas: An Overview

As a ubiquitous movement in the ocean, tides are vital for marine life and numerous marine activities such as fishing and ocean engineering. Tidal dynamics are complicated in the East Asian marginal seas (EAMS) due to changing complex topography and coastlines related to human activities (e.g., land reclamation and channel deepening) and natural variability (e.g., seasonal variations of ocean stratification and river flow). As an important tool, numerical models are widely used because they can provide basin-scale patterns of tidal dynamics compared to point-based tide gauges. This paper aims to overview the development history of the numerical simulation of tides in the EAMS, including the Bohai Sea, the Yellow Sea, the East China Sea, the East/Japan Sea, and the South China Sea, provide comprehensive understanding of tidal dynamics, and address contemporary research challenges. The basic features of major tidal constituents obtained by tidal models are reviewed, and the progress in the inversion of spatially and temporally changing model parameters via the adjoint method are presented. We review numerical research on how a changing ocean environment induces tidal evolution and how tides and tidal mixing influence ocean environment in turn. The generation, propagation, and dissipation of internal tides in the EAMS are also reviewed. Although remarkable progresses in tidal dynamics have been made, nonstationary tidal variations are not fully explained yet, and further efforts are needed. In addition, tidal influences on ocean environment still receive limited attention, which deserves special attention.

EURO-CORDEX: A Multi-Model Ensemble Fit for Assessing Future Hydrological Change?

Human-induced changes in climatic behavior and variations in future river flows has been at the fore-front of recent academic and political discourse. Future climate projections are a vital tool in tackling climate change and supporting future adaptation, however until recently models have been viewed individually with a lack of uncertainty quantification. A multi-model ensemble (MME) with a wide range of general circulation models, regional climate models and emissions scenarios, EURO-CORDEX provides climate projections as well as flow series projections across the European domain from 1950 to 2100. This paper explores the validity of the 68 chain MME flow projections by investigating its ability to match observed flow records in the UK over the period 1975–2004. The work explores magnitude through quantile matching and seasonality matching by time-series decomposition of trends. Two statistical tests [Mann-Whitney, and Mean Average Arctangent Percentage Error (MAAPE)] were used to compare EURO-CORDEX flow projections to observed river flows recorded by the National River Flow Archive (NRFA) across 1,436 UK river catchments. Results indicate a high degree of similarity justifying the application of this dataset for assessing future hydrological changes across a regional scale. Discretizing the flow projections into regional and hydrometric areas highlights the variability in performance between neighboring domains and the strong influence local features may have on climate model performance. The validation of EURO-CORDEX flow projection data regionally enables a wide range of applications including the exploration of future changes in local and national river flows.

Growth history of pollarded black poplars in a continental Mediterranean region: A paradigm of vanishing landscapes

Pollarded woodlands are iconic components of European rural landscapes. Pollarding is a traditional management technique used to obtain timber and firewood. However, these woodlands are subjected to different stressors in rapidly depopulating rural regions under continental Mediterranean areas where riparian black poplar (Populus nigra) pollards are widespread but still understudied. First, the rapid rural depopulation has lead to the abandonment of pollarding creating trees with abundant, thick and heavy branches. Second, climate warming and alteration of river flows reduce soil moisture which could contribute to growth decline of riparian pollards. We investigated how these stress factors have impacted radial growth in seven sites located in four river basins of southern Aragón, north eastern Spain. We used dendrochronology to reconstruct the changes in radial growth during the period 1890–2020 and to assess how growth has responded to changes in temperature, precipitation and river flow variability. Since 1900 growth suppressions, probably corresponding to pollarding events, occurred in several decades (1910s, 1960s, 1980s and 1990s) and showed a high variability among sites and river basins. Suppressions peaked during the 1940s, probably associated to intense pollarding related to high timber and firewood demand after the Spanish Civil War. Poplar radial growth increased in response to high precipitation and river flow from March to April, particularly in sites located away of river banks. Pollarding abandonment and declines in soil moisture availability threaten the persistence of veteran black poplars. Active management through pollarding and protection should be implemented to preserve these iconic, anthropogenic woodlands due to their multiple ecological and cultural services.

An Assessment of the Impacts of Snowmelt Rate and Continuity Shifts on Streamflow Dynamics in Three Alpine Watersheds in the Western U.S.

In semiarid to arid regions of the western U.S., river flow availability and variability are highly subject to shifts in snow accumulation and ablation in alpine watersheds. This study aims to examine how shifts in snowmelt rate (SMR) and snow continuity, an indicator of the consistent existence of snow on the ground, affect snow-driven streamflow dynamics in three alpine watersheds in the U.S. Great Basin. To achieve this end, the coupled hydro-ecological simulation system (CHESS) is used to simulate river flow dynamics, and multiple snow metrics are calculated to quantify the variation of SMR and snow continuity, the latter of which is measured by snow persistence (SP), snow residence time (SRT), and snow season length (SSL). Then, a new approach is proposed to partition streamflow into snow-driven and rain-driven streamflow. The statistical analyses indicate that the three alpine watersheds experienced a downward trend in SP, SRT, SSL, and SMR during the study period of 1990–2016 due to regional warming. As a result, the decrease in SMR and the decline in snow continuity shifted the occurrence day of 25% and 50% of the snow-driven cumulative discharge, as well as peak discharge, toward an earlier occurrence. Moreover, the magnitudes of snow-driven annual streamflow, summer baseflow, and peak discharge also decreased due to the declined snow continuity and the reduced SMR. Overall, by using multiple snow and flow metrics, and by partitioning streamflow into snow-driven and rain-driven flow via the newly proposed approach, we found that SMR and snow continuity determine the streamflow hydrographs and magnitudes in the three alpine watersheds. Given that warming can significantly affect snow dynamics in alpine watersheds in semiarid to arid regions, this has important implications for water resource management in the snow-dominated region when facing future climate warming.

An update on reservoir operating rules following changes on the effective capacity due to land erosion

Reservoirs play a role in decreasing the temporal variability of river flow by regulating the reservoir water release for several downstream water needs. The Keuliling Reservoir was built to meet the needs of irrigation water. However, the dry season in Aceh Besar Regency significantly impacts irrigation areas because water from the Keuliling Reservoir cannot meet the demands. During the dry season, which is also the beginning of the second rice planting season (for gadu rice variety), the water source of the Keuliling Reservoir significantly decreases. The rate of land erosion leads to sedimentation, which may cause a reduction in the effective reservoir capacity. A decline in reservoir function due to sedimentation can affect the reservoir’s performance. The reservoir operating rules need to be adjusted due to a decline in capacity caused by sedimentation. This study aims to develop updated reservoir operating rules that can be used as an operational guideline for the Keuliling Reservoir. The study used a non-linear program to optimize the reservoir operation, which required objective functions and constraints. Optimization will result in reservoir operations that can supply water according to the target rice field area in normal and wet years. The irrigation area is 578 hectares for Group I (Keuliling Upstream Irrigation Area) and 1053 ha for Group I (Keuliling Downstream Irrigation Area). However, in the dry year of Group I (DI Keuliling Hulu), with an irrigation area of 578 hectares, the rice planting pattern (one rice planting season) begins with the planting season in October I. In addition, in Group II (DI Keuliling Hilir), with an irrigation area of 781 ha, the rice planting pattern (one rice planting season) starts the planting season in October II. The reduced inflows during dry years have decreased the target irrigation area by 113 ha. This Keuliling Reservoir operating manual can determine the reservoir water release to balance it with needs and storage targets.

Key Drivers Influencing the Presence and Absence of Micropterus salmoides and Their Effect on Native Fish Communities and Biotic Integrity

Invasive alien fish species (IAFS) influence recipient ecosystems in multiple ways, from altered native fish communities to poor ecological health and higher economic losses to control and eradication. We tested key drivers and connections between an IAFS (Micropterus salmoides) presence, absence, geomorphological, hydro-chemical, physical habitat, native fish assemblages, and large river basins biotic integrity during 2016–2019. A total number of 62,121 individuals (TNI) representing 74 fish species were observed, out of which 68 species (45,677 TNI) belonged to the Geum River (GR) basin, while 63 species (16,444 TNI) were from the Mankyong/Dongjin River (MDR) basin. The results illustrated a significant contrast based on stream order, catchment area, altitude, stream gradient, and width among the sites with and without largemouth bass. However, fluctuations in nutrients (nitrogen and phosphorus) were not affected by variations in pH, dissolved oxygen, conductivity, suspended solids, and river flow. The largemouth bass has emerged as the 8th largest fish population in the GR and swiftly occupies the MDR basin with a constancy value of 45.5. Native sensitive (r = −0.38), insectivore (r = −0.252), carnivores (r = −0.085), and TNI (r = −0.512) displayed a negative correlation with increasing largemouth bass abundance. Largemouth bass induced significant regime transformation in the carnivore species. A significant difference (p < 0.01) of biotic integrity was illustrated among the largemouth bass population sites. A conspicuous interplay between ‘poor’ ecological health (r = 0.33, p = 0.038, n = 41) sites and ‘fair–excellent’ (r = −0.38, p < 0.001, n = 622) sites as compared to the overall ecological health linked with largemouth bass abundance (r = −0.397, p < 0.001, n = 663) alluded to stronger impact of the IAFS. In conclusion, the largemouth bass has potentially altered the native fish assemblage and ecological health. Further, we conclude that rapidly shifting flow patterns supported by the expanding anthropogenic interventions (weirs and dam) are the most approving factors of impending fish invasions.

Spatio-temporal hydro-climate variability in Omo-Gibe river Basin, Ethiopia

Hydroclimatic variables have changed globally mainly due to human intervention; those hydroclimatic changes alter the distribution behavior of rainfall and temperature at different scales. This study examined the magnitude of temporal and spatial variation of hydroclimatic variables in the Omo-Gibe River Basin (OGRB) using rainfall and temperature data from 1981 to 2016 and river flow data from 1981 to 2014. Mann-Kendall and Sen's slope estimator trend test were used to analyze the distribution and trends of rainfall, temperature, surface runoff, and river flow. The result shows rainfall variability has been higher in the northern and central parts and decreasing towards the southern part of the OGRB to its southern part. Results also show that seasonal and annual mean temperatures have increased significantly in the recent two decades. The northern and central OGRB summer and autumn seasons' rainfall shows a statically insignificant positive trend. However, the basin has been experiencing less to high spatio-temporal seasonal and monthly rainfall variability. Runoff and flow of the basin were constant in all rivers during the period 1981 to 1997. However, the basin experienced peaks and diminished runoff and flowed, particularly in the recent two decades. The mean seasonal trend of runoff increased insignificantly, whereas the river flow increased significantly during the summer, spring, and autumn seasons by 0.069, 0.014 and 0.197 m3s−1/year, respectively. Overall, the mean annual runoff and river flow observed an insignificant increasing trend in the entire basin. In general, the erraticity of rainfall, rising temperature, and the highest spatial and temporal variation of river flow and runoff witnessed in OGRB suggest that the basin water resource is at risk due to these reinforcing challenges, and much needs to be done by all the concerned actors to save water resources.

Resilience of hydropower plants to flow variation through the concept of flow elasticity of power: Theoretical development

Fluctuation in hydro-electricity production is primarily attributed to natural and human-induced flow variations. Reduced electricity generation because of unavailability of flow inflicts significant upward pressure on the sources and prices. Despite studies on the impact of externalities on river flow variation, there is a distinct research gap on the responsiveness of hydropower plants to change in flow. This study has introduced a novel concept of flow elasticity of power (ε) to assess the resilience of hydropower projects to flow variation. The theoretical aspect has been established for run-of-river (ROR) and storage-type (ST) cases separately and validated at two projects, one of each type, located in the Budhigandaki Basin in central Nepal. Responsiveness of hydro-projects to the topographical parameters are also dealt with here. For ROR systems, wide-ranging values of ε indicate varying levels of resilience to power generation and loss of resources. For ST projects, the response differs according to emptying, filling and ROR-equivalent phases. Furthermore, strong topographical implications on power production and its elasticity are evident. This concept of ε sets out a significant research contribution in the hydropower sector and demonstrates its possibility of direct application in projects ‘inpriori’ as well as ‘posteriori’ while planning/designing and operating/updating stages, respectively. The ε coefficient scientifically informs the planners and developers on the sensitivity of the powerplants to hydrological variations and topography ultimately benefitting the existing global challenge to minimize the loss of precious resources for sustainable hydropower development.

Comparing linear and non-linear data-driven approaches in monthly river flow prediction, based on the models SARIMA, LSSVM, ANFIS, and GMDH.

River flow variations directly affect the hydro-climatological, environmental, and ecological characteristics of a region. Therefore, an accurate prediction of river flow can critically be important for water managers and planners. The present study aims to compare different data-driven models in predicting monthly flow. Two river catchments located in the Guilan province in Iran, where rivers play an essential role in agricultural productions (mainly rice), are studied. The monthly river flow dataset was provided by Guilan Regional Water Authority during 1986-2015. The models are derived from two different numerical types of stochastic and machine learning (ML) models. The stochastic model is seasonal autoregressive integrated moving average (SARIMA), and the MLs are least square support vector machine (LSSVM), adaptive neuro-fuzzy inference system (ANFIS), and group method of data handling (GMDH). The inputs were selected by autocorrelation and partial autocorrelation functions (ACF and PACF) from the flow rates of the previous months. The data was divided into 75% of training and 25% of testing phases, and then the mentioned models were implemented. Predictions were evaluated by the criteria of root mean square error (RMSE), normalized RMSE (NRMSE), and Nash Sutcliff (NS) coefficient. According to the calculated values of different criteria during the test phase, RMSE = 1.138 cms, NRMSE = 0.109, and NS = 0.826, it can be concluded that the SARIMA model was superior to its ML competitors. Among the ML models, GMDH had the best performance (by RMSE = 1.290 cms, NRMSE = 0.124, and NS = 0.777) because it has more optimization parameters and sample space for network make-up. The models were also evaluated in hydrological drought conditions of both rivers. It was resulted that the rivers' flow can be well predicted in drought conditions by using these models, especially the SARIMA stochastic model. According to the NRMSE values (ranged between 0.1 and 0.2), the accuracy of predictions is evaluated in the appropriate range, and the present study shows promising results of the current approaches. Consequently, a comparison between the performance of linear stochastic models and complex black-box MLs, reveals that linear stochastic models are more suitable for the current region's monthlyriver flow prediction.

Uncovering the mechanisms of seasonal river–groundwater circulation using isotopes and water chemistry in the middle reaches of the Yarlungzangbo River, Tibet

Alpine catchments are severely impacted by climate change and have been extensively studied from glaciological and hydrological perspectives. However, groundwater in such catchments is rarely mentioned, and the role of the groundwater system in sustaining streamflow in alpine catchments remains unknown. This study used an integrated framework with multi-tracer data (major ions and isotopes (2H, 3H, 18O, and Sr)) to identify seasonal water sources and to uncover the recharge–discharge mechanism of the river–groundwater system in the middle reaches of the Yarlungzangbo River (YR). The results show that surface waters collected in the dry season major ions exhibit higher solute concentrations and stable isotopes (H and O) are more enriched in river water than in the wet season. In addition, river δ18O values exhibit a distinct spatial variation that decreases and then increases along the flow direction in the dry season, but this is greatly attenuated during the wet season. Estimation results show that groundwater maintains the winter–spring baseflow (contributing 45.1%), including the discharge of deep circulating groundwater through macro structures, such as south–north oriented active tensile faults (contributing 19.6 ± 9.9%). During the wet season, precipitation (contributing 31.0 ± 3.6%) and tributaries (contributing 30.0 ± 8.2%) are the principal recharge end members of the river water. The rapid recharge of phreatic groundwater occurs in alpine regions through faults and fissures. Like the YR basin, the phreatic groundwater system is primarily maintained by modern meltwater and precipitation originating from oceanic moisture. The groundwater is younger than 20 years and recharges at a seasonal scale. Precipitation is likely the principal mechanism governing annual river flow and water level variations. Therefore, groundwater storage and total runoff in the YR Basin will increase greatly with climate warming in Tibet. Simultaneously, hydrological accidents are also likely to occur, requiring advanced monitoring and prevention measures.

Impacts of climate variability and changing land use/land cover on River Mpanga flows in Uganda, East Africa

We analyzed River Mpanga Catchment (RMC) land use/land cover (LULC) types based on Landsat images for 2000, 2008 and 2014. Soil and Water Assessment Tool (SWAT) was driven by daily meteorological data from 2000 to 2011 to investigate impacts of LULC changes on river flow variation. In 2000, 2008, and 2014, cropland covered 33.0%, 69.1%, and 72.2% of RMC area, respectively. However, the fractions of the RMC area covered by grassland in 2000, 2008, and 2014 were 39.4%, 12.5%, and 10.4%, respectively. The portion of RMC area covered by human settlement increased from 0.2% in 2000 to 0.5% by 2014. RMC was characterized by increasing trends in annual rainfall and river flows. SWAT calibration and validation at daily scale over the periods 2000–2005 and 2006–2011 yielded Nash Sutcliffe Efficiency of 0.77 and 0.75, respectively. Contribution from transitions in LULC types to river flow changes over the period 2000–2008 was 7.65%. Generally, 70.46% of the total river flow variation was contributed by climate variability in terms of changes in climatic conditions. However, 21.89% of the total river flow variance remained unexplained and this could be attributed to other factors not considered in this study including extra impacts of human activities such water abstractions for agricultural, industrial and domestic needs. These findings are important for planning predictive land and water resources management amidst impacts of climate variability and human activities on water resources.

Modeling an arrested salt-wedge estuary subjected to variable river flow

In this study we present an approach to calibrate a three-dimensional hydrodynamic model of a salt-wedge estuary, the Araranguá Estuary, southern Brazil, based on the Delft3D-FLOW model. The calibration was carried out in four steps to predict the vertical salinity structure along the estuary in an efficient and effective way. Skill assessment was used to evaluate the calibration quality. The model is forced by water-level elevation along the offshore open boundary and river-discharge inflows from the two major tributaries. The hydrodynamic model was calibrated using field observation of water level, currents and longitudinal salinity structure. Calibration was performed adjusting vertical grid resolution, bottom-friction coefficient and background eddy viscosity. The model achieves high skill values at water level and currents variations during a 113-day period (in 2008) covering a wide range of river discharge and tidal forcing. Water surface fluctuations obtained from the model are in good agreement with the field data. Modeled depth-averaged currents reproduce the temporal pattern of observed data. Longitudinal salinity structure is also well reproduced, although the vertical structure is more diffusive than the observations. Results also demonstrate that the model predicts the overall measured phenomena and the effects of the flash-flood event, with the discharge affecting water level, currents and salinity.

Features of the impact of thermal power plants on the environment on the example of the Uy River Basin

The probabilistic analysis of intra-annual and interannual variability of river flow in the Uy river basin is carried out using the theory of random processes. The results of the analysis are summarized in terms of a probabilistic model. The regulatory capacity of the catchment area and man-made structures is estimated. Materials of observations made it possible to assess the hydrological structure of flowing water bodies and the impact of waste water from thermal power plants. Analysis of the hydrological and hydrochemical regime of reservoirs has shown that dynamic mixing plays a significant role in the regime of water bodies.

Catchment processes can amplify the effect of increasing rainfall variability

By filtering the incoming climate signal when producing streamflow, river basins can attenuate—or amplify—projected increases in rainfall variability. A common perception is that river systems dampen rainfall variability by averaging spatial and temporal variations in their watersheds. However, by analyzing 671 watersheds throughout the United States, we find that many catchments actually amplify the coefficient of variation of rainfall, and that these catchments also likely amplify changes in rainfall variability. Based on catchment-scale water balance principles, we relate that faculty to the interplay between two fundamental hydrological processes: water uptake by vegetation and the storage and subsequent release of water as discharge. By increasing plant water uptake, warmer temperatures might exacerbate the amplifying effect of catchments. More variable precipitations associated with a warmer climate are therefore expected to lead to even more variable river flows—a significant potential challenge for river transportation, ecosystem sustainability and water supply reliability.

The 2019/2020 floods in the UK: a hydrological appraisal

The 2019/2020 floods in the <scp>UK</scp>: a hydrological appraisal

Effects Euphrates river flow variation in Geographical distribution sand Minerals and path the weathering from AL Baghdadi city to AL Fallujah city

Petrographic study Minerals of very fine sand were carried in two terraces of Euphrates river. which starting from AL Baghdadi in the Northwest to- AL Fallujah in the East south. the study were including petrography characterization of light and heavy minerals. The aims of this study to know the ratio of minerals and spatial geographical distribution as well as to explain the effect of the Euphrates river in this distributed and weathering state. The results of this study showed; Convergence ratio of light and heavy minerals in all terraces ancient and modern. The weathering of light minerals increased in the old desert terraces. The heavy minerals (Rutile) showed the pedo stratigraphy between the modern and ancient terraces on the long the path.

Storage and Regulation of River Flows by Dams and Reservoirs

Water management in Texas is driven by dramatic spatial and temporal hydrologic variability, continual rapid population growth, declining groundwater supplies, and intensifying demands on surface water resources. Dams and reservoirs are essential for providing reliable water supplies and reducing flood risks. Numerous reservoir projects, most constructed during the 1940s through 1980s era of large scale water project construction nationwide, are operated throughout the state to store and regulate extremely variable river flows for beneficial purposes. This paper explores river system hydrology in Texas, operation of dams and reservoirs statewide to deal with extreme flow fluctuations, and associated complexities, issues, and water management strategies. The central focus of the paper is the role of large reservoirs in managing hydrologic variability and associated future uncertainty in an environment of growing demands on limited resources. Received 18 October 2019, Accepted 5 January 2021, Published online 22 February 2021 Citation: Wurbs RA. 2021. Storage and regulation of river flows by dams and reservoirs. Texas Water Journal. 12(1):10-29. Available from: https://doi.org/10.21423/twj.v12i1.7106.