Low-flow Frequency Research Articles

The ecohydrological vulnerability of a large inland delta to changing regional streamflows and upstream irrigation expansion

AbstractFuture climate change and anthropogenic interventions can alter historical streamflow conditions and consequently degrade the health and biodiversity of freshwater ecosystems. Future ecohydrological threats, however, are difficult to quantify using the cascade of climate and hydrological models due to various uncertainties involved. This study instead uses a fully bottom‐up approach to evaluate the ecohydrological vulnerability of the Saskatchewan River Delta (SRD), the largest inland delta in North America, to changing streamflow regime and irrigation expansion. An ensemble of perturbed streamflow sequences, along with scenarios of current and expanded irrigation, was generated and fed into a regional water resource system model. Results show that the streamflow regime in the delta is more sensitive to upstream changes in annual flow volume than peak flow timing and/or irrigation expansion. The sensitivity to changes in flow volume, however, may be intensified when combined with changes in peak timing. Shifts in the upstream peak flow timing can alter the magnitude and timing of peak flow to the delta, with prime importance to aquatic biota that are adapted to historical rhythmicity in peak flows and timing. Irrigation expansion decreases the magnitude and frequency of the peak flows, alters the frequency of average and low flows, and slightly shifts the timing of the mean annual peak flow in the SRD. This can lead to isolation of lakes and wetlands from the main stream. Our results highlight the ecohydrological vulnerability of the SRD under potential changing conditions and can assist in proposing adaptation policies to protect this ecosystem.

Climate variability and irrigation impacts on streamflows in a Karst watershed—A systematic evaluation

Abstract The study area is the Lower Flint River Basin which is at the center of water conflicts in the southeastern USA. This study focuses on a systematic evaluation and separation of El Nino Southern Oscillation (ENSO) induced droughts and irrigation water withdrawal impacts on flow levels using a novel and powerful statistical technique, called JRFit. JRFit procedure was applied to quantify significant differences in streamflows, baseflows, and low flow statistics during non-irrigation (NI) and irrigation (IR) periods associated with ENSO phases. The results indicate that overall streamflow levels have decreased by approximately 20% after the introduction of irrigation in the study area. Lowering of flow levels mainly occur during La Nina phases which gets exacerbated (decreased by 50%) during growing season of IR compared to NI periods. Flow duration curve analysis showed that the frequency of low flows has increased during IR period impairing aquatic ecosystem. This is the first time an elimination approach is used to separate and quantify the impacts of anthropogenic and climate signals on water resources. This approach avoids the need of using complex and data intensive groundwater/surface water models in studying climate-stream-aquifer interactions which can be replicated easily in other data scarce watersheds. This study provides useful information to policymakers to devise irrigation water withdrawal policies during La Nina growing seasons for maintaining flow levels in the study area.

Use of a nonstationary copula to predict future bivariate low flow frequency in the Connecticut river basin

AbstractFrequency analysis of streamflow provides an essential ingredient in our understanding of hydrologic events and provides needed guidance in the design and management of water resources infrastructure. However, traditional hydrologic approaches often fail to include important external effects that can result in unpredictable or unforeseen changes in streamflow. Moreover, previous studies investigating multiple characteristics of streamflow do not address a nonstationary approach. This study explores nonstationary frequency analysis of bivariate characteristics, including occurrence and severity, of annual low flow in the Connecticut River Basin, United States. To investigate bivariate low flow frequency, copulas and their marginal distributions are constructed by using stationary and nonstationary approaches. Our study results indicate that streamflow used in this study demonstrate significant nonstationarity. Over time, the occurrence and severity of low flows are shown to be lower with the same probability based on the results of nonstationary copulas. Bivariate low flow frequencies in the years 1970, 2000, and 2030, and their joint return periods are estimated under the nonstationary copulas. Copyright © 2016 John Wiley & Sons, Ltd.

Multi-metric calibration of hydrological model to capture overall flow regimes

Summary Flow regimes (e.g., magnitude, frequency, variation, duration, timing and rating of change) play a critical role in water supply and flood control, environmental processes, as well as biodiversity and life history patterns in the aquatic ecosystem. The traditional flow magnitude-oriented calibration of hydrological model was usually inadequate to well capture all the characteristics of observed flow regimes. In this study, we simulated multiple flow regime metrics simultaneously by coupling a distributed hydrological model with an equally weighted multi-objective optimization algorithm. Two headwater watersheds in the arid Hexi Corridor were selected for the case study. Sixteen metrics were selected as optimization objectives, which could represent the major characteristics of flow regimes. Model performance was compared with that of the single objective calibration. Results showed that most metrics were better simulated by the multi-objective approach than those of the single objective calibration, especially the low and high flow magnitudes, frequency and variation, duration, maximum flow timing and rating. However, the model performance of middle flow magnitude was not significantly improved because this metric was usually well captured by single objective calibration. The timing of minimum flow was poorly predicted by both the multi-metric and single calibrations due to the uncertainties in model structure and input data. The sensitive parameter values of the hydrological model changed remarkably and the simulated hydrological processes by the multi-metric calibration became more reliable, because more flow characteristics were considered. The study is expected to provide more detailed flow information by hydrological simulation for the integrated water resources management, and to improve the simulation performances of overall flow regimes.

Influence of hydrological regime and land cover on traits and potential export capacity of adult aquatic insects from river channels.

Despite many studies highlighting the widespread occurrence and effects of resource movement between ecosystems, comparatively little is known about how anthropogenic alterations to ecosystems affect the strength, direction and importance of such fluxes. Hydrological regime and riparian land use cause well-documented changes in riverine larval invertebrate communities. Using a dataset from 66 sites collected over 20 years, we showed that such effects led to spatial and temporal differences in the density and type of larvae with winged adults within a river reach, altering the size and composition of the source pool from which adult aquatic insects can emerge. Mean annual larval densities varied 33-fold and the temporal range varied more than 20-fold between sites, associated with the hydrological regime and land cover and antecedent high and low flows, respectively. Densities of larvae with winged adults were greater in sites that had more algal coverage, agricultural land use, seasonally predictable flow regimes and faster water velocities. More interestingly, by influencing larval communities, riparian land use and the magnitude and frequency of high and low flows affected the size structure, dispersal ability and longevity of adults available to emerge from river reaches, potentially influencing the spatial extent and type of terrestrial consumers supported by aquatic prey. This suggests that anthropogenic alterations to land use or river flows will have both spatial and temporal effects on the flux and potential availability of adult aquatic insects to terrestrial consumers in many rivers.

Climate change impacts on streamflow availability for the Athabasca Oil Sands

Future bitumen production in the Athabasca Oil Sands, one of the largest remaining reserves of petroleum on the planet, is a key factor in global climate policy and politics. Climate warming in the Athabasca River Basin (ARB) has the potential to limit future streamflow availability for aquatic ecosystem needs, as well as for water withdrawals in oil sands mining operations. This study applies the land surface model IBIS and the hydrological routing algorithm THMB, with forced output from CMIP5 global climate models, to examine the response of streamflow in the ARB to climate change this century. In comparison to the small impact of water withdrawals on streamflow, climate change impacts are projected to be the primary driver of future low flow occurrences. Although winter flows are most sensitive to water withdrawals under the historical hydroclimatological regime, future climate change is projected to increase winter flows and decrease summer flows instead, with the frequency of summer low flows projected to rise by up to 85 % in the highest future emissions scenario by the end of the century. A decline in water availability due to more frequent low flows could interrupt oil sands water withdrawals and subsequent daily bitumen production for an additional 2–3 months each year by mid-century. Adaptation to climate warming in the ARB will need to recognize these changing seasonal patterns of flow in order to maintain available flows for ecological needs and water withdrawals.

Simulation and classification of the impacts of projected climate change on flow regimes in the arid Hexi Corridor of Northwest China

AbstractTraditional assessment approaches of climate change on flow regimes usually focus on flow magnitude and cannot capture the overall variation of flow regimes (e.g., variability, frequency, duration, timing, and rating). The Hexi Corridor, which is a typical arid and semiarid region in Northwest China, was selected as the study area. Streamflows were simulated by an integrated water system model in a historical period (1985–2005) and three future periods (2030s, 2050s, and 2070s). Twenty‐nine global climate models were picked from the Coupled Model Intercomparison Project Phase 5 based on projection performance, and the high (RCP85) and intermediate (RCP45) ranges of Representative Concentration Pathways were selected for future scenario analysis. All the streamflows were characterized in detail by flow regime metrics, including the magnitude, variability, and frequency of the overall flow events. The regional impacts of climate change were assessed and clustered into several similar spatial patterns. Results showed that the projected climate change would sensibly increase the magnitudes of average and low flows (75th percentile), as well as the frequencies of low and high flows (25th percentile), but decrease the flow variability. By contrast, it would not sensibly change the magnitude of high‐flow events. The flow regime variations of all scenarios and periods were clustered into three robust classes (highly, moderately, and slightly impacted classes) in the entire region. The flow regimes would be highly and moderately impacted in the middle stream and downstream with large‐sized and semidesert catchments but slightly impacted in the upper and middle streams with small‐sized and montane vegetation catchments. The impacted classes will sensibly vary at most stations in different future periods because of the spatial differences of climate change. This study would provide scientific support to implement the integrated adaptive water resource management for climate change at regional scales in the arid Hexi Corridor.

Assessing temporal and spatial alterations of flow regimes in the regulated Huai River Basin, China

The assessment of flow regime alterations is fundamental in understanding the potential impact of reservoirs and other water infrastructures on aquatic ecosystems and biota. Previously used methods to classify flow regimes have not captured temporal changes between unregulated and regulated flow regimes at individual stations. In this study, a combination of hierarchical classification and trend analysis was used to assess spatial and temporal flow regime alterations in the Huai River Basin, China. Two categories of flow regime indices were selected to characterize the impacts of reservoir and sluice regulation, including the basic flow indices for mean variation, and the cumulative variation indices for long-term alteration. The overall impact of reservoirs and sluices on flow regime included the decrease of high flow magnitudes but the increase of low flow magnitudes through time. Moreover, on average, the flow variability, and the high and low flow frequencies were reduced, while their durations were increased. Reservoirs had a greater impact on flow regimes than sluices. The flow regimes at 18 of 30 stations were altered significantly from a pre-regulation condition and were divided into three main types of alteration corresponding to operational rules of reservoirs and sluices. From a management perspective, water projects in China should address the environmental flow requirements of the rivers, particularly in terms of the hydrologic indices affected mostly by reservoirs and sluices. This study will promote the application of flow regime classification and river restoration in highly regulated basins in China. (C) 2015 Published by Elsevier B.V.

Low flow frequency analysis for stream with mixed populations

A methodology is developed for the estimation of annual low-flow quantiles for streams with annual low flows occurring in both the summer and winter. Since the low flow generating processes are different in summer and winter, independent seasonal analyses are required. The methodology provides recommendations for assessment of record length, randomness, homogeneity, independence and stationarity, as well as guidelines for distribution selection and fitting for seasonal distributions. The seasonal distributions are then used to develop the combined distribution for annual low flow estimation. Four worked examples of long-term Canadian hydrometric stations are provided.

Quantifying hydrological responses of small Mediterranean catchments under climate change projections

Catchment flow regimes alteration is likely to be a prominent consequence of climate change projections in the Mediterranean. Here we explore the potential effects of climatic change on the flow regime of the Thau and the Chiba catchments which are located in Southern France and Northeastern Tunisia, respectively. The Soil and Water Assessment Tool (SWAT) hydrological model is forced with projections from an ensemble of 4 climate model (CM) to assess changes and uncertainty in relevant hydrological indicators related to water balance, magnitude, frequency and timing of the flow between a reference (1971–2000) and future (2041–2071) periods. Results indicate that both catchments are likely to experience a decrease in precipitation and increase in temperature in the future. Consequently, runoff and soil water content are projected to decrease whereas potential evapotranspiration is likely to increase in both catchments. Yet uncertain, the projected magnitudes of these changes are higher in the wet period than in the dry period. Analyses of extreme flow show similar trend in both catchments, projecting a decrease in both high flow and low flow magnitudes for various time durations. Further, significant increase in low flow frequency as a proxy for hydrological droughts is projected for both catchments but with higher uncertainty in the wet period than in the dry period. Although no changes in the average timing of maximum and minimum flow events for different flow durations are projected, substantial uncertainty remains in the hydrological projections. While the results in both catchments show consistent trend of change for most of the hydrologic indicators, the overall degree of alteration on the flow regime of the Chiba catchment is projected to be higher than that of the Thau catchment. The projected magnitudes of alteration as well as their associated uncertainty vary depending on the catchment characteristics and flow seasonality.

Comparison of Distribution Methods of Low Flow Analysis for Bandar Segamat, Johor

During the monsoon season, certain areas in Malaysia are experiencing a flood. While during the transition period Malaysia is experiencing a drought. This phenomenon could lead to severe disaster and precaution monitoring is needed to avoid this occurrences. Low flow during the dry season could lead to several negative effects on the river ecosystem. Thus, this study was conducted to determine the low flow frequency and intensity for the Segamat city. The duration for 2 years to 100 years based on the previous 20 years of stream flow data were used to calculated. Stream flow data were obtained from the Department of Irrigation and Drainage (DID). Two prominent distribution analyses methods known as Gumbel Distribution and Log pearson Type III Distribution were applied. The distribution results were validated using Root Mean Square Error (RMSE) and California method and Weibull method are selected. Based on the analyses results, it clearly shows that the distibution of low flow are between 1 m3/s to 10 m3/s. The flow are significantly correlate with the rainfall intensity. RMSE was selected based on the lowest value of 0.721 for the Gumble Distribution and 1.831 for Log Pearson Type III Distribution. Chi-square test shows a good agreement for Gumble Distribution (7.615<12.59) and Log Pearson Type III(5.201<11.07) using 5% significant level. The confident level form both tests are valid (p>0.05), thus, this results could be used for further analyses to alleviate the low flow in the study area.

The role of seasonal and occasional floods in the origin of extreme hydrological events

Abstract. Extreme hydrological events on the rivers of European part of Russia are closely related to the hydrological regime transformation answering recent climate changes. Rivers in this region used to be traditionally attributed to the Eastern-European type with well-pronounced seasonal flood wave and quite low flow period during summer and winter. During the last twenty years the role of the occasional floods became more and more important. Number of winter floods, connected with thaws rose dramatically, in the same manner as summer flash floods. In this study, the frequency and duration of extreme low flow and high flow events is analyzed. The deficits during hydrological year were calculated. Due to results increase in natural runoff regulation, does not reduce frequency of extreme events, in some regions it raises.

Regional low-flow frequency analysis with a recession parameter from a non-linear reservoir model

• Recession parameters are used in a regional model to estimate low-flow quantiles. • The non-linear reservoir model is considered as well as the classical linear model. • Performances with the non-linear model are superior. • The performances of the regional model at partially gaged catchments are evaluated. Several studies have shown that improvements in the regional prediction of low-flow characteristics can be obtained through the inclusion of a parameter characterising catchment baseflow recession. Usually, a linear reservoir model is assumed to define recession characteristics used as predictors in regional models. We propose in this study to adopt instead a non-linear model. Predictors derived from the linear model and the non-linear model are used separately in low-flow regional models along with other predictors representing physiographical and meteorological characteristics. These models are applied to selected gaged catchments. Results show that better performances are obtained with the parameter from the non-linear model. One drawback of using recession parameters for regional estimation is that a streamflow record is required at the site of interest. However, recession parameters can be estimated with short streamflow records. In this study, to simulate the performances obtained at partially gaged catchments, the recession parameters are estimated with very short streamflow records at target sites. Results indicate that, with a streamflow record as short as one year, a model with a recession parameter from the non-linear model leads to better performances than a model with only physiographical and meteorological characteristics.

Detecting changes in extreme streamflow in the Tarim River, Northwest China

We analyzed the characteristics of streamflow changes in the Tarim River Basin using daily data collected at 7 hydrological stations. We ran the nonparametric Mann–Kendall test to detect trends in hydrological extremes. We also applied the Indicators of Hydrological Alteration (IHA), to assess flow regime variations. The results indicate that: (1) the hydrological extremes in headwater experienced increases in magnitude, duration, and high flow frequency; the mainstream exhibited increases in low flow duration and low flow frequency, and a decrease in high percentile flow and high flow frequency; (2) The trends of extremes related to minimum flow is greater than maximum flow; the date of maximum flow in both the headwater and mainstream has advanced; the most drastic changes in extreme streamflow occurred during winter; (3) Climate change has considerably altered flow regime in the headwater. Although climate change has profoundly affected the water supply upstream, human activities are dominant in determining flow regime.

Turkey Creek—A Case Study of Ecohydrology and Integrated Watershed Management in the Low-Gradient Atlantic Coastal Plain, USA

Water yield, water supply and quality, wildlife habitat, and ecosystem productivity and services are important societal concerns for natural resource management in the 21st century. Watershed-scale ecohydrologic studies can provide needed context for addressing complex spatial and temporal dynamics of these functions and services. This study was conducted on the 5240 ha Turkey Creek watershed (WS 78) draining a 3rd order stream on the Santee Experimental Forest within the South Carolina Atlantic Coastal Plain, USA. The study objectives were to present the hydrologic characteristics of this relatively undisturbed, except by a hurricane (Hugo, 1989), forested water-shed and to discuss key elements for watershed management, including water resource assessment (WRM), modeling integrated water resources management, environmental assessment, land use planning, social impact assessment, and information management. Runoff coefficients, flow duration curves, flood and low flow frequency curves, surface and ground water yields were assessed as elements of the WRM. Results from the last 10 years of interdisciplinary studies have also advanced the understanding of coastal ecohydrologic characteristics and processes, water balance, and their modeling including the need of high resolution LiDAR data. For example, surface water dynamics were shown to be regulated primarily by the water table, dependent upon pre- cipitation and evapotranspiration (ET). Analysis of pre- and post-Hugo streamflow data showed somewhat lower but insignificant (α = 0.05) mean annual flow but increased frequency of larger flows for the post-Hugo compared with the pre-Hugo level. However, there was no significant difference in mean annual ET, potentially indicating the resiliency of this coastal forest. Although the information from this study may be useful for comparison of coastal ecohydrologic issues, it is becoming increasingly clear that multi-site studies may be warranted to understand these complex systems in the face of climate change, sea level rise, and increasing development in coastal regions.

Frequency Analysis of Minimum Ecological Flow and Gage Height in Suwannee River, Florida

ABSTRACT Nnaji, G.A.; Huang, W.; Gitau, M.W., and Clark II, C., 2014. Frequency analysis of minimum ecological flow and gage height in Suwannee River, Florida. Hydrological frequency analysis has been conducted to estimate minimum ecological flow and gage height for protection of the ecosystem in Suwannee River, Florida, USA. By comparing to observations, results indicate that both Log Pearson Type III and Weibull distributions provide reasonable predictions of low flow frequency curves. However, Log Pearson Type III distribution provides more accurate predictions than Weibull distribution in low flow analysis in Suwannee River. The 7Q10 method, which has been used by United States Geological Service in USA, is defined as the lowest 7-day average flow that occurs on average once every 10 years, which has been used by some water management agencies in USA for river ecological study. Based on 7Q10 method and frequency analysis, the minimum ecological flow and gage height in Suwannee River are proposed for w...

Extreme low flow of the Topolovets and Voinishka Rivers (Danube tributaries, Bulgaria)

The minimal stream flow is the most sensitive characteristic of stream flow. The aim of the paper is the assessment of the duration and the frequency of low flow through threshold method on daily discharges. The daily data of the two Danube tributaries (the Topolovets and Voinishka) have been used. The results present the following: low flow typically appears in the summer and episodically in the spring and winter; the duration varies between some days to month; the spatial distribution of extreme minimum flow is discrete and depends on climatic and anthropogenic activities. The method of quantiles gives good threshold level for defining extremely low stream flow, but have to apply in keeping with concrete conditions and purposes.

Illustrating a new global-scale approach to estimating potential reduction in fish species richness due to flow alteration

Abstract. Changes in river discharge due to human activities and climate change would affect the sustainability of freshwater ecosystems. To globally assess how changes in river discharge will affect the future status of freshwater ecosystems, global-scale hydrological simulations need to be connected with a model to estimate the durability of freshwater ecosystems. However, the development of this specific modelling combination for the global scale is still in its infancy. In this study, two statistical methods are introduced to link flow regimes to fish species richness (FSR): one is based on a linear relationship between FSR and mean river discharge (hereafter, FSR-MAD method), and the other is based on a multi-linear relationship between FSR and ecologically relevant flow indices involving several other flow characteristics and mean river discharge (FSR-FLVAR method). The FSR-MAD method has been used previously in global simulation studies. The FSR-FLVAR method is newly introduced here. These statistical methods for estimating FSR were combined with a set of global river discharge simulations to evaluate the potential impact of climate-change-induced flow alterations on FSR changes. Generally, future reductions in FSR with the FSR-FLVAR method are greater and much more scattered than with the FSR-MAD method. In arid regions, both methods indicate reductions in FSR because mean discharge is projected to decrease from past to future, although the magnitude of reductions in FSR is different between the two methods. In contrast, in heavy-snow regions a large reduction in FSR is shown by the FSR-FLVAR method due to increases in the frequency of low and high flows. Although further research is clearly needed to conclude which method is more appropriate, this study demonstrates that the FSR-FLVAR method could produce considerably different results when assessing the global role of flow alterations in changing freshwater ecosystems.

American White Pelican Predation on Cui‐ui in Pyramid Lake, Nevada

AbstractAnthropogenic changes to the Pyramid Lake–Truckee River ecosystem in Nevada are suspected to have altered the predator–prey balance between American white pelican Pelecanus erythrorhynchos and Cui‐ui Chasmistes cujus. We estimated the loss of the adult Cui‐ui population to pelican predation over a 13‐year period by netting and tagging Cui‐uis as they aggregated at the mouth of the Truckee River prior to their spawning migration into the Truckee River. Cui‐ui access to the Truckee River typically required traversing a shallow delta (a foraging advantage for these American white pelicans). Dams and greater frequency of low stream flows also contributed to American white pelican foraging success. We used tag recoveries from Pyramid Lake's nesting colony of American white pelicans along with an experiment to estimate the chance of tag recovery within the colony to calculate the number of tagged fish taken by American white pelicans. We also used numbered tags to test whether there was a size preference for Cui‐uis taken. Our results showed that the primary source of adult Cui‐ui mortality was from American white pelican predation in the Truckee River. Within a 13‐year period American white pelicans had taken 90% of the tags deployed during the first 7 years of the interval. There was no preference for the size of Cui‐uis taken. A better understanding of the effects of heavy cropping by American white pelicans on Cui‐ui population dynamics is still needed.Received March 26, 2013; accepted October 8, 2013Published online January 24, 2014

Non-Parametric Low-Flow Frequency Analysis Using RCPs Scenario Data : A Case Study of the Gwangdong Storage Reservoir, Korea

In this study, we applied an advanced non-parametric low-flow frequency analysis using boundary kernel by Representative Concentration Pathways (RCPs) climate change scenarios through Arc-SWAT long-term runoff model simulation at the Gwangdong storage reservoir located in Taeback, Gangwondo. The results show that drought frequency under RCPs was expected to increase due to reduced runoff during the near future, and the variation of low-flow time series was appeared greatly under RCP8.5 scenario, respectively. The result from drought frequency of Median flow in the near future (2030s) compared historic period, the case of 30-year low-flow frequency was increased (the RCP4.5 shows +22.4% and the RCP8.5 shows +40.4%), but in the distant future (2080s) expected increase of drought frequency due to the reduction of low-flow (under RCP4.5: -4.7% and RCP8.5: -52.9%), respectively. In case of Quantile 25% flow time series data also expected that the severe drought frequency will be increased in the distant future by reducing low-flow (the RCP4.5 shows -20.8% to –60.0% and the RCP8.5 shows -30.4% to –96.0%). This non-parametric low-flow frequency analysis results according to the RCPs scenarios have expected to consider to take advantage of as a basis data for water resources management and countermeasures of climate change in the mid-watershed over the Korean Peninsula.