Minimum Low Flow Research Articles

A framework for implementation of environmental flow requirements through community perceptions – the case of Bargi Dam, Jabalpur District, Madhya Pradesh

A framework for implementation of environmental flow requirements through community perceptions – the case of Bargi Dam, Jabalpur District, Madhya Pradesh

A new nonparametric copula framework for the joint analysis of river water temperature and low flow characteristics for aquatic habitat risk assessment

This study proposed a nonparametric copula hazard framework in the joint risk of river water temperature (RWT) and low flow (LF) events for aquatic ecosystems, specifically ectotherm fish. This nonparametric copula density can adapt to any mutual dependence structure, providing greater flexibility. This can reduce the risk of misspecification if the underlying assumption is violated compared to conventional parametric or semiparametric copula settings. The analysis uses nonparametric copulas densities like Beta kernel copula estimator (BKCE), Bernstein copula estimator (BCE), and Transformation kernel estimator (TKE), conjoined with Gaussian Kernel density estimations (GKDEs) and parametric marginals for joint annual maximum RWT (AMRWT) and LF. The study compares different models for analyzing five Swiss river basins: parametric copulas with best-fitted GKDE and parametric margins, versus nonparametric copula. Six bandwidth selectors are estimated to fit GKDE. BKCE with GKDE margins outperformed most stations, while TKE and BCE density with GKDE margins work best for only one station. However, at one station, BKCE with best-fitted parametric margins is outperformed. All stations except Station 2473 are characterized by temperature and low flows that may be conducive to stress of a number of aquatic species, causing high AMRWT (exceeding 19 °C) and minimum LF or specific discharge, SD) quantiles at low AND-joint return periods (RP). AND (i.e. low flow AND high temperature) hazard events are less likely to occur together than OR hazard events, while univariate RPs happen more often than OR-joint RPs. In addition, the joint RP of AMRWT, given LF at different percentiles, significantly affected AMRWT for various LF conditions. Higher AMRWT with low flow conditions results in lower joint RP (except station 2473), and this stress level would be reduced when conditioned with high LF events at the same AMRWT. Station 2473 has high LF even at low percentiles, and with low AMRWT makes it very less stressful than other station under different LF conditions. Summer river flow maintenance can improve aquatic environments with high RWT. Analyzing joint statistics is crucial to understanding mutual risk in freshwater ecosystems.

Achieving sustainable low flow using hydropower reservoir for ecological water management in Glomma River Norway

Generally, low flow in rivers occur as a result of extended period of dryness which is likely attributed to drought. Drought is a natural occurrence as an outcome of reduction in precipitation in a region for a long time. Hence, low flow is a growing concern as there are possibilities of more reduced flows in rivers. However, reservoirs can be utilized to mitigate negative effects on the supply of water in dry periods and supply water for other purposes. This study aims at verifying how the low flow condition of Glomma River in Norway has been progressively sustained by hydropower reservoirs. Water Evaluation and Planning Systems (WEAP) software was used for modelling the natural streamflow condition of Glomma River, which is the longest river in Norway, using two unregulated sub-basins within the Glomma catchment. Findings from this study presents that the period between January and March are critical periods in Glomma River. Results show that the values the annual minimum low flow gotten from the three gauges suggest the flow after regulation has increased significantly as opposed to before regulation. The daily average flow is simulated by WEAP to be an average of 100 m3/s during the low flow periods and an average discharge of 350 m3/s during the summer. However, the result indicates that the flow in the summer has reduced by 80% in majority of the years. In addition, Nash Sutcliffe efficiency (NSE) for the two sub basins used for this study was 0.9 and 0.76, respectively. Also, the calculation of the coefficient of determination (R2) resulted in 0.85 and 0.78 respectively for the two sub basins. In particular, findings from this study presents evidence on the low flow condition in Glomma River prior to its regulation and how the regulation has sustained the flow.

Effects of environmental flows in a restored floodplain system on the community composition of fish, macroinvertebrates and macrophytes

Floodplains were extensively altered by anthropogenic activities, resulting in modified flow dynamics essential for maintaining diverse riverine communities. There is growing interest in restoring environmental flows by artificially modulating discharge as a potential management option in regulated rivers. In the context of a large floodplain restoration project along the upper Danube, the effects of different magnitudes of discharge on fish, macroinvertebrates and macrophytes in different habitat types of the floodplain system were studied. Community composition of fishes and macroinvertebrates changed after peak-flows of up to a 20-fold increase of mean discharge, whereas species richness and coverage of macrophytes were hardly affected. Over all habitat types, similar community response patterns were evident for macroinvertebrates, whereas in fishes, the most pronounced changes occurred in floodplain ponds that only become connected to the main channel at high flows. Community changes for fish and macroinvertebrates were mostly attributed to higher numbers of individuals (3-fold increase for fishes) rather than to changes of species richness (maximum fish species richness change <10%), however, rheophilic specialists such as Barbus barbus were much more abundant after e-flows. These findings suggest that environmental flows can have meaningful and desired conservation effects on the aquatic community composition of fishes and macroinvertebrates, depending on the magnitude of the flow and on the specific habitat type. They also stress the importance of managing dynamic flow regimes that must comprise both minimum low flows as well as flood extremes to sustain freshwater biodiversity of high conservation value.

A modeling approach to establish environmental flow threshold in ungauged semidiurnal tidal river

Due to shortage of flow monitoring data in ungauged semidiurnal river, ‘environmental flow’ (EF) determination based on its key component ‘minimum low flow’ is always difficult. For EF assessment this study selected a reach immediately after the Halda-Karnafuli confluence, a unique breeding ground for Indian Carp fishes of Bangladesh. As part of an ungauged tidal river, EF threshold establishment faces challenges in changing ecological paradigms with periodic change of tides and hydrologic alterations. This study describes a novel approach through modeling framework comprising hydrological, hydrodynamic and habitat simulation model. The EF establishment was conceptualized according to the hydrologic process of an ungauged semi-diurnal tidal regime in four steps. Initially, a hydrologic model coupled with a hydrodynamic model to simulate flow considering land use changes effect on streamflow, seepage loss of channel, friction dominated tidal decay as well as lack of long term flow characteristics. Secondly, to define hydraulic habitat feature, a statistical analysis on derived flow data was performed to identify ‘habitat suitability’. Thirdly, to observe the ecological habitat behavior based on the identified hydrologic alteration, hydraulic habitat features were investigated. Finally, based on the combined habitat suitability index flow alteration and ecological response relationship was established. Then, the obtained EF provides a set of low flow indices of desired regime and thus the obtained discharge against maximum Weighted Usable Area (WUA) was defined as EF threshold for the selected reach. A suitable EF regime condition was obtained within flow range 25–30.1 m3/s i.e., around 10–12% of the mean annual runoff of 245 m3/s and these findings are within researchers’ recommendation of minimum flow requirement. Additionally it was observed that tidal characteristics are dominant process in semi-diurnal regime. However, during the study period (2010–2015) the validated model with those reported observations can provide guidance for the decision support system (DSS) to maintain EF range in an ungauged tidal river.

Trends in low flows of German rivers since 1950: Comparability of different low‐flow indicators and their spatial patterns

AbstractClimate change, land‐use shifts, reservoir storage, and water withdrawals impact low flows in rivers, creating challenges for ecological integrity and human uses. A systematic investigation of river discharges was carried out for 79 stream gauges in Germany. Available time series between 1950 and 2013 were analysed for trends in annual minimum low flows, discharge deficits, and low‐flow durations. The application of different low‐flow indicators led to similar spatial patterns, although each metric is used for different purposes in water management applications.Statistical tests identified significant discharge trends at more than half of the stations investigated. Low‐flow trends since 1950 tended to be catchment specific, suggesting that climate change has not been the dominant driver. Most of the gauges investigated showed statistically significant increases in low flows. This can be mainly attributed to reservoir management. For rivers showing snow‐ and icemelt‐dominated flow regimes, such trends are probably overlain by climate‐driven changes (increasing amounts of rainfall, earlier snowmelt in spring). In contrast, stations showing statistically significant decreases in low flows were correlated with areas of decreasing mining activity. Hydrologic impacts of climate change are widespread and significant, but the results here suggest that human river management remains the dominant hydrologic driver on many rivers.

Impact of Global Climate Change on Stream Low Flows in a Hydraulic Fracking Affected Watershed

The impact of fresh water withdrawals for hydraulic fracturing has concerned water resource scientists and communities interested in sustainable water resource management. Specifically, low flow conditions in watersheds may be further reduced due to global climate change, as it has the potential to decrease streamflow. Since an earlier study found that the current rate of fracking had some impact on water availability, this study was conducted in order to ascertain whether or not the current fracking trend will have an impact in stream low flow in the future. This study was conducted on the Muskingum watershed in Eastern Ohio, which has been subjected to the rapid expansion of hydraulic fracking. The watershed model, Soil and Water Assessment Tool (SWAT), was used for watershed simulation using the climate output of Coupled Model Intercomparison Project Phase 5 (CMIP5). Precipitation and temperatures outputs from Max Planck Institute Earth System Model (MPI-ESM) were used to evaluate the variation in streamflow during the 21 st century using three Representative Concentration Pathways (RCP) scenarios: RCP 2.6; RCP 4.5; and RCP 8.5. Three future periods, namely, 2035s (2021-2050), 2055s (2051-2070) and 2085s (2070-2099) were set against the baseline condition (1995-2009). Lowest flow was projected to increase across the watershed during 2035s period compared to the remaining 50 years period, under the highest forced climate scenario (RCP8.5). Similarly, mean flow also could be expected to decrease during 2035s in the eastern, north-western and south western portion of the watershed. Additionally, the streamflow was simulated using current fracking scenarios and 2035s climate output in order to assess the impact of water withdrawal for a continuous trend of current fracking rates. A modest effect on stream low flow was detected, when extreme scenario (RCP 8.5) was considered, especially in the headwater streams. While results indicate that 14 of 32 subbasins were affected, with maximum difference up to 55% in lowest 7 days minimum low flow (considered lowest value from each year), negligible impact was detected on mean monthly and annual streamflow. Analysis with RCP 2.6 and RCP 4.5 indicated that stream low flow would not be affected especially in higher order streams. Even though a localized effect of hydraulic fracking to reduce the environmental flow was detected; this research indicated that future climate change may not have additional adverse impacts if hydraulic fracking trends are stable.

A comparison of the suspended and dissolved matter dynamics of two large inter‐tropical rivers draining into the Atlantic Ocean: the Congo and the Orinoco

AbstractThis study compares the total suspended sediment (TSS), total dissolved solids (TDS), and dissolved organic carbon (DOC) dynamics of two major inter‐tropical rivers, the Congo in Central Africa and the Orinoco in South America, focusing on sampling undertaken during the period 2006–2010. Both rivers are characterized by similar mean annual discharges into the Atlantic Ocean, on its eastern and western margins, respectively. For both rivers, the results presented are placed in the context of the available longer‐term hydrological time series (Congo: 1903–2010; Orinoco: 1926–2010). The key features of the recent records of material flux for both rivers were established and compared with other published data from the 20th century. The available discharge time series show that the rivers are characterized by similar maximum monthly discharges (Congo: 75 500 m3 s‐1; Orinoco: 85 500 m3 s‐1) and similar inter‐annual variability (Congo: 1.69; Orinoco: 1.66). However, contrasts in low‐flow regime (minimum low flows: Congo: 23 000 m3 s‐1; Orinoco: 2300 m3 s‐1) and seasonal variability (Congo: 3.3; Orinoco: 37.2), as well as in material fluxes were identified. Specific suspended sediment yields for the Orinoco (89 t km‐2 yr‐1) were very significantly higher than those for the Congo (9.4 t km‐2 yr‐1). These differences are mainly explained by contrasts in the physiographic characteristics of the two river basins, such as their contrasting relief. The differences between the TSS fluxes calculated for the Orinoco in this study and those indicated by published data from the second half of the 20th century can be explained by the impact of the hydroelectric dams built in the foothills of the Andean Cordillera. Changes in the TSS fluxes of the Congo are mainly explained by the impact of climatic change on total runoff. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Regression‐based approach to low flow prediction in the Maryland Piedmont region under joint climate and land use change

AbstractWe examine the low flow records for six urbanized watersheds in the Maryland Piedmont region and develop regression equations to predict annual minimum low flow events. The effects of both future climate (based on precipitation and temperature projections from two climate models: Hadley and the Canadian Climate Centre (CCC)) and land use change are incorporated to illustrate possible future trends in low flows. A regression modelling approach is pursued to predict the minimum annual 7‐day low flow estimates for the proposed future scenarios. A regional regression model was calibrated with between 10 and 50 years of daily precipitation, daily average temperature, annual imperviousness, and the daily observed flow time‐series across six watersheds. Future simulations based on a 55 km2 urbanizing watershed just north of Washington, DC, were performed. When land use and climate change were employed singly, the former predicted no trends in low flows and the latter predicted significant increasing trends under Hadley and no trends under CCC. When employed jointly, however, low flows were predicted to decrease significantly under CCC, whereas Hadley predicted no significant trends in low flows. Antecedent precipitation was the most influential predictor on low flows, followed by urbanization. Copyright © 2006 John Wiley &amp; Sons, Ltd.

LONG‐TERM CHANGES IN REGIONAL HYDROLOGIC REGIME FOLLOWING IMPOUNDMENT IN A HUMID‐CLIMATE WATERSHED1

ABSTRACT: We analyzed the type of hydrologic adjustments resulting from flow regulation across a range of dam types, distributed throughout the Connecticut River watershed, using two approaches: (1) the Index of Hydrologic Alteration (IHA) and (2) log‐Pearson Type III flood frequency analysis. We applied these analyses to seven rivers that have extensive pre‐and post‐disturbance flow records and to six rivers that have only long post‐regulation flow records. Lastly, we analyzed six unregulated streams to establish the regional natural flow regime and to test whether it has changed significantly over time in the context of an increase in forest cover from less than 20 percent historically to greater than 80 percent at present. We found significant hydrologic adjustments associated with both impoundments and land use change. On average, maximum peak flows decrease by 32 percent in impounded rivers, but the effect decreases with increasing flow duration. One‐day minimum low flows increase following regulation, except for the hydro‐electric facility on the mainstem. Hydrograph reversals occur more commonly now on the mainstem, but the tributary flood control structures experience diminished reversals. Major shifts in flood frequency occur with the largest effect occurring downstream of tributary flood control impoundments and less so downstream of the mainstem's hydroelectric facility. These overall results indicate that the hydrologic impacts of dams in humid environments can be as significant as those for large, multiple‐purpose reservoirs in more arid environments.

Nonparametric kernel estimation of low flow quantiles

A nonparametric kernel estimation model is proposed and developed for estimating low flow quantiles. Based on annual minimum low flow data and Monte Carlo simulation tests, the descriptive and predictive ability of the proposed model is compared with that of Weibull models. The results indicate that it has small bias and root mean square error in low flow quantile estimates. Application of the model to data from the Blue Nile has shown that the nonparametric approach is a viable alternative to the Weibull models.

The Enhancement of Drained Salmonid Rivers in lreland - A Bioengineering Perspective

The authors, a fisheries biologist and drainage engineer have been involved in enhancing drained salmonid rivers in lreland over the last decade. Our objective has been to increase the extent of productive salmon (Salmo salar L.) and trout (Salmo trutta L.) water in rivers which have been subjected to arterial drainage schemes. This paper draws on the experience of the authors to describe, with hindsight, how one should ideally plan such a study from the drainage design phase through to the postdrainage fisheries enhancement programme. Such a programme must be regarded as a bio-engineering exercise if it is to prove successful. Information required in this area will include detail in relation to channel and bank substrate types, a longitudinal profile of all channels, bank heights and hydrographs. In relation to the latter area particular attention should be paid to both peak flood, mean (x) and minimum low flow discharges. The fisheries biologist should ideally compile a detailed ecological profile of the catchment encompassing information on bankside and instream vegetation, macroinvertebrate fauna and fish numbers with particular reference to defining the extent to which, and the reasons why, particular channel lenghts function effectively as salmonid spawning, nursery or adult areas. When the drainage scheme is being designed, the biologist, using the aforementioned data base, should examine the proposals, at draft stage, with a view to adjusting same to the advantage of fishery interests. The various ways in which the pre-drainage bio-engineering data base can be used to minimise the impact of drainage and hasten recovery are described. Ideally, post-drainage, most instream physical works designed for fisheries enhancement should not be undertaken for two years after the dredging is completed. The logic for this approach is outlined. Some of the physical enhancement works programmes undertaken by the authors are outlined and their relative success is documented. Collaborative bio-engineering ventures in relation to minimising the ecological impact of drainage design are also discussed. The objectives of the drainage engineer and the fisheries biologist are very different. However, the authors would contend that the co-operation of both disciplines in this area can help to minimise the disruptive influence of drainage programmes and, there-after, restore the productivity of channels in fisheries terms.

Some aspects of the hydrology of one‐day annual minimum low flows of malawian rivers

AbstractFive aspects of the hydrology of one‐day annual minimum flows QIM, have been studied using data from twelve catchments in Malawi. Results indicate that the log‐normal distribution can be fitted to all twelve catchments. Four of the rivers studied are intermittent. Application of statistical methods developed in meterology to the dichotomous‐transformed data of these catchments revealed that two are ‘flow‐dominant’ and the other two are ‘dry‐dominant’. Another catchment is entirely dominated by a hydraulic gradient towards the Shire River and Elphant Marsh and so dries up every dry season for considerable periods of time despite the relatively high rainfall in the catchment. QIM, t‐days after the date of occurrence of QIM(May), can be better estimated from simple regression than from an empirically determined recession constant.