Changes In Flow Regime Research Articles

A Climatic Perspective on the Impacts of Global Warming on Water Cycle of Cold Mountainous Catchments in the Tibetan Plateau: A Case Study in Yarlung Zangbo River Basin

Global warming has a profound influence on global and regional water cycles, especially in the cold mountainous area. However, detecting and quantifying such changes are still difficult because noise and variability in observed streamflow are relatively larger than the long-term trends. In this study, the impacts of global warming on the catchment water cycles in the Yarlung Zangbo River Basin (YZRB), one of most important catchments in south of the Tibetan Plateau, are quantified using a climatic approach based on the relationship between basin-scale groundwater storage and low flow at the annual time scale. By using a quantile regression method and flow recession analysis, changes in low flow regimes and basin-scale groundwater storage at the Nuxia hydrological station are quantified at the annual time scale during 1961–2000. Results show annual low flows (10th and 25th annual flows) of the YZRB have decreased significantly, while long-term annual precipitation, total streamflow, and high flows are statistically unchanged. Annual lowest seven-day flow shows a significantly downward trend (2.2 m3/s/a, p < 0.05) and its timing has advanced about 12 days (2.8 day/10a, p < 0.1) during the study period. Estimated annual basin-scale groundwater storage also shows a significant decreasing trend at a rate of 0.079 mm/a (p < 0.05) over the study period. Further analysis suggests that evaporation increase, decreased snow-fraction, and increased annual precipitation intensity induced by the rising temperature possibly are the drivers causing a significant decline in catchment low flow regimes and groundwater storage in the study area. This highlights that an increase in temperature has likely already caused significant changes in regional flow regimes in the high and cold mountainous regions, which has alarming consequences in regional ecological protection and sustainable water resources management.

The Impact of Multi-Projects on the Alteration of the Flow Regime in the Middle and Lower Course of the Hanjiang River, China

A large number of water resources development projects have significantly changed the natural flow regime of the middle and lower reaches of the Hanjiang River, especially the Danjiangkou Reservoir, cascade reservoirs, the South-to-North Water Diversion Middle Line Project and their compensation projects, completed in 1973, 2000, and 2014, respectively. The daily streamflow data of three stations in the middle and lower mainstream of the Hanjiang River are divided into four periods corresponding to pre-impact (1954–1973), interim (1974–1999), transition (2000–2013) and post-impact (2014–2018). Eco-flow metrics and indicators of hydrologic alteration (IHA) were used to study the change of natural flow regime. The annual streamflow decreased gradually during the four periods. The construction of the Danjiangkou Reservoir increased streamflow, minimum flow value, and the number of reversals in the dry season along the middle and lower course of the Hanjiang River. Moreover, the dam reduced streamflow, maximum flow value, low pulse duration, and the rise and fall rates in the wet season. Additionally, the streamflow reduced corresponding to the completion of cascade reservoirs and the Middle Route of South-to-North Water Diversion Project. In particular, the streamflow decreased drastically from July to September, affected by the Middle Route of the South-to-North Water Diversion Project. Furthermore, the compensation projects, such as the Yangtze-Hanjiang Water Diversion Project, mitigate the reduction of streamflow from July to September in the downstream. The study provides insights into the ecological and economic benefits associated with water resources development and use in the mainstream of the middle and lower course of the Hanjiang River for the achievement of sustainable development in the region.

Future streamflow regime changes in the United States: assessment using functional classification

Abstract. Streamflow regimes are changing and expected to further change under the influence of climate change, with potential impacts on flow variability and the seasonality of extremes. However, not all types of regimes are going to change in the same way. Climate change impact assessments can therefore benefit from identifying classes of catchments with similar streamflow regimes. Traditional catchment classification approaches have focused on specific meteorological and/or streamflow indices, usually neglecting the temporal information stored in the data. The aim of this study is 2-fold: (1) develop a catchment classification scheme that enables incorporation of such temporal information and (2) use the scheme to evaluate changes in future flow regimes. We use the developed classification scheme, which relies on a functional data representation, to cluster a large set of catchments in the conterminous United States (CONUS) according to their mean annual hydrographs. We identify five regime classes that summarize the behavior of catchments in the CONUS: (1) intermittent regime, (2) weak winter regime, (3) strong winter regime, (4) New Year's regime, and (5) melt regime. Our results show that these spatially contiguous classes are not only similar in terms of their regimes, but also their flood and drought behavior as well as their physiographical and meteorological characteristics. We therefore deem the functional regime classes valuable for a number of applications going beyond change assessments, including model validation studies or predictions of streamflow characteristics in ungauged basins. To assess future regime changes, we use simulated discharge time series obtained from the Variable Infiltration Capacity hydrologic model driven with meteorological time series generated by five general circulation models. A comparison of the future regime classes derived from these simulations with current classes shows that robust regime changes are expected only for currently melt-influenced regions in the Rocky Mountains. These changes in mountainous, upstream regions may require adaption of water management strategies to ensure sufficient water supply in dependent downstream regions. Highlights. Functional data clustering enables formation of clusters of catchments with similar hydrological regimes and a similar drought and flood behavior. We identify five streamflow regime clusters: (1) intermittent regime, (2) weak winter regime, (3) strong winter regime, (4) New Year's regime, and (5) melt regime. Future regime changes are most pronounced for currently melt-dominated regimes in the Rocky Mountains. Functional regime clusters have widespread utility for predictions in ungauged basins and hydroclimate analyses.

Development of a comprehensive framework for assessing the impacts of climate change and dam construction on flow regimes

The undeniable fact of climate change and dam construction alters the hydrological systems and threatens aquatic ecosystems of rivers around the world. Quantifying the impact of climate change and dam construction on flow regime is essential for water resources management and environmental protection. However, previous studies have rarely separated the effects of two factors on flow regimes, and the individual impact of each remains insufficient to date. Moreover, the existing methods have not fully captured the characteristics and temporal changes of flow regimes. In this study, we propose a new framework that integrates a streamflow reconstruction technique, indicators of hydrologic alteration (IHA), indicators of intra-annual flow variations, a revised range of variability approach to assessing the climate change and dam-induced impacts on the flow regime. The Upper Yellow River Basin (UYRB) was selected as the study area. The results show that climate change significantly reduces the monthly flow, extreme water conditions and the intra-annual indicators, and advances the Julian date of annual maximum flow. Dam construction delays the Julian date of annual maximum flow that opposes climate change impact, reduces the monthly flow in the flood season and the annual maximum flow, but increases the monthly flow in the dry season and annual minimum flow. Changes in flow regimes in the UYRB are found to be mainly due to climate change albeit there exists a cascade of dams. Based on the range of variability approach (RVA), fifteen of forty indicators are moderately changed. While the number increases to thirty-seven when considering the temporal order alteration of flow regime. The case study demonstrates that the developed framework can serve as a useful tool to evaluate the impact of climate change and dam construction on flow regimes.

Evaluation of laminar airflow heating, ventilation, and air conditioning system for particle dispersion control in operating room including staffs: A non-Boussinesq Lagrangian study

Impacts of the laminar airflow ventilation system design factors on contaminant removal and thermal comfort condition in an operating room have been investigated by means of Lagrangian-based particle transport using the non-Boussinesq modeling of the buoyancy effects. An operating room including staffs and a patient with realistic human geometries and two surgery lights are included in simulations. The laminar airflow system is placed on the ceiling with a surrounding fixed-height partial wall and the air barrier supply grills. Effects of density change in mixed convection flow regime are included by the non-Boussinesq modeling of the exact air density variation. The predicted mean vote, the age of air, the colony-forming units per cubic meter, the average temperature, the average velocity, the relative humidity, the density distribution, and the positions of particles are calculated to assess the indoor air ventilation quality. A total of 27 simulation cases have been considered to determine the impact of three main design factors including the laminar airflow system area, the supply air, and the air barrier velocities on the performance of the system. It is concluded that for the curtain velocity of 2 m/s, the thermal comfort reduces with increasing the laminar airflow velocity, but for the third staff, the results show that for small laminar airflow areas, the speed of the inlet port should be reduced and for the larger sizes, the inverse of this trend is recommended. Moreover, for all cases the humidity varies within the range of 55%–56%, which agrees well with the suggested standard humidity range between 50% and 60%. It is concluded that the cases of the laminar airflow velocity equal to 0.3 and 0.5 at the curtain velocity of 1 m/s are generally more appropriate than other cases due to less accommodation of particles near the entire body of the patient.

The impact of river regulation in the Tigris and Euphrates on the Arvandroud Estuary

The Arvandroud river (also known as Shatt-al-Arab) and its estuary have been degraded due to the changing river flow regime in the Tigris and Euphrates. This study assessed changes in flow from the major rivers and the impacts on the estuary. To assess the river flow changes, three major flow regime attributes were computed: timing (TIF), magnitude (MIF), and variability (VIF). By combining these indices, the total flow regime impact factor (IF) was scaled between 0 and 1, and classified into five groups: Low (0.80<IF<1.0), Incipient (0.60<IF<0.80), Moderate (0.40<IF<0.60), Severe (0.2<IF<0.40), and Drastic (0.0<IF<0.20). Flow regime impact maps were then created for 1941–1955, 1960–1970, 1975–1984, and 1990–2000. These revealed that, over time, the impact has extended along the basin from downstream to upstream, with a significant flow regime change from 1941–1955 to 1990–2000 in the Tigris, Euphrates, and Arvandroud. Analysis of remote sensing data revealed that the change in the flow regime has led to land degradation in the Arvandroud estuary during the past 46 years (1972–2018). In addition, the impact of the Iran–Iraq war (based on degradation of vegetation cover between 1985 and 1988) is 5.1 times of mean rate of change during 1972–2018. This study thus contributes new information on estuaries and the impact of upstream land and water use change.

Assessment of land use impact and seepage erosion contributions to seasonal variations in riverbank stability: The Iju River, SW Nigeria

The Iju (Atuwara) River is an important component of the Owo River catchment (ORC), which supports the livelihood of millions of people in Lagos and Ogun States of southwestern Nigeria. However, rapid urbanisation and numerous anthropogenic activities have caused significant changes in the natural flow regime of the river, resulting in serious bank erosion. In many riparian areas, accelerated bank erosion has been attributed to the combined effects of seepage erosion and fluvial undercutting of the bank toe due to the hydraulic stress of the river on the bank. This research, therefore, investigated the combined effects of seepage erosion, riparian vegetation (root cohesion), tension crack, and land use/land cover (LULC) change on the stability of riverbanks on the Iju River, Nigeria. Multi-temporal LULC datasets acquired from remotely sensed Landsat images of 1999, 2009, and 2019 were used to map LULC changes in the ORC. Laboratory tests were conducted to determine the geotechnical properties of the riverbanks followed by bank stability analysis and evaluation of the erosion potential of the riverbanks using the Bank Stability and Toe Erosion Model (BSTEM) and Bank Erosion Hazard Index (BEHI), respectively. The BSTEM results indicate that the factor of safety (Fs) decreased with an increase in seepage undercutting distance (du), irrespective of the bank angle. The correlation of Fs with root cohesion (cr) and depth of tension crack (zc) shows that Fs was positively correlated with cr but decreased with an increase in zc. LULC change results show that the natural flow regimes of rivers within the ORC have been adversely affected by the combined decrease in vegetation and wetlands, with a corresponding increase in the spatial extents of the built-up area and cultivated land/open spaces. These research findings are essential for the development of a watershed-scale natural disaster management framework for the southwest ecoregion of Nigeria.

The evolution of the terrestrial‐terminating Irish Sea glacier during the last glaciation

ABSTRACTHere we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land‐terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time‐transgressive moraine‐ and bedrock‐dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build‐up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120‐km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS‐3. Early retreat during GS‐3 reflects piracy of ice sources shared with the Irish‐Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS‐2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over‐deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments.

Losses and damages connected to glacier retreat in the Cordillera Blanca, Peru

The mountain cryosphere is one of the strongest affected systems by climate change. Glacier shrinkage leads to cascading impacts, including changes in river flow regimes, availability of water resources for downstream populations and economy, changes in the occurrence and severity of natural hazards, and cultural changes associated with landscape character and identity. In this study, we analyze impacts of mountain cryosphere change through a lens of Loss and Damage (LD (ii) glacial hazards; and (iii) variability of water availability. We identify the damage and losses in terms of the number of people affected by glacial hazards, monetized agricultural crop loss due to water loss, and non-economic values local people attribute to glacier loss. We find that different levels of warming have important negative but differentiated effects on natural and human systems. We also contend that the extent of loss and damage will largely be determined by governance and adaptation decisions such as water resource management and disaster risk management. We suggest that these lines of evidence are more explicitly taken into account in L&D policies.

The role of hydro-environmental factors in Mayfly (Ephemeroptera, Insecta) community structure: Identifying threshold responses.

Freshwater organisms are threatened by changes in stream flow and water temperature regimes due to global climate change and anthropogenic activities. Threats include the disappearance of narrow‐tolerance species and loss of favorable thermal conditions for cold‐adapted organisms. Mayflies are an abundant and diverse indicator of river health that performs important functional roles. The relative importance of key hydro‐environmental factors such as water temperature and flow volumes in structuring these communities has rarely been explored in the tropical regions of Africa. Here, we investigate the response of mayfly species diversity to these factors in the Luvuvhu catchment, a strategic water source area in the arid northeastern region of South Africa. Mayfly larvae were sampled monthly in stones‐in‐current biotopes across 23 sites over a one‐year period. The relationship between these environmental drivers and mayfly diversity was modeled using linear mixed effects models (LMMs) and a model‐based multivariate approach. Threshold Indicator Taxa Analysis (TITAN) was used to model the response of mayfly species to important gradients and identify thresholds of change. Site‐specific characteristic were the most important predictor of mayfly diversity, and there was considerable variation over time, with mayfly diversity peaking during winter. Along this, gradient temperature was the best predictor of assemblage structure, with five out of six reliable indicator species being cold‐adapted, and a community threshold response at 19°C. Results support laboratory‐based thresholds of temperature for mayfly species survival and development, extending empirical evidence to include field‐based observations. Increased global (climate change) and local (riparian vegetation removal, impoundments) changes are predicted to have negative impacts on mayfly diversity and ultimately on ecosystem function.

Experimental study on liquid-vapor two-phase pressure drop of pulsating flow in an evaporator

Pulsating liquid-vapor, two-phase, flows, characterized primarily by periodic oscillations in the mass flux, can occur naturally due to thermal-hydraulic conditions imposed on a flow, and they can be created by design in pursuit of improved thermal performance in heat pumping, air-conditioning, and refrigeration systems. Such flows are not fully understood, especially if the flow oscillations give rise to significant changes in liquid-vapor interface morphology (changes in two-phase flow regime). In this work, the pressure drop of R134a liquid-vapor, two-phase pulsating flows is measured under varying pulsation periods (2s to 24s), mass fluxes (100 to 200 kg•m−2•s−1), and inlet/outlet vapor qualities (0.1-0.4/0.6-0.8). The flow regimes and liquid-vapor interface evolution are also observed. Experimental results show the pressure drop increases sharply at the start of flow and drops quickly as the flow ceases in a pulsation cycle. The peak of pressure drop as the pulsation starts is larger at a higher inlet vapor quality, but the valley as flow ceases is lower. With an increasing mass flux, the rate of pressure drop increase is closely related to the pulsation period and vapor quality. A higher rate of increasing pressure drop is observed in flows with a shorter pulsation period and higher inlet vapor quality. Fluctuations in the pressure drop are also observed, and are more pronounces in low mass flux and low inlet vapor quality flows, a result attributed to fluctuations in the liquid-vapor interface and changes in two-phase flow regimes.

Impacts of Mixed‐Wettability on Brine Drainage and Supercritical CO2 Storage Efficiency in a 2.5‐D Heterogeneous Micromodel

AbstractGeological carbon storage (GCS) involves unstable drainage processes, the formation of patterns in a morphologically unstable interface between two fluids in a porous medium during drainage. The unstable drainage processes affect CO2 storage efficiency and plume distribution and can be greatly complicated by the mixed‐wet nature of rock surfaces common in hydrocarbon reservoirs where supercritical CO2 (scCO2) is used in enhanced oil recovery. We performed scCO2 injection (brine drainage) experiments at 8.5 MPa and 45°C in heterogeneous micromodels, two mixed‐wet with varying water‐ and intermediate‐wet patches, and one water‐wet. The flow regime changes from capillary fingering through crossover to viscous fingering in the micromodels of the same pore geometry but different wetting surfaces at displacement rates with logCa (capillary number) increasing from −8.1 to −4.4. While the mixed‐wet micromodel with uniformly distributed intermediate‐wet patches yields ~0.15 scCO2 saturation increase at both capillary fingering and crossover flow regimes (−8.1 ≤ logCa ≤ − 6.1), the one heterogeneous wetting to scCO2 results in ~0.09 saturation increase only at the crossover flow regime (−7.1 ≤ logCa ≤ − 6.1). The interconnected flow paths in the former are quantified and compared to the channelized scCO2 flow through intermediate‐wet patches in the latter by topological analysis. At logCa > − 6.1 (near well), the effects of wettability and pore geometry are suppressed by strong viscous force. Both scCO2 saturation and distribution suggest the importance of wettability on CO2 storage efficiency and plume shape in reservoirs and capillary leakage through caprock at GCS conditions.

Climate change and dam development: Effects on wetland connectivity and ecological habitat in tropical wetlands

AbstractWetlands are one of the most threatened ecosystems on earth. Globally, there is growing demand to develop infrastructure to harvest water resources to support agriculture, threatening the ecological integrity of associated wetland ecosystems. We investigated the potential ecological impacts on floodplain wetland connectivity in northern Australia in response to changes in flow regime due to dam construction and climate change. Results for this study indicate that a drier climate and/or dam construction in catchments have the potential to reduce the effective size of the floodplain and reduce wetland connectivity. A drier climate will reduce rainfall and subsequent catchment run‐off, resulting in a decrease in the magnitude of riverine flows. In contrast, dams in the upper catchment will reduce the magnitude of flows downstream. The reduction in flows under both dam development and a drier climate will result in reduced extent and duration of floodplain inundation and decreased wetland connectivity. As a result, we anticipate that this loss of connectivity will reduce the capacity for nutrients, carbon and primary production to be flushed into the river channel, as well as reduce the ability for biota such as fish and turtles to move between in‐channel and off‐channel habitats.

Effect of Additional Pin Electrode Placing at the Bottom of the Plasma Jet and Flow Behavior on Radical Generation and Propagation

In this article, the effect of an additional pin electrode at the bottom of the plasma jet on a double electrode atmospheric pressure plasma (APP) jet in radical generation and propagation along the jet were investigated. An additional pin electrode at the bottom of the plasma jet connecting to the ground voltage resulted in triggered glow discharge near the additional pin electrode is similar to the streamer-triggered glow discharge at the ground electrode for double electrode configuration. This leads to an increase in the intensity of excited radicals along the plasma jet with the secondary radical generation at the bottom of the plasma jet. The effect of changes in flow behavior from laminar to turbulent flow on the generation and propagation of radicals along the jet were also investigated for the double electrode configuration. Experimental observations confirm that changes in flow regimes affecting the radical generation and propagation. Increase of flow in the laminar regime increases the radical intensity and decreases the intensity as the flow becomes turbulent.

Implementation of the EU ecological flow policy in Italy with a focus on Sardinia

River ecosystems are characterised by a naturally high level of hydrodynamic perturbations which create aquatic-terrestrial habitats indispensable for many species, as well as for the human beings' welfare. Environmental degradation and habitat loss caused by increasing anthropogenic pressures and global change affect freshwater aquatic ecosystems worldwide and have caused changes in water flow regimes and channels morphologies. These, in turn, decreased the natural flow capacity and reduced habitat availability, thus causing severe degradation of rivers' ecological integrity. The ecological flow (e-flow) is commonly intended as the quantity, timing, duration, frequency and quality of water flows required to sustain freshwater, estuarine and near‐shore ecosystems and the human livelihoods and well‐being. Maintaining the e-flow represents a potential tool for restoring and managing river ecosystems, to preserve the autochthonous living communities, along with environmental services and cultural/societal values. In the last decade, methods for the determination of the e-flow in European rivers moved from a simply hydrological approach towards establishing a linkage between the hydrological regime and the good ecological status (GES) of the water bodies, as identified by the European Water Framework Directive (WFD; 2000/60/EC). Each Member State is required to implement and integrate into the River Basin Management Plans (RBMP) a methodology for the determination of the e-flow, ensuring that rivers can achieve and maintain the GES. The competent river basin authorities have thus to ascertain whether national methodologies to can be applied to different river typologies and basin environment characteristics. In this context, we narratively review the e-flow assessments in the heterogeneous Italian territory, in particular on a water scant region such as Sardinia, by analysing laws, guidelines and focusing on study cases conducted with micro and meso-scale hydraulic-habitat approaches. In the sight of a more ecological-based application of national e-flow policy, we suggest that meso-habitat methods provide a valuable tool to overcome several limitations of current e-flow implementation in the Italian territory. However, to face future challenges, such as climate change adaptation, we stress the need for further experimental studies to update water management plans with greater attention for nature conservation.

Using a coupled dispersion model to estimate depletion of a tritium oxide plume by a forest

Tritium processing facilities may release tritium oxide (HTO) to the atmosphere which poses potential health risks to exposed co-located workers and to offsite individuals. Most radiological consequence analyses determine HTO dose by applying Gaussian plume models to simulate the transport of HTO. Within these models, deposition velocity is used to assess the sum of all deposition processes acting on the plume. While this may account for vegetative and soil uptake or respiration processes, it may currently lack inclusion of the complex interactions within heterogeneous forested environments. In this complex morphology, dispersion patterns are significantly altered by changing flow regimes above and below the forest canopy and by the transfer of plume material across the canopy boundary. To determine the effects of a heterogeneous forest canopy on an airborne HTO plume, a Gaussian plume model coupled with an advection-diffusion plume model was applied to estimate transport in the free atmosphere above the forest and within the forest canopy and understory. During 2012, wind speed and wind direction measurements taken at 5 heights, ranging from 2-m to 28-m, on an instrumented meteorological tower located in a loblolly pine forest at the Department of Energy (DOE) Savannah River Site (SRS), near Aiken, SC. From these measurements, model predictions were made over a full spectrum of meteorological conditions. Deposition and resuspension velocities were calculated based on the model-predicted flux of plume material across the top of the forest canopy. Additionally, net deposition velocity of the plume material was calculated as the difference between the deposition and resuspension velocities. The 1st and 5th percentile net deposition velocities were estimated to be 0.7 cm s−1 and 1.2 cm s−1, respectively.

Modeling the impact of climate change on the environmental flow indicators over Omo-Gibe basin, Ethiopia

The study focuses on climate change impacts on the environmental flow indicators from hydrologic method point of view using IWMI’s Global Environmental Flow Calculator and Indicators of Hydrologic Alteration. It also discusses how the changes in flow magnitude and duration of annual extreme conditions, timing of annual extreme water condition, frequency and duration of high and low pulses, rate and frequency of water condition changes will affect the ecosystem. Climate change disturbs the ecology by directly affecting the functions of individual organisms (growth and behavior), modifying the population (size and age structure), and altering the ecosystem structure, functioning (e.g., decomposition, nutrient cycling, water flows, and species composition and species interactions) and its distribution within landscapes (Gitay et al., 2002). Ecosystem regime shifts can occur naturally and by anthropogenic factors (Muenich et al. in Ecol Model 340:116–125, 2016). Climate change effects on flow regime are expressed by different indicators such as mean annual runoff, mean river discharge, low and high flows, mean seasonal discharge, and changes from permanent to intermittent flow or vice versa. Understanding of changes in flow regimes is important for the well-being of humans and freshwater-dependent biota with respect to water and habitat availability (Doll and Schmied in Environ Res Lett 7(1):14037, 2012). Even though the basin is rich in fish species, peoples living in lower Omo-Gibe basin and Turkana region are undertaking a traditional fishing culture. Wildlife in the parks, pastoralist communities using the flood recession farming and livestock farming are dependent on the river. The environmental flow that sustains these activities is inevitably necessary for the survival of the biodiversity. Understanding of the flow variability helps to protect the freshwater biodiversity and maintenance of goods and services that the river provides.

What are the effects of flow-regime changes on fish productivity in temperate regions? A systematic map

BackgroundThere is growing evidence of the potential negative consequences of altered flow regimes, in terms of magnitude, frequency, timing, duration or season pattern, on fluvial ecosystems and the fisheries they support. The scientific and policy communities have acknowledged the need for a better understanding of the effects of flow alteration on fish productivity. We conducted a systematic map to provide an overview of the existing literature base on the effects of flow-regime changes on direct outcomes of freshwater or estuarine fish productivity in temperate regions to inform stakeholders and policy makers.MethodsTo identify relevant articles for inclusion in this systematic map, we searched six bibliographic databases, 29 organizational websites, one search engine, and 297 reviews, and solicited grey literature through relevant sources. We screened articles at title and abstract, then by full-text using predefined inclusion criteria. Included studies were coded for key variables of interest, along with a very basic critical appraisal for internal validity (i.e., susceptibility to bias). The quantity and characteristics of the available evidence, knowledge gaps and subtopics with sufficient coverage for full systematic reviewing are reported in a narrative synthesis. The distribution and frequency of examined effects of flow-regime changes on fish productivity outcomes are presented in visual heatmaps.Review findingsA total of 1368 studies from 1199 articles were included in the systematic map database and used to identify a number of interesting themes in the evidence base: (1) large evidence bases were found in temperate regions of United States of America (USA), Canada, and Australia; (2) most studies either used a temporal or spatial trend design i.e., lacking a ‘true’ before intervention time period, or no intervention control sites; (3) the most studied causes of altered flow regime were natural (e.g., floods, droughts, climate change), hydroelectric facilities (hydro), and dams with no hydro; and (4) there were clear clusters of studies evaluating effects of changes in magnitude and surrogate measures (e.g., velocity, water depth) on fish productivity outcomes, in particular abundance and diversity metrics. A number of potential knowledge gaps were identified: including geographic (Northern Africa, and possibly parts of Asia), causes of altered flow regime (restoration, land-use change, and water abstraction/extraction/diversion), interventions (flow duration, frequency, rate of change, or timing), outcomes (population viability) and specific intervention/cause/outcome groups (e.g., changes in flow magnitude due to hydro or natural causes and fish survival, performance, and reproduction). A few aspects in methodology were also identified across studies, primarily a lack of true comparators (e.g., temporal or spatial trend designs).ConclusionsThis map suggests subtopics warranting future evidence synthesis include, examinations into how changes in flow magnitude affects: (1) fish abundance for dams with no hydro causes; (2) fish abundance, diversity/richness, migration, and growth for hydro causes; and (3) fish abundance, diversity/richness, growth, community structure, recruitment, and migrating fish abundance for natural causes. More comprehensive evidence is needed to understand how: (1) fish productivity metrics are affected by changes in flow regime due to restoration, land-use change, and water withdrawal/diversion activities; (2) how fish productivity is affected by changes to components of flow regime other than magnitude (e.g., flow duration, frequency); and (3) changes in flow magnitude due to hydro or natural causes affect fish survival, performance, and reproduction; and (4) changes in flow regime (all causes, all interventions) affect population viability.

Displacement of springs and changes in groundwater flow regime due to the extreme drop in adjacent lake levels: The Dead Sea rift

Lake-level fluctuations brought on by climatic changes and anthropogenic factors may affect the flow regime in adjacent aquifers that discharge toward those lakes. Such fluctuations may also cause displacement of springs that discharge these aquifers. Using a calibrated numerical model, an extreme example of such phenomenon is observed in the Dead Sea rift valley and the adjacent Eastern Mountain Aquifer of the Judea and Samaria Mountains. Lake levels along the Dead Sea rift have changed dramatically and rapidly by hundreds of meters, followed by changes in the lake areas by hundreds of square kilometers. Simultaneously, the aquifer exhibited spring displacements, both on large and small scales. Currently, 50% of the aquifer water discharge in the Zuqim zone, and 10% north of the Dead Sea. But in the past, only 30% discharged at Zuqim and 40% north of the Dead Sea. There is evidence for such an occurrence in the past, and it is likely to recur in the future, based on the predicted progressive decline of the current Dead Sea level. This may have an impact on wetland habitats along the coast.

Variation in b-sigmoids with flow regime transitions in support of a new 3-segment DCA method: Improved production forecasting for tight oil and gas wells

This study uses a commercial reservoir simulator to generate production rate data for shale wells with systematic variations in fracture treatment design parameters using a plausible range of reservoir properties. The synthetic well data is then used to generate diagnostic log-rate log-time plots, which allow for a distinction of four types of flow regimes. Such a distinction of flow regimes is of practical relevance, because of the inverse link with reservoir properties and fracture treatment design parameters. Each flow regime has a characteristic slope, which traditionally has been attributed to typical flow conditions in the reservoir. The synthetic production data from the reservoir simulator are used to constrain b-sigmoid patterns for narrow discrete time increments of production (1 month) throughout the various flow regimes occurring during the economic life of each synthetic well model. Nearly a hundred different models were generated as a basis for our analysis. From the analysis of the DCA parameters for time series, using the difference in inverse of decline rates (loss ratio) for two adjacent time steps, it appears possible to recognize systematic shifts in the instantaneous decline rates and temporal b-values. In particular, the generated b-value patterns (b-sigmoids) appear diagnostic for flow regime changes recognized on diagnostic log-rate log-time plots. The results demonstrate that it is possible, based on well design and reservoir parameters, to establish correlation trends between b-sigmoids and flow regime changes using time series of the DCA parameters. The results are subsequently used to improve the accuracy of a modified 3-segment DCA method based on Arps equation. The proposed method is applied to synthetic production data, generated based on an Eagle Ford shale oil well (with known reservoir and fracture properties), to demonstrate the practical value for production forecasting and reserves estimation. This research paper paves the way for wider, future application of the methods described.