Changes In Flow Regime Research Articles

Flow-induced noise generation at the outlet of a capillary tube

The aim of this work is the identification of noise generation mechanisms at the outlet of an adiabatic capillary tube used as throttling device in a cooling cycle. For this purpose, experiments are carried out on a R-600a test bench designed for systematic investigations on flow-induced capillary noise. The experiments are performed using a copper capillary tube with an inner diameter of 0.6 mm. The test bench enables process control with a continuous change of the capillary outlet pressure, while the inlet pressure and temperature remain constant. A similar process takes place in a refrigerator at the beginning of the on-cycle, when the compressor starts to pull down the evaporation pressure. Correlations between various operating conditions and the emitted airborne noise can thus be established. The evaluation of the sound pressure level profiles provides a method to indicate the change of flow regimes at the capillary tube outlet, using flow pattern maps from literature. We identify two different noise generation mechanisms: In case of intermittent flow regimes, pressure pulses evoked by the fluid lead to fluctuating unsteady noise excitations. During non-intermittent flow regimes, on the other hand, uniform noise excitations strongly correlate with the vapor velocity of the two-phase flow.

Geochemical and biological controls on the ecological relevance of total, dissolved, and colloidal forms of trace elements in large boreal rivers: review and case studies

The concentrations of trace elements (TEs) in large boreal rivers can fluctuate markedly due to changing water levels and flow rates associated with spring melt and variable contributions from tributaries and groundwaters, themselves having different compositions. These fluctuating and frequently high concentrations create regulatory challenges for protecting aquatic life. For example, water quality criteria do not account for changes in flow regimes that can result in TE levels that may exceed regulatory limits, and neither do they account for the markedly different lability and bioaccessibility of suspended solids. This review addresses the geochemical and biological processes that govern the lability and bioaccessibility of TEs in boreal rivers, with an emphasis on the challenges posed by the colloidal behaviour of many TEs, and their relationship to the dissolved fraction (i.e., <0.45 μm in size). After reviewing the processes and dynamics that give rise to the forms and behaviour of TEs in large boreal rivers, their relevance for aquatic organisms and the associated relationships between size and lability and bioaccessibility are discussed. The importance of biological variables and different forms of TEs for limiting lability and bioaccessibility are also addressed. Two case studies emphasize seasonal fluctuations and accompanying changes in the distribution of TE amongst different size fractions and associated colloidal species in large boreal rivers: the Northern Dvina and one of its tributaries, the Pinega River, both in Russia, and the Athabasca River in Alberta, Canada. Water quality in the Athabasca River is briefly discussed with respect to Canadian guidelines.

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the “Grain for Green” project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt’s test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the “Grain for Green” period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

Spawning periodicity and synchrony of bluehead chub (Nocomis leptocephalus) and a nest associate, yellowfin shiner (Notropis lutipinnis), across local streams

AbstractWe studied daily spawning periodicity of a nest‐building species, bluehead chub (Nocomis leptocephalus), and a nest associate, yellowfin shiner (Notropis lutipinnis), in three streams in the upper Piedmont region of South Carolina, USA. Field observations were conducted for 89 consecutive days in 2016 by recording the number of active nests and environmental variables. A total of 71 nests were located across study streams; bluhead chub and yellowfin shiner spawned between April and June. Spawning was observed periodically at intervals of 4–6 days within the same stream and across different streams, indicating broad‐scale influences of the same environmental factors leading to synchrony. A generalized linear auto‐regressive and moving average model showed that the periodic spawning pattern was likely caused by changes in water temperature, with effects of water level varying by stream. Specifically, spawning was triggered by a short‐term (2‐day) increase in water temperature and was observed under stable flow conditions (i.e. a lack of precipitation). This study showed that spawning periodicity of bluehead chub and yellowfin shiner tracked daily variation in in‐stream conditions, indicating that their reproduction might be affected by anthropogenic disturbances that affect the rate of change in thermal and flow regimes at the fine temporal scale (e.g. hydroelectric dams and impervious cover).

Future shifts in extreme flow regimes in Alpine regions

Abstract. Extreme low and high flows can have negative economic, social, and ecological effects and are expected to become more severe in many regions due to climate change. Besides low and high flows, the whole flow regime, i.e., annual hydrograph comprised of monthly mean flows, is subject to changes. Knowledge on future changes in flow regimes is important since regimes contain information on both extremes and conditions prior to the dry and wet seasons. Changes in individual low- and high-flow characteristics as well as flow regimes under mean conditions have been thoroughly studied. In contrast, little is known about changes in extreme flow regimes. We here propose two methods for the estimation of extreme flow regimes and apply them to simulated discharge time series for future climate conditions in Switzerland. The first method relies on frequency analysis performed on annual flow duration curves. The second approach performs frequency analysis of the discharge sums of a large set of stochastically generated annual hydrographs. Both approaches were found to produce similar 100-year regime estimates when applied to a data set of 19 hydrological regions in Switzerland. Our results show that changes in both extreme low- and high-flow regimes for rainfall-dominated regions are distinct from those in melt-dominated regions. In rainfall-dominated regions, the minimum discharge of low-flow regimes decreases by up to 50 %, whilst the reduction is 25 % for high-flow regimes. In contrast, the maximum discharge of low- and high-flow regimes increases by up to 50 %. In melt-dominated regions, the changes point in the other direction than those in rainfall-dominated regions. The minimum and maximum discharges of extreme regimes increase by up to 100 % and decrease by less than 50 %, respectively. Our findings provide guidance in water resource planning and management and the extreme regime estimates are a valuable basis for climate impact studies. Highlights Estimation of 100-year low- and high-flow regimes using annual flow duration curves and stochastically simulated discharge time series Both mean and extreme regimes will change under future climate conditions. The minimum discharge of extreme regimes will decrease in rainfall-dominated regions but increase in melt-dominated regions. The maximum discharge of extreme regimes will increase and decrease in rainfall-dominated and melt-dominated regions, respectively.

CO2 injectivity behaviour under non-isothermal conditions – Field observations and assessments from the Quest CCS operation

Commercial-scale deployment of Carbon Capture and Storage (CCS) as a viable greenhouse gas (GHG) emissions reduction technology requires that the CO2 be continuously injected at predictably significant and cost-efficient rates into geological formations (e.g. deep saline aquifers).The Quest CCS operation (located in Alberta, Canada) is a fully integrated carbon capture, transport and storage facility operated by Shell Canada. Quest continuously captures and stores about 1.1 Mt of CO2 per year, and it’s expected to continue until 2040. Quest is a dedicated geological storage project (no EOR component) with multiple injectors and monitoring wells. Injection operations started in August 2015 and by mid-October 2018, more than 3.45 Mt of CO2 has been stored using only 2 out of 3 planned injection wells. To date Quest has observed significant injectivity variability relating to seasonal variation in injected CO2 and bottom-hole temperatures.The high-resolution time-series data from the Quest operations gathered over the first 3 years of CO2 injection indicate the standard models of CO2 injectivity leave out some important physics. Prior to the start of injection, theoretical CO2 injectivity at the CO2 injector wells was initially modelled and calculated to decrease by ∼5% - 8% with decreasing CO2 bottom-hole temperature within the temperature range 20 °C–60 °C at the wellbore largely due to increased fluid viscosity at lower temperatures. However, field observations made to date at the Quest CCS site indicate an inverse relationship between CO2 injectivity and bottom-hole temperature, where injectivity increases of up to 10% due to colder CO2 have been observed in the bottom-hole temperature range of 21 °C–33 °C. This paper presents the field observations of injectivity compared to the theoretically expected and modelled 3D isothermal and non-isothermal conditions of injectivity at various CO2 bottom-hole temperatures, together with an assessment of the dominant controlling mechanisms and parameters that could influence CO2 injectivity under non-isothermal conditions. The assessment results indicate that the seasonal CO2 injectivity correlating inversely with bottom-hole temperature (BHT), cannot be explained by CO2 PVT behaviour under non-isothermal conditions. The inverse correlation is driven by near-wellbore permeability (k), relative permeability (kr) and (non-darcy) dynamic skin factor parameters varying in an inverse relationship with bottom-hole temperature through reversible temperature-driven mechanism(s) such as fluid flow regime changes, fluid-rock interactions and thermally-induced micro-fractures leading to increases in dynamic injectivity at lower CO2 bottom-hole temperatures.A full understanding of the non-isothermal processes and their relative impacts on CO2 injectivity are not only crucial for successful deployment of CCS projects but can also have wider beneficial applications in CO2-EOR modelling and operations cost optimisation.

Change in Separation Flow Regimes over Obstacles in Subsonic Gas Flow as a Manifestation of Viscous Forces: Numerical Results

The unsteady subsonic viscous gas flows over forward- and backward-facing steps on a flat surface are numerically simulated at a free-stream Mach number of 0.1 by applying compact difference schemes of the 14th order of accuracy. The characteristics of the boundary layer separation zones are investigated at Reynolds numbers ranging from 103 to 107. The computations are based on the nonstationary Navier–Stokes equations supplemented, if necessary, with the formulas of the one-parameter differential SA model of turbulent viscosity. The conditions for pulsing separation zones arising in the boundary layer are determined, and the subsequent transition to a turbulent flow regime is physically justified.

Numerical investigation of heat transfer of laminar and turbulent pulsating Al2O3/water nanofluid flow

PurposeThe purpose of this paper is to investigate the heat transfer of laminar and turbulent pulsating Al203/water nanofluid flow in a two-dimensional channel. In the laminar flow range, with increasing Reynolds number (Re), the velocity gradient is increased. Also, the Nusselt number (Nu) is increased, which causes increase in the overall heat transfer rate. Additionally, in the change of flow regime from laminar to turbulent, average thermal flux and pulsation range are increased. Also, the effect of different percentage of Al2O3/water nanofluid is investigated. The results show that the addition of nanofluids improve thermal performance in channel, but the using of nanofluid causes a pressure drop in the channel.Design/methodology/approachThe pulsatile flow and heat transfer in a two-dimensional channel were investigated.FindingsThe numerical results show that the Al2O3/Water nanofluid has a significant effect on the thermal properties of the different flows (laminar and turbulent) and the average thermal flux and pulsation ranges are increased in the change of flow regime from laminar to turbulent. Also, the addition of nanofluid improves thermal performance in channels.Originality/valueThe originality of this work lies in proposing a numerical analysis of heat transfer of pulsating Al2O3/Water nanofluid flow -with different percentages- in the two-dimensional channel while the flow regime change from laminar to turbulent.

Development of Flow Duration Curves and Eco-Flow Metrics for the Tawi River Basin - (Jammu, India)

A Flow duration Curve (FDC) and eco-metrics are one of the principal techniques employed to study the changes in flow regimes and flow discharge in any river basin. Stream flows vary widely over a year and this variability can be assessed by using FDC’s which is a curve plotting stream flows (Q) on the vertical axis and the percent of time the flow is equalled or exceeds (P) a critical discharge threshold on the horizontal axis for a particular river basin. Flow Duration curves (FDCs) are imperative instruments which are fundamental for water asset distribution and administration, which can further be analysed to get a great deal of hydrological data to understand the impact of climate changes on water asset frameworks. Results got from the flow duration curves are required by hydrologists and specialists associated with various water asset ventures such as assessing the hydropower capabilities of a waterway, stream health, surge control examines such as recurrence outlines, runoff estimations, figuring the dregs stack and broken down solids of a stream, and contrasting the adjacent catchments. Apart from these classical uses, the FDCs can also be used to survey the health status of the streams in terms of its ecological status. The present study has been undertaken with an objective to identify the ecological health status of the Tawi River, based on ecoflow metrics. Eco-surplus and eco-deficit are known as the indicators of Hydrologic Alteration (IHA) and are used to study intra and inter annual variations in river flows. The daily stream flow data at Gulab Singh Bridge, Jammu from the Hydrological Data Centre of the Central Water Commission (CWC), Jammu has been used to develop the Flow Duration Curve (FDCs) for the different periods like daily, monthly, annual etc. Finally, 10- daily time series have been used to identify the ecosurplus and the ecodeficit years and their respective magnitudes. Further, an eco-flow metric for the Tawi River was prepared for the 30 years daily discharge data from the period 1977 to 2007. The results of the study conclude that Tawi River is an ecosurplus river, in most of the years of the study period. The ecology of Tawi River is at par for the study period except for the years 1999 and 2000. Although the ecology is under sustaining conditions, but the metric has been falling in course of time, which can be a signal of ecological deterioration in the future.

Magnetic Fields Enhanced the Performance of Tubular Dichalcogenide Micromotors at Low Hydrogen Peroxide Levels.

Propulsion at the microscale has attracted significant research interest. In this work, a numerical simulation to explain the speed boost of up to 34 % experienced by transition metal dichalcogenides (TMD) based micromotors under the effect of applied magnetic fields is described. The simulations show that, when an external magnetic field is applied, the flow regime changes from turbulent to laminar. This causes an increase in the residence time of the fuel over the catalyst surface, which enhances the oxygen production. The more efficient generation and growth of the bubbles lead to an increase of the capillary force exerted by them. Interestingly, the effect is more pronounced as the level of fuel decrease. The validity of the model is also proven by comparing both theoretical and experimental results. Interestingly, the speed enhancement in magnetic mode depends on geometrical factors only, as a similar phenomenon was observed in a variety of microjets with a variable surface roughness. The understanding of such phenomena will open new avenues for understanding and controlling the motion behavior of high-towing-force catalytic micromotors.

Short-term streambed drying events alter amphipod population structure in a central European stream

Temporary streams are becoming increasingly common, but ecological responses to streambed drying are poorly characterized in the temperate continental region of central Europe. In addition, global research has focused on community responses to drying, whereas effects on individual populations remain unknown. We explored the population structure of Gammarus fossarum (Crustacea: Amphipoda) in a central European temporary stream. Benthic gammarids were sampled on five dates during a flow recession, one date between two drying events (of 10 and 20 days, respectively), and five dates after flow resumed. Additional benthic samples were taken from isolated pools and dry sediments during drying events, and freeze cores were collected to compare the vertical distribution of amphipods during wet and dry phases. Gammarids were measured, adults distinguished from juveniles, adults sexed, and female reproductive state determined. Densities increased during flow recession, potentially reflecting both a decline in submerged habitat availability and seasonal increases in juvenile abundance. Persistence within dry benthic sediments was minimal, whereas pools and saturated subsurface sediments supported high population densities. Juveniles comprised 80 % of the subsurface population, suggesting that their ability to inhabit small interstices promotes persistence within the dry reach. Juveniles also comprised 92 % of pool inhabitants, despite their potential exposure to predation. Adults dominated after flow resumed, and population structure was altered post-drying by the loss of spring-recruited juveniles and reproductive females. Our results suggest that streambed drying may have longer-term effects than typically characterized by community-level studies. We recommend management actions that support populations of ecologically important species as they adapt to changing flow regimes.

Unrestricted ramping rates and long‐term trends in the food web metrics of a boreal river

AbstractLong‐term monitoring of the food web of a regulated hydropeaking river was conducted to assess if previously documented effects of changing ramping rates (RRs) were maintained with the addition of 6 years of data. Using carbon and nitrogen stable isotope analyses, we hypothesized that: (1) macroinvertebrates and fish inhabiting areas below peaking hydrodams would be higher in δ15N and lower in δ13C due to increased flow velocity and the influence of light respired dissolved inorganic carbon, relative to those sampled from areas with a natural flow regime; (2) the increase in δ15N of macroinvertebrates would lead a shorter food web length in the regulated river, but δ13C and niche width would be similar between the restricted and unrestricted RR periods (i.e., the BACI analysis); and (3) isotopic metrics (e.g., δ13C, δ15N, niche width [SEAB], and food chain length [Δ15N]) would correlate with variations in flow characteristics through time. Consistent with previous analysis conducted over a shorter time period, a shift toward higher δ15N values was observed for both fish and invertebrates, but, contrarily, only invertebrates (not fish) had a lower δ13C value downstream of the dam. Over the long term, the before‐after‐control‐impact analysis found no effect of RRs on any of the food web metrics, implying that the change in operation did not affect the river food web. However, analysis of the time series data indicated that flow metrics and trophic metrics were often correlated, including a negative effect of RR (invertebrates) and discharge (fish) on food chain length. This study illustrates the difficulty in detecting changes in food web structure and function under changing flow regime influenced by natural and anthropogenic effects. As such, this study highlights the need for considering large spatial and temporal scales to differentiate between confounding effects of climate, natural variability, and altered flow regimes on food webs in regulated rivers.

Disentangling the Simultaneous Effects of Inertial Losses and Fracture Dilation on Permeability of Pressurized Fractured Rocks

AbstractHow fluids flow through pressurized fractured rocks is relevant to many engineering applications and geophysical processes including fault rupturing, hydraulic fracturing, induced seismicity, fluid extraction, and contaminant transport. With increasing fluid pressure and concomitantly elevated hydraulic gradient, the permeability of fractured rock is reduced because of inertial losses within the fluid. There is an accompanying flow regime change when this happens. On the other hand, increasing pressure causes fracture dilation which enhances permeability. In this case, the fracture geometry changes. These two competing consequences of increasing pressure had always been studied independently. Here we present an analytical expression for fractured rock permeability where flow regime and medium geometry simultaneously co‐evolve. The theory was applied to core and field flow tests. With continuously increasing fluid pressure, the inertial effect on permeability first dominates over that of fracture dilation and this dominance theoretically reverses at Forchheimer number = 1/3.

Smaller future floods imply less habitat for riparian plants along a boreal river.

Climate-change projections suggest large changes in riverine flow regime, which will likely alter riparian communities. In northern Europe, forecasts propose lower annual spring flood peaks and higher winter flows, resulting in narrower riparian zones. To estimate the impact of climate change on habitat extent of riparian plants, we developed a framework estimating the sensitivity and exposure of individual species to streamflow change, and surveyed five reaches along the free-flowing Vindel River in northern Sweden. We modeled the hydrologic niche of riparian plant species based on the probability of occurrence along gradients of flood frequency and duration and used predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) to calculate changes in flow-related habitat availability of individual species. Despite projected increases in runoff, we predict most species to decrease in riparian elevational extent by on average 12-29% until the end of the century, depending on scenario. Species growing in the upper, spring-flood-controlled part of the riparian zone will likely lose most habitat, with the largest reductions in species with narrow ranges of inundation duration tolerance (decreases of up to 54%). In contrast, the elevational extent of most amphibious species is predicted to increase, but conditions creating isoëtid vegetation will become rarer or disappear: isoëtid vegetation is presently found in areas where ice formed in the fall settles on the riverbank during the winter as water levels subside. Higher winter flows will make these conditions rare. We argue that our framework is useful to project the effects of hydrologic change caused by climate change as well as other stressors such as flow regulation also in other regions. With few rivers remaining unaffected by dams and other human stressors, these results call for monitoring to detect species declines. Management to alleviate species losses might include mitigation of habitat degradation from land-use activities, more environmentally friendly flow schemes, and more intensive management options such as mowing riparian meadows no longer regularly maintained by recurrent floods.

Assessing the effects of the Three Gorges Dam and upstream inflow change on the downstream flow regime during different operation periods of the dam

AbstractAs the largest hydroelectric dam in the world, the Three Gorges Dam (TGD) has raised wide concerns over the environmental and ecological impacts since its dramatic effect on the downstream flow regime of the Yangtze River. Since 2003, the TGD has progressed from the initial operation period to the full operation period, with different effects on the downstream flow regime over each period. Although the upstream inflow change (USIC) of the TGD is a possibly additional factor affecting the downstream flow regime, this has drawn little attention. This study aims to quantify the individual contributions of the TGD and the USIC to the changes of the downstream flow regime over different operation periods of the dam. Using the Muskingum routing model and the Xin'anjiang rainfall–run‐off model, we reconstruct the discharge unregulated by the TGD for the post‐TGD period from 2003 to 2015. On this basis, the effects of the TGD and the USIC on the downstream flow regime are quantitatively assessed. Benchmarked against the flow regime during the pre‐TGD period from 1955 to 2002, it is found that the TGD and the USIC play considerable and comparable roles in affecting the downstream flow regime during the whole post‐TGD period from 2003 to 2015. Furthermore, the TGD appears to have a limited effect on the downstream flow regime during the initial operation period from 2003 to 2008 relative to the USIC. In contrast, during the full operation period from 2009 to 2015, the TGD plays a dominant role in changing the downstream flow regime, although the effect of the USIC cannot be neglected. The findings of this study are helpful to understand the exact impacts of the TGD on the downstream flow regime, thereby facilitating the development of a rational strategy for operating the dam.

Climate and rivers

AbstractOver the last few decades as hydrologists have slowly raised their line of sight above the watershed boundary, it has become increasingly recognised that what happens in the atmosphere, as a major source of moisture for the terrestrial branch of the hydrological cycle, can strongly influence river dynamics at a range of spatial and temporal scales. Notwithstanding this, there is still a tendency for some in the river research community to restrict their gaze to the river channel or floodplain. However, Geoff Petts, the person to which this special issue is dedicated, understood well and widely encouraged a holistic view of river catchment processes. This included an acknowledgment of the role of climate, in its broadest sense, in shaping what happens within and without the river channel. The purpose of this paper therefore is to offer a broad overview of the role of some aspects of climate science in advancing knowledge in river research. Topics to be addressed include the role of climate in influencing river flow regimes, a consideration of the large‐scale climate mechanisms that drive hydrological variability within river basins at interannual to decadal timescales and atmospheric rivers and their link to surface hydrology. In reviewing these topics, a number of key knowledge gaps have emerged including attributing the causes of river flow regime changes to any one particular cause, the nonstationary and asymmetric forcing of river regimes by modes of climate variability and establishing links between atmospheric rivers, and terrestrial river channel processes, fluvial habitats, and ecological change.

Performance of ANN, SVM and MLH techniques for land use/cover change detection at Sultan Marshes wetland, Turkey.

Wetlands are among the most productive ecosystems that provide services ranging from flood control to climate change mitigation. Wetlands are also critical habitats for the survival of numerous plant and animal species. In this study, we used satellite remote sensing techniques for classification and change detection at an internationally important wetland (Ramsar Site) in Turkey. Sultan Marshes is located at the center of semi-arid Develi closed basin. The wetlands have undergone significant changes since the 1980s due to changes in water flow regimes, but changes in recent years have not been sufficiently explored yet. In this study, we focused on the changes from 2005 to 2012. Two multispectral ASTER images with spatial resolution of 15 m, acquired on June 11, 2005 and May 20, 2012, were used in the analyses. After geometric correction, the images were classified into four information classes, namely water, marsh, agriculture, and steppe. The applicability of three classification methods (i.e. maximum likelihood (MLH), multi-layer perceptron type artificial neural networks (ANN) and support vector machines (SVM)) was assessed. The differences in classification accuracies were evaluated by the McNemar's test. The changes in the Sultan Marshes were determined by the post classification comparison method using the most accurate classified images. The results showed that the highest overall accuracy in image classifications was achieved with the SVM method. It was observed that marshes and steppe areas decreased while water and agricultural areas expanded from 2005 to 2012. These changes could be the results of water transfers to the marshes from neighboring watershed.

Reduced Soil Macropores and Forest Cover Reduce Warm‐Season Baseflow below Ecological Thresholds in the Upper Delaware River Basin

AbstractWe examined the impacts of changes in land cover and soil conditions on the flow regime of the upper Delaware River Basin using the Water Availability Tool for Environmental Resources. We simulated flows for two periods, c. 1600 and 1940, at three sites using the same temperature and precipitation conditions: the East Branch, West Branch, and mainstem Delaware River at Callicoon, New York. The 1600 period represented pristine forest and soils. The 1940 period included reduced forest cover, increased agriculture, and degraded soils with reduced soil macropore fractions. A model‐sensitivity test examined the impact of soil macropore and land cover change separately. We assessed changes in flow regimes between the 1600 and 1940 periods using a variety of flow statistics, including established ecological limits of hydrologic alteration (ELOHA) thresholds. Reduced forest soil macropore fraction significantly reduced summer and fall baseflows. The 1940 period had significantly lower Q50 flows (50% exceedance) than the 1600 period, as well as summer and fall Q90 and Q75–Q90 flows below the ELOHA thresholds. The one‐ to seven‐day minimum flows were also lower for the 1940 period, by 17% on the mainstem. 1940 flows were 6% more likely than the 1600 period to fall below the low‐flow threshold for federally endangered dwarf wedgemussel (Alasmidonta heterodon) habitat. In contrast, the 1940 period had higher flows than the 1600 period from late fall to early winter.

Experimental study on evolution of lacustrine shallow-water delta

In the process of delta evolution, the flow regime and sediment transport change with the development of topography. Flow is the dynamic factor of shaping topography, while sediment scouring and silting is the direct cause of topography formation, and they are constrained and influenced by topographic changes simultaneously. In order to explore rules of water and sediment movement and topographic sedimentation of delta under microscale conditions, we studied the phenomena, rules and evolution mechanism of flow movement, sediment transport, particle sorting, topographic sedimentation, and flow path generation, merger and recombination under microscale conditions from the perspective of physical experiment. The influence of different external conditions on lacustrine shallow-water delta evolution and the self-organization of delta evolution are studied through comparative experiments under the condition of distinct sediment supplied rates or lake levels and repeatability experiments under the same conditions. Some rules of flow movement, sediment transport and topographic sedimentation such as characteristics of each stage during the process of evolution of lacustrine shallow-water delta, the periodic change of flow regime and the prediction model, the characteristics of sedimentary morphology under different conditions, and the influence of stochastic factors on delta evolution are summarized. The experiments suggest coupled linkage of interaction of water and sediment, self-organization of flow path evolution and the equilibrium tendency of delta structure under the action of coupling interaction of multiple factors of water, sediment and topographic sedimentation.

Semi-analytical prediction of critical oil rate in naturally fractured reservoirs with water coning

Naturally fractured reservoirs (NFRs) with bottom water are generally produced above their critical oil rate (maximum possible oil production rate without water breakthrough) that is difficult to determine as it varies between wells, depending on the well's location in the fracture network. In principle, wells can either be completed in matrix or fractures. Present formulas of critical-rate in NFR are oversimplified ignoring the network heterogeneity and anisotropy ratio of fractures, and they also do not consider the difference between on-fracture/off-fracture well completion placements. Presented is development of a new semi-analytical formula that considers these effects– with emphasis given to well placement assessment.The critical rate model is derived from mechanistic principles and then improved with statistical calibration. The mechanistic approach (Chaperon (1986)) considers vertical equilibrium of viscous and gravity forces for a hemispherical flow to a point-source well in a dual porosity/dual permeability model of naturally fractured reservoirs. The model considers the water cone instability, and anisotropy ratio of NFR only for a short-perforated completion interval. The model is tested for wide variety of NFRs for short completions. The model is then statistically calibrated to including the effect of long penetration ratio, using a designed matrix of simulated experiments covering wide ranges of NFR properties. This statistical approach allows the model to consider any change in flow regime from semi-spherical to non-radial distorted flow.The comparison of Chaperon's analytical model and NFR simulations shows that the model is good for NFRs for penetration ratio smaller than 0.35. For penetration ratio greater than 0.35, a new semi-analytical model of critical-rate for NFR is developed by statistically calibrating the Chaperon's analytical model. The new model considers the parameters ignored in the previous models of NFR. Finally, a new mechanistic derivation of critical rate for wells completed in matrix block of NFR is determined by analytically including the effect of well's distance to fracture in a critical rate formula for NFR. The model matches well with the simulated data when compared with it. The model shows that the wells accidently completed off-fractures may display higher values of critical rates and the difference relates to their distance to the nearest fractures. It is also shown that the off-fracture well's formula reduces to the on-fracture well's formula when the distance is reduced to zero.