Baseflow Characteristics Research Articles

Alpine Hydrogeology: The Critical Role of Groundwater in Sourcing the Headwaters of the World.

Groundwater discharge in alpine headwaters sustains baseflow in rivers originating in mountain ranges of the world, which is critically important for aquatic habitats, run‐of‐river hydropower generation, and downstream water supply. Groundwater storage in alpine watersheds was long considered negligible, but recent field‐based studies have shown that aquifers are ubiquitous in the alpine zone with no soil and vegetation. Talus, moraine, and rock glacier aquifers are common in many alpine regions of the world, although bedrock aquifers occur in some geological settings. Alpine aquifers consisting of coarse sediments have a fast recession of discharge after the recharge season (e.g., snowmelt) or rainfall events, followed by a slow recession that sustains discharge over a long period. The two‐phase recession is likely controlled by the internal structure of the aquifers. Spatial extent and distribution of individual aquifers determine the groundwater storage‐discharge characteristics in first‐ and second‐order watersheds in the alpine zone, which in turn govern baseflow characteristics in major rivers. Similar alpine landforms appear to have similar hydrogeological characteristics in many mountain ranges across the world, suggesting that a common conceptual framework can be used to understand alpine aquifers based on geological and geomorphological settings. Such a framework will be useful for parameterizing storage‐discharge characteristics in large river hydrological models.

Global stability analysis of axisymmetric boundary layer: Effect of axisymmetric forebody shapes

This paper presents the effect of axisymmetric forebody shapes on the global stability characteristics of axisymmetric boundary layer developed on a circular cylinder. Axisymmetric forebodies like sharp-cone, ellipsoid, and paraboloid with a fineness ratio (FR) of 2.5, 5.0 and 7.5 are considered. The boundary layer starts to develop at a stagnation point on the forebody geometry and grows in spatial directions. The inflow velocity component is parallel to the axis of the cylinder, and hence the angle of attack is zero. The base flow is axisymmetric, non-parallel and non-similar. The linearised Navier–Stokes equations are derived in the cylindrical polar coordinates for the disturbance flow components. The discretised linearised Navier–Stokes equations along with appropriate boundary conditions form a general eigenvalue problem and it has been solved using Arnoldi’s algorithm. The global temporal modes have been computed by solving the two-dimensional eigenvalue problem. The extent of a favourable pressure gradient developed in streamwise direction depends on the shape of axisymmetric forebody. The temporal and spatial growth of the disturbances has been computed for axisymmetric ($$N = 0$$) mode for different Reynolds numbers (Re). The forebody shapes have a significant effect on the base flow and stability characteristics at low Re.

Optimization of artillery projectiles base drag reduction using hot base flow

The CFD numerical simulations were carried out to investigate the base drag characteristics of a projectile with base bleed unit with a central jet. Different base bleed grain types with different combustion temperatures were used. The goal was to find a way to effectively control the base flow for base drag reduction and optimisate the latter using an adequate CFD software. Axisymmetric, compressible, mass-averaged Navier-Stokes equations are solved using the k-? SST, transition k-kl-?, and RSM turbulence models. The various base flow characteristics are obtained by the change in the non-dimensionalized injection impulse. The results obtained through the present study show that there is an optimum bleed condition for all base bleed grains tested. That optimum is dependent on the temperature of the grain combustion products. The optimum reduces the total drag for 6,9% in the case of air injection at temperature of 300 K and reaches up to 28% in the case of propellant combustion products injection at almost 2500 K. Besides, the increasing of molecular weight has a role no less important than temperature of the combustion products in terms of base drag reduction.

Historical and predicted variations of baseflow in China's Poyang Lake catchment

AbstractBaseflow availability and its contribution to streamflow are critical for planning and management of catchment hydrology and ecology. This study uses a digital filtering technique, statistical methods, and hydrological projection to investigate historical and future baseflow characteristics with respect to climate and land use impacts, exemplified by the large Poyang Lake catchment (China). Digital filtering results show that annual baseflow varied between 25 × 108 and 820 × 108 m3/year for the catchment rivers during 1953–2014. The results reveal that on average 62% of the long‐term streamflow in the catchment is derived from baseflow contribution. Statistics show a generally increasing trend in the annual baseflow and baseflow index (BFI) for most of the rivers over the past 60 years, with the major frequencies varying between 5 and 20 years. Although the trends in baseflow and BFI are attributable to the combined effects of climate and land use change across the catchment, baseflow variations are expected to be more sensitive to climate than land use changes. In general, precipitation plays a dominant role in controlling baseflow and can be used as an indication of the variations in baseflow at the subcatchment scale. Hydrological projection shows that annual baseflow and BFI are likely to increase by up to 31% and 13% during 2018–2035, respectively, based on historical baseflow trends. Our results indicate that management approaches for the catchment that consider groundwater and surface water as a joint resource will be needed to effectively manage the current and future river regime, its water resources, and water quality.

Assessment of Baseflow Estimates Considering Recession Characteristics in SWAT

Baseflow is influenced by incoming groundwater to aquifers and is closely related to watershed characteristics. Understanding baseflow characteristics is of great importance to river ecosystems and water management. Baseflow estimation typically depends on the observed streamflow in gauged watersheds, but accurate predictions of streamflow through modeling can also be useful in estimating baseflow. However, uncertainty occurs in the baseflow estimation process when modeling streamflow. Therefore, the purpose of this study is to compare the method that is proposed by Arnold and Allen (Scenario I) to an improved recession prediction method where the alpha factor (baseflow recession coefficient) is recalibrated and is applied to SWAT (Scenario II). Although the differences between the results (NSE, R2, RMSE, MAE, d) of Scenarios I and II were small regarding streamflow and recession, the Scenario II method more accurately reflected the recession characteristics than the Scenario I method. Furthermore, the Scenario II method was better in baseflow prediction than for the Scenario I method proposed by Arnold and Allen. Therefore, these outputs pave the way and contribute to an efficient method for water management in watersheds.

Annual baseflow variations as influenced by climate variability and agricultural land use change in the Missouri River Basin

The Missouri River system has a large water storage capacity, where baseflow plays an important role. Understanding historical baseflow characteristics with respect to climate and land use impacts is essential for effective planning and management of water resources in the Missouri River Basin (MORB). This study evaluated statistical trends in baseflow and precipitation for 99 MORB minimally disturbed watersheds during 1950–2014. Elasticity of baseflow to climate variability and agricultural land use change were quantified for the 99 studied watersheds. Baseflow was derived from daily streamflow records with a recursive digital filter method. The results showed that baseflow varied between 38 and 80% (0 and 331mm/year) of total streamflow with an average of 60%, indicating that more than half of streamflow in the MORB is derived from baseflow. The trend analysis revealed that precipitation increased during the study period in 78 out of 99 watersheds, leading to 1–3.9% noticeable increase in baseflow for 68 of 99 watersheds. Although the changes in baseflow obtained in this study were a result of the combined effects of climate and land use change across the basin, upward trends in baseflow generally coincide with increased precipitation and agricultural land use trends in the basin. Agricultural land use increase mostly led to a 0–5.7% decrease in annual baseflow in the basin, except toward east of the basin where baseflow mostly increased with agricultural land use increase (0.1–2.0%). In general, a 1% increase in precipitation and a 1% increase in agricultural land use resulted in 1.5% increase and 0.2% decrease in baseflow, respectively, during the study period. These results are entirely dependent on the quality of data used; however, they provide useful insight into the relative influence of climate and land use change on baseflow conditions in the Great Plains region of the USA.

Numerical Studies on Chemical Non-Equilibrium Flow of the Base-Bleed Unit Wake

ABSTRACTNumerical studies of compressible base flows with base bleed injection as an effective way to control the base flow for the base drag reduction and heat energy addition of axisymmetric projectiles with a boattailed afterbody in supersonic freestream are carried out by considering the base burning process. The idea developed in the study is to obtain the lowest base drag by analyzing the complex fluid dynamic characteristics found in a supersonic base flow field, including combined effects of boattailing and secondary combustion of the wake under different conditions. Overall fluid dynamic and chemical non-equilibrium flow are then simulated by incorporating the H2-CO combustion model with 12 reaction steps involving eight reactive species (H, H2, H2O, OH, CO, CO2, O, and O2) into a Navier–Stokes computer code. Various base flow and component distribution characteristics are obtained by changing injection parameter I, which is defined as the bleed mass flow rate normalized by the product of the base area and the freestream mass flux, and the bleed temperature. The results obtained through the present study show that, with increasing injection parameter I, the average base pressure is found to increase quickly initially, attain a slow increase near an injection parameter of I = 0.007, and then remain constant with further increase in I. Moreover, based on changing the bleed temperature, the base pressure rises and the heat energy addition as well as mass addition mechanisms associated with base secondary combustion are found to be higher than that without base secondary combustion. The secondary combustion results in a significant increase in flame temperature and changes the product composition, which cannot be ignored, although the chemical kinetics and fluid dynamic will fulfill another important role. Thus, a better effect on base drag reduction as well as base pressure increase can be attained by adopting appropriate injection parameter and bleed temperature.

Effect of clustering on linear plug nozzle flow field for overexpanded internal jet

Experiments were carried out to analyze the flow field development of a linear plug nozzle wherein the internal nozzle was operating in the overexpanded regime. Steady and unsteady pressure measurements were taken along with the schlieren and oil flow visualization techniques to describe the flow field. Over the range of pressure ratios considered, the overexpanded shock pattern from the internal nozzle has been explained with regard to differential end conditions on either side of the core jet. The unsteady characteristics of the pressure fluctuations have been discussed with respect to the foot of the overexpansion shock on the plug surface. The effect of internal nozzle clustering on the plug nozzle flow field has been studied for two different cluster nozzles. The cluster module jet wave interactions along the spanwise direction have been explained with respect to the limiting streamline pattern on the plug surface. In addition to these, the base flow characteristics for these overexpanded internal nozzle pressure ratios have been discussed for two different truncated plug lengths.

Comparison of Total flow, Base flow and Water-Quality Characteristics Trend in Arazkuseh Hydrometric Station

Comparison of Total flow, Base flow and Water-Quality Characteristics Trend in Arazkuseh Hydrometric Station

Baseflow characteristics in alpine rivers — a multi-catchment analysis in Northwest China

As a component of streamflow, baseflow is critical for regulating seasonal distribution of river flows and stabilizing water supplies. Water resources in the arid area of Northwest China are mainly from multiple catchments in the alpine that could be influenced by varieties of climatic, land cover, soil and geological factors. While numerous studies have been done on streamflow, systematic analysis of baseflow in the alpine river systems is scare. Based on historical daily streamflow data and the automated digital filter method of baseflow separation, this study investigated characteristics of hydrographs of overland flow, streamflow and baseflow of river systems fed by rainfall, snowmelt, glacier melt or mixtures of these. This study also calculated the recession constants and baseflow indices of 65 river systems. While the recession constant was 0.0034–0.0728 with a mean of 0.018, the baseflow index was 0.27–0.79 with a mean of 0.57. Further, Spearman’s correlation analysis showed that the baseflow index was significantly correlated with catchment climatic factors (e.g., precipitation and temperature), topographic factors (e.g., elevation and slope) and aquifer properties represented by the recession constant. Multiple regression analysis indicated that the factors explained 65% of the variability of baseflow index in the study area.

Comparative analysis of baseflow characteristics of two Andean catchments, Ecuador

Baseflow in the Andes is commonly considered to be related with the release of water stored in páramos. Páramo is the predominant ecosystem above 3500 m a.s.l. and is characterized by a rainy and cold climate with low evapotranspiration. However, this baseflow concept is based on hydrological process studies in small Andean catchments of a few square kilometre with a homogeneous land cover. Middle-sized Andean catchments, like the subcatchments of Tarqui and Yanuncay, Ecuador, are rarely homogeneous or uniformly covered by páramo. The objectives of this study are therefore to investigate baseflow characteristics in heterogeneous Andean catchments and to identify relationships between baseflow processes and physical characteristics such as storage and recharge. Hereby, the contribution to baseflow of páramo and other sources such as alluvial aquifers is quantified. This study uses nonlinear recession analysis, physically based filters and digital filters for comparison of baseflow of neighbouring but distinct subcatchments. The Yanuncay subcatchment shows a clearly different storage capacity and recession. The storage capacity of Yanuncay is 50% higher than for Tarqui because of its higher coverage of páramo. On the other hand, considerable storage capacity has also been found in the Tarqui subcatchment, which has a limited páramo area but a significant alluvial aquifer. It is shown that improved understanding of the specific baseflow characteristics such as storage and recharge and its relationships to the heterogeneity of the land cover in Andean catchments will lead to a better assessment of the water resources and give new insights for effective management actions. Copyright © 2014 John Wiley & Sons, Ltd.

토지이용변화에 따른 미계측 유역의 기저유출량 산정 및 평가

Baseflow gives a significant contribution to stream function in the regions where climatic characteristics are seasonally distinct. In this regard, variable baseflow can make it difficult to maintain a stable water supply, as well as causing disruption to the stream ecosystem. Changes in land use can affect both the direct flow and baseflow of a stream, and consequently, most other components of the hydrologic cycle. Baseflow estimation depends on the observed streamflow in gauge watersheds, but accurate predictions of streamflow through modeling can be useful in determining baseflow data for ungauged watersheds. Accordingly, the objectives of this study are to 1) improve predictions of SWAT by applying the alpha factor estimated using RECESS for calibration; 2) estimate baseflow in an ungauged watershed using the WHAT system; and 3) evaluate the effects of changes in land use on baseflow characteristics. These objectives were implemented in the Gapcheon watershed, as an ungauged watershed in South Korea. The results show that the alpha factor estimated using RECESS in SWAT calibration improves the prediction for streamflow, and, in particular, recessions in the baseflow. Also, the changes in land use in the Gapcheon watershed leads to no significant difference in annual baseflow between comparable periods, regardless of precipitation, but does lead to differences in the seasonal characteristics observed for the temporal distribution of baseflow. Therefore, the Guem River, into which the stream from the Gapcheon watershed flows, requires strategic seasonal variability predictions of baseflow due to changes in land use within the region.

Development of Web-Based RECESS Model for Estimating Baseflow Using SWAT

Groundwater has received increasing attention as an important strategic water resource for adaptation to climate change. In this regard, the separation of baseflow from streamflow and the analysis of recession curves make a significant contribution to integrated river basin management. The United States Geological Survey (USGS) RECESS model adopting the master-recession curve (MRC) method can enhance the accuracy with which baseflow may be separated from streamflow, compared to other baseflow-separation schemes that are more limited in their ability to reflect various watershed/aquifer characteristics. The RECESS model has been widely used for the analysis of hydrographs, but the applications using RECESS were only available through Microsoft-Disk Operating System (MS-DOS). Thus, this study aims to develop a web-based RECESS model for easy separation of baseflow from streamflow, with easy applications for ungauged regions. RECESS on the web derived the alpha factor, which is a baseflow recession constant in the Soil Water Assessment Tool (SWAT), and this variable was provided to SWAT as the input. The results showed that the alpha factor estimated from the web-based RECESS model improved the predictions of streamflow and recession. Furthermore, these findings showed that the baseflow characteristics of the ungauged watersheds were influenced by the land use and slope angle of watersheds, as well as by precipitation and streamflow.

Globally mapping baseflow characteristics

Characterizing baseflow, the slowly varying portion of streamflow, is important for water resources management, hydropower generation, tracking contaminant transport, and other applications. Most previous studies of baseflow have analyzed small groups of catchments with similar characteristics. Now, to develop globally applicable models of baseflow characteristics, Beck et al. studied observations from 3394 catchments around the world with a variety of climatic, hydrological, and physiographic characteristics. Their novel approach investigates the relationship between catchment characteristics and baseflow characteristics, showing how baseflow is related to annual potential evaporation, mean snow water equivalent depth, abundance of surface water bodies, and other landscape characteristics. Their global maps of baseflow characteristics—which could be useful for benchmarking and calibrating hydrological models and for a variety of other hydrological applications—are freely available at http://www.hydrology‐amsterdam.nl.

Global patterns in base flow index and recession based on streamflow observations from 3394 catchments

[1] Numerous previous studies have constructed models to estimate base flow characteristics from climatic and physiographic characteristics of catchments and applied these to ungauged regions. However, these studies generally used streamflow observations from a relatively small number of catchments (<200) located in small, homogeneous study areas, which may have led to less reliable models with limited applicability elsewhere. Here, we use streamflow observations from a highly heterogeneous set of 3394 catchments (<10,000 km2) worldwide to construct reliable, widely applicable models based on 18 climatic and physiographic characteristics to estimate two important base flow characteristics: (1) the base flow index (BFI), defined as the ratio of long-term mean base flow to total streamflow; and (2) the base flow recession constant (k), defined as the rate of base flow decay. Regression analysis results revealed that BFI and k were related to several climatic and physiographic characteristics, notably mean annual potential evaporation, mean snow water equivalent depth, and abundance of surface water bodies. Ensembles of artificial neural networks (ANNs; obtained by subsampling the original set of catchments) were trained to estimate the base flow characteristics from climatic and physiographic data. The catchment-scale estimation of the base flow characteristics demonstrated encouraging performance with R2 values of 0.82 for BFI and 0.72 for k. The connection weights of the trained ANNs indicated that climatic characteristics were more important for estimating k than BFI. Global maps of estimated BFI and k were obtained using global climatic and physiographic data as input to the derived models. The resulting global maps are available for free download at http://www.hydrology-amsterdam.nl.

Assessing impact of urban impervious surface on watershed hydrology using distributed object-oriented simulation and spatial regression

In this study, we investigated the relation- ship between watershed characteristics and hydrology using high spatial resolution impervious surface area (ISA), hydrologic simulations and spatial regression. We selected 20 watersheds at HUC 12 level with different degrees of urbanization and performed hydro- logic simulation using a distributed object-oriented rainfall and runoff simulation model. We extracted the discharge per area and ratio of runoff to base flow from simulation results and used them as indicators of hydrology pattern. We derived percentage of ISA, distance from ISA to streams, and stream density as the watershed characteristics to evaluate the relationship with hydrology pattern in watersheds using ordinary least square, spatial error and spatial lag regression models. The comparison indicates that spatial lag regression model can achieve better performance for the evaluation of relationship between ratio of runoff to base flow and watershed characteristics, and that three models provide similar performance for the evaluation of relationship between discharge per area and watershed characteristics. The results from regression analyses demonstrate that ISA plays an important role in watershed hydrology. Ignorance of spatial dependence in analyses will likely cause inaccurate evaluation for relationship between ISA and watershed hydrology. The hydrologic model, regression methods and relationships between watershed characteristics and hydrology pat- tern provide important tools and information for deci- sion makers to evaluate the effect of different scenarios in land management.

Investigation of the turbulent wake flow of generic launcher configurations via a zonal RANS/LES method

A numerical analysis of the turbulent wake flow of a generic space launcher at supersonic freestream conditions (Ma∞ = 6.0 and ReD = 1.7 × 106) is performed using a zonal RANS/LES method. To investigate the influence of various components of a rocket model on the base flow, three supported wind tunnel configurations with the same main body geometry and different aft-body extensions consisting of a blunt base, a nozzle dummy, and a full flowing underexpanded TIC nozzle (Mae = 2.52, pe/p∞ = 100) are considered. Flow topologies for three cases are described in detail including an estimate of the impact of the wind tunnel model support on the flow field. To validate the applied numerical method, the computed flow fields are compared to experimental data from high-speed schlieren measurements provided by DLR Cologne. The influence of the used aft-body extensions on the steady-state and dynamic base flow characteristics is evaluated by a detailed analysis and comparison of the pressure distribution and its spectra along the base and nozzle walls for three investigated configurations. The numerical findings are compared to experimental wall pressure oscillation measurements provided by DLR Cologne. The major results are the non-negligible influence of the model support on the wake even on the strut averted side, the base drag reduction effect of the aft-expanding jet plume consisting of an increase of the base pressure level from \(p/p_\infty\approx0.2-0.25\) (blunt base and nozzle dummy configurations) up to \(p/p_\infty\approx0.7\) leading to a decrease of the base pressure drag coefficient from CDp base = 0.032 to 0.012 correspondingly, and the identified dominant low-frequency modes of the base pressure oscillations at SrD ≈ 0.05, SrD ≈ 0.1, and SrD ≈ 0.2 also detected in the experiments.

Nonlinear instabilities of a non-self-similar boundary layer on an airfoil: Experiments, DNS, and theory

Transition prediction of a laminar boundary layer developing on a two-dimensional airfoil section at pure subsonic speeds is still a challenge, because the commonly used semi-empirical prediction tools are mainly based on results derived from the linear stability theory (LST). This approach completely neglects non-linear interactions at later stages of the transition development and therefore provides limited accuracy for cases when the non-linear part has significant length in comparison to the linear stage. Nevertheless, the later one can be of significant importance for airfoil design. The onset and further development of non-linear, in general resonant wave interactions is depending on the pre-history of the boundary layer and the specific linear and non-linear stability characteristics driven by the pressure gradient, which varies in streamwise direction for typical airfoil sections. The variation of the pressure gradient leads to a non self-similar boundary layer development connected with a continuous change of the resonance conditions for wave interactions. The present paper is devoted to the detailed experimental, numerical and theoretical study of weakly nonlinear subharmonic resonant interactions of Tollmien–Schlichting waves in such a two-dimensional non self-similar boundary layer on an airfoil. The experimental approach is based on phase locked hot-wire measurements under controlled disturbance conditions in a low turbulence wind tunnel at a Reynolds number of Re=0.7×10 6. Direct numerical simulations (DNS) based on the vorticity–velocity formulation of the complete Navier–Stokes equations are utilized to provide a detailed comparison for the test cases. The results of weakly non-linear theory (WNT) enabled a profound understanding of the underlying physical mechanisms observed in the experiments and simulations. The joint study provides a complete set of data, starting from the base flow and stability characteristics up to non-linear disturbance development with different involved wave triplets. The phase synchronization mechanism is investigated in detail as well as the resonance efficiency for tuned cases with respect to the exact subharmonic frequency. In general, a good agreement between the experiment, DNS and WNT is found. The essential non-self-similarity of the airfoil boundary layer does not prevent strong resonant interactions and in accordance with investigations in self-similar flows, rapid, close to double-exponential amplification of subharmonic modes is observed. At the resonant stage, the phase-synchronization condition is shown to be satisfied, which provides equal phase speeds for all involved modes. For tuned cases, the initial phase relation between fundamental and subharmonic modes can lead, partly, to a suppression of the subharmonic wave amplification. Variation of the fundamental wave frequency shows that the integral resonance efficiency is significantly decreased with the reduction of the frequency. This effect is explained as a frequency dependence of the nonlinear coupling coefficients as well as the detuning of the subharmonic-fundamental phase speed associated mainly with the base-flow non-self-similarity. Depending on the frequency content of the initial disturbances this can lead to a direct influence on the corresponding transition position.

THE ROLE OF VEGETATION COVER AND CATCHMENT CHARACTERISTICS ON BASEFLOW IN BALI ISLAND

Studies of the role of combined vegetation cover and catchment characteristics on base flow condition are required to address the controversy of correlation between vegetation and hydrological properties. Objectives of the research were: 1) to assess the hydrological role of vegetation on baseflow condition; and 2) to study the influence of vegetation cover in relation to catchment characteristics on the baseflow. Field survey, digital filter method, remote sensing technique, and statistical analysis were used to derive and assess the correlation among variables. Results of the research were: 1) a negative significant correlation between vegetation cover and baseflow recession coefficient, despite the fact that it is not a single factor and related to various catchment characteristics; 2) vegetation cover is not a single factor in determining the baseflow characteristics, since it also involves drainage density and infiltration rate.

An Evaluation of the Influence of Seasonal Base Flow and Geomorphic Stream Characteristics on Coastal Plain Stream Fish Assemblages

AbstractWater regulation and use have been identified as important limiting factors influencing stream‐dwelling fishes. To develop effective water management strategies, fisheries biologists need tools for assessing the effect of reduced streamflows on fish communities. We studied fish assemblages in the lower Flint River basin, Georgia, during two drought years with very low streamflow (2001–2002) and two postdrought years (2003–2004) with average to above‐average streamflow. Fishes were sampled and stream discharge was measured during the spring, summer, and winter of each year. Analysis of fish assemblage metrics indicated that fish species richness and total fish density were strongly and positively related to seasonal 10‐d low discharge. However, the effect of discharge varied with stream size and geomorphic channel characteristics, which suggested that a single low‐flow standard was unlikely to have the same effect across all streams in the basin. The effect of seasonal base flows also was greater in the spring and summer than in winter. Hierarchical occupancy models indicated that the fish species most sensitive to low base flows were those that were large bodied as adults, were intolerant to anthropogenic alterations, and occupied deep and fast current velocity habitats. When conducting environmental flow assessments at regional scales, managers should consider the effects of local stream reach characteristics on the response of fishes to streamflow alteration.