Base Flow Model Research Articles

Impact of the model structure and calibration strategy on baseflow modeling in the German low mountain range

ABSTRACT Baseflow is a vital component of the water balance. The fractured hard rock aquifers of the German low mountain range are in danger of increased water stress due to climate change because they react rapidly to deficits in precipitation and groundwater tables decline sharply. Therefore, simulation software must be able to model baseflow accurately. Three soil moisture simulation and two monthly factor-based baseflow models are evaluated using two calibration strategies. Models were calibrated to total flow (S1) or stepwise to baseflow and then total flow (S2). Results were not significantly different for total flow. Regarding baseflow, S2 proved significantly better with median values (S1 calibration, validation | S2 calibration, validation) of SSE (20.3, 20.3 | 13.5, 13.8), LnNSE (0.15, 0.17 | 0.47, 0.34), and PBIAS (27.8, 21.6 | 2.5, −0.8). Parallel linear reservoir proved best at modeling baseflow with a median SSE (S2: 6.1, 5.9), LnNSE (S2: 0.64, 0.71), and PBIAS (S2: 3.8, 3.8). The new modified monthly factor approach is a simple and robust alternative with SSE (13.0, 13.3), LnNSE (0.61, 0.61), and PBIAS (9.8, −8.6). The results are useful regarding selection of baseflow model structure and calibration strategy in low mountain ranges with fractured hard rock aquifers.

How Will Baseflow Respond to Climate Change in the Upper Colorado River Basin?

AbstractBaseflow is critical to sustaining streamflow in the Upper Colorado River Basin. Therefore, effective water resources management requires estimates of baseflow response to climatic changes. This study provides the first estimates of projected baseflow changes from historical (1984–2012) to thirty‐year periods centered around 2030, 2050, and 2080 under warm/wet, median, and hot/dry climatic conditions using a hybrid statistical‐deterministic baseflow model. Total baseflow supplied to the Lower Colorado River Basin may decline by up to 33%, although this value may increase in the near future by 6% under warm/wet conditions. The percentage of baseflow lost during in‐stream transport is projected to increase by 1%–5% relative to historical conditions. Results highlight that climate‐driven changes in high‐elevation hydrology have impacts on basinwide water availability. Study results have implications for human and ecological water availability in one of the most heavily managed watersheds in the world.

Shaping a baseflow model through multiple regression analysis: the Çoruh watershed example

Abstract In today's conditions, where the frequency of events related to global climate change is increasing, it is important to employ water science to utilize water with maximum efficiency and to keep water under control in the areas close to its consumption zone. It is also important to determine how much of the flow in the stream during dry periods is the baseflow and how much of it is direct flow. This study designed a model of the baseflow index (BFI) and the baseflow rate (Qb) in one of the watersheds in Turkey. The smoothed minima method designed by the United Kingdom Institute of Hydrology (UKIH) was used to calculate the BFI and Qb at 10 flow observation stations in the Çoruh watershed. The Çoruh Watershed Baseflow Model was designed using BFI and Qb values with watershed characteristics and other variables. The determination coefficient of the BFI model was calculated as R² = 0.842, and the Qb model determination coefficient was calculated as R² = 0.99. The usability of the Çoruh model was proven by using the UKIH's smoothed minima method and comparing its relative errors with the BFI and Qb in the Çoruh model.

Assimilation of Experimental Data to Create a Quantitatively Accurate Reduced-Order Thermoacoustic Model

Abstract We combine a thermoacoustic experiment with a thermoacoustic reduced order model using Bayesian inference to accurately learn the parameters of the model, rendering it predictive. The experiment is a vertical Rijke tube containing an electric heater. The heater drives a base flow via natural convection, and thermoacoustic oscillations via velocity-driven heat release fluctuations. The decay rates and frequencies of these oscillations are measured every few seconds by acoustically forcing the system via a loudspeaker placed at the bottom of the tube. More than 320,000 temperature measurements are used to compute state and parameters of the base flow model using the Ensemble Kalman Filter. A wave-based network model is then used to describe the acoustics inside the tube. We balance momentum and energy at the boundary between two adjacent elements, and model the viscous and thermal dissipation mechanisms in the boundary layer and at the heater and thermocouple locations. Finally, we tune the parameters of two different thermoacoustic models on an experimental dataset that comprises more than 40,000 experiments. This study shows that, with thorough Bayesian inference, a qualitative model can become quantitatively accurate, without overfitting, as long as it contains the most influential physical phenomena.

Continuous modelling of the Bouregreg watershed (Morocco) using the HEC-HMS model

A deep understanding of the rainfall-runoff mechanism is essential to estimate the runoff generated in a given basin. In this regard, this paper aims to develop a continuous hydrological model of the Bouregreg watershed. The objective of this modelling is to evaluate the inflow to the Sidi Mohamed Ben Abdellah (SMBA) dam, located at the outlet of this basin. To this end, using the HEC-HMS model, the Soil Moisture Accounting (SMA) Loss Method was used to model infiltration losses. The SCS Unit hydrograph (SCS UH) and the Recession method were chosen as transform model and baseflow model, respectively. As a result, the comparison shows an acceptable agreement between observed and simulated flow in terms of streamflow distribution and peak values (NSE=0.57, R2=0.58). During validation, the model retained its ability to sufficiently reproduce the rainfall-runoff mechanism of the studied basin with a slight overestimation of peaks (NSE=0.61, R2=0.60). This study allows to assess and predict the inter-annual and intra-annual variation of the SMBA dam reservoir’ inflows, and therefore to forecast the climate change impact on this basin.

Effects of Fuel Staging on the Hydrodynamic Stability of Multinozzle Swirl Flows

Abstract Hydrodynamic instability in lean premixed gas turbine combustors can cause coherent flow velocity oscillations. These can in turn drive heat release oscillations that when favorably coupled with combustor acoustic modes can result in combustion instability. The aim of this paper is to understand the impact of fuel staging on the characteristics of hydrodynamic modes in multinozzle combustors. We extend our recent numerical study on the hydrodynamic stability characteristics of a multinozzle combustor having three nozzles in a straight line with uniform fuel–air ratio in each nozzle, to the nonuniform fuel–air ratio case. As before, we construct the base flow model for this study by superposing contributions from individual nozzles, determined using a base flow model for a nominally axisymmetric single nozzle, at every point in the computational domain. The impact of fuel staging is captured by changing the burnt to unburnt gas density ratio parameter in the individual contribution from each nozzle. We investigate the characteristics of the most locally absolutely unstable mode for two cases. The first one is when the middle nozzle is made fuel rich when compared to the side nozzles and the second is when the side nozzles are made fuel rich relative to the middle nozzle. The impact of nonuniform fuel/air ratio on the local absolutely unstable temporal eigenvalues is seen to be small. However, significant changes in the spatial structure of the flow oscillations associated with the hydrodynamic eigenmodes are observed. In the first case, the flow oscillations with a different locally azimuthal nature on the middle nozzle when compared to the side nozzles emerge as the middle nozzle is made richer. In the second case, the oscillations on the two side nozzles are suppressed leaving the middle nozzle in a state that closely matches that of a single unconfined nozzle with the same nominal base flow velocity field. These types of internozzle variations in flow oscillation characteristics can explain the emergence of nonuniformity in heat release oscillation characteristics between individual nozzles in multinozzle combustors.

Optimal reservoir operation based on hydrological and hydraulic methods incorporating the multiple water replenishment process

A reservoir usually functions as multi-objectives. Different objective has various requirement in water volume and temporals process due to the fact that some objectives require different constant base flow in different months and some objectives demand ephemeral flood pulse. How to balance reservoir functioning and water allocation of multiple targets has become increasingly significant at present. In the past, the multi-objectives operation was usually designed based on water quantity balance, neglecting the coupling with the hydrodynamic process. Sometimes the coupling is so important for some ecological factors and the neglecting may result in failure to meet the hydraulic requirements of the downstream ecological environment. By coupling the hydrologic and hydrodynamic methods, an integrated reservoir model for multiple-objectives optimal operation was presented including water balance model, one-dimensional unsteady flow model, two-dimensional depth-averaged model and ecological baseflow model. The different process demands include water allocation at the dam site, unsteady flow process at different sections downstream the dam site. Taking a reservoir in northern China as an example, the minimum change of the hydrological process in the river mouth section was set as the objective function for the optimal operation. Regarding the demand for aquatic organisms, the low and high baseflow schemes were suggested by the comprehensive use of different ecological flow methods (the Tennant method, the flow duration curve method and the wetted perimeter method). According to the ecological flooding during the wetland water supplement, the Wetland Water Replenishment Model was applied to calculate the replenishment process under different flood cases. The Lake Water Replenishment Model was used for flow scheduling of the downstream lake. Regarding the wet years, the objective functions at the river mouth section were 16.0% with the low baseflow scheme and 15.5% with the high baseflow scheme, whereas for the dry years, it is 18.2% with the low baseflow scheme and 15.5% with the high baseflow scheme. Comparison showed that the high baseflow scheme was optimal for the reservoir operation. The result could provide a reference for decision-makers in reservoir scheduling design. It shows that the coupling of hydraulic and hydrological methods could provide a more reliable basis for reservoir optimal operation.

Numerical realization of helical vortices: application to vortex instability

The need to numerically represent a free vortex system arises frequently in fundamental and applied research. Many possible techniques for realizing this vortex system exist but most tend to prioritize accuracy either inside or outside of the vortex core, which therefore makes them unsuitable for a stability analysis considering the entire flow field. In this article, a simple method is presented that is shown to yield an accurate representation of the flow inside and outside of the vortex core. The method is readily implemented in any incompressible Navier–Stokes solver using primitive variables and Cartesian coordinates. It can potentially be used to model a wide range of vortices but is here applied to the case of two helices, which is of renewed interest due to its relevance for wind turbines and helicopters. Three-dimensional stability analysis is performed in both a rotating and a translating frame of reference, which yield eigenvalue spectra that feature both mutual inductance and elliptic instabilities. Comparison of these spectra with available theoretical predictions is used to validate the proposed baseflow model, and new insights into the elliptic instability of curved Batchelor vortices are presented. Furthermore, it is shown that the instabilities in the rotating and the translating reference frames have the same structure and growth rate, but different frequency. A relation between these frequencies is provided.

Effect of Time-Area Percent Curves in Development of Clark Model Unit Hydrograph

This paper describes the effect of time – area percent curves in the development of Clark model unit hydrograph. This hydrology modelling study refers to event base modeling in order to derive the unit hydrograph from Clark instantaneous unit hydrograph. For this study, Kelani river basin up to Hanwella gauging site has been represented as the study area. Hydrologic Modelling System software developed by HEC, USA (HEC-HMS) has been used for the development of unit hydrographs under the Clark UH transform model. Three numbers of different time – area percent curves of Kelani river basin have been asynchronously used as input to the Clark UH transform model in order to obtain different simulations. The parameters, time of concentration Tc and storage coefficient R values were calibrated and validated individually, against the various percent curves for the future analysis. The best suitable percent curve is identified based on the goodness of fit criteria, Nash-Sutcliffe Efficiency (NSE) with high accuracy. For the Loss model, initial and constant rate method was preferred. In the Meteorological Model, Gaged weight was considered for rainfall analysis. For the Transform Model or Direct Runoff Model, Clark UH is considered. For the Base flow model Recession, constant option was preferred. The Calibration (manual and automatic) was conducted for the storm events of May 2017, December 2014 and November 2012.Validation was conducted for the storm event of June 2014. The calibration and validation process was conducted for analyzing the hourly rainfall-runoff data for storm events observed during the monsoon seasons of the relevant years. The conclusions of the study would be very much applicable for the key personnel for taking structural and non-structural measures against the flood menace which is a frequent challenge over the study area concerned.

Non-periodic phase-space trajectories of roughness-driven secondary flows in high- boundary layers and channels

Turbulent flows respond to bounding walls with a predominant spanwise heterogeneity – that is, a heterogeneity parallel to the prevailing transport direction – with formation of Reynolds-averaged turbulent secondary flows. Prior experimental and numerical work has determined that these secondary rolls occur in a variety of arrangements, contingent only upon the existence of a spanwise heterogeneity (i.e. from complex, multiscale roughness with a predominant spanwise heterogeneity, to canonical step changes, to different roughness elements). These secondary rolls are known to be a manifestation of Prandtl’s secondary flow of the second kind: driven and sustained by the existence of spatial heterogeneities in the Reynolds (turbulent) stresses, all of which vanish in the absence of spanwise heterogeneity. Herein, we show results from a suite of large-eddy simulations and complementary experimental measurements of flow over spanwise-heterogeneous surfaces. Although the resultant secondary cell location is clearly correlated with the surface characteristics, which ultimately dictates the Reynolds-averaged flow patterns, we show the potential for instantaneous sign reversals in the rotational sense of the secondary cells. This is accomplished with probability density functions and conditional sampling. In order to address this further, a base flow representing the streamwise rolls is introduced. The base flow intensity – based on a leading-order Galerkin projection – is allowed to vary in time through the introduction of time-dependent parameters. Upon substitution of the base flow into the streamwise momentum and streamwise vorticity transport equations, and via use of a vortex forcing model, we are able to assess the phase-space evolution (orbit) of the resulting system of ordinary differential equations. The system resembles the Lorenz system, but the forcing conditions differ intrinsically. Nevertheless, the system reveals that chaotic, non-periodic trajectories are possible for sufficient inertial conditions. Poincaré projection is used to assess the conditions needed for chaos, and to estimate the fractal dimension of the attractor. Its simplicity notwithstanding, the propensity for chaotic, non-periodic trajectories in the base flow model suggests similar dynamics is responsible for the large-scale reversals observed in the numerical and experimental datasets.

Influence of Nonaxisymmetric Confinement on the Hydrodynamic Stability of Multinozzle Swirl Flows

Interaction between coherent flow oscillations and the premixed flame sheet in combustors can result in coherent unsteadiness in the global heat release response. These coherent flow oscillations can either be self-excited (e.g., the precessing vortex core) or result from the hydrodynamic response of the flow field to acoustic forcing. Recent work has focused on understanding the various instability modes and fundamental mechanisms that control hydrodynamic instability in single nozzle swirl flows. However, the effect of multiple closely spaced nozzles as well as the nonaxisymmetric nature of the confinement imposed by the combustor liner on swirl nozzle flows remains as yet unexplored. We study the influence of internozzle spacing and nonaxisymmetric confinement on the local temporal and spatiotemporal stability characteristics of multinozzle flows in this paper. The base flow model for the multinozzle case is constructed by superposing contributions from a base flow model for each individual nozzle. The influence of the flame is captured by specifying a spatially varying base flow density field. The nonaxisymmetric local stability problem is posed in terms of a parallel base flow with spatial variations in the two directions perpendicular to the streamwise direction. We investigate the case of a single nozzle and three nozzles arranged in a straight line within a rectangular combustor. The results show that geometric confinement imposed by the combustor walls has a quantitative impact on the eigenvalues of the hydrodynamic modes. Decreasing nozzle spacing for a given geometric confinement configuration makes the flow more unstable. The presence of an inner shear layer (ISL) stabilized flame results in an overall stabilization of the flow instability. We also discuss qualitatively, the underlying vorticity dynamics mechanisms that influence the characteristics of instability modes in triple nozzle flows.

Regional Patterns of Baseflow Variability in Mexican Subwatersheds

One of the challenges faced by subwatershed hydrology is the discovery of patterns associated with climate and landscape variability with the available data. This study has three objectives: (1) to evaluate the annual recession curves; (2) to relate the recession parameter (RP) with physiographic characteristics of 21 Mexican subwatersheds in different climate regions; and (3) to formulate a Baseflow (BF) model based on a top-down approach. The RP was calibrated utilizing the largest magnitude curves. The RP was related to topographical, climate and soil variables. A non-linear model was employed to separate the baseflow which considers RP as a recharge rate. Our results show that RP increases with longitude and decreases with latitude. RP displayed a sustained non-linear behavior determined by precipitation rate and evapotranspiration replace the P/E parts with \(\frac{P}{E}\) over years and subwatersheds. The model was fit to a parameter concurrent with invariance and space-time symmetry conditions. The dispersion of our model was associated with the product of replace the P/E parts with \(\frac{P}{E}\) by the aquifer’s transmissivity. We put forward a generalized baseflow model, which made the discrimination of baseflow from direct flow in subwatersheds possible. The proposed model involves the recharge-storage-discharge relation and could be implemented in basins where there are no suitable ground-based data.

Applying an Exact Solution of the Brutsaert and Nieber Baseflow Model for Watershed Yield Prediction: A Case Study for the Spoon River at Seville, Illinois, USA

Applying an Exact Solution of the Brutsaert and Nieber Baseflow Model for Watershed Yield Prediction: A Case Study for the Spoon River at Seville, Illinois, USA

The prediction of axial aerodynamic coefficient reduction using base bleed

To reduce axial aerodynamic force as leading aerodynamic load during projectile flight, one of the possible solutions is to redesign the projectile base, using limited flow as base bleed. Base bleed design needs accurate turbulent supersonic base flow model over a cylindrical afterbody and needs to be developed. Predictions and analysis of the aerodynamic behavior of the base bleed projectile with such a model can reduce development cost and test effort. There are three ways of achieving results of a suitable flow model: by theoretical prediction, by numerical simulation and by restricted experimental measurement. The base bleed effects on the aerodynamic axial coefficient, as increase of the base pressure, and decrease of the eddy component of axial aerodynamic coefficient. Results of the axial aerodynamic coefficient of projectile, without base bleed obtained by experimental and predictional calculation. A validation calculation was performed for several types of projectiles. Computed results show reasonable trends in the base pressure increase – base drag reduction, base corner expansion and downstream wake closure location.

Estimation of groundwater recharge using the soil moisture budget method and the base-flow model

Estimation of groundwater recharge is extre- mely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. The main purpose of this paper is to apply a water balance concept with two methods to estimate the groundwater recharge in the Ching-Shui watershed, Tai- wan. First, a soil moisture budget method is established to estimate the infiltration, runoff, evapotranspiration, and groundwater recharge in the watershed, where the moisture content of the soil is tracked through time. Both soil-water properties of the unsaturated zone and climatic conditions must be fully considered. Second the base-flow model uses the base-flow separation from the total streamflow dis- charge to obtain a measure of groundwater recharge so that groundwater evapotranspiration is negligible. In contrast to the soil moisture budget method, base-flow estimation does not require complex hydrogeologic modeling and detailed knowledge of soil characteristics. In a previous study, we suggested that high base-flow is caused by rainstorm events. Using model analysis, depths of recharge esti- mated by stable-base-flow analysis are adopted to obtain more reasonable groundwater recharge values. The results indicate that assessment of the average annual recharge obtained with a soil moisture budget and the base-flow are very close; the ratio of the two methods is about 95.3%.

Estimation of groundwater recharge using water balance model

The main purpose of this paper is to apply a water balance concept with two models in the Ching-Shui watershed to describe the groundwater recharge. First of all, a soil moisture budget model is established to estimate the infiltration, runoff, evapotranspiration, and groundwater recharge in the watershed, where the moisture content of the soil is tracked through time. Secondly, the groundwater recharge was also estimated by the model of the base-flow-record estimation, with the assumption that groundwater evaporation is negligible. In addition, since the analyzed base-flow trends are high, when executing model analysis, the depths of infiltration estimated by stable-base-flow analysis is used to obtain more reasonable groundwater recharge value. The coefficients of groundwater recharge by the precipitation in the Ching-Shui watershed estimated from the established soil moisture budget model and the base-flow model were 12.40% and 9.92%, respectively. Comparison show the result of both models to be close.

Compressible Linear Stability of Confluent Wake/Boundary Layers

The linear stability of a compressible confluent wake/boundary layer is studied. The base flow model considered is the superposition of a compressible boundary layer and a Gaussian-like wake located above the boundary layer. The linear stability equations have been solved by using a global numerical method. The stability modes of interest have been identified as the boundary-layer modes, the antisymmetric wake mode, and the symmetric wake mode. The effects of wake height on the first Tollmien-Shlichting mode and the second mode associated with the boundary layer are discussed. Results for unstable modes associated with the wake are also presented

The Fluid Dynamics of Safety Valve Vent Stacks

The flow through a safety valve vent stack system has been modeled and analyzed theoretically and experimentally. The theoretical analysis is based on the well known Chapman-Korst base flow theory. The base flow model is augmented with an empirically determined recompression factor to improve agreement between the theoretical analysis and experimental results. A computer program has been developed to solve the equations and provide necessary information to designers.

Projectile Thrust-Drag Optimization with External Burning

Theme A analysis using the method of characteristics with heat addition and the Crocco-Lees base flow model is described for calculating the external supersonic flow with heat addition about the wake of a 5-in. projectile. Various amounts and locations of heat addition are found to generate a net thrust, and an optimum location for the combustion zone is predicted. Good agreement is observed between calculated and experimental base pressure measurements using a free-jet combustion simulator. The results from computing base pressure ratio over a wide range of Reynolds numbers are also presented.