Inflow Model Research Articles

Predicting Open Pit Mine Inflow and Recovery Depth in the Durvuljin soum, Zavkhan Province, Mongolia

Increasingly, mine issues and water resources are being managed on a watershed basis, while addressing problems at the local mine scale. A good example of this developed when empirical and analytical modelling of the potential inflow to an open pit mine in the Durvuljin soum, a region in northwest Mongolia, indicated that inflow would be on the order of 0.3 to 10.5 L/s. In this study, the radius of influence due to open pit mining was estimated to be between 0.6 and 3 km. Based on simulated drawdown contours and transient pit inflow figures that captured the impact of mining and groundwater inflow rate variations over a period of time, it appeared that advanced dewatering will not be required at this mine, unless currently unknown major fractured structures are intercepted. In-pit basal sumps and pumps should be sufficient to remove water from the mine floor. However, an assessment of the final pit level is also crucial to planning the post-mining surface and groundwater quality/eco-system and mitigation requirements during recovery. Our post-mining water table recovery estimate indicated that inflow will exceed evaporation and that a shallow lake will likely form. While such solutions, which do not rely on complex numerical models nor excessive input data, are not appropriate for all hydrogeologic situations, they are relevant to the conditions encountered at most mine sites.

Validation of engineering dynamic inflow models by experimental and numerical approaches

The state of the art engineering dynamic inflow models of Pitt-Peters, Øye and ECN have been used to correct Blade Element Momentum theory for unsteady load prediction of a wind turbine for two decades. However, their accuracy is unknown. This paper is to benchmark the performance of these engineering models by experimental and numerical methods. The experimental load and flow measurements of an unsteady actuator disc were performed in the Open Jet Facility at Delft University of Technology. The unsteady load was generated by a ramp-type variation of porosity of the disc. A Reynolds Averaged Navier-Stokes (RANS) model, a Free Wake Vortex Ring (FWVR) model and a Vortex Tube Model (VTM) simulate the same transient load changes. The velocity field obtained from the experimental and numerical methods are compared with the engineering dynamic inflow models. Velocity comparison aft the disc between the experimental and numerical methods shows the numerical models of RANS and FWVR model are capable to predict the velocity transient behaviour during transient disc loading. Velocity comparison at the disc between the engineering models and the numerical methods further shows that the engineering models predict much faster velocity decay, which implies the need for more advanced or better tuned dynamic inflow models.

Improved Inflow Modeling in Stochastic Dual Dynamic Programming

AbstractStochastic dual dynamic programming (SDDP) is a widely used technique for operation optimization of large-scale hydropower systems in which reservoir inflow uncertainty is modeled with discrete scenarios produced by statistical time series models, such as the family of periodic auto-regressive (PAR) models. It is a common practice in statistical modeling of hydrologic time series to fit a well-known probability distribution (usually normal distribution) to the data by applying proper transformation. Box-Cox transformation is a commonly used transformation in the case of normal distribution fitting. The convexity requirement of SDDP means that nonlinearly transformed time series cannot be used for statistical inflow model calibration. In this paper, a linear approximation is proposed to estimate the expected value of the next stage inflow. In the proposed approach, next-stage inflows are estimated by a model that uses transformed time series. Furthermore, using the proposed linear approximation, it...

Dynamic Evaluation of Lavage Efficacy in Upper Compartment of the Temporomandibular Joint

The aim of this study was to determine the most efficient temporomandibular joint (TMJ) lavage technique for complete irrigation and removal of synovial fluid. The corresponding total lavage fluid volume needed also was investigated. Three-dimensional TMJ lavage models of the classic double- and single-needle techniques with modified cannula sizes (diameters, 2.4 and 0.8mm) were generated based on a constructed upper compartment model. Models were integrated with 2-phase flow models to predict fractional fluid volume (α value) changes of lavage saline and synovial fluid within the upper compartment of the TMJ. Fluid flow diagrams, velocity vectors, and intra-articular pressure data were collected and compared among the models. Models were validated by clinical synovial fluid concentration analyses, with vitamin B12 used as an internal standard. In all 8 models, lavage fluid initially gathered around the inflow portal, with a stable mixture of synovial and lavage fluids eventually being established in the compartment. Use of the double-needle technique with a large inflow portal resulted in thorough lavage (α= 100%). When the single-needle or Shepard cannula technique was used, some areas within the upper compartment remained devoid of brisk flow. The 2.4-mm inflow model coupled with a 0.8-mm outflow portal resulted in a stably and persistently high intra-articular pressure (>2.7 × 104Pa). A minimum volume of 109mL of lavage fluid was necessary for complete replacement of synovial fluid by saline. When a 2.4-mm inflow portal needle was applied, a lavage rate of 100% was obtained with a minimum lavage volume of 109mL. Using a small inflow portal could lead to inadequate flow, residual synovial fluid, and, ultimately, treatment failure.

Assessment of Helicopter Model Accuracy Through Inverse Simulation

The paper deals with the assessment of the reliability of simplified rotorcraft models in the evaluation of maneuvering potential using inverse simulation. Inverse solutions obtained for the same maneuver from models of different complexity and fidelity are compared with the objective of identifying the most appropriate model for a consistent evaluation of vehicle handling qualities at the minimum computational cost. A total of nine rotor blade models, three main rotor inflow models, and two fuselage aerodynamic databases are combined for deriving 10 different helicopter simulation models analyzed in five maneuvers. Inverse solutions are obtained by means of an integration method for hurdle-hop, slalom, and lateral repositioning maneuvers. Once the maneuvers are solved for the baseline rotorcraft model, the uncertainty associated with the command law identified by means of simpler models is determined. The quantitative evaluation of model reliability from a set of simulation tests is further analyzed on a pop-up-pop-down maneuver and a 180 deg fast turn for validating the approach. The results show that uncertainty intervals are correctly identified, although with some degree of conservativeness when less demanding maneuvers are dealt with.

Variations of effective volume and removal rate under different water levels of constructed wetland

Water depth is a key parameter in the design and operation of constructed wetlands. In this study, the effect of water depth on the effective volume and the removal rate was explored through dye tracer experiments in water depths of 20cm, 40cm, and 60cm at a constructed wetland located at the Center Station of Irrigation Experiment, Nanchang City, China. The One-dimensional Transport with Inflow and Storage (OTIS) model and a so-called CSTRs+PFD (continuously stirred tank reactors+plug flow with dispersion) model were calibrated for analysis of the hydraulic parameters. The results are summarized as follows. (1) When the water depth increased from 20cm to 60cm, the hydraulic efficiency λm decreased, as did the effective volume ratio e determined by both moment analysis and the OTIS model. (2) A combination of effective volume ratio and the number of continuously stirred tank reactors, N could better reflect the effect of water depth on the removal efficiency. (3) Theoretical analysis showed that the removal efficiency decreased with increasing water depth, which was caused by a decrease of reaction rate. Therefore, the reaction rate has a larger effect on the removal efficiency than residence time. (4) Dye tracer tests showed that the mean residence time and effective volume first rose and then fell slightly with increasing water depth. The changes in the mean residence time and reaction rate suggest that increasing the water depth would do little to improve the removal efficiency.

Verifying the Blade Element Momentum Method in unsteady, radially varied, axisymmetric loading using a vortex ring model

AbstractAlthough the Blade Element Momentum method has been derived for the steady conditions, it is used for unsteady conditions by using corrections of engineering dynamic inflow models. Its applicability in these cases is not yet fully verified. In this paper, the validity of the assumptions of quasi‐steady state and annuli independence of the blade element momentum theory for unsteady, radially varied, axi‐symmetric load cases is investigated. Firstly, a free wake model that combines a vortex ring model with a semi‐infinite cylindrical vortex tube was developed and applied to an actuator disc in three load cases: (i) steady uniform and radially varied, (ii) two types of unsteady uniform load and (iii) unsteady radially varied load. Results from the three cases were compared with Momentum Theory and also with two widely used engineering dynamic inflow models—the Pitt‐Peters and the Øye for the unsteady load cases. For unsteady load, the free wake vortex ring model predicts different hysteresis loops of the velocity at the disc or local annuli, and different aerodynamic work from the engineering dynamic inflow models. Given that the free wake vortex ring model is more physically representative, the results indicate that the engineering dynamic inflow models should be improved for unsteady loaded rotor, especially for radially varied unsteady loads. © 2016 The Authors. Wind Energy Published by John Wiley & Sons, Ltd.

Free-Wake–Based Dynamic Inflow Model for Hover, Forward, and Maneuvering Flight

Free-Wake–Based Dynamic Inflow Model for Hover, Forward, and Maneuvering Flight

Effects of Passive and Structural Stream Restoration Approaches on Transient Storage and Nitrate Uptake

Understanding nitrogen dynamics in headwater streams is important for ascertaining how they influence downstream nutrient loads and identifying strategies for reducing loading through stream restoration. We compare nitrate uptake associated with two restoration approaches in headwater streams, Sheep Creek and Nunn Creek, of northern Colorado, USA. Segments of Sheep Creek were exclosed (fenced off) from open rangeland cattle grazing in the 1950s, allowing riparian corridors of these segments to naturally revegetate (passive approach), while other segments have been continually grazed. In 2003, restoration structures including cross vanes, J‐hook vanes, rootwads, log vanes, and bank riprap (structural approach) were installed along portions of Nunn Creek for trout habitat enhancement and local bank stabilization. We performed detailed physical characterizations and multiple nutrient injections of Br⁻ and NO₃ ⁻ to estimate transient storage and nitrate uptake in four reaches along Sheep Creek (two reaches exclosed from grazing and two grazed reaches) and two reaches along Nunn Creek (one with restoration structures and one without structures). Parameters of transient storage and nitrate uptake were estimated with the one‐dimensional transport with inflow and storage model run through universal inverse modelling code for optimization. Responses of transient storage and nitrate uptake to restoration techniques depended upon the type and extent of restoration implemented, as well the context and physical setting of each study reach. For example, in the higher‐gradient pair of Sheep Creek reaches, the restored reach showed greater nitrate uptake, while in the lower‐gradient pair of reaches, the non‐restored reach had greater uptake. At Nunn Creek, the reach with instream wood but without restoration structures exhibited more transient storage and nitrate uptake when compared with the reach with extensive J‐hook vane structures. Copyright © 2016 John Wiley & Sons, Ltd.

Spatio-temporal hydro forecasting of multireservoir inflows for hydro-thermal scheduling

Hydro-thermal scheduling is the problem of finding an optimal dispatch of power plants in a system containing both hydro and thermal plants. Since hydro plants are able to store water over long time periods, and since future inflows are uncertain due to precipitation, the resulting multi-stage stochastic optimization problem becomes challenging to solve. Several solution methods have been developed over the past few decades to compute practically useful operation policies. One of these methods is stochastic dual dynamic programming (SDDP). SDDP poses strong restrictions on the forecasting method generating the necessary inflow scenarios. In this context, the current state-of-the-art in forecasting are periodic autoregressive (PAR) models. We present a new forecasting model for hydro inflows that incorporates spatial information, i.e., inflow information from neighboring reservoirs of the system, and that also satisfies the restrictions posed by SDDP. We benchmark our model against a PAR model that is similar to the one currently used in Brazil. Three multi-reservoir basins in Brazil serve as a case study for the comparison. We show that our approach outperforms the benchmark PAR model and present the root mean squared error (RMSE) as well as the seasonally-adjusted coefficient of efficiency (SACE) for each reservoir modeled. The overall decrease in RMSE is 8.29 percent using our approach for one month-ahead forecasts. The decrease in RMSE is achieved without additional data collection while only adding 11.8 percent more state variables for the SDDP algorithm.

Helicopter Unsteady Maneuver Analysis Using Inverse Flight Dynamics Simulation and Comprehensive Analysis

This paper describes the development of an inverse flight dynamics simulation for helicopters and its application for blade loads prediction using comprehensive analysis for a helicopter undergoing unsteady maneuvers. The inverse simulation is carried out for an unsteady pull-up maneuver and the estimated control angles are used as input to University of Maryland Advanced Rotorcraft Code comprehensive analysis for prediction of blade loads. Inverse simulation is carried out using an integration-based approach using a simplified helicopter dynamics model with rigid blades having only flap degree of freedom, quasi-steady aerodynamics, and Drees inflow model. The predicted control angles and blade loads are compared against the flight-test data for a UH-60A Black Hawk helicopter. The inverse flight dynamics with simple rotor dynamics is able to predict the correct trend of variation of control angle time history for this severe maneuver. The control angle time history estimated using the linear aerodynamics-model-based inverse simulation predicts all three stalls. Advancing blade transonic stall is predicted for the first time using a coupled lifting-line-based analysis. The magnitude of negative peak of stall loads and corresponding structural loads prediction is less satisfactory.

Finite element method (FEM) groundwater inflow modeling associated with an unconfined aquifer into the open-pit coalmine of the Phulbari area, NW Bangladesh

This paper uses a two-dimensional finite element method (FEM) numerical modeling to predict groundwater inflow from an unconfined aquifer into the open-pit coalmine in the Phulbari area of northwest Bangladesh. The rock mass of the unconfined aquifer in the Phulbari coal deposit is highly porous and permeable. Interconnected pores within rock mass are the main paths for groundwater flow. Model assumes groundwater inflow rate through the rock mass associated with interconnected pores. Eleven stages of computation associated with variable overall pit slope angle (OPSA) 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, and 35° are presented here. Model reveals that the probable inflow rate from unconfined aquifer in the open-pit coalmine would be about 377.68, 364.93, 354.38, 340.20, 331.29, 326.36, 316.86, 315.36, 308.03, 302.86, and 298.00 m3/h with relevant slope angles of 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, and 35°, respectively. It is reasonable to emphasize that the computed inflow rate (m3/h) in the present numerical model would be effective through unit width of rock strata up to the pit depth of about 320 m in the Phulbari coal deposit. From the simulation results, it is thought that the open-pit coalmine in the Phulbari area would be an environmentally challenging issue because of regional unconfined mega-aquifer.

Phase and amplitude of spontaneous retinal vein pulsations: An extended constant inflow and variable outflow model

The constant inflow and variable outflow (CIVO) theory correctly predicts that spontaneous pulsation of the retinal veins will be visible close to the point where the vein exits the eye at the lamina cribrosa but will decrease rapidly in amplitude and become too small to see only a short distance upstream. However, the phase of vein oscillation relative to the oscillation of the intraocular pressure (IOP) predicted by CIVO has been unclear and controversial. We show that the CIVO model is indeterminate in predicting such phase relations. We propose a simple extension of the CIVO model that retains its basic equations but applies them to a larger domain that includes not only the intraocular (pre-laminar) portion of the vein but also the retrobulbar (post-laminar) portion of the vein behind the eye. We show that this extended CIVO model makes definite predictions about the phase of vein oscillation relative to the oscillation of IOP. This phase relationship is determined by the relative amplitude and phase of pulsations of the IOP and of the cerebrospinal fluid pressure (CSFP). If IOP and CSFP oscillate in phase, then the pre-laminar vein oscillates in phase with IOP when the amplitude of CSFP exceeds the amplitude of IOP but oscillates in counter phase with IOP when the amplitude of IOP exceeds that of CSFP. These relationships are modified when there is a phase difference between the oscillations of IOP and CSFP. When CSFP leads IOP, the phase of vein oscillation is advanced if the amplitude of CSFP exceeds that of IOP and is delayed if the amplitude of IOP exceeds that of CSFP. The result in each case is that maximum vein size occurs during the rising phase of IOP (ocular systole). We conclude that the driving force of vein oscillation is the difference between the oscillations of IOP and CSFP. The phase of this difference determines the phase relationships above. We show that additional delays in the phase of venous pulsation relative to that of IOP are induced by constriction of the vein within the lamina cribrosa and by recording the vein pulsations upstream from the lamina cribrosa. The amplitude of vein oscillation is proportional to the amplitude of the driving force and to the venous capacitance. Loss of spontaneous retinal vein pulsation with increase in mean CSFP is determined primarily by reduced venous capacitance. Increased amplitude of pulsation may occur when IOP is increased. It is the result of increased venous capacitance and possibly increased driving force of the pulsation. However, in chronic glaucoma the increase in capacitance may be counteracted by venous outflow obstruction, and the increase in driving force may be counteracted by reduced ocular blood flow. As a result retinal vein oscillation may be reduced in amplitude.

Generalized Aerodynamic Modeling of Dynamic Wake Curvature for Open Rotors With Slender Blades

This paper elaborates on the theoretical development of an analytical approach, capable of modeling the effect of dynamic wake curvature on the aeroelastic response of open rotors with slender blades. The classical solution of incompressible, potential flow derived for a curved vortex tube of uniform vorticity strength is employed. The previously developed curved vortex tube analysis is mathematically generalized to account for arbitrary radial and circumferential variations of circulatory disk loading. An orthogonality analysis is carried out to obtain a finite set of inflow perturbation coefficients that describe the aerodynamic effect of wake curvature in a generalized manner. The end result is a set of integral expressions that provide the interharmonic coupling between the inflow perturbations on the rotor disk due to a curved trailing wake and the corresponding variations of disk loading. The obtained perturbation coefficients are subsequently superimposed upon an existing finite-state induced flow model that assumes a skewed, noncurved cylindrical wake. The developed mathematical approach for fluid mechanics is coupled with an unsteady blade element aerodynamics model, a rotor blade structural mechanics model, and a nonlinear rotor dynamics model. The combined formulation is implemented in an existing helicopter flight mechanics code. The overall method is initially employed to assess the effect of wake curvature on the dynamic response of a small-scale articulated rotor with a flap frequency ratio equal to unity. Subsequently, the integrated model is deployed to investigate the influence of wake curvature and inflow modeling fidelity on the predicted oscillatory blade loads and transient control response of a full-scale helicopter rotor. Comparisons are carried out with flight test measurements as well as with complex free-wake analysis methods. It is shown that including the effect of wake curvature is essential for predicting the transient control response of the investigated rotor. Good agreement is demonstrated between the proposed analytical model and nonlinear predictions carried out by resolving the complex wake geometry. The developed fluid mechanics formulation is a time-accurate method derived from first-principles and is applicable to both axial and nonaxial flow conditions.

Joint Modelling of Wind Power and Hydro Inflow for Power System Scheduling

This paper concerns the joint modelling of wind power and hydro inflow for long-term power system scheduling. We propose a vector autoregressive model applied to deseasonalized series to describe the joint generating mechanism of wind and inflow. The model was applied to daily and weekly bivariate time series comprising wind and inflow from seven regions in Norway. We found evidence of both lagged and contemporaneous dependencies between wind and inflow, in particular, our results indicate that wind is useful in forecasting inflow, but not the other way around. The forecasting performance of the proposed VAR models was compared to that of independent AR models, as well as the persistence forecasts. Our results show that the VAR model was able to provide better forecasts than the AR models and the persistence forecast, for both the daily and weekly time series.

Application of Inflow Model for Weir Irrigation System without Upstream Dam

This research was conducted in the upstream watershed of the Mae Yom Irrigation Project, which was located in the Upper Yom River Basin in Phrae Province, Thailand. The most common troublesome in this area is flood and drought and leads to poor water management by difficult river flow forecasting to an existing large weir without upstream dam. The Soil And Water Assessment Tool (SWAT) model was applied for the simulation of the hydrological system and predicting the daily river flow to the upstream weir during flood season in 2006 and 2011 as for simulating and comparing with observed data. The results were fitted to the observed data with Nash and Sutcliffe efficiency (NSE) of ?0.65, and root mean square error (RSME) of 228.0 whereas the mean inflow discharge during wet season in both years was 173.3 cubic meters per second, respectively.

Optimal Design and Acoustic Assessment of Low-Vibration Rotor Blades

An optimal procedure for the design of rotor blade that generates low vibratory hub loads in nonaxial flow conditions is presented and applied to a helicopter rotor in forward flight, a condition where vibrations and noise become severe. Blade shape and structural properties are the design parameters to be identified within a binary genetic optimization algorithm under aeroelastic stability constraint. The process exploits an aeroelastic solver that is based on a nonlinear, beam-like model, suited for the analysis of arbitrary curved-elastic-axis blades, with the introduction of a surrogate wake inflow model for the analysis of sectional aerodynamic loads. Numerical results are presented to demonstrate the capability of the proposed approach to identify low vibratory hub loads rotor blades as well as to assess the robustness of solution at off-design operating conditions. Further, the aeroacoustic assessment of the rotor configurations determined is carried out in order to examine the impact of low-vibration blade design on the emitted noise field.

Inflow Prediction and First Principles Modeling of a Coaxial Rotor Unmanned Aerial Vehicle in Forward Flight

When the speed of a coaxial rotor helicopter in forward flight increases, the wake skew angle of the rotor increases and consequently the position of the vena contracta of the upper rotor with respect to the lower rotor changes. Considering ambient air and the effect of the upper rotor, this study proposes a nonuniform inflow model for the lower rotor of a coaxial rotor helicopter in forward flight. The total required power of the coaxial rotor system was compared against Dingeldein’s experimental data, and the results of the proposed model were well matched. A plant model was also developed from first principles for flight simulation, unknown parameter estimation and control analysis. The coaxial rotor helicopter used for this study was manufactured for surveillance and reconnaissance and does not have any stabilizer bar. Therefore, a feedback controller was included during flight test and parameter estimation to overcome unstable situations. Predicted responses of parameter estimation and validation show good agreement with experimental data. Therefore, the methodology described in this paper can be used to develop numerical plant model, study non-uniform inflow model, conduct performance analysis and parameter estimation of coaxial rotor as well as other rotorcrafts in forward flight.

Coupled Heuristic Prediction of Long Lead-Time Accumulated Total Inflow of a Reservoir during Typhoons Using Deterministic Recurrent and Fuzzy Inference-Based Neural Network

This study applies Real-Time Recurrent Learning Neural Network (RTRLNN) and Adaptive Network-based Fuzzy Inference System (ANFIS) with novel heuristic techniques to develop an advanced prediction model of accumulated total inflow of a reservoir in order to solve the difficulties of future long lead-time highly varied uncertainty during typhoon attacks while using a real-time forecast. For promoting the temporal-spatial forecasted precision, the following original specialized heuristic inputs were coupled: observed-predicted inflow increase/decrease (OPIID) rate, total precipitation, and duration from current time to the time of maximum precipitation and direct runoff ending (DRE). This study also investigated the temporal-spatial forecasted error feature to assess the feasibility of the developed models, and analyzed the output sensitivity of both single and combined heuristic inputs to determine whether the heuristic model is susceptible to the impact of future forecasted uncertainty/errors. Validation results showed that the long lead-time–predicted accuracy and stability of the RTRLNN-based accumulated total inflow model are better than that of the ANFIS-based model because of the real-time recurrent deterministic routing mechanism of RTRLNN. Simulations show that the RTRLNN-based model with coupled heuristic inputs (RTRLNN-CHI, average error percentage (AEP)/average forecast lead-time (AFLT): 6.3%/49 h) can achieve better prediction than the model with non-heuristic inputs (AEP of RTRLNN-NHI and ANFIS-NHI: 15.2%/31.8%) because of the full consideration of real-time hydrological initial/boundary conditions. Besides, the RTRLNN-CHI model can promote the forecasted lead-time above 49 h with less than 10% of AEP which can overcome the previous forecasted limits of 6-h AFLT with above 20%–40% of AEP.

Uncertainty analysis of groundwater inflow into underground excavations by stochastic discontinuum method: Case study of Siah Bisheh pumped storage project, Iran

This paper presents a framework for the near-field stochastic discontinuum modeling and uncertainty analysis of groundwater inflow into underground excavations by direct utilization of discrete fracture network (DFN) concept. The sources of uncertainty in the groundwater inflow into underground excavations in fractured rocks were classified into two different groups including the geometrical and hydraulic properties of fractures. The main input data for stochastic discontinuum modeling of groundwater inflow were captured from site investigations in Siah Bisheh pumped storage project in Iran. Detailed measurements of groundwater inflow into powerhouse and transformer caverns provided the possibility to determine the hydraulic aperture through back calibration. The validity of calibrated hydraulic aperture was explored by simulation results of the groundwater inflow into transformer cavern, and shows high accuracy when compared with data obtained from field measurements. The statistical results of these groundwater flow simulations with constant calibrated hydraulic aperture reflected the uncertainty associated with geometrical properties of fractures. Finally, the role of hydraulic properties of fractures on the uncertainty of groundwater inflow was investigated by the variation of standard deviation of hydraulic aperture through the sensitivity analysis. The results of this study demonstrated that the geometrical properties of fractures did much greater uncertainty in the groundwater inflow into underground excavations than hydraulic properties. Moreover, it was found that both the mean and standard deviation of simulated groundwater inflow into underground excavations decrease non-linearly by increasing the standard deviation of hydraulic aperture even though it is generally anticipated that the uncertainty of hydrogeological systems increases by increasing the variance of hydraulic parameters.