Values Of Hydraulic Parameters Research Articles

Uncertainty assessment of aquifer hydraulic parameters from pumping test data

Data from pumping tests is a noisy process, and therefore, performing the pumping test numerous times will not get the same drawdown values. As a consequence, various pumping experiments lead to different values for aquifer parameter estimates. The data of pumping tests are usually analyzed using traditional methods (aquifer tests and AQtesolv software), which depend on trial and error technique. During these methods, non-unique values of hydraulic parameters are selected, which usually have a high level of uncertainty. Uncertainty must be taken into account in determining aquifer parameters, especially when using groundwater models for decision makers. The main goal of this study is to build a comprehensive tool for quantifying uncertainty associated with hydraulic parameter estimation from different pumping test conditions for fully penetrating wells in confined and semi-confined aquifers. To achieve the previous objective, a FORTRAN code was developed to apply the Markov Chain Monte Carlo (MCMC) algorithm using different likelihood functions (exponential, inverse, and log). This developed tool can be used to detect the most probable range of aquifer parameters that are consistent with pumping test data with a high degree of confidence. The tool was successfully used to several hypothetical cases to demonstrate the uncertainty in the quantification of aquifer parameters and compare the findings to the standard method's results. Also, the concept was verified numerically (using Modflow program) with satisfactory results using a hypothetical case with well-known aquifer parameters. Finally, the tool was applied for actual pumping test data with good results.

Determination of the in situ hydraulic parameters of the Callovo–Oxfordian clay rock in a long-term hydraulic interference testing at Andra's Underground Research Laboratory (CMHM)

Abstract. Between 2009 and 2015, Andra has conducted a unique long-term hydraulic interference test in two parallel boreholes 1 m apart from each other and air core drilled in the undisturbed Oxfordian Clay rock at Andra's Underground Research Laboratory (CMHM) in Bure, France. The experimental set-up consisted of six test intervals positioned along the parallel boreholes drilled from a drift located within the Callovo–Oxfordian clay at around 500 m b.g.l. (below ground level). The 20 m boreholes were oriented around 30∘ downwards. The pressure sensors linked to six intervals of 1 m length each allowed for continuous pressure measurement over 6 years and a slanted borehole for the observation of rock displacements (see Fig. 1). Additionally, flow rates were measured during water injection tests that lasted weeks or months. This extensive set of hydraulic data allowed, for the first time, a precise determination of the in situ Callovo–Oxfordian clay rock permeability and anisotropy and its specific storage at the metre to decametre scale. It was achieved based on an automated calibration, using a 3D flow model and explicitly considering all the relevant hydraulic elements acting on the flow system (such as rock mass, borehole disturbed zone and sealing elements) and the drift acting as a steady sink due to the underground ventilation (see Fig. 2). The history matching was performed on the transient pressure measurements. The obtained numerical calibration results were in close agreement with the hydraulic parameter values of the Callovo–Oxfordian clay determined at a smaller scale (single borehole tests and rock core samples in the laboratory), therefore demonstrating the reliability of the very low permeability of the Callovo–Oxfordian clay at the metre to decametre scale. Furthermore, the modelling illustrated the impact of the measurement set-up and its details on the observed hydraulic behaviour. The analysis methodology and the main findings will be presented.

The Method of Predicting the Confidence Interval by the Culvert Capacity of Channels at the Design Stage

The purpose of the research is to develop a methodology for predicting confidence intervals of functional parameters of main channels at the design stage, taking into account the probability of absolute changes occurring in their hydraulic parameters during construction and operation. In this regard, taking into account that during the construction and operation of main channels, the frequency of absolute changes in the values of the living cross-section area, wetted perimeter, hydraulic radius and bottom slope obeys the normal distribution law, and the channel roughness coefficient is an increasing and arbitrarily variable random variable, the possibility of predicting the probable confidence interval for the channel’s culvert over the period of operation is investigated. For this purpose, the Monte Carlo method and the Excel program were used, and a method for predicting the confidence interval of the design value of the channel flow rate was proposed. The corresponding analyses were carried out according to the design values of hydraulic parameters on the studied sections of the main channels operated in the Republic of Azerbaijan. Assuming that the design value of each hydraulic parameter is an average value, and the mean square deviation is within the probability, the generation of normally distributed random variables is compiled (provided that the channel roughness coefficient is an increasing and arbitrarily variable value in the appropriate limit), and according to the flow formula for a steady uniform movement, the maximum flow rate of the channel is calculated. The confidence interval of the average value of the predicted maximum flow rate is determined and compared with the design value of the maximum flow rate on the studied section of the trunk channel. Based on the proposed method, the effect of influencing the average value of the maximum flow rate was analyzed in the case of the roughness coefficient of the channel remains unchanged, and probabilistic scattering of other hydraulic parameters occurs around the design values, as well as, in general, the corresponding hydraulic parameters are scattered around the design values.

Stochastic Merging of Soil Hydraulic Properties for Vadose Zone Hydrological Modeling

Soil hydraulic properties (SHPs) are commonly determined in soil samples with replicas. Whether these replicas are taken at a same location to represent a specific point or at several locations to represent a larger area, the results should be merged into a final data set to be used in modeling. For this data set to be representative, standard errors and a correlation matrix must be considered in the merging process. We present a method to perform this merging and give an example using stochastic realizations of van Genuchten-Mualem (VGM) parameters generated by Cholesky decomposition to merge the SHP and associated statistics into a merged parameter set. To do so, we used VGM parameters obtained at sample scale in three replicas from a Brazilian savanna soil through inverse modeling of laboratory evaporation experiments. The effectiveness and representativeness of the proposed methodology were evaluated by observing the frequency distribution of different levels of output, comparing individual and merged sample properties. The outputs include VGM parameters, retention and conductivity characteristics, and water balance components stochastically predicted by a hydrological model. The performed stochastic merging correctly represented the variability of the combined replicas, especially with respect to hydrological model outputs of soil water balance components. Using the mean hydraulic property parameter values to deterministically predict water balance components may yield values that are substantially different from the mean values of stochastic realizations. This suggests that the deterministic prediction using mean parameter values in vadose zone hydrological modeling may result in unrepresentative outputs.

A productivity prediction method for multi-fractured horizontal wells in tight oil reservoirs considering fracture closure

The closure fracture phenomenon increases the complexity of well testing and reduces the accuracy of productivity forecasts when tight oil reservoirs are exploited. However, most existing productivity models tend to ignore this. Therefore, a productivity prediction model for multi-fractured horizontal wells in tight oil reservoirs considering fracture closure has been developed by considering the stress sensitivity in the formation and combining the physical parameters of actual production. The model is solved by the Laplace transform, perturbation transform, Pedrosa transform, and Stehfest numerical inversion. Drawing productivity impact curves and discussing productivity influence factors based on the model results from this study show that the model is reasonable. In the actual production process, the hydraulic fracture parameter values are not as high as possible, and they have a reasonable range of values. The fracture closure pressure has a significant impact on the production of tight oil reservoirs. The higher the fracture closure pressure is, the greater the fracture conductivity decreases sharply, and the larger the proppant elastic modulus is, the stronger the fracture conductivity. The influence of fracture conductivity on the production in tight oil reservoirs has an obvious point, and when the value is less than the point, the production effect is good. Improved production can be achieved by balancing the relationship between fracture parameters. The findings of this study can help to better understand the influence of fracture parameters on productivity and contribute to increasing well production and improved development of tight oil reservoirs.

Effect of spatial variation of spoil material properties on slope displacements under rapid drawndown of pit lakes

In many European countries, lignite or brown coal is used as a fuel source in steam-electric power generation. Upon completion of mining activities, a reclamation plan is imperative to ensure environmental and social prosperity of local areas. Abandoned mine pits are often reclaimed by creating a pit lake. Reclamation of large lignite open pit mine sites may use large amounts of previous overburden materials or “spoils” to create the slopes of the pit lake. Spoils are anthropogenic materials with large spatial variation in properties, hence, considering mean values of shear strength and hydraulic parameters to assess stability and seasonal displacements will not fully simulate actual field conditions. This paper considers the effect of spatial variation on slope stability and ground movements during rapid drawdown events (a critical case) using coupled flow-deformation 2D finite element analyses, incorporating unsaturated soil suctions above the phreatic surface. Effects of heterogeneity and randomness of spoils on the response of the slope are considered through random field modelling and the Monte-Carlo simulation technique. Four lognormally distributed random variables (spoil cohesion, friction angle, void ratio, and permeability coefficient) are examined. The effect of spatial variability of spoils is shown to be important; a significant number of the random field analyses resulted in larger displacements compared to a benchmark deterministic analysis adopting uniform mean parameter values.

Assessment of Aquifer Protective Capacity, Against the Surface Contamination. A Case Study of Kaduna Industrial Village, Nigeria

Geo-electric soundings was carried out in 22 different locations at Kaduna Refinery Petrochemical Corporation (KRPC) and White Oil and Gas Layout, Mahuta, Kaduna. The aquifer protective capacity and Hydraulic characteristics of the study area was computed from the Geoelectric parameters using Dar-Zarrouk and hydrological parameters. The interpreted data were presented in tabular form, Geoelectric/geology soil profiles and contoured maps. The results show that the study area aquifer is relatively protected with an average value of 0.5 mhos with an indication of infiltration of contaminant in some location. The hydraulic parameter values also show that the study area aquifer has the capacity to produce water non-stopping if the wells are sited based the geophysical investigation. The computed hydraulic characteristics and transmissivity of the area has an average value of 5.5 m/day and 6.1 /hour, which implies that, the study area has the capacity to transmit groundwater through a distance of 5.5 m in 24-hour and can covers 6.1 in one hour.

Hydrogeophysical Inversion of Time‐Lapse ERT Data to Determine Hillslope Subsurface Hydraulic Properties

AbstractTime‐lapse electrical resistivity tomography (ERT) data are increasingly used to inform the hydrologic dynamics of mountainous environments at the hillslope scale. Despite their popularity and recent advancements in hydrogeophysical inversion methods, few studies have shown how time‐lapse ERT data can be used to determine hydraulic parameters of subsurface water flow models. This study uses synthetic and field‐collected, hillslope‐scale, time‐lapse ERT data to determine subsurface hydraulic properties of a two‐layer, physics‐based, 2‐D vertical flow model with predefined layer and boundary locations. Uncoupled and coupled hydrogeophysical inversion methods are combined with a fine‐earth fraction optimization scheme to reduce the number of parameters needing calibration and interpret the influence of the hydraulic parameters on the hydrologic model predictions. Inversions of synthetic ERT data recover the prescribed fine‐earth fraction bulk density to within 0.1 g cm−3. Field‐collected ERT data from a mountain hillslope result in hydrologic model dynamics that are consistent with previous studies and measured water content data but struggle to capture measured groundwater levels. The uncoupled hydrogeophysical inversion method is more sensitive to changes in hydraulic parameter values of the lower hydrologic model layer than the coupled hydrogeophysical inversion method. Time series of minimum objective function value simulations indicate that periodically collected ERT data may recover hydraulic parameters to a similar level of uncertainty as daily ERT data. Using simple hydrologic model domains within hydrogeophysical inversions shows promise for providing reasonable hydrologic predictions while maintaining relatively simple calibration schemes and should be explored further in future studies.

Use of the Kalman Filter for the Interpretation of Aquifer Tests Including Model and Measurement Errors

The hydraulic parameters representative of actual aquifer conditions can be obtained through aquifer tests formerly known as pumping tests. Diverse methodologies based on analytical or numerical solutions have been proposed for the interpretation of aquifer tests; however, measurement and model errors are often neglected, which could lead to hydraulic parameter values that do not reflect the aquifer conditions. In this paper, a new alternative is presented for the interpretation of aquifer tests in confined aquifers based on the Cooper–Jacob solution by means of the dynamic Kalman filter and a nonlinear optimization method. This proposal was tested in two previously published case studies; the measured drawdowns were filtered by considering measurement and model errors to match the Cooper–Jacob solution. For the case studies, the results show that filtering the measured drawdowns leads to variations of up to 49.97% in the values for T and 150% for S when compared to the values determined by methodologies that neglect measurement and model errors. A poor match between filtered and measured data reflects large measurement errors and considerable deviations of the aquifer conditions with respect to the proposed model.

ВОПРОСЫ РЕКОНСТРУКЦИИ КРУПНЫХ КАНАЛОВ И ОЦЕНКА ИХ ЭФФЕКТИВНОСТИ

Purpose: to define the efficiency of large irrigation canals on the example of the Donskoy main canal and the Bolshoy Stavropol canal during their reconstruction. Materials and methods. The use of geocomposite materials is of interest to creating combined linings of large canals. A geocomposite anti-seepage structure made without a protective layer at the bottom and part of the slope and a concrete-film element in the zone of wave and ice impact is considered. The application of such a combined lining makes it possible to reduce the cost of the anti-seepage screen, to shorten the construction time, to reduce the canal roughness and to increase its water-carrying capacity. The method of hydraulic research is based on the field data of the Bolshoy Stavropol and the Donskoy main canals for average and maximum values of hydraulic parameters. In particular, it was necessary to determine the roughness coefficients of the canal in the area between the sections. Results. A feature of the reconstruction of the most dangerous sections of the Donskoy main canal is the close location of the groundwater level to the surface, which leads to the transition of free filtration to a banked-up one. According to the results of calculations, the total losses are 13.7×10³ cubic meters/day in the section 57–70 km, and with canal lining – 0.504 cubic meters/day, which is 2.09 times less than with banked-up filtration in the earthen bed. Conclusions. The most effective types of linings with the use of geocomposites which, as shown by field surveys, are reliable combined coatings, are presented. Anti-seepage facilities made of concrete and reinforced concrete have high impermeability, though at the same time they are destroyed over time under the influence of water and freezing-thawing processes.

How to relevantly characterize hydraulic properties of saline and sodic soils for water and solute transport simulations

Proper sets of soil hydraulic parameters are important for modeling water flow and solute transport. Using field saline water and laboratory tap water, this study systematically analyzed and compared laboratory saturated hydraulic conductivity, Kls and soil water retention curve, SWRC of saline soil within three soil multi-layered profiles to find out the adequate initial hydraulic parameter set of a hydrological model. Falling and constant head methods were applied on three undisturbed samples per pedogenic horizon. SWRC were established on the same samples, using both saline and tap water. Results showed the spatial variability of hydraulic properties in vertical and horizontal dimensions when comparing soil profiles' properties. The constant head method with saline water resulted in the highest Kls values followed by the falling head method with saline water, the constant head method with fresh water, and the falling head method with fresh water. The differences in Kls were up to two orders of magnitude when comparing all datasets. Fresh water reduced soil water retention significantly. A significant correlation between the hydraulic properties and some physical and chemical properties suggests that the effects of soil texture, structure, calcium carbonate and gypsum content, and CEC (clay mineralogy) were larger than those of salt content. The change in hydraulic properties and the dependency on the procedure use may be attributed to aggregate breakdown and plugging of macropores, clay heterogeneity and dispersion, calcium carbonate and gypsum dissolution, all damaging soil structure. Simulation runs illustrated that hydraulic properties obtained with saline water resulted in better model performance than when using the conventional procedures with fresh/tap water. A proper set of initial hydraulic parameter values is an important step in model calibration and thus must be characterized correctly. Therefore, to hydraulically characterize saline soil, procedures should be standardized. Moreover, the approach and results of this study may provide a reference for characterization of soil hydraulic properties of saline and sodic soils effectively.

Stratigraphic modeling and hydraulic characterization of a typical basaltic aquifer system in the Kadva river basin, Nashik, India

The primary objective of the study is to characterize the hydrogeologic status and identify the trend in groundwater storage of aquifer system to provide an improved understanding of the groundwater flow system in the Kadva river basin, India. This is accomplished by the integrated use of stratigraphic modeling, pressure derivative approach, and pumping test analysis. The results of the stratigraphic modeling indicate that the unconfined aquifer thickness ranging from 8.2 to 34.2 m and generally occur to the depth of 2.2–36.5 m below ground level (bgl), whereas semi-confined aquifer thickness ranges from 6.1 to 58.3 m and generally occurs 30.6 m bgl over the study area with an interconnected semi-confining unit of thickness ranging from 1.6 to 22.3 m. The pumping test results of unconfined aquifer in the study area show that the transmissivity varies from 15.66 to 98.18 m2/day, and the specific yield ranging from 8.2 × 10–4 to 3.2 × 10–2. Pumping test data and derivative analysis show that the deep aquifers are semi-confined with transmissivity ranging from 14.4 to 111.2 m2/day, storage coefficient varies from 1.56 × 10–4 to 4.83 × 10–4, and hydraulic resistance ranges from 93 to 1270 days. The values of hydraulic parameters revealed a remarkable spatial variability, suggesting that the basaltic aquifer system has strong heterogeneity. The results of the present study are helpful in the formulation of efficient policies for sustainable groundwater management in basaltic aquifers system in India in particular and worldwide in general.

Proposal of optimal operation strategy applied to water distribution network with statistical approach

Inefficiency of sanitation companies’ operation procedures threatens the population’s future supplies. Thus, it is essential to increase water and energy efficiency in order to meet future demand. Optimization techniques are important tools for the analysis of complex problems, as in distribution networks for supply. Currently, genetic algorithms are recognized by their application in literature. In this regard, an optimization model of water distribution network is proposed, using genetic algorithms. The difference in this research is a methodology based on in-depth analysis of results, using statistics and the design of experimental tools and software. The proposed technique was applied to a theoretical network developed for the study. Preliminary simulations were accomplished using EPANET, representing the main causes of water and energy inefficiency in Brazilian sanitation companies. Some parameters were changed in applying this model, such as reservoir level, pipe diameter, pumping pressures, and valve-closing percentage. These values were established by the design of experimental techniques. As output, we obtained the equation of response surface, optimized, which resulted in values of established hydraulic parameters. From these data, the obtained parameters in computational optimization algorithms were applied, resulting in losses of 26.61%, improvement of 16.19 p.p. with regard to the network without optimization, establishing an operational strategy involving three pumps and a pressure-reducing valve. We conclude that the association of optimization and the planning of experimental techniques constitutes an encouraging method to deal with the complexity of water-distribution network optimization.

The Sensitivity of Groundwater Recharge to the Rock Pore Connectivity Parameter in the Vadose Zone

Data on groundwater recharge is necessary for solving different classes of hydrogeological problems. One of the recharge estimation methods is flow simulation in the vadose zone. Soil hydraulic parameters are used to estimate the recharge by flow in the vadose zone. One of these hydraulic parameters is the pore connectivity l. The estimated recharge sensitivity to the pore connectivity, especially under humid climate conditions, has not been studied thoroughly. In this study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest conditions on sand and field conditions on loam) have been used to estimate the groundwater recharge. The recharge was also estimated at l = 0.5 and at reported values of the l parameter for a certain type of sediment. According to the calculation results, the use of a fixed value of l = 0.5 leads to a significant overestimation of recharge under both forest and field conditions, which emphasizes the importance of experimental determinations of soil hydraulic parameters for the groundwater recharge estimation. According to the data from an analysis on water balance components, the increase in the estimated recharge with an increase in l is mainly related to a decrease in a top soil evaporation.

Sensitivity of recharge estimation to the pore connectivity parameter of vadose zone rocks

Information on recharge value is necessary for solving different classes of hydrogeological problems. One of the methods of recharge estimation is simulation of flow in vadose zone. Soil hydraulic parameters are used to estimate recharge by flow in vadose zone. One of the hydraulic parameters is the pore connectivity parameter l. The sensitivity of estimated recharge to the value of pore connectivity parameter, especially under humid climate conditions, is studied insufficiently. In present study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest landscape on sand and field landscape on loam) were used to estimate recharge.Recharge estimation was also carried for the value of l=0,5 and for reported values of l parameter for certain type of sediment. Analysis of calculation results demonstrated that using fixed value of l=0,5 leads to significant overestimation of calculated recharge both for forest and filed landscapes, which emphasizes the importance of experimental definitions of soil hydraulic parameters for recharge estimation. The analysis of the water balance components showed that the increase of estimated recharge with enhancement of l value is mainly associatedwith the decrease of evaporation from the upper soil layer.

Raising of Hydraulic Efficiency and Operational Reliability of Large Canals

The article considers the flow efficiency and operational reliability of large canals. In order to raise efficiency and reliability of exploitation of canals hydraulic control model to change the flow depth was created. It was determined by the law of water transmission in optional time. Patterns based on determination of hydraulic relations under changing values of hydraulic parameters of water flow in the trapezoid cross-section irrigation canal were examined.

An experimental study of two-phase flow instability in a multi-loop natural circulation system

In this research, an experiment was carried out in a multi-loop natural circulation system to study its response behaviors under single-phase and two-phase flow instability conditions. The experimental facility consists of primary and secondary natural circulation loops, as well as an external forced circulation loop, which serves as a final heat sink to the system. The secondary loop is meant to simulate passive residual heat removal system found in the advanced reactors and some small modular reactors. The experiment was carried out under low-pressure conditions and constant heating powers. Within single-phase region, the thermal hydraulic parameters were found to vary linearly with the heating powers. By gradually increasing the power beyond the single-phase region, oscillation of the thermal hydraulic parameters was observed in both natural circulation loops. Critical conditions for the occurrence of instabilities in both natural circulation loops were determined. Flow-induced instabilities causing vibrations and acoustical noises were observed in the shell and tube heat exchanger connecting the two natural circulation loops. At higher power, fully mature oscillations were observed and characterized. In addition, effect of temperature rise in the system heat sink was also investigated. The oscillation period of the observed oscillations is about twice the boiling channel residence period. The oscillation amplitudes increase with increasing heater’s inlet temperature and heat sink temperature for the primary and secondary loops respectively. However, the influence of the heater’s inlet temperature on the flow instability is observed to be non-linear. This paper can contribute in the identification and determination of threshold values of thermal hydraulic parameters that are capable of triggering flow instabilities, which are important in the design and safe operations of natural circulation systems. It can also provide some useful information about how temperature rise in the system heat sink can influence the occurrence and amplification of flow instability in a natural circulation system.

Hydraulic properties of peat soils along a bulk density gradient—A meta study

AbstractOur understanding of hydraulic properties of peat soils is limited compared with that of mineral substrates. In this study, we aimed to deduce possible alterations of hydraulic properties of peat soils following degradation resulting from peat drainage and aeration. A data set of peat hydraulic properties (188 soil water retention curves [SWRCs], 71 unsaturated hydraulic conductivity curves [UHCs], and 256 saturated hydraulic conductivity [Ks] values) was assembled from the literature; the obtained data originated from peat samples with an organic matter (OM) content ranging from 23 to 97 wt% (weight percent; and according variation in bulk density) representing various degrees of peat degradation. The Mualem‐van Genuchten model was employed to describe the SWRCs and UHCs. The results show that the hydraulic parameters of peat soils vary over a wide range confirming the pronounced diversity of peat. Peat decomposition significantly modifies all hydraulic parameters. A bulk density of approximately 0.2 g cm−3 was identified as a critical threshold point; above and below this value, macroporosity and hydraulic parameters follow different functions with bulk density. Pedotransfer functions based on physical peat properties (e.g., bulk density and soil depth) separately computed for bog and fen peat have significantly lower mean square errors than functions obtained from the complete data set, which indicates that not only the status of peat decomposition but also the peat‐forming plants have a large effect on hydraulic properties. The SWRCs of samples with a bulk density of less than 0.2 g cm−3 could be grouped into two to five classes for each peat type (botanical composition). The remaining SWRCs originating from samples with a bulk density of larger than 0.2 g cm−3 could be classified into one group. The Mualem‐van Genuchten parameter values of α can be used to estimate Ks if no Ks data are available. In conclusion, the derived pedotransfer functions provide a solid instrument to derive hydraulic parameter values from easily measurable quantities; however, additional research is required to reduce uncertainty.

Paleohydrological modeling of penesaline reflux dolomitization: Avon Park Formation (Middle Eocene), East Central Florida

Previous geochemical, petrological, and sedimentological investigations of the Middle Eocene Avon Park Formation (Middle Eocene) of Florida suggest that dolomitization occurred in the Eocene from normal to hypersaline seawater. Reflux of penesaline water (i.e., seawater evaporatively concentrated below evaporite mineral precipitation) is the most likely mechanism to supply the required magnesium. Density-dependent solute-transport modeling was performed to evaluate whether penesaline reflux under known or inferred Middle Eocene paleohydrological conditions could have provided enough magnesium to account for the mass of dolomite present in three cores of the upper part of the Avon Park Formation from the City of Daytona Beach. Rather than a simple down and out flow pattern, the modeling results indicate that an initial rapid vertical convection-dominated flow regime first occurs in which native groundwater is displaced by refluxed brine, and followed by a longer-duration regime dominated by steady-state lateral flow. Dolomitization from a brine with a 89.6 ppt TDS concentration would require an average minimum reflux (at 100% dolomitization efficiency) on the Florida Platform of about 8130 m3 per m2 to provide the required magnesium. Modeling results indicate that such reflux could occur over 0.7–3 million years, depending upon the aquifer hydraulic parameter values. Longer time periods would be required for the reflux of lower salinity brines and lower dolomitization efficiencies. Penesaline reflux is thus hydrologically plausible for the dolomites of the upper Avon Park Formation.

Modeling and Control of Fluid Flow Networks with Application to a Nuclear-Solar Hybrid Plant

Fluid flow networks (FFNs) can be utilized to integrate multiple once-through heat supply system (OTHSS) modules based on either the same or different energy resources such as the renewable, nuclear and fossil for multi-modular and hybrid energy systems. Modeling and control is very important for the safe, stable and efficient operation of the FFNs, whose objective is to maintain both the flowrates and pressure-drops of the network branches within specific bounds. In this paper, a differential-algebraic nonlinear dynamic model for general FFNs with multiple pump branches is proposed based on both the branch hydraulics and network graph properties. Then, an adaptive decentralized FFN flowrate-pressure control law, which takes a proportional-integral (PI) form with saturation on the integral terms, is established. This newly-built control not only guarantees satisfactory closed-loop global stability but also has no need for the values of network hydraulic parameters. This adaptive control is then applied to the flowrate-pressure regulation of the secondary FFN of a two-modular nuclear-solar hybrid energy system and numerical simulation results show the feasibility and high performance of this network control strategy. Due to its concise form, this new flowrate-pressure FFN controller can be easily implemented practically.