Modeling of storm responses in conduit flow aquifers with reservoirs (original) (raw)
Related papers
Water
It is widely accepted that spring hydrographs are an effective tool for evaluating the internal structure of karst aquifers because they depict the response of the whole aquifer to recharge events. The spring hydrograph is affected by various factors such as flow regime, geometry, type of recharge, and hydraulic properties of conduit. However, the effect of conduit network geometry received less attention and required more comprehensive research studies. The present study attempted to highlight the impact of the two most frequent patterns of karst conduits (i.e., branchwork and network maze) on the characteristic of the spring hydrograph. Therefore, two conduit patterns, branchwork and network maze, were randomly generated with MATLAB codes. Then, MODFLOW-CFP was used to quantify the effect of conduit pattern, conduit density, and diffuse or concentrated recharge on the spring hydrograph. Results reveal that peak discharge, fast-flow recession coefficient, and the return time to bas...
Water Resources Research, 2018
Due to the duality in terms of (1) the groundwater flow field and (2) the discharge conditions, flow patterns of karst aquifer systems are complex. Estimated aquifer parameters may differ by several orders of magnitude from local (borehole) to regional (catchment) scale because of the large contrast in hydraulic parameters between matrix and conduit, their heterogeneity and anisotropy. One approach to deal with the scale effect problem in the estimation of hydraulic parameters of karst aquifers is the application of large‐scale experiments such as long‐term high‐abstraction conduit pumping tests, stimulating measurable groundwater drawdown in both, the karst conduit system as well as the fractured matrix. The numerical discrete conduit‐continuum modeling approach MODFLOW‐2005 Conduit Flow Process Mode 1 (CFPM1) is employed to simulate laminar and nonlaminar conduit flow, induced by large‐scale experiments, in combination with Darcian matrix flow. Effects of large‐scale experiments w...
Journal of Hydrology, 2010
Karst aquifers are heterogeneous media where conduits usually drain water from lower permeability volumes (matrix and fractures). For more than a century, various approaches have used flood recession curves, which integrate all hydrodynamic processes in a karst aquifer, to infer physical properties of the movement and storage of groundwater. These investigations typically only consider flow to the conduits and thus have lacked quantitative observations of how pressure transfer and water exchange between matrix and conduit during flooding could influence recession curves.
Advances in Water Resources, 2013
Physics-based distributed models for simulating flow in karst systems are generally based on the discrete-continuum approach in which the flow in the three-dimensional fractured limestone matrix continuum is coupled with the flow in discrete one-dimensional conduits. In this study we present a newly designed discrete-continuum model for simulating flow in karst systems. We use a flexible spatial discretization such that complicated conduit networks can be incorporated. Turbulent conduit flow and turbulent surface flow are described by the diffusion wave equation whereas laminar variably saturated flow in the matrix is described by the Richards equation. Transients between free-surface and pressurized conduit flow are handled by changing the capacity term of the conduit flow equation. This new approach has the advantage that the transients in mixed conduit flow regimes can be handled without the Preissmann slot approach. Conduit-matrix coupling is based on the Peaceman's well-index such that simulated exchange fluxes across the conduit-matrix interface are less sensitive to the spatial discretization. Coupling with the surface flow domain is based on numerical techniques commonly used in surface-subsurface models and storm water drainage models. Robust algorithms are used to simulate the non-linear flow processes in a coupled fashion. The model is verified and illustrated with simulation examples.
Hydrology and Earth System Sciences Discussions, 2016
The aim of this study is to present a framework giving new keys to characterize the spatio-temporal variability of lateral exchanges for flows and fluxes in a karst conduit network during flood events. An inverse model using an analytical solution of the diffusive wave model is applied on data from two successive gauging stations to simulate exchange dynamics after recharge. The study site is the karst conduit network of the Fourbanne aquifer in the French Jura Mountains, which includes two reaches of 5–10 km characterizing the network from sinkhole to cave stream, and to the spring. The model is applied after separation of the base and the flood components on discharge and total dissolved solids (TDS) in order to assess lateral flows and mass-fluxes and compare them to help identify water origin. Our results showed various lateral contributions in space – between the two reaches located in the unsaturated (R1), and in both unsaturated and saturated zone (R2) &nda...
Modeling karst spring hydrograph recession based on head drop at sinkholes
Journal of Hydrology, 2016
Spring discharge often responds to rainfall with a rapid increase followed by a slower recession, and the mode of recession is often exponential-like. We propose a new model of the response of spring discharge to rainfall based on the square law for turbulent conduit flow. The new non-exponential model is compared against the exponential model under specific constraints. A hydrograph of St. Marks River in Florida is used to illustrate that when the change in "sinkhole head" (defined as the hydraulic head at the upstream end of the karst conduit connected to the spring) is relatively small, the solution of the new model is close to that of the exponential model, which extends the validity and application of the exponential solution. When the change in sinkhole head is very large, the solutions from the two models clearly differ from each other. Limitations of the non-exponential model are analyzed by simulation of a hydrograph observed downstream of Wakulla Springs. It is concluded that both solutions are applicable when spring response is smaller than or comparable to the base flow, but are nonphysical when the response is much larger than the base discharge.
Journal of Hydrology, 2014
The conduit system of mature karstified carbonate aquifers is typically characterised by a high hydraulic conductivity and does not impose a major flow constriction on catchment discharge. As a result, discharge at karst springs is usually flashy and displays pronounced peaks following recharge events. In contrast, some karst springs reported in literature display a discharge maximum, attributed to reaching the finite discharge capacity of the conduit system (flow threshold). This phenomenon also often leads to a non-standard recession behaviour, a so called ''convex recession'', i.e. an increase in the recession coefficient during flow recession, which in turn might be used as an indicator for conduit restricted aquifers. The main objective of the study is the characterisation and modelling of those hydrogeologically challenging aquifers. The applied approach consists of a combination of hydrometric monitoring, a spring hydrograph recession and event analysis, as well as the setup and calibration of a non-linear reservoir model. It is demonstrated for the Auja spring, the largest freshwater spring in the Lower Jordan Valley. The semi-arid environment with its short but intensive precipitation events and an extended dry season leads to sharp input signals and undisturbed recession periods. The spring displays complex recession behaviour, exhibiting exponential (coefficient a) and linear (coefficient b) recession periods. Numerous different recession coefficients a were observed: $0.2 to 0.8 d À1 (presumably main conduit system), 0.004 d À1 (fractured matrix), 0.0009 d À1 (plateau caused by flow threshold being exceeded), plus many intermediate values. The reasons for this observed behaviour are the outflow threshold at 0.47 m 3 s À1 and a variable conduit-matrix cross-flow in the aquifer. Despite system complexity, and hence the necessity of incorporating features such as a flow threshold, conduit-matrix cross-flow, and a spatially variable soil/epikarst field capacity, the developed reservoir model is regarded as relatively simplistic. As a number of required parameters were calculated from the hydrogeological analysis of the system, it requires only six calibration parameters and performs well for the highly variable flow conditions observed. Calculated groundwater recharge in this semi-arid environment displays high interannual variability. For example, during the 45-year simulation period, only five wet winter seasons account for 33% of the total cumulative groundwater recharge.
Water Resources Research, 2009
1] The responses of karstic aquifers to storms are often used to obtain information about aquifer geometry. In general, spring hydrographs are a function of both system geometry and recharge. However, the majority of prior work on storm pulses through karst has not studied the effect of recharge on spring hydrographs. To examine the relative importance of geometry and recharge, we break karstic aquifers into elements according to the manner of their response to transient flow and demonstrate that each element has a characteristic response timescale. These fundamental elements are full pipes, open channels, reservoir/constrictions, and the porous matrix. Taking the ratio of the element timescale with the recharge timescale produces a dimensionless number, g, that is used to characterize aquifer response to a storm event. Using sets of simulations run with randomly selected element parameters, we demonstrate that each element type has a critical value of g below which the shape of the spring hydrograph is dominated by the shape of the recharge hydrograph and above which the spring hydrograph is significantly modified by the system geometry. This allows separation of particular element/storm pairs into recharge-dominated and geometry-dominated regimes. While most real karstic aquifers are complex combinations of these elements, we draw examples from several karst systems that can be represented by single elements. These examples demonstrate that for real karstic aquifers full pipe and open channel elements are generally in the recharge-dominated regime, whereas reservoir/constriction elements can fall in either the recharge-or geometry-dominated regimes. Citation: Covington, M. D., C. M. Wicks, and M. O. Saar (2009), A dimensionless number describing the effects of recharge and geometry on discharge from simple karstic aquifers, Water Resour. Res., 45, W11410,
Journal of Hydrology, 1998
In karst aquifers, water moves from the recharge area (sinkhole plains and swallets) to the discharge area (springs), traveling kilometers through the groundwater system in a period of hours to days. Transit times through karst aquifers are a function of the conduit geometry and connectedness, intensity and duration of the recharge event, and antecedent soil moisture. Often many of these factors are unknown or difficult to quantify. Therefore, predicting the response of a karst basin to recharge is difficult. Numerous researchers have attempted to understand the response of a karst basin, but a good understanding of whether the response is dependent on local features or regional effects is currently lacking. From April 1994 to May 1995, flood pulse hydrographs from a karst aquifer with well-developed and well-documented conduits (Devil's Icebox cave system) were obtained from a gaging station near the spring of the karst basin. Data were also collected from within the conduit system in an attempt to determine whether flow was locally controlled by constrictions in the conduits. Based on an application of Bernoulli's equation, analyses of the changes in kinetic head and potential head over time indicated local control during storm events. The observed sediment patterns and water level variations also support localized flow control during storm events. A numerical model of the constrictions was tested and reproduced the responses observed at the spring during initial periods of storm events. The model illustrated that the constricted flow was very sensitive to recharge. It also illustrated the transition from local control due to constriction to regional controls due to the aquifer matrix.
2017
The aim of this study is to present a framework giving new keys to characterize the spatio-temporal variability of lateral exchanges for flows and solutes in a karst conduit network during flood events, treating both phenomena, the diffusive wave equation and the advection-diffusion equation, with the same mathematical approach assuming uniform lateral flow and solutes. An inverse model, based on an analytical solution of the diffusive wave model is then applied on data from two successive gauging stations to simulate flows and solute exchange dynamics after recharge. The study site is the karst 5 conduit network of the Fourbanne aquifer in the French Jura Mountains, which includes two reaches of 5-10 km characterizing the network from sinkhole to cave stream, and to the spring. The model is applied after separation of the base and the flood components on discharge and total dissolved solids (TDS) in order to assess lateral flows and concentrations and compare them to help identify ...