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1.
The major obstacles for modelling flood processes in karst areas are a lack of understanding and model representations of
the distinctive features and processes associated with runoff generation and often a paucity of field data. In this study,
a distributed flood-modelling approach, WetSpa, is modified and applied to simulate the hydrological features and processes
in the karst Suoimuoi catchment in northwest Vietnam. With input of topography, land use and soil types in a GIS format, the
model is calibrated based on 15 months of hourly meteorological and hydrological data, and is used to simulate both fast surface
and conduit flows, and groundwater discharges from karst and non-karst aquifers. Considerable variability in the simulation
accuracy is found among storm events and within the catchment. The simulation results show that the model is able to represent
reasonably well the stormflows generated by rainfall events in the study catchment. 相似文献
2.
The effects of climate change on the groundwater systems in the Grote-Nete catchment, Belgium, covering an area of 525 km2, is modeled using wet (greenhouse), cold or NATCC (North Atlantic Thermohaline Circulation Change) and dry climate scenarios. Low, central and high estimates of temperature changes are adopted for wet scenarios. Seasonal and annual water balance components including groundwater recharge are simulated using the WetSpass model, while mean annual groundwater elevations and discharge are simulated with a steady-state MODFLOW groundwater model. WetSpass results for the wet scenarios show that wet winters and drier summers are expected relative to the present situation. MODFLOW results for wet high scenario show groundwater levels increase by as much as 79 cm, which could affect the distribution and species richness of meadows. Results obtained for cold scenarios depict drier winters and wetter summers relative to the present. The dry scenarios predict dry conditions for the whole year. There is no recharge during the summer, which is mainly attributed to high evapotranspiration rates by forests and low precipitation. Average annual groundwater levels drop by 0.5 m, with maximum of 3.1 m on the eastern part of the Campine Plateau. This could endanger aquatic ecosystem, shrubs, and crop production. 相似文献
3.
Bart Rogiers Thomas Vienken Matej Gedeon Okke Batelaan Dirk Mallants Marijke Huysmans Alain Dassargues 《Environmental Earth Sciences》2014,72(5):1303-1324
Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for efficient hydraulic conductivity (K) characterization along vertical profiles with sampling resolutions of up to a few centimetres. Until date, however, only a limited number of studies document high-resolution in situ DP data for three-dimensional conceptual hydrogeological model development and groundwater flow model parameterization. This study demonstrates how DP technologies improve building of a conceptual hydrogeological model. We further evaluate the degree to which the DP-derived hydrogeological parameter K, measured across different spatial scales, improves performance of a regional groundwater flow model. The study area covers an area of ~60 km2 with two overlying, mainly unconsolidated sand aquifers separated by a 5–7 m thick highly heterogeneous clay layer (in north-eastern Belgium). The hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests (CPTs). The hydrogeological parameter K was derived from a combined analysis of core and CPT data and also from hydraulic direct push tests. A total of 50 three-dimensional realizations of K were generated using a non-stationary multivariate geostatistical approach. To preserve the measured K values in the stochastic realizations, the groundwater model K realizations were conditioned on the borehole and direct push data. Optimization was performed to select the best performing model parameterization out of the 50 realizations. This model outperformed a previously developed reference model with homogeneous K fields for all hydrogeological layers. Comparison of particle tracking simulations, based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields, demonstrate the impact DP-derived subsurface heterogeneity in K can have on groundwater flow and solute transport. We demonstrated that DP technologies, especially when calibrated with site-specific data, provide high-resolution 3D subsurface data for building more reliable conceptual models and increasing groundwater flow model performance. 相似文献
4.
Marijke Huysmans Philippe Orban Elke Cochet Mathias Possemiers Benedicta Ronchi Katherine Lauriks Okke Batelaan Alain Dassargues 《Mathematical Geosciences》2014,46(5):519-537
This study investigates the effect of fine-scale clay drapes on tracer transport. A tracer test was performed in a sandbar deposit consisting of cross-bedded sandy units intercalated with many fine-scale clay drapes. The heterogeneous spatial distribution of the clay drapes causes a spatially variable hydraulic conductivity and sorption coefficient. A fluorescent tracer (sodium naphthionate) was injected in two injection wells and ground water was sampled and analyzed from five pumping wells. To determine (1) whether the fine-scale clay drapes have a significant effect on the measured concentrations and (2) whether application of multiple-point geostatistics can improve interpretation of tracer tests in media with complex geological heterogeneity, this tracer test is analyzed with a local three-dimensional ground-water flow and transport model in which fine-scale sedimentary heterogeneity is modeled using multiple-point geostatistics. To reduce memory needs and calculation time for the multiple-point geostatistical simulation step, this study uses the technique of direct multiple-point geostatistical simulation of edge properties. Instead of simulating pixel values, model cell edge properties indicating the presence of irregularly shaped surfaces are simulated using multiple-point geostatistical simulations. Results of a sensitivity analysis show under which conditions clay drapes have a significant effect on the concentration distribution. Calibration of the model against measured concentrations from the tracer tests reduces the uncertainty on the clay-drape parameters. The calibrated model shows which features of the breakthrough curves can be attributed to the geological heterogeneity of the aquifer and which features are caused by other processes. 相似文献
5.
6.
This paper presents a Bayesian Monte Carlo method for evaluating the uncertainty in the delineation of well capture zones and its application to a wellfield in a heterogeneous, multiaquifer system. In the method presented, Bayes' rule is used to update prior distributions for the unknown parameters of the stochastic model for the hydraulic conductivity, and to calculate probability-based weights for parameter realizations using head residuals. These weights are then assigned to the corresponding capture zones obtained using forward particle tracking. Statistical analysis of the set of weighted protection zones results in a probability distribution for the capture zones. The suitability of the Bayesian stochastic method for a multilayered system is investigated, using the wellfield Het Rot at Nieuwrode, Belgium, located in a three-layered aquifer system, as an example. The hydraulic conductivity of the production aquifer is modeled as a spatially correlated random function with uncertain parameters. The aquitard and overlying unconfined aquifer are assigned random, homogeneous conductivities. The stochastic results are compared with deterministic capture zones obtained with a calibrated model for the area. The predictions of the stochastic approach are more conservative and indicate that parameter uncertainty should be taken into account in the delineation of well capture zones. 相似文献
7.
Study of cavernous underground conduits in Nam La (Northwest Vietnam) by an integrative approach 总被引：1，自引：0，他引：1
V. T. Tam F. De Smedt O. Batelaan L. Q. Hung A. Dassargues 《Hydrogeology Journal》2005,13(5-6):675-689
This paper presents the result of an investigation of underground conduits, which connect the swallow holes and the resurgence of a blind river in the tropical, highly karstified limestone Nam La catchment in the NW of Vietnam. The Nam La River disappears underground in several swallow holes near the outlet of the catchment. In the rainy season this results in flooding upstream of the sinkholes. A hypothesis is that the Nam La River resurges at a large cavern spring 4.5 km east of the catchment outlet. A multi-thematic study of the possible connections between the swallow holes and the resurgence was carried out to investigate the geological structure, tectonics, cave structure analysis and discharge time series. The existence of the underground conduits was also tested and proven by tracer experiments. On the basis of a lineament analysis the location of the underground conduits were predicted. A remote sensing derived lineament-length density map was used to track routes from the swallow holes to the resurgence, having the shortest length but highest lineament density. This resulted in a plan-view prediction of underground conduits that matches with the cave and fault development. The functioning of the conduits was further explained by analysing flooding records of a nearby doline, which turns out to act as a temporary storage reservoir mitigating flooding of the catchment outlet area.
Resumen Este artículo presenta el resultado de una investigación de conductos subterráneos, los cuales conectan dolinas y la resurgencia de un río ciego en la cuenca tropical Nam La, compuesta por calizas altamente karstificadas, en el noroeste de Vietnam. El Río Nam La desaparece en el subsuelo por medio de varias dolinas cerca de la salida de la cuenca. Durante la estación lluviosa esto resulta en inundaciones aguas arriba de las dolinas. Una hipótesis es que el Río Nam La resurge en un manantial de caverna grande a 4.5 km al oriente de la salida de la cuenca. Se llevó a cabo un estudio multi-temático de las conexiones posibles entre las dolinas y la resurgencia para investigar la estructura geológica, tectónica, análisis estructural de cavernas, y series de tiempo de descarga. Se evalúa y se demuestra también la existencia de conductos subterráneos por medio de experimentos con trazadores. En base a análisis de lineamientos se predice la localización de los conductos subterráneos. Se utiliza un mapa de densidad de longitudes de lineamientos construido a partir de sensores remotos para seguir las rutas de las dolinas a la resurgencia, teniendo longitudes más cortas pero densidad de lineamientos más altas. Esto da por resultado una predicción en vista de planta de conductos subterráneos que se ajustan con el desarrollo de cavernas y fallas. El funcionamiento de los conductos se explica posteriormente mediante el análisis de registro de inundaciones de una dolina cercana la cual actúa como un reservorio de almacenamiento temporal que mitiga inundaciones en el área de salida de la cuenca.
Résumé Cet article présente les résultats de linvestigation de conduits souterrains, qui mettent en connexion les pertes et les résurgences dune rivière souterraine dans le bassin versant de Nam La, dans une région tropicale fortement karstique du NW du Vietnam. La rivière Nam La disparaît dans le sous-sol via plusieurs pertes à proximité de lexutoire du bassin. Durant la saison des pluies, les pertes se mettent en charge et des inondations apparaissent. Une hypothèse serait que la rivière ressort 4.5 km à lEst de lexutoire du bassin, dans une grande caverne. Une étude multi-thématique visant les connexions possibles entre les pertes et les résurgences a été réalisée. Elle comprend létude de la structure géologique, la tectonique, lanalyse de la structure karstique et des chroniques de débits. Lexistence des conduits souterrains est également testée et prouvée par des essais de traçages. Sur base de lanalyse des linéaments, la localisation des conduits souterrains est prédite. Grâce à la télédétection et une cartographie de la densité et de la longueur des linéaments, on peut deviner le cheminement de leau entre les pertes et la résurgence (via le chemin le plus court et la densité de fracturation la plus importante). Il en résulte une vue en plan prédisant la localisation des conduits, qui correspond par ailleurs avec le développement des cavités et des failles. Le fonctionnement des conduits est ensuite expliqué sur base de lanalyse des chroniques de débits enregistrés à proximité dune doline, qui joue le rôle dun réservoir temporaire, mitigeant les inondations à la zone de lexutoire du bassin-versant.相似文献
8.
Baseflow in the Andes is commonly considered to be related with the release of water stored in páramos. Páramo is the predominant ecosystem above 3500 m a.s.l. and is characterized by a rainy and cold climate with low evapotranspiration. However, this baseflow concept is based on hydrological process studies in small Andean catchments of a few square kilometre with a homogeneous land cover. Middle‐sized Andean catchments, like the subcatchments of Tarqui and Yanuncay, Ecuador, are rarely homogeneous or uniformly covered by páramo. The objectives of this study are therefore to investigate baseflow characteristics in heterogeneous Andean catchments and to identify relationships between baseflow processes and physical characteristics such as storage and recharge. Hereby, the contribution to baseflow of páramo and other sources such as alluvial aquifers is quantified. This study uses nonlinear recession analysis, physically based filters and digital filters for comparison of baseflow of neighbouring but distinct subcatchments. The Yanuncay subcatchment shows a clearly different storage capacity and recession. The storage capacity of Yanuncay is 50% higher than for Tarqui because of its higher coverage of páramo. On the other hand, considerable storage capacity has also been found in the Tarqui subcatchment, which has a limited páramo area but a significant alluvial aquifer. It is shown that improved understanding of the specific baseflow characteristics such as storage and recharge and its relationships to the heterogeneity of the land cover in Andean catchments will lead to a better assessment of the water resources and give new insights for effective management actions. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
A cross‐sectional model, based on the two dimensional groundwater flow equation of Edelman, was applied at seven transects distributed over four geological cross sections to estimate groundwater heads and recharge from/or groundwater discharge to Lake Nasser. The lake with a length of 500 km and an average width of 12 km was created over the period 1964–1970, the time for constructing the Aswan High Dam (AHD). The model, constrained by regional‐scale groundwater flow and groundwater head data in the vicinity of the lake, was successfully calibrated to timeseries of piezometeric heads collected at the cross sections in the period 1965–2004. Inverse modeling yielded high values for the horizontal hydraulic conductivity in the range of 6.0 to 31.1 m day?1 and storage coefficient between 0.01 and 0.40. The results showed the existence of a strong vertical anisotropy of the aquifer. The calibrated horizontal permeability is systematically higher than the vertical permeability (≈1000:1). The calibrated model was used to explore the recharge from/or groundwater discharge to Lake Nasser at the seven transects for a 40‐year period, i.e. from 1965 to 2004. The analysis for the last 20‐year period, 1985–2004, revealed that recharge from Lake Nasser reduced by 37% compared to the estimates for the first 20‐year period, 1965–1984. In the period 1965–2004, seepage of Lake Nasser to the surrounding was estimated at 1.15 × 109 m3 year?1. This led to a significant rise of the groundwater table. Variance‐based sensitivity and uncertainty analysis on the Edelman results were conducted applying quasi‐Monte Carlo sequences (Latin Hypercube sampling). The maximum standard deviation of the total uncertainty on the groundwater table was 0.88 m at Toshka (west of the lake). The distance from the lake, followed by the storage coefficient and hydraulic conductivity, were identified as the most sensitive parameters. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
10.
B. Rogiers P. Winters M. Huysmans K. Beerten D. Mallants M. Gedeon O. Batelaan A. Dassargues 《Hydrogeology Journal》2014,22(6):1345-1358
Saturated hydraulic conductivity (K s) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. The hand-held air permeameter technique was investigated for high-resolution hydraulic conductivity determination on borehole cores using a spatial resolution of ～0.05 m. The suitability of such air permeameter measurements on friable to poorly indurated sediments was tested to improve the spatial prediction of classical laboratory-based K s measurements obtained at a much lower spatial resolution (～2 m). In total, 368 K s measurements were made on ～350 m of borehole cores originating from the Campine basin, northern Belgium, while ～5,230 air permeability measurements were performed on the same cores, resulting in a K s range of seven orders of magnitude. Cross-validation demonstrated that, using air permeameter data as the secondary variable for laboratory based K s measurements, the performance increased from R 2?=?0.35 for ordinary kriging (laboratory K s only) to R 2?=?0.61 for co-kriging. The separate treatment of horizontal and vertical hydraulic conductivity revealed considerable anisotropy in certain lithostratigraphical units, while others were clearly isotropic at the sample scale. Air permeameter measurements on borehole cores provide a cost-effective way to improve spatial predictions of traditional laboratory based K s. 相似文献