Risk Assessment Methodology for Karst Aquifers: (1) Estimating Karst Conduit-Flow Parameters (original) (raw)
Ecological Indicators
Karst water sources already meet about a quarter of the world's drinking water needs, and their importance is growing. Due to the complexity of water flow in carbonate aquifers, karst water sources require particularly appropriate protection. The scientific literature lacks analytical evidence of the effects of the current legislative frameworks and improved methodological approaches for ecological indications to design alternative strategies. This gap is addressed in the present study, which draws on a combination of investigation methods considering specifics of water flow in karst and on a comprehensive database of general knowledge to gain relevant understanding of the hydrological system functioning. An advanced, multi-methodological approach, which was developed in this study and includes geological and hydrogeological mapping, spring monitoring, tracer tests, water balance and groundwater vulnerability assessment, enabled achievement of optimized indicators for the adequate karst water source protection measures. It demonstrates, that protection zoning based solely on fundamental hydrogeological knowledge, general prediction of groundwater residence times or distance criteria may lead to a high degree of imprecision. Currently valid protection measures may therefore generally be associated with great uncertainties and the high vulnerability of karst areas may be underestimated. In addition to the existing legal requirements for karst water source protection zoning, environmental indicators such as natural and artificial tracers should be considered, which most reliably confirm the directions and characteristics of groundwater flow in karst. Similarly, mapping of groundwater vulnerability to contamination can be of particular importance for the implementation of freshwater protection and spatial planning at least in karst-rich countries. The approach enables scientists to gain relevant insights into the functioning of the hydrological system and environmental managers to protect karst water sources.
Hydrological Processes, 2012
A structure model was used to analyse solute-transport parameter estimates based on tracer breakthrough curves. In the model system, groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels. The discharge through the fully filled conduits is limited owing to void geometries and turbulent flow; thus, a hierarchic overflow system evolves where conduits are (re-)activated or dried up depending on the flow condition. Exemplified on the Lurbach-Tanneben karst aquifer, the applicability of the model approach was tested. Information derived from multi-tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network, under constraint of the geomorphological and hydrological evolution of the site. Depending on the flow rate, groundwater is divided into up to eight flow paths. The spatial hierarchy of flow paths controls the sequence of flow path activation. Conduits of the topmost level are strongly influenced by reversible alteration processes. Sedimentation or blocking causes an overflow of water to the next higher conduit. Flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge.
Differentiated characterization of karst aquifers: some contributions
Carbonates and Evaporites, 2013
Because of the small radius of investigation of hydrogeological standard testing methods, the characterization of karst aquifers is still a challenge. The development of a karst conduit system introduces an element of large contrast in hydraulic conductivity in the hydraulic parameter field of a karst aquifer. It leads to complex flow patterns and transport phenomena that differ significantly from those observed in porous and fissured media. While on a local, i.e., borehole scale, the fissured matrix of karst aquifers can be regarded as a continuum, on a regional, i.e., catchment scale, the drainage of the aquifer system is controlled by the conduit system, which may have a highly anisotropic geometry. Therefore, characterization of karst aquifers requires a differentiated approach by the combination of various hydrogeological field methods or the application of large-scale tests, which cover the scale of dominant aquifer heterogeneities. Existing numerical modeling approaches can be applied for integral data interpretation on catchment scale.
Karst Aquifers Vulnerability or Sensitivity?
Acta Carsologica, 2016
UDC: 551.44:556.3 Gregor Kovaèiè & Nataša Ravbar: Karst aquifers vulnerability or sensitivity? The concept of karst aquifer vulnerability mapping is commonly used for the determination of water protection zones and planning of land use in the background of the captured karst sources and wells. Several different methodologies for karst aquifer vulnerability mapping exist and the examination of scientific literature shows considerable variations in the definition of the term vulnerability. The authors suggest the distinction between the terms vulnerability and sensitivity of karst aquifers, since the former includes more information, which are required for efficient protection. The interpretation of the applied terms is founded on the conceptual background of the environmental vulnerability studies, which are declared with the Slovene 1993 Environmental Protection Act.
Karst groundwater: a challenge for new resources
Hydrogeology Journal, 2005
Karst aquifers have complex and original characteristics which make them very different from other aquifers: high heterogeneity created and organised by groundwater flow; large voids, high flow velocities up to several hundreds of m/h, high flow rate springs up to some tens of m 3 /s. Different conceptual models, known from the literature, attempt to take into account all these particularities. The study methods used in classical hydrogeology-bore hole, pumping test and distributed models-are generally invalid and unsuccessful in karst aquifers, because the results cannot be extended to the whole aquifer nor to some parts, as is done in non-karst aquifers. Presently, karst hydrogeologists use a specific investigation methodology (described here), which is comparable to that used in surface hydrology. Important points remain unsolved. Some of them are related to fundamental aspects such as the void structureonly a conduit network, or a conduit network plus a porous matrix-, the functioning-threshold effects and nonlinearities-, the modeling of the functioning-double or triple porosity, or viscous flow in conduits-and of karst genesis. Some other points deal with practical aspects, such as the assessment of aquifer storage capacity or vulnerability, or the prediction of the location of highly productive zones.
Intrinsic vulnerability assessment in karst areas: A numerical modeling approach
Water Resources Research, 2008
1] The main objective of this study was to quantify the intrinsic vulnerability of karst springs by numerical modeling. A global approach is used, modeling the discharge of a karst spring. This approach includes the hydrological dynamics of karst systems and is applicable to complex karst settings, where structural and hydraulic characteristics cannot be spatially resolved with sufficient accuracy. A basis model and four extended versions were set up to determine the individual characteristics of the present karst system and to include different flow processes that could affect the vulnerability of the system. All these model setups consider, besides recharge (soil and epikarst system), the conduit and the diffuse flow system as the main characteristics of the karst aquifer. The extended setups additionally account for surface runoff, an intermediate flow system, exchange flow between the conduit and the diffuse system and seasonal variation in the water storage capacity of the recharge system. Potential use of the calibrated models to quantify the intrinsic vulnerability of karst springs is discussed on the basis of (1) the temporally changing contributions of the conduit and diffuse flow systems to spring discharge, and (2) modeled breakthrough curves resulting from a standardized contaminant input into the karst system. The modeling approach complements vulnerability mapping methods by addressing temporal and quantitative aspects of vulnerability.
Karst Groundwaters Vulnerability Assessment Methods
2016
A major socio-economic and scientific issue is represented by karst hydrostructures vulnerability mapping, which qualitatively and quantitatively highlights their exposure degree. Two research trends have been developed, one taking into account the environment features exclusively – the aquifer and protective cover type, permeability, aquifer depth, recharge rate, etc. (intrinsic vulnerability), the other focused on the types and quantities of pollutants (specific vulnerability). MAGIERA (2000) described and compared 69 methods, grouped in 5 types: hydrogeological complex and setting methods, index models and analogical relations (AF, AVI, Ekv, ∆hT’), parametric system models (DRASTIC, DWSAP, SINTACS, EPPNA, GOD, EPIK, REKS, PI, GSI, GLA), mathematical models (VULK, FAVA) and statistical methods (CALVUL). However, it is also possible to classify the methods on the basis of other criteria, such as scale (local, regional, national), aim (land use planning, protection zoning, site asse...
Research frontiers and practical challenges in karst hydrogeology
Acta Carsologica, 2010
Besides t�e possible future impacts of climate c�ange, t�ere are many ot�er urgent groundwater-related environmental problems. Accessibility to safe drinking water in sufficient quantities for �uman needs is t�reatened by different types of contamination, overexploitation, saltwater intrusions, and inappropriate irrigation practices. Soil erosion, natural disasters, and t�e protection of ecosystems and biodiversity are ot�er important water-related issues. These problems exist today, but will get worse in many regions according to t�e current climate c�ange scenarios. All of t�ese issues are interrelated and are especially relevant in karst areas. For example, deforestation leads to ecosystem degradation and a loss of biodiversity, but also promotes soil erosion (Fig. 1), w�ic� increases t�e vulnerability of groundwater resources to contamination, alters rec�arge processes and reduces t�e water storage and buffering capacity of t�e �ydrogeologic system, t�us posing a t�reat to quality and quantity of drinking water and ultimately to public �ealt�. Furt�ermore, t�e degradation of soil and vegetation also releases CO 2 and reduces t�e efficiency of karst processes as a natural sink of t�is green�ouse gas (Liu & Z�ao 2000). Finding solutions to all of t�ese problems requires a multidisciplinary approac�, to w�ic� karst and groundwater researc�ers could and s�ould contribute more t�an t�ey currently do.