Saša Milanović

Analysis of the utility and management of karst underground reservoirs: case study of the Perućac karst spring

The construction of an underground dam and reservoir to provide an artificial water storage and karst control groundwater discharge regime is one of the most complex systems of tapping structure in karst. There are not many examples of underground dams, which increase the importance of risk management in their construction. This study proposes a procedure for constructing the underground karst reservoirs, focusing on the example of Perućac spring located in the Dinaric karst in Western Serbia. Possible effects of building of the underground reservoir are analyzed and a solution for a tapping structure is proposed. The applied concept is based on the karst groundwater budget, which provides valuable information on storage changes in the karst aquifer, enables further predictions of the optimal exploitation rate, and facilitates karst groundwater management. The results of this study give a basis for several possible technical solutions for a future tapping structure. These solutions were additionally analyzed in the process of multicriterial ranking to find the optimal process.

Monitoring of Karst Groundwater

Monitoring of groundwater in karst aquifer (quantitative and qualitative characteristics) is of great importance for its abstraction and its long-term and safe use, particularly for the purposes of water supply. In order to obtain relevant information about the functioning of karst aquifer it is necessary to implement a series of actions and measures (monitoring) to track the quantity and quality of groundwater. Consideration of the capacity and chemical composition of groundwater, as well as the establishment of a system of monitoring, is the first step in this process. The establishment of a monitoring network involves the definition of a number of observation points, observation frequency, and the quantitative and qualitative parameters needed for further analyses. Monitoring of karst groundwater provides data that give us a basic outline of the groundwater and the ability to define recommendations and measures for its use or for the improvement of its protection. Reliable monitoring of groundwater quality and quantity in any terrain is difficult, but in karst terrains it is especially hard. The main points and types of groundwater monitoring in karst terrains are shown in this chapter.

Karstification depth and storativity as main factors of karst aquifer regimes: some examples from southern Alpine branches (SE Europe and Middle East)

Karstic aquifers are the main groundwater source in Southeastern Europe and the Middle East. Many large springs and sources which drain Alpine orogenic belt and its branches are tapped and utilized for drinking water supply. Due to the unstable regime of the karstic springs, the main challenge for most of the waterworks is to ensure water supply during recession periods which coincide with the dry season, usually summer and early autumn months. Besides the problem of water shortage, water pollution of this open and generally very permeable type of aquifer is another major constraint in local water management. However, in comparison with other type of aquifers, the highly developed karst and its significant storage capacity as found in the studied areas may attenuate significant rainfall/runoff variations and possible climate changes. Most commonly, intensive rain episodes do not result in extreme floods in the studied karst terrains, while stored groundwater provides sufficient base flows for dependent ecosystems during the recession or periods of drought. Several typical hydrographs and results of some models applied for forecasting climate change impact presented in this paper represent a good example of specific karst aquifer behaviours and importance of considerable storage capacity in deeper parts of the aquifer.

Karst Groundwater Availability and Sustainable Development

The hydraulic behavior of karst aquifers under several hydrologic conditions is described. Different parts of a spring hydrograph have been associated with hydrodynamics of karst aquifers, starting from a strong recharge event up to a long-term flow recession condition. As karst aquifers are characterized by a complex conduit network developing in a fractured carbonate rocks, an exchange of water between conduit and matrix/fractures generally occurs. Under strong recharge conditions, concentrated infiltration favors an increase in the hydraulic head in the conduit network, and a rapid pressure pulse is forced through the phreatic conduits giving a hydrographic peak at the spring. Later, after the end of recharge processes, the karst conduit network drains the saturated zone of the aquifer, and water table decreases. After prolonged rainfall deficit, a meteorological drought can induce a groundwater drought, and the water table falls to a minimum height; this hydrologic condition highlights the hydraulic behavior of karst aquifers under droughts. Statistical analyses could forecast a groundwater drought using rainfall data series, and provide a useful tool for water management. An example for karst aquifers of Picentini Mountains (Southern Italy) has been described, where spring discharge time series are available for several decades. Besides, the exceptional spring discharge increase after 1980 Irpinia earthquake is also described. The underground flow through karstic aquifer depends on the size, shape, nature, filling, and interconnection of cavities and voids. The transformation of rainfall into karst spring discharge can be very rapid, or the process can be rather slow and long lasting, due to the storage potential and retardation capacity of the underground voids. Autocorrelation and cross-correlation analyses can be very useful tools for evaluation of discharge regime and forecast of karstic aquifer behavior under different circumstances. In addition to these analysis, this section provides a theoretical base of a linear multiple regression model used for karst spring discharge simulations based on daily values, as well as examples based on autoregressive models (AR), cross-regressive models (CR), and most often used hybrid models (ARCR). The theoretical basis of transformation functions which is used for simulation of daily values of karst spring discharges was explained in detail. For the purposes of assessing partially (insufficiently) gauged karst springs, developed model presented in this section can be used for extending recorded discharge time series, for computing the real evapotranspiration, catchment size, and dynamic storage volume of the karst aquifer. The estimation of the groundwater potential for exploitation is of utmost importance, particularly during the planning or in the initial stages of the regulatory system development. This section examines two different concepts of the possible implementation of regulatory systems: first one, based on water “borrowing” from natural storage—static reserves—and second one is based on the increase in the dynamic groundwater storage by the construction of underground reservoir. By simulating different scenarios of groundwater exploitation, along with knowledge of hydrogeological behavior, a realistic basis for future optimal control of karst outflow regime can be created. This implies the analyses of storage changes in karst water reservoirs under natural conditions, and calculation of the future potential exploitation. The applied concept is based on the karst groundwater budget, which provides valuable information on storage changes in the karst aquifer, enables further predictions of the optimal exploitation rate, and facilitates karst groundwater management. Several examples are use to illustrate model performances and outputs. In hydrogeological and engineering geological surveys of karst interior, the only research methods that allow direct observation, investigation, and exact geological mapping of channels and caverns are speleology and cave diving. Data collected during speleological and cave diving exploration significantly contribute to the reconstruction of the evolution of karst processes, which is very important in assessing the depth of karstification which is in turn important for tapping of deep siphonal springs for water supply, as well as for other hydrotechnical structures in karst. Section 15.4 is an overview of four phases of speleological and cave diving explorations, from planning through exploration to the final data analysis. The examples of research given in this chapter are only a part of the experiences that point to significant development of karstic channels in karst areas. Speleodiving and speleology research in defining the position and functioning of karstic aquifer have contributed significantly to solving water supply problems, and to the implementation of hydrotechnical and other structures in karst. Although karst aquifers are one of the main water sources for drinking water supply worldwide, it is well known that they are at the same time one of the most problematic resources. Due to the unstable flow and great variation of the discharge of the karstic springs, during recession (lean) periods, the local population often suffers from water shortage. If aquifer is well karstified and has adequate storage in its deeper parts, it is often possible, just as it is in the case of open water reservoirs, to regulate and manage minimal flow by various engineering interventions. Such an option provides opportunities to satisfy water demands not only of direct consumers but of ecosystems as well by ensuring ecological flow downstream. In this section, possible engineering solutions to regulate groundwater flow in karst and physical, ecological, and economical implications of such interventions are discussed. The three prerequisites for implementation of an engineering regulation project which should be fulfilled are as follows: Regulation is physically possible; regulation is environmentally sound and friendly; and regulation is economically feasible and sustainable. Each of them is explained, and guidance for a realistic evaluation is provided. Several case studies facilitate understanding of the regulation opportunities and threats as well as identify some helpful surveying methods used in water practice. The two main groups of engineering regulation for controlling karstic groundwater are discussed in detail: (1) regulation of discharge zone and (2) regulations, i.e., interventions in the wider catchment area. The former can be achieved by spring overpumping, drilling the wells or other supplementary intakes, constructing a subsurface (underground) dam, or by artificial recharge. The riverbed regulation, directing groundwater to other more promising catchment areas, closing or regulating ponors (swallow holes), and building impermeable barriers are some of the measures which can be applied in the wider catchment to maintain seasonal flow. A few successfully implemented projects of aquifer discharge control and lessons learned in management of groundwater reserves are also presented in this section.

Decision Support Procedure for Constructing Karst Underground Reservoirs – a Case Study on Perućac Karst Spring (Western Serbia)

One of the most complex systems of tapping structure in karst is construction of an underground dam and reservoir to provide artificial water storage and a karst controlled groundwater discharge regime. Examples of underground dams are not so numerous; and, therefore, the risk component in their building is much emphasized. In this paper, a proper procedure for building a support system for constructing underground karst reservoirs was proposed, focusing on the example of the Perucac spring, located in Dinaric karst, in Western Serbia, and analyzing possible effects of building an underground reservoir and selecting tapping using this procedure.

Attenuation of Bacteriological Contaminants in Karstic Siphons and Relative Barrier Purifiers: Case Examples from Carpathian Karst in Serbia

Karstic groundwater, because of its unique hydrological characteristics, is extremely sensitive to contamination by pathogens. For this reason more attention has recently been paid to the relationship between pathogens and the hydrogeological and geological characteristics of karst aquifer. This paper presents causes of contamination of three large sources located in the karst aquifers in the Carpathian-Balkanides in eastern Serbia. The bacteriological analyses and their correlation with physical and chemical characteristics in seasonal intervals provide an insight into the functioning of studied karst aquifers. It has been confirmed that ascending springs which drain deeper siphonal systems or the presence of adjacent porous aquifers as an additional purifier barrier mitigate bacterial waves and have much better water quality than gravity springs with an unstable discharge regime. For the latter, typical fast draining does not allow the activation of the attenuation capacity of the aquifer system.

Physical Modeling of Karst Environment

It is very difficult to define hydrogeological parameters in an anisotropic media and in carbonate matrix. Even after the employment of many different methods, it is a problem to define hydrogeological parameters. Still, in the past few years, a whole new branch of karst investigations has become widely used in the earth sciences and generally can be recognized as 3D modeling of karst aquifers and karst conduits. Modeling of karst environment generally combines state-of-the-art solids and parameter modeling with advanced survey technologies to produce decision support tools that are vastly superior to standard groundwater flow models. This kind of modeling visually conveys the real morphology and hydrogeology data of a conduit system in as much detail as was recorded by the geological, hydrogeological, speleological, cave diving, and other habitual survey methods. The main focus in this chapter is on 3D reconstruction and modeling of karst physical interior as a new approach in karst hydrogeology. Powerful tools such as ArcGIS and other software for three-dimensional modeling enable fast quantitative analysis and reconstruction of karstic conduits from the surface (sinkholes, pits, dolines, ponors) to the discharge zone (karstic springs) in 3D environment.

Prevent Leakage and Mixture of Karst Groundwater

Choosing optimal dam sites is a very complicated task due to the nature of karst and the insecurity of water storage often resulting in leakage from reservoirs. An appropriate project concept prior to exploration can significantly reduce the risks of water losses or at least minimize them to acceptable levels, while the absence or reduction of exploratory works can increase them. Many analyses show that once the reservoir is filled up, groundwater flow currently oriented toward the future reservoir would saturate the upper part of the karstified rocks, reactivate currently unsaturated (fossilized conduits) pathways, and form a reverse discharge outside of the reservoir area. The geological, hydrogeological, speleological, and other special investigation procedures should be permanent activities during the design stage, during the construction of the dam site and filling of the reservoir, as well as during exploitation. Having a good map, database, models, and geological, hydrogeological, and other 2D and 3D layers increases the chances of choosing a successful dam site and minimizes the possibilities of further leakage from reservoirs below the dam site and through the reservoir and dam site embankment. This chapter summarizes the necessary procedures for the acquisition of some of the basic information for choosing an optimal dam site and preventing leakage from reservoirs in karst formations through chosen characteristic examples. Several case studies involving mineral ore extraction and mine drainage in a karst aquifer environment are presented in this section. Mining operations often entail extremely high rates of groundwater inflow, which is a threat to safe mining. Insufficient knowledge about the hydrogeological setting and a lack of preventative drainage often lead to sudden inrushes. In the past, this has caused rapid mine flooding, material losses, and even human casualties. In the case of evaporite karst, ground subsidence resulting from rather fast dissolution of evaporite rocks is a special problem. The practical experience discussed in the section shows that various measures are undertaken to drain mining operations (including drainage wells on the ground surface, underground dewatering boreholes, drainage galleries, drainage shafts, and the like), as well as that grouting of karst conduits and caverns has not always been effective. The quality of karst groundwater, before it enters the zone of mining operations, is generally good. However, after the groundwater comes into contact with ore deposits, this quality frequently deteriorates. Numerous examples show that karst groundwater, when abstracted before it reaches mining operations, can be used for drinking water supply, irrigation water supply, and other similar purposes. The majority of karst terrains are characterized by a high degree of heterogeneity. The results obtained by applying methods for the assessment of local karstification (e.g., borehole tests) often cannot be reliable to extrapolate to a wider area. The use of remote sensing provides the opportunity to assess the spatial distribution of karstification in the subregional scale. Analysis of satellite and aerial images allows the identification of geomorphological and tectonic forms that may indicate the highly karstified zones. From the factors that indicate the karstification, and which can be mapped by remote sensing, two factors are selected: surface karstification (K sf) and density of faults (T f). By overlapping maps of these two factors using geographical information systems (GIS) techniques, the final map expressed through a KARST (karstification assessed by remote sensing techniques) index is obtained. For the first time, the mapping approach has been applied to the catchment area of Karuc springs (Montenegro). By surveying the catchment area after the preparation of the map of the KARST index, it was noted that the assessed degree of karstification by using remote sensing mainly matches to the field assessment of shallow karstification. The application of this approach provides an image of the spatial distribution of karstification, even for areas that are inaccessible for direct field research. The obtained map can be used as a basis for solving some of engineering problems in karst that are related to the regulation of water, extraction of groundwater, and protection of karst aquifers from contamination. The mixture of fresh groundwater and surface water is a frequent problem in karst, and most problematic for the sustainable use of fresh groundwater. This is mostly a result of a high permeability and low attenuation capacity of karst aquifers, particularly those formed in open (unconfined) structures. The problem becomes more complicated when karst aquifer is in contact with seawater and tapping coastal aquifers and distinguishing fresh from seawaters is regularly a very difficult task. For this purpose, the Phoenicians constructed special intake structures and still today, many attempts to address this problem are made and similar devices constructed. The regions in which a large number of submarine springs exist are the Mediterranean basin, Florida, the Caribbean basin, the Black Sea, the Persian Gulf, and the Pacific islands. The section includes an explanation of the classical Ghyben-Herzberg formula, which defines the relationship and interface between fresh and salty water, but also states that its application, as in the case of Darcy law, should be used with caution in the case of karst aquifers. Several chosen case studies from different locations (Yucatan Mexico, Libya, France, and Montenegro) provide an overview of problematic and very difficult management of littoral karstic aquifers. It is often the case that even implementation of sophisticated engineering works and controlled pumping of fresh groundwater cannot completely diminish salt water intrusion.