Karst Water Resources (Proceedings of the Ankara - Antalya Symposium, July 1985), IAHSPubl. no, 161

SPECIFIC V.FL \ - KARST WATER RESOURCES

Vujica Yevjevich Research Professor and Director International Water Resources Institute The George Washington University Washington, B.C., U.S.A.

Abstract

Karst water resources have many particular features that often clearly distinguish them from water resources of other, less pervious geologic formations. Therefore, it is common to talk about their specificities. Features of karst terrains of Southern Turkey (the Taurus Mountain Range) are used here to demonstrate versatilities of specific problems of karst water resour­ces. The sizes of karst aquifers, springs, lakes, poljes and other karst features of Turkey are among the largest in the world, five groups of these specific features are described and discussed in this paper, particularly with respect to practice of water resources development. Large aquifers that feed large karst springs often are of water residence times that classical methods of input/output identification, such as dye or tracer test, are not applicable. Only the study of underground free surface wave propagation, after local rainstroms occur, permit to pinpoint underground watersheds. Coastal karst aquifers with saline water intrusions, and the connected coastal and submarine springs of fresh or brackish water present significant challenge in the search for maximal recovery of fresh waters along the coast of Turkey, as it is the case with the other karst coastal areas of the world. Many storage reservoirs in Southern Turkey leak water in appreciable quantities, posing the problem of leakage reduc­tion or elimination. Techniques are needed not only to determine the leakages in function of reservoir level and water levels in receiving karst formation, but also on how to decrease them. Turkey has many natural lakes which partially or folly drain through karst under­ground. Problems of determination of water regimes of underwater inflows/leakages a wait advanced investigative methods and technological solution for reducing leakage. Southern Turkey abounds with small, medium and large karst poljes (plains), that are drained only by underground karst systems of channels. Their water regimes are often very complex, effects of human activities (flood control, water storage, irrigation, drainage, water supply) are versatile and usually difficult to assess accurately, and economical solutions of water resources problems require long investigation and planning processes.

Introduction

Karst of Turkey as an example of karst water resources problems and development op­portunities. The characteristics of karst water resources of Turkey may be considered as

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typical for the carbonate rock formations of Southern Europe, Alps, Dinaric Alps, Northern Africa and the Middle East. One basic difference may be the karst phenomena and features of Turkey, which by their dimensions exceed, nearly by an order of magnitude, those of some other regions around the Mediterranean Sea. The largest karst springs in the world, measured either by the minimum or by the average flow from one hole outlet or from multiple outlets, are likely to be found in Turkey.

Also, the largest karst aquifers, measured either by the total volume of accumulated water or the residence time of recharge waters may be in Turkey. A significant number of natural lakes in karst of Turkey, are fed either by karst water or lake water leaks through karst features, is found in Turkey. Some of the largest and most complex karst water regimes occur in karst poljes of Turkey, with varieties of sizes, features and karst phenomena. Coastal karst aquifers, and coastal and submarine springs, are common features along many coastal areas of Turkey. Therefore, a general presentation of several features of Turkish karst water resources are appropriate as the introduction to an international symposium on karst water resources, held in Turkey. The material of this presentation is partially based on the report "Karst Water of Southern Turkey", prepared by the writer for the United Nations Development Program (1981 ).

Surface and subsurface karst terrains of Turkey. Carbonate rocks cover about one - third of Turkey. This territory belongs to the Mediterranean part of the Alpine orogenic belt. Figure 1 presents the areas covered by carbonate rocks, according to the basic geological

Fig. 1 - Carbonate rocks of Turkey (After Eroskay and Giinay, 1979).

Specificities of karst water resources 5

eras (Eroskay and Giinay, 1979). If the carbonate rocks of Turkey occurring at depths that can be economically reached for withdrawal of their waters were also included in Figure 1, the total area of carbonate rock formations, of interest to water resources development, would likely reach two fifths of the country's surface. This percentage of area covered by limestones, dolomites and other karstified rocks shows the importance of these rock formations for the solution of economical problems in various regions of Turkey, in general, and for water resources developments, in particular.

Most carbonate rocks of Turkey are intensely karstified. It is sufficient to overlap two maps of the same scale to demonstrate it. These maps are the carbonate rocks of Figure 1 and the map of caves in Turkey (Baser, 1972, as reported in Eroskay and Giinay, 1979). Whereas Figure 1 shows a relatively large area of carbonate rock formations, the map of caves of Turkey also shows a large concentration of caves.

The basic reasons for a large karstification of most carbonate rocks in Turkey are: (a) the strong orogenic movements have lifted carbonate rocks much above the sea level; (b) the created level differences and powerful energy gradients for surface and underground water circulation have highly karstified these rocks; (c) the intensive orogeny of folded, faulted, up - thrusted, over - thrusted and highly fractured rocks provided both the openings for the initial water circulation and the opportunities for the subsequent large rock solution and the creation of secondary porosity; and (d) the orographic processes and the resulting high mountain ranges represented barriers for the movement of air masses, forcing them to significantly rise and precipitate rain and snow, thus providing ample quantities of water for a rapid infiltration, circulation and solution of carbonates.

Many external and internal factors are responsible for the type and degree of karstification of an area of carbonate rocks. The basic fact is that the general geological structure, the orogeny and the connected tectonics provide the basic framework which permits, enhances or impedes the processes of karstification. The Alpine orogeny and the following epirogenic movements in Turkey have been important factors in karstification.

The intense karstification is spread almost all over Turkey. It is found particularly in the regions of the Taurus Mountain range, in Western and Southwestern Anatolia, in Konya closed water basin, in Eastern Anatolia (Keban Reservoir region) and in Southern Anatolia (large Ceylanpinar plain). As Figure 1 shows, small areas of carbonate rocks may be found in any region of the country. According to Eroskay and Giinay (1979), four karst regions can be differentiated in Turkey: Taurus region, Southeast Anatolia region, Central Anatolia region, and Northwest Anatolia and Trace Region. For the general presentation of geological aspects of the karst, and the description of karst regions around the world, the reader is reffered to Herak and Stringfield (1972) and Herak (1977).

As an example of the above described regions, the Taurus Mountain range, considered as an extension of the Alps into Anatolia, has the width of about 200 km between the Mediterranean Sea and Central Anatolia, stretching from the Aegean Coast through Eastern Anatolia all over to Iran. The range reaches heights of 2500-3000 meters, with high mountains, sharp peaks, deep valleys, narrow gorges and rugged plateaus. It is full of karst features such as dolines, uvalas, poljes, springs, ponors, estavelles, karst lakes, underground (lost) rivers, caves, aquifers, coastal and submarine springs, and similar features. Because of

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a complex geology, it is not always feasible to explain the various hydrogeological charac­teristics in a simple way and the factors responsible for the occurrence of some water resources phenomena of the Taurus Mountain karst region, such as hydrological characteristics of specific springs, lakes, aquifers, karst poljes, etc. The widespread non -carbonate rocks of Turkey, with impervious formations, often control the karstification.

Karst water resources'of Turkey. Karst terrains of Turkey are rich in water and as such are very important for the economic development of the country. High mountain chains are responsible for important characteristics of these water resources: large average annual precipitation, large level differences toward the sea with relatively short distances, which give large hydroelectrical potential to water resources; melting of accumulated snow at high elevations which sustain low flows well into the first half of the dry summer seasons; high mountains with small water evaporation and runoff being a large portion of the total precipitation; and similar properties.

Karst terrains of Turkey are also responsible for some negative characteristics. The underground drainage leads to a smaller density of streams per unit area in comparison with the case of non - carbonate terrains. This small density often leads to relatively specific water resources. Rain and snowmelt infiltrate fast at high elevations and appear at low levels thus making difficult either the access to it or the utilization of its hydroelectrical power potential, except in a limited number of cases of high - level lakes and rivers. Water resources often appear as large springs at low levels close to the sea, where the limited areas for irrigation and the relatively small hydroelectrical power heads preclude the utilization of their full potential.

The complexity of underlying geology of most karst regions makes it often very difficult to determine boundaries of underground catchments of large karst springs, aquifers or rivers. Some aquifers of Turkey, by their total volume of stored water, by their water residence (travel) time and by the discharge of their springs, are of such sizes or time scales that they are of an order of magnitude larger than the similar karst aquifers and springs in many parts of the world. When the volume of stored water at any time in some aquifers is estimated to be of billions or of tens of billions of cubic meters, or the residence time of tens or even of hundreds of years or more, or discharge at many springs in the minimum ranges between 15 and 30 m /sec, then these aquifers and springs must be considered as unique in the world in general, and in the Mediterranean belt of karst terrains in particular.

Because of the geological and hydrogeological complexities and of sizes of aquifers and spring flows, the understanding of properties of karst water resources in Turkey require special investigative methods. Approaches and techniques in solving problems for water resources development, conservation, control and protection should be of wide interest, much beyond the interests of governmental agencies and specialists of a couple of univers­ities of Turkey. For many reasons the study of Turkish karst should have a worldwide significance (such reasons as the transfer of experience, and the innovative character of investigative methods and technology for the solution of water resources problems of karst terrains). Ozis (1979) gives a description of major karst river basins of Turkey, with gauging stations, modeling of runoff, investigations by using tracers, rainfall - runoff relationships and some other information on karst water resources. The list of 85 references provides a general picture of hydrological studies of karst terrains in Turkey.

Specificities of karst water resources 7

Patterns of rock fractures and folds often predeterm ne the underground karst water channels and/or aquifers. As an example, Figure 2 gives the map of fractures of Antalya region of the Taurus Mountains, obtained from the Landsat-I remote sensing image. This region has served as a pilot study area of karst water resources problems and solutions for many years, in a jointly sponsored investigative project by the United Nations Development Program and the Turkish Government, The map of Figure 2 helps draw hypotheses on sub­surface watershed boundaries as well as where waters may go through the underground, and where they are likely to surface again.

Fig. 2 - Map of fractures of Antalya Region of Taurus Mountains, obtained by Landsat-I remote sensing image (Sipahi and Baçterzi, 1978).

Practical objectives of specialized investigations on karst water resources. Major objectives in studying the karst water resources in a region are usually:

(1) Delimitation of boundaries of surface and subsurface karst water systems of limestones and other karstified water - bearing and water -transmitting rocks;

(2) Understanding and description of geological, hydrogeological and hydrological phenomena and the determination of their characteristics, which affect planning of karst water resource development, conservation,control and protection;

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(3) Quantification of water budget of major karst units in an area, particularly by determining the budget equation terms such as precipitation, evaporation, recharge,storage capacities, discharge, and the other terms, as they vary in time and space (to avoid counting of the same water two or more times at, different rivers, aquifers and springs in water resources planning);

(4) Study of potential for transfer of surplus surface and subsurface karst waters to areas that are highly deficient in water resources, since high karst terrains often have large precipitation with excess water beyond the greatest potential water demand in these regions;

(5) Investigation of connections of springs to recharge karst waters, in general,and to waters sinking at swallow holes in particular;

(6) Study of dependence of discharge of springs or spring zones which are supplied by the same aquifers or the same underground systems of karst channels;

(7) Study of regional and local hydrogeological conditions for the construction of impervious reservoirs in the leakage risk - prone karst terrains;

(8) Investigation of subsurface karst waters with special reference to coastal aquifers and the coastal and submarine springs, with the potential defense against intrusion of saline or brackish waters;

(9) Location and quantification of underground lake or reservoir karst water inflows or outflows;

(10) Studies on how to use the existing karst aquifers as water storage capacities, or the karst porosity for the underground storage reservoirs;

(11) Studies for protection of karst underground water systems from a long - range or even permanent contamination by organic, mineral or toxic pollutants;

(12) Investigation of water regimes of enclosed karst poljes (plains) with only under­ground drainage, for purposes of their best utilization;

(13) Understanding and protection of special, often very precarious, ecosystems in karst areas;

(14) Study of the relationship of karst water resources and the planning, design, construction and maintenance of various karst - specific or general man - made structures; etc.

Many other objectives can be cited here, if an exhaustive approach is used to enumerate them. The reader is referred to the book "Karst Water Research Needs". (Yevjevich, 1981), which describes 150 karst - related research topics,considered important by a group of specialists for a better future development of karst water resources.

A significant characteristic in fulfilling the above objectives is their multidisciplinary aspect. They need a large number of disciplines for problem solving, such as general geology,

Specificities of karst water resources 9

special geological disciplines of engineering geology and hydrogeology, geophysics, geotechnical sciences, geography, geomorphology, climatology, hydro meteorology, hydrology, hydraulics, isotope hydrology, coastal hydrology and hydraulics, geochemistry, instrumentation science, data processing technology, engineering of various specialities, and others.

Often the distinction is not clearly delineated between the karst hydrogeology and the hydrology of subterranean waters of karstified terrains. The likely ; reasons for it are two, the high complexity of the environment and the multidisciplinary character of water problems with the stress on a variety of aspects related to identification and solution of water resources problems in higly karstified terrains.

Hazards inherent in development of karst water resources. Karst terrains present many types of hazards in development of karst water resources. They include land subsidences, underground cave - ins, water and mud break - ins in excavation, leakage of water at dam sites or from reservoirs, land and rock accidents, salt water intrusion, dry holes in drillings for well water, and similar hazards. Difficulties and failures in water resources development are as important as the land and rock accidents. They include large water leakage of reservoirs and lakes, diversions depriving existing or planned projects of expected water, earthquakes cutting underground connections by diverting water to other localities, structures that do not fulfill the original objectives, and similar difficulties and failures.

Hazards are great in karst terrains that the upstream water interventions (say the drainage of karst poljes with decreasing of their inundation season, or irrigation) may significantly increase the non - uniformity of water regimes of the important downstream springs. The eventual diversion of water from lakes that leak and feed downstream springs may affect significantly their spring water budgets. Many reservoirs in karst regions of the world never filled up, an everywhere, including Turkey, one finds reservoirs for which up to 50 % of water budget leaks, often in the undesirable directions.

Karst Aquifers and Springs

Examples of large aquifers and springs. Turkey offers very interesting examples of except­ionally large karst springs, draining large aquifers in the Taurus Mountain range. Such cases are: the Kirkgozler Springs at the northwestern edge of the Antalya travertine plateau, the Olukkoprii Springs near Be§konak, northeast of Antalya, and the Dumanh Spring near Oymapinar Dam on the left bank of the Manavgat River. The huge aquifers with the long water residence times, say tens of years of water travel or through - flow times, are the particular aquifer feature that needs attention, namely for the selection of proper investig­ative techniques for understanding and descripton, and development of new concepts for utilization.

Travel time through aquifers and types of water movements. The travel times t s - t Q of particuTâr^vatëFmolecules that enter the underground at the time tQ and show at the springs at the time t are much longer in huge aquifers than the travel times of water waves in the unsteady free - surface movement in the free - surface aquifer. Misunderstandings abound in hydrogeology of how water moves in large free - surface karst aquifers. These aquifers are composed of large channels, caves, caverns, fissures, and of both the fine primary and fine secondary porosity. The convenient division of the aquifer into dynamic and static parts of storage, as shown in Figure 3, is misleading. Water moves in both parts in similar ways.

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The real flow of water is through the entire aquifer, in deep karst aquifers as Figure 4 visualizes. Three basic flows mutually interact all the time: gravity flow represented by the streamline network flow, the convective vertical movement that results from differences in temperature and water density, and movement of water by density currents. The new cold water from a recent high mountain inflow may sink into the aquifer and be replaced by the water of deeper layers, which has acquired a higher temperature from the interior heat flux. The fact that the spring water temperature is often nearly constant throughout the year from these large aquifers points to the effect of interior heat of deep limestone layers and the huge water storage volume, which are needed for the temperature to equalize.

Fig. 3 — Concepts of static and dynamic storage of classical hydrogeology.

Recent I n f i l t r a t i o n

Fig. 4 - Realistic network of flow streamlines and convective interchanges and mixing in a deep karst aquifer.

The outflow of water from unsteady inputs in governed by wave celerity instead of being governed by simple small water velocities through the porous media or slow water movement through channels. Figure 5 schematically represents this phenomenon of wave movement that is controlled by wave celerity. The effects of sudden storms over the catchment with the relatively rapid increase of flow at the springs (in a couple of days or weeks) do not contradict the findings of long water residence time in aquifers, obtained by studies of natural isotopes or inferred by the other investigative methods. The propagation

Specificities of karst water resources 11

of unsteady free - surface waves in karst aquifers may be conceived as the fastest traveling signal between the places of input and the places of output. This phenomenon creates a feasibility for a new investigative method in case of long - residence karst aquifers. This may help substantially the identification of surface and subsurface watersheds of karstified catchments.

Determination of watershed boundaries by wave propagation^ A new technique based on rapid wave propagation in large karst aquifers may be developed for locating the under-

Fig. 5 — The general, conceptual visualization of travel of free - surface water waves in karst aquifers, with given wave celerities, in contrast to slow movement of molecules.

ground watershed boundaries. This investigation method must be applied during the thunderstorm seasons. An isolated large storm produces a localized water input, as Figure 5 shows. It creates an underground wave at the water table, which travels fast from the location of input to karst spring(s). This approach requires a dense precipitation network over the karst area, or a combination of radar observations and a less dense but basic pre­cipitation network of gauges. Accurate observations of a couple of years at this network, simultaneously with observations of outflows at all the surrounding springs, would provide information necessary to pinpoint areas of surface and subsurface watersheds of catchments that feed aquifers and springs.

The Taurus Mountain of Southern Turkey has several large aquifers and springs of the type of the Kirkgozler Springs, with large and well regulated spring flow and significant low flows. The tracer techniques have not been feasible for investigation of such aquifers. The classical geophysical and hydrogeological methods of establishing karst water connections (swallow holes - to - springs dye test, determination by hydrogeological methods, finding quantities of leakage water from karst lakes, etc.), are not applicable to very large karst aquifers. Apart from the Kirkgozler Springs, with Qm j n = 10-15 m" /sec, the Dumanh Spring of the Manavgat River has Qm j n = 20-25 m3/sec, and the Olukkôprli Springs about Q m ! n = 20-30 m3/sec. Other springs in the region have Qm j n = 5-10 m /sec.

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All these springs drain aquifers of relatively large residence times (somewhere between 1 0 -15 years or more) as shown through investigation by natural isotopes.

Types of aquifers. The investigation of catchment areas in the Taurus Mountain region and itsloothliî7b77everal Turkish geologists and hydrogeologists in the last 10-20 years has revaled important karst features. Tectonic movements of pervious limestones and of associated impervious formations may have "compartmentalized" limestone into mosaic -type aquifers. These compartments often occur in the same limestone formation. They follow one another, often separated by thin impervious formations. A mosaic - type aquifer has these compartments connected to produce large springs.

Several explanations of these "compartmentalized" aquifers are: (a) water spills in underground over the impervious barrier between compartments; (b) impervious formations are thin, locally missing, eroded in window places, with underground connection occurring through these windows; (c) lenses of karstified formation may occur in an impervious formation, permitting karstification and water leakage; and (d) impervious formations are broken or thinned out in deep layers, permitting connections. This type exemplified by the Dumanh Spring aquifer.

The other type of large aqifers is exemplified by the Kirkgôzler (forty - eyes) aquifer with springs. Figure 6 represents its spring area, while Figure 7 gives two most characteristic geological profiles.

Fig.6 - The location of the Kirkgôzler Springs on the contacts of pervious limestone (Gi—formation), pervious travertines (G2—formation) and impervious radiolarite -peridotite rocks (G3—formation).

Specificities of karst. water resources 13

Fig. 7 — Geological profiles, west - east, at two places, Kovanhk (upper cross section) and the Kirkgôzler Springs - Biyikh Sinkhole (lower cross section), showing the general geological structures: (1) Quaternary alluvial deposites; (2) Quaternary pervious travertines of the Antalya Plateau; (3) Upper Trias - Upper Cretaceous formation; (4) Upper Trias - Senonien formation; (5) Jurassic - Cretaceous pervious limestone; and (6) The Springs location. (Hydrogeology of the Antalya-Kirkgôzler Karst Springs, by Dr. Giiltekin Glinay, in cooperation with Temel Yajar Yayan, Ankara, 1979).

It was always evident that the Kirkgôzler Springs are the main water resource of the Antalya travertine plateau. These springs have created the plateau by depositing travertine. They are the only surface overflow of the large underground karst aquifer (or a system of interconnected karst aquifers), with water forced to the surface by the impervious, tectonically created barrier. This barrier covers the southern and eastern flanks of the highly pervious limestone formations. The subsurface water flow occurs from limestone to travertine but in quantities not yet determined (Figure 7). The aquifer is very deep, created by several overthrusts of the same limestone formation. The estimates lead to a figure of 50 billion cubic meters of stored water in this aquifer.

Pumping water from this aquifer (Kovanhk, Figs. 6 and 7) showed a large yield per well. This aquifer can be developed also as an additional storage capacity by using the highly pervious rocks immediately above and below its water table and by changing its present highest and lowest levels at the outlet by proper hydrotechnical interventions.

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Springs. An example of large springs, the Dumanh Spring (the largest karst spring in the wôrïcTwhen the lowest spring discharge from one outlet is used as the measure of karst spring size), is an important water contributor to the Manavgat River and to the Oymapinar Reservoir. It is now an underwater group of springs in this reservoir. Its average flow is 55-70 m3/sec, historic minima ranged from 22-30 m3/sec, and a maximum of about 100 m3/sec. The water contributing area is not yet definitely determined, though many hydrological studies have delineated the likely boundary of its catchment in an approximate way.

Figure 8 gives the recession hydrograph of flows of the Dumanh Spring (plus some minor upstream springs), in the semi - logaritmic scale, showing that

as an exponential recession curve (linear reservoir outflow curve), is a good fit, with Q0 = the initial discharge (in this case 60 m3/sec) and the recession parameter a = 0.0026. After 147 days (nearly five months of recession flow) the discharge still was high, about 40 cm' / sec, meaning that compartments of its mosaic - type aquifer are all large, with a linear relationship of the outflow discharge and the stored water volume above the level of zero outflow.

': Q t - b ' O e " 0 " ' " '

/

ICO

; '. o

20

i y s E

1 9 7 7

Fig. 8 - Recession hydrograph of the Dumanh Spring (plus some other minor springs) during the summer of 1977.

Specificities of karst water resources 15

Coastal and Submarine Springs and Aquifers.

Karst and the sea. Many coastal areas around the world are dotted with karst spring. Looking at a map of the northern side of the Mediterranean Sea, one is amazed at how settlements along the coast are made feasible by karst springs. Water supply availability was the major factor. Many irrigational areas, old and new, are based on water of coastal karst springs and aquifers. Expertise exists in many countries in how to capture and use fresh water of these springs. Some modern problems are posed that require practical solutions. Several problems are posed for submarine springs when attempts are made to recover their fresh water.

Sedimentary carbonate rocks are often found along the coastal areas, both above and beneath the levels of seas and oceans. This common occurrence is to be expected because a large proportion of sedimentary rocks are deposited inside the seas, with the other being deposited mainly in inland lakes. The orogaphic movements lifted these rocks from their locations of deposition and solidification to levels above the sea. The sea level fluctuated highly in the last two million years of the Pleiostocene ice age. The orogeny of plate tec­tonics significantly affected the karstification processes along the coastal areas.

The most recent karstification has been controlled by the present sea level. The melting of ice sheets of the Northern hemisphere (Europe, North America) and of most glaciers at high mountains all around the world increased the sea water level in the recent geological past by about 100-125 meters (even 150 meters by some estimates) in comparison with the previous lowest sea water levels. Therefore, the sea has "submerged" the karstification systems. This submergence process has created some very important properties of coastal karstified carbonate rocks all around the world.

The submerged vadose zone of the aquifer (Figure 9) created the significant "static" aquifer storage and produced aquifers with water circulation in both the "static" and "dynamic" parts of the total aquifer. This permitted an easy water exchange between the higher layers of the aquifer and the lower submerged secondary porosity, so that the heat flux from earth's interior could be easily absorbed by the aquifer. One or more of the old springs became the submarine springs, with the largest ones (or those of independent old karstification channel systems) known as the "blue holes." The water emerges into the sea in relatively large quantities, especially in wet seasons, and appears at the sea bottom. For a viewer from the sky this appears as an especially blue water spot, therefore the source of the popular name "blue hole." In many cases these submarine springs already flow as the brackish water, because the intrusion of sea water into the karst systems through many old outlets and connecting channels likely produces the mixing of fresh and sea water far inside the aquifers.

Springs along the coastal line, usually at it or close to it, result from the shorter routes to the sea of many old karst channels, regardless of submarine springs (Figure 9). These coastal karst springs may have either fresh or brackish water at outlets, or they may have fresh water during high flows in wet seasons and brackish water that increases in salinity as the discharge decreases to low flows in dry seasons.

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Fig. 9 - Schematic representation of effects of sea level fluctuations on coastal karst aquifers and springs : (1) lowest past sea level; (2) intermediate sea level; (3) present sea level; (4) lowest submarine springs (blue holes); (5) and (6) intermediate submarine springs; (7) shallow water submarine spring; (8) coastal (fresh or brackish water) springs; (9) present karst water system; (10) karst water system feeding the intermediate submarine springs; and (11) the lowest channel system feeding theblueholes (80-120 meters deep).

The three basic features of coastal karstified carbonate rocks are: submerged aquifers, submarine springs and coastal springs. Aquifers are highly affected by the saline water intrusion and its mixing with fresh waters either by natural processes or because of inappropriate methods of planning and operation of water withdrawals from these aquifers. These aquifers are very important for water supply and irrigation of coastal areas. The experience is already available for development of these water resources.

Coastal springs and aquifers. Charasteristics of coastal karst springs and aquifers are their type, water regime, techniques used for tapping fresh water, feasibility of recovering additional fresh water during the low flows, best operational methods, etc. The basic types of karst springs have been identified as: fresh water springs, brackish water springs, springs with steep approaching water gradients, and submarine springs.

Fresh water springs have outlets sufficiently above the sea water level so that water flows out of the karst aquifer all the time. Several such springs exist along the southern coast of Turkey. Water of most of them is used either for irrigation by gravity or by pumping. Most of these springs are only a couple of meters above the sea level. Over-pumping water from wells close to these springs, or from springs themselves (by inserting the suction pipes into the spring cavities) threatens to produce an intrusion of saline water, resulting in brackish spring water. Projects for an increase of fresh water recovery during the dry season require careful experiments and field test before a project is implemented.

Specificities of karst water resources 17

Coastal springs close to the sea often outflow water with different degrees of salinity in Southern Turkey. Often an increase of the level of spring outlets results in fresh water by using such small embankments or dikes close to the coast or in sea bays. By increasing the level difference between the outflow of spring water and the sea level the mixing of fresh and saline waters in the aquifer may be avoided. Usually an increase in outflow level results in a decrease or even in the total elimination of salinity. This is often done at the expense of the total fresh water recovery in comparison with the discharge of brackish water.

Some coastal karst springs may have a relatively steep water level gradient from the hinterland to the sea. They are also frequent in Southern Turkey, especially in case of small karst springs. It can often be approached to higher water level in underground caverns or collapsed terrains close to the spring. It is sometimes feasible in these cases to intercept the underground flow before water reaches the sea. Horizontal tunnels, exploration drilling, speleological investigation and other methods may be used to intercept and/or recover the fresh water. Furthermore, high level intakes decrease the pumping cost in lifting water. The underground water course may often be intercepted before the fresh water mixes with the saline water.

Fresh water of submarine springs can be sometimes taken at the sea bottom, if it is not already mixed with the saline water. The location of groundwater routes may help to reach the channel spots before the hydraulic conditions induce mixing of fresh and saline waters.

Submarine springs. The origin, water regime and methods of fresh water recovery of submarine springs represent some of the most difficult karst hydrogeological and hydro-logical coastal problems. To obtain the fresh water from submarine springs, detailed in­vestigations of geological, hydrogeoiogical and hydrological characteristics are required, especially in the light that the sea water level was much lower during the peak of the ice age. During times of the lowest sea water levels, rapid erosion and karst development brought karst springs closer toward the sea levels of those times. When ice sheets melted, the sea level submerged coastal karst springs and they became submarine springs. Some fresh water is discharged close to the new coastal lines but only as much as the old channels and connections permit. However, submarine springs in many cases still discharge water much below the sea surface. The "blue holes" are often mentioned by fishermen. Such a hole exits southwest of the Antalya Bay in Southern Turkey. Supposedly a large underground spring of fresh or brackish water comes out into the sea.

The typical submarine problems are encountered at the Ovacik Springs in the coastal area between Silifke and Antalya. These are relatively shallow - sea submarine springs, close to the coastal line. The feasibility for the fresh water recovery of shallow submarine springs is much greater than in the case of deep submarine springs. For these springs, the problem is how to find whether the fresh water could be economically intercepted before it starts to mix with the saline water. Five big submarine springs occur on a fault line in the sea near the coast. The total discharge of the submarine springs is estimated to be around 1.0 m3/sec at a depth of 3 to 8 meters below the sea level (Giinay, 1973). Figure 10 presents a schematic visualization of likely karst water flow through the privileged routes and the adjacent diffused porosity. It also implies that a very complex mechanics of mixing of fresh

18 V. Yevjevich

and saline waters may be responsible for the submarine springs at the sea inlets having already brackish water. This point is very important because the major objective of the investigations on the Ovacik Springs has been to capture fresh water that recharges the submarine springs for irrigation.

Storage Reservoirs in Karst Terrains of Southern Turkey

Four visited reservoirs. The field visited by the writer in August 1980 were: the Onac flood coTitrol reservoir near Bucak and Kestei Polje, the Cevizli irrigation reservoir near Cevizli in the Taurus Mountain range, and the May and Apa irrigation water supply reservoirs on the borders of the Konya region. All these four bodies of water leak water in different degrees in comparison with the size of the body and its total average annual inflow. Some are not constructed to retain water except for the purpose of flood control(Onaç Reservoir).

Sinkhol®

Fig. 10 — A schematic visualization of the likely mechanics of the water flow and mixing of the Ovacik submarine springs (after Giinay, 1973).

Some have a useful function regardless of the original irrigation - intended storage of water, like the recharge of a karst formation that underlies the Konya plain (May Reservoir). Some quickly lose the bulk of stored water intended for irrigation through ponors in the reservoir (Cevizli Reservoir), while the leakage of a large percentage of stored water from the Apa Reservoir needs further studies to ascertain how much and where the leaked water goes. The recently built Oymapmar Reservoir on the Manavgat River does not leak water. It shows that when modern investigations and construction methods are used in karst regions, safe and leak - proven reservoirs can be built.

Figure 11 shows a schematic longitudinal cross section of the Cevizli Reservoir in Southern Turkey. Simply, an assumption that an impervious formation (1) serves as a barrier for waters of pervious formation (3), came out to be erroneous. The water of filled

Specificities of karst water resources 19

Fig. 11 — Longitudinal cross section of the Cevizli reservoir, with a roc kf il I dam of about 20 meters, showing: (1) the impervious formation on which the dam is located; (2) alluvial materials; (3) the pervious limestone; and (4) ponor (swallow hole) opened in the bottom during the first year filling in the winter season 1979/1980.

reservoir simply emptied through vertical sinkholes beneath the impervious formation. It also shows that small reservoirs, which likely do not justify economically a large program of investigative and impermeabilization measures, have much greater probabilities to leak water than the large reservoirs, well studied and properly constructed.

Investigative piezometric boreholes. For the collection of geological and hydrogeological information in the area that contributes water to reservoirs in karst, or to study potential losses of water from reservoirs, investigative boreholes are drilled. Some are equipped as observational piezometric boreholes. To take maximum advantage of the investment, it is beneficial to use boreholes for additional objectives, such as the forecast of reservoir inflow, the study of karst aquifer characteristics (estimation of aquifer water transport and storage properties), use of dyes or other tracers to find where water that passes boreholes flows, observation of water temperature and chemical properties, etc. The major problem is a proper interpretation of levels, pressures and other hydraulic phenomena that occur in boreholes and are directly or indirectly observed.

Subsurface storage physically coupled with surface storage. The subsurface storage that is physically connected with the surface storage may or may not be significant. Figure 12 shows schematically the physically coupled surface and subsurface storage capacities. If the subsurface water tables in limestone formations in a broad area around the reservoir fall very low during the dry season, say to the level of valley bottom springs, the filling of surface storage to a high elevation will submerge all the porosity space (primary and secondary) that can be filled and later emptied in a relatively short period of days, weeks or months. The subsurface storage may be significant. If, however, the water tables come out to be high and steep, the subsurface storage may come out to be less significant.

The total subsurface capacity between the groundwater surface for the maximum level and the groundwater surface for the optimal minimum operational level of the reservoir will depend on these factors : (1) the total volume of pervious subsurface formations that will have water between the maximum and minimum reservoir - induced groundwater

20 V. Yevjevich

Fig. 12— A schematic presentation of physically coupied surface and subsurface storage capacities.

tables- (2) the average porosity of that volume, that can be filled and emptied (active porosity) during the regular filling - emptying cycles in the reservoir operation (say the porosity somewhere between 1 % and 3 %); (3) the water transport characteristics of the active porosity volume; (4) factors that determine the groundwater backwater table surface, because the table may significantly increase as the distance from the reservoir increases; and (5) the optimal operational, lowest level of the reservoir, if a non - negligible subsurface storage turns out to be feasible to utilize.

The factors that normally lead to a neglect of subsurface storage, and not to be calculated as an additional storage coupled with the beneficial surface storage, are: small fluctuation of reservoir level in operation, groundwater table gradients are relatively steep, effective limestone porosity is very small, and water transmissivity of aquifer is low.

Lakes in Karst Formations and Water Storage

Karst lakes. The four karst lakes extensively studied in Southern Turkey are Egridir, Kovada, Bey$ehir and Sugla (Figure 2). They all leak water in various quantities. The Bey-fehir Lake is the largest body of water. It shows nearly all the karst water problems needing solutions, especially related to water leakage, underwater inflows in wet season, need for an increase of water budget, implementation of special regulating regimes, etc. Similarly, the Egridir Lake closes water underground, either directly to the west into the karst or indirectly through the Kovada Lake. Also, the Sugla Lake loses water in various quantities depending on the lake level.

One of the major water resources problems of these lakes is how to make them impervious or at least to decrease water leakage to quantities that will be economically acceptable. Besides, for most of these karst lakes the precise conditions of leakage, and particularly the quantities leaked as function of hydrological and hydrogeological factors, are not yet well understood.

Dynamics of underground lake inflow and outflow. The dynamics of underground inflows and outflows at the northwestern part of the Beyçehir Lake deserves best investigations, with solutions to keep or even increase the underground inflows into the Lake and to

Specificities of karst water resources 21

decrease the leakage out of the Lake. Figure 13 presents the assumed general scheme of subsurface inflow - outflow dynamics of the Upper Bey§ehir Lake. The Upper Bey§ehir Lake has either a large number of estavelles only, or of estaveiles, ponors and springs intermixed over a large area.

One of the investigative methods of dynamics of inflow and outflow is by studying the cross sections of piezometric level in observations in boreholes. This can be accomplished by drilling 2—3 piezometric boreholes in each of these profiles from the lake shore to the west, as the topography permits. A selection of boreholes at the faults or at the large fissure lines would likely be most productive, expecting to encounter the system of fissures in underground that will reflect accurately the piezometric levels as they change during the year.

The benefits from observations of piezometric levels in boreholes will likely be : (1) determination of time periods of precipitation and snowmelt during which the piezometric levels in underground behind the Lake are above the Lake level, with water flowing into the Lake through estavelles; (2) determination of time periods of no or minimal exchange of water between the karst aquifer (system of channels) and the Lake; (3) determination of

Fig. 13 — Schematic cross section of the northwestern part of the Beyçehir Lake showing the hypothesized dynamics of inflows and outflows (leakage) : (1) leakage (outflow) of water during dry season; (2) inflow of water through estavelles in wet season; (3) schematic piezometric levels during the rainy season; and (4) schematic piezometric levels during the dry season.

time periods of water leakage from the lake into underground; (4) a general assessement of the length of shoreline, and the eventual bottom area of the Lake, through which the exchange of water and water leakage occur between the Lake and the underground; (5) finding how the Lake level affects these processes, if at all;and (6) acquiring experience on how how much water may be coming in or out of the Lake, that would lead to economic solutions to leakage problems, by maximizing the water budget of the Lake through proper technical measures.

22 V. Yevjevich

Besides the study of dynamics of leakage from the Lake, two other studies may be beneficial; (7) an inventory of all swallow holes (underwater or at the Lake rims),estavelles and springs, with eventual instrumentation designed that can be used from boats to find the areas where water is either being lost from the Lake or flows into the Lake; and (8) special studies to design devices (valves) that will permit water under aquifer pressure to enter the Lake in rainy season, but either fully or partially stop the water leakage in dry periods.

Leakages. Studies of directions of underground flows, and springs to which lake water leaks for the four lakes have partially answered the above questions; however, no definite results ara available, The aquifers of the three large springs (Kirkgozler, Olukkoprii, and Dumanh) must be some of the most important receivers of lake water leakages. Therefore, are change in the karst water regimes of these large lakes by various schemes and works must be analyzed in function of repercussions on the present water budgets of their aqui­fers.

Lakes as storage capacities. The most economical way of obtaining large water storage capacities in karst regions is often by making the leaking lakes the impervious or non -leaking storage reservoirs. This is the case especially when conditions exist for : (1) eco­nomical increase of maximum lake levels; (2) feasibility to decrease minimum operational levels; (3) to reduce completely or significantly the water leakage from lakes; and (4) to increase the total water budget of lakes by economically feasible diversions of various types.

The four lakes of Southern Turkey, taken as examples of karst bodies of water in this paper, all offer good conditions, and some already are used as storage capacities (Beyjehir, Egridir), for becoming reservoirs (Sugla, Kovada), with further improvements of their storage capacity roles in water resources developments.

This factor is important in Turkey. The southern flanks and coastal areas of the Taurus Mountain range are rich in water due to precipitation patterns. The north flanks of this range, including large areas of Anatolia (and the fertile closed Konya basin) are in "rain shadow," with relatively small average annual precipitation. Therefore, these large lakes serve now, and may still serve more so in the future, as basic storage capacities for the transfer of surplus waters from southern flanks to northern flanks of the Taurus Mountain range.

Reclamation of Karst Poljes

Karst poljes. Enclosed bottom, mainly flat karst lands with underground water drainage, are called karst poljes. The Southern Turkey has many karst poljes of small, medium and large sizes. The karst areas of the Taurus Mountain range have scarce land resources. Often the karst poljes represent the best agricultural land. Usually, settlements are either at the edges of karst poljes or very close to them.

Most karst poljes of Southern Turkey are inundated by floods during the rainy and snowmelt season. According to how humid this season is, the duration of inundation may be short or long, not only with a fluctuation from year to year of submergence duration but

Specificities of karst water resources 23

also of the maximum flooding levels. To put land to agricultural production early, it has always been a trend among the land owners in karst poljes to press the Government for better drainage conditions of these poljes. The first steps in alleviating inundations consisted most often of cleaning the debris at ponors (swallow holes or sinkhole zones), so that the head losses at their entrances are decreased and swallow capacities increased.

The problem of irrigation in dry seasons is often the next demand. Adding to them the modern water supply for humans and livestock, the local problems of karst poljes become a four - purpose endeavor of flood evacuation, land drainage, irrigation and water supply.

Often most or all the water in the area of karst poljes is either drained away prior to dry season, or it is to be found only in deep layers of karst aquifers. Water of perennial springs and streams at the edges or along the karst poljes have been allocated for irrigation long time ago, with water rights defined by historic claims. For an expanded irrigation or for the completely new irrigational projects, the first task is to locate the potential water sources for irrigation of karst poljes.

Sources of water for karst poljes. The primary sources of water for karst poljes, apart from perennial streams and springs are: (1) groundwater in pervious layers that are deposited in poljes or at their rims; (2) karst aquifers beneath or in close vicinity of poljes; (3) polders (enclosed storage ponds) built within the karst polje, especially when located over the impervious layers of central or lower parts of karst poljes, that can be created by dikes, and filled with water during the wet season (often the inundation submerges poljes and thus fills the polders); (4) storage of water in impervious reservoirs either built over the impervous parts of the polje or in valleys in its vicinity; and (5) pumping water from perennial sources of water, that are at elevations and distances for an economical water pumping and conveyance to the polje. The rainwater collecting surfaces artifically made impervious, with the connected storage tanks are basically used only for water supply of villages and livestock.

Example of Eynif Polje. The Eynif Polje in the Manavgat River basin, 35 kms straight north from the town of Manavgat, has been investigated for its karst hydrogeology, hydrology and water resources, as a pilot case.

The Polje is inundated in wet seasons. Precipitation is about 1350 mm per year. Floodings last most of the wet season and water is drained away during the first part of dry season. Little time is available for cultivation and a full growing season, so the land is mostly used as pasture for livestock. The geology and topography of the polje is given in Figure 14. Both its northern and its southern parts are drained through sink zones and swallow holes.

The Eynif Polje, with the long axis in the north - south direction, is covered by alluvium. Grain sizes in alluvium in the northern and southern parts of the Polje are coarse pebble and very fine in its central part. The area covered by alluvium reaches 30 meters. The layers of coarse sands and pebbles have interstitial water. Since a large portion of the alluvium is clayey, it is impervious. The alluvium is not considered as an aquifer.

24 V. Yevjevich

KARST HWROCEOUXIAL MAP OF THE EYNIF POLJE

ig. 14 - Geological and hydrogeological map of the Eynif Polje and its surroundings (after Atalay and Baltan, 1979).

Technology for investigation and solution of water problems of karst poljes. Several structural geological topologies of karst poljes can be distinguished in the Taurus Mountain range of Southern Turkey. These poljes can be classified into types by various criteria. This is a good method of transfer of knowledge from one polje to another. It is likely that these geological structural types of poljes (say one - fault graben,grabens of two parallel faults, a sequence of faults, etc.) may be found feasible to classify karst poljes, because the same basic geological lithology, similar and repetitive orogenic movements of folding, overthrusting and faulting, and the sequences of pervious, semi -pervious and impervious formations, all together must have produced hydrogeologically similar types of karst poljes. The classification of karst poljes according to various criteria is a subject that deserves attention. It will have many practical implications, much beyond a simple transfer of inform­ation and technical solutions.

Specificities of karst water resources 25

The basic flood control technology used in karst poljes of Southern Turkey consisted of three alternatives : (a) cleaning of swallow holes so as to maintain their swallow capacity throughout the flood season (Kestel Polje); (b) drilling of flood control tunnels between the karst poljes and the nearby lower valley and rivers (diversion tunnel to Kovanlik area close to the Antalya travertine plateau); and (c) construction of flood control reservoirs (Onaç near Bucak). These three alternatives will continue to be major approaches in the future. The fourth alternative way may include the flood water recharge over highly pervious limestones, by diverting surplus waters over the sinkholes areas in the watersheds of karst poljes.

After flood control and related drainage, the second most important water resources problem of karst poljes in Southern Turkey is the utilization of the alluvial and karst aquifers, the storage of water in reservoirs, existing lakes and eventual polder ponds. Technologies of investigation, planning, design and construction are already available.

Conclusions

Karst water resources are usually very specific in the sense of their occurrence, various karst phenomena involved, and technologies used to solve various problems. Usually investigations are costly, prolonged and very specific, representing a relatively much larger percentage of the total cost of any significant water resources project. Experienced profess­ionals have often failed in karst areas, basically by neglecting these specificities and the need of time and means to investigate thoroughly the karst water problems, and to find appropriate, economically feasible solutions.

This paper has stressed basically the applied side of karst hydrogeology, hydrology and water resources, by using some of the most characteristic features of karst phenomena, particularly those of karst springs and aquifers, coastal aquifers and coastal and submarine springs, building of reservoir storage capacities, using lakes in karst terrains to augment water budget and store water, and finding appropriate solutions for versatile water problems in karst poljes.

REFERENCES

Eroskay, S. Okay and Giiltekin Gunay, 1979, Tecto - genetic classification and hydro-geological properties of the karst regions in Turkey, paper in proceedings of Internat­ional Seminar on Karst Hydrogeology, Oymapinar (Antalya), Turkey, October 9-19, 1979 (published by DSI, Ankara, Turkey), 41 pages.

Glinay, Giiltekin, 1973. Hydrogeological investigation of Ovacik submarine springs, paper presented at the Second International Symposium on Groundwater, Palermo, Italy, April 28-May3,

Herak, M., and Stringfield, V.T., 1972. Karst, Important Karst Regions of the Northern Hemisphere, Elsevier, New York, 550 pages.

Herak, M., 1977. Tecto - genetic approach to the classification of karst terrains, KRS Jugoslavije (Karst of Yugoslavia), 9/4, pp. 227-238, Zagreb, Yugoslavia.

26 V. Yevjevich

Ozif, Onal, 1979, An outlook on karst hydrology studies in Turkey, paper in proceedings of International Seminar on Karst Hydrogeology, Oymapinar (Antalya), Turkey, October 9-19,1979 (published by DSI, Ankara, Turkey), 11 pages.

United Nations Development Program, (prepared by V. Yevjevich) 1981» Karst Water of Southern Turkey, D.S.I., Ankara, Turkey (in English).

Yevjevich, Vujica (Editor), 1981* Karst Water Research Needs, Water Resources Publications, Littleton (PUB 2841), Colorado 80161.