Mersin-Taşucu-Boğsak kaynağı ve dolayının karst hidrojeolojisi

Abstract

ÖZET `Mersin - Taşucu Boğsak Kaynağı ve Dolayının Karst Hidrojeolojisi` konulu bu tez kapsamında, yörenin jeolojisi ve karst hidrojeolojisi incelenmiş, tuzlanmış olan Boğsak karst kaynağı ve akiferinden yararlanabilme olanakları araştırılmıştır. Bölgenin yerleşim yoğunluğu, doğal güzelliği, tarihi ve ekonomik zenginliğinin yanısıra bol ve kullanılabilir suya olan ihtiyaç, konusunda ilk defa yapılan böyle bir araştırmaya gerek göstermiştir. İnceleme alanına ilişkin önceki araştırmaların derlenmesi, meteorolojik analizlerin yapılması, bölgenin hava fotoğrafları ve uydu filimleri ile morfolojik - jeolojik yönden tanınması sonunda, 1/10.000 ölçekli topoğrafik haritalar kullanılarak ayrıntılı bir jeoloji haritası hazırlanmıştır. Kayaç birimleri petrografik - litolojik yönden adlandırılmış ve paleontolojık tanımlama yapılarak bu birimlere yaş verilmiştir. Karst ile morfoloji ve jeoloji arasındaki etkileşimi belirlemek amacıyla, bölgenin drenaj ağı ve yüzey - yeraltı karst şekillerinin boyutsal analizi istatistik yöntemlerle araştırılmıştır. Ayrıca inceleme alanındaki çeşitli karbonat kayaçları üzerinde boşlukluluk. geçirimlilik ve bağıl eriyebilirlik deneyleri yapılmıştır. Sağlanan veriler kayaçların kimyasal analız sonuçları ile desteklenerek inceleme alanındaki yüzey-yeraltı karstını ve karstlaşmayı denetleyenparametreler açığa çıkarılmıştır. Mevcut verilerden hareketle bölgenin l/10.000 ölçekli ayrıntılı bir hidrojeoloji haritası hazırlanmış, ayıtlılan hidrojeolojik ortamların karakteristikleri listelenmiştir. inceleme alanının genel jeolojik ve hidrojeolojik özeliklerini açığa çıkaran bu çalışmalar sonrasında Boğsak vadisinin tuzlanmış yeraltısuyunun seviyesinde ve kimyasal bileşimindeki değişimler, denizsuyu girişiminin boyutları ve tuzlanmanın önlenmesi konuları ele alınarak mevcut yeraltısuyunun kullanılabilirliği değerlendirilmiştir. Araştırmanın bütününden sağlanan veriler, Boğsak akıferinin hidrojeolojik özeliklerinin sayısal olarak saptanmasına temel oluşturmuştur. Sonuçta, Boğsak kaynağının tuzluluğunu gidermeye çalışmaktansa, Boğsak kaynağının karst akiferinden bir sondajla tatlı yeralusuyu alınabileceği ve bunun en ekonomik çözüm olacağı saptanmıştır.

The KARST HYDROGEOLOGY of the MERSIN-TAŞUCU-BOGSAK KARST SPRING and its SURROUNDING AREA SUMMARY In this dissertation, entitled 'The Karst Hydrogeology of the Mersin-Taşucu-Boğsak Karst Spring and its Surrounding Area`, geology and karst hydrogeology of the study area were investigated as a possible way to utilize the Boğsat Spring and its aquifer, which both contain high salt content due to sea-water interference. This dissertation is made of seven chapters. The first chapter describes the purpose of the study and discusses the need for early investigation of the karst springs and aquifers particularly in the dry regions. The second chapter summarizes the geographic condition, morphological properties and meteorological values of the study area. The brief summaries of geological and hydrogeological studies conducted by various researches are given in the third chapter. Geological studies performed in about 60 sq. km area in the vicinity of Boesak Spring is described in the foruth chapter. Also a geological map with 1/1Ö.000 scale, a panel diagram and some cross-sections are given in the same chapter. The analyses of the drainage network of the investigated area, results of the karstification laboratory experiments conducted with the various rock samples from study area, the types of areal karst landforms and their dimensional analyses and finally introduction of hydrogeological media are discussed in the fifth chapter.In the sixth chapter, changes of the groundwater level and chemical composition of water in the Boğsak valley were studied, and the sea-water encroachment and usage of present-day groundwater were investigated. Data gathered during these studies were used as a basic input for numerical determination of the occurence, discharge, water chemistry and utilization and various properties of the Boğsak aquifer in the seventh chapter. The results of these study are summarized as follows. L Geology The Paleozoic (Lower Silürien, Upper Devonien, Lower Carboniferous, Upper Permian), Mesozoic (Jurassic, Upper Cretaceous) and Senozoic (Lower Miocen, Quaternary) sedimentary rock are present in the study area and they are located in the Central Taurus Section of Taurides Tectonic Belt and in the Geyikdağı Secondary Tectonic Complex. Limestones and dolomites with different petrographic properties are the main lithological units. The sandstone-quartzite and claystone-siltstone in alternate sequences also exist in the same area. Approximately 600 m thick autochthonous series deposited in a continental shelf environment. The most distinctive angular unconformities lie between Mesozoic, and Paleozoic and Senozoic units, whereas the widest unconformity is present in Triassic series. The general bedding orientations are £şINW-NE><SSE-SW), while the inclination angles are between 25° and 35°. The joint systems are in (NW-NE)-(SE-SW) direction and are developed between 5fr and 6!r inclination angles. The younger faults cutting all the other discontinuities are in the NNW-SSE direction, whereas the older faults forming the drainage network of highest grade lie alongthe NEE-SWW direction. The only overtnrust is located around the Bağbaşı (Tokmar) area and occurred by the displacement of the Lower Carboniferous onto Jurassic rocks.The important contributions of this dissertation about geology of the study area are summarized at below. a) A detailed geological map with 1/10.000 scale of the study area, about 60 sqJan, the Mersin - Taşucu Boğsak Spring and its surrounding area was prepared. b) It was discovered that the eastern boundary of the Lower Silürien age basement rocks is near the Boğsak village and 10 km further to east of Haciishakh (Ovacık) as opposed to Hacıishaklı (Ovacık) which had ben pointed out by the former researchers. c) The Jurassic and Cretaceous series which are called as `Comprehensive Series` in the Taurus Mountains, were individiually distinguished and seperately mapped according to the petrographic properties and their fossil assemblages or these units in this study contained d) Upper Cretaceous sediments were deposited in the form of carbonate deposition in a quite neritic environment and also apparent sharp clastic materials input does not exist. Because of these two resasons it is suggested that the study area is far from qphiolites, which were located further to N. This observation has a contradiction with the theory postulated that the Troodos ophiolites nappe crosses the Taurus limestone axis from N. e) It is concluded that the young tectonic movements still exist today based on the facts that the Miocen formation is folded structure and it is intercrossed by young faults. 2. Karst Hydrogeology The study area is located in the Taurides Karst Belt and composed of almost all carbonate rocks. Limestones and dolomites identify as soluble rock units, whereas the sandstone - quartzite and claystone - siltstone identify unsoluble rock units. All these rocks contain various closed drainage areas in densely karstificated regions with numerically identified linear and areal properties. Rivers and dry streams of high grade occured depending on the oldest fault systems whereas ones in low grade depending on the youngest fault and fracture systems with transversal jointing character. The effect of bedding orientation on the developments of surface drainage network does not exist. The local water resources are related to the fault springs by seasonally controlled. The different petrographic properties and chemical compositions of the dolomites, and the microsparitic - micritic - sparitic limestones, as found in the relative solubility experiments, which suggest that gives diagenesis took place in the different steps and relatively soluble scale. The primary porosities and permeabilities of these rocks do not practically exist Under the light of all collected data the effect of karstification parameters on the properties of types and dimensions of the karst landforms in the limestones and dolomites have been investigated in the study area, and also, a karstification model is suggested the explanation of development of the karstification in regional scale. The surface karst landforms exhibit various types of `karren`, which are better developed than limestones and less xmdeveloped than dolomites. The underground karst landforms occur as sinkholes and dolines. The sinkholes are located in the cross-sections of the faults, fractures and well developed joint systems that are connected with underground caves following by the direction of young faults. The short axis of the dolines which are both single and combined, is in the NW-SE direction remarking the primary period of the karstification and also the long axis is in the NE-SW direction remarking the developing period of the karstification. The four different hydrogeological media of karst in the study area are recognized at the end of field, laboratory and office studies that were integrated all together. These four media are the permeable - soluble granular media, the local permeable - low soluble rock media, the local impermeable - medium soluble rock media and the impermeable - unsoluble rock media. The most important contributions of this dissertation about the karstic hydrogeology in the study area are summarized at below. a) A detailed karstic hydrogeological map with 1/10.000 scale of the study area, about 60 sq.km, the Mersin - Taşucu Boğsak Spring and its surrounding area was prepared. b) The importance of this investigation is interrelations between the linear and areal properties of the drainage nets and the various types of discontinuites on estimating the orientation of karstification and the direction of groundwater flow have been proved numerically, based on morphological conditions in the karst areas. c) The evaluation of `EC=f(t)` experiments in laboratory on the rock samples collected from the karst areas is defined interms of relative solubility grade of these rock sand clearly explained that regional karstification process cause surface and underground Karst landforms. Thus, the regional relative solubility ranges can be established and the regional development model of karstification can be built up. As a result of synthesis of these studies, it has been realized that in every area studied, the general range of relative solubility and the general karstification model can be established for each karst area and finally for all the karst belt is obtained by taking the combined data into consideration from every karst area. Such an approach will provide numerical data of the karstification properties and the karst in various regions necessary for every kind of engineering works. 3. Boğsak Karst Spring and its Aquifer At the beginning, the changes of salted groundwater level in Boğsak valley and the analysis of water chemistry were evaluated. The mean value of hydroûc inclination of groundwater is 0,04 and it has drowned down 20 cm between 1978-1982 years, approximately. The origin of all groundwater income is related to the limestones and dolomites in the area investigated. The inequality of ^II<Mg++<NaI+KT in salted groundwater and of Ca >Mg >Na +K in fresh gronudwater are distinctive in this region. Meaningful correlations valid among the measured values of groundwater levels, Q` and EC The reason of salt content in groundwater is seawater encroachment as illustrated with 3 polluted zones in these maps. None of the water resources, except a few wells, are not suitable neither for drinking nor irrigating. All the water resources have incrustive but not aggressive effect on the concrete and metal. xivThe discharge of Boğsak karst spring have been changing due to precipitation and flow taking place in the regional water budged. The regression analyses with least squares have been applied to the decreasing period of spring discharge ana it has been shown that the `Q=f(t)` curve matches the TLSON equation. Also, the changes of EC^ Q` and hardness values of spring water, and the values of precipitation and discharge have been examined depending on time and an apparent delay in ionic values, that must be minimum on maximum discharge, have been observed. This delay is explained by considering displacement of salty water placed in the aquifer pores by an instantaneous precipitation water. Boğsak karst spring has been discharging a karst aquifer in the type of confined character in general. The thickness of this karst aquifer is 170 m at the spring point The lowest 70 m section shows a poor aquifer character and consists of local impermeable levels. This aquifer does not have a continuous ground drainage area. The aquifer consists of many closed underground drainage areas (bowls; at different elevations and drains the water to only one neighbouring drainage area from only one point. The underground drainage lines lie in NW-SE direction in short distances and NE-SW direction in long distances in general. The maximum and minimum values of the coefficent of transmissibflity (T), permeability (K) and storage (S) of the aquifer were determined from the maximum and minimum values of the discharge of Boğsak karst spring and also the flow value in the regional water budged. Based on this determination, the underground drainage area of the aquifer was estimated. The total, static and dynamic reserves of the groundwater m aquifer have been calculated from the hydraulic parameters and the dimensional properties of the aquifer. Based on these facts, it is concluded that trying to prevent the encroachment of seawater to the spring will be unsuccesfull and uneconomic in general. Therefore, leaving the spring in its own flow condition is useful only in January and February, when it has maximum discharges and discharging the fresh water by a possible production well located at 1 km distance on SW of the spring with 250-300 m depth is probably the most economical and realistic solution. The important contributions of this dissertation is to cover the investigation of the karst spring and the aquifer of Boğsak, or a spring and an aquifer in general, are summarized at below. a) In the coastal aquifers salted by seawater such as Boğsak Spring, the saltation zones can be identified by using the limit values of Q` content based on TS 266 and obtained from the isochlorium map showing the encroachment direction and the grade of pollution. Thus, a practical and easily usable way to establish the saltation zones is established. b)An aquifer model possessing many closed underground drainage areas (bowls) taking place at different elevations, which is proposed drains then- water to only one neighbouring underground drainage area from only one point, when the groundwater level of the static reservoir exceeded. This new aquifer model is prepared by hydrogeological sections. Also, it explains both the discharge of the spring and the process of the saltation. This new aquifer model will open new sights into to karstic hydrogeology and the general xvhydrogeologic studies. c) The defiencies of the classical way in the analysis of discharge of a karst spring depending on the time in decreasing period of spring discharge are explained numerically such as shown in the example of the Boğsak karst spring. One of the most important defiencies is violiting assumptions regarding the relations described in the discharge equations. Particularly, in order to avoid the effect of excessive precipitation m winter on the spring discharge, the months with zero excess precipitation in water budged have to be considered in the decreasing period in discharge. Morever, the excessive evaporation and the months with highest consumptions are not to be considered in calculations. In this dissertation, the proposed approach and the classical approach are applied to the discharge in decreasing period Comparasion of the results shows the validity of the approach proposed in this study. xvi