Göllerdeki hidrodinamik dengeye sismik salınımların etkisinin araştırılması
Investigation of the effects of seismic waves on hydrodynamic regime of lakes
Yazar: MURAT AKSEL
Danışman: PROF. DR. MEHMET SEDAT KABDAŞLI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kıyı Bilimleri ve Mühendisliği Ana Bilim Dalı / Kıyı Bilimleri ve Mühendisliği Bilim Dalı
Derece: Doktora, 2017
Konu: Mühendislik Bilimleri = Engineering Sciences ; Çevre Mühendisliği = Environmental Engineering ; İnşaat Mühendisliği = Civil Engineering

Özet:
Türkiye coğrafi konumu dolayısıyla önemli depremlerin meydana geldiği bir bölgede yer almaktadır. Son yüz yıl içinde Türkiye'de 15'in üzerinde şiddetli ve tahribatı fazla deprem meydana gelmiştir. Bu tez çalışmasında Türkiye'de ve dünyada meydana gelmiş önemli depremlerin Eğirdir Gölü ve Van Gölü üzerindeki olası etkileri incelenmiştir. Tarihsel olarak çalışılan göller ile ilişkili depremlerin etkileri araştırıldığı gibi dünya deprem literatürü açısından önemli bir deprem olan El-Centro Depremi'nin  (1940) kurgusal olarak Eğirdir Gölü üzerindeki etkisi de incelenmiştir. 
Tez çalışması kapsamında, iki farklı göl sistemi olan Eğirdir Gölü ve Van Gölü örnek çalışma alanı olarak alınmıştır. Göllerin deprem altındaki davranışlarının modellenmesinde Flow-3D programı kullanılmıştır. Van Gölü'nde yakın tarihli meydana gelmiş Ekim ve Kasım 2011 depremlerinin etkilerinin araştırılması için hidrodinamik modelleme çalışması yapılarak üç boyutlu deprem ivme serisi tüm göl üzerine etkitilerek göldeki dinamik değişimler hesaplanmıştır. Bu iki depremde hesaplanan dalga yükseklikleri Van Gölü'nde sürekli ölçüm yapan Devlet Su İşleri göl su seviyesi ölçüm istasyonunun deprem günündeki ölçüm değerleri ile karşılaştırılmış ve değerlerin birbiriyle uyumlu olduğu görülmüştür. Modelleme parametreleri ve kabullerin uygunluğu Van Gölü modelinde kontrol edilerek çalışma alanı olarak daha küçük olan Eğirdir Gölü'nün deprem altındaki davranışı da incelenmiştir. Eğirdir Gölü içinse hem Eğirdir için tarihi önemi olan Dinar Depremi hem de kurgusal olarak El-Centro Depremi'nin gölde meydana getirdiği dinamik etkiler incelenmiş ve karşılaştırılmıştır. Eğirdir Gölü için hazırlanan senaryo çalışmalarında gölün depreme tepkisinin daha iyi anlaşılması için Dinar ve El-Centro depremlerinin sadece Doğu-Batı, sadece Kuzey-Güney ve üç boyutlu deprem ivmeleri farklı farklı senaryolarda tek olarak göl kütlesine etkitilmiştir. 
Tüm modelleme sonuçları göl bazında kendi aralarında değerlendirildiği gibi iki farklı boyut ve şekildeki göl için farklı şiddetlerdeki depremlerin etkileri karşılıklı olarak da incelenmiştir. Van ve Eğirdir Gölleri için deprem etkisi altındaki salınım periyodlarının literatürde bulunan doğal salınım periyodlarından daha küçük olduğu hesaplanmıştır. İki göl sisteminde de depremin şiddetine bağlı olarak sığ bölgelerde su baskını riskleri görülmüştür. Eğirdir Gölü için yapılan tek doğrultu analizlerinde gölün kuzey ve güney olmak üzere iki farklı çanak şeklinde depreme tepki gösterdiği bulunmuştur. Van Gölü için göl ortasında kıyı bölgelerinden daha sayhe adı verilen dalgalar hesaplanmasına rağmen bu durum Eğirdir Gölü için tam tersi olarak bulunmuştur. Hem Van Gölü hem Eğirdir Gölü modellleme ve ölçüm sonuçları göstermektedir ki deprem sonrasında gölün büyüklüğü ve depremin şiddetine bağlı olarak depremin meydana getirdiği salınımlar ve bu salınımlar sonucunda meydana gelen sayheler günlerce sürebilmektedir.
Eğirdir Gölü senaryolarında depremin göl hidrodinamiği üzerindeki etkileri araştırıldığı gibi taban ve askı malzemesinin askıya kalkma, taşınma ve çökelme süreçleri de incelenmiştir. Eğirdir Gölü'nde meydana gelebilecek askıda katı madde kirliliğinin çökelme sürecine depremin etki edeceği, çökelme sürecini uzatacağı ve depremin hakim doğrultusunda yayılım yaparak çökelmesine neden olacağı görülmüştür. Eğirdir Gölü tabanında kurgusal olarak tanımlanan silt ve kum karışımı taban malzemesinin Dinar Depremi etkisiyle geçici bir süreliğine askıya kalktığı hesaplanmıştır. Eğirdir Gölü taban malzemesi olarak kurgulanan karakterdeki kum malzemenin bir kısmı deprem sonrasındaki 5 inci saniyede askıya kalkarak kısa süre içinde çökelmektedir. Silt malzeme ise depremin bitiminden dakikalar sonrasında en yüksek askı konsantrasyonu sağlamakta ve uzun bir süre askıda kalmakta olduğu tespit edilmiştir.

Abstract:
Behavior of large water bodies, especially natural and artificial lakes, under earthquake is investigated for various purposes in various research branches. In limnology, earthquake induced waves are investigated for sediment movements and stratigraphic changes at the bottom of the lake and changes in the lake girder due to the coastal depression. About artificial lakes, especially in dam lakes related to ground mechanics, the liquefaction of the ground and possible impacts on the dam structure were hardly examined. Particularly stratified, it is extremely important to examine the lakes where the mixture is less or not at all, and when the lakes are hydrodynamically stable, the hydrodynamic condition changes by seismic effects affect the whole system. The hydrodynamic balance of the present state of the lake is known, and the effects of this hydrodynamic balance to create a sudden and severe depression are not fully predictable and still require research.
Turkey is located in a serious earthquake zone. In the last century, more than 15 severe and demolishing earthquakes have occurred in Turkey. Considering the investigated effects of the major earthquakes in Turkey, numerous research reports and review studies have been conducted. Investigation and evaluation reports on different public institutions and universities as well as independent organizations about earthquakes and their effects has been prepared and presented. Structural damage, loss of life, geological effects caused by earthquake, soil liquefaction and damage due to liquefaction, etc. are main topics in these reports. These issues have been examined in detail in the reports and are continuing to be reviewed.
In this thesis study, possible effects of major earthquakes in Turkey and around the world on Lake Eğirdir and Lake Van were investigated. Dinar Earthquake (1995) for Eğirdir Lake and October and November 2011 Van Earthquakes for Van Lake were studied. In addition to recorded earthquakes in the history which effect the lakes, El-Centro Earthquake (1940), which is an important earthquake in earthquake literature, on Eğirdir Lake is also investigated as fictional.
In this thesis, Eğirdir and Van Lakes which are two different lake systems were taken as case study area. Flow-3D program was used to model the behavior of the lakes under earthquake condition. Earthquake were defined in model as timeserie of earthquake caused additional acceleration. In order to investigate the effects of the October and November 2011 earthquakes in Van Lake, a hydrodynamic modeling study was carried out and three dimensional earthquake acceleration series were applied on the whole lake body to calculate the hydrodynamic response of the lake. Calculated wave heights were compared with measured values at the earthquake day of the State Water Works lake water level monitoring stations which continuously measure in Van Lake. State Water Works monitoring stations in Van Lake are located in Gevas, Tatvan and Van Center port. And aslo in model same coordinates were selected as historical probe points and timeseries of water surface displacement, pressure, velocity etc. parameters were calculated for these points. Measured values by State Water Works were compatible with the calculated ones in historcial probe points in Flow-3D. The highest water surface displacement (seiche wave) was calculated as 0.40 – 0.45 m. In monitoring stations up to 50 cm water surface displacement (seiche wave) was also recorded in the Van Lake on the November Earthquake day in 2011. As a result of modeling, it was calculated the highest change in water surface displacement in the middle of the Van Lake and the lowest was in Erciş Gulf.
Time serie of Van Lake surface area change was calculated within the result of the two scenarios and when the dominant periods of the calculated time series were excluded, it was found that the North - South direction's period was compatible with analytically calculated natural period of the lake. Main oscillation direction in both earthquakes that occurred in Van Lake were calculated as N - S direction.
Behavior of earthquake of Lake Eğirdir examined, which is smaller than Lake Van, after the checking of modeling parameters. For Eğirdir Lake, first the dynamic effects of the Dinar Earthquake, which is both a historic event for Eğirdir was performed. Secondly, the El-Centro Earthquake was examined fictionally and effects of both earthquakes were compared. In the scenario studies prepared for Eğirdir Lake, East-West only, North-South only and three-dimensional earthquake accelerations of Dinar and El-Centro earthquakes were affected to lake body. Different scenarios compared to understand interaction between lake's two seperated basins under oscillation. Dominated acceleration direction of the earthquake that the lakes are under influence is oscillating at a period close to the natural period in that direction. This result has been achieved by evaluating the Eğirdir Lake scenarios.
All modeling results were compared between the lake-based ones, as well as the effects of earthquakes of different magnitudes for two different size lake. For Lake Van and Eğirdir, oscillation period under earthquakes were calculated smaller than the period of natural in the literature. In two lake systems, flood risk were observed in shallow coastal regions. The seiche waves calculated in the middle of Lake Van smaller than coasts but in Lake Eğirdir exact opposite situation was determined. Modelling and survey results shows that, oscillations caused by earthquake and resulting seiches can continue for days long depending on the magnitude of earthquake for both lakes. When earthquakes that affect the closed or semi-closed systems like lakes and gulfs occur, there is a flood risk due to the earthquakes in the coastal areas in these regions. The flood risk area in both lakes were calculated as approximately 1 km2. Considering the surface area of Lake Van, this value is important for Lake Eğirdir with its small size. Under earthquake effect on water body, the vertical velocity in any domain element in the lake is smaller than the velocities in the horizontal direction and the flow condition is transient. In particularly, the vorticity in the horizontal direction is the rotational extent in the vertical direction. These vortisities are high in shallow regions except for the wave break region where the depth is enough and the effect of the vortisity lasts for a long time.
In Lake Eğirdir scenarios, in addition to earthquake effects on lake hydrodynamics, settle, suspended and bed load sediment transport processes were studied with and without earthquake condition. Fate and transport mechanism was effected because of the earthquake induced oscillations. It was calculated that the silt and sand base material which is defined fictionally on the base of Eğirdir Lake is temporarily suspended by Dinar Earthquake. Sand settled after a short period but silt suspended for hours. Comparing the fictional suspended solid contaminated scenario (number 8) with the results of control scenario (number 1) which has no earthquake acceleration effect, suspended solid precipitated to the north with the effect of depression. In the control scenario, any hydrodynamic effect has been deposited in the area where the suspension material is not exposed. Suspended material exposed to three dimensional earthquake acceleration moved northward and formed dunes in E - W direction.
This thesis study provided a better understanding of the processes that were experienced or experienced when the earthquake occurred in Van and Eğirdir Lakes. It is important in the literature to investigate the effects of a shallow lake such as Eğirdir Lake and a deep and large lake, such as Van Lake, under the effects of earthquake. As a result of the calculations, considering the effects of the vertical velocity change due to the earthquake, the effects of the cyclic and base materials, two dimensional hydrodynamic models are found to be inadequate in investigating the behavior of lakes under earthquakes. Taking into account the earthquake-related issues that occur in closed or semi-enclosed systems such as lakes and gulfs, the design and coastal use characteristics of coastal structures should be observed in this regard, especially in deep and large lakes such as Van Lake. The risk of earthquake-induced damage should be determined and closed and semi-closed systems should be determined and plans should be made about these systems. In these systems, ground - coastal surveys of historical sites should be done and the deficiencies in the literature about the subject should be completed.
Investigation of the behavior of semi-enclosed systems under earthquake effects and the investigation of hydrodynamic changes of these systems under earthquake effects are very important in terms of putting the effects on the structural, ecological and morphological systems made in the mentioned areas. Seismicity is an important parameter in the study of the dynamics of closed and / or semi-enclosed systems in the planning of infrastructures and superstructure facilities around the lake and the gulf, such as storms, floods, it is clear that the effects created by meteorological anomalies should be investigated, as well as the immediate and short-term effects that may be caused by earthquakes. Infrastructure facilities, environmental sensitive areas, lakes, coastal facilities, etc. earthquake effects should be investigated for the areas, earthquake impact must be included in the planning process while planning for such areas and facilities.