Mediterranean Marine Science

Mediterranean Marine Science

Mediterranean Marine Science Vol. 18, 2017 Water Exchange through Canal İstanbul and Bosphorus Strait SÖZER A. ORDU University, Fatsa Faculty of Marine Sciences ÖZSOY E. Eurasia Institute of Earth Sciences, Istanbul https://doi.org/10.12681/mms.1877 Copyright © 2017 Mediterranean Marine Science To cite this article: SÖZER, A., & ÖZSOY, E. (2017). Water Exchange through Canal İstanbul and Bosphorus Strait. Mediterranean Marine Science, 18(1), 77-86. doi:https://doi.org/10.12681/mms.1877 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/10/2020 15:19:37 | Research Article Mediterranean Marine Science Indexed in WoS (Web of Science, ISI Thomson) and SCOPUS The journal is available on line at http://www.medit-mar-sc.net DOI: http://dx.doi.org/10.12681/mms.1877 Water Exchange through Canal İstanbul and Bosphorus Strait A. SÖZER1,2 AND E. ÖZSOY2,3 1 Fatsa Faculty of Marine Sciences, Ordu University, Ordu, Turkey 2 Institute of Marine Sciences, Middle East Technical University, Erdemli-Mersin, Turkey 3 Eurasia Institute of Earth Sciences, İstanbul, Turkey Corresponding author: [email protected] Handling Editor: Takvor Soukissian Received: 11 August 2016; Accepted: 8 December 2016; Published on line: 13 February 2017 Abstract The Turkish Straits System (TSS) regulates the transports of water, material and energy between the Black Sea and the Mediterranean Sea. Amidst existing environmental threats to the region surrounding İstanbul, the environmental footprint of the proposed Canal İstanbul project needs to be evaluated through methods of natural science. We take the elementary step to answer the particular problem of coupled strait dynamics by adding the Canal to an existing hydrodynamic model and estimate changes in their common response. Compared to the virtually unmodified exchange flow in the Bosphorus, the flow in the Canal has a weak lower layer current component, contrasted with intense currents at the exit controls at its junction with the Marmara Sea. The upper and lower layer transports through this simplest hypothetical TSS configuration are slightly increased for a given net barotropic flow across the system. The modified regime is expected to have climatological consequences. Keywords: Canal İstanbul, Bosphorus, strait dynamics, exchange flows, hydrodynamic modeling. Introduction ine the coupled behavior of the entire TSS including the straits (Sannino et al., 2015, 2016; Gürses, 2017; Gürses Located at the junction of Asia Minor and Europe, the et al., 2016). Turkish Straits System (TSS) is a natural wonder (Fig. 1a): In 2011, the “Canal İstanbul” project was first an- a complex system consisting of Dardanelles and Bospho- nounced, proposing to build a secondary waterway in rus Straits and Marmara Sea, interconnecting the Black parallel to the existing natural channel of the Bosphorus Sea with the Mediterranean Sea, thereby regulating the ex- Strait, with the declared aim to reduce the congested ma- changes of water and materials between these Seas. High rine traffic in the Bosphorus, but also as part of a plan to population and industrial pressures of the megapolis of develop “New İstanbul”. The pros and cons of the pro- İstanbul, earthquakes, climatic variability and changes un- posed construction have been subjects of active discus- der high local gradients make the TSS an environmentally sion, with a series of implications on marine transport, sensitive region (e.g. Beşiktepe et al., 1994; Gündüz & maritime security, international trade and international Özsoy, 2005; Lionello et al., 2006; Georgievski & Stanev, law regulating the rights of passage through the TSS. 2006; Yanko-Hombach et al., 2006). While some of the declared socio-economical mo- Based on his experimental discovery of the Bosphorus tives behind the Canal have been scrutinized often from exchange flow, Marsigli (1681) put forward the first the- the points of view of economic and political interests, ory of strait dynamics, thereby laying the foundations of possible environmental effects have received little atten- modern ocean science (Defant, 1961). Detailed measure- tion to date. The essential background information focus- ments more than three centuries later have revealed unique ing on the environmental issues relevant to the intended features of the Bosphorus exchange and its influence on Canal have been issued in few reports released by non- the adjacent seas (Ünlüata et al., 1990; Özsoy et al., 1998, profit civic organizations (TEMA, 2014; WWF, 2015), 2001; Gregg et al., 1999, Gregg & Özsoy, 2002; Jarosz et proclaiming an urgent need for baseline studies. al., 2011a,b; Schroeder et al., 2012; Jordà et al., 2016). Despite active debates following the announcement For the past thirty years, a limited number of mod- of the project in 2011, much needed baseline studies of elling studies of the Bosphorus flow have been carried environmental data collection, analyses of the environ- out, with either simplified physics or geometry (Johns mental effects, or the development of engineering design & Oğuz, 1989; Oğuz et al., 1990; Oğuz, 2005; Ilıcak et alternatives to alleviate such effects have not been ad- al., 2009; Maderich & Konstantinov, 2002; Maderich et dressed to date. The details of the channel design, such al., 2015) or utilizing fully three-dimensional solutions as the location, shape and associated development objec- (Öztürk et al., 2012; Sözer, 2013; Sözer & Özsoy, 2016), tives and engineering applications are not yet clear and with recent fine resolution modeling extended to exam- have not been publicly announced. Medit. Mar. Sci., 18/1, 2017, 77-86 77 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/10/2020 15:19:37 | Although questions on environmental effects are an- tween the current situation and the imaginary future case, swerable only by methods of natural sciences, they are especially focusing on the impacts on the fluxes and the amongst the least rationally discussed and objectively structure of currents. evaluated at present. In addition to effects on land eco- A variable resolution rectilinear grid (163*716) of systems, the project would most likely influence the deli- dx=50-200m (cross-channel) and dy=50-325m (along- cate marine ecosystems of the region. Key questions to be channel) is used, while a vertical resolution of dz=0.7- asked are: (1) Would the existing hydrodynamic regime 2.85m is obtained with 35 evenly spaced s-levels. The of the Bosphorus be changed due to the construction of domain is extended into the neighboring seas in the form the Canal? (2) In which way does the newly created re- of artificial rectangular boxes with open boundary condi- gime of the Canal differ from the existing exchange flows tions specified at the ends. High resolution bathymetry of the Straits? (3) Would the water and material fluxes be- data obtained from Gökaşan (2005), those sampled on tween the Black Sea and Mediterranean Seas be perma- board the NATO research vessel NRV “Alliance” (1995- nently changed? (4) What are the expected short-term or 1996) and digitized from maps of the Turkish Navy Of- climate-scale regional impacts on sensitive ecosystems fice of Navigation, Hydrography and Oceanography of the region? (ONHO) have been combined with data from the Gen- With experience gained from modeling the Bospho- eral Bathymetric Chart of the Oceans GEBCO 08 (http:// rus, and based on preliminary and rather vague informa- www.gebco.net) and coastline data from METU-IMS tion available on the path and dimensions of the Canal, (Middle East Technical University, Institute of Marine we have designed a preliminary experiment to investigate Sciences) to construct the model bathymetry, which later the combined response of the system, with the proposed has been minimally smoothed, setting minimum depth of channel functioning simultaneously with the Bosphorus. 25m for shallower regions gently joined with the steep On the other hand, it is very important to mention that interior topography. This setup forms the basis of the the model totally neglects time-dependent hydrodynamic “ONLYBOS” case. For the “DUALBOS” simulations a effects at this stage, as well as the coupling with the ad- second passage is placed between the Black Sea and the jacent shelf regions. In reality, these certainly important Marmara Sea at a distance of ∼9 km from the the Strait, aspects of the system behavior deserve further investiga- to exclude direct interactions of the inflow and outflow tion in the future, towards a better understanding of the patterns of the individual Straits. This second channel has long-term environmental consequences of the project. a constant depth of 25m and a constant width of 150m For this preliminary evaluation, we assumed the simplest allowing three grid points across the channel with grid straight channel configuration, immediately to start ad- resolution of 50m, as shown in Figure 1. dressing the above questions, in particular items (1-3). Four simulations are performed (Table 1), repre- The model setup is described in Section 2, and results senting various cases of uniform and stratified reservoir and conclusions are provided respectively in sections 3 conditions under moderate (300km3/yr ≈ 9460 m3/s) to and 4. low (175km3/yr ≈ 5420 m3/s) values of barotropic flux, respectively corresponding to those estimated by Ünlüata Model setup et al. (1990) and typically observed during the September 1994 measurements of Gregg & Özsoy (2002). The modeling approach used in this study is based on Simulations with uniform

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