Preprint Article Version 1 This version is not peer-reviewed

Hydrodynamic and Hydrographic Modeling of Istanbul Strait

Version 1 : Received: 27 August 2019 / Approved: 28 August 2019 / Online: 28 August 2019 (15:23:55 CEST)

How to cite: Koşucu, M.M.; Demirel, M.C.; Kirca, V.O.; Özger, M. Hydrodynamic and Hydrographic Modeling of Istanbul Strait. Preprints 2019, 2019080299 (doi: 10.20944/preprints201908.0299.v1). Koşucu, M.M.; Demirel, M.C.; Kirca, V.O.; Özger, M. Hydrodynamic and Hydrographic Modeling of Istanbul Strait. Preprints 2019, 2019080299 (doi: 10.20944/preprints201908.0299.v1).

Abstract

The aim of this study is to model hydrodynamic processes of the Istanbul Strait with its stratified flow characteristic and calibrate the most important parameters using local and global search algorithms. For that two open boundary conditions are defined, which are in the North and South part of the Strait. Observed bathymetric, hydrographic, meteorological and water level data are used to set up the Delft3D-FLOW model. First, the sensitivities of model parameters on the numerical model outputs are assessed using PEST toolbox. Then, the model is calibrated based on the objective functions focusing on the flowrates of upper and lower layers. The salinity and temperature profiles of the Strait are only used for model validation. The results show that the calibrated model outputs of Istanbul Strait are reliable and consistent with the in-situ measurements. The sensitivity analysis reveals that the Spatial Low-Pass Filter Coefficient, Horizontal Eddy Viscosity, Prandtl-Schmidt Number, Slope in log-log Spectrum and Manning Roughness Coefficient are most sensitive parameters affecting flowrate performance of the model. The agreement between observed salinity profiles and simulated model outputs is promising whereas the match between observed and simulated temperature profiles is weak showing that the model can be improved particularly for simulating the mixing layer.

Subject Areas

Istanbul Strait; stratified flow; gravity driven flow; numerical modelling

Comments (1)

Comment 1
Received: 9 September 2019
The commenter has declared there is no conflict of interests.
Comment: This study mainly suffers from the straightforward application of the numerical model, DELFT3D, without any insight into the basic oceanographic principles of the Bosphorus Strait. Complete dependence on Delft 3D might lead only to erroneous scientific conclusions, as is the case in this study. Herein, the logical thinking is completely overlooked. The following points may shed light for the improvement of the paper.
1-It has surprisingly seen in the paper that the authors applied water level BC at stations Anadolu Kavagı and Pendik in Fig. 1 of their original manuscripts. Water level measurements should be placed offshore, close to the open boundary. However, it is seen that Pendik station is almost on the land. This station might reflect long term variations (like tides). What about the short term effects? Besides, islands just in front of this station might influence the water level fluctuations, which can lead to erroneous predictions. Pendik station should not be applied as boundary condition.
2-No information is given about the sampling rate of the stations. The quality of the measured data is neither checked nor discussed.
3-It is quite obvious that authors did not perform the literature review in detail. The most comprehensive and accurate environmental monitoring system is installed in the Bosphorus between September 2004 and January 2006, in relation to the design and construction requirements of the Bosphorus Tube Crossing Project. (Guler et al., 2006; Yuksel et al., 2008; Aydogan et al., 2010). Yuksel et al., (2008), Ozturk et al., (2012), Erdik et al., (2019) employed this monitoring system, at the northern and southern of Bosphorus, respectively, with 10-min sampling rate. This monitoring system is the most reliable and accurate data system in Bosphorus. Besides, stations are exactly at the northen and southern boundaries of the Bosphorus.
4-The proposed model has some deficiencies. The authors claim that “the calibrated model outputs of Istanbul Strait are reliable and consistent with the in-situ measurements”. My first question is where is the calibration? Do authors really think that the prediction of monthly upper and lower layer discharges satisfy the calibration purposes? Hydrodynamic conditions in Bosphorus vary on a daily basis, driven by meteorological, oceanographic conditions, and hydrologic conditions. Monthly discharge prediction might be applicable to main rivers in the globe but not to the chaotic straits, as is the case with Bosphorus. Please check with Jarosz et. al., (2011) to obtain daily discharges.
5- The prediction capacity of the best model is achieved with R=0.447. I have not seen nor heard any model, which claims to accurately predict discharges with R2=0.20.

References

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Jarosz, E.W., Teague, J., Book, J.W., Besiktepe, S. Observed volume fluxes in the Bosphorus Strait. Geophysical Res Letters, 2011, 38, L21608.
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