Yalçın Yüksel

Cross-Shore Sorting on a Beach under Wave Action

Abstract Sorting of sediment on a beach occurs when the cross-shore profile consists of graded sediments. Each grain-size fraction within a mixture responds differently to the same hydrodynamic regime. Sorting of sediment under wave action takes several forms. Stratified layers of finer and coarser sediment are formed, depending on wave climate, grain size, and beach slope. Grain size and sorting studies are of great importance in characterizing the dynamic beach environment. Some field data have been reported in the literature. In the present study, the cross-shore distribution of sediments, as well as the corresponding beach profiles, were measured in a wave basin on 1:5 beach slope for regular waves. Eighteen sets of experiments were performed on cross-shore sorting mechanisms using two different sand beds. The sorting of bed material and the formation of armor coats along beach profiles were defined by grain-size distribution and dimensionless parameters in this study. The experiments showed that finer material was deposited on the crest of bar-type beach profiles, but coarser grains accumulated on the foreshore, trough, ridge, and toe sections. Finer materials settled on the foreshore and crest of step-type profiles while coarser grains were deposited on the ridge and toe sections. The effect of the movement of a particular fraction on the sediment transport rate was also studied. Calculated sediment transport, modified to include the effects of sorting, was compared with transport rates measured in the wave basin. This suggested that the results under the experimental conditions were satisfactory for the description of sediment transport in the surf zone using the partial sediment transport mechanism over the beach profiles.

Longshore Sediment Transport—Field Data and Estimations Using Neural Networks, Numerical Model, and Empirical Models

ABSTRACT Ari Güner, H.A.; Yüksel, Y., and Ç evik, E.Ö., 2013. Longshore sediment transport—field data and estimations using neural networks, numerical model, and empirical models. This work suggests an alternative approach, namely, the use of an artificial neural network (ANN), for the estimation of longshore sediment transport (LST). The ANN technique provides a powerful utility for input–output mapping if there is sufficient data and can be useful for modeling processes about which adequate knowledge of physics is limited, such as sediment transport. A feed-forward network was developed to predict the LST from a variety of causative variables. The best network was selected after testing many alternatives. The network was validated by experimental and field data. In addition, the ANN method was applied to the case study area (Karaburun, Turkey), located on the SW coast of the Black Sea. The accuracy of the ANN predictions was evaluated against the measured LST rate at Karaburun and compared with two well-known empirical formulas (CERC formula, Kamphuis formula), and a numerical model (LITPACK). The average, net, annual LST rate for the study area was determined based on the morphological volume differences between the surveys. The volume differences were obtained from the accretion at the secondary breakwater of the harbor located at the western end of the 4-km sandy beach. The harbor acted as a total trap, and the beach surveys were extended to an adequate depth. The measured net LST rate was 72,000 m3/y, and the calculated rates were 370,000, 77,000, 83,000, 85,000, and 80,000 m3/y based on the CERC formula (Ksig  =  0.39), the modified CERC formula (Ksig  =  0.08), the Kamphuis formula, the LITPACK computer program, and the ANN. All methods employed in this study estimated the LST rates well, except the CERC formula. The CERC formula overestimated the LST rate by a factor of five; nevertheless, with the adjustment of the empirical Ksig value (0.39) to 0.08, the fit to the observed data improved significantly. The Kamphuis formula produced results similar to those predicted by the field data. This confirms the use of the Kamphuis formula in conditions of low-wave energy with breaker heights of less than 1 m, which correspond to the study areas wave condition.

An Integrated Approach to Temporal Monitoring of the Shoreline and Basin of Terkos Lake

ABSTRACT Bayram, B.; Seker, D.Z.; Acar, U.; Yuksel, Y.; Guner, H.A.A., and Cetin, I., 2013. An integrated approach to temporal monitoring of the shoreline and basin of Terkos Lake. In this study, the combinatorial shoreline and land-use/cover (LULC) changes in the shoreline and basin of Terkos Lake were examined using Landsat satellite images taken in 1986, 2001, and 2009. Terkos Lake is one of seven freshwater-supplying reservoirs of Istanbul, and its borders are very close to the Black Sea. Terkos Lake is in danger because of the approach of its borders to the Black Sea. Changes in the lakes shoreline have been measured using an algorithm based on a hybrid region growing image-segmentation method. The LULC changes have been monitored using object-oriented image-processing software to provide understanding of the impact of these changes on the shoreline. Overall accuracy of the classification reached 92% for 1986, 94% for 2001, and 93% for 2009. The maximum shoreline change measured was 280 m in 23 years. Also, the obtained shoreline and LULC changes have been integrated into the long-term analysis of wave and wind characteristics and sediment-transport calculations. The calculations have been validated with shoreline changes, which have been automatically extracted from Landsat satellite images. The basic outcomes and proposals have been suggested to deal with uncontrolled human activities in the study area.

3D Numerical Modeling of Stratified Flows: Case Study of the Bosphorus Strait

AbstractThe Bosphorus Strait is a typical example of a narrow sea strait and, in general, has a two-layer flow structure. Driven by the water level difference between the Black Sea (north) and the Sea of Marmara (south), a lighter upper layer flows from north to south. A denser lower layer flow is caused by the density difference between the adjacent seas and flows in the opposite direction. In this study, the three-dimensional (3D) flow structure of the Bosphorus strait was modeled using the MIKE 3 hydrodynamic numerical code. Selecting the drag coefficient (cf), buoyancy parameter (cɛ3), and turbulence Prandtl number (σt) as calibration parameters, the model was calibrated using genetic algorithms with available current measurements at three different depths for one given location. The root-mean-square errors of the calibrated model were calculated to be 0.266, 0.201, and 0.163 m/s at the depths considered, respectively. The model was also validated temporally, for four different time periods and spatia...

Determination of Shoreline Evolution: A Case Study

In the present work, the shoreline changes of a sandy beach in Karaburun, Turkey, are studied by using a numerical simulation model (LITPACK). The work is motivated by the considerable erosion and siltation problems caused a sediment deposition near and inside the harbor entrance which prevented the boat traffic and caused a vital problem for the harbor operations. The study’s scope is two-fold: to help in understanding the dynamics of the beach based on results of the field work and to study the responses of this beach by numerical simulation, utilizing the topographic and sediment field data and measured wave data. The validation and verification of the numerical model was perfomed by RTK-GPS measurements. The results of the numerical simulation concerning the coastline evolution are found to be in agreement with the measurements.