O. Yagci

Application of the drag force approach to model the flow‐interaction of natural vegetation

Abstract Recent approaches in two and three‐dimensional numerical models have used a drag force term in the momentum equations to model the stem drag imposed by plants which project through a significant amount of the water depth. This approach reduces the ability to subsume under‐represented processes and data uncertainties in the calibration process which are inherent in roughness closures using a bed friction term such as the Mannings n. This paper examines the data uncertainties when applying the drag force approach to flow through natural plants by an a priori determination of the projected area of the plants as a function of height and explores the implications of this relationship on the computed velocity profile. Using eight individual trees of species Salix fragilis, geometric parameters including diameter and volume were measured and the projected area as a function of tree height was determined. Velocity measurements were conducted in the Wienfluss river in Austria and the relationship of drag force as a function of plant height was established for emergent leafless trees. If the velocity profile is fairly constant with plant height it is found that the projected area/plant height relationship may govern the drag force profile. It has been shown that the uniform drag force approach based on a basal or an equivalent diameter results in negligible difference in the computed velocity profile. In both channel cases the uniform approach results in relatively greater velocities in the region close to the bed and lower velocities in the upper region, compared to the non‐uniform approach. This resulted in a relative difference of 150% in the computed bed shear stress between the two approaches.

Alternative placement technique for antifer blocks used on breakwaters

Abstract In this study, a placement technique named as “alternative placement technique” was developed for antifer blocks and the results of its application to a breakwater model were presented. This placement technique was compared with the existing techniques such as the “regular placement technique”, the “irregular placement technique” and the “sloped wall placement technique” by experiments. The comparison was carried out considering armor layer stability, prototype placement, clarity of the placement technique’s definition, armor layer cost, and wave runup. As a result of this investigation the “alternative placement technique” was found to be superior to the other existing placement techniques.

Performance of an inclined thin plate in wave attenuation

ABSTRACT Açanal, L., Loukogeorgaki, E., Yagci, O., Kirca, V.S.O. and Akgül, A., 2013. Performance of an inclined thin plate in wave attenuation In practice, in some cases, tandemly applied pile-mounted horizontal or inclined thin plates emerge as functional coastal structures in terms of diminishing wave height in front of Rubble Mound Breakwaters (RMBs) and consequently, reduce the required armor unit size and RMBs overall weight. In this study, the hydrodynamic performance of an Inclined Thin Plate (ITP) under regular waves is experimentally investigated. The objective of the laboratory experiments is the assessment of the ITPs efficiency in terms of wave attenuation. Various inclination angles in combination with different submergence degree of the structure under various wave conditions are examined. Regarding the examined ITP configurations, three different inclination angles are considered, i.e. 5, 10, and 15 deg as well as a horizontal plate on the free surface. For the inclined configurations, ITP was placed in a manner such that 2/3 and 3/4 of its length was submerged. The findings revealed that the transmission coefficients can be reduced down to 0.2–0.3. The findings revealed that a tandemly applied ITP has great functionality in diminishing the wave height at the seaward side of a RMB. In this way, the overall weight of the RMB and the weight of the armor units of the RMB are markedly reduced, which is highly necessary in cases where the foundation stability is poor.

The effect of an emergent vegetation (i.e. Phragmistes Australis) on wave attenuation and wave kinematics

ABSTRACT Akgul, M.A., Yilmazer, D., Oguz, E., Kabdasli, M.S., Yagci, O., 2013. The effect of an emergent vegetation (i.e. Phragmistes Australis) on wave attenuation and wave kinematics Coastal vegetation acts as a natural barrier at many coastal zones, protecting the landside against wave effects and coastal erosion. It is known that coastal vegetation affects wave properties, and studies regarding this topic have been made in a wide variety, mostly focusing on wave attenuation. In this study, laboratory experiments have been conducted in a wave basin to inspect the effect of an emergent vegetation on wave attenuation, wave transformation and wave kinematics. A blank area is present along the reed field, which enables energy transformation during wave propagation. Three different regular waves have been sent to a natural reed field, and wave heights and kinematics have been measured around the structure. The results indicate that crest-parallel energy transmission takes place as the waves propagate along the reed field, which is boosted at the end of the reed, and the transmission becomes faster on waves with higher wave steepness. Measured water particle velocities have been evaluated to obtain the steady-cyclic and fluctuation components, by which, turbulence intensities in front and at the wake of the reed field have been evaluated. The results indicate that turbulence intensity increases at the mid-depth at the wake of the structure, becoming higher with increasing wave steepness. Thus, one may conclude that energy dissipation takes further place after the end of the reed field due to turbulence.

Discussion of “Depth-Averaged Drag Coefficient for Modeling Flow through Suspended Canopies” by David R. Plew

O. Yagci; U. Turker; and D. Ozkum Associate Professor, Istanbul Technical Univ., Civil Engineering Faculty, Division of Hydraulics, 34469 Maslak, Istanbul, Turkey (corresponding author). E-mail: yagciora@itu.edu.tr Assistant Professor, Eastern Mediterranean Univ., Civil Engineering Dept., Division of Hydraulics, Gazimagusa, North Cyprus, Turkey. Assistant Professor, Near East Univ., Faculty of Pharmacy, Division of Pharmaceutical Botany, Dikmen, Lefkosa, North Cyprus, Turkey.

Wave Damping and Retardance by Emergent Vegeatation

Although in the past great attention has been devoted to coastal stabilization, the effect of aquatic vegetation on wave characteristics (damping and retardance etc) is still not well known. In this context an experimental study was performed in an irregular wave flume to explore the effect of reeds (phragmites australis) on wave damping and retardance. Further for a given vegetated area the effect of wave characteristics (i.e. wave height, wave period and wave steepness) on wave damping and retardance were discussed. Real reeds (phragmites australis) with diameter less than 5 mm were employed throughout the experiments for the emergent case. A dimensionless number was introduced to characterize both the vegetated area magnitude and the effect of the vegetation on wave damping and retardance.