Parameters which affect the temporal rate coefficient of equilibrium bar volume


Kömürcü M. I. , YÜKSEK Ö., Kankal M., Karasu S.

7th International Conference on the Mediterranean Coastal Environment, MEDCOAST 2005, Kusadasi, Turkey, 25 - 29 October 2005, vol.2, pp.1137-1144 identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 2
  • City: Kusadasi
  • Country: Turkey
  • Page Numbers: pp.1137-1144

Abstract

Coastal profiles are one of the important factors in designing of coastal structures. Accretion (berm) or erosion (bar) profiles may arise depending on wave, sediment and topographic factors. In this study, attention is focused on the growth of a bar profile, especially on growth of bar volume (V) toward equilibrium bar volume (Veq). As a bar grows, it moves offshore and increases in volume to approach an equilibrium size. The equilibrium bar volume, however, is not entirely reached in most cases. In such cases, an objective method for determining equilibrium bar volume becomes very important. Generally, an expression of exponential type is employed in growth problems where an equilibrium state exists. In this expression, the bar volume is assumed to grow toward the equilibrium volume according to V=Veq(1-e -αt) , where t is time and α is an empirical temporal rate coefficient which controls the speed at which equilibrium bar volume is attained. Various studies were performed to relate α to some wave, sediment and beach parameters. In this study, the results of a series of experimental studies, which were carried out to relate α (dependent variable) to deepwater wave height (H), wave period (T), grain size (D) and initial bed slope (m) (independent variables), are presented. Physical model studies were performed at the Hydraulic Laboratory Wave Flume, with the dimensions 30*1.4*1.2 m, in the Civil Engineering Department of the Karadeniz Technical University (KTU), Trabzon. Monochromatic waves with various heights (H varies from 6.5 cm to 30 cm), two periods (T=1.46 and 2.03 sec), four bed material grain size (D=0.18, 0.26, 0.33 and 0.40 mm) and three initial bed slopes (m=1/10, 1/15 and 1/25) were employed. Totally 52 experiments were carried out. The duration of experiments was 10 to 14 hours. By using the experimental results, a non-linear regression analysis was performed between dependent (α) and independent (H, T, D and m) variables and correlation coefficient was found R=0.783. The resultant regression equation implies that, α increases with deepwater wave height, wave period and bed slope; and decreases with grain size. H is the most important parameter and accounts for 75.3 percent of the variation in the data. D, m and T account for 19.9, 2.8 and 2.00 percent of the variation, respectively.