Development of subaqueous barchanoid‐shaped dunes due to lateral grain size variability in a tidal inlet channel of the Danish Wadden Sea

Abstract

[1] High-resolution bathymetry at centimeter-scale accuracy acquired with a multibeam echo sounder system revealed the existence of barchanoid-shaped large (i.e., length 10-100 m) to very large (i.e., length >100 m) dunes in the Grådyb tidal inlet channel in the Danish Wadden Sea. The development of these dunes is due to an increase in dune celerity from 12 m/yr in the center of the channel to around 30 m/yr at the sides. This increase in dune celerity can be explained by the fact that dune heights decrease from 3.1 m in the center of the channel to 1.4 m at the sides, as a smaller sediment volume has to be moved per unit time for equal dune celerity. Water depth is uniform across the channel. Likewise, high-resolution acoustic Doppler current profiler measurements across the channel showed a uniform distribution of both ebb and flood flow. Thus no correlation between dune dimensions and water depth or flow velocity was established. Instead, high-accuracy bed sampling along the crests of the dunes showed a decrease in mean grain size from 0.63 mm in the center to 0.36 mm at the sides of the channel. The decrease in dune height is ascribed to this decrease in grain size, given that flow depth and flow velocity are uniform across the channel. The lateral decrease in grain size is suggested to result from sorting effects by secondary currents directed from the center toward the sides of the channel in the trough/lee side region of the barchanoid-shaped dunes.

A simple model of bedform migration

“…Kostaschuk and Villard, 1996;Kostaschuk, 2000;Bartholdy et al, 2002;Bartholomä et al, 2004;Bartholdy et al, 2005;Ernstsen et al, 2005Ernstsen et al, , 2006; Ernstsen et al, 2007;Duffy and Hughes-Clarke, 2005;Parsons et al, 2005;Nittrouer et al, 2008) and translating the results of detailed fl ume studies into relevant information for natural scaled conditions have improved considerably (e.g. McLean et al, 1994, Bennett and Best, 1995, McLean et al 1996.…”

Influence of compound bedforms on hydraulic roughness in a tidal environment

“…They commonly present a complex three-dimensional morphology with crestline bifurcations and lateral variations in bedform dimensions, along and across-bedform grain-size variations and the presence of superimposed bedforms (e.g., Ernstsen et al 2005). Due to their large dimensions, these compound bedforms have a strong local influence on the overlying flow; for instance, flow acceleration over the bedform crest with flow separation at the edge and subsequent flow recirculation on the leeward side.…”

Morphological Characteristics and Control Factors of Bedforms in Southern Gyeonggi Bay, Yellow Sea

“…또한 층면구조의 발달을 제어하는 물리적 요인들을 이해하 기 위한 많은 선행연구는 층면구조의 형태가 주로 수심, 입도 그리고 해류(조류)에 의해서 제어됨을 보 고하였다 (Yalin, 1964;McCave, 1971;Southard, 1971;Rubin and McCulloch, 1980;Dalrymple, 1984;Van Rijn, 1984;Aliotta and Perillo, 1987;Ashley, 1990;Dalrymple and Rhodes, 1995;Carling et al, 2000;Bartholdy et al, 2002;Ernstsen et al, 2005;Li and King, 2007). 그러나 자연상태의 층면 구조는 다른 제어요인인 퇴적물 유용도에 의해서 영 향을 받을 수 있고 (Aliotta an Perillo, 1987;Dalrymple and Rhodes, 1995;Carling et al, 2000;Hoekstra et al, 2004), 현재 존재하는 층면구조와 수 리학적 조건이 다른 상태를 보일 수 있기 때문에 제 어 요인들과 층면구조의 형태 사이의 관계가 일정하 게 관측되지 않으며 지역적, 시간적으로 차이를 나타 내고 있다.…”

“…수중사구의 크기와 입도의 상관관계 표층퇴적물의 입도와 수중사구의 크기인 파고와 파 장의 상관관계는 일반적으로 입도가 조립할수록 그 위에 발달한 수중사구의 파장과 파고는 증가하며 반 대로 입도가 세립해질수록 파고와 파장은 감소하여 입도가 수중사구의 크기에 영향을 미친다 (Flemming, 2000;Bartholdy et al, 2002;Ernstsen et al, 2005). (Fig.…”