Multibeam Bathymetric Investigations of the Morphology and Associated Bedforms, Sulina Channel, Danube Delta

Abstract

In the Danube Delta, on the Sulina branch, the morphology, sediment, and bedform characteristics were investigated. Three-dimensional (3D) bathymetry, flow velocity, suspended-load concentration, and liquid and solid discharge data were acquired throughout several cross sections along the Sulina channel, in order to investigate the distribution of water and sediment discharges and their influence against the river bed. A single observation (in February 2007) was made regarding the geometry, sediment composition, and hydraulic conditions under which the dunes grew and degenerated. The investigation focuses here mostly on the geometrical parameters of these bedforms, such as height, length, as well as grain size characteristic of the sediment and water dynamics. Based on in-site measurements, different hydraulic parameters were calculated, such as bed shear stresses and Reynolds number. During the field campaign, the measured water mean velocity was from v = 0.22–1.13 m∙s−1. At the same time, the measured range of shear stresses within the dune field formation was from τ0 = 2.86 N·m−2 (on the cutoffs) to 8.62 N·m−2 (on the main channel). It was found that the correlation between height (H) and length (L) of the Sulina branch dunes describes the formula: H = 0.093L0.5268. The bedforms of the Sulina channel are, in general, developed in fine sand (D50 between 0.06 and 0.35 mm).