Spectral analysis of seabed elevation from the Danish Wadden Sea

Bedforms both reflect and influence shallow water hydrodynamics and sediment dynamics. A correct characterization of their spatial distribution and dimensions is required for the understanding, assessment and prediction of numerous coastal processes. A method to parameterize geometrical characteristics using two-dimensional (2D) spectral analysis is presented and tested on seabed elevation data from the Knudedyb tidal inlet in the Danish Wadden Sea, where large compound bedforms are found. The bathymetric data were divided into 20x20 m areas on which a 2D spectral analysis was applied. The most energetic peak of the 2D spectrum was found and its energy, frequency and direction were calculated. A power-law was fitted to the average of slices taken through the 2D spectrum; its slope and y-intercept were calculated. Using these results the test area was morphologically classified into 4 distinct morphological regions. The most energetic peak and the slope and intercept of the power-law showed high values above the crest of the primary bedforms and scour holes, low values in areas without bedforms, and intermediate values in areas with secondary bedforms. The secondary bedform dimensions and orientations were calculated. An area of 700x700 m was used to determine the characteristics of the primary bedforms. However, they were less distinctively characterized compared to the secondary bedforms due to relatively large variations in their orientations and wavelengths. The method is thus appropriate for morphological classification of the seabed and for bedform characterization, being most efficient in areas characterized by bedforms with regular dimensions and directions.

(Table 1) Mean sizes of Hydrobia ulvae juveniles in the littoral zone of the Chernaya Inlet (Kandalaksha Bay, White Sea) in July-September 1995

Based on observations and experiments carried out within the White Sea silty-sandy littoral zone in 1994-1997 data on biology of development and behavior of Hydrobia ulvae juveniles over water column and in sediments were obtained. Hydrobiid juveniles 0.125-0.150 mm in size appear in plankton during the second half of June and in two to three weeks they precipitate on sediments reaching 0.300-0.350 mm in size. Specific biological features of the White Sea hydrobiids are a short reproductive period and a short period of juvenile growth related to long under-ice time and decelerated warming of shallow waters. Distribution of juvenile individuals of H. ulvae is primarily determined by hydrodynamics and microtopography of the littoral zone. Redistribution of the juveniles permanently takes place, since all size groups of the juveniles are equally subjected to migration. During the first few weeks after settling mortality of juvenile mudsnails is 85%.

Results of a joint U.S.A./U.S.S.R. hydrodynamic and transport modeling project /

"February 1979."

Hydraulics and dynamics of North Inlet, South Carolina, 1975-76 /

"September 1978."

WAVERTF, wave propagation over obstacles and irregular topography : a user's manual /

Includes abstract.

Perry Creek Conduit, Sioux City, Iowa : hydraulic model investigation /

Cover title.

Depth-averaged numerical modeling for curved channels /

Cover title.

A finite element scheme for shock capturing /

At head of title: "In-house Laboratory Independent Research Program."

HIVEL2D : a two-dimensional flow model for high-velocity channels /

At head of title: "Repair, Evaluation, Maintenance, and Rehabilitation Research Program."

A solution for the wave velocity field existing on an underwater portion of an impervious sloping breakwater /

"Contract No. DA-22-079-civeng-63-104."

Evaluation of numerical models for a floating breakwater /

"Monitored by Coastal Engineering Research Center, US Army Engineer Waterways Experiment Station."

Drag on naturally rippled beds under oscillatory flows /

Includes abstract.

Lower Green Bay hydrodynamic and mass transport : numerical model study /

"December 1987."

Basic studies in heat transfer and fluid flow.

"Quarterly progress report".

Oceanographic and meteorological conditions during a ship mooring force study /

"August 1985."