Investigation of echo sounding parameters for the characterisation of bottom sediments in a sub-tropical reservoir

Abstract

<p>The increasing number of reservoirs around the world today reaches a surface area of around 500,000 km², equaling one third of that of non-artificial surface water bodies. By impounding rivers through the construction of dams, riverine systems and biochemical cycles are disrupted. Different types of transported materials are trapped behind the dams and form layers of sediment. A method to characterise the spatially extensive sediment volumes with an EA 400 echo sounder was tested in the Vossoroca reservoir in the southeast of Brazil, Paraná State. A number of core and grab samples was taken and analysed for a variety of chemical and physical parameters. These data served as ground truthing for the hydro-acoustic assessment of the sediment. Eight hydro-acoustic parameters were derived from the echo signals using the Sonar5-Pro software. The major objective of defining the optimal survey parameters for the echo sounder as well as determining the difference between core and grab samples was reached by correlating the various single parameters and identifying the best combinations. Density and grain size distribution represented the best detectable sediment features with <em>r</em>-values of 0.94 and 0.95. The lower 38 kHz frequency generally had a better performance than the 200 kHz frequency. Results show that core samples reached a significantly higher quality of correlation for sediment characterisation. Additionally, it is was found that shorter pulse lengths yield a better characterisation. The results underline the potential of single beam echo sounders for extensive sediment characterisation. This methodology may be used for future mass balance estimations of large reservoirs.</p>

Acoustic Mapping of Gas Stored in Sediments of Shallow Aquatic Systems Linked to Methane Production and Ebullition Patterns

“…The envelope of the backscatter profile across the sediment-water interface is generally characterized by an increase of the backscatter strength at the sediment surface, reaching a peak amplitude (maximum backscatter), and followed by a decay with increasing depth (Sternlicht and de Moustier, 2003) (see Supplementary Figure S1). Attack is defined as the vertically integrated backscatter strength values occurring over a duration of one pulse length from the bottom detection point (Hilgert et al, 2016) and was used to estimate the organic content in the sediment (see below). The maximum backscatter (named as bottom peak in Sonar5-Pro), is the maximum value (dB) of the backscatter that occurred starting from the detected bottom downward and searched by the software until three transmitted pulse lengths (Balk et al, 2011).…”

Sediment classification in a Brazilian reservoir: Pros and cons of parametric low frequencies

“…The Decay calculated at 6 kHz, also represents a satisfying correlation coefficient with density (Pearson-r=0.61). However, the coefficient is positive contrary to the published literature which states that decay values should have a negative correlation with density (Hilgert et al, 2016). As explained before, we assume the layering of the echogram to be the dominant factor when calculating the acoustic parameters.…”

“…1). For the static profiles, the sediment was ensonifed for a minimum of 30 seconds in order to have a data set with more than 500 samples for each echogram (Hilgert et al, 2016). Hydroacoustic ensonification was followed by sediment sampling.…”

Sediment distribution and accumulation in Lake Naivasha, Kenya over the past 50 years

“…Further, a series of survey lines (transects and tie lines) with 50, 100, 200 m and 2 km spacing were subsequently created in ArcGIS to guide the boat during the survey. The close spacing of 50 m was used at Crescent Island Lake to allow for better detection of steep slopes (Hilgert, Wagner, Kiemle, & Fuchs, ). The predetermined transects and tie lines pattern were maintained during the survey, except where obstructions were encountered (e.g.…”