Evaluation of ADCPs to estimate Suspended Sediment Transport

LATOSINSKI FRANCISCO GUILLERMO; SZUPIANY RICARDO NICOLÁS; AMSLER MARIO LUIS; PUJOL ALFONSO; GALLEGO MANUEL

Bahía Blanca

Simposio; II Simposio de Métodos Experimentales en Hidráulica - MEH 2011; 2011

Instituto Argentino de Oceanografía (Conicet - UNS)

The standard procedures used for sampling suspended sands in large streams require the vessel to be anchored at a proper number of verticals during a certain period of time. These methods are usually time-consuming, rather expensive, and have a limited spatial resolution. Additionally, a potential risk for the vessel safety exists in navigable rivers. The acoustic Doppler technology applied to measure accurately the water discharge, may be also a tool to have quantitative information on suspended sediment concentrations through the analysis of the backscattering signal strength avoiding several drawbacks implicit in the traditional methods. Though important efforts have been conducted concerning these topics, results obtained so far are not as reliable as the engineering practices require. In this paper correlations between the backscatter intensity of two Acoustics Doppler Currents Profilers (ADCP) (Sontek 1000 kHz and Teledyne RD 1200 kHz) and suspended sand concentrations obtained from classic depth-integrated samplings, are presented and discussed. Samples were taken simultaneously with the ADCP measurements at cross sections in the Colastiné and Paraná rivers between Santa Fe and Paraná cities, Argentina. Depth information from a single-beam echo-sounder and positioning from a DGPS complemented the measurements. The simplified sonar equation was used to correct the backscatter signal data for the effects of geometric spreading and absorption. The resulting correlations compared fairly well with the theoretical straight line slopes suggested by the equipments manufacturers. It was concluded that the similarity between the suspended sand sizes in the Paraná River and the type of particles which present maximum sensitivity to the backscatter intensity according to the inherent characteristics of the ADCP equipments used in this case, is a crucial issue to explain the consistency of results. Finally, a comparison of suspended bed sediment transport across a section at the Colastiné river computed from the data of the two ADCPs data and from the suspended bed sediment sampler, is presented.