Estimation of suspended sediment concentration in rivers using acoustic methods

Abstract

Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study sitȩ where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings obtained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC measurements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate analysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events. Keywords

Sediment Size Effects in Acoustic Doppler Velocimeter-Derived Estimates of Suspended Sediment Concentration

“…Predictions are derived by empirically relating device output (typically acoustic signal-to-noise ratio or return signal amplitude in counts or decibels) and the SSC of the water [37][38][39][40][41][42]. When an acoustic instrument is calibrated for a water system in which suspended sediment properties display little time dependence, no additional sensor is needed to measure the SSC.…”

“…Although developed to measure water velocities, over the past few decades several studies have demonstrated the successful implementation of these devices to estimate SSC in the field and in the lab [40,41].…”

“…Several researchers have investigated the performance of acoustic Doppler current profilers for the prediction of SSC in various water environments, including coastal environments and rivers [32][33][34][35][36]. Predictions are derived by empirically relating device output (typically acoustic signal-to-noise ratio or return signal amplitude in counts or decibels) and the SSC of the water [37][38][39][40][41][42]. When an acoustic instrument is calibrated for a water system in which suspended sediment properties display little time dependence, no additional sensor is needed to measure the SSC.…”

Observational and Numerical Methods for Quantifying and Modeling of Turbulence in a Stratified Reservoir

“…Elçi et al (2009) andElçi, (2008) discussed sampling of the sediments of Tahtali Reservoir bottom and the water column. Based on these studies, mean diameter of the sediment is assumed as 0.068 mm and sediment density is assumed as 1.65 kg/m 3 in the calculations.…”

Estimation of suspended sediment concentration from turbidity measurements using artificial neural networks

“…Minella et al (2008) assessed the relationship between SSC and turbidity for a small (1.19 km 2 ) rural catchment in southern Brazil, and evaluated two calibration methods by comparing the estimates of SSC obtained from the calibrated turbidity readings with direct measurements obtained using a suspended sediment sampler. Elci et al (2009) improved the methodology for predicting SSC using Acoustic Doppler Velocimeter (ADV) backscatter data in a quasisteady scenario as found in a river or stream. The effects of water temperature and particle size distribution on predictive capability were investigated through measurements conducted in different streams in low flow and flood conditions.…”