Characterizing the Composition of Sand and Mud Suspensions in Coastal and Estuarine Environments Using Combined Optical and Acoustic Measurements

Abstract

Quantifying and characterizing suspended sediment is essential to successful monitoring and management of estuaries and coastal environments. To quantify suspended sediment, optical and acoustic backscatter instruments are often used. Optical backscatter systems are more sensitive to mud particles (< 63µm) and flocs, whereas acoustic Accepted ArticleThis article is protected by copyright. All rights reserved.Confidential manuscript submitted to JGR-Oceans allows us to estimate whether there are more sand or mud particles floating through the water. The relationship between "seeing" and "hearing" can be described in a single number, the sediment composition index (SCI). We successfully tested this approach in laboratory experiments and then applied it to a site on the coast of the Netherlands. This approach gives us a new way to understand environments that are both sandy and muddy.

The Existence and Origin of Multiple Equilibria in Sand‐Mud Sediment Beds

“…We can simplify this to an overall constant mud concentration, regardless of the local mud content in the bed, whereas sand concentrations in the water column would decrease with increasing mud content in the bed. This is supported by the findings of Colosimo et al ( 2020) and Pearson et al (2021), combined with the fact that muddy beds mainly prevail in calm environments. In the next section we test this simplification of the deposition fluxes, for the Wadden Sea and for tidal basins in general, and we explore its relevance for the observed bimodality of p mud in the sediment bed.…”

The Existence and Origin of Multiple Equilibria in Sand‐Mud Sediment Beds

“…We can simplify this to an overall constant mud concentration, regardless of the local mud content in the bed, whereas sand concentrations in the water column would decrease with increasing mud content in the bed. This is supported by the findings of Colosimo et al ( 2020) and Pearson et al (2021), combined with the fact that muddy beds mainly prevail in calm environments. In the next section we test this simplification of the deposition fluxes, for the Wadden Sea and for tidal basins in general, and we explore its relevance for the observed bimodality of p mud in the sediment bed.…”

Estimation of Mud and Sand Fractions and Total Concentration From Coupled Optical‐Acoustic Sensors

“…Our previous study, Pearson et al. (2021) showed that for such cases, in both laboratory and field settings, the functionality and application of SCI‐functions still hold. This is because both optical/acoustic signals altered, but the ratio between them remains constant.…”

“…First, it allows researchers to take advantage of the historical data to acquire new meaningful information, that is, the fraction and concentration of mud/sand in suspension. In long‐term sediment dynamics monitoring, both optical turbidity and acoustic sensors are often used together (Fettweis et al., 2019; Fugate & Friedrichs, 2002; Pearson et al., 2021; Sahin et al., 2017; Voulgaris & Meyers, 2004). However, they are treated as individual measurements and are calibrated separately for different purposes.…”

“…Specifically, at least three, preferably five, water samples from a deployment which covers the spring‐neap tidal cycle should be used to provide detailed data on mud/sand fraction and total mass concentration. For pure mud conditions, one should take water samples at a calm period, for example, minimum wave and current during the neap tide (Pearson et al., 2021). The other samples should be taken at mild and energetic conditions when sand is more likely to be resuspended.…”

Deriving bottom sediment grain size in tidal channels using remote sensing and numerical modeling

“…The integration of remote sensing and numerical modeling for estimating bottom sediment grain size in estuarine environments represents a significant methodological advancement. Traditional in situ sampling techniques, while effective for high‐accuracy grain size measurements, are inherently limited in spatial coverage and temporal frequency (Bale and Morris 1987; Blott et al 2004; Pearson et al 2021). The reliance on point‐based sediment sampling often fails to capture the dynamic nature of sediment transport in tidal systems, where grain size distribution can shift due to seasonal hydrodynamic changes (Agrawal and Pottsmith 2000; Nowacki et al 2015; Xing et al 2012; Yang et al 2008).…”

The Existence and Origin of Multiple Equilibria in Sand‐Mud Sediment Beds

“…We can simplify this to an overall constant mud concentration, regardless of the local mud content in the bed, whereas sand concentrations in the water column would decrease with increasing mud content in the bed. This is supported by the findings of Colosimo et al ( 2020) and Pearson et al (2021), combined with the fact that muddy beds mainly prevail in calm environments. In the next section we test this simplification of the deposition fluxes, for the Wadden Sea and for tidal basins in general, and we explore its relevance for the observed bimodality of p mud in the sediment bed.…”

Estimation of Mud and Sand Fractions and Total Concentration From Coupled Optical‐Acoustic Sensors

“…Our previous study, Pearson et al. (2021) showed that for such cases, in both laboratory and field settings, the functionality and application of SCI‐functions still hold. This is because both optical/acoustic signals altered, but the ratio between them remains constant.…”

“…First, it allows researchers to take advantage of the historical data to acquire new meaningful information, that is, the fraction and concentration of mud/sand in suspension. In long‐term sediment dynamics monitoring, both optical turbidity and acoustic sensors are often used together (Fettweis et al., 2019; Fugate & Friedrichs, 2002; Pearson et al., 2021; Sahin et al., 2017; Voulgaris & Meyers, 2004). However, they are treated as individual measurements and are calibrated separately for different purposes.…”

“…Specifically, at least three, preferably five, water samples from a deployment which covers the spring‐neap tidal cycle should be used to provide detailed data on mud/sand fraction and total mass concentration. For pure mud conditions, one should take water samples at a calm period, for example, minimum wave and current during the neap tide (Pearson et al., 2021). The other samples should be taken at mild and energetic conditions when sand is more likely to be resuspended.…”

Deriving bottom sediment grain size in tidal channels using remote sensing and numerical modeling

“…The integration of remote sensing and numerical modeling for estimating bottom sediment grain size in estuarine environments represents a significant methodological advancement. Traditional in situ sampling techniques, while effective for high‐accuracy grain size measurements, are inherently limited in spatial coverage and temporal frequency (Bale and Morris 1987; Blott et al 2004; Pearson et al 2021). The reliance on point‐based sediment sampling often fails to capture the dynamic nature of sediment transport in tidal systems, where grain size distribution can shift due to seasonal hydrodynamic changes (Agrawal and Pottsmith 2000; Nowacki et al 2015; Xing et al 2012; Yang et al 2008).…”

The Existence and Origin of Multiple Equilibria in Sand‐Mud Sediment Beds

“…We can simplify this to an overall constant mud concentration, regardless of the local mud content in the bed, whereas sand concentrations in the water column would decrease with increasing mud content in the bed. This is supported by the findings of Colosimo et al ( 2020) and Pearson et al (2021), combined with the fact that muddy beds mainly prevail in calm environments. In the next section we test this simplification of the deposition fluxes, for the Wadden Sea and for tidal basins in general, and we explore its relevance for the observed bimodality of p mud in the sediment bed.…”

Estimation of Mud and Sand Fractions and Total Concentration From Coupled Optical‐Acoustic Sensors

“…Our previous study, Pearson et al. (2021) showed that for such cases, in both laboratory and field settings, the functionality and application of SCI‐functions still hold. This is because both optical/acoustic signals altered, but the ratio between them remains constant.…”

“…First, it allows researchers to take advantage of the historical data to acquire new meaningful information, that is, the fraction and concentration of mud/sand in suspension. In long‐term sediment dynamics monitoring, both optical turbidity and acoustic sensors are often used together (Fettweis et al., 2019; Fugate & Friedrichs, 2002; Pearson et al., 2021; Sahin et al., 2017; Voulgaris & Meyers, 2004). However, they are treated as individual measurements and are calibrated separately for different purposes.…”

“…Specifically, at least three, preferably five, water samples from a deployment which covers the spring‐neap tidal cycle should be used to provide detailed data on mud/sand fraction and total mass concentration. For pure mud conditions, one should take water samples at a calm period, for example, minimum wave and current during the neap tide (Pearson et al., 2021). The other samples should be taken at mild and energetic conditions when sand is more likely to be resuspended.…”

Deriving bottom sediment grain size in tidal channels using remote sensing and numerical modeling

“…The integration of remote sensing and numerical modeling for estimating bottom sediment grain size in estuarine environments represents a significant methodological advancement. Traditional in situ sampling techniques, while effective for high‐accuracy grain size measurements, are inherently limited in spatial coverage and temporal frequency (Bale and Morris 1987; Blott et al 2004; Pearson et al 2021). The reliance on point‐based sediment sampling often fails to capture the dynamic nature of sediment transport in tidal systems, where grain size distribution can shift due to seasonal hydrodynamic changes (Agrawal and Pottsmith 2000; Nowacki et al 2015; Xing et al 2012; Yang et al 2008).…”