A novel method for sampling the suspended sediment load in the tidal environment using bi-directional time-integrated mass-flux sediment (TIMS) samplers

• Published in: Estuarine, coastal and shelf science Vol. 199; pp. 14 - 24
• Main Authors: Elliott, Emily A., Monbureau, Elaine, Walters, Glenn W., Elliott, Mark A., McKee, Brent A., Rodriguez, Antonio B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 05.12.2017
• Subjects: Core sound; Estuarine dynamics; North Carolina; Sediment analysis; Sediment samplers; Sediment traps; Suspended sediment load; North Carolina; SS; PS; Estuarine dynamics; Suspended sediment load; Sediment traps; Core sound; SSL; Sediment samplers; Sediment analysis; OD; ID; TIMS; PIV; PVC
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2017.08.029

Identifying the source and abundance of sediment transported within tidal creeks is essential for studying the connectivity between coastal watersheds and estuaries. The fine-grained suspended sediment load (SSL) makes up a substantial portion of the total sediment load carried within an estuarine system and efficient sampling of the SSL is critical to our understanding of nutrient and contaminant transport, anthropogenic influence, and the effects of climate. Unfortunately, traditional methods of sampling the SSL, including instantaneous measurements and automatic samplers, can be labor intensive, expensive and often yield insufficient mass for comprehensive geochemical analysis. In estuaries this issue is even more pronounced due to bi-directional tidal flow. This study tests the efficacy of a time-integrated mass sediment sampler (TIMS) design, originally developed for uni-directional flow within the fluvial environment, modified in this work for implementation the tidal environment under bi-directional flow conditions. Our new TIMS design utilizes an ‘L’ shaped outflow tube to prevent backflow, and when deployed in mirrored pairs, each sampler collects sediment uniquely in one direction of tidal flow. Laboratory flume experiments using dye and particle image velocimetry (PIV) were used to characterize the flow within the sampler, specifically, to quantify the settling velocities and identify stagnation points. Further laboratory tests of sediment indicate that bidirectional TIMS capture up to 96% of incoming SSL across a range of flow velocities (0.3–0.6 m s−1). The modified TIMS design was tested in the field at two distinct sampling locations within the tidal zone. Single-time point suspended sediment samples were collected at high and low tide and compared to time-integrated suspended sediment samples collected by the bi-directional TIMS over the same four-day period. Particle-size composition from the bi-directional TIMS were representative of the array of single time point samples, but yielded greater mass, representative of flow and sediment-concentration conditions at the site throughout the deployment period. This work proves the efficacy of the modified bi-directional TIMS design, offering a novel tool for collection of suspended sediment in the tidally-dominated portion of the watershed. [Display omitted] •Suspended sediments dominate the estuarine sediment load.•Suspended sediment sampling is expensive and difficult in tidal, bi-directional flow.•Bi-directional Time Integrated Mass Sediment (TIMS) samplers offer a novel approach.•Design was rigorously tested for flow dynamics and efficiency in laboratory and field.•Bi-directional TIMS design efficacy shown for estuarine suspended sediment sampling.