The influence of neap–spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

Abstract

Sediment flux in marsh tidal creeks is commonly used to gauge sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended‐sediment concentration (SSC), velocity and depth were measured near the mouths of two tidal creeks during three 6‐ to 10‐week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally averaged suspended‐sediment flux (SSF) in the tidal creeks varied from slightly landward to strongly bayward with increasing tidal energy. SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF for each deployment. During ebb tides following the highest tides, velocities exceeded 1 m s−1 in the narrow tidal creeks, resulting in negative tidally averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally averaged SSF was positive in wavy conditions with moderate tides. Spring tide sediment export at the creek mouth was about twice that at a station 130 m further up the tidal creek. The negative tidally averaged water flux near the creek mouth during spring tides indicates that in the lower marsh some of the water flooding directly across the bay–marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well. Copyright © 2018 John Wiley & Sons, Ltd.

Impact of Vegetation on Lateral Exchanges in a Salt Marsh‐Tidal Creek System

“…In this study, a negative (seaward) suspended sediment flux was identified during the tidal cycle. A similar pattern was also found in tidal creeks in northern San Francisco Bay, even during a storm surge (Lacy et al., 2018). Positive (landward) sediment fluxes mainly occur under wave‐dominated suspension and moderate tidal conditions, producing greater‐than‐average SSC values during the flood tidal period (Green & Hancock, 2012; Lacy et al., 2018; X. Li, Plater, & Leonardi, 2018; Li et al., 2019).…”

“…Coastal salt marshes are characterized by vegetated platforms that are regularly flooded with tidal water delivered through a network of channels (Chirol et al., 2018; Lacy et al., 2018; McOwen et al., 2017; Xie et al., 2018). Vegetation in salt marshes significantly increases the sediment capture efficiency in highly turbid estuarine environments (Field et al., 2012; Larsen, 2019).…”

“…Impulse‐like alternating ebb and flood flows are often observed at the edges of tidal creeks and mudflats (Shi et al., 2017a; Xie et al., 2018); these flows can modify flood‐ebb dominance over a distance, affect the vegetation types, and excite geometrically controlled eddies. Asymmetric flows and eddies vary significantly with salt marsh elevation, geometric shape of the creek, and tidal intensity and phase (Chen et al., 2008; Lacy et al., 2018; Poirier et al., 2017). It is difficult to accurately estimate these transports by either field measurements with limited coverage or by models that do not resolve vegetation.…”

Seasonal Variation in Sediment Delivery Across the Bay‐Marsh Interface of an Estuarine Salt Marsh

“…Based on the marker‐horizon results, we estimate that approximately 24 tons per year of sediment was supplied to the 60 m of marsh landward of the transition zone across the bay‐marsh interface along 200 m of shoreline (the distance between creek mouths), or 120 kg/yr per m of shoreline. Measurements of SSF in Creek D showed 30 to 40 tons of export during the largest spring tides of each season, and approximately 10 tons of import per month during more moderate tides, to the entire Creek D drainage area (Lacy et al, ). These bulk estimates indicate that supply across the bay‐marsh interface cannot be neglected in the sediment budget of the marsh, and provide further evidence that the common practice of basing marsh sediment budgets on fluxes through tidal creeks is insufficient for marshes with extensive wave‐exposed margins (French & Stoddart, ; Temmerman et al, ).…”

“…We assess sediment supply across the bay-marsh interface and its variation with season and wave energy from the difference between flood-and ebb-tide SSC and from spatial gradients in estimated suspended-sediment flux, and compare to accretion measurements. This paper builds on previous work at this site, which investigated wave attenuation at the marsh edge and temporal variation in sediment flux in tidal creeks (Foster-Martinez et al, 2018;Lacy et al, 2018).…”