Measuring sediment accretion in early tidal marsh restoration

John Y. Takekawa; Isa Woo; Nicole D. Athearn; Scott A. Demers; Rachel J. Gardiner; William M. Perry; Neil K. Ganju; Gregory Shellenbarger; David H. Schoellhamer

doi:10.1007/s11273-009-9170-6

USGS · 70199773

Measuring sediment accretion in early tidal marsh restoration

John Y. Takekawa·Isa Woo·Nicole D. Athearn·Scott A. Demers·Rachel J. Gardiner·William M. Perry·Neil K. Ganju·Gregory Shellenbarger·David H. Schoellhamer

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Abstract

Sediment accretion is a critical indicator of initial progress in tidal marsh restoration. However, it is often difficult to measure early deposition rates, because the bottom surface is usually obscured under turbid, tidally-influenced waters. To accurately measure early sediment deposition in marshes, we developed an echosounder system consisting of a specialized acoustic profiler, differential global positioning system unit, and laptop computer mounted on a shallow-draft boat. We conducted a bathymetry at the Tubbs Setback tidal restoration site on San Pablo Bay, California, along north–south transects at 25-m intervals. Horizontal position was recorded within 1 m each second and water depth to 1 cm every 0.05 s. Bottom elevations were adjusted for tidal height with surveyed tide gages. We created detailed bathymetric maps (grid cell size: 12.5 m x 12.5 m) by interpolation with inverse distance weighting. During the third year after restoration, sediment accretion averaged 57.1 ± 1.1 cm and the estimated sediment gain was 132,900 m3. The mean difference between the elevations from the bathymetry system and the 9 sediment pins was 2.0 ± 1.0 cm. The mean difference of the intersection points of east–west and north–south survey transects was 2.1 ± 0.2 cm, which provided a measure of repeatability with changing water levels. Our echosounder system provided accurate and repeatable measurements of sediment accretion of a recently restored tidal wetland, and this system proved to be a viable tool for determining sediment deposition in marshes and assessing early restoration progress.

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John Y. Takekawa, Isa Woo, Nicole D. Athearn, Scott A. Demers, Rachel J. Gardiner, William M. Perry, Neil K. Ganju, Gregory Shellenbarger, David H. Schoellhamer. 2010-02-11. Measuring sediment accretion in early tidal marsh restoration. https://doi.org/10.1007/s11273-009-9170-6

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