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Flow and Drag in a Seagrass Bed
Author(s) -
Monismith Stephen G.,
Hirsh Heidi,
Batista Natasha,
Francis Holly,
Egan Galen,
Dunbar Robert B.
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014862
Subject(s) - drag , seagrass , drag coefficient , flow (mathematics) , geology , mechanics , canopy , parasitic drag , physics , geography , ecology , archaeology , ecosystem , biology
Abstract We report direct measurement of drag forces due to tidal flow over a submerged seagrass bed in Ngeseksau Reef, Koror State, Republic of Palau. In our study, drag is computed using an array of high‐resolution pressure measurements, from which values of the drag coefficients, C D , referenced to measured depth‐averaged velocities, V , were inferred. Reflecting the fact that seagrass blades deflect in the presence of flow, we find that C D is O(1) when flows are weak and tends toward a value of 0.03 at the highest velocities, behavior that is consistent with existing theory for canopy flows with flexible canopy elements. A limited subset of velocity profiles obey the law of the wall, producing values of shear velocity that, while noisy, broadly agree with values inferred from the pressure measurements.