Numerical investigation of shallow wake behind a patch of rigid emergent vegetation

Abstract

The shallow water flow through and around a patch of rigid emergent vegetation was investigated numerically. The mean flow field and turbulent structures were studied, especially their dependence on the solid volume fraction (SVF) of the patch and the bed friction. Two streamwise velocity scales, U1s at the starting point of the steady wake and U1e at the downstream end of the steady wake, and the length of the steady wake L1 were used to describe the steady wake behind the patch. U1s was found to be related to SVF only. However, U1e and L1 were influenced by both the SVF and the wake stability parameter S. For a sparse patch, U1e was equal to U1s, and L1 decreased with the increase of S. For a mid-dense patch, U1e was always smaller than U1s, and it increased with S and gradually approached U1s. The increase of U1e reduced the lateral velocity difference between the flows inside and outside the wake, which resulted in the increase of L1. For a highly dense patch, U1e and L1 did not increase unless S was larger than a critical value. A new parameter, r, was proposed to represent the development rate of the steady wake. The numerical results showed that r increased monotonously with S for mid-dense patches.