PNNL

Abstract

Many nearshore restoration projects are currently underway at coastal locations where human influence and development have disrupted natural habitat and coastal ecological systems. Objectives of these projects in general are to restore the lost estuarine functions to the tidal marshland. Often these projects are conducted with little understanding of the potential effects of other nearby projects within the ecosystem, and similarly it is easy to neglect the effect of the local project on the larger estuarine scale. In this paper, a modeling study is presented to evaluate the hydrodynamic responses of multiple restoration projects and their cumulative effect in the Snohomish River estuary in Washington, USA. The concept of absolute mean tidal flow is introduced and used to measure the cumulative effect of the proposed restoration projects on the estuarine hydrodynamics. Results show that the hydrodynamic responses due to multiple restoration projects are additive in the estuary and the effect is nonlinear. The hydrodynamic response under restoration condition depends on the sizes of the restoration area and the geometric configuration of the existing river channels. Within a complex braided estuary such as the Snohomish, influence of a specific restoration project is not only experienced locally but is also found to significantly affects tidal flow in all distributary branches within the system.