Sediment Transport and the Temporal Stability of the Seafloor in the Hampton-Seabrook Estuary, NH: A Numerical Model Study

TitleSediment Transport and the Temporal Stability of the Seafloor in the Hampton-Seabrook Estuary, NH: A Numerical Model Study
Publication TypeThesis
Authorsvon Krusenstiern, K
Degree and ProgramMaster of Science
Number of Pages68
Date PublishedMay 7
UniversityUniversity of New Hampshire
LocationDurham, NH

Observations of sediment transport pathways and bathymetric change are often difficult to obtain over spatial and temporal scales needed to maintain economic and ecological viability in dynamic coastal and estuarine environments. As a consequence, numerical models have become a useful tool to examine the sediment transport and evolution of inlets, estuaries, and harbors. In this work, sediment transport at the Hampton-Seabrook Estuary (HSE) in southern New Hampshire is simulated using the Coupled Ocean Atmospheric Waves and Sediment Transport (COAWST) modeling framework to assess bathymetric change over a 5-year period from September 2011 to November 2016. Initial bathymetry and sediment grain size distribution are established from observations and smoothed onto a 30 m rectilinear grid that encompasses the entirety of the HSE system and extends two km offshore into the Gulf of Maine. Careful consideration is made to include hardened structures, such as jetties and sub-surface bulkheads, into the model framework. The model is forced with observations of water levels (including subtidal and tidal motions) from a local tide gauge. Field observations of sea surface height and currents are used to validate model hydrodynamics and establish bottom boundary conditions. The verified model predicts bathymetric change in the harbor consistent with observed changes obtained from bathymetric surveys conducted at the beginning and end of the five-year study. Of particular interest is a cut through the middle ground of the flood tidal delta and the filling in of the navigational channel leading to the Seabrook side of the Harbor that is qualitatively well reproduced by the model. In general, the model qualitatively well-predicts the gross 5-year evolution of the flood tidal delta and the channels leading to the upstream rivers suggesting that hydrodynamically-verified numerical models can be used to qualitatively predict depositional and erosional regions over inter-annual time scales at Hampton Harbor.