Morphodynamics of Ebb-Tidal Deltas
type: CreativeWork
description: The purpose of this study was to learn more about the significant drivers of ebb-tidal delta morphology using observational methods and fundamental physical relationships between forcing conditions and morphological response. Two techniques were adapted in a novel way to study the dynamics of geomorphic features at an ebb-tidal delta. A 5-year long record of video imagery was used to observe a natural mixed-energy ebb-tidal delta in the field. A semi-analytical ebb-jet model, which was coupled to an exploratory morphological model, was developed and used to explore the interactions between tidal currents, waves, and morphology, and to test the sensitivity of morphological development and response to changes in forcing conditions. A detailed video-based observational record was used to identify and track geomorphic features over 5 years at an ebb-tidal delta on the energetic west coast of New Zealand at Raglan by using depth-limited wave-breaking patterns as a proxy for the position of shallow sandbars. Oblique 20-minute averaged time-exposure images were geo-rectified to provide detailed spatial measurements of ebb-tidal delta features such as the terminal lobe, mouth bar, channel margin linear bars (or levees), and swash bars over the 5-year duration. Movements of these features were quantified and related to wave and tidal forcing, including seasonal and interannual trends in wave climate. In general, the low-energy restorative summer waves led to a more cuspate terminal lobe, while in the high-energy erosive winter waves straightened the terminal lobe and moved it further seaward than the long-term average. Movements throughout the delta were intermittent between less active periods, with the fastest swash bar migrations occurring during the transition between seasons, namely winter to spring and summer to autumn. A semi-analytical model for ebbing tidal jet flow was developed based on the balance of momentum between inertia, bed friction, turbulent mixing, and w…
abstract: The purpose of this study was to learn more about the significant drivers of ebb-tidal delta morphology using observational methods and fundamental physical relationships between forcing conditions and morphological response. Two techniques were adapted in a novel way to study the dynamics of geomorphic features at an ebb-tidal delta. A 5-year long record of video imagery was used to observe a natural mixed-energy ebb-tidal delta in the field. A semi-analytical ebb-jet model, which was coupled to an exploratory morphological model, was developed and used to explore the interactions between tidal currents, waves, and morphology, and to test the sensitivity of morphological development and response to changes in forcing conditions. A detailed video-based observational record was used to identify and track geomorphic features over 5 years at an ebb-tidal delta on the energetic west coast of New Zealand at Raglan by using depth-limited wave-breaking patterns as a proxy for the position of shallow sandbars. Oblique 20-minute averaged time-exposure images were geo-rectified to provide detailed spatial measurements of ebb-tidal delta features such as the terminal lobe, mouth bar, channel margin linear bars (or levees), and swash bars over the 5-year duration. Movements of these features were quantified and related to wave and tidal forcing, including seasonal and interannual trends in wave climate. In general, the low-energy restorative summer waves led to a more cuspate terminal lobe, while in the high-energy erosive winter waves straightened the terminal lobe and moved it further seaward than the long-term average. Movements throughout the delta were intermittent between less active periods, with the fastest swash bar migrations occurring during the transition between seasons, namely winter to spring and summer to autumn. A semi-analytical model for ebbing tidal jet flow was developed based on the balance of momentum between inertia, bed friction, turbulent mixing, and w…
author: Harrison, Shawn Robert
keywords: Ebb-tidal delta, jet model, coastal morphodynamics, Raglan, photogrammetry
license: https://researchcommons.waikato.ac.nz/bitstreams/f79e14c1-31d6-41ac-a0d0-129f93a29b96/download
date published: 2015
date modified: 2026-07-24T05:57:55Z
provider: University Waikato
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Waikato