My PhD research is to study microbial water quality at non-point source beaches. We examine the source loading, transport and fate mechanisms of fecal indicator bacteria, particularly enterococci. Previous studies indicated that beach sands are pervasive sources of bacteria but few models have capacity to simulate microbe release from the sediments. We develop a coupled microbe-hydrodynamic-morpholgical model based on XBeach model and also use larger-domain Delft3D simulations to provide boundary conditions for XBeach. We also develop point model using water column microbial balnace and simplified transport and biological processes. This is intended as a handy tool to predict enterococci level, a guideline for local beach managers to issue advisory and to protect human health at recreational beaches.

In the proposed research work, I invest tidal dynamics under a new way, dynamic tidal power, to employ tidal energy.

I am interested in exploring the different processes, both small and large scale that contribute to the exchange of estuarine water with the sea through tidal inlets. Since these systems are so large, a complete characterization using only field data is not feasible. Delft 3D not only allows me to forecast conditions and plan a more targeted field effort, it enables me to assimilate the data we collect and better examine the physics behind the system.

This study focusses on two substantial characteristics of mangroves: sediment trapping and attenuation of waves. Our aim is to study these processes both in the field and through numerical modelling. The field data will provide a sound basis for model calibration and validation. Subsequently, the modelling will allow for a thorough analysis of these processes and of their sensitivity to changes to the system.

We collected data in several coastal mangrove sites along the Andaman coast of Southern Thailand. For half a year, we mapped bottom elevation and vegetation cover, measured flow velocities, water levels and wave heights, and monitored sediment concentrations and deposition rates. Basic analysis of these field data has provided some insights already in the routing of water and sediments and the attenuation of waves in mangroves.

Delft3D will be applied to create a numerical model of one of the field sites in order to simulate tidal-scale hydro- and morphodynamics in this area (the attenuation of waves will be studied in SWAN). The challenge is to create an accurate yet fast model, coping with the highly variable (in space and time) conditions in mangroves. This model will be deployed to study tidal-scale flow routing and sediment deposition in greater detail and to simulate the potential effects of loss of vegetation, sediment deficits and increased exposure.

In the proposed thesis, the complex interaction of hydrodynamics and morphology leading to the evolution of embayed beach environments shall be investigated using a process-based numerical modelling approach. This is addressed primarily from a schematic perspective, as measurements of wave-induced circulation and corresponding short- to medium-term morphological changes are rare for embayed beach environments. In order to obtain measured data, the wave dominated, low energy Tairua and Pauanui beaches in New Zealand, with highest waves occurring during ex-tropical cyclones or mainly swell that is generated by Pacific cyclones, will be monitored for a 9-month period. From this, the influence the single or multiple extreme storm events on the morphological response of the embayment shall be deciphered and compared with average conditions.

This research aims to answer one important question: How do offshore hydrodynamic processes influence the water quality and habitat for biota in the inshore, such as in coastal embayments?

Predicting long-term response of rivers has been a challenging task for researchers of several disciplines during the last decades. Interaction between the bed topography evolution of channels and the dynamics of opposite banks and floodplains affects the morphological response of rivers to external forcing. This morphological response consists of erosion and accretion processes of river bed and banks. Nevertheless, research conducted so far has focused more on changes of bed topography and on the erosion process of river banks rather than on bank accretion even if accretion is a fundamental process leading to the channel width formation. River bank accretion is governed by geologic and climatic characteristics and is a result of the interaction between water flow, sediment dynamics and vegetation; which in turn affects morphology and development of habitats. Meandering rivers exhibit a rather constant and uniform width on the long term. This means that meandering rivers are characterized by a long-term equilibrium between bank retreat at one side and bank advance at the other side. Since their origins in the early 80s, meander migration models consider that the outer bank in meander bends is eroded at a rate driven by the flow, and as a response the depositing bank of the bend migrates at the same rate passively, maintaining a roughly constant width. This PhD research will develop a physics-based bank accretion model that allows analyzing the joint effect of bed topography and opposite banks dynamics in order to find the conditions for the long-term equilibrium between river bank retreat and advance on meandering rivers. The research will take into account vegetation and fine sediment processes, as well as many other processes (alternation of high and low flows etc.), including different temporal and spatial scales to study the process of river bank accretion. To achieve this, within the current research several strategies will be considered: mathematical analysis, numerical modelling, experiments in laboratory, and field campaigns.