Using small scale morphological features on estuarine tidal flats as indicators for large scale morphological shape and development

Abstract

Intertidal flats and salt marshes can protect hinterland against wave energy and flooding by tides or storm surges. Thus, the development of tidal flats is important to foresee. The presence of specific small scale features could indicate a certain development and large scale morphological shape. The shape is a predictor for development and it is expected to influence small scale feature formation. Tidal flat management could benefit from technological process, e.g. in drones, if these indicators can be used. Hence, the aim of this research is to find indicators and gather sufficient knowledge to make them applicable.

The main research question is: "Can small scale morphological features on estuarine tidal flats be used as indicators for large scale morphological shape and development?”. The main question contains two aspects. The first facet is whether the small scale morphological features are indicators for large scale morphological shape and development. It focuses on detecting indicators. The second part is about gathering knowledge to properly use the indicators. It is investigated which mechanisms explain the found indicator roles of the small scale morphological features. The focus is on the identification of the mechanisms. Two sub-questions can be extracted from the above:
1. Are the small scale morphological features on estuarine tidal flats indicators for large scale morphological shape and development?
2. Which mechanisms explain the found indicator roles of small scale morphological features?

Indicators are detected with the analysis of aerial photographs and elevation measurements at transects in the Eastern and Western Scheldt. New and already in literature known features are identified and classified in this process. The mechanism that form and erase the small scale morphological features and their dependence on large scale morphological shape are investigated to explain the found indicators. The mechanisms are determined in various ways: Two 1D models are created, a field campaign is conducted, (subsequent) aerial photographs are looked into, elevation measurements are analyzed in detail and literature research is done.

Small scale morphological features on estuarine tidal flats can be used as indicators in the Western Scheldt. This research detects and explains features that indicate large scale morphological shape, development, hydrodynamic conditions and ecological activity of an area. However, the applicability of the indicators in other systems should be proven by extending this research to other situations. A specific sequence of small scale morphological feature categories between salt marsh and waterfront, a build-up, has been identified as indicator for convex large scale morphological shape and indirectly for accreting behavior. All the features in the build-up are indicators on their own. Megaripples, seen within build-up, indicate (future) convex profiles. Furthermore, all of the features indicate a certain relative height and slope when they are seen within the build-up. These individual indicator roles are clarified by elaborating on the hydrodynamic conditions that form and erase the features. Therefore, the prevailing conditions can also be determined with the indicators.