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2. Objectives

5 research topics were developed by the TIDE project partners:

1. Which factors influence the amplification of the tide in an estuary? How can the tidal amplification in an estuary be stopped or even be reduced?
   These questions are directly related to flood protection along estuaries and measures that could be introduced to improve the safety against flooding.
   
   
2. Higher average flow velocities in an estuary result in less intertidal and shallow water area. This hypothesis looks at the effect of flow on habitat occurrence. The availability of different habitat areas is not only relevant within the hydro-geomorphology study, but is also important for the ecosystem services and bird studies performed within TIDE.
   
   
3. What are the similarities and differences between the estuaries with regard to their suspended sediment loads in relation to their tidal and riverine characteristics? Which factors influence the position of the turbidity maximum?
   A high amount of sediment transport may lead to some important challenges for estuarine management, e.g. with regard to port accessibility. Moreover, suspended sediments play an important role in the primary production which is important for the ecology of estuaries.
   
   
4. What are the differences in residence time in the different estuaries?
   Residence times influence the time that particles in the watercolumn, e.g. sediments, nutrients or phytoplankton, stay in a certain area of an estuary. Residence times are thus not only important for the hydro-geomorphology study but also for the ecology study within TIDE.
   
   
5. What is the impact of increasing tidal range along all estuaries on the tidal marsh ecosystems? Did the increasing high water levels result in increased tidal flooding of the tidal marshes or was vertical sediment accretion in the marshes sufficiently high so that the elevation of the marshes could grow in accordance with the growing high water level? And moreover, if vertical sediment accretion was important, did this result in steepening of the intertidal area and hence in increased landward erosion of the tidal marsh shorelines?

For each topic several relations between different parameters will be investigated for each estuary.

• Topic 1: relation between tidal (HW, LW, tidal range, tidal amplification), geometrical characteristics (width, wetted section, depth) and derived parameters (damping and amplification of the tide).
• Topic 2: relation between habitat occurrence (habitat width), and the horizontal tide (flow velocity) and vertical tide (tidal range)
• Topic 3: relation between salinity, turbidity maximum, and tidal energy.
• Topic 4: relation between residence time, tidal and fresh water characteristics.
• Topic 5: relation between salt marsh characteristics (e.g., increase in platform elevation), hydrodynamics and sediment characteristics.

After a first analysis of the data, research topic 2 and 5 were reformulated. For research topic 2 we did not find any relationship between flow velocities (horizontal tide) and  habitat occurrence. Therefore we additionally related habitat occurrence to tidal damping/amplification (vertical tide).  For research topic 5, historical data on tidal marsh edges are very scare. As a consequence, we related the increase in MHWL only to changes in marsh platform elevation and not to changes in tidal marsh shoreline.

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