'De Slufter' is a nature conservation area located in the Northwest of the Dutch Wadden island Texel which is inundated with seawater during storm events. The landward side of De Slufter is a sand dike which is part of the primary coastal defence ring of the island. HHNK, which is responsible for the coastal safety of Texel, currently relocates the dynamic gully in the slufter mouth every time it reaches one of the dune heads (every 5-6 years approximately) because uncontrolled gully migration might widen the slufter mouth. This could lead to more wave attack on the sand dike, possibly affectingthe coastal safety of Texel. Still, HHNK is planning on ceasing the relocations of the gully. The goal of this thesis is to assess the effects on the present and future coastal safety of De Slufter. First, based on a field data analysis of annual topography and bathymetry measurements it is expected that the gully migration is governed by wave-induced longshore transport, curvature-induced secondary flow due to tidal forcing, overwash from the beach flat into the gully during storms and by the distance to the dune heads (which inhibits migration) To investigate the effect of ceasing relocations of the gully on present and future coastal safety a modelling study was performed with XBeach Surfbeat. 15 scenarios were created to assess the effects of different bathymetry and of sea level and bed level rise
Failure was assessed on two failure mechanisms: 'Grensprofiel', which consists of two aspects. A minimum sand dike volume above storm surge level must be available in every transect alongshore in the sand dike. Also, each post-storm sand dike transect must be large enough to contain a legally defined 'limit profile'. The second mechanism is 'Initiation of flooding', which means that failure occurs when at any point landward of the 'Waterstaatswerk' boundary (the outer border of the primary coastal defence) a depth of at least 20 cm is observed. In all present scenarios no failure occurs for a normative 1/3000 year storm. De Slufter is therefore considered 'safe'. Maximum wave heights did not increase significantly for different bathymetry configurations due to the large amount of dissipation occurring in the slufter valley. No overwash or overtopping occurred in any of the modelled scenarios and morphological impact on the sand dike itself was relatively low. Failure does occur for the 1/3000 year storm with a sea level rise of 1.95 m and 3.17 m. Failure does not occur in the middle of the sand dike where the majority of the wave attack happens but in the southwestern and northeastern parts due to inundation over the ridge there (‘Initiation of flooding’). It is expected that the 'tipping point' of De Slufter, which is the sea level rise magnitude beyond which De Slufter does not adhere to safety standards, is at a sea level rise magnitude of 1.70 m.

The main goal of this project is to determine the optimal location for an OTEC installation with a minimum lifespan of 30 years off the coast of Barranquilla and to make an anchor mooring design for the floater on which this installation is located. Bluerise has identified an area near the coast of Barranquilla for which OTEC can be applied. This area is situated within Colombia’s territorial waters (within 12 nautical miles, or 22.2 kilometres), where two locations have been identified by Bluerise: Location 1: 11.2028 latitude, -75.0003 longitude, Location 2: 11.2772 latitude, -74.9208 longitude.

Environmental conditions -
The daily wind direction is NE-ENE. There is no clear extreme wind direction. The daily waves have a dominant Northeast direction while the extreme waves have a dominant Northern direction. The extreme waves are generated far north of Barranquilla by very high wind speeds which explains the relatively high extreme significant wave heights in the area and the relatively low extreme wind speeds. The yearly average (nautical) surface current direction at the two possible floater locations is predominantly south or southeast. The top 20 strongest current speeds in the past few decades have come from the west or southwest however and therefore these are the normative current directions. The environmental conditions are equal for both possible floater locations. A temperature difference of 20_C is reached at warm water intake and cold
water intake depths of 30 and 763 meters, respectively. The depths at which a temperature
difference of 22_C is reached are 36 and 1023 meters (with temperatures of 27 and 5 degrees, respectively). The influence of the Magdalena river and upwelling is concluded to be negligible.

Marine traffic - The two locations with safety zones are located in a traffic-dense area. The area is getting more traffic intense in the upcoming years. However, it will not pose an immediate threat to the operation. As location 2 has slightly less traffic, it would be preferable from a safety point of view.

Seawater intake- and return pipes - Assuming a cold seawater intake temperature of 5C and a warm seawater intake temperature of 27C, the intake pipe lengths become 1023 and 36 meters, respectively. Based on the equation
of state, the mixed water return flow pipe length becomes 130 m. At this depth, the effects of a difference in density between the surrounding seawater and the mixed returned water are minimized. Also, the depth is outside of the euphotic zone which minimizes algae growth. If the intake water is higher than 27 degrees, the discharge temperature will have a higher temperature. Calculations with the Equation of State reveal that the warmer the discharge temperature,
the lower the density of the discharge water is. Whenever the discharge temperature is higher than the output temperatures, less depth is needed in order for the discharge water to be naturally buoyant. As the intake temperature fluctuates throughout the year, it is therefore advised to design the length of the discharge pipe at 120 meters.

Anchor mooring design - The proposed anchor mooring design consists of a spread-moored 4x3 taut mooring system. The lines are composed of three parts: a 50 meter chain connected to the ship, a 1290 meter fibre line part and another 150 meter chain at the end that is connected to the anchor. The floater is positioned in a 58,05 angle with respect to the north in a northeast direction. This ensures comfortable operation during daily conditions and will reduce fatigue build up. The hurricane conditions were found to be governing. The design complies with the basis of design stated in section 5.3 and with the DNV-OS-E301 code and the API Recommended Practice 2SK.