The impact of re-surfacing groins on hydrodynamics and sediment transport at the Delfland coast

The impact of re-surfacing groins on hydrodynamics and sediment transport at the Delfland coast

Hendriks, A.J.H.

Stive, M.J.F. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

Coastal Engineering

2011-12-09

Objective Due the coastal protection program along the Dutch coast, the groins that first defended the coast against erosion, are now covered under sediment. Due to erosion the covered groins will resurface however. The objective of this study is to investigate the effect of the resurfacing groins on the hydrodynamics and sediment transport. Modeling A schematized model is made to reduce effects due to a complex bathymetry and to get a clear view of the occurring processes. Three profiles are schematized at a suitable location based on the 1990, 2009 and 2010 Jarkus transects. Also a test case is modeled with a constant slope to get a view on the effect that groins have on several hydrodynamic properties and transports. The effects due to the bathymetry and the groin can now be separated. Results From this follows that the groins do not affect the alongshore current velocity significantly when the groins are relatively small, in the order of 50 meters or less. The offshore directed currents are considered more dangerous and are present and increasing with increasing groin length, although they are also small when groins are relatively small. When the groin length increases to 150 meters, both the longshore and the offshore currents become significantly larger. In the test case the increase in alongshore velocity is around 15% compared to small or no groins. The increase in current velocity depends largely on the bathymetry and the position of bars however. The sediment transports decrease quite constantly with increasing groin length when the foreshore has a constant slope, in case of a profile with bars the decrease of transport may not be constant anymore. In the schematized cases the sand transport in 1990 with groins of 140 meter is in the order of 50% smaller than in the 2010 situation without groins. Scour holes can increase the offshore directed transports and velocities, but further research is needed here.

groin
Delfland
re-surfacing
hydrodynamics
sediment transport

http://resolver.tudelft.nl/uuid:ad8ac93d-798e-475a-aade-02974033ce12

Student theses

master thesis

(c) 2011 Hendriks, A.J.H.