Piers and trestles
Rather long structure with a horizontal deck on series of piles extending perpendicular to the coast into the sea. Serving as a landing place for vessels, as a recreation facility, as a measuring facility for coastal processes or as a part of sand by-pass facility.
The aims to construct piers and trestles are in fact sufficiently mentioned in the preceding definition of this type of structures. Only the possible impact of these structures on the coastal processes needs some discussion. The supporting piles might cause some impact. Especially if the number of piles is rather large and/or with large diameters of the piles, obliquely arriving waves will cause an area with reduced wave heights in the lee of the structure. The sediment transports will be reduced as well; spots with some accretion might occur (in general at both sides since waves will approach from both sides). Especially for measuring piers this might yield a-typical measuring conditions.