Piers and trestles are rather long structures with a horizontal deck on a series of piles extending perpendicular to the coast into the sea (see Fig. 10.20). These structures serve as a landing place for vessels, as a recreation facility, as a measuring facility for coastal processes or as a part of a sand bypass facility.
The supporting piles might impact the adjacent coast. Especially if a large number of large diameter piles have been applied, obliquely arriving waves will cause in the lee of the rows of piles an area with reduced wave heights. The sediment transports may be reduced as well; spots with some accretion might occur (in general at both sides since waves will approach from both sides). In this way a measuring pier creates atypical measuring conditions.