If you intend to build near the coastline of a sandy or muddy shore, you should be aware that the position of the coastline is not fixed and is constantly changing. This is due to the dynamic of the coastal morphological processes. If not, you will have to take into account extra costs for protection of the building against erosion . When making a seawater inlet, e.g. for flushing a shrimp pond, you should be aware that a coast is always a dynamic pehenomenon. The inlet should be constructed at a location where there is no excessive erosion or sedimentation.
Erosion can endanger the stability of the inlet, while sedimentation can block the water inlet.
The same is true for an outlet, but an extra complication is water quality. When the outlet is a sewer for municipal or industrial effluent, the sea can be polluted. This can be detrimental to fishery interests or to the bio-diversity in the region, but it can also contribute to coastaol erosion in the long term. This is e.g. the case where coral reefs form a natural protection. These reefs can die because of pollution and lose their protective ability.