See Coastal management. Oosterscheldekering sea wall, the Netherlands. ...

Event warning systems

Tsunami

Tsunamis cannot be prevented or precisely predicted, but there are some warning signs of an impending tsunami. Regions with a high risk of tsunamis may use specific warning systems (with sensors) to detect them, and warn the general population before the wave reaches land and to permit evacuation of coastal areas. Insert non-formatted text here For other uses, see Tsunami (disambiguation). ... Wikipedia does not have an article with this exact name. ... It has been suggested that Low coasts mitigation be merged into this article or section. ...

Tsunami warnings for most of the Pacific Ocean are issued by the Pacific Tsunami Warning Center (PTWC), operated by the United States's NOAA in Hawaii. A second NOAA's Tsunami Warning Center is located in Alaska, and issues warnings for the west coast of North America. (http://www.tsunamiready.noaa.gov)

Both of the tsunami warning centers use earthquake information, tide gauges and now a new tool from NOAA - tsunami detection buoys. In late June 2006, a warning system became active for the Indian Ocean (IOTWS). In addition to international warning systems there are regional (or local) warning system centres that use seismic data about nearby earthquakes to determine if there is a possible local threat of a tsunami.

see this picture on Deep-ocean Assessment and Reporting of Tsunamis (DART). Buoys location.

and also at this picture from NOAA

Finally, this image shows the seismic and water level stations of the tsunami Pacific warning system