Regarding the design ground level or elevation of the plant, I still maintain that no consideration for a Tsumami was ever included in the design. The 5.7 metres that Tepco no proudly quote as design basis was an afterthought and result of a 2007 study
The 5.7 metre is necessary to weather waves driven by winds on top of a hurrican storm surge on top of high tide. The level is given as OP+5.7 (OP being uncovered lowest low tide), From these tide tables
we can see already a high tide of 1.48 metres on May 19, so we have 4.2 metres safety left for waves and a hurricane surge.
The foundations of the reactor building are about 5 metres below seal level and have an intricate drainage system to pump the sub soil dry under normal operation, now this sub-soil is contaminated.
From an operational point of view, the NPP should be as low as possible to minimise the energy lost in lifting cooling water, with hindsight, yes the NPP should have been build 50 metres high and a small hydro-electric power station could have been included to recover the potential energy of the cooling waster.
Who designed Fukushima NPP, Ebasco a subsidary of GE so lets not blame the Japanese too much on this issue
The same tsunami dangers also apply to the USA NPP at San Onofre. Historical accounts of The Santa Barbara, California, Earthquakes and Tsunami(s) of December 1812 report of 30 to 35 ft tsunami.