A joint research team from Yokohama National University, and University of Tokyo, surveyed the city of Ofunato, in Iwate Prefecture.

Things like fishing gear and remains of boats were found on a cliff.  The only way the stuff could have gotten to the top of the cliff was if the Tsunami was at least 29.6 meters high (97 feet).

The height of the March 11 tsunami varies along the Japanese coast line, because of the shape of the land. The bay at Ofunato is very narrow and would force the wave higher.