Residual water level in design of harbour structures is decided with standard based on experience.
　Filed observation of residual water level of quay-walls (gravity-type, sheet pile, cellulor bulkhead-type, etc) was done to get a rasional standard of residual water level.
　From this observation some results are gotton;
1.Present design standard value gives safty value in case of sheet pile quay-wall, and safty (at first) or unsafty value (becoming in time) in case of gravity-type quay-wall.
2.Permeability of quay-wall is cleared.