Abstract: A local scour depth formula is applied in the calculation of scour depth around a groyne head in a closure work, and the unit discharge (or velocity) around the groyne head is computed by use of the potential flow theory in seepage field. A formula reflecting the stabilization of riprap in a closure work and of groyne head apron is thus deduced. The calculation results of scour depth and stabilization of riprap are consistent with the actual situation.