  A structure capable of substantially amplifying water waves over a broad
range of frequencies at selected locations is proposed. The structure consists
of a small number of C-shaped cylinders arranged in a line array, with the
cylinder properties graded along the array. Using linear potential-flow theory,
it is shown that the energy carried by a plane incident wave is amplified
within specified cylinders, for wavelengths comparable to the array length, and
for a range of incident directions. Transfer matrix analysis is used to
attribute the large amplifications to excitation of Rayleigh--Bloch waves and
gradual slowing down of their group velocity along the array.
