  We investigate symmetry-protected topological water waves within a
strategically engineered square lattice system. Thus far, symmetry-protected
topological modes in hexagonal systems have primarily been studied in
electromagnetism and acoustics, i.e. dispersionless media. Herein, we show
experimentally how crucial geometrical properties of square structures allow
for topological transport that is ordinarily forbidden within conventional
hexagonal structures. We perform numerical simulations that take into account
the inherent dispersion within water waves and devise a topological insulator
that supports symmetry-protected transport along the domain walls. Our
measurements, viewed with a high-speed camera under stroboscopic illumination,
unambiguously demonstrate the valley-locked transport of water waves within a
non-hexagonal structure. Due to the tunability of the energy's directionality
by geometry, our results could be used for developing highly-efficient energy
harvesters, filters and beam-splitters within dispersive media.
