Intertidal Multiple Sand Bars in a Low-Energy Environment

The morphology of intertidal multiple sand bars of Okoshiki Beach in Ariake Bay, Japan is examined to provide insight into the factors controlling the bar characteristics in the low wave environment. Cross-shore profiles of intertidal multiple sand bars were measured monthly for $2\text{years}$ from July 2003 to July 2005. Each measured profile is separated into a mean profile and a bar geometry using quadratic polynomial fitting. Superimposed on the mild foreshore $(1∕250)$ are at least seven low height $(0.1–0.6\mathrm{m})$ ridges with an average wavelength of $40\mathrm{m}$ . The sand bar morphology appears to be a permanent feature in both form and position. The bars occur approximately between the mean high and low water levels during neap tides. This bar zone is related to the zone where the tide-induced moving shoreline velocity is largest in the cross-shore. The calculated depth-averaged tidal currents indicate that sediment movement occurs less than 4% of the tidal period of $12.5\mathrm{h}$ . The bed load transport rate estimated from the bar height and migration velocity is on the order of $1\times {10}^{-4}{\mathrm{m}}^2∕\text{day}$ and very small.