Study of 31 oval, enclosed tidal basins of (including the Trinity - Galveston Bay Complex) a variety of sizes in soft sediments shows approximate dynamic equilibrium, regardless of basin origin, between average width and maximum depth, scour and fill, fetch (width), and wave base to the maximum observed depth of 16.5 feet. On the humid eastern coast, basins are commonly wide, shallow and directly alluviated by rivers. Equation of straight line average where y=depth in feet, and x=width in miles, is y=0.41x+3.0. On the non-humid southwesten coast, basins are proportionately narrower; straight line average is y=x, or a ratio of 1:1. Here, most elongate water bodies have become segemented to oval form by spits, bar, tidal deltas, and washover fans. Alluviation commmonly overcomes disposal in inner segements entered by river, filling them while leaving outer segments in equilibrium. Depths in tidal channel are not used. Water bodies for which data are incomplete, those with very irregular outlines, and unsegmented parts of coastal lagoon are excluded.