Hydrology. The water source for these wetlands is provided by frequent floods of short to long duration and ground water tables. Water tables range in depth from above the surface on ponded areas to 2 feet below the surface, with the highest levels occurring during the winter and early spring months. Subsurface water typically moves through the large cracks and between the structural units of the clay soils. These areas often have sandy surface layers near channel banks that are slightly higher and better drained.