In wet climates, backswamps and marshes form in the low lands adjacent to the stream channel. As the floodwaters overflow the banks and natural levees, the water spreads out, the velocity drops, and the finer silt and clay settle on top of these marshy areas.
For rivers with more developed floodplains, the floodbasin (or floodplain) between distributary channels can vary from merely having a shallow groundwater table to containing a lacustrine (lake) environment. These areas, characterized by high organic productivity, low rates of sedimentation and shallow groundwater tables, are suitable environments for the deposition of plant debris which often become peat deposits.
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