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The upper delta plain is the most landward section of a delta, which is a low-lying plain formed by sediments deposited by a river at its mouth. This area begins where a river leaves its valley walls and its channels spread out, forming the apex of the delta. The entire upper delta plain is created by riverine processes and lies above the highest tidal level, meaning it is not influenced by marine actions. Between the river channels, you'll typically find freshwater marshes, swamps, or shallow lakes.12

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