ABSTRACT
A river delta is an accumulation of sediment on a coastline adjacent to a river. Deltas can form on any coastline, and recognizing them on satellite images is not always straightforward, especially if the “sediment accumulation” of the delta is small or not easily visible. We defi ne two geomorphic criteria for recognizing deltas. These criteria are chosen because they imply substantial sediment accumulation. First, deltas may have a noticeable depositional protrusion (or bump) that causes deviation from the mean shoreline position and is unambiguously linked to the river (see Fig. 1E for example). The minimum scale of the protrusion is not easy to defi ne, but it should be wider (in a shore-perpendicular direction) than a few multiples of the river width to avoid confusing deltas with prograding river mouths or tie channels that have no delta.[5] The second criterion is clear evidence for a distributary channel network (Fig. 1A-D). Distributary channels are river channels that branch off from a parent channel and do not rejoin before intersecting the coast (Fig. 1B). By their nature, these channels facilitate sediment accumulation as they
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distribute sediment over a broad area. Only one of these criteria is necessary for classifying a geomorphic feature as a delta, and often deltas exhibit both a protrusion and a distributary network (Fig. 1C).
