Land loss is quite high, amounting to some 100 km 2 per year during the past decade over the entire delta plain. Although a rising sea level has contributed to this loss, subsidence, wave reworking, and modification by man, causing salt-water intrusion, have been responsible for a high percentage of this total land loss. This newest delta has prograded over a relatively thick sequence of prodelta clays and, as a result of differential sediment loading, has built a relatively thick but laterally restricted deltaic sequence. In contrast, the older Recent deltas, mostly built over shallow bay and shelf deposits, are laterally widespread and relatively thin. This type of pattern normally is associated with extremely low offshore slopes and low wave energy.
Sedimentation rates are relatively low.
The bays receive sediment only during periods of overbank flow associated with floods. The bay fills comprise the most common geomorphic landforms in the active delta. Each bay fill forms initially as a break in a nearby major distributary natural levee during flood stage, gradually increases in flow through successive floods, reaches a peak of maximum deposition, wanes, and becomes inactive. New bay fills are no longer being formed, due to diking by man to maintain flow in the major navigation channels. The circular patterns represent well sites associated with buried salt diapiric intrusions.