Even when north winds have flushed virtually all the water off the mud flats one or two miles south of the causeway, Chocolatta Bay, immediately north of the Causeway, retains much of its water, with very few areas of exposed mudflats. In the days before the causeway, we can't imagine such a differential in water levels occuring, as there was nothing to separate the shallow mud flats of the larger bay from the shallow mud flats of Chocolatta. We would also imagine that these open bays might prove to be significant alternate discharge points, and not simply backwaters, during periods of high flow. Maurice James, the corps hydrologist in Mobile, says that its reasonable to assume that high freshwater flows are now retained for longer periods of time throughout the Delta, particularly in semi-impounded areas like Chocolatta Bay. As we will discuss in the next section on sedimentation, these high flows may have once been important erosional and depositional events, depending on where the water maintains its velocity and where it runs slack.
Similar impacts are apparent in Polecat Bay.
The impacts of high freshwater flow velocity erosion, deposition, flushing, water and nutrient exchange are simply no longer reaching these areas in the shadow of the causeway. Of course, freshwater is not actually held in reserve for any great length of time, as it would be behind a larger managed dam, but the rate of discharge and the manner of discharge would almost inevitably affected by such a drastic restriction of the openings, particularly during high-flow seasons. The result is that the remaining open channels function as spillways, carrying water at a higher velocity and in deeper channels than they would have before the causeway was built. The higher velocity part of that equation is assumed, but the deeper channels may be demonstrable. If there is an error in the earlier readings, it was a strangely inconsistent error, as surrounding areas and mid-basin channels seem to have become shallower over the same time period.