The hole would fill with water before the system got close to flood stage and once it is full it would stay full, providing no capacity for flood storage. The U.S. Army Corps of Engineers will do that comparison. It does both depending on specific location. This would do nothing to relieve flooding in the basin. Several people shared localized problems they are familiar with.
Some people feel that using an inflatable rubber crest weir is a disaster waiting to happen.
The project is also looking at other ways to raise the height of the dam. It is very accurate where we have observed data to calibrate the model - within a couple of inches. Where we do not have observed data it is not as accurate. It is the best tool we have available. This model does not do flood frequency analysis.