To simulate the hydrodynamics of the region the
ADCIRC
(Advance Circulation Model for Coastal Ocean Hydrodynamics) model was selected. ADCIRC
is a system of computer models for solving time-independent, free-surface circulation
and transport problems in two dimensions. It was developed to model tidally and wind-driven
circulation in coastal waters, and for forecasting hurricane storm surge and flooding. It has
been applied extensively to New Orleans, the most severally threatened coastal region in the
country.
Unlike other similar models of the waterways in the metropolitan
region, ADCIRC can represent coastal flooding, showing the extent to which floodwaters reach inland
and then retreat. To make use of this capability, a unique database had to be developed for the
metropolitan region that seamlessly integrates bathymetric and topographic data. Bathymetric data
showing water depths and topological data showing land elevations have been developed for different purposes by different government agencies at different times,
and they are referenced to different vertical datums. Moreover, both the bathymetric and topographic datums themselves have changed over time. Tidal datum levels
change spatially because of spatial changes in tide range, dredging of waterways, and changes in weather conditions, and sea-level rise. Both bathymetric and topographic
data were converted to North American Datum of 1983 (NAD 83). Using data from many different sources available in early 2002. Improved data continues to become available
due to changing terrain and improved technology (e.g. LiDAR) we anticipate
that the combined bathymetric-topographic database will be updated as our
interests expand to larger areas and better data becomes available.
When there is a difference between the modeled and the observed, an
operational model may enact bias correction - future predictions include a
correction offset based on a running average of past observed error.
Our group runs ADCIRC as a research model - when there is error we keep that
error with the aim of understanding its fundamental cause. This reduces the
operational usefulness of our model, but does not silently mask deep rooted
problems. In the long run this will lead to better models, with better
physics, for all.
