Hydrology is how much water. Hydraulics is where it goes and how deep. An H&H model is those two questions in a form a floodplain administrator, a Corps reviewer, or a contractor can review.
Design engineers use H&H modeling for both evaluation of existing conditions in order to inform design, as well as to evaluate a proposed design to assess its effects.
The graphics produced are appealing, but it is not a rendering. It is not a software list. If the model does not inform or change a design, a floodplain management outcome, or a permit, it was a demo.
What we actually run
- Hydrology. Rainfall to runoff: watershed area, soils, land cover, storage, and a storm (or a record). HEC-HMS and similar tools. On a small site this can be a rational or SCS calculation. On a bayou it is a hydrograph.
- Hydraulics. The channel, overbank, structures, and tide or tailwater. HEC-RAS (1D or 2D), culvert and bridge routines, sometimes a storm-sewer model for the pipe network.
- Water quality and coastal when the job is a restoration or an estuary — see the Bayou Auguste hydrodynamic work. That is still a model with a decision attached and a resulting built design, not a paper.
The service line writeup is Civil Engineering Modeling. This page is about what the model is for.
What it is for on a Gulf Coast job
- A no-rise certification or a CLOMR in a floodway.
- Culvert and bridge replacements that cannot raise flooding levels for neighbors.
- Whether a restoration or a levee setback actually drops stages — or just moves them.
- Site stormwater: pond routing, outfall capacity, whether the post-development hydrograph is honest.
- Watershed plans: existing vs future land use, locating where stormwater storage actually helps.
A 2D model is not automatically better. It is better when water leaves the channel and the 1D overbank is a lie. It is worse when you do not have the bathymetry or the mesh is decoration.
What has to be true
Same storm, same method, existing vs proposed. Survey that matches the structures you are claiming. A tailwater that is not a fantasy (tide, downstream constriction, a blocked outfall). Documentation a reviewer can rebuild.
We do not hide a rise in a color flood map and call it resilient. If proposed conditions go up, the model should say so.
How we use it
We pick the simplest model that answers the question, run existing and proposed, and write the memo the permit desk asked for. Sometimes that is a no-rise. Sometimes it is “this pad floods the street; move the outfall.” The modeling service page is the engagement; this is the work.
Cypress Environment & Infrastructure works from Biloxi, Mobile, and Pensacola, throughout the Southeast. Office hours are Monday–Friday, 9 a.m.–5 p.m.
See structural stormwater infrastructure and What is a watershed management plan?.