City planners, developers, and others have a great interest in using available land. Sometimes that land is close to areas that flood, so precautions need to be taken so the build site is not too close to (or directly in) the potential flood area. Failure to properly plan and delineate a floodway can potentially cause millions of dollars in flood damage as well as potential losses in property values. Hurricanes Harvey and Florence, with their extreme rainfall amounts, are prime example of why floodway delineation is so important.
In addition to the guidance provided by the Federal Emergency Management Agency (FEMA), the new Floodway tool in SMS allows the extents of a floodway area to be more clearly defined. This tool allows planners, developers, and others to run multiple simulations to determine the safest places to build as well as the places which may be most impacted during a significant flooding incident.
To use the Floodway tool in SMS, a project must have a either a Cartesian grid, a 2D mesh, or a 2D scatter set that has simulation result datasets for at least water depth and velocity. Two coverages are also required: a 1D hydraulic centerline coverage and a 1D hydraulic cross section coverage.
The way the Floodway tool works is by calculating how far in from both sides of a river or stream that vertical walls can be placed and raise the center of flow by the targeted maximum rise. FEMA suggests this rise should be no more than 1 foot. These calculations use the input provided by the water depth dataset, the velocity dataset, and the two hydraulic coverages to define the floodway extents along the entire length of the study area.
Once these extents are known, the data can be used when making area planning and development decisions at all levels of government and businesses. You can try out this feature in SMS 13.0 beta today.