Illinois Administrative Code
Title 17 - CONSERVATION
Part 3700 - CONSTRUCTION IN FLOODWAYS OF RIVERS, LAKES AND STREAMS
Section 3700.20 - Definitions
As used in this Part, the words and terms listed shall have the meanings ascribed to them as follows:
"Bridge or Culvert Reconstruction" - The total replacement of an existing bridge or culvert, including substructure and superstructure, on the existing road alignment or on an alignment within 100 feet upstream or downstream of the existing alignment in an urban area, or within 500 feet upstream or downstream of the existing alignment in a rural area.
"Construction" - The placement, erection or reconstruction of any building or structure, any filling or excavation, the installation of any utility, or the storage of any materials. Construction includes, but is not limited to, modifications to an existing building that would increase the building's outside dimensions, channel modifications and enclosures, roads, bridges, culverts, levees, bank protection, walls, fences, and any other man-made activity that would modify the physical features of a floodway with respect to the storage or conveyance of flood waters. Construction does not include normal maintenance and repair activities or farming operations such as discing and plowing.
"Department" - The Illinois Department of Natural Resources.
Floodplain - The land area adjacent to a stream or watercourse with ground surface elevations at or below the 1% annual chance of exceedence (100-year frequency) flood elevation.
"Floodway" The channel of a river, lake or stream and that portion of the floodplain that is needed to store and convey the 1% annual chance of exceedence flood discharge with no more than a 0.1 foot increase in stage due to the loss of flood conveyance and storage. Where floodways have been delineated for regulatory purposes, the mapped lines show the floodway encroachment limits and will be used. For other areas, the entire floodplain shall be considered to be in the floodway unless an analysis is approved by the Department demonstrating that a project site is outside of the floodway. The Department will review floodway delineation analyses provided by the applicants to verify that the resulting loss of flood conveyance and storage will result in no more than a 0.1 foot increase in stage. The Department will either approve or disapprove floodway delineation analyses and inform applicants of the reason for disapproval.
"Office of Water Resources" - The Office of Water Resources of the Illinois Department of Natural Resources.
"Permittee" - The entity issued a permit pursuant to this Part.
"Rural Areas" - All areas of the State not classified as urban areas.
"Urban Areas" - Areas of the State where residential, commercial or industrial development currently exists or, based on land use plans or controls, is expected to occur within 10 years after the application date. In determining urban areas, the Department will consider the expertise of local officials, regional and local planning commissions, city and county planners, or private development planners, as well as all available mapping. Areas with only isolated or widely scattered buildings will not be classified as urban areas.
"Worst-case Analysis" - The calculation of the maximum increases in flood heights, velocities and damages a project would cause due to conveyance and storage losses considering both the project alone and the combined effects of other existing construction and reasonably anticipated equally obstructive construction on other similarly situated properties in the locality. Flood events up to and including the flood which has a 1% annual chance of exceedence shall be used in this analysis (see Section 3700.75 for exception).
