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City of Lincoln
Overview of Existing Floodplain/Stormwater Regulations

Written Overview


October 2001

• Definition of floodplain.
Floodplain is defined by the 100-year floodplain as designated on the FEMA floodplain maps. Floodplain regulations generally do not apply to areas unmapped by FEMA.
• Administration of floodplain permits.
Applications for development within the floodplain are made to the Department of Building and Safety.
• Floodway and flood fringe.
Regulations divide the 100-year floodplain into the floodway and the flood fringe (see attached diagram of the 100-year floodplain).
Floodway.
The floodway is defined as the stream channel plus that portion of the overbanks that must be kept free from encroachment in order to discharge the 100-year flood without raising the flood elevation by greater than 1 foot.The FEMA floodplain regulations anticipate that flood heights may rise 1 foot if the flood fringe is fully developed, however, this is not reflected in the boundaries of the floodplain shown on the floodplain maps.
Flood Fringe.
The flood fringe is the balance of the floodplain where encroachments are allowed as long as they are protected by being elevated or floodproofed, as described below.
• Development within the floodway.
Development within the floodway must certify that it will not result in any increase in the base flood elevation. No new residential development can occur within the floodway.
• Development within the flood fringe.
Development may occur within the flood fringe as long as building areas are protected as described below and all other floodplain requirements are met.
• Residential buildings in the floodplain.
Residential buildings must be elevated to 1 foot above the 100-year flood elevation. The most common method of elevating building is on fill. This can also be accomplished by elevating on piers or columns or by elevating on walls or a crawlspace.
• Non-residential buildings in the floodplain.
Non-residential buildings must be either elevated 1 foot above the 100-year flood elevation or floodproofed to 1 foot above.
• Hydraulic studies required for floodplain development.
Where floodways are mapped, there is no restriction on the amount of fill that can be placed in the flood fringe. Where floodways are not mapped, a study must be completed to show that the proposed development, "when combined with all other existing and reasonably anticipated developments or substantial improvements," will not increase the 100-year flood elevation by more than 1 foot.
• Minimum flood corridor.
Stormwater regulations require a 'minimum flood corridor' to be preserved along tributaries outside of the mapped floodplain which drain at least 150 acres. The corridor is the existing channel bottom width plus 60 feet, plus 6 times the channel depth and is centered on the channel.
• Drainage studies required.
The subdivision ordinance requires a drainage study to be submitted with all topographic, drainage, and floodplain information, including the 100-year flood elevation in FEMA-mapped floodplains, and the 100-year 'storm' elevation along un-mapped tributaries.
• Stormwater Detention.
The design standards for subdivisions require stormwater detention or retention facilities with release rates that do not exceed the pre-development rates for stormwater runoff during the 2-year, 10-year, and 100-year storm events. This provision relates only to the effect of additional stormwater runoff from developments (e.g., more water running off rooftops or streets which would have soaked into the ground prior to the development). It does not address the impact a development may have upon the storage or conveyance of flood waters within a floodplain area (e.g. displacement of flood waters due to buildings or fill - the 'bathtub' analogy).
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Overview of Existing Floodplain/Stormwater Regulations