Upper Goose Creek and Twomile Canyon Creek Floodplain Mapping Update
On July 28, 2015 City Council approved the revised floodplain mapping for Twomile Canyon Creek and Upper Goose Creek and the city submitted the revised mapping to FEMA for review. As of 18 August 2016, FEMA has formally accepted the revised mapping as effective.
The revised 2015 Floodplain Maps and the 2015 Hydraulic Report are located on the right side of the page under Floodplain Maps.
If your flood insurance provider is requiring proof that your property has been removed from the floodplain, the LOMR Approved by FEMA may be adequate documentation. However, the city can provide a floodplain information request stating that the property has been removed on city letterhead. Please fill out the foodplain application form and follow instructions for submittal on the form. The process costs $28 and takes about two business days to process. Requests that are paid for by credit card must be dropped off in person or faxed to ensure that credit card information is secure.
Currently, these drainageways are undergoing a flood mitigation study and alternatives analysis. Please see the mitigation plan web page for more information.
The city contracted with ICON Engineering to develop updated floodplain maps for Upper Goose Creek and Twomile Canyon Creek. Anderson Consulting Engineers provided a peer review of the engineering study. The Urban Drainage and Flood Control District (UDFCD) is a co-sponsor of this project.
Floodplain mapping studies provide the basis for flood management by identifying the areas subject to flooding. This information is essential for determining areas where human safety is threatened and property damage is likely. Floodplain maps must be updated periodically to reflect changes in the floodplain resulting from land development, flood mitigation improvements, new study technologies and the impacts of major floods that may have occurred.
Upper Goose Creek and Twomile Canyon Creek were first studied by Greenhorne & O'Mara in 1987. The resulting Flood Hazard Area Delineation (FHAD) delineated the 100-year floodplain along these creeks. The Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM) approved for these creeks were originally based on the 1987 FHAD and included a federally-regulated one foot rise floodway. In 1989, Love and Associates delineated the High Hazard Zone and City of Boulder Conveyance Zone (1/2 foot rise floodway). The delineations were based on the hydraulic models used in the 1987 FHAD.
In 1991, the city commissioned Love and Associates to restudy Twomile Canyon Creek. Based on that study, FEMA issued a Letter of Map Revision (LOMR) for Twomile Canyon Creek on April 5, 1994.The limit of the LOMR was between the confluence of Twomile Canyon Creek and Upper Goose Creek to just upstream of Linden Avenue. In 2004, McLaughlin Water Engineers, Ltd. updated flood mapping for Goose Creek to reflect channel improvements. The limits of the LOMR for this project extended from 30th Street to approximately 1,900 feet upstream of Folsom Street.
The Upper Goose and Twomile Canyon Creek Mapping Study was submitted to and was approved by FEMA as a Letter of Map Revision (LOMR). Traditionally, the city submits mapping updates as a Physical Map Revision (PMR). The main difference between a PMR and a LOMR is that a PMR changes the physical FIRM map and the LOMR is more like an attachment to the FIRM map. Find out if your property is located in a floodplain using the Interactive Floodplain Map. For property-specific information about the land development requirements for all floodplain zones, contact Planning and Development Services at [email protected] or 303-441-1880.
For information on Map Revision Process Options, please visit FEMA's webpage at: https://www.fema.gov/flood-map-revision-processes
"Once initiated, FEMA will process a request to revise the flood hazard maps based on as-built conditions by one of two methods - Physical Map Revision (PMR) or Letter of Map Revision (LOMR). A PMR is an action whereby one or more map panels are physically revised and republished. A PMR is used to change flood risk zones, floodplain and/or floodway delineations, flood elevations, and/or planimetric features. To ensure that those affected by the PMR have the opportunity to provide input, a PMR has procedures that include a community comment period and a 6-month compliance period to update ordinances while the new maps are printed and distributed. Because of the large amount of flood hazard information that is incorporated into the maps and the number of people that will be affected by that information, a PMR can take as long as 18 months to complete. FEMA charges the requester of a PMR a fee for review of the data submitted in support of certain types of requests such as those concerning structural measures. PMRs must be requested by the Chief Executive Officer (CEO) of the community because the community is responsible for adoption of the revised flood hazard information into their specific floodplain management ordinances and regulations.
A LOMR is a document that officially revises a portion of the effective NFIP map according to requirements and procedures outlined in Part 65 of the NFIP regulations. A LOMR allows FEMA to revise flood hazard information on an NFIP map via letter without physically revising and reprinting the entire map panel. This process typically takes less time and is less expensive than a PMR. LOMRs include the revised portion of the flood hazard map, affected flood profiles, and floodway data tables from the Flood Insurance Study (FIS) report as attachments to the letter. LOMRs are essentially like PMRs in that they are used to change flood risk zones, floodplain and/or floodway delineations, flood elevations, and/or planimetric features; however, because of their limited distribution, LOMRs are primarily intended for small areas of change and areas where flood hazards are typically decreasing. FEMA charges the requesters of LOMRs a fee for review of the flood hazard data submitted in support of certain types of requests such as those concerning structural measures. As with PMRs, a LOMR must be requested through the CEO of the community because the community is responsible for the adoption of the revised flood hazard information into the community's floodplain management ordinances and regulations.
Property owners or other persons who wish to follow the progress of a particular PMR, LOMR, or other map revision are advised to consult the community's Floodplain Administrator. This is the local official who keeps all of the community's flood hazard maps and FIS report, and who corresponds with FEMA at various stages of the revision process. Often this is an official such as the City/County Engineer or the Director of Planning or Zoning Administrator. The status of ongoing map revisions can also be checked on the FEMA website, or by calling the FEMA Map Information eXchange toll free at 1-877-FEMA MAP (1-877-336-2627)."