Regulatory floodplains are extracted from FEMA or provided by consultants to the City. Non regulatory floodplains are provided by consultants, but their accuracy is not guaranteed.FEMA floodplains can either be amended by Letters of Map Revision (LOMR), or Physical Map Revisions (PMR). Historic data between 7/17/1978 and 5/31/2018 rely on PMRs to FIRM Panels; from 5/31/2018 onwards, FEMA exposed a web API that made tracking LOMRs much easier. This is why changes to the floodplain after this date look more "piecemeal" rather than entirely replaced. FEMA Floodplains are automatically updated by a scripted process on a monthly basis.High Hazard Zones are solely recognized by the city as areas which represent the highest risk to loss of life. More information can be found here. These zones are delineated by engineering firms on behalf of the city. They are updated manually by GIS staff.Non-Regulatory Floodplains are updated infrequently.Data: Records with Null INEFFDATEs are the current floodplains.FLOODZONEs beginning with "A" have a 1% chance of flooding (e.g. the 100 Year floodplain)FLOODZONEs equal to "X" are areas with a 0.2% chance of flooding (e.g. the 500 Year floodplain)FLOODZONEs equal to "HHZ" are the High Hazard ZonesFLOODWAYs equal to 1 are Conveyance Zones

The 2013 urban flood extent data was developed using field surveys completed by City of Boulder staff and consultants, Digital Globe Worldview-2 satellite imagery (9/13/13), and public input from the Boulder Crowd Sourcing online map as well as discussions with affected property owners. Only drainages with a FEMA mapped floodplain were surveyed. Other areas of Open Space and Mountain parks land without a regulatory floodplain were not included.The flood extent data is current as of 3/28/2014 and includes information received from recent community meetings. The City of Boulder will make additional updates to this data to incorporate relevant information.The 2013 urban flood extent data does not supersede the Special Flood Hazard Area Designation (SFHA), or 100 yr floodplain, used by FEMA for Digial Flood Insurance Rate Maps or the proposed floodplain delineations from ongoing flood studies.This data is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon.

SummaryThe City of Boulder recognizes two categories of regulatory floodplains: (1) Those released by the Federal Emergency Management Agency (FEMA) on Flood Insurance Rate Map (FIRM) Panels, and (2) High Hazard Zones. Non-regulatory floodplains include delineations from 10-, 25-, 50-, and 200-Year flood events. Effective dates for non regulatory floodplains are provided, but not guaranteed.Regulatory floodplains are extracted from FEMA or provided by consultants to the City. Non regulatory floodplains are provided by consultants, but their accuracy is not guaranteed.FEMA floodplains can either be amended by Letters of Map Revision (LOMR), or Physical Map Revisions (PMR). Historic data between 7/17/1978 and 5/31/2018 rely on PMRs to FIRM Panels; from 5/31/2018 onwards, FEMA exposed a web API that made tracking LOMRs much easier. This is why changes to the floodplain after this date look more "piecemeal" rather than entirely replaced. FEMA Floodplains are automatically updated by a scripted process on a monthly basis.High Hazard Zones are solely recognized by the city as areas which represent the highest risk to loss of life. More information can be found here. These zones are delineated by engineering firms on behalf of the city. They are updated manually by GIS staff.Non-Regulatory Floodplains are updated infrequently.Data: FLOODZONEs beginning with "A" have a 1% chance of flooding (e.g. the 100 Year floodplain)FLOODZONEs equal to "X" are areas with a 0.2% chance of flooding (e.g. the 500 Year floodplain)ZONE_SUBTY equal to FLOODWAY are conveyance zones

The original source was the inundated areas as drawn by the National Geospatial Agency, which only covered major flooding along Boulder Creek and St Vrain Creek. This was supplemented by Boulder County Land Use and Parks and Open Space using imagery from the Digital Globe First Look product. Multiple images, taken on different days were used to determine the high water mark due to cloud cover. The high water mark has not been field verified. Inundated areas in the mountains were particularlly difficult to draw due to cloud and tree cover. Areas within the City of Longmont and Boulder were not drawn as it is assumed these cities will be creating their own layer. Areas within the other incorporated areas were drawn: Jamestown, Lyons, Louisville, Lafayette, and Erie. This dataset has further been refined by using Pictometry imagery flown October 2013 after the flood and using damage assessment data points. This dataset is updated as of 8/6/2014.