City of Boulder, Colorado Floodplain Overlay Districts
The City of Boulder, Colorado’s Land Use Code (Boulder, Colorado Revised Municipal Code Title 9, Chapter 3) includes provisions to establish and implement Floodplain Overlay Districts that provide restrictions or additional requirements for all development in areas of the city subject to flooding. This includes the 500 and 100-year floodplains, Conveyance Zones, preserved corridors that allow flood waters to travel to creeks, and High Hazard Zones, areas with the greatest threat of human loss. The districts are intended to protect the city’s public health, safety, and welfare by mitigating negative impacts from flooding.
The city’s regulatory floodplain consists of the 500-year (0.2% chance) and 100-year (1% chance) floodplain and Conveyance and High Hazard zones that include different restrictions or requirements for development depending on the potential for and severity of flood risks.
- 500-year Floodplain: Critical facilities (e.g., hospitals, police stations, day care facilities and utility treatment facilities) and lodging facilities must be floodproofed (i.e., so that a structure is “substantially impermeable to the passage of water and in a manner requiring no human intervention”) or elevated to or above the flood protection elevation identified by the city. In a 500-year floodplain, the flood protection elevation is the lower of either one foot above the water surface of a 500-year flood or the 100-year flood protection elevation (See below). These facilities must also have an approved emergency management plan in order to be eligible for a development permit.
- 100-year Floodplain: Residential structures (both new and existing residential structures that are expanded or enlarged) must be elevated to or above the flood protection elevation, which is generally two feet above the water surface of a 100-year flood, whereas non-residential structures can either be floodproofed or elevated to the required height. Additionally, electrical, heating, ventilation, plumbing, air conditioning equipment, and other service facilities must be designed to withstand flood damage (e.g., by floodproofing or elevating the components). Rental property owners must post notifications on the exterior of their buildings that state the property is subject to flooding.
- Conveyance Zone: This zone includes areas preserved to allow flood waters to return to creek corridors in order to prevent those waters from increasing flood depths or impacts (e.g., redirecting flood waters). No person can establish or change any use in a conveyance zone that will result in any “rise in the elevation of the one-hundred year flood.”
- High Hazard Zone: This type of zone is the most restrictive of the four because it includes areas in the floodplain with the greatest risk of loss of human life. Property owners and developers cannot convert or build new residential structures (i.e., to prevent against increased human occupancy) or establish new parking lots or campgrounds in high hazard zones.
Other notable provisions of the Boulder Land Use Ordinance (Land Use Code, 9-3-8) related to flooding include:
- Nuisance declaration: Every development placed or maintained in the floodplain in violation of the code constitutes a public nuisance that “may be enjoined or abated by suit or act by the city or any resident of the city.”
- High Hazard Zone post-flood residential redevelopment restriction and property acquisition by the city: After a flood, residential structures that are both located in a High Hazard Zone and damaged by more than 50% of its pre-flood value, cannot be repaired or replaced and can no longer be used for human occupancy. Within 90 days of the damage and subject to available funds, the city “shall agree to contract or purchase the land upon which the structure was located at its fair market value after the damage occurred."
Publication Date: 2014
- City of Boulder, Colorado