Floodplain Management

Boulder County joined the National Flood Insurance Program in 1974 and the county has been active in floodplain management since that time. 

The goals of the program are to reduce flood hazards by:
  • Regulating floodplain activities;
  • Adopting floodplain policies;
  • Mapping floodplains; and,
  • Educating the public about floods and floodplains.


Floodplain Maps

Boulder County has 13 major drainages with mapped floodplains. The floodplain maps provide the foundation for Boulder County's floodplain management program. Floodplain maps direct the program goals by identifying areas at risk during times of flood that threaten life and safety.

The floodplain maps help property owners determine if their property is at risk for flooding and if the property is within a regulatory floodplain. The Boulder County Assessor’s property search site includes flood risk by address.

List of Floodplain Maps

State of Colorado Hazard Mapping

In response to the changes to flood impacted watersheds, the State legislature has allocated funds to the Colorado Water Conservation Board (CWCB) to conduct natural hazard mapping, including updating the previous floodplain maps and creating new floodplain maps where none currently exist.

The CWCB and its consultant AECOM are currently conducting the land surveys in stream reaches throughout the county. A map of where surveying is in progress is available at the Colorado Hazard Mapping website.

Learn more about the county's involvement in the Floodplain Remapping Project

Interim Floodplain Map

The county is in the process of acquiring updated floodplain information as a result of the changes cause by the September 2013 flood. Please see the Interim Floodplain Map information page for updates on the information that is currently available.

These maps are for illustration purposes only. For an official determination about your property contact the Transportation Department at floodplainadmin@bouldercounty.org or 303-441-3900

 Flood Insurance

National Flood Insurance Program

Boulder County participates in the National Flood Insurance Program (NFIP). The NFIP makes federally backed flood insurance available for all buildings, whether they are in a floodplain or not. Flood insurance covers direct losses caused by surface flooding, including a river flowing over its banks, a lake or ocean storm, and local drainage problems.

The NFIP insures buildings, including mobile homes, with two types of coverage: structural and contents. Structural coverage is for the walls, floors, insulation, furnace, and other items permanently attached to the structure. Contents coverage may be purchased separately provided the contents are in an insurable building.

What homeowners should know:

  • Boulder County participates in the NFIP’s Community Rating System (CRS) and maintains a number of activities under CRS that correspond to a credit rating of 5, which translates to as much as a 25% reduction in flood insurance premiums for property owners in unincorporated Boulder County
  • General homeowners' insurance does not cover floods
  • Flood insurance is available to all homeowners in Boulder County
  • There is a 30-day waiting period when purchasing flood insurance
  • Flood insurance is backed by the federal government, but can be purchased through a local agent.

Visit FEMA’s Flood Smart page for more information and to find an agent in Boulder County who can help.



Residents Should Consider Purchasing Flood Insurance

Flood Insurance Workshop- Part 1

Flood Insurance Workshop- Part 2


Regulatory Requirements

FEMA administers the National Flood Insurance Program (NFIP). In exchange for access to this program, which includes both flood insurance products for homeowners as well as access to significant financial support for local governments, Boulder County adopts and enforces FEMA-approved floodplain regulations. These regulations, found at Section 4-400 of the Boulder County Land Use Code, apply to land located in unincorporated Boulder County that lies within the Floodplain Overlay Zoning District, the extent of the mapped 100-year floodplain.

Through enforcement of current regulations, preservation of floodplains, and development of hazard mitigation and emergency response plans, Boulder County has been able to preserve flood prone areas, prevent adverse impacts and unwise uses in the floodplain.

Collaborative work by Boulder County with outside agencies through stream enhancement, mitigation and flood control projects has demonstrated a focus on accommodating floods instead of controlling them.

If you are a property owner and want to build on your property, you may need to meet certain requirements.

Development Requirements



Buildings located in the floodplain overlay district may be required to be floodproofed. Floodproofing includes methods such as elevating the structure's lowest floor to or above flood protection elevation, building with flood resistant materials, and installation of flood vents.

Substantial Damage/Substantial Improvement

FEMA regulations specify that Substantial Improvement of existing buildings (remodeling, rehabilitation, improvement, or addition) or buildings that have sustained Substantial Damage must be brought into compliance with floodproofing requirements for new construction.

A structure is considered Substantially Damaged when the cost of restoring the structure would equal or exceed 50% of the pre-damage market value of the structure.

A structure is considered Substantially Improved when an improvement is made that equals or exceeds 50% of the market value of the structure prior to the start of work.

To make a Substantial Improvement/Substantial Damage determination, Boulder County compares the cost of the proposed improvement or repairs to the market value of the building (excluding land, accessory structures, landscaping, bridges, water wells, onsite wastewater treatment systems, and other incidental items). If the resulting ratio equals or exceeds 50%, the existing building must be brought into compliance with the floodplain management requirements for new buildings.

Projects invlolving buildings in the floodplain usually require a Floodplain Development Permit and Building Permit. Learn more about building permits.

Private Access Bridges and Culverts

Stream Restoration

 Drainage & Flood Control

Drainage and Flood Control

The Transportation Department coordinates with outside agencies, other government jurisdictions and the public on:

  • storm water drainage
  • flood control
  • hydrology and hydraulic engineering

Storm Water Drainage

Boulder County is a member of the Keep It Clean Partnership which is dedicated to protecting water quality and reducing stormwater pollution.

The Keep It Clean Partnership has developed programs to meet requirements established by the EPA regarding stormwater regulations. These regulations require our communities to help maintain water quality and stream health. Maintaining clean water is critical to both our health and the health of our ecosystem.

Flood Control

Boulder County is located within the Urban Drainage and Flood Control District. Urban Drainage was created to assist local governments with drainage and flood control problems.

As part of the Urban Drainage, Boulder County receives help in floodplain management to prevent new sources of flooding, flood warning forecasts and design, construction and maintenance for specific development projects within the floodplain.

Hydrology and Hydraulic Engineering

Boulder County supports and participates in periodic updates to the floodplain maps with neighboring communities and FEMA. These updates ensure that the floodplain maps reflect current conditions.

Natural Floodplain Functions

With over 98,000 acres of open space, Boulder County is committed to conserving natural, cultural, and agricultural resources. While, open space in Boulder County provides opportunities for recreation, education, and agriculture, it also serves an important function of maintaining an undeveloped floodplain to allow natural flooding to occur while minimizing damage to homes and infrastructure.

Boulder County Parks and Open Space Map

 Community Rating System

Community Rating System

The National Flood Insurance Program's Community Rating System (CRS) was implemented in 1990 as a program for recognizing and encouraging community floodplain management activities that exceed the minimum NFIP standards. Under CRS, flood insurance premium rates are adjusted to reflect the reduced flood risk resulting from community activities that meet the three goals of CRS:

  1. Reduce flood losses
  2. Facilitate accurate insurance rating
  3. Promote the awareness of flood insurance

Unincorporated Boulder County has received a CRS rating of 5. As of Nov. 1, 2015, any structures located in the regulatory 100-year floodplain of unincorporated Boulder County will receive a 25% discount and all other structures outside the 100-year floodplain will receive a 10% discount. Rate reductions will happen automatically as policies are renewed.