Floodplain Overlay District Overview
Colorado winter storms and heavy rains may create an increase flood risk. A floodplain is an area near a water source that is at a greater risk of being covered by flood water as a result of larger storm events.
Floodplains in Jefferson County are the lower areas adjacent to rivers, lakes, and creeks that are periodically flooded at intervals of varying frequency. Floodplains are important components of their respective watersheds. Floodplains are hydrologically important, environmentally sensitive and ecologically productive areas within a watershed that perform many natural functions.
Floodplains contain a wealth of cultural and natural resources that are of enormous value to society. Riverine floodplains, such as the floodplains found in Jefferson County, vary in steepness, width, stream flow, sediment deposition and erosive characteristics. The natural functions that are associated with a particular floodplain depend in part on its location within this system. The frequency, duration and extent of flood events will also vary among different types of floodplains, dependent upon their hydrology, geology, and amount of floodplain development.
Floodplains are formed and modified by the dynamics of stream and river migration and periodic flooding. Although many riverine floodplains usually flood during the spring storms, they can also experience multiple flood events within the same year with duration varying from hours to days. Periodic flooding of riverine systems and the related processes of erosion and deposition determine, to a considerable extent, the shape of the floodplain; the depth and composition of soils; the type and density of vegetation; presence and extent of wetlands; richness and diversity of wildlife habitats; and depth to the groundwater.
The major flood conveyance component of the floodplain is the floodway. The National Flood Insurance Program (floodsmart.gov) defines the floodway as that area of the watercourse and adjacent floodplain necessary to carry the base flood without increasing the water surface elevation more than a designated amount (generally 0.3 feet in Colorado). The base flood is the flood that has a one percent chance of being equaled or exceeded in a given year. Communities are required to prohibit development within the floodway that would cause an increase in flood heights. This requirement has the effect of limiting development in floodways that in turn helps to maintain some of the floodplain’s most important natural resources and functions.
There are a number of walking trails and bike paths throughout many of the floodplains in Jefferson County. These paths provide an opportunity for our citizens to enjoy the vegetation and wildlife that thrives in our floodplains.
Documents and Links:
- National Flood Insurance Program (floodsmart.gov)
- Flood Insurance (FEMA)
- Colorado Water Conservation Board Flood Information & Resources (CWCB)
Many people think they are not in danger of flooding if they don’t live near a stream or creek. Unfortunately, this is not true. Flooding is the nation’s number one natural disaster. Flash floods, inland flooding and seasonal storms flood every region of the country and floodplain maps don’t show all areas at risk! Flooding can and often does occur outside the mapped floodplain. Flooding often occurs along smaller streams and creeks that are not shown on any flood maps. Non-creek flooding can occur from overwhelmed storm sewers, low-lying areas that do not have proper drainage, or water mains that break. Much of the true risk of flooding is its unpredictability.
Colorado’s flood season, which is historically from May through October, includes both snowmelt and thunderstorm flooding. Snowmelt floods result from the melting of the winter snowpack in the high mountain areas which becomes spring runoff. Thunderstorm floods are caused by intense rain over relatively small areas. Because there is little to no warning time, the term flash flood is often used to describe thunderstorm floods. Between 20 and 30 large floods occur in Colorado every year and Colorado experiences a major flood disaster roughly once every five years.
The County’s Planning & Zoning Division has copies of FEMA Elevation Certificates for buildings constructed in the floodplains since 2004.
You can reduce your risk of flooding by being prepared and knowing how to respond when there is a flood. Below are links to learn more about flood safety, flood recovery, flood Insurance, how to be prepared before a flood, how to develop an emergency plan, and what to do during a flood.
Flood Safety Resources:
- Floods and Water Quality for Water Supply Wells (PDF)
- Jeffco Emergency Preparedness Resources
- Sign up to Receive Emergency Notifications
Quick Tips for Flood Safety
- Be aware of possible flash flooding hazards. If there is any possibility of a flash flood, move immediately to higher ground. Do not wait for instructions to move.
- Listen to radio or television stations for local information.
- Be aware of streams, drainage channels, canyons or other areas known to flood suddenly. Flash floods can occur in these areas without such typical warning signs as rain clouds or heavy rain.
- If local authorities issue a flood watch, prepare to evacuate.
- Secure your home. If you have time, tie down or bring outdoor equipment and lawn furniture inside. Move essential items to the upper floors.
- If instructed, turn off utilities at the main switches or valves. Disconnect electrical appliances. Do not touch electrical equipment if you are wet or standing in water.
- Fill bathtubs with water in case water becomes contaminated or services cut off. Before filling the tub, sterilize it with a diluted bleach solution.
- Do not walk through moving water. Six inches of moving water can knock you off your feet. If you must walk in a flooded area, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you.
- Do not drive into flooded areas. Six inches of water will reach the bottom of most passenger cars causing loss of control and possible stalling. A foot of water will float many vehicles. Two feet of water will wash away almost all vehicles. If floodwaters rise around your car, abandon the car and move to higher ground, if you can do so safely. You and your vehicle can be quickly swept away as floodwaters rise.
The Local Flood Hazard
The local flood hazard is discussed in detail in FEMA’s January 20, 2019 Flood Insurance Study (FIS). Read a portion of the FIS, including the Community Description and Principal Flood Problems(FEMA).
Floods are one of the most common hazards in the United States. However, all floods are not alike. Riverine floods develop slowly, sometimes over a period of days. Flash floods can develop quickly, sometimes in just a few minutes, without any visible signs of rain. Flash floods also often have a dangerous wall of roaring water that carries a deadly cargo of rocks, mud and other debris, which can sweep away many things in its path. Overland flooding occurs outside a defined river or stream, such as when a levee or dam is breached. Flooding can also occur from a dam break producing effects similar to flash floods. Be aware of flood hazards no matter where you live, but especially if you live in a low lying area, near water or downstream from a dam. Even very small streams, gullies, creeks, culverts, dry stream beds or low lying grounds that appear harmless in dry weather can flood.
Map of the Local Flood Hazard
Planning and Zoning staff can answers questions related to floodplain management, including determining if a property is located within a floodplain within Jefferson County. In addition, you can access the Jefferson County interactive mapping application.
Flood Warning System
LookoutAlert Regional Emergency Notification System
LookoutAlert is the official emergency notification system of the regional collaborative of Jefferson County and all cities within it, the City and County of Broomfield and the City of Westminster. Through LookoutAlert, emergency responders are able to provide emergency and public safety messages to residents.
Jefferson County is moving the mass emergency notification system to the Smart911 platform because of the enhanced capabilities of this system. You can receive free emergency alerts via text message, email, and/or voice message. Sign up on the Emergency Management LookoutAlert page.
Emergency Alert System (EAS)
The Emergency Alert System (EAS) is one tool that Jefferson County can use to warn its citizens in case of an impending disaster on participating radio and television stations. In most cases however, the National Weather Service has already activated EAS.
Documents and Links:
- Jeffco Emergency Preparedness Resources
- LookoutAlert Notifications - sign up here
- Jefferson County interactive mapping application
- FEMA Jeffco Flood Insurance Study (FEMA)
- Real-time Storm and Flood Map (MHFD)
- National Oceanic and Atmospheric Administration (NOAA) (NOAA)
The Elevation Certificate (FEMA) is an important administrative tool of the National Flood Insurance Program (NFIP). It is to be used to provide elevation information necessary to ensure compliance with community floodplain management ordinances, to determine the proper insurance premium rate, and to support a request for a Letter of Map Amendment or Revision (LOMA or LOMR-F).
Required to Property Rate Post-FIRM Buildings
The Elevation Certificate is required in order to properly rate post-FIRM buildings, which are buildings constructed after publication of the Flood Insurance Rate Map (FIRM), for many flood insurance Zones, including AE and A (with BFE). The Elevation Certificate is not required for pre-FIRM buildings unless the building is being rated under the optional post-FIRM flood insurance rules.
As part of the agreement for making flood insurance available in Jefferson County, the NFIP requires the county to adopt a floodplain management regulations that specifies minimum requirements for reducing flood losses. One such requirement is for Jefferson County to obtain the elevation of the lowest floor (including basement) of all new and substantially improved buildings and maintain a record of such information. The Elevation Certificate provides a way for Jefferson County to comply with this requirement.
Jefferson County Planning and Zoning maintains copies of Elevation Certificates. Copies of Elevation Certificates can be found below.
Mile High Flood District (MHFD) Official Notice Brochure
The MHFD Official Notice Brochure contains information on 100-year floodplains in specific areas of Jefferson County. Its purpose is to inform citizens of this flood hazard, and to suggest mitigating actions.
Documents and Links:
Floodplain Requirements, Maintenance, and Violations
Floodplain Development Permit Requirements
Always check with Jefferson County before building, grading, fencing or otherwise altering your property. Any work with our Floodplain Overlay District requires a Floodplain Permit from Jefferson County. Contact Planning and Zoning with any questions including reporting of an illegal floodplain development.
Substantial Improvement/Damage Requirements
"Substantial improvement" means any rehabilitation, addition, or other improvement of a building when the cost of the improvement equals or exceeds 50 percent of the market value of the building before start of construction of the improvement. Substantial improvements shall be counted cumulatively for a period of 5 years from the Start of Construction date of the first approved building permit. The term includes buildings that have incurred "substantial damage." "Substantial damage" means damage of any origin sustained by a building when the cost of restoring the building to its pre-damaged condition would equal or exceed 50 percent of the market value of the building before the damage occurred. Substantial damage is determined regardless of the actual repair work performed.
Substantial improvement or damage does not, however, include any project for improvement of a building to correct existing violations of State or local health, sanitary, or safety code specifications identified by local code enforcement officials as the minimum specifications necessary to assure safe living conditions. Also excluded from the substantial improvement requirement are alterations to historic buildings as defined by the NFIP.
Drainage System Maintenance
Jefferson County prohibits impeding or interfering with the flow of storm water in the natural drainage ways, unimproved channels or watercourses, or improved ditches, channels or canals in such a manner as to cause flooding where it would not otherwise occur. This includes debris, branches, or other material that may interfere with the flow of water.
Contact Planning and Zoning with any questions regarding maintenance or including reporting of a violation.
Any grading construction requires a floodplain development permit prior to any of these activities. Otherwise, a zoning violation may be issued.
Documents and Links:
Floodplain Development Permits
A floodplain development permit must be obtained before doing any work within the floodplain overlay district. Floodplain Development Permits are accepted through the Jefferson County Citizen Portal. A signed application (PDF) is still required to be uploaded with the online application.
If wetlands are present, a permit must be obtained from the US Army Corps of Engineers. Depending on the work within a floodplain, a floodplain study by a Professional Engineer licensed in Colorado may be required with the permit application. A Letter of Map Amendment or Letter of Map Revision Based on Fill through FEMA may also be required depending on the type of work. Please refer to the Floodplain Overlay District Section 37 (PDF) of the Zoning Resolution and the Storm Drainage Design and Criteria (PDF) for more information on Floodplain permits in Jefferson County.
Documents and Links:
- Engineering and Earthwork Webpage
- Floodplain Development Permit Application Form
- Jefferson County Citizen Portal Start Page
- FEMA Processes - Letter of Map Amendment or Letter of Map Revision Based on Fill (FEMA)
- Zoning Resolution Section 37: Floodplain Overlay District
- Storm Drainage Design and Criteria
- Mile High Flood District Criteria Manuals (MHFD)
- Colorado Water Conservation Board Floodplain Resources (CWCB)
Planning and Zoning staff can answers questions related to floodplain management, including determining if a property is located within a floodplain within Jefferson County. Copies of elevation certificates can be obtained on the Floodplains Elevation Certificates page or by contacting the Planning and Zoning Division.