The Fluvial Hazard Zone (FHZ) is the area a stream has occupied in recent history, may occupy, or may physically influence as it stores and transports water, sediment, and debris.

 

The UAWP hired Round River Design to conduct an assessment of stream corridor hazards and floodplain connectivity in Chaffee County, also commonly known as fluvial hazard zone (FHZ) mapping. The assessment looked at 64 miles of stream corridor including sections Cottonwood Creek, Chalk Creek, Browns Creek, North Fork of the South Arkansas River, South Arkansas River, Little Cochetopa Creek, Poncha Creek and Ute Creek.

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The goal was to assess and identify opportunities to mitigate or reduce flood hazard zone risks. The UAWP assessment identified many potential opportunities to do so on all of these tributaries of the Arkansas River.

 

Please be aware that while our FHZ mapping may identify opportunities/projects on both public and private land, none of these mapped FHZ mitigation opportunities will be pursued without the full cooperation, support and buy-in from all respective landowners. 

 

Also note that while Chaffee County recently adopted FHZ mapping in their updated county land use codes in December 2024, the UAWP assessment is not the FHZ map the county will use for their regulations. See the updated Chaffee County Land Use Codes here. 

Description of Fluvial Hazard Zone Mapping

Fluvial geomorphic processes are natural phenomena within stream corridors and include commonly observed occurrences such as erosion, the transport and deposition of sediment, the recruitment and jamming of wood, and the structural influences of plants and animals. Fluvial geomorphic processes become hazardous when they encounter infrastructure, houses, businesses, and other investments within and adjacent to the stream corridor.

In order to recognize and assess the hazards associated with erosion, sediment deposition, and other dynamic river processes, the Colorado Water Conservation Board (CWCB) has developed a technical protocol to identify and map the areas where fluvial hazards may exist in order to help communities better understand their existing risk.

The State of Colorado’s Fluvial Hazard Zone (FHZ) Mapping Program represents a significant and necessary step forward in adaptively managing stream corridors, preparing for, and mitigating flood impacts, and making informed land use decisions based on an awareness of fluvial processes. In Colorado, flood hazard identification and mitigation must recognize that streams are naturally dynamic, prone to move within a corridor, and apt to modify their margins as they transport and deposit water, sediment, and debris inputs from their watersheds.
 

Flood insurance claims and property loss data demonstrate that in Colorado, reliance on traditional flood inundation maps alone does not provide a comprehensive characterization of the hazards imposed by fluvial processes. Fluvial Hazard Zone Mapping process considers these dynamic stream processes and represents an important step forward in identifying and communicating these hazards.

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Fluvial Hazard Zone Maps are created by fluvial geomorphologists—scientists who study how flowing water shapes and modifies the Earth’s surface through erosional and depositional processes. Mapping is completed through the interpretation and synthesis of geomorphic, geologic, hydrologic, and biotic information (i.e., data that describes the physical location, form, flooding intensity, active sediment and debris transport, and ecological conditions of a riverine system).

Fluvial Hazard Zone maps provide communities, individual property owners, and emergency response teams with information on flood- and stream-related hazards beyond those identified by traditional floodplain mapping. Fluvial Hazard Zone maps may be adopted and used for land use regulation at the local level, however, they are not and will not be regulated nor mandated by the State of Colorado. As stream corridors are environmentally and economically important areas, Fluvial Hazard Zone maps can also aid in prioritizing lands for conservation or maintenance of fluvial hazard compatible land uses. As Colorado’s Fluvial Hazard Zone Mapping Program progresses, it is also demonstrating value for post-wildfire flood planning and response.

In addition to providing information related to community safety, Fluvial Hazard Zone maps provide a delineated area where many of the complex physical, chemical, and biological interactions of stream systems could be expected to occur. Recognizing that stream corridors (i.e., streams and their associated riparian, subsurface and in-channel areas, as well as geomorphic floodplains) move and store sediment, debris, and water and employing management practices that avoid conflict with these processes are important; this recognition is important not only for our safety and financial investments, but also because these natural river processes are foundational for
preserving the ecosystem services found in riparian corridors.

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Read First -  Introductory Cover Letter - Chaffee County FHZ Mapping​​

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UAWP Stream Corridor Hazard & Floodplain Connectivity Assessment - Chaffee County Fluvial Hazard Zone Map Addendum

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Online Webmap of the Study Area

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UAWP Stream Corridor Hazard & Floodplain Connectivity Assessment - Opportunities for Fluvial Hazard Mitigation & Improved Stream Corridor Function

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The "Stream Corridor Hazard and Floodplain Connectivity Assessment" was completed for the Upper Arkansas Watershed Partnership's Healthy River Corridors Project by Round River Design.  The project focused on identifying fluvial hazard corridors where public safety should be considered and where opportunity exists to maintain or restore healthy functioning floodplains. This project was intended to develop DRAFT map products for planning purposes only. These maps are not regulated at this time. Third-party review to refine the maps has not yet been conducted. 

Note: Downtown Buena Vista lies on an alluvial plain with numerous historic channels braiding through town. Floodplain hazards in this area are more likely to be a result of inundation flooding rather than fluvial processes. FHZ map was delineated broadly for this draft mapping exercise, refinement in this area is awaiting improved floodplain inundation models from CWCB

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DISCLAIMER: 

Fluvial Hazard Zone (FHZ) maps are intended to delineate the area a stream has occupied in recent history, may occupy, or may physically influence as it stores and transports water, sediment, and debris. FHZ maps do not predict the magnitude, frequency, or rate of fluvial geomorphic hazards. The intended use of these FHZ maps is to supplement other on-going and completed studies that are examining land use planning, floodplain management, and stream corridor conservation efforts. The information presented in FHZ maps should always be used in conjunction with other studies and analysis, especially on a site-development basis.

The Fluvial Hazard Zone map authors make no representations or warranties, expressed or implied, as to the accuracy, completeness, timeliness, or rights to the use of FHZ maps. The authors shall not be liable for any errors, omissions, or inaccuracies in such information regardless of their cause, and shall not be liable for any decision made, action taken, or action not taken by the user in reliance upon such information. The authors shall not be liable for any general, special, indirect, incidental, or consequential damages including, but not limited to, lost revenues or lost profits resulting from the use or misuse of the information contained on FHZ maps.