Fluvial Hazard Mapping in Colorado

Year: 2020
Presenter/s: Katie Jagt
Symposium Session: 2020 - 08 Pre-Disaster: An ounce of prevention is worth a pound of cure
Topics covered: beavers, community involvement, lessons learned, outside PNW, risk, and urban


ABSTRACT

In order to recognize and assess the hazards associated with erosion, sediment deposition and other dynamic river processes, the Colorado Water Conservation Board has developed a program to identify and map fluvial hazards to help communities better understand all hazards associated with flood events. The State of Colorado’s Fluvial Hazard Zone (FHZ) mapping program represents a significant and necessary step forward in stream corridor management, flood and wildfire mitigation and preparedness and conservation practices. This presentation will discuss the Colorado FHZ Program establishment and evolution as well as its goals, funding sources, technical advancements, regulatory recommendations, and communication strategies.
Flood insurance claims and on-going property loss data demonstrate that in Colorado, reliance on flood inundation maps alone does not provide a comprehensive characterization of hazards imposed by river processes. Recognizing this gap and spurred by four billion dollars in damage in 2013, in 2014 the Colorado legislature allocated funding to study the feasibility of and develop an “Erosion Hazard” mapping program.

The program began with a proof-of-concept study in 2015 where several existing technical standards were reviewed and tested for their applicability within the state. Major recommendations from this work were: 1) Colorado develop more flexible and robust technical standards 2) Colorado implement a locally-sponsored, voluntary, and incentive-based hazard mapping program and 3) The name of the program be changed to “Fluvial Hazard Zone Mapping” rather than “erosion hazard mapping” as there are substantial hazards in addition to erosion that must be considered.

In 2017, Colorado began the Fluvial Hazard Zone Mapping Pilot program. The program is built on three goals: 1) to develop a scientifically defensible set of mapping standards for Colorado (i.e. develop a protocol that can be used anywhere within the state) 2) implement fluvial hazard mapping throughout the state and 3) reduce damage from future flood events by increasing awareness of fluvial hazards thereby leading to better land use decisions. The technical work has been executed with several partners and has resulted in an advancement of the understanding of both the driving forces (hydrology) and the fluvial responses after disturbance, particularly as they relate to stream power. Several studies were completed that assessed the response and associated damages that communities sustained and correlated this with geomorphic characteristics. FHZ mapping was completed for 8 pilot communities in a diversity of physiographic regions throughout the state and covered approximately 450 miles of stream corridors. For communities who sought to adopt regulations for land use within the FHZ, a model ordinance was developed to provide to pilot communities. After several iterations, it was clear that the best regulatory support that could be provided to communities was a short, concise ordnance from which each community could build regulations that were both applicable and palatable with the overall objective of avoiding damages during future floods. As the FHZ program evolves, it is showing value to the State of Colorado in wildfire planning and response as well as for the identification of conservation areas and watershed-scale restoration projects.