Regional Floodplain Management in the Carson River Watershed

Challenge

Although floods are not new in the Carson River Watershed, floodplain development is causing flooding in areas that did not previously flood. After the New Year’s Eve flood event in 1997, affected communities in the Carson River Watershed knew they needed to address the increasing pressure of development, changes to natural flooding routes, and the steady decrease of natural floodplain functions.

Solution

Following the 1997 flood event, affected communities convened a two-day workshop and created the Carson River Coalition (CRC). The CRC is a large, watershed-wide stakeholder group that brings together the following entities: Carson City, Churchill County, Douglas County, Lyon County, and Storey County in Nevada, Alpine County, California, state and federal entities, nonprofits, producers, and private property owners to discuss water issues and possible solutions. The Carson Water Subconservancy District (CWSD), a unique multicounty, bi-state agency dedicated to establishing a balance between the needs of the communities within the Carson River Watershed, was asked to facilitate and coordinate the CRC and integrated the watershed planning process. 

The CRC developed the Regional Floodplain Management Plan which took over three years and involved several workshops and meetings similar to FEMA’s Risk Mapping, Analysis, and Planning (Risk MAP) Discovery process. All counties adopted the plan and, instead of developing structural flood channels, have committed to the “living river” concept that allows the flood water to access the open floodplain. 

When Risk MAP was initiated in this area, the integrated watershed approach and stakeholder group for the Carson River were already active. One of the first projects under Risk MAP was to remap the Carson River floodplain. Due to the unique characteristics of the area, the project takes into account the water storage capacity of the floodplain using unsteady state modeling versus more basic steady state modeling. The new unsteady state modeling considers flood timing and volume to determine a more accurate floodplain storage capacity at different times during a flood. The unsteady state model results will inform communities regarding future development by effectively assessing cumulative impacts and floodplain capacity on a regional level. The model also helps developers, who typically need to fund a study to model the impact of each proposed development, by providing a ready-to-go model for their use.

Outcome/Results

Linking the Risk MAP project to the previously adopted Regional Floodplain Management Plan has benefited both efforts. The regional approach to floodplain management has reduced the impact of flood damage on a watershed scale, primarily by protecting floodplains from further development and maintaining the natural function of the floodplain. Ultimately, the Carson River Coalition’s goals are: 

  • Apply a living river approach 
  • Retain the natural state of critical floodplain lands 
  • Remove restrictions to allow flood water access to the floodplains 
  • Prevent additional restrictions from being created 
  • Implement a watershed-wide community outreach program 
  • Focus on regional management 

Benefits

Adopting a living river approach in the Carson River Watershed provides the following benefits:

  • Connects the river with its floodplain
  • Minimizes disruption and alteration of the river and riparian habitat
  • Conveys variable flows, slowing and spreading water, and restoring habitat
  • Balances sediment input with sediment transport
  • Enhances water quality and supply
  • Keeps structures out of unstable and unsafe areas
  • Maintains aesthetic and recreational qualities
  • Provides a low-cost alternative to a structural approach
  • Avoids increased flood damages that occur when floodplains are developed
  • Maintains open floodplains for agricultural and open space land uses
  • Generally enhances the human environment

Lessons Learned

Risk Mapping, Assessment, and Planning Program (Risk Map) Phases

This project involved the following Risk MAP phases:

  • Data Development and Sharing
  • Risk Awareness and Mitigation Outreach
  • Proposed NFIP Map Changes and Impacts
  • Preliminary Map Release and Mitigation
  • Due Process and Path Forward

Risk Map Goals Advanced

The Risk MAP goals that were advanced through this project included:

  • Increasing Awareness
  • Advancing Action

The focus on local partnerships plays a vital role in achieving supported solutions. The Cooperating Technical Partner (CTP) agreement with FEMA enables CWSD to receive funding from FEMA and take the lead in updating the flood maps and Risk MAP products, which helps to avoid challenges from the local community that can lead to animosity, mistrust, or conflict. 

With these strong partnerships in place, FEMA and the local entities were able to enter into a Risk MAP Charter. This document recognizes the good-faith desire of federal, state, and local government entities working in the watershed, to share data, communicate findings, and plan mitigation activities that protect the communities from flood risk. The CTP, the Regional Floodplain Management Plan, and the Charter together provide a cooperative path toward a resilient Carson River Watershed. 

Resources

Nevada Flood Awareness Committee  

Living River fact sheet

Carson Water Subconservancy District

Contact Information

cwsd@cwsd.org 

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Last updated April 28, 2021