When a significant percentage of a state’s population resides in a watershed with significant flood risk, that watershed will receive focused attention by many agencies with different perspectives. The Boise River watershed, located in southwestern Idaho, is home to over 600,000 residents, more than one-third of Idaho’s population. Despite upstream federal storage projects and community participation in the National Flood Insurance Program, the watershed has more than $10 billion of infrastructure at risk for flood damage. The watershed is one of the highest flood risk priorities for USACE Walla Walla District.
To reduce this risk, many agencies are currently involved in studies to better prepare for and respond to flood events, or to mitigate risk. For example, USACE is conducting a General Investigation (GI) with the Idaho Water Resource Board for flood risk reduction and water supply. FEMA completed the Risk MAP Discovery process and is developing updated Boise River flood insurance rate maps (FIRMs). Ada City-County Emergency Management (ACCEM) has recently completed an updated County Hazard Mitigation Plan and is interested in developing inundation maps to plan emergency flood response activities. The National Weather Service (NWS) is developing inundation map libraries to post on its Advanced Hydrologic Prediction Service webpage. All of these activities rely on floodplain models and maps.
The Idaho Silver Jackets capitalized on the team’s ability to network, coordinate and cooperate to successfully leverage data, analyses and other resources to develop one version of the “truth” about flood risk in the Boise River watershed. The Silver Jackets team provided the forum to coordinate analyses and resources of several agencies to develop a series of Boise River inundation maps. The hydraulic model used to create the inundation maps was initially developed during a USACE GI study. Local governments contributed additional funds, technical assistance and GIS support to partner with USACE to use the model to map additional flows under the Planning Assistance to States Program. USGS furnished updated river gage data and analyses. NWS provided technical review and funded placement of the inundation map library on its webpage. The Idaho Silver Jackets team developed and executed a watershed flood risk outreach strategy.
The end result was a consistent picture of flood risk and a hydraulic model used by many in the watershed for several purposes at a cost savings to agencies and the taxpayers. Availability of the flood inundation maps on the NWS webpage provides community leaders and residents with a better understanding of flood hazards and assists with planning, mitigation and flood response. Boise residents can go online to evaluate flooding scenarios and determine if flood insurance is necessary. Visit the NWS webpage to access the interactive flood maps posted at:
Google Earth fly-through of 0.2-percent chance flood event (500-year chance) on the Boise River in Idaho. Boise State University’s famous blue turf football stadium is on the left.
In May 2010, the City of Frankfort, KY, was impacted by a major flood. The event underlined the need for an active Silver Jackets team to take full advantage of the window of opportunity in moving flood risk management forward. One of its first priorities was to work with the City of Frankfort to promote flood awareness and assist in flood risk management. Eleven state and federal agencies including Kentucky Utilities partnered with the City of Frankfort and Franklin County to take full advantage of USACE Silver Jacket Pilot Project funding to promote multi-agency collaboration and coordination while addressing community needs. Frankfort was an excellent candidate since there were already several organizations committed to projects in the area. For example, FEMA was in the process of updating the Flood Insurance Rate Maps, the USGS was planning a flood inundation mapping initiative in response to the 2010 floods, and the electric utility was interested in updating an Emergency Action Plan for an electricity-generating dam upstream of the city. In addition, the levee system protecting Frankfort had been accredited by local officials. The Kentucky Silver Jackets charter was awarded Pilot Project funding to build upon these ongoing initiatives.
The scope of the Pilot Project covers three major activities: development of flood inundation maps for a 7 mile reach of the Kentucky River through the City of Frankfort and Franklin County, completion of a levee failure analyses for two reaches along the Kentucky River, and the preparation of Dix River Dam inundation mapping to be incorporated into an updated Emergency Action Plan. Even though these three separate activities are driven by different agencies, they share common goals and resources. There are significant cost savings in leveraging resources from federal, state, and community sources. Some of the resources leveraged include LIDAR data, hydraulic modeling on the Kentucky River, high water mark data, surveys and bathymetry, levee and dam failure analyses, local property valuation data, and funding.
Once the project is completed, there will be many tangible benefits that will result in risk reduction. The web-based, interactive flood inundation mapping product will lead to an increased awareness of flooding in general on the Kentucky River and the site specific risks of living near a levee or downstream of a dam. The interactive maps can be used as a planning tool for identification of accessible evacuation routes. An assessment of levee failure and overtopping of the Dix River Dam will include impacted areas, business interruptions, and long term recovery requirements. All the above information will be readily available to assist the City of Frankfort in updating their Flood Mitigation Plan. The project will lead to a financial savings for individual home and business owners since flood insurance premiums are expected to be reduced through the Community Rating System.
The experience of combining resources and funding for the City of Frankfort will put the Silver Jackets Team in a better position when another flood event occurs. The multi-agency approach to problem solving provides a broader and more pro-active solution. In the near future, the Team will build upon the success of this project and use a similar approach in other areas of the state.
A Silver Jackets pilot project on Wildcat Creek in and near the City of Manhattan, Riley County, Kansas, demonstrates the advantages of leveraging resources and collaborating on a shared vision for a flood risk management solution. Wildcat Creek had severe flooding in 2007, 2010, and again in June 2011. The most recent event resulted in the evacuation of over 200 people. Future flooding in the 100 square mile watershed is inevitable and could get worse unless mitigation action occurs.
With the recent flooding event fresh in the public’s mind, there was a window of opportunity available to promote flood risk management planning. In support of the multiagency need to communicate the flood risks and address the problem, the Kansas Hazard Mitigation Team working through the USACE Silver Jackets Coordinator procured Silver Jackets Pilot Project funds for a new flood warning system and flood inundation maps for the area in to enable public understanding of flood risks. For Wildcat Creek, the USACE utilized a NWS web-based process referred to as the Advance Hydrologic Prediction Service (AHPS) to produce inundation maps that depict the extent and depth of floodwater in the vicinity of a NWS forecast location. This allowed users to visualize flooded areas for discrete river levels ranging from minor flooding through the largest observed flood of record. Flood categories follow the commonly used color coding for increasing severity, similar to radar intensities. The final mapping product allows end users to simply move the mouse pointer over the various stages, and the corresponding inundation map quickly appears.
A team effort was required to produce these three dimensional flood inundation maps. The USACE started with an existing updated hydraulic model recently used by the county to update FEMA Flood Insurance Rate Maps. The county and the Kansas Division of Water Resources used current LiDAR to better define flooding delineations. The USGS recently installed two new stream gages on the creek to augment the gaging network and provide a forecast point. The city, county, and USGS had previously collected high water marks following the June 2011 flood. The USACE Kansas City District utilized the hydraulic model under the guidance of a NWS hydrologist to follow the AHPS process for establishing a range of flood elevations at a NWS newly establish forecast point. The USACE calibrated the model to the high water marks and generated incremental water surface elevations at one-foot increments to a stage above the flood of record. The generated water surface profiles processed into depth grids and met AHPS web mapping standards. After a NWS hydrologist validated the depth grid, the final product was subjected to rigorous quality control by the entire team. In August 2012, the NWS began hosting the flood inundation mapping live on the web as a tool for the public that live and work by the Wildcat Creek. The county also is capable of sending automatic flood warning messages to subscribers based on the NWS flood stages.
In conjunction with the mapping, a strategic master plan or Floodplain Management Plan (FMP) for managing flood risks in the Wildcat Creek watershed was written. The USACE collaborated with a Wildcat Creek working group and their six committees to develop a FMP. The plan documents the flood risks and committee decisions on managing flood risks while establishing action items for future mitigation efforts. The FMP meets the requirements to be eligible for both the USACE construction funds, as well as the FEMA National Flood Insurance premium reduced rates through the Community Rating System. The success of this FMP is largely due to harnessing the public within the committees immediately following the flood event. The level of public interest is much higher in that window of opportunity.
The Silver Jackets Pilot Project is integrating products from a diverse set of agencies, each offering their own square in a patchwork quilt in order to address the flood hazard problem. By the time the FMP will be completed, at least seven different government entities will be involved in providing support in such areas as: hydraulic modeling, LiDAR, GIS, gage installation and maintenance, mitigation planning, and outreach. The Wildcat Creek project is an example of how multiple agencies can collaborate to develop one flood risk management solution.
Floodplain Management Plan:
Recurring significant flood events and resultant physical damages to levees throughout the Midwest region have increased interest in implementing non-structural alternatives to levee repairs. Public Law 84-99 (P.L. 84-99) provides USACE with the authority and responsibility to either repair flood-damaged levees enrolled in its levee program or to implement non-structural alternatives to those structural repairs.
Following the Midwest floods of June 2008, the Iowa Interagency Levee Work Group (now Iowa Flood Risk Management Team [Iowa Silver Jackets]) identified and coordinated a precedent-setting non-structural alternative to full repair of the Louisa County, Iowa, #11 Levee District's levee system. The alternative is a combination of over 300 acres of Natural Resources Conservation Service flood plain easements with significantly reduced structural repairs to protect a state highway. The alternative required the cooperation of the levee's public sponsor, the county and state mitigation agencies, USACE and Natural Resources Conservation Service(NRCS) to implement. This non-structural alternative consisted of leaving five breaches in the lower end of the levee system open while repairing two breaches in the upper end of the system. The remaining increment of repaired levee will continue to provide flood deflection benefits for a major county road and approximately 400 acres of agricultural lands within the levee district.
This alternative provides reconnection of nearly 3,200 acres of previously isolated floodplain with the Iowa River as well as increased flood storage benefits to downstream interests; construction is complete. As a result of collaboration, over 1200 acres of formerly protected area was returned to the floodway, gaining not only improved environmental habitat but increase flood storage capacity while continuing to protect an important state road. The NRCS (Emergency Watershed Protection) easements were crucial in the sense that protection of those lands no longer provided benefits to support full structural repair. As implemented, the cost to PL 84-99 was estimated to be $187,000 less than the full structural repair.
The Iowa team was encouraged by this success and is currently working to implement another non-structural alternative with the Green Island Levee and Drainage District at the confluence of the Maquoketa and Mississippi Rivers (downstream of the [former] Lake Delhi Dam). USACE is providing assistance to NRCS in the development of a Wetland Reserve Enhancement Program project proposal request to acquire easements on nearly 1,400 acres of cropland previously protected by the Green Island levee.
Real Time Flood Inundation Model, Indiana