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Olsson helps tame flooding and protect communities

Friday, May 23, 2014

Sarah Ferdico, Communications

Spring rains bring with them the promise of warmer weather and greener landscapes. They replenish our waterways and help our crops and plants grow. But when these rains turn destructive, they can unleash torrents of water that overrun streambanks and cause untold destruction on lives and property.

Olsson Associates has been involved with numerous flood control and mitigation projects that successfully help protect people and facilities from flooding. Below are a few recent examples of projects where Olsson’s Water Resources staff members have provided their services.

Upper Antelope Creek Flood Reduction Improvements; Lincoln, Nebraska

Upper Antelope CreekOlsson Associates completed design work on a flood reduction project along Lincoln’s Antelope Creek, and its construction is now complete. The project was a follow-up effort to the Antelope Valley Project, which confined flooding to the channel banks in the east downtown area of Lincoln along lower Antelope Creek. 

The upper Antelope Creek project reach was a perennially flood-prone area that included many commercial and residential facilities and the Lincoln Children’s Zoo. The stream channel included a popular pedestrian trail and was adjacent to a major arterial road. Design elements included adding two box culverts to supplement an existing bridge under one of Lincoln’s major streets near the zoo, realigning a portion of the bike and pedestrian trail, constructing two flood-control berms to create detention storage in Antelope Park along the tributary to Antelope Creek, installing a small detention cell in Antelope Park, and constructing channel improvements along with new retaining walls in Antelope Creek.

The goals of the project entailed the following:

  • Reducing the extent of the floodplain in the project area and removing 430 homes, businesses, and structures from the 100-year floodplain
  • Stabilizing the bed and banks of Antelope Creek

Boulder Creek Flood Repairs; Boulder, Colorado

Boulder Creek near 95th Street (Copyright 2013 Google)One of the catastrophic results of the September 2013 Colorado flooding was the flooding of Boulder Creek. Between September 11 and 15, approximately 17 inches of rain caused Boulder Creek to fill and overflow. The power of the rushing water broke down creek banks and created new, disruptive pathways that adversely affected the community well beyond the temporary presence of the floodwaters. Since then, Olsson has been working on two projects to help get Boulder Creek back to pre-flood conditions.

One project is at 61st Street, where flooding shifted the water flow, bypassing a diversion established to irrigate up to 600 acres of land. Olsson designed repairs to divert flows back to the original channel and allow for water rights to be exercised.

The other project is at 95th Street, where floodwaters pushed out of a tight meander bend, creating a new pathway that flooded over 95th Street in Boulder County and forced the road to be closed. Following the flood, an emergency repair channel was excavated to direct water back into the channel and allow the road to be opened. As part of a restoration plan for the project area, Olsson completed a design to reestablish a meander bend and use the emergency repair channel as a split flow during high-flow events. This secondary channel will help decrease the pressure on the reestablished meander bend to keep it in place during future high-flow events. Construction of the project is complete.

Cleveland Lake; Belton, Missouri

Cleveland LakePlanned and designed by Olsson Associates, the Cleveland Regional Lake in Belton, Missouri, was constructed and opened in the fall of 2013. The project is the city’s first multi-purpose recreational and flood control lake. The primary goal and benefit of the lake is to reduce downstream flood levels to protect 22 homes and two major roadways located in the FEMA 100-year floodplain. The lake and park also provide a popular recreational amenity that is used by citizens daily for its pedestrian trails, wetland boardwalks, boat launch, greenspaces, and forested areas.

The design also included an outdoor classroom area that is used by the nearby Belton schools. The trail system constructed with the project, and partially funded by the Missouri Department of Natural Resources, connects the outdoor classroom with the lake wetlands, boardwalks, and fishing jetties. Other key elements designed by Olsson include:

  • Pretreatment wetlands with boardwalks and interpretive signage
  • Pretreatment sediment forebays
  • Earthen dam and spillway system
  • Recreational amenities including interpretive trails, a boat launch, vistas, outdoor classrooms, and parking lots
  • Sanitary sewer relocations

Olsson completed a feasibility study, final design documents for construction, geotechnical investigations and design, all permitting through the US Army Corps of Engineers and FEMA, and construction observation services.  Olsson also facilitated creating a stream conservation easement to help offset 404 stream mitigation costs.

State of Kansas Floodplain Modeling and Mapping; Kansas Division of Water Resources

RiskMap Flood Risk ReportOver the last three years, Olsson’s Water Resources Practice has completed the two first Federal Emergency Management Agency (FEMA) RiskMAP projects for the State of Kansas, Division of Water Resources. This is an innovative new process that goes beyond FEMA’s standard floodplain mapping by helping communities and agencies within a large watershed work to identify flood risk and plan and take action to mitigate those risks.

Olsson completed RiskMAP projects for the Lower Big Blue and Lower Little Blue watersheds in northern Kansas that, together, totaled nearly 2,000 square miles. Olsson’s first task involved extensive outreach efforts with community meetings and follow-up correspondence to identify known problem areas in cities and unincorporated areas. In parallel, Olsson developed digital terrain and floodplain mapping data using geographic information system (GIS) to identify where flood risks would be the highest. More than a basic floodplain map, these maps illustrate the flood risk zones with depth grids and percent chance of flooding over a 30-year period to help citizens better understand how risk fluctuates within given flood zones. These maps were combined with community input and historical knowledge to identify areas with the highest mitigation needs.

These RiskMAP products are near completion and will serve to position communities within the watershed for future mitigation funding and as a blueprint for communities to work together to manage flood risk within their watershed.

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