Oxbow Restoration is a Win for the Environment and Communities
The Nature Conservancy • Iowa
Solution Overview
Client:
The Nature Conservancy
Business Challenge:
- Restore vital avian and riparian habitat while ensuring the safe, effective management of existing watershed quality
Solution:
- Develop a plan to address both structural and environmental aspects of oxbow restoration
- Execute excavation while maintaining riverbank integrity following the installation of wildflowers and grasses designed to restore native species habitat
Results:
- Reduced nitrate levels in the river
- Renewed wildlife habitats
- Improved water quality
- Ensured flood management for the arboretum
Challenge
Rivers naturally want to curve and meander through our landscape. Over time, the force of the water erodes through bends and river banks causing portions of the old channel to become abandoned as the river creates a new path. These abandoned channels in the river are called oxbows.
In the 20th century, farmers straightened rivers to increase land availability. Floodwaters, instead of soaking into the water table, sliced straight down the river channels, which in turn increased erosion, nutrient runoff, and the likelihood of downstream floods. At the same time, farmers began spreading manufactured nitrate fertilizer on their fields. That nitrate washes out into river channels, contaminating water sources.
Over time, many oxbows dried up and disappeared, and with them, the habitat for hundreds of species of birds and fish, and in Iowa, this included the endangered Topeka shiner.
Additionally, since oxbows provide storage for 1M gallons of floodwater per acre of oxbow wetland, their disappearance and degradation impacts local flooding and can lead to adverse impacts to nearby infrastructure.
Since 2017, 14 oxbows have been recreated in communities across Iowa under a partnership between The Nature Conservancy and the Polk Soil and Water Conservation District (SWCD). Apex Companies was hired to provide safe, effective water resource management in an additional local watershed, which The Nature Conservancy seeks to protect and preserve.
Solution
To restore an oxbow, restoration crews excavate accumulated sediment down to the original level of the stream channel. The restored oxbow is left to fill with water and the banks are seeded with natural vegetation. Once reconstructed and naturally refilled, oxbows:
- Offer an efficient way to rebuild water storage
- Create a habitat for both birds and fish
- Help control flooding
- Provide reliable water sources for livestock
- Remove and sequester 45-90% of nitrates from water runoff
- Create enhanced recreational fishing opportunities
After the Brenton Arboretum, a 141-acre botanical garden in Iowa was identified as a site where oxbow restoration could lead to significant benefits, our Apex team excavated 3K+ cubic yards of soil from a 400-foot section of abandoned river channel. After the oxbow was created, the team seeded the banks to a mix of native wildflowers and grasses before installing straw matting to hold soil and seed in place during the establishment phase.
Results
Our work restored the oxbow which reduced nitrate levels in the river, established wildlife habitats for a variety of species, filtered water for improved quality, and helped ensure flood management for the arboretum.