In June 2010, the Middle Fork Popo Agie River rushed into the City of Lander, Wyoming at levels equivalent to a 50-year flood.  The flooded river destroyed two bridges, washed away a small cabin and caused other infrastructure damage throughout the city.  After the flood, IMA was contracted by the Popo Agie Conservation District and the Wyoming Game and Fish Department to come up with a restoration plan that could withstand future flooding while still providing fish habitat during low flow periods when irrigation withdrawals drain the river to below 10 cubic-feet per second.  Besides the wide range of flow events to consider, other project challenges included heavily armored outside banks that were rip-rapped by private landowners before and after the flood, numerous bridges crossing the river, and high rates of sediment transport through the study reach.  After surveying two miles of the river using Total Station technology, IMA performed a geomorphic analysis and compared conditions before the flood to those observed after.  IMA also analyzed sediment transport and used HEC-RAS modeling in the FEMA-mapped section to ensure that restoration designs will not result in a rise of future flood elevations.  Due to the changing geomorphic conditions through the two mile reach, IMA divided the project into reaches and a final design was prepared for the City Park section.  Construction of this section is slated for February 2016.  Concept designs were developed for the remaining reaches so that landowners can implement restoration projects that not only protect from flooding damage but also absorb energy and provide quality fish habitat at a range of flows.

Design Plan

Design Plan

Design Plan

Design Plan

2015 - Post-flood.  Large cobble is all that remains in the channel

2015 - Post-flood.  Large cobble is all that remains in the channel

2015 - Post-flood.  Rip-rapped banks and a channel with little definition or habitat

2015 - Post-flood.  Rip-rapped banks and a channel with little definition or habitat

June 2010 flooding

June 2010 flooding