Emergency Watershed Protection
Recovery After Wildfires + Floods
Upper Fourmile Creek at Wall Street
Located 10 miles west of Boulder, the Wall Street community and surrounding Upper Fourmile Creek Watershed have experienced a sequence of compounding disasters over the last decade.
In 2010, the Fourmile Canyon Fire burned 23 percent of the watershed, destroyed more than 160 homes, and left the comminuties in the canyon vulnerable to flooding. Typical summer thunderstorms over the burned area in 2011 and 2012 produced flash floods that transported a significant amount of sediment and debris into the creek corridor, plugging culverts and reducing the channel capacity.
The following year, the September 2013 flood unleashed 13-18 inches of rain over the wildfire’s burn scar, inundating the canyon with floodwaters, sediment, and debris. The flood destroyed local roads and homes built within the active creek corridor, and washed out every crossing in the Wall Street neighborhood. Some residents were stranded due to impassable roads and had to hike to a nearby ridge and await helicopter evacuation.
September 2013: Flood damage in the Upper Fourmile Creek Watershed--note the scorch marks on the trees on the hillside from the 2010 Fourmile Fire. Photo: Fourmile Fire Protection District
Stabilize streambanks to protect against additional damage to existing infrastructure
Restore the stream discharge capacity to pre-disaster levels where feasible
Remove sediment and provide storage locations for future sediment pulses
Rebuild diversion structures and protect holding ponds and cisterns used for firefighting in the watershed
Improve water quality through the reduction of sediment loading caused by bank erosion; establish cover on critically eroding land.
Enhance riparian habitat through revegetation. Improve fish habitat through revegetation, improved water quality, and better in-stream habitat complexity
The Wall Street EWP project was built to mitigate flood damage in the watershed by removing sediment and debris from the channel and floodplains. Anticipating large amounts of sediment entering the creek over the coming years due to debris flows and hillslope erosion in the burned watershed, the project increased the ability of the creek corridor to convey future floodwaters and provided locations for sediment to be deposited away from homes and roadways.
Additionally, the Wall Street project revegetated nearly four acres of land in the creek corridor. Disturbed areas were stabilized with native plants that will stabilize soils and stream banks as they establish.
The project also constructed two fish-friendly diversion structures that feed water to ponds used by the Four Mile Fire Protection District for fire fighting and wildfire mitigation activities.
The project's design gave the river room to adjust and to protect assets at the margins of the creek corridor. In locations where bank protection was necessary, the project stabilized eroding and failing streambanks with several different types of bioengineering treatments, consisting of combinations of rock and plant materials. All treatments were installed in conjunction with live willow plants. As the plants establish, their root systems will intertwine and develop mats that are more resistant to erosive forces than bare soil alone.
The project was designed and constructed for the Fourmile Watershed Coalition and was completed as part of the flood recovery and restoration activities associated with the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Phase 2 Emergency Watershed Protection (EWP) Program. This design work is supported by NRCS Phase 2 EWP Program Technical Assistance (TA) funding but is based upon the previous work undertaken in the reach as a part of the Community Development Block Grant – Disaster Relief (CDBG-DR) Planning for Resilience Program Study. Match funding and funding for the diversion structures was provided by the Fourmile Watershed Coalition via the Fourmile Fire District though a grant funded by the CDBG-DR Watershed Resilience Pilot Program. The total project cost was approximatly 1.4 million dollars.