Walden Ponds Wildlife Habitat was severely damaged during the September 2013 flood event. Damage was extensive and impacted visitor facilities as well as water infrastructure. The Boulder County Parks and Open Space Department (BCPOS) has developed the following proposal for recovery at the open space to bring it back to an enjoyable place for walking, birding, fishing and watching wildlife.
Trails
Trail damage at Walden Ponds and on the Heatherwood Trail was extensive. More than 5,000 feet of trail needs to be repaired, from replacing lost crusher fines to rebuilding the bank of Boulder Creek and installing a completely new trail bed.
Pond Breaches
The flood waters created two breaches between ponds. Based on post-flood damage assessment, it seems that both banks were over-topped by water and then eroded until failure. The furthest west breach, from Bass Pond into Cottonwood Marsh, is about 90-feet wide while the breach from Cottonwood into Wally Toevs is 30-feet wide.
The two breaches impact trails, as well as water control and fisheries management. The trail system is extremely popular and our goal is to restore access to the park, where permitted in the Walden Ponds Management Plan. The breach also impacted the movement of water between ponds which allowed staff to maintain fisheries and wildlife habitat. In the past, the department used a series of structures between ponds to regulate water depth. The separations between the ponds allowed us to stock Wally Toevs Pond for recreational fishing while keeping Cottonwood Marsh as wildlife habitat. Any restoration plan will need to address all of these services provided by the banks and water structures.
The breach between Cottonwood and Wally Toevs is small, but at an awkward location right at the northern edge of both ponds. The trail at this location provides a flat surface for fishing access to Wally Toevs. Future work will need to regulate water depth and block fish from moving between the ponds. Keeping in mind all these requirements, recreation and facilities staff propose a bridge across the breach with a concrete structure that could act as a spillway and an impediment to fish movement.
The second breach, between Bass Pond and Cottonwood Marsh, is large. The location and length of the bank on either side of the breach pose a different challenge. Beyond restoring trail access, the department wants to manage water movement without recreating a condition that would breach in a future flood. Department staff propose a sloped crossing made of either concrete or riprap and concrete that would lower the bank height but create an armored section that would be unlikely to fail in future flooding.
Next Steps
In concert with the Federal Emergency Management Agency (FEMA), Parks and Open Space has developed a plan to restore the trails at Walden Ponds Wildlife Habitat and the Heatherwood Trail. Repair work began this summer but it cannot be fully completed until the breaches are repaired. The repair of the two breaches requires an additional process with FEMA. In order to change a damaged facility from pre-flood condition, we will need to prove that the change improves the facility and that the new facility will be less likely to be damaged in future flooding. This process will continue into 2015.