West of Lyons off Highway 7 on Old South St. Vrain Road
- To restore the access road to its pre-flood function, location, and capacity
- To protect the roadway from erosion during future flooding
- To realign South St. Vrain Creek sufficient to allow for reconstruction
- To employ design strategies that support the ecosystem functions of the riparian corridor
The purpose of Hall Ranch 2 Access Road Repair (the project) is to restore access to Boulder County’s Hall Ranch 2 open space property from Old South St. Vrain Road by repairing damage to the road caused by the 2013 flood and by moving South St. Vrain Creek back to its pre-flood location. Mitigation measures are also incorporated into the design of the project to minimize the potential for flood-caused erosion in up to 100-year events. The important ecosystem functions of the riparian area are supported by the inclusion of natural channel design elements and by minimizing the overall project footprint while also complementing the objectives of other flood recovery projects along the creek such as the Boulder County South St. Vrain Creek Restoration Project at Hall Meadows.
The project is located along a one-half mile section of damaged access road. Flooding and high water velocities during the disaster stripped the gravel road surface, eroded gullies through the road surface and sub-base, and damaged culverts. Debris flows across the road also clogged roadside ditches with sediment and other debris. Most significantly, a 240 foot section of the access road was completely eroded where the channel of South St. Vrain Creek shifted into the road alignment. In order to reconstruct the road in this area, it is necessary to move the creek channel back to its pre-flood location in order to make room for the proposed road reconstruction. The channel will be constructed such that it safely conveys the 100-year flood event. A low-water crossing is also being added to convey drainage from a tributary to the creek that must cross the road to connect to South St. Vrain Creek.
Even though an open space management plan has not yet been adopted for this property, it shares many of the same open space values and functions as the adjacent Hall Ranch and Heil Valley Ranch open space properties. An interdisciplinary team of Parks and Open Space staff have been involved in the design development process to ensure these values and characteristics have been thoughtfully considered in the design.