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City of Longmont Resilient St. Vrain Project Sandstone Ranch Reach Improvements Summary The City of Longmont's Resilient St. Vrain Project has been submitted to the U. S. Army Corps of Engineers under Section 404 Permit Application NWO-2015-02224-DEN. The project is part of Longmont's September 2013 flood recovery work and is supported by various levels of the Colorado State government including the Governor's Office of Flood Recovery, and the Colorado Water Conservation Board (CWCB), a sister division of the Division of Reclamation, Mining and Safety (DRMS) in the Colorado Department of Natural Resources. The Sandstone Ranch Reach of the Project includes properties within the boundaries of DRMS Permit No. M-1989-029, Longmont Distel Operations, which is operated by Aggregate Industries. In support of Aggregate Industries' application to DRMS for an amendment to Permit No. M-1989-029, the following provides a summary of the City's Resilient St. Vrain Project and also includes a summary of agency and public coordination related to this project. Overview The primary goals of stream channel improvement activities in the Sandstone Reach are stabilizing portions of the channel banks of St. Vrain Creek to protect private property, restore City and County- owned open space lands, and repair the regional recreation trail. Post-flood conditions are allowing the formation of a broad area of riparian, wetland, and aquatic habitat ideal for native fish and wildlife. The City is proposing to keep the post-flood channel in its current post-flood alignment to promote natural hydraulic, geomorphic, vegetative, and wildlife habitat development in this open space area. Additionally, Spring Gulch #2, which intersects the pre-flood St. Vrain Creek channel from the north, would include construction of a diversion structure that would allow flow to the pre-flood channel to support existing wetland and riparian habitat. The selective stabilization of the St. Vrain Creek banks in the Sandstone Reach would enhance the aquatic, wetland, and riparian functions of the post-flood and pre-flood St. Vrain Creek channels. Channel migration through geomorphological processes is a natural and acceptable process for the Sandstone Ranch Reach. Input from Colorado Parks and Wildlife included the request to minimize impacts to the stream due to the fishery,which includes rare, native species.As proposed, areas likely to erode in the vicinity of critical infrastructure along St. Vrain Creek in the Sandstone Reach would be stabilized. The primary improvements proposed in the Sandstone Reach are: • Bank stabilization • Repair of multiple breaches of the pre-flood St. Vrain Creek channel • Greenway Trail improvements including one pedestrian bridge • One buried riffle drop structure • A check structure and diversion structure to allow flows to be diverted from Spring Gulch#2 to the pre-flood St. Vrain Creek channel 1