2016-03-25_REVISION - M1989029 - Laserfiche WebLink

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It is noted that City funds are not able to be used on private parcels. The City is supporting the private land owners in the area through coordination with other potential funding providers. Bank Protection Improvements The first type of bank protection consists of laying back the banks to a slope of 4H:1V or flatter. Type M soil riprap (D50 = 12 inches) or Type VH void filled riprap (D50 = 24 inches) would be placed along the bank for erosion protection and would extend downward and be keyed in below the channel invert.The second type of bank projection consist of laying back the banks to a 4H:1V slope or flatter and incorporates root wads placed strategically along the creek banks near the water surface elevation to provide habitat and sanctuary for fish and aquatic species, and allow for an increase in biodiversity. Areas of root wads could have either buried riprap or soil lifts to help protect the bank slopes. The third type of bank stabilization would consist of regrading portions of the banks to a 4H:1V slope or flatter and placing native vegetation. Other Improvements The pre-flood St. Vrain Creek breached its south bank in three locations. The three breach locations will be repaired using the bank stabilization techniques discussed above. The City is repairing an existing pedestrian bridge damaged in the 2013 flood and installing a new pedestrian bridge. The existing bridge crosses the pre-flood St. Vrain Creek channel immediately downstream of the confluence with Spring Gulch #2.The repaired trail would be constructed directly to the south where a new pedestrian bridge would be constructed over the post-flood St. Vrain Creek channel.The trail will continue to the south and reconnect the greenway path. The buried riffle drop structure consists of void-filled Type VH riprap (D50 = 24 inches) and is located in the St. Vrain Creek post-flood alignment at the pedestrian bridge. No grout is included in the riffle drop structure and the slope of the drop is approximately 2%to allow for fish passage. A U.S. Army Corps of Engineers 404 permit is being obtained for the project. Native upland and riparian vegetation will be used to revegetate repaired and disturbed areas, to both give nature a jump start towards restoration and to be in compliance with the 404 permit. Agency Coordination The City has or is coordinating the proposed Resilient St. Vrain Project improvements with the following agencies and companies: • Federal Emergency Management Agency (NEPA Environmental Assessment and FEMA floodplain mapping changes) • U.S. Army Corp of Engineers (404 Permit) • U.S. Fish and Wildlife Service • U.S. Environmental Protection Agency • Boulder County • Weld County • Colorado Division of Reclamation, Mining, and Safety • Colorado Parks and Wildlife • Colorado Department of Public Health and Environment • Colorado Division of Water Resources 2