South Platte River Segment 15 Phase II Habitat Improvements

The Metro Wastewater Reclamation District (district) provides advanced secondary treatment of Denver area wastewater via its 830,000 cubic meters per-day (cmd) Robert W. Hite treatment facility (RWHTF). RWHTF effluent is discharged to Segment 15 of the South Platte River, which extends 42 kilometers from the Burlington Ditch headgate north to the river's confluence with Big Dry Creek near Fort Lupton. In Segment 15, gravel mining operations, water supply development and irrigation diversion dams have created barriers to fish migration and the possible reduction of fish populations due to flow diversion. Modifications to the river channel have replaced much of the natural aquatic habitat with steep, armored banks to prevent erosion and sharply reduced diversity in riverbed structure. The river flow regime is highly regulated by water storage and diversion facilities. Low flows are dominated by the discharge of treated wastewater effluent from the district's RWHTF. Studies conducted by the district and CDM Smith in the 1990s to support the adoption of a site-specific dissolved oxygen (DO) standard for Segment 15 revealed that overall, habitat quality in the segment is low for indigenous fish species. Scarcity of cover, stream size, shifting sand substrate and fluctuations in flow may limit aquatic species distribution and reproductive success. These findings were confirmed by a subsequent aquatic life habitat assessment completed in 2006. Based on these studies and in accordance with agreements with regulatory agencies, the district is implementing a habitat improvements program in Reach 9 of Segment 15 (Brantner Ditch diversion to 124th Avenue). The improvements are intended to provide increased aquatic habitat diversity and channel structure through varying flow depth, velocity and protective cover. The program is being conducted in six phases starting in 2008 and concluding in 2016. Phase I included habitat improvements and bank stabilization upstream of the 120th Avenue bridge. Construction of phase I improvements started in October 2008 and were completed in April 2009. Phase II habitat improvements have been designed. This includes additional habitat improvements in the general vicinity of phase I improvements. Proposed improvements include enhancing features from the original phase II improvements identified in the segment 15 Aquatic Life Assessment Report and additional improvements based on phase I monitoring and additional field reconnaissance. Construction of phase II improvements is anticipated to start in October 2011.