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ProCessional Activities (Continued from page 2) John Doerfer, Project Hydrologist, Master Planning Program "Chairman of the Stormwater Quality Committee, Colorado Association of Stormwater and floodPlain Managers (CASFM). "Chairman of Awards Committee, 1997 CASFM Annual Conference. "1nsIructor on "Stormwater Systems" at Collection and Distribution Systems Short Course sponsored by Rocky Mountain Chapter of Water Environment Federation and APW A in Boulder in November. Marl< Hunter, Chief. Ma1ntenanee Program "Member ofInternatlonal Erosion Control Association (lECA) standards committee on riprap, standards committee on articulating blocks, and the by-laws committee. *SecretaIy of the Board of Directors for the mCA-Mountain States Chapter. Paul Hindman, Project Engineer, Design and Construction Program *Received Master of Science degree in Management from the Uuiversity of Colorado at Denver in May. *Treasurer of the Colorado Chapter of APW A. ,. , I i f ALTERNATIVE BANK STABII T7",TION ON THE SOUTH PLATTE RIVER By Bryan w. Koblenberg, P.E., Projoct Engineer South Platte Ri_ Program , ~ Actively eroding hanks along the South Platte River are typically vertical with minimal amounts of vegetation along the too. The traditional method for stabilization involves laying back to a 2:1 slope and armoring the slope with riprap. In the last 10 years the District has modified this by providing a flatter slope and using buried revegetated riprap to enhance the riparian habitat Recently the South Plattl River program has tried usingbendway weirs (i.e., rock jetties) to arrest hank erosion. In a typical river bend, surface water currents tend to move toward the outer bank, concentrating flow and higher velocities along the hank edge, resulting in severe hank erosion. The traditional rock riprap revetment installation resists this increased hank velocity. The bendway weir method, however, involves redirecting the hank velocity away from the hank towards the middle of the bend. With a series of weirs angled upstream along the outside of a bend, the current is redirected through the bend and into the downstream crossing. For the last four years, a bending reach of the South Platte River in Adams County was observed to have moved 50 feet laterally, endangering several //14// \ PLAN , I I I ../i.-;!a.--_--..-OG--..--- ELEVATION IN-STREAM WEIRS SECTIDN matore cottonwood trees. Since the traditional method required removal of the trees, the weir concept was tried for hank stabilization. At a cost equivalent to the hank lining method, the District installed a series of five jetties along the outside bend of this river reach at approximately 15200 Avenue in Adams County. The jetties are essentially small berms of 12 inch (dso) riprap keyed into the existing bank, extending into the low flow channo:\ approximately 40 feet and angled 5 to 15 degrees upstream (See Figure). The rock was mixed with in- situ soils and revegetated with willows and native grass where possible. Since construction early this year we have observed: 23 . SMiment deposition between jetties and adjacent to the vertical hank. . New scour holes at the jetty points (great fish habitat). . Erosion along the vertical hank has stopped. . Woody debris can be placed between jetties with little or no anchoring needed. The District will try additional installations such as this and will continue to monitor them over the next few years. We will report our finding< in future issues of Flood Hazord News.