Missionary Ridge Wildfire Rehabilitation

The Missionary Ridge wildfire of 2002 burned more than 28,000 hectares (ha) (70,000 acres [ac]) near Durango, Colorado. Risks posed by increased runoff and sediment and debris flow potential were widely recognized, prompting implementation of rehabilitation measures in many areas that had burned. This paper describes the successful implementation of rehabilitation measures by the Florida Water Conservancy District (FWCD) with the assistance of Wright Water Engineers, Inc. (WWE) in the Knight Canyon and South Drainage watersheds. The watershed is located above the spillway of the Lemon Reservoir, consisting of 184 ha (454 ac), over half severely burned in the wildfire. FWCD officials were concerned with the protection of the reservoir spillway from debris flows and the potential for heavy sediment loading to the Florida River and downstream water supply intakes. FWCD, with assistance from WWE, obtained a Section 319 grant through the Colorado Department of Public Health and Environment (CDPHE) for implementation of rehabilitation measures. Rehabilitation measures implemented in the Knight Canyon and South Drainage watersheds included log erosion barriers (LEBs) over 93 ha (230 ac), at a density of 220 to 615 per ha (90 to 250 per ac) and 13 check dams and detention basins. These measures have been regularly maintained and repaired since they were installed. Five debris racks ranging in width from 5 to 14 meters (m) (15 to 47 feet [ft]) were installed along major drainage paths, and as of October 2003, had trapped nearly 150 cubic meters (m³) (200 cubic yards [yd³]) of debris. Other practices, including hand seeding of approximately 41 ha (100 ac) and mulching and hand crimping of 30 ha (75 ac) have proven effective. The effectiveness of the rehabilitation measures was truly put to the test when 6.27 centimeters (cm) (2.47 inches [in]) of rain fell over a 13-hour period on September 9, 2003. Runoff, sediment, and debris from the Knight Canyon watershed during this event were substantially less than from other comparably sized, nearby watersheds that had not received such extensive treatment. This paper also provides an overview of the effects of the Missionary Ridge wildfire of 2002 on the Knight Canyon and South Drainage, a roughly 184-ha (454-ac) watershed adjacent to the spillway of the Florida Water Conservancy District's (FWCD's) Lemon Reservoir near Durango, Colorado. The paper describes: 1) the post-fire hydrologic assessment and analyses performed by WWE in conjunction with FWCD, 2) rehabilitation efforts by FWCD including measures implemented and sources of funding, 3) effectiveness of rehabilitation measures during rainfall events since the 2002 wildfire, and 4) "lessons learned" for future rehabilitation efforts.