RUNOFF, EROSION, AND EFFECTIVENESS OF REHABILITATION TREATMENTS AFTER THE 2002 HAYMAN FIRE, COLORADO FRONT RANGE

In May-June 2002 the Schoonover and Hayman fires collectively burned over 500 km2 in the Colorado Front Range southwest of Denver. Post-fire effects on runoff and erosion are of tremendous public concern because runoff directly affects Denver's water supply and the number of people in and adjacent to the burned area. The primary goals of our work are: (1) to evaluate the effects of these fires on runoff, erosion, and aquatic resources at both the hillslope and small-catchment scales; and (2) evaluate the effectiveness of the post-fire rehabilitation treatments.

At the hillslope scale we are using sediment fences in 15-20 paired swales to measure post-fire erosion rates and the effects of different post-fire rehabilitation treatments. Within each pair one swale is an untreated control and the other is being subjected to one of four treatments: hydromulching, harrowing and seeding, application of a polyacrylamide, or dry mulching. Rainfall is being recorded with tipping bucket rain gages, and for each swale we are measuring the independent variables of percent cover, soil water repellency, hillslope and swale axis gradients, and contributing area.

Runoff, water quality, and channel characteristics are being assessed in catchments that are 3.0 and 6.2 km2, respectively. Approximately the upper two-thirds of each catchment was burned at high severity, and the larger catchment will be treated by aerial mulching with the other being left as a control. Runoff is being monitored with 0.76-m H-flumes that were installed prior to or just after the fire. Water quality samples had been collected approximately monthly for one year prior to the fire, and will be collected on a more frequent basis after burning. Study reaches were established in these two catchments as well as two other catchments that were burned in June 2002, and these are being remeasured in early and late summer 2002.

Studies on other fires in the Colorado Front Range have shown that the largest runoff events and approximately 90% of the annual erosion is caused by convective storms from mid-July to early September. Hence the results from the first four months after burning should represent most of the hydrologic and geomorphic effects expected for the first year after burning.