Paper No. 331-10
Presentation Time: 4:20 PM
IMPACTS OF A RECENT WILDFIRE AND MAJOR FLASH FLOOD ON ENDANGERED HUMPBACK CHUB HABITAT - SHINUMO CREEK, GRAND CANYON
Shinumo Creek, a major tributary by discharge (median = ~ 0.4 cms) to the Colorado River within Grand Canyon, is one of two translocation sites for the endangered humpback chub (Gila cypha). The drastically lower temperatures produced by hypolimnetic releases from Glen Canyon Dam have reduced populations of this species, as has predation by non-native trout. Shinumo Creek is a relatively high gradient perennial stream (92 m/km) that receives baseflow from springs primarily in the Redwall-Muav limestone formations. Overland flow from the Kaibab Plateau, also the recharge area for the springs, occurs following the winter snows and during brief intense monsoonal storms during summer months. The lightning-caused Galahad Fire was discovered May 23,2014, and burned 2484 hectares of ponderosa pine forest in the headwaters of the creek (~10% of the watershed), with a portion burned below the rim on extremely steep slopes. Subsequent monsoonal events caused two large floods later in the summer: the first was observed to carry substantial charcoal and ash into the Colorado River; the latter was larger with a stage approximately 5 m above base. Site visits following the floods found no fish in the mainstem of the creek, an almost totally denuded woody riparian zone, and channels severely altered with sequenced scour and fill reaches. The purpose of this study is to monitor the channel response following the fire and flood to determine when the system is appropriate for new humpback chub relocations and to determine the likelihood of future catastrophic events for the mainstem channel. Preliminary surveys indicate that the channel still retains substantial mineral fine sediment that have filled pools and fish refugia. The time required for channel stabilization will be evaluated through streamgage analysis, repeat cross-sections, pebble counts, repeat photography, and fine grained sediment mapping for the entire mainstem.