Unique observations and forecasts of flash floods and debris flows on the Spring Creek burn scar, Colorado, USA
Abstract
The 2018 Spring Creek wildfire in southeast Colorado was the third largest in the state's recorded history, burning 108,045 acres (437 km2). The scale and especially hot temperatures of the fire, combined with steep channel gradients draining into the low-lying town of La Veta, have led to a high probability of catastrophic flooding. In response to this threat, state and federal agencies have partnered with local authorities to deploy ground observations and unique remote-sensing instruments to protect lives by providing early warning of impending natural hazards. Given that over half of all Colorado State residents live in wildfire risk areas, the results of this study will also provide valuable insight into coordinating post-fire early warning efforts in the future.
This presentation discusses the ground instrumentation that was deployed to provide early flood warning during the monsoon season of 2019. An X-band mobile weather radar was deployed approximately 25 km to the east of the burn scar to supplement NEXRAD radar coverage at low levels. Post-wildfire flood products were developed through comparisons of real-time radar rainfall estimates to established flooding and debris flow thresholds at 15-, 30-, and 60-min accumulation periods. These products were made available to National Weather Service forecasters in Pueblo to enable longer alert lead times. On the ground, a network of rain gauges and stream radars were put in place to provide ground validation of flooding at points of interest including bridges, culverts and roads. The deployment configuration was put to the test on July 22, 2019 when the mobile weather radar measured moist, easterly flow moving upslope. Storms initiated on the north side of the burn scar and then propagated to the south, covering most of the burn scar above La Veta with intense rainfall rates, some in excess of 1.5 inches/hr. The storms produced small hail and outflow in excess of 50 knots as measured by the mobile radar. On the ground, emergency management officials provided eight reports of flash flooding with the most serious being Indian Creek "2 feet out of its banks and more than 100 yards wide". A stream radar on Upper Indian Creek recorded a surface velocity of 17.4 feet/second, a record for the instrument's manufacturer. Fortunately, damages were minimal for this event, due in part to community preparedness, inter-agency collaboration, and overland and in-stream mitigation activities. Monitoring efforts will continue in the monsoon season of 2020, demonstrating the value of unique observations and early alerts of flash flooding and debris flows on burn scars.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H31H..08G
- Keywords:
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- 1813 Eco-hydrology;
- HYDROLOGY;
- 1824 Geomorphology: general;
- HYDROLOGY;
- 1860 Streamflow;
- HYDROLOGY;
- 1871 Surface water quality;
- HYDROLOGY