Overview

CGS is tasked with reducing the impact of geologic hazards on the citizens of Colorado by providing geologic advice and information to homeowners and other landowners as well as local governments. As part of the Colorado School of Mines, CGS is also tasked with conducting geological engineering and earth science research on applied problems that directly impact the safety of citizens of Colorado. Landslides are a common geologic phenomenon in Colorado. These include debris and mud flows especially those generated in post-wildfire environments. Impacts to developed areas, especially to roads and homes can be significant and dangerous both to property and life. Systems typically used to aid the prediction of debris flows involve real time weather and radar data. Where detailed rainfall models are available, with knowledge of past duration and intensity records leading to debris flows, this can lead to the development of rainfall “trigger points” for emergency managers in charge of public safety and evacuation notifications. However, there is no data available on the soil properties of the material that mobilizes into a debris flow. The strength of the soils, water content, and point that the soil will mobilize into a debris flow is typically unknown. Soil properties combined with weather data may increase accuracy in developing the trigger points for early warning of debris flows.

To advance the early warning capabilities for debris flow prediction, CGS partnered with Dr. Ning Lu and Dr. Alexandra Wayllace with the Civil and Environmental Engineering department of the Colorado School of Mines. Dr. Ning Lu presented the 2017 Ralph B. Peck Lecture: A New Paradigm for Slope Stability Analysis provided below. The Peck lecture includes background on rainfall-induced landslide prediction framework developed by Dr. Lu in collaboration with the USGS. The framework includes data collection in the field, lab, and subsequent numerical modeling to determine “trigger points” of rainfall leading to debris flows.

Project

This pilot project was initiated to develop an early warning system for areas with known debris flow/shallow landslide problems in a post-fire environment that pose a direct threat to life and property. The focus area for this project is Ingram Gulch in Boulder County, which was affected by the Fourmile Fire in 2010. The Fourmile Wildfire occurred on September 7, 2010 and lasted eight days destroying 169 homes. Following the fire, debris flows and flowing occurred in 2011 and 2013. The area remains prone to rainfall-induced events, including debris flow, mudflow, and flooding.

CGS began work modeling debris flow hazards in the Gold Run drainage in 2017. CWCB funds became available to help research rainfall and soil property thresholds that could be used in an early warning system.

The site is in a steep-sided gulch intensely burned during the wildfire event. The underlying bedrock of granodiorite with pegmatite dikes forms highly fractured and loose outcrops. The surface deposits include rockfall debris, finer material weathered from the bedrock, and shallow soils. This surficial material is readily transported during rainfall events.

An objective of this pilot project in Ingram Gulch is to design an early warning system that can benefit Boulder County but also other areas of Colorado at risk from debris flows, especially post-fire debris flows. Additional objectives include understanding the main mechanisms that affect hillslope stability in Ingram gulch. The data provided in this web page is part of a designed system developed to forecast hillslope instability at Ingram Gulch. This system integrates field monitoring, laboratory testing, and numerical modeling.