Grizzly Creek Fire: Water Quality, Rain Gauge and Soil Moisture Monitoring In and Near the Burn Scar

Grizzly Creek fire and post fire photos courtesy CDOT, Mike Sawyer, Frank Martin and MCWC.

In 2021, MCWC worked with partners to set up a water quality and precipitation information network to address immediate needs in the year following the fire. Equipment purchases in 2021 included placing rain gauges in seven locations in Glenwood Canyon to monitor storm events, placing a 6-parameter data sonde at No Name Creek for water quality monitoring, and purchasing a refrigerated ISCO sampler and an Isokinetic sampler with associated deployment equipment for automatic water quality sampling on the Colorado River. Synoptic water quality sampling included baseline measures prior to the first runoff post fire as well as sampling during and after runoff events and during post fire debris flows.

Project work in 2022 continued to address water quality issues created from debris flows, runoff, ash flows, sedimentation and nutrient loading. Soil moisture sensors and additional in-channel water quality monitoring at downstream locations were added to the information network to monitor changes to water quality and quantity. Continued support of the rain gauge network provided data to the National Oceanic and Atmospheric Administration (NOAA), the National Weather Service, and the Colorado Department of Transportation (CDOT) to inform the decision-making process when issuing flash flood watches and warnings in Glenwood Canyon. In addition, an integrated and customizable Data Dashboard was created to display real-time information for water quality, precipitation and soil moisture conditions.

The USGS installed a ISCO auto-sampler at the Colorado River above the Roaring Fork River near Glenwood Springs, CO in April 2022. The unit is controlled by a python script running on the pre-existing data logger. The script interprets the turbidity values from the water-quality sonde in real time, and activates the sampler based on predefined thresholds. It can also be activated remotely via cellular telemetry.

The refrigerated sampler was installed to collect samples during runoff events which originated within the Grizzly Creek Fire burn scar. These events have very short travel times and are often in the middle of the night. This makes it unlikely that samples can be obtained using traditional methods (via personnel sampling from the bridge). Additionally, the nutrient analytes require preservation which is achieved in the short-term via the refrigeration function of the Avalanche sampler.

In addition to the ISCO sampler located at the Colorado River above the Roaring Fork River confluence, a custom mobile crane was fabricated to mount to a USGS UTV or pickup truck, allowing USGS to collect equal-width-increment samples from the nearby pedestrian bridge.

In 2022, the USGS continued the collection of discrete water quality samples at the following locations within or near the Grizzly Creek burn scar:

·       Grizzly Creek above Colorado River Mouth near Glenwood Springs

·       No Name Creek above Colorado River Mouth near Glenwood Springs

·       Colorado River above Roaring Fork River at Glenwood Springs

·       Mitchell Creek at County Road 136 near Glenwood Springs

The sampling locations on Grizzly Creek, No Name Creek, and the Colorado River all receive runoff from the Grizzly Creek Fire burn scar, while the Mitchell Creek location provides data for “baseline” conditions, as it was not impacted by the Grizzly Creek Fire. Four discreate samples were collected at each location.

The timing of each sample in 2022 captured a broad range of hydrologic conditions which can be observed in the Colorado River above the Roaring Fork River hydrograph below. Each yellow triangle represents a sampling event.

The discrete samples at these 4 locations are being analyzed for the following analytes:

·       Major Ions

·       Nutrients

·       Trace Elements

·       Dissolved Organic Carbon

·       Alkalinity

·       Ultraviolet Absorbance

·       Nitrogen and Oxygen Isotopes

Mid-reach Water Quality Monitoring Station

To reduce impacts to downstream water users and to promote operation of facilities receiving water impacted by post-fire contaminants and turbidity, additional monitoring equipment was installed to operate seasonally in the Colorado River in 2022. Due to a 61-mile gap between the USGS monitoring stations at Cameo and South Canyon on the Colorado river, adding mid-stream station locations allowed for more accurate water quality monitoring for downstream locations.  Equipment purchased and installed by USGS included an ISCO auto-sampler and a YSI 5-parameter water quality sonde at Rulison, and a 2-parameter water quality sonde provided by USGS was installed at a site above Silt.

Silt 2-P Sonde installation and 5-P Sonde at Rulison

Meteorological Stations

Seven rain gauges were installed within the Grizzly Creek Fire burn scar in 2021 at the following locations:

·       Windy Point Met Station

·       No Name Met Station

·       East Fork Dead horse Met Station

·       Coffee Pot Met Station

·       Cinnamon Creek Complex Met Station

·       Cinnamon Creek Met Station

·       Deadmans Creek Met Station

These stations allow for 5-minute readings and data upload via telemetry every 15 minutes. Instantaneous alerts were sent to the National Weather Service (NWS), which was crucial during two separate radar outages during the 2022 monsoon season.

Soil Moisture Sensors

Soil moisture is measured in the Grizzly Creek Fire burn scar area to determine levels of absorption for melting snowpack and precipitation. With drier soils, the snowpack will first be absorbed before contributing to runoff, which results in lower water levels in rivers, streams, and reservoirs. Soil moisture values will help refine rainfall thresholds for future events.

Seven soil moisture sensors were placed at four of the rain gauge locations in Glenwood Canyon. All sensors are approximately 10 centimeters below the surface in undisturbed soil. The Coffee Pot, Deadmans, and E.F. Dead Horse sites each have redundant sensors and sensors.

Coffee Pot Soil Moisture Monitoring

The soil moisture sensors will help inform precipitation thresholds when flow is detected in the channels. Flows can be due to storm intensity and saturation excess. Many of the storms in 2022 experienced excess driven infiltration, but there were no debris flows with the rain events.

The soil moisture sensors are intended to monitor soil moisture conditions and report them on the USGS NWIS website in near-real time. The instruments are co-located at precipitation gauge locations and are intended to represent local site conditions, i.e. the open meadows at the precipitation sites and not areas under a closed canopy nearby.

If the soil is dry, it first will be saturated by rain before additional rain percolates into the soil. Some sites have a better soil moisture response due to soil type, where the sensor is located, and various other external reasons. At the beginning of relaying data, there was some concern on whether the monitors were transmitting data correctly, but USGS was able to justify the responses through correlation with the associated rain gauges and other soil moisture sensors.