Avalanches that recently slid from the high ridges of the Castle and Maroon creek valleys down to the creeks demonstrated a vulnerability in the city of Aspen’s water system, as a snowslide could potentially clog local streams and prevent water from reaching intake pipelines that collect it for municipal use.
A slide on Saturday reached Castle Creek above the city’s main water diversion, but it did not deliver enough debris into the channel to block flows. Two or three additional slides as well over the past few days covered Maroon Creek, where the city also collects water for delivery to the treatment plant above Aspen Valley Hospital on Doolittle Drive.
Those slides temporarily curtailed flows in Maroon Creek, but the water was able to find a way through within a matter of hours, said Tyler Christoff, the city’s deputy director of utilities. The city limited diversions to its hydroelectric turbine fed by Maroon Creek as a proactive measure out of concern for limited flows, he said.
Throughout the incidents, the city was able to maintain normal water operations, where most water fed into the system comes from Castle Creek, augmented by roughly a day’s worth of storage at winter demand levels held in Thomas Reservoir at the water treatment plant.
Officials were on high alert, particularly by Friday, when avalanche danger had reached extreme levels, thanks to feet of heavy, wet snow on top of an already fragile snowpack. Christoff said he communicated with Pitkin County officials on Friday evening, hours before the slide that closed Castle Creek Road until 8 p.m. Saturday, “to make them aware of the connection between the river and our water system.”
If that slide had blocked flows in the creek, the city would hope that Maroon Creek was flowing and take all its water from that source.
The problem, Christoff noted, is that terrain in the Castle and Maroon creek valleys shares similar characteristics, and if slides are coming down in one drainage they are also likely happening in the other.
Avalanches that reach the creeks are relatively rare but will happen from time to time, sure as the snow falls. A prior incident in the early ’90s did impact the city’s ability to collect water from the creeks.
In the event that water is cut off from the city’s intake pipelines, the city would seek water reductions from users. Given that water demand is lower in the winter than the summer because of the lack of outdoor irrigation, overall demand is lower this time of year.
Depending on the severity of the creek blockage, the city would work with the Army Corps of Engineers on a plan to remove the debris, Christoff added.
The threat to the creeks from an avalanche, or potentially wildfire in the summer contaminating water, are among the reasons the city has been seeking water storage. Officials are moving away from conditional water rights held since the 1960s to store water in potential reservoirs on upper Castle and Maroon creeks, and are evaluating the feasibility of an off-channel reservoir located near Woody Creek, which would require a pipeline and pump station to get water back uphill to Aspen.
The city is also looking to update its stream gauge on Castle Creek to a U.S. Geological Survey gauge, which is the type of gauge used on Maroon Creek. Those gauges deliver real-time info available to the public online. The city’s current gauge on Castle Creek relays data on an internal system, and that data is subject to a half-hour to hour delay, Christoff said.