AGCI Insight

Muddy waters don’t always mean the blues

May 7, 2015

Rivers running red may sound ominous, but in the Roaring Fork Watershed it is a common spring phenomena. Heavy (or persistent) rains wash the red, iron-rich soil from steep areas of the slopes surrounding the Frying Pan into the swift-flowing waters of the river. This sediment laden water is carried downstream to Basalt where it joins the also high-flowing Roaring Fork River, creating a striking visual at the confluence.

That there has been a lot of erosion in the last few days is no surprise. Over the last week, all of our soil moisture stations showed a total of over .95 inches of rain, with the Brush Creek station (near Snowmass Village) and Glassier Ranch station (near Basalt) showing as much as 1.39 inches in a single week. Between .8 and .9 inches of that rain fell in just 24 hours. To put that in scale, the Roaring Fork Valley receives only 16-19 inches of precipitation on average per year. Last year, the most rain falling in a single 24 hour period was around .8 inches. Last year, such deluges did not occur until late summer.

In the arid state of Colorado, a moderate soaking is generally considered a good thing. What this heavy rain in early May means for water availability during the rest of the growing season is (like the Frying Pan) unclear. The rate at which soil dries depends on a number of related factors including air temperature, humidity, and plant water use. Consequently, weather conditions over the coming months will play a big role in how long this moisture sticks around in the soil.

So far, this week’s rain has raised soil moisture by the notable amount of between 7 and 10% at our sites at a 2 inch depth. Soil moisture at the 8 and 20 inch depths has only risen by between 1 and 2% so far, but as water from the shallow depths has time to percolate, these numbers may rise further.

As we continue to move toward summer, collection of data from the research sites will help to illuminate the relationship between precipitation, temperature, and soil moisture. In the meantime, the vegetation shows its response to the rain by making the valley look especially verdant and bright.

Data from the Smuggler Mountain Site from 4/30/15-05/07/15. It is important to note that the scales of water moisture are not consistent across the three graphs. As a result, although all lines visually appear to rise by similar amounts, the 2in depth is actually showing a much greater increase numerically. Image Credit: AGCI, using Hobolink data collection and graphs.