Spring Snowmelt and Flow on the Tuolumne River
Given the intense heat over the last few days, it is hard to remember that today is only the first day of summer.
Our wild and wet winter included some intense rainstorms but also left oodles of snow in the high country. The rate of snowmelt has increased as the weather heated up during the spring.
Daily flow data is measured or calculated at a number of stations, inlcuding those shown below. Water managers, rafters and kayakers, and yours truly keep close track of what is happening in the watershed.
The (data rich) chart below plots daily values for
Some of the early spikes in flow are due to rain, with decreased temperature (April 7 for example). As the spring progressed, however, Tuolumne River flows have corresponded largely with warming temperatures which melt snow in the high country.
The highest flow, 20,149 cubic feet per second, occurred on the last day of spring as the average temperature at Tuolumne Meadows reached 60 degrees (up to 80 degrees during the day but down to 42 degrees at night)
Note that in the late spring, the majority of the Tuolumne's flow comes into Hetch Hetchy along the main river and into Cherry Reservoir. By May, rainfall and lower elevation snowmelt is less of a factor.
July flows are expected to be about one half of what we have seen in June. By August, the snow will be mostly gone and we can start thinking about what 2018 will bring.