This letter from Dave Amman, MT State Hydrologist, is an update on the low water level situation at Georgetown Lake.
November 2, 2015
The lake level started October at 6427.81 feet, dipped to 6427.74 feet and ended the month again at 6427.81 feet. Early in the month, outflow was set at 16 cfs, then adjusted downward to 11 cfs at mid-month. The average outflow for October was 13.3 cfs and since the lake did not gain or lose overall, net inputs were thus also 13.3 cfs. That corresponds to an average input of only 58% of normal for October. On November 1, the water surface was at 6427.86 feet.
With very little evaporation occurring now and cold air (and water) temperatures, every storm counts. The storm this past weekend dropped over half an inch of moisture at Pburg, and more than an inch at Peterson Meadows, raising the lake elevation this morning to 6427.91 feet. That’s an increase of one-tenth of a foot (about an inch and a quarter) over the last few days. Hopefully the large storm that is forecast for tonight through the week pans out and drops its six or seven inches of snow at the lake, and even more at higher elevations.
I ran the model using 58% of normal inputs (that should increase this week at least) and with outflow held at 11 cfs. (See the graph below.) Using these parameters, the model shows the lake not quite filling by the end of June and then tapering off through the summer, very similar to this year. An input figure of even 75% would substantially increase the rate of water storage and the corresponding monthly water elevations.
Thanks,
Dave
