Flathead Lake & the Drought of 2001

The drought of water year 2001 was comparable to the droughts of 1941, 1944, and 1977. The operator of Kerr Dam, on its own initiative, reduced the outflows from Kerr Dam below the minimums mandated in Article 56 of the license, and began filling the lake much earlier than usual. The lake reached its 2001 peak of 2892.67 on June 21. Thereafter, the lake's elevation dropped steadily. As compensation for the unauthorized reduction in flows during the spring, the summer minimum flows were increased to the point where the outflow from Kerr dam exceeded the inflow to the lake. By July 8, the lake was below 2892. By August, it was below 2891.50. By 15 September, the nominal end of the boating season, the lake was at at 2891 and some keels were scraping the bottom.

We present two reference years, one, 1944, before Hungry Horse Dam, and 1977, after Hungry Horse Dam (which began filling on 21 September 1951).

The North and Middle Forks of the Flathead are free flowing streams. The South Fork is fully regulated. The mainstem river at Columbia Falls is partially regulated. Below Flathead Lake, the Flathead River is fully regulated. (The box ecompasses 50 percent of the data. The horizontal line through the box identifies the median. The bars above and below the box identify the bounds of data that are a "reasonable distance" from the mean; usually, two standard deviations. Outliers are the little white disks above and/or below the bars. The outlier for the South Fork identifies the summer when Hungry Horse Dam first was being filled.)

The operation of Kerr Dam has inverted the Lake's hydrograph. Of note in the graph above is the early decision to begin refilling the lake in 2001.

The small blue dots display the range of lake elevations for each day of the year for 1941 through 2000 (this technique is used in most of the graphs below). Heavy flooding in 1948 filled the lake above 2893, as did the flash flood of 1964. The drought of 1944 occurred before Hungry Horse Dam was constructed. The drought of 1977 is the benchmark drought of the post-war era, as well as the benchmark drought of the post-Hungry Horse Dam era.

The same graph as above, but displaying data only for July through August.

The major unregulated rivers flowing into the lake -- the Flathead River's middle and north forks, and the Swan River -- were at record or near record lows. Second, outflows from Hungry Horse Dam were considerably less than the outflows during the same period in 2000. Please see all of the graphs below. One should keep in mind that the minimum required outflows from Kerr Dam are the functional equivalent of the drought flows for the river at Polson prior to Kerr Dam.

During 1977, Hungry Horse Dam released huge amounts of water for days on end, then throttled back to a minimum flow -- and began the cycle again.

This graph is a key to understanding why Flathead Lake was lower than usual during the summer of 2001. Because the Bureau of Reclamation was conserving water in the HungryHorse Reservoir, the outflows from the dam were well below what they had been the previous year. The lowness of those flows notwithstanding, they still were higher than the median streamflow for the South Fork prior to Hungry Horse Dam. Odd as it may seem at first, there is a good argument that the outflows from Hungry Horse Dam lessened the effect of the drought on the elevation of Flathead Lake.

The summer of 1977 was a nightmare for fish in the South Fork Flathead River below Hungry Horse Dam. For days at a time the dam's outflow was unnaturally high, then, suddenly, it was reduced to a trickle.

Just as Kerr Dam keeps Flathead Lake artifically high during the summer, it keeps the Flathead River below the dam artifically low during much of that period. Because low outflows from Kerr Dam left the river a biological desert, a provision known as Article 56 was inserted into the dam's license when it was renewed. Article 56 establishes the minimum flows. As can be seen from the graphs above and below, the Article 56 flows are functionally equivalent to the lowest flows on record before Kerr Dam was built.

Lake Levels During July & August Lowest Since 1940

Webmaster's note. The graphs below were posted in mid-August, 2001.

Flathead Lake is at its lowest level for July and August since 1940, a wet June notwithstanding. The cause is a dry winter in the high country that resulted in a very low snowpack. This drought, a continuation of last year's drought, is comparable to the droughts of 1944 and the benchmark drought of 1977. The situation is illustrated in the graphs below.

The four graphs below employ a somewhat unusual graphing technique. The small blue bars in the background show the level of the lake or the streamflow of a river on a particular day. There 60 observations for each day, but some overlap. The bars show the range of levels for each day in July and August for the 60-year period 1941-2000. The red, yellow, and whiteish lines are hydrographs or projections for individual years. To view pre-dam lake elevations, please visit our lake levels history page.

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