Lake Levels During Summer, 2001: Lowest Since 1940Flathead Lake reached its 2001 peak in mid-June. Thereafter, the lake's elevation dropped due to (a) extremely low flows in the middle and north forks of the Flathead River, and (b) releases from Hungry Horse Dam that were decidedly more modest than in 2000. HHD peaked at approximately 20 feet below full pool, and the Bureau of Reclamation was conserving water for later in the year. Two reference years are presented. The most severe drought after Kerr Dam but before Hungry Horse dam was 1944. The most severe drought after Hungry Horse Dam (1951) was 1977.
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. 
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