Evaluation of Historical Sediment Deposition 



increase. First, the dating precision for these 

 early dates is less certain than for more recent 

 dates. Thus, this small increase in lake sedimen- 

 tation may not be significant. Nevertheless, 

 there were a number of land disturbance activi- 

 ties in the basin in the early 1900s which could 

 have contributed to an increase in lake sedimen- 

 tation. 



A few small homesteads began to appear in 

 the basin in the early 1900s. Cattle were brought 

 into in the upper part of the basin near Condon 

 around 1910; however, early cattle ranching 

 efforts were abandoned in 1912 (Art Whitney 

 personnel communication). Wildfires in 1910 

 fire burned a small portion of the basin above 

 Condon. A road was built along the north shore 

 of Swan Lake in 1916-1917. In addition, fires in 

 1919 bumed several thousand acres near the 

 head of Swan Lake. Finally, early logging ac- 

 tivity commenced near the head of Swan Lake 

 in 1914. During the late teens and early 1920s, 

 logging activities intensified. A 3 mile-long 

 railroad spur was built from the head of Swan 

 Lake up to S. Lost Creek. Logs were cut and 

 then pulled by horses down to South and North 

 Lost Creeks. In addition, a sluice dam was built 

 on South Lost Creek during this period (Art 

 Whitney personnel communication). Water was 

 released by blasting out the dam during spring 

 run-off and large numbers of logs were swept 

 downstream into the Swan River and subse- 

 quently into Swan Lake. 



The mean lake sedimentation rate increased 

 to 33.4 mg/cmVyr for the period between 1920 

 and 1933. This increase represents a doubling 

 over background levels during pre-setdement 

 years. There are a number of factors which may 

 have contributed to this increase. Timber har- 

 vest activities including log drives and rail 

 operation continued near the head of Swan 

 Lake through the early 1920s. Log drives on S. 

 Lost Creek and the Swan River likely caused 

 considerable stream-bank erosion. The fires of 



1919 and construction of a road along Swan 

 Lake also likely increased sediment transport to 

 the lake. Given the present information, it is not 

 possible to estimate the relative importance of 

 these various factors in contributing to increased 

 lake sedimentation. The actual causes likely 

 involve a combination of factors. 



Some of the early land disturbance activi- 

 ties such as rail-line construction and early log 

 drives appear to have preceded the lake sedi- 

 mentation increase by several years or more. 

 Delays in lake sedimentation could have been 

 caused by the nature of the Swan River above 

 Swan Lake. The Swan River passes through a 

 broad meandering delta area which extends for 

 several miles above the lake. This appears to be 

 an area of sediment deposition. As such, this 

 area could buffer, dampen, or delay transport of 

 sediments from the river into the lake. 



The lake sedimentation rate declined to 27 

 mg/cmVyr from the mid- 1930s to the mid- 

 1940s. This decline corresponds with a decline 

 in land disturbance activity in the basin. From 

 the mid- 1920s to 1940, there was virtually no 

 timber harvest or road construction in the Swan 

 Lake basin. Fires burned a relatively small 

 portion of the upper basin in 1936. 



The mean sedimentation rate increased to 

 37 mg/cmVyr for the time period between 1 946 

 and 1957. This increase corresponds with con- 

 struction of the Swan Highway as well as a re- 

 sumption of timber harvest activities. Work on 

 the new highway began in the late 1940s and in- 

 cluded relocation of portions of the old road 

 closer to Swan Lake. In particular, this work 

 included bank excavation and filling along the 

 lakeshore just north of the Swan Lake camp- 

 ground. By 1956, the road extended past the 

 head of the lake, up to Goat Creek, some 15 

 miles above Swan Lake. The road reached the 

 head of the drainage in the late 1950s. 



In addition, substantial logging and associ- 

 ated road building activity commenced again in 



Flathead Basin Cooperative Program Final Report 



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