Evaluation of Historical Sediment Deposition 



Conclusions 



( 1 ) Lake coring analyses indicated that past 

 human land disturbance activities were 

 correlated with increased fine sediment 

 deposition up to 10- fold in Whitefish 

 Lake, 4 to 5-fold in Lake McDonald, 

 and 3-fold in Swan Lake. 



(2) Lake McDonald 



(a) Initial road construction and up- 

 grading of the Going to the Sun 

 Road from Lake McDonald to the 

 continental divide at Logan Pass 

 during the 1930s and 1940s were 

 followed by substantial increases 

 in sediment deposition in Lake 

 McDonald. 



(b) After the road was paved in the 

 early 1950s the sediment deposi- 

 tion rate in Lake McDonald de- 

 clined substantially; however, 

 sedimentation rates still remain 

 above background levels. 



(3) Whitefish Lake 



(a) Large increases in sediment depo- 

 sition occurred during the early 

 part of this century (1900-1910) 

 and were attributed to railroad 

 construction along the lakeshore, 

 logging activity around the lake, 

 and the 1910 fires. 



(b) The largest sedimentation in- 

 creases occurred in the early 1 930s 

 when substantial logging and as- 

 sociated road and railline construc- 

 tion were concentrated in the Lazy 

 Creek drainage and Lower Swift 

 Creek, near the head of Whitefish 

 L«J^9- 



(c) Sedimentation rates also were 

 elevated near 1950 and again in 

 the 1960s. These increases were 

 largely attributed to substantial 

 logging and associated road build- 

 ing activity, which extended to 

 upper portions of the Whitefish 

 Lake drainage. 



(d) Recent logging activities in the 

 Whitefish watershed appear to 

 have had less impact on lake sedi- 

 mentation that past activities. 

 Possible explanations for reduced 

 sediment impacts include use of 

 pre-existing roads, logging on less- 

 erodible lands, improved logging 

 and road building practices, and a 

 series of comparatively mild run- 

 off years. 



(4) Swan Lake 



(a) Sedimentation rates increased 

 during the 1920s following a 

 number of land disturbance ac- 

 tivities including road construc- 

 tion, fires, and timber harvest ac- 

 tivities that included sluice dams, 

 log drives, and rail line construc- 

 tion. 



(b) Sedimentation rates increased 

 again in the 1950s in concert with 

 a resumption of timber harvest 

 and road building activities. 



(c) From the early 1970s up to the 

 present, the lake sedimentation rate 

 reached its highest level. This 

 increase occurred as timber har- 

 vest intensified, more than dou- 

 bling the previous maximum har- 

 vest level in the basin. 



Page 38 



Flathead Basin Cooperative Program Final Report 



