An Analysis of the Effect of Timber Harvest on Streamflow Quantity and Regime 



same time period. This was attributed 

 to insufficient weather recording sta- 

 tions rather than to an uncorrelated 

 relationship. Mountain precipitation is 

 currently unmeasured outside of accu- 

 mulated snow pack during winter. Thus 

 high precipitation events are underesti- 

 mated by valley precipitation record- 

 ings. 



(2) When the climatic factors that drive 

 spring runoff are accounted for by com- 

 paring years of similar temperature re- 

 gimes and the data are transformed 

 based on available snow pack, the ac- 

 cumulated volume of the spring runoff 

 of Hathead Basin Rivers occurs earlier 

 in the runoff period in years since tim- 

 ber management compared to years 

 prior to such management. Simply 

 stated, spring runoff waters are coming 

 into the Flathead Rivers earlier in the 

 year today than prior to extensive tim- 

 ber harvests. 



(3) Comparison of long term trends of an- 

 nual maximum and minimum discharge 

 relationships (Qmax:Qmin) suggest 

 that the Middle Fork of the Flathead 

 River, which has experienced relatively 

 little logging, is becoming increasingly 

 stable in its QmaxrQmin relationship 

 while the North Fork, which has had 

 significantly more timber harvest, is 

 becoming increasingly variable in its 

 Qmax:Qmin relationship. In other 

 words, the North Fork is trending to- 

 ward a discharge pattern of higher 

 maximum flows compressed over a 

 shorter time period while the Middle 

 Fork is tending toward a discharge pat- 

 tern in which peak flows are lower and 

 the higher discharge of spring runoff 

 extends over a longer time period. This 

 is particularly important in light of the 



decrease in fires in both drainages, 

 which presumably would result in a 

 longer runoff period. Thus, the Middle 

 Fork, which had similar area to that of 

 the North Fork involved in forest fires 

 prior to the advent of broad scale fire 

 prevention (that is, since the 1930s), 

 has been progressing to increased dis- 

 charge stability, while the North Fork 

 has decreased in discharge stability 

 since the advent of extensive logging. 



Conclusions 



The analyses conducted within the auspices 

 of this study provide some insight into the 

 effects of timber harvest on streamflow. How- 

 ever, they were limited by the lack of long-term 

 data collection among the smaller watersheds. 

 All of the long-term databases of streamflow in 

 the Flathead Basin are restricted to the major 

 streams and rivers (for example, North Fork, 

 Middle Fork, Swan River, etc.). This is a par- 

 ticularly important consideration since it is the 

 lower order watersheds that are likely to re- 

 spond most dramatically and quickly to altera- 

 tion of the landscape. 



Nonetheless, important conclusions can be 

 drawn from this study. 



(1) The North Fork and Middle Fork drain- 

 ages experienced several large fires 

 between 1 880 and 1930. Subsequently, 

 fire suppression efforts have greatly 

 reduced forest fire frequency and size. 



(2) The North Fork and Swan River drain- 

 ages have experienced a substantial 

 quantity of timber harvest in compari- 

 son to that of the Middle Fork drainage. 

 Most of this timber harvest has oc- 

 curred since 1950. 



(3) The accumulation of spring runoff 

 waters has occmred earlier in the North 



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Flathead Basin Cooperative Program Final Report 



