CHAPTER 1 



HISTORY AND DESCRIPTION OF THE 

 CLARK FORK BASIN 



This chapter describes the Clark Fork Basin and provides 

 a chronology of the major activities and events that have led 

 to current environmental conditions in the drainage. 



INTRODUCTION 



The Clark Fork originates at the confluence of Silver 

 Bow and Warm Springs creeks in the Deer Lodge Valley of west 

 central Montana (Figure 1-1). The river drains over 22,000 

 square miles, including nearly all of Montana west of the 

 Continental Divide and a small part of northern Idaho. The 

 Clark Fork flows north and west from its headwaters for 

 about 340 river miles through a variety of terrain, including 

 broad, semi-arid valleys, high mountain ranges, and steep- 

 sided valleys. It terminates at Lake Pend Oreille in 

 northern Idaho, approximately seven miles west of the 

 Montana-Idaho border. 



The drainage can be divided into 13 subbasins (Figure 

 1-2) . With the exception of water quantity issues, the six 

 subbasins forming the Flathead Basin above Kerr Dam are not 

 covered in this report because Flathead Lake and its drainage 

 basin form a distinct aquatic ecosystem. This area has been 

 studied extensively, and the Flathead Basin Commission was 

 established in 1983 to coordinate water quality management 

 programs in that basin. 



SURFACE WATER 



The Clark Fork is often described in terms of upper, 

 middle, and lower river segments because the character of 

 the river and the nature of the problems differ substantially 

 from one area to another. The upper river segment extends 

 about 125 river miles from the headwaters to below Milltown 

 Dam (Figure 1-3) . Major tributaries that feed the river in 

 this segment include Silver Bow Creek, Warm Springs Creek, 

 the Little Blackfoot River, Gold Creek, Flint Creek, Rock 

 Creek, and the Blackfoot River. Below the Milltown Reser- 

 voir, the average annual discharge of the Clark Fork is 

 approximately 3,000 cubic feet per second (cfs) . Streamflows 

 in this segment are determined by weather conditions, 

 geology, and irrigation. Most of the annual flow occurs 

 during spring runoff, which is quite variable both in timing 

 and volume (Casne et al. 1975). 



1-1 



