61 



For habitat management, it i6 convenient to divide the Basin into three parte: 

 Grays Harbor, including all the tidal waters bearing that name, the Humptulips 

 River System, and the Chehalis River System (Figure 1). 



The distinction of inner from outer Grays Harbor (Figure 2) is useful because 

 the inner Harbor has suffered more water pollution than the outer Harbor, and 

 because Chehalis System fish must migrate through the inner Harbor whereas 

 Humptulips System fish pass only through the outer Harbor (Figure 2). 



HYDROGRAPHIC DESCRIPTION 



Table I . Relative size and stream flows of major tributaries to tAe Chehalis 

 Basin (Hahlum 1976). 



Annual rainfall varies from 40 inches in Centralia to 220 inches in the 

 southern Olympics (Harper, in prep.); about 85 percent falling between October 

 and April. Peak streamflows usually occur between November and March. After 

 April, flow gradually subsides to late August or early September lows (Figure 

 3). 



Mean annual freshwater flow into Grays Harbor has not been directly measured 

 but is estimated at 11,208 cfs (Mahlum 1976). Table 1 Illustrates the 

 relative sizes of the Chehalis River near Porter and other significant 

 tributaries based on streamflow data. 



