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after disease outbreaks. Such events have never been proven to occur, but 

 were among the many hypotheses considered during the investigation of the 1989 

 Black River fish kill. Aguaculture pond discharges are regulated under state 

 and federal law, and are monitored periodically for compliance. 



URBANIZATION AND INDUSTRIALIZATION 



Stonuattr Runoff 



Urbanization creates impermeable surfaces in the watershed due to roofs, 

 streets, and parking lots. The Puget Sound Water Quality Authority (1990) 

 lists five effects of urbanization on water quantity: 



(1) Peak storm runoff volume and stream discharge increases. 



(2) Runoff reaches streams much more quickly. 



(3) Flooding increases in frequency and severity. 



(4) Stream velocities are higher. 



(5) Streamflow during dry weather is reduced because less water has soaked 

 into the ground and moved slowly into the stream. 



All these problems degrade fish habitat by creating wider, lees stable stream 

 channels and accelerating stream bank erosion. The resulting sediment fills 

 ponds, streambede, and stonnwater facilities (Pressley and Hartigan 1991). 

 Urbanization-related sedimentation is considered an issue within the Chehalis 

 Basin (CRC and Lewie County CD 1992); of their 20 recommendations to reduce 

 ecological damage associated with improper stonnwater management, six are in 

 some way related to sedimentation. 



Surface runoff that would have otherwise seeped into the ground instead washes 

 dust, soot, leaves, and whatever else is on the pavement into streams. This 

 material tends to decompose in the water, thus increasing the oxygen demand. 

 The contribution to total instream BOD is difficult to measure but the 

 increase is directly proportional to the amount of impermeable land in the 

 watershed, unless good stonnwater management systems are in place. Stonnwater 

 also carries unwanted chemicals such as oil, fertilizer, and herbicides into 

 streams. These problems are common to most urbanized areas (Puget Sound Water 

 Quality Authority 1990), although poorly documented in the Chehalis Basin. 

 One example is the Southwest Washington Fairgrounds where stonnwater 

 collecting from the surrounding areas is considered by WDOE to potentially 

 threaten Salzer Creek with contaminated runoff (Pickett 1992). 



Bank Hardening 



Farmers, seeking to protect their fields from stream erosion, harden the 

 streambank with rock riprap, tires, or other materials. Many non-agricultural 

 miles of Chehalis Basin streams have also been riprapped, primarily to protect 

 roads and urbanized areas. Pressure to harden the bank is particularly heavy 

 in the Newaukum system, where agriculture is widespread and the bank is 

 largely loose sand and gravel. Aside from the effects of vegetation removal 

 (and resulting increased temperatures) which usually go along with bank 



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