Heavily silted streams do not stop the upstream migration of mature 

 salmon, Salmon are obsei^ed to spawn in glacial streams which carry- 

 large quantities of suspended material. The available literature 

 provides good evidence, however, that the most successful spawning 

 does not occur in the heavily silted waters, but in the clear water 

 of tributaries. 



Most salmon streams carry natural silt during flood stages. This 

 material reaches stream channels by (l) surface runoff, (2) under- 

 cutting of channel banks, (3) slow gravitational creep of mantle 

 material, and (4) avalanches and landslides. The formation of mud 

 flats and the presence of silt at the mouths of most creeks and 

 rivers in Southeast Alaska attest to the magnitude of the siltation 

 process under natural conditions. 



Most logging activities on watershed slopes tend to disturb the 

 soil and result in increased erosion. Construction of logging roads, 

 however, is generally considered to be the principal soTirce of 

 stream turbidity and sedimentation. Road construction on the Maybeso 

 Creek drainage has not resulted in excessive stream siltation becaiose 

 they have been located well away from the streams and have generally 

 been constructed by borrowing and end-hauling sub-grade material; 

 sidehiU road construction and sidecasting have been held to a 

 minim-um. 



Material suitable for road sub-grade and surfacing is limited in this 

 region. Two sources of road building material are available; stream 

 deposits, and rock outcrops. Stream deposits are largely glacial 

 till which has been reworked by streams and contain a rather high 

 content of silt and clay. It is generally necessary to first remove 

 these fines before the material is used for road building purposes. 

 Washing is done in local streams. Rock outcrops, which consist 

 mostly of shales and greenstone, must be quarried. 



Use of streambed material may damage spawning beds by causing excess- 

 ive sedimentation. To date, a large portion of the road-building 

 material used in the Maybeso Greek sale area has been obtained fran 

 a small stream (Half-I^ile Creek) which empties into the tidal zone 

 below the mouth of I'laybeso Creek. Approximately 100,000 cubic yards 

 of sub-grade and surfacing material have been removed from Half -Mile 

 Creek. The operation has resulted in the deposition of approximately 

 5,000 cubic yards ^ of silt at the mouth of this stream with material 

 being deposited to depths as great as several feet. The sediment in 

 this little stream is considerably higher than in the study streams 

 as shown in table 9« 



The study clearly indicates the undesirability of allowing road 

 building materisQ. to be removed from, and washed in, tributary streams 

 which empty directly into salmon streams. To date, no gravel removal 

 has been allowed in streams tributary to Maybeso Creek with the 

 exception of a few cubic yards taken by mistake and which immediately 

 showed up in the beaver pond below the point of gravel removal. 

 See table 9. 



- 39 



