The importance of intertidal zones in the life cycle of the pink 

 salnion necessitated a study begun in 1950 to measure qiiantitatively 

 the movement of sedLments vrhich occiu* from, jj-ear to year in the 

 intertidal zone at the confluence of Harris River and Indian Creek. 

 This zone is unstable under natural conditions and subject to con- 

 siderable movement of streambed materialj more so thcin material above 

 high-tide level. For one thing, the intertidal section consists of 

 deposits of alluvial material which are easily m.olded and reworked 

 and which have been transported from \ipstream sectior-s« Secondly, 

 the intertidal zone may be more susceptible to sediment deposition 

 because tidal action in this reach produces a fluctuating reservoir. 

 Deposition is induced during periods of slack water because the 

 incoming tide reduces the particle -carrying capacity of the fresh- 

 water stream. Deposition of material is also induced by the chemical 

 action of flocc\£Lation and precipitation. The greatest amo\mt of 

 shifting usually occurs during periods of high stream runoff, parti- 

 cularly d-uring the fall months when eggs are in the gravel. 



The average depth of pink salmon nests is 6 to 8 inches-^; it usually 

 ranges from 4 to 12 inches. Scouring which removes material to a 

 depth of 9,0 inches or more would wash a high percentage of the 

 deposited eggs from their nests. The percent of streambed receiving 

 disturbance greater than 9»0 inches was small, however, averaging 

 only 2 percent over the period, with values ranging from 1,3 to 3»7 

 percent. 



Percent of streambed receiving cutting disturbance in the 5«1- to 

 9,0-inch class is relatively high. Average yearly disturbance is 

 almost 7 percent with values ranging from 1,6 to 12,2 percent, 

 Scoin'ing in this depth-class would very likely have a significant 

 effect on egg survival. The eggs which were not washed from their 

 nests would be covered vrLth only a thin layer of gravel. These eggs 

 might be more susceptible to low water temperatures than eggs which 

 have a thicker covering of gravel. 



The effect of additional material on top of pink salmon eggs which are 

 buried at a normal depth of 6 to 8 inches is not known. Addition of 

 a few inches of gravel probably has little effect on the buried eggs. 

 An additional over-b\irden of 9 or more inches might possibly have 

 significant consequence on both eggs and fry. This consideration is 

 probably one of small significance, however, as an average of only 

 3,2 percent of the stream was affected by deposition greater than 

 9 inches depth. 



The principal factor is the nature of the deposition material, i,e,, 

 whether gravel, sand, silt, or clay. Finer deposits such as woiold 

 result from the dropping of siispended sedim.ent loads would be parti- 

 cularly harmful. The "reservoir action" at the intertidal zone may 

 cause deposition of considerable quantities of suspended sedi.ment 

 which might silt the spawning beds and cause heavy mortality to both 

 eggs and fry buried in the gravels. Part of tliis load would probably 

 be carried out to sea again by ebb tide currents, but part of it 

 undoubtedly remains in place. This phase has not been investigated 



to d^te, \ 



2/ Hanavan, Mitchell G,, and B, E, Skud, Intertidal spawning of 

 pink salmon. Fishery Bulletin 95, Vol, 56, pp. 167-185, 1954. 



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