Table 13.--Relationship between flood peaks greater than 6.0 feet, 
and scouring at intertidal zone, Harris River-Indian Creek 
Flood Crests : Cut 
period © Ue O0NGa 7.00 ft, *« Cross-sectional area 
> 6.99 ft. ‘* and greater * undergoing heavy and 
percent 
1950-51 i 0 iG 
1951-52 2 i Sar 
1952-53 0 0 ee 
1953-54 2 0 L5 
The average depth of pink salmon nests is 6 to 8 inches (9), ranging 
between approximately four to twelve inches. Scouring which removes 
material to a depth of 9.0 inches, or more, would wash a high per- 
centage of the deposited eggs from their nests. The percent of stream- 
bed 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.l- to 
9.0-inch class was relatively high. Average yearly disturbance was 
almost 7 percent with values ranging from 1.6 to 12.2 percent. 
Scouring in this depth-class would very likely have a significant 
effect on egg and fry survival. The eggs and fry which were not washed 
from their nests would be covered with only a thin layer of gravel, and 
would be more susceptible to low water temperatures than eggs and fry 
having a thicker covering of gravel. 
The effect of additional material on top of pink eggs which are buried 
at normal depth is not known. The addition of a few inches of gravel 
probably has little effect on the buried eggs. An additional over- 
burden of 9 or more inches might possibly have a significant effect on 
both eggs and fry. This consideration is probably one of small signi- 
ficance, however, as an average of only 3.2 percent of the stream was 
affected by deposition greater than 9 inches. 
The principal factor regarding deposition is the nature of the deposi- 
tion material, i.e., whether gravel, sand, silt, or clay. Fine 
deposits which result from the dropping of suspended sediment loads 
would be particularly harmful. The "reservoir action" at the inter- 
tidal zone may cause deposition of considerable quantities of suspended 
sediment which might silt the spawning beds and cause heavy mortality 
to both eggs and fry buried in the gravels. Part of this 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 date. 
Se 
