The volume deterrnination shows clearly the unstable nature of the inter- 

 tidal zone in terms of cubic yards of material moved during a typical 

 winter period. Five hundred fifty-six cubic yards of material were moved 

 in a 200-foot section between July 1953 and July 1954. An examination of 

 nine cross sections vmiformly spaced over the study area shows that 

 deposition which occxirred in the reach between stations 4 00 and 2 4 00 

 was typical of the other cross sections also, A total net volume of 

 approxiinately 4,100 cubic yards of material was probably moved over the 

 1375 lineal feet of stream included in the study. 



The apparent high sensitivity of the Harris River-Indian Creek intertidal 

 zone to the actions of scouring and deposition make it an excellent area 

 in which to study this phase of the investigation. The cross sections in 

 this area will be remeasured yearly to determine whether a significant 

 change occiirs after logging begins on the Harris River watershed. 



Sedimentation 



Erosion material alters the environment of fish in a number of different 

 ways and is generally recognized as harmful to fish populations. One of the 

 most important effects is the blanketing of salmon beds with heavy silt 

 \>rhich causes mortality to the buried eggs by retarding the free circulation 

 of dissolved oxygen to the salmon spawn. Other changes include (l) 

 creation of unfavorable stream bottom conditions by the retention of 

 organic material and other substances, (2) alteration of temperature change 

 rates, and (3) screening out light. Silt may limit the available food 

 supply. 



Several studies have been made by Fisheries men which offer rather con- 

 clusive evidence that heavy stream siltation may cause severe mortality 

 of salmon eggs and larvae. 



Figure 13. — Discharge 

 measurements can be 

 made by wading when 

 water is at normal 

 level, feybeso Creek, 



38 - 



