The welfare of salmon eggs and fry which are buried in the streambed 
gravels is directly affected by the magnitude of movement of frag- 
mental mineral debris in important spawning areas. Heavy mortality 
of eggs and fry might occur as a result of deposition of fine material, 
or streambed scouring which removes the protective covering of gravel. 
Another agent of disturbance in intertidal areas is the action of ice. 
Large sheets of ice are broken and moved over the spawning beds. This 
action results in considerable grinding and scouring of streambeds. 
The importance of intertidal zones as spawning areas necessitated a 
study to determine the extent of sediment movement in these areas. A 
study was begun in 1950 to measure quantitatively the movement of 
fragmental debris which occur from year to year in an intertidal zone. 
Thirty-three cross-section stations were established in 1950 at the 
confluence of Harris River and Indian Creek (fig. 17). Elevations of 
the stream channel were determined to the nearest 0.1-foot at 5-foot 
intervals along each cross section. Yearly measurements have been 
made from 1950 to 1955, inclusive, and show elevational changes from 
July of one year to July of the following year. 
Six cross sections were selected for analysis to show the extent of 
gravel movement. These are shown in heavy lines in fig. l/7. 
Four depth-classes were established, based on depth of material moved 
from year to year: 
Depth Class Disturbance 
(inches) 
Light Lote SiG 
Moderate 531 Vea 9 30 
Heavy QoL tor La 0 
Severe 15.1 and over 
Changes less than 1.2 inches were not considered significant since 
elevations were taken only to the nearest 0.1-foot. The number of 
lineal feet in each depth-class was determined for each cross section 
for the periods 1950-1951, 1951-1952, 1952-1953, and 1953-1954. Per- 
cent of stream width in each depth-class was then determined for each 
section. Percent depth-class for all six cross sections was averaged 
to show mean change per year. Fig. 16 A-D shows in detail yearly 
stream channel changes which occurred at station 8 + 00 on Harris 
River during the period 1950 to 1954, inclusive. 
A further step was taken to determine the cubic volume of material 
moved in a typical reach of the stream. The volume of material moved 
during July 1953 to July 1954 was determined in the reach between cross 
section station 0 + 00 and 2 + 00 in the confluence by use of the 
prismoidal formula (10): 
es ie 
