3456 789 10 



TIDE LEVEL (FEET) 



Figure 2. — Percent of time different tide levels in Olsen 

 Creek were covered with tide water. 



standpipes buried 8 to 10 inches in the gravel 

 at the 8-, 9-, 10-, and 11-foot tide levels. 

 The standpipes were too short to obtain 

 samples at lower tide levels. A description 

 of the methods used to sample intragravel 

 water from standpipes and a comparative 

 evaluation of the hydrometer method of salinity 

 determinations is given in Hanavan and Skud 

 (1954). When samples were taken from both 

 the gravel surface and from beneath the 

 gravel surface, the salinity of the intragravel 

 water generally was higher than the gravel 

 surface water. Salinity in the gravel surface 

 water between the 8- and 12-foot tide levels 

 was not measurable unless the tide covered 

 the level to a depth of more than 2 feet. On 

 one occasion samples were collected at the 6- 

 and 8-foot tide levels during an ebbing tide. 

 Within 1 hour after the creek water level had 

 returned to normal fresh-water discharge, 

 salinity of the intragravel water dropped from 

 22°/oo to less than lo/oo. 



Not enough samples were taken to show the 

 effects of tide height and stream discharge 

 on the salt-water intrusion into the stream and 

 intragravel water. During average stream dis- 

 charge and with a 13.3-foot tide, the salinity 

 of the intragravel water was 1.2°/oo at the 

 10-foot tide level and was at the 11 -foot 

 tide level. No intragravel water samples were 

 obtained at higher tides. The only gravel sur- 

 face water sample at the 12-foot tide level 

 was obtained during a 14.6-foot tide when the 

 salinity was I.60/00. During this same tide, 

 the salinity of the gravel surface water at the 

 11-foot tide level was 2.0°/oo. The highest 

 salinity sample from the 11-foot tide level, 

 9.3°/oo. was obtained during a 14.5-foot tide. 

 Stream discharge at this time was approxi- 

 mately one-half as much as during the 14.6- 

 foot tide. 



Gravel temperature .- -Pink salmon eggs in 

 the intertidal area are subjected to tempera- 

 ture variations caused by tidal movement. The 

 temperature variations in the gravel at any 

 particular point depend on the temperature of 

 the creek water and the tidal water, the height 

 of the tide at that point, permeability of the 

 streambed, and the amount of fresh water dis- 

 charged from the creek. 



Temperature records from the Olsen Bay 

 intertidal area during two complete tide cycles 

 on July 20 and August 30, 1961, are shown in 

 figures 3 and 4. 



Electronic thermometer probes were buried 

 8 to 10 inches deep at each foot of elevation 

 from the 3- to the 10-foot tide level, and the 

 leads were brought to a central point so that 

 simultaneous temperature readings could be 

 made. Probes at the 6-, 7-, and 9-foot levels 

 were broken and could not be used for the 

 full study period. 



Elevations up to the 8-foot level were subject 

 to temperature variations up to 10° F., de- 

 pending on the height of the tide. Tempera- 

 ture changes of this magnitude occurred within 

 a 1-hour period. 



The 10-foot tide level was affected less and 

 for shorter periods than lower levels. No 



lOFOOT TIDE LEVEL 



5-FOOT TIDE LEVEL 



5 6 7 8 9 10 



AM 



12 I 2 3 4 5 6 

 NOON P M 



Figure 3. — Simultaneous temperature readings in the 

 gravel (8-10 Inches deep) at various tide elevations in 

 Olsen Creek on an ebbing tide cycle, July 20, 1961. 



