244 
BULLETIN OP THE BUREAU OF FISHERIES 
Table 26 . — Effect of tide on -physical conditions in Milford Harbor, August 21 h 1925 
Tide 
Time 
Depth, 
feet 
Salini- 
ty, per 
mille 
Tem- 
pera- 
ture, 
° C. 
pH 
Tide 
Time 
Depth, 
feet 
Salini- 
ty, per 
mille 
Tem- 
pera- 
ture, 
° C. 
pH 
8 a. m 
0 
25. 35 
20.9 
7. 2 
High water . . 
2 p. m __ 
15 
28. 10 
21. 0 
7.4 
7.6 
7.4 
7.5 
7.3 
7.3 
7.2 
Do 
. __.do_- 
10 
27. 66 
21.8 
7.4 
Ebb 
4 p. m 
0 
27. 66 
23. 3 
10 a. m__ 
0 
26. 78 
21. 4 
7.4 
Do 
do _ 
13 
28. 12 
22 0 
Do -- 
11 
28. 04 
20.0 
7.8 
Last ebb 
6 p. m 
0 
26. 18 
24. 2 
Do 
12 m 
0 
27. 88 
21.9 
7.8 
Do__ 
__*__do 
12 
27. 82 
23. 0 
Do 
_ ___do 
13 
28. 10 
20.2 
7.6 
Low water 
8 p. m 
0 
25. 50 
24.0 
High water 
2 p. m 
0 
27. 75 
22.2 
8.0 
Do 
do . 
10 
20. 75 
23.0 
Since the range of tide on this particular date is but 0.2 foot above the mean range, 
the changes in water conditions can be regarded as intermediate between those which 
would occur with extreme spring or neap tides. Changes in salinity are least at the 
time of neap tides and greatest with spring tides. The differences in the salinity 
between top and bottom samples were generally less than 1 per mille and naturally 
were greatest above the town dock, where fresh water entered the harbor from the 
Wepawaug River, and least at the mouth of the harbor. Occasionally, however, 
extreme differences were found following heavy rains or with the change of tide from 
low water to flood. An example of the first instance occurred on July 9, 1925, when 
the surface was covered with a layer of water from 6 inches to a foot deep which was 
practically fresh, or of a salinity of about 5 per mille, while that on the bottom was 25 
per mille. 
HYDROGEN-ION CONCENTRATION 
The water in the harbor is naturally alkaline and ranges during the summer 
from pH 7.2 to 8.4. During July an average pH value of 7.8 was observed, while in 
August the readings became higher and ranged from 8.0 to 8.2. The lowest pH 
values were found in samples taken at low tide following heavy rains and the highest 
in afternoon samples taken near the time of high water. An example of the surface 
and bottom changes in pH during a complete tidal cycle is shown in Figure 28 and 
Table 26. 
TIDES AND CURRENTS 
The vertical and horizontal movement of the water as a result of the tide is 
important because it produces considerable variation in its temperature, salinity, 
and pH.f. In Milford Harbor the mean range of tide is 6.6 feet and the spring range 
7.7 feet. During spring tides the maximum range recorded during the summer was 
9 feet, while with neap tides the minimum range was 4.2 feet. The tide here is of 
the semidiurnal type with two high and two low waters occurring during each tidal 
day, with little difference between the morning and afternoon tides and their dura- 
tion of rise and fall, each of which is about 6 hours. 
From a biological point of view both the rise and fall of the water and the hori- 
zontal movement or tidal current are of considerable importance. In Milford 
Harbor the tidal movement is of the stationary-wave type, the strength of the cur- 
rent coming midway between high and low water while the slack of the current comes 
near the times of high and low water. The tide and current relationships for Milford 
Harbor entrance are shown in Figure 29. The tidal currents vary in strength from 
day to day in accordance with the regular changes in the range of tide. The strongest 
currents come with the spring tides of full and new moon and the weakest currents 
