in the past. Should changes be made in the water levels, or the canals be dredged wider and/or deeper, the rate of movement of the wedge and tongues of salty encroaching water would be changed. For instance, should the Miami Canal be dredged to a depth of 25 feet as far as N. W. 36th Street Bridge as has been proposed recently highly saline water from Biscayne Bay would probably immediately penetrate inland the whole length of the deeply dredged section. It is probable that the natural fresh water flow in the canal would be insufficient to keep the salty water below the head of the 25-foot dredged section except possibly during periods of very
heavy rainfall. It is entirely possible, moreover, that pockets of salty water would remain in portions of the deeply dredged section most if not all of the time. These pockets of salty water would be a constant source of contamination of the nearby shallow ground water particularly during dry periods when the water table is low. This would, in effect, rejuvenate the movement of the Miami Canal salt tongue, both laterally and upstream. However, the inland advance of the salt tongue could be held in check by maintaining an average yearly water table height of two and one-half feet above mean sea level at the head of the deeply dredged channel.
From the foregoing discussion of salt water encroachment, the fact that the present well field is ultimately threatened with permanent salt contamination is apparent. The danger is not imminent, however, nor in the near future if conditions remain as they now are. But to insure the perpetual use of the present well field the two and one-half foot average annual contour on the water table must pass to the east of the well field, and this will require the establishment of controls in the canals to raise the water level behind the controls to that heJght. Under the present