action without the use of barriers.
The second method involves operations very much the same as those employed by the City during the past two low water periods when a pneumatic type of tidal gate at 36th Street effectively prevented free upstream movement of salt water. It is evident, however, that the successful continued use of such a barrier will require larger discharges during low water periods than can be provided under the present state of development of the canal basin upstream.
The third method, which is a combination of the first two, appears to be the most practicable. A somewhat higher low water flow in the Canal could be achieved by relatively minor improvements which would increase the capacity and decrease the rate of loss from the storage area above the County Line dam. This includes the placing of additional barriers at strategic locations on the canals bordering and leading from the storage area. These canals collect and drain off the stored water at a more rapid rate than desirable. With the degree of regulation of flows thus established and proper regulation of the present tidal dam sea water would be effectively held below such a barrier except perhaps during times of high wind or hurricane tides.
Protection from Salt Water Encroachment at Depth in the Aquifer.-Although the advance of the salt water front does not immediately endanger the Miami well field nor the potentially important supply areas to the west, north, and south, the problem as described in earlier sections is nevertheless sufficiently acute to demand early attention. In the light of scientific data now available the salt water encroachment is shown to be the
result of .overdrainage, not only of the Everglades but also of the Coastal