form of a generally tubular pipe with a generally circular cross section although it could also have any other suitable cross sectional shape conduit 32 also preferably has an inlet 38 located in the open sea area 36 and an outlet 40 located in an inner harbor area 42 inlet 38 and outlet 40 are preferably submerged below the low tide water levels of the open sea area 36 and inner harbor area 42 respectively in addition inlet 38 is preferably submerged at a depth sufficient to allow it to avoid the adverse effects of waves and surface currents caused by storms weather conditions etc conduit 32 is also preferably entirely submerged to a depth at which it is entirely below at least the high tide water levels or preferably low tide water levels of the open sea area 36 and inner harbor area 42 moreover inlet 38 and outlet 40 are preferably submerged at approximately the same depth relative to low tide or high tide levels in the inner harbor or open sea areas submerging the inlet 38 and outlet 40 ends as well as the conduit 32 allows water pressure differential between the open sea area and the inner harbor area to effectuate water flow therebetween because of the time lag between rising tide and high tide in the open sea area 36 and rising tide and high tide in the inner harbor area 40 during the time period represented by area 28 in fig1 water levels in the sea area 36 are higher than the inner harbor area 40 due to this difference in water levels there is a tidal water pressure differential between the inner harbor area 40 and the open sea area 36 at the same depth or level relative to the.