WRRCTMR No.76 Membrane Water-Storage Enclosures: A Pilot Study in East Loch, Pearl Harbor, Hawaii

Abstract

Pilot field tests were conducted in the continuing conceptual development of using impermeable membranes as separating liners to store fresh stream water in an embayment. The storage of fresh water in the ocean was conceived as a less expensive way of storing surplus stream water for subsequent use than in land-based rigid dams and reservoirs. Three basic types of membrane storage enclosures were tested: floating reservoir, bag,and curtain. Each has its particular advantages and disadvantages which determine their suitability to any particular application. The testing took place in East Loch of Pearl Harbor, a protected inland estuarine embayment, to capture the freshwater flow from Kalauao Springs near Pearlridge on Oahu, Hawaii. The tidal effect, particularly low tide, has a significant effect on the enclosures. On the curtain, the effect was the amount of slack needed to retain the water captured at high tide as the tide recedes. With the open reservoir and bag, low tide left the enclosure grounded and unsupported on the muddy bottom. A site needs sufficient water depth to keep the enclosures afloat at all times. A rotating collar would prevent the bag and open reservoir from becoming twisted around an anchor point. A membrane floating canal and pipeline for water transmission on the ocean surface were also developed and tested successfully. In all testing, 6-mil polyethylene film was used as the membrane during this proof-of-concept stage. Sufficient progress has now been attained that in the next stage a first priority effort should be the selection of a suitable operational quality membrane. No adverse environmental impacts were detected during or after the pilot study.