An additional large reservoir will soon be needed in Hong Kong and the only suitable sites are for dams founded in the sea, similar to the recently completed Plover Cove dam. A sparker reflection survey has been carried out to compare three sites. To assist the interpretation, boreholes and drillholes were completed at possible centre-lines.

Results show that Pleistocene valleys were eroded deeply below present sea level and were subsequently infilled. Soft marine sediments cover compact alluvium above bedrock. The earth/rock fill dams would probably be founded on alluvium and the main object of the investigation was to find suitable foundation levels.

The sparker survey gave far more geological information than would have been obtained from exploratory holes drilled at the equivalent cost. The results were accurate enough to produce relative capital cost/capacity curves for the reservoir sites.

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