Illustrative Plate 6 shows tide characteristics. A datum for immediate use can be obtained by adjusted simultaneous obser= vations of tidal variations, as described under scope and sequence of field work. This datum will be approximate Mean Low Water Springs arrived at by ap- plying corrections obtained from the U.S. Coast and Geodetic Survey publication "Tide Tables of the Pacific Ocean", Additional checks taken by this method should result in a tidal datum plane significant to less than a foot. This is within the requirements of preliminary design. Scope and Sequence of Field work. It is recommended that surveys be per- formed at the project site under supervision of the Chief Surveyor. Approxi- mately 1 February 1919, the Chief Surveyor and a survey party should proceed to the site to obtain basic information for design and to establish horizontal and vertical control. The scope of each operation follows and will be in the sequence shown subject to changes made necessary by later developments. (a) Profiles of craters. Sufficient profiles or cross sections will be taken of the craters to control grading to specified requirements. To expedite this survey, an assumed datum and local control should be satisfactory. Stakes will be set as required for the grading operation. (bo) Topegraphy. Location of the approximate mean high tide line of the project islands will be mapped and sufficient elevations taken to show relative heights above tide level where essential to design purposes. Existing improvements will be located where essential to design, but it is not considered necessary to locate all existing improvements within the areas. Offshore profiles will be taken as required for water intakes, Iv - 8