HOLMES ta HASLER SNGINEERS JCb NON4C eh Vertical Control As no records are available of vertical control established here by previous Pacific Southwest Region Reproduced from the holdings of the National Archives surveys a temporary datum is being established on each of the project islands as surveys are made, This datum may be described as follows, "A datum approximating mean low wate r springs was arrived at by applying corrections from the 0.S. Coast and Geodetic publication "Tide Tables of the ' Pacifie Ocean” te a series of tidal observations. This is a temporary datum but should be significant to less than a foot", The procedure is to erect a tide staff at a suitable location at each island and take periodical observations as surveys are made at these islands. After ap- plying corrections a mean of these corrected observations is accepted as the temporary datum. This datum is transferred to a permanent monument in the vicinity which becomes the point of origin of all vertical control on the particular island, At. a later date when personnel are available at these Yooations a longer series of observations will be taken and corrections applied to the datah;. It is not an- ‘ticipated that any temporary datum now in use will be refined by more than a few tenths of a foot. When datums are established at all project islands a further check can be made by taking simultaneous observations at all tide staffs to check the relation between the individual datume. Due to little knowledge of currents in the lagoon it is doubtful if any refinement of the ind4vidual datums can be made by this method. A list of the bench marks follows: Aaraanbiru -- To be established at later date. A Lucy Lcev. 6.44 fomon -- Triangulation station Aomon = Elev. 8.41 Biijiri -- Traverse station Biijiri - Elev. 7.67 Bogallua -- Triangulation station Boga - Elev. 7.14 Bokonearappu -- Triangulation station Bokon - Elev. 10.40 Engebi -- Triangulation station Engebi (Elgin) - Elev. 10.08 i 108