HOLMES ‘% AY LER ENGINEERS JO3 NQG64C Vertical Contrel As no records are available of vertical control established here by previous surveys a temporary datum is being established on each of the preject islands as surveys are made. This datum may be described as follows, "A datum approxizating pear low wate r springs was arrived at by applying sorreetions from the U.S. Coast and Geodetic publication "Tide Tables of the Pacifte Ocean” te a series of tidal observations. This is a tesporery datun sat should be significant te less than a foot’, The proceedure is to erect a tide staff at a suitable Location at each islend and take periodical observations as surveys are made at thase islands, After ap- dlying corrections a mean of these corrected observations is accepted as the tea- sorery detwn. This datum is transferred to a permanent monument ta the vicinity thick becomes the point of origin of all vertical control on the particuler island, At a later date when persomel are available at these ‘Yooat ions a longer series sf ebeervations will be taken and corrections applied te the tatigis -Et 48 not an- ‘ieipated that any temporary datum now in use will be refined by wore than a few senths of a foot, When datums are established at al) project islends a further check can be sade xy taking simultaneous ebservations at all tite steffa:t9 check the relation between the individual datums, Due to little knowlatge of currents in the lagoon it is loubtful if any refinement ef the individual datums can be made by this method. i list of the bench marks follows: araanbirn -~ To be established at later date. omen -- Triangulation station Aomon - Elev. 8.4 ‘1jiri -- Traverse station Biijiri - Elev, 7.67 ogalinua -- Triangplation station Boga - Elev. 7.14 okonaarappe -- Triangulation station Bokon - Flew. 10.40 mngebdi -- Triangulation station Engebi (Elgin) - Elev, 10.08 |