‘HOLMES ts NARLER
ENGINEERS
JOH NOG
Vertical Control
As no records are available of vertical control established here by previous
Surveys a temporary datum is being established on each of the project islands as
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surveys are made,
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This datum may be described as follows,
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"A datum approximating mear low wate r springs was arrived at by applying
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is ' corrections from the U.S. Coast and Geodetic publication "Tide Tables of the
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Pacific Ocean" te a series of tidal observations.
This is a temporary datum
SE but should be significant to less than a foot",
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The procedure is to erect a tide staff at a suitable location at each island
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and take periodical observations as surveys are made at these islends.
After ap-
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plying corrections a mean of these corrected observetions is accepted as the ten-
ig
porary datum.
ie
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 Tocations a longer series
or observations will be taken and corrections applied to the dati, It 4s not an-
. t1etpated 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 individuel datums. Due to little knowledge of currents in the lagoon it is
doubtful if any refinement of the ind ‘vidual datums can be made by this method.
'A list of the bench marks follows:
Aaraanbiru -- To be established at later date.
Aomon <= Triangulation station Aomon = Elev. 8.41
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Biijiri -- Traverse station Biijiri ~ Elev. 7.67
:Bogallua -- Triangulation station Boge - Elev. 7.14
.Bokonearappu -- Triangulation station Bokon ~ Elev, 10.40
Ergebt -- Triangulation station Engebi (Elgin) - Elev. 10.08
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