Zanzibar (Tanzania) Site History

History Summary

The tide gauge is situated at the seaward end of the main jetty in Zanzibar harbour. It is a Munro IH109 instrument complete with a stilling well and tide staff. The stilling well is 19cm in diameter with walls of 12.5mm cast iron.

The data were supplied by the Department of Lands and Surveys as tabulations of hourly heights; confirmatory charts were also supplied. All times have been converted to GMT.

A permanent tide gauge benchmark (TGBM) was established at a stable site within 30m of the instrument and connected by secondary levelling to the primary benchmark BM1, some 300m distant at the roundabout outside the dock gates.

Datum relationships

BM1 is the fundamental benchmark to which all other levelling in Zanzibar is related and has a fixed value of 3.800m above Land Survey Datum (LSD). TGBM is 0.005m below BM1 and thus has a height of 3.795m above LSD.

Data relative to
Chart Datum
0.000m
Data relative to
Land Survey Datum
-2.080m
Data relative to
Tide Gauge Zero
1.000m
Tide Gauge Zero relative to
Land Survey Datum
-3.080m
Tide Gauge Zero relative to
Tide Gauge Benchmark
-6.875m
Chart Datum relative to
Land Survey Datum
-2.080m

Tide levels drop 0.2m below Chart Datum at spring tides thus a datum shift has been incorporated in the setting of the tide gauge pen so that Chart Datum occurs at +1.000m. The data are referred to chart datum.

The following gap occurs in the data.

Start End
0900h 26 Oct 1984 0900h 26 Oct 1984