The datum for tide gauges is not the same as the geodetic datum (i.e tide gauge zero is different from elevation zero) used for elevation above mean sea-level) because tidal range varies and the Earth is not a perfect sphere. Tide datums are often based on the lowest low tide water level, and thus are lower than mean sea-level. The Point Atkinson datum is 3.04 m lower than the geodetic datum used for the DEM on the previous assignment. A tide gauge water level of 4.50 m is therefore 1.46 m elevation above mean sea-level. DATA: 20 year Mean Slope (1999-2018) = 0.0040668 (4.0668 mm/yr) 20 year annual slope (1999-2018) = 0.002, 2 mm/yr 100 yr = 5.608 m 500 yr = 5.689 m Which of flood maps (1m, 2m or 3m) might you need to consult to plan for a 100 or 500 year flood? Remember that the flood maps are based on the geodetic datum