Why is a datum essential when measuring water levels at tide gauges?

A datum is crucial in hydrology and hydrographic surveying because it serves as a reference point to express measurements consistently. In the context of tide gauges, a datum provides a fixed baseline from which water levels can be measured. This allows for the comparison of data collected at different times, locations, or under varying conditions.

Using a common reference, like a tidal datum, ensures that water level readings are comparable and standardized, regardless of local variations in topography, local water fluctuations, or atmospheric conditions. It also facilitates the integration of data from various sources or tide gauges, enabling a comprehensive understanding of tidal dynamics over time.

In essence, expressing water levels relative to a common datum ensures clarity and consistency in the data, which is essential for effective analysis, navigation, and coastal management.