Total Sea Level (TSL)

Total sea level (TSL) is the full water level at a coast, the sum of mean sea level, the astronomical tide, and the non-tidal residual (storm surge). It is the quantity a tide gauge measures and the one that determines flooding, combining the slow mean-sea-level trend with the deterministic tide and the stochastic surge. Extreme TSL is analyzed with extreme-value statistics to set return periods and design levels, and adding the wave contribution (setup and run-up) gives the extreme water level for defense overtopping. Sea-level rise raises the mean-sea-level baseline, lifting the whole TSL distribution and shortening every flood return period.