Quantitative relationships between the tidal current limit, tidal level limit and river discharge in the changjiang river estuary

Estuaries are areas where runoff and tide interact. Tidal waves propagate upstream from river mouths and produce tidal currents and tidal level variations along rivers. Based on the hydrological frequency analysis of river discharge in the dry season and flood season at the Datong hydrological station over the past 70 years, a three-dimensional estuary numerical model was used to produce the quantitative relationships between the tidal current limit, tidal level limit and river discharge in the Changjiang River estuary. The positions of tidal current limit and tidal level limit depend not only on river discharge but also on river topography. When river discharge varies from a hydrological frequency of 95% to 5%, the relationship between the tidal current limit and river discharge is y = 2 × 10⁻¹³ x³ +3 × 10⁻⁸ x² − 0.0074x + 359.35 in the flood season, with a variation range of 90 km, and y = −4 × 10⁻¹⁰ x³ − 1 × 10⁻⁵ x² − 0.1937x − 1232.9 in the dry season, with a variation range of 200 km. The relationship between the tidal level limit and river discharge is y = 6 × 10⁻⁸ x² − 0.0096x + 775.94 in the flood season, with a variation range of 127 km, and y = 0.3428x² − 17.9x + 777.55 in the dry season, with a variation range of 83 km, which is located far upstream of the Datong hydrological station.