Abstract: To better understand the characteristics of saltwater intrusion in the Modaomen estuary in dry season, fortnight ship-mounted observations of the waterway were carried out three times in the dry season of 2017-2018, and hydrological and meteorological data of the waterway were collected for this period. This paper presents an analysis of the correlations between the saline intrusion length with inflow discharge, tidal range, sea level, and north wind speed, in combination with analysis of the features of longitudinal and plane topographies for different waterway sections. The results show changes in channel topography impose a significant impact on these correlations. Due to the modulation of the bifurcating reaches, correlation coefficients for the downstream section featured with central bars are smaller than those for the whole section observed. In the upstream section with a narrow, deep single main channel, the location of saltwater upper boundary has higher correlation with runoff discharge and tidal range; and it tends to accelerate saltwater intruding. We also find the influence of runoff on saltwater movement may be weakened and lose its dominating role when the combined action of other factors–such as tide, wind and topography–becomes prominent, although it is usually the most relevant dominant factor.

Key words: saltwater intrusion, estuary observation, Modoamen estuary, topographic effect