Huang, J.B. and Xie, D.F., 2020. Detecting the river-sea influenced boundary changes in a macro-tidal estuary based on morphodynamic modeling. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 804–812. Coconut Creek (Florida), ISSN 0749-0208.

The delineation of river-sea boundary of estuaries is of major significance to clarify the scopes and responsibilities of coastal managers and promote the sustainable estuarine resource development and protection. So far, the spatial and temporal variations of natural geographical conditions, such as bed level changes and tidal ranges, etc., have hardly been taken into account when defining the river-sea boundary, probably due to the lack of long time series of field data. Taking the macro-tidal Qiantang Estuary as an example, this contribution explores the feasibility of defining the river-sea boundary by key natural geographical parameters, based on a morphodynamic model. The most remarkable morphological feature within the estuary, a large longitudinal bar, was reproduced firstly using an idealized morphodynamic model. Then numerical experiments were carried out to test the influences of the large-scale regulation and narrowing project implemented in the last decades on the morphological and hydrographic conditions. It is turned out that the locations of the relatively stable bed evolutions, and river-tide discharge ratio and the maximum tidal range of the estuary were consistent with each other. Due to the large-scale river narrowing project, their locations have moved seaward by about 20 km. Furthermore, if the river mouth is narrowed further, the river-sea boundary would move seaward further accordingly. It is necessary to adjust promptly the river-sea boundary of the Qiantang Estuary. The methods for the river-sea boundary delineation in this study can also be applicable to other similar estuaries in the world.