Nowadays, climate changes result in frequent heavy rainfall, and increasing runoff would alter the initial equilibrium state of a lagoon. To figure out the geomorphological evolution in Qilihai Lagoon caused from increasing runoff, an ideal model is established for simulation. The findings are as follows: 1) With increasing runoff, tidal creeks are enlarged in both width and length; 2) The tidal creeks would extend to the river mouths once the runoff is over the record; 3) Enhancing width of tidal creeks would combine the tidal creeks together; 4) The deposition amount descends while the erosion amount increases with increasing runoff.
Nowadays, with climate changes, extreme rainfall occurs more and more frequently. The regional short-term heavy rainfall is likely to cause the flood in a water basin. The influence resulted from flood would affect the downstream and the estuary. A lagoon system is usually generated in a semi-closed estuary and has great ecological benefits (Barbier et al., 2011). In previous study, Kim et al. (2002) found that both rainfall and urbanization would increase the annul runoff in the Indian River Lagoon watershed, Florida. It is clear that, besides heavy rainfall, human activities also have influence on the hydrodynamic conditions to a lagoon. For the development of coastal zone, human activities, involving land reclamation (Breber et al., 2008; De Pippo et al., 2004), dredging (Taylor, 2012) and relocating estuary, would alter the initial equilibrium state of a lagoon, and the new hydrodynamic condition would bring about the geomorphological and ecological evolution. Fortunately, ecological restoration of lagoon provides an effective approach to protect the coasts from deterioration (Leruste et al., 2016; De Wit et al., 2017; 2020). In general, it costs approximately 20 years to restore the ecological stability, but the previous influence is irreversible, so neither hydrodynamic conditions nor geomorphological conditions would be restored to the initial (Spencer et al., 2017; Chen et al., 2020).