Shallow lake water exchange process before and after water diversion projects as affected by wind field

For shallow lakes, the water exchange process is a crucial factor that affects lake eutrophication, which can be solved by a water diversion project (WDP). However, the water exchange process in shallow lakes is complex and affected by hydrological characteristics (the water level and inflow stream) and external forcing (the wind field). It is of profound significance to evaluate the process of lake water exchange by combining dynamic and static methods. In this study, for hydrological characterization, a Morlet wavelet analysis was used for the periodic analysis of 24-year water level data. The monthly discharge of the main rivers over three hydrological years was calculated by a hydrological frequency curve and water balance theory. The external wind field was studied by the wind sheltering coefficient to simulate an uneven distribution. The water age model and particle tracking model were coupled to explore the water exchange process of Dianchi Lake with the influence of two major WDPs. The results show that in each scenario, the distribution of the water age presents a radial distribution and decreases in age from the centre of the lake to the shore, and the largest proportion of the oldest water occurs without exception at the centre of Dianchi Lake. Moreover, the water mass in Dianchi Lake generally circulates counter clockwise around a circle of a fixed size. When the Niulanjiang Water Diversion Project (NWDP) and the Dianzhong Water Diversion Project (DWDP) are combined for water diversion, the annual water diversion volume accounts for 76% of the lake water volume, which can reduce the water age of the lake centre by 38%–52%.