The study on the time lag of water level in the Three Gorges Reservoir under the regulation processes

The identification of the water level time lag (WLTL) under the regulation processes is of great significance for environmental impact, flood control, and sediment transport of huge reservoirs. The traditional hydrodynamic method can calculate the flood inflow process and the water level change process along the river channel, but it is difficult to estimate the time difference of the reservoir water level fluctuation to the dispatching process. To quantitatively evaluate the reservoir regulation effect on the WLTL in the Three Gorges Reservoir (TGR), the daily water level data from 2011 to 2017 of five stations in the TGR are analyzed in this paper. The results revealed that there is a significant water level difference along the reservoir from April 1 to October 31. The gap between the end of the reservoir and the Three Gorges Dam (TGD) is the largest, reaching 23.67 m on July 2. The longer the distance from the TGD, the longer the time lag. Furthermore, the WLTL is also different at the four different operating periods of the reservoir in a year. During the low water level operation period and high water level operation period, the time lag is 3 days which is the greatest, while in the water level decline period and water level rise period, the time lag is within 2 days.