Quantifying the Impact of Seasonal Lake Level Changes on Shallow‐Water Delta Sedimentary Characteristics

Shallow‐water deltas are widely distributed in global lake systems, but due to climate warming and human damming activities, lake levels fluctuate frequently. However, the response mechanisms of shallow‐water deltas to these seasonal lake level changes are still poorly understood. Based on Delft3D numerical simulation and modern satellite imagery, and referencing the hydrological conditions of lakes such as Poyang Lake in China and Lake Baikal in Russia, this study conducted comparative experiments on different frequencies and amplitudes of seasonal lake level changes to quantify their impact on the geometric characteristics, individual sandbar morphology, and sedimentary architecture units of shallow‐water deltas. The results show that: (1) The frequency of seasonal lake level changes controls the macroscopic planar geometric characteristics of deltas, while the amplitude of seasonal lake level changes controls the characteristics of individual sedimentary architecture unites within the delta. (2) With the increase of the frequency of lake level fluctuations (from 100 years to 1 year), shallow‐water deltas gradually evolve from complex network/floral shapes to bird's‐foot shapes, with the number of sandbars and tortuosity decreasing step by step. (3) There are three response relationships between shallow‐water deltas and seasonal lake level fluctuations: low amplitude (Δ H < 3 m), critical amplitude (3 m < Δ H < 5 m) and high amplitude (5 m < Δ H ). As the fluctuation amplitude increases, the dimensionless width and length of sandbars, the number of shallowly incised distributary channels, and the thickness of levees all exhibit a nonlinear trend of first increasing and then decreasing. (4) Seasonal lake level fluctuations regulate the development of levee and improve the stability of distributary channels by driving the resuspension and settling of fine‐grained muddy sediments, thereby reshaping the delta morphology. The seasonal lake level fluctuation range (3 m < Δ H < 5 m) is the optimal dynamic balance range between levee accretion and sediment transport. At this time, the levee thickness of the shallow‐water delta is the thickest, the number of distributary channels is th1e fewest, and the stability is the highest. Deviating from this critical range will lead to a more complex delta morphology. This study established quantitative empirical formulas relating shallow‐water delta geometry, characteristics of single sedimentary architecture unites, and parameters of seasonal lake level changes, providing a theoretical basis for predicting delta evolution and subsurface reservoir architecture anatomy under dynamic water level conditions.