The Matai Estuary Beach reach is located in the fluctuating backwater area of the Nuozhadu Reservoir on the Lancang River.Upstream,Hutiaoshi Beach is characterized as a narrow and shallow shoal,while downstream,the Matai Estuary Beach becomes a shallow and swift shoal at the stream mouth during the low-water level.Before the implementation of channel regulation works,the comprehensive criterion E value for the Matai Estuary Beach during high flow periods of the drawdown exceeded the permissible limit by 2-3 times,presenting significant challenges for navigation improvement.To address this issue,optimization trials are conducted for the downstream Matai Estuary Beach using a physical river model,aiming to meet the navigation improvement goals while minimizing upstream water level drops caused by the engineering works.The recommended plan involves dredging to increase the channel dimensions and expanding the discharge area at Matai Estuary Beach,accompanied by backwater measures through filling deep pools beneath the shoal.For the upstream Hujiaoshi Shoal,obstacle clearance is proposed to enhance channel dimensions.These measures have significantly improved the navigation conditions in the Matai Estuary Beach reach.However,under conditions of low water levels in front of the Nuozhadu Dam and high discharge from the Dachaoshan Dam,resistance to navigation at the Matai Estuary Beach remains considerable.The study further analyzes the impact of raising the operational water level in front of the dam on the navigation conditions of the recommended plan,and concludes that appropriately raising the water level in front of the dam could meet the requirements for ships to pass through the shoal.