The main flood-control challenge in the middle and lower Hanjiang River lies in the mismatch between river discharge capacity and upstream inflow. Under basin-wide above-standard floods

it is necessary to conduct a refined assessment of the joint operation strategy for flood diversion and storage polders in order to reduce flood-control pressure and population relocation pressure on important towns along the river. Taking the Lianhe

Chenji

Huangzhuang

Dachaihu

and Shipai polders in the Huangzhuang-Shayang reach of the lower Hanjiang River as study objects

this study established a two-dimensional mathematical model of flood routing for the river channel-polder system and simulated the flood diversion process under design flood and 100-year flood scenarios. The results show that:( 1) flood propagation is faster in relatively flat flood storage polders

with more than 80% of the area inundated within

12 h; and( 2) to cope with the excess flood volume of 770 million m

3

in the middle and lower Hanjiang River under the 1935 flood scenario

the joint operation of the Lianhe

Chenji

Dachaihu

and Shipai polders is recommended. This scheme can shorten the flood diversion duration by more than 50% compared with the single use of the Dachaihu polder. The findings provide references for the construction of the Hanjiang River flood-control system

flood-control and disaster-reduction management

and the protection of people's livelihoods.