Change of stream network connectivity under polder‐type flood control measure

Abstract Polder is usually used for flood control in the river delta area. With the rapid development of urbanization, the dikes or pumps cut the original stream network system, and the stream network connectivity (SNC) and the river system pattern have changed. The dikes or pumps generally force up the river's water level, and regional flood formation mechanisms and processes have changed. In order to quantitatively describe the characteristics of polder‐type flood control measure (PFCM) and the change law of SNC, firstly, the streams inside polders were generalized as virtual streams, a hydrological‐hydrodynamic model was constructed by connecting Hydrologic Engineering Center‐Hydrologic Modeling System and MIKE11 model. Secondly, an SNC evaluation model was constructed based on flow resistance and hydrological process. Finally, the SNC under different scenarios was simulated and evaluated to reveal the influence of the PFCM on SNC. And the dominance analysis method obtained the main control factors of SNC changes. The results showed that the pumps as the main drainage facility under the PFCM, SNC after the opening of the pumps were increased by 0.060, 0.103, and 0.311 for 50%, 30%, and 3% frequency flood scales compared with the pumps closed, respectively. However, compared with the natural stream (without the PFCM), the SNC decreased by 0.391, 0.456, and 0.487, respectively, at the same time of the same flood scale. The PFCM negatively impacted the SNC, and the number of pumps was the main control factor of the SNC.