Hydrological Characteristics Analysis And Water Exchange Modeling For Polders In Plain River Network Area

Large amounts of polders exist in plain river network area. The natural flow paths are cut off by dykes of polders, and water exchange is controled by human through the culvert, gates and pumping stations. Distributed hydrological model is one of the primary means of hydrological simulation and forecasting. But the existing distributed hydrological models are lack of polder module which makes it difficult to simulate the complex and unique hydrological process of plain river network area. Therefore, studing of the hydrological characteristics of polders and proposing the method that suitable for distributed hydrological modeling in plain river network area has theoretical and practical significance for improving the applicability of distributed hydrological model and improving watershed ecology environment in plain river network area.This article selects the Liyang basin of West Lake Taihu Basin as a research area. The water transport mechanism between different types of polders and rivers outside the dike is fegured out by analyzing structure and characteristics of polders in plain area. Then this paper establishes a polder water exchange model and embed it as a functional module in the SWAT model. Result shows that this polder model has a good applicability in plain river network area.The main contents and results are as follows:(1) By analyzing the types, spatial structure and hydrological characteristics of the polders in plain river network area, polders will be classified into hillside polders, flat polders and uneven polders. According to the rules of polder irrigation and the mechanism of water exchange between different types of polders and rivers outside the polder dike, a polder water exchange model is established.(2) By analyzing the structure of the SWAT model, the polder hydrological process simulation module is integrated in the SWAT model. It’s finished by modifying the source code of the stream routing process and customizing the corresponding parameter files.(3) Liyang basin is a typical plain river network polder area in West Lake Taihu Basin. Simulation by the SWAT model which is integrated by polder module gives the results. Relative error, correlation coefficient and the relative Nash coefficient of the results increase from37%,0.70and0.39to28%,0.81and0.75in Hujiawei Station,37%,0.69and0.56to26%,0.82and0.78in Shanqianqiao Station. The new model avoids the high runoff peak, ahead of runoff peak and fast runoff falling phenomenon occured in the original simulation of SWAT model in plain river network area. This indicates that the water exchange polder model established in this paper can help improving the accuracy of the simulation of hydrological processes and providing a way for distributed hydrological model to improve the applications in plain network river area.