Research on relationship between drainage modulus and drainage area in large urbanized polder

Large urbanized polders, are always with developed economy and concentrated population, in which the lacking river storage capacity makes the risk of flood and waterlog increase. Therefore, it´s much more necessary to study more accurate method of drainage calculation and the relationship between the drainage modulus and the drainage area for the drainage strategy in urbanized polder. According to the analysis of the characteristics of urban drainage, Unsteady Flow Equations was used to calculate in details. In the process, the node with drainage pump stations was treated as the virtual outer river in order to suit the characteristics of pump draining. With the drainage area changing, relationship between the drainage modulus and the area was gained, which can provide the basis for choosing appropriate drainage strategy.