An Applicable Method to Calculate Drainage Modulus in Urbanized Low Lying Area

Urbanization of agricultural lowlying area in China has generally changed the natural surface drainage system and increased economic losses compared to the past by equivalent inundations. The drainage system in urbanized lowlying area has its own particularity, combining rivers and pipe network. Currently, no special method has been developed to obtain appropriate drainage modulus in order to prevent inundation and reduce the economic losses in urbanized lowlying area. According to the principle of water balance, the drainage in urbanized lowlying area is analyzed with aim of its particularity. In this paper, the calculation formula of drainage modulus was basically derived with full consideration of river-storage capacity. By means of case study, the graphical method and tabular solution were applied to solve the nonlinear relationship in the formula. Results indicated that the two solutions were found to be effective.