Modelling Support to Drainage Master Plans for Yuen Long and North Districts, Hong Kong

As part of the urban development planning the Drainage Services Department of the Government of the Hong Kong Special Administrative Region of the People’s Republic of China (HKSAR) is regularly updating its drainage master plans. This paper describes the most recent update of the drainage master plans for the Yuen Long and North Districts at the border with the mainland China and in particular the way in which simulation models have been developed and applied. The basis for these models is the SOBEK modelling system of Deltares, the Netherlands. It combines in one integrated environment the description of rainfall-runoff processes, open channel flow, pipe flow and overland flow. Drainage channels in Hong Kong are usually very steep and storm events are of short and intense nature. For example, on June 7, 2008 the Hong Kong Observatory registered a rainfall of 145.5 mm during one single hour. As a result, flood waves are of flashy nature, with very high flow velocities. For this reason a modelling system with very robust numerical algorithms was required. The paper describes details of the schematization method and comments on the way the model was calibrated before it could be used for scenario simulations.