There are frequent extreme rainfall events in recent years due to abnormal global climate. The traditional diking could no longer effectively prevent flooding, in addition, dense urbanization has limited the available land for flood channel widening, land development has reduced infiltration, increased runoff volume and flood discharge more than ever. Therefore, the government is urgent to promote the runoff allocation and outflow control policy for waterway and land to share the surface runoff to reduce flood damages caused by inundation. In order to coordinate with the requirements of the runoff allocation and outflow control policy, the draft technical handbook for runoff allocation and outflow control need to be formulated separately for the guidance of the following implementation.
In order to meet the requirement of formulating the runoff allocation and outflow control policy, researches on the issue such as urban flood detention space and flood control regulation were commenced in 2012 for the preparation of promotion and implementation of the policy in 2019, the related regulations were issued, and draft technical handbooks were completed. It is announced that flood management has stepped forward to a new area.
The schematic diagram of runoff allocation and outflow control results is as Figure 1. The public service department is responsible for the promotions and implementations of outflow control, mainly by using public spaces for flood detention. The public spaces could maintain their original functions and provide flood retention during the flooding period. For any development exceeding a certain scale, the land developer must submit an outflow control plan to avoid the increase of runoff caused by land development and ensure the safety for the region.
Figure.1 Schematic Diagram of Runoff Allocation and Outflow Control Results