Water Resources Planning Branch, WRA, MOEAWater Resources Planning Branch, WRA, MOEA

Basic Concept

In order to adapt the impact of the global climate change, developed countries in the world have changed their flood concept into “no fear of flooding, coexist with the flood” by actively training their adaptability against flooding, transforming the existing environment and creating cities that are no fear of flooding. The runoff allocation and outflow control measure is to share surface runoff that is originally drained by waterways becoming share together with land. It is required that land development and building construction must share the responsibility of resistance to flooding to achieve the goal of resilient city, as indicated in Figure 1.

Figure.1 Schematic Diagram of Runoff allocation and Outflow control Concept

Scope of Promotion

To start up the promotion and implementation of the runoff allocation and outflow control policy, government agency has completed the modification of the parent law and formulated and issued the relevant sub-regulation for the basis of implementing processes for submitting, reviewing, approval and announcement of the related results of runoff allocation and outflow control. The scope of promotion for runoff allocation and outflow control follows:

1. Runoff allocation: For “specific river basin or regional drainage area” published by central governing agency, the public service department should be responsible for corporation after the completion of the runoff allocation and outflow control plan. The plan should follow the principle of integrated use of inhibition of runoff, allocation of runoff, detention of runoff and coexistence of low land and inundation area using structure and non-structure measures adapted to local conditions supplemented with disaster sheltering measures.
2. Outflow control: The land developer must submit an outflow control plan for any development exceed certain scale to avoid the increase of runoff caused by land development and to ensure the safety for the region.

Key Points of Technical Handbook

For the purpose of promoting runoff allocation and outflow control policy, the existing technologies and experiences were integrated to formulate the related technical handbooks of runoff allocation and outflow control for the guidance of the follow up implementation.

1. Runoff allocation Technical Handbook

   The flow chart of conducting runoff allocation plan is presented in Figure 2.The process are divided into three stages including Runoff allocation evaluation report, Runoff allocation planning report and runoff allocation plan. The key points of the flow chart are as follows:

   1. Problem analysis and explorations: The planning of runoff allocation and outflow control should analyze important issues faced by the planning area. Analysis and exploration of problems should be gone through well communications, discussion and analysis.
   2. Formulate plan goal: The design basis of river and drainage flood control and regional flood protection level should be formulated first for delineating the Runoff allocation implementation limit of a river basin or drainage area, estimating Runoff allocation quantity and detailing Runoff allocation measures.
   3. Runoff allocation feasibility elevation: Clarification of Runoff allocation locations and shaving quantity required according to the established flood control goal of each location.
   4. Planning of runoff allocation scheme: The planning of runoff allocation scheme should consider the principles of integrated use of inhibition of runoff, allocation of runoff, detention of runoff and coexistence of low land and inundation area using structural and non-structural measure adapted to local conditions supplemented with disaster avoidance measures.

2. Outflow control Technical Handbook

   For development area more than 2 hectare and caused surface runoff to increase, the developer should prepare an outflow control plan and submitted to the purpose authority for application. For land use change, partition of non-urban district land or land use change partition of urban district land or land use change partition of public facility, the oblige should prepare an outflow control planning report and submitted to the purpose authority for application at the land use charge stage. The flow chart of conducting outflow control plan is presented in Figure 3.