Project Background and Objectives
Traditional drainage improvement and flood-control projects can gradually enhance flood protection standards, but they generally require substantial funding and several years to complete, making it difficult to alleviate flooding problems within a short period of time.
To provide a more flexible and timely approach to flood risk reduction, the Water Resources Agency (WRA) has introduced the concept of Local Flood Retention. Through close communication and coordination with local communities, farmland surrounding flood-prone areas can be used as temporary flood-retention space, allowing the land to temporarily absorb and store floodwater. This approach enhances the flood resilience of the land and helps reduce the probability and severity of inundation.
Main Activities
Implementation History and Achievements
1. Youcai Village Demonstration Area
Taiwan is frequently affected by typhoons and heavy rainfall, which can cause serious flooding. Although considerable financial and human resources have been invested in flood-control infrastructure, engineering measures alone require substantial budgets. In recent years, the increasing frequency and intensity of extreme rainfall events have also caused flooding that may exceed the design capacity of existing drainage systems. In some areas, various constraints may further prevent planned improvement projects from being fully implemented.
To address these challenges, the WRA proposed Local Flood Retention as a non-structural flood-management strategy, with the Water Resources Planning Branch assisting in its implementation.
In September 2020, a 2.07-hectare site owned by the Taiwan Sugar Corporation in Youcai Village, Baozhong Township, Yunlin County, was selected as the first demonstration area. Based on nature-based concepts, the project used existing farmland for temporary flood retention without land expropriation. The demonstration produced favorable results and confirmed the feasibility of Local Flood Retention as an alternative approach to flood management.
2. Expanded Demonstration Area
Following the successful demonstration at Youcai Village, the Water Resources Planning Branch launched the Expanded Demonstration Assessment and Planning for Local Flood Retention in the Youcailiao Drainage Area in 2021.
In April 2022, the Fifth River Management Branch established a 1,150-hectare demonstration area. Through zoned runoff management within the catchment, the project effectively reduced drainage-channel water levels and peak flows, facilitated the discharge of local runoff, and helped mitigate flood risk in surrounding communities.
Rolling Review of Guidelines Supporting Local Flood Retention
Unlike conventional flood-control approaches, Local Flood Retention uses existing farmland as temporary flood-retention space while maintaining its original land use. This reduces the need for land expropriation and large-scale infrastructure while enhancing regional flood resilience.
To encourage landowners and actual cultivators within Local Flood Retention areas to participate, the Water Resources Agency established the Guidelines for Incentives and Compensation for Local Flood Retention by WRA and Its Affiliated Agencies
Under the Guidelines, participating landowners and cultivators may receive Local Flood Retention incentive payments. Actual cultivators whose crops or land are damaged as a result of flood retention may also apply for compensation, subject to on-site inspection and confirmation in accordance with the applicable requirements.
The Guidelines were promulgated on July 26, 2021, and amended on March 29, 2024.
The Water Resources Planning Branch will continue to review practical cases and refine the implementation mechanism on a rolling basis. Through continued improvement in planning and implementation procedures and the sharing of experience, Local Flood Retention can be progressively promoted in flood-prone areas to strengthen overall flood resilience.
Screening and Assessment of Potential Sites for Local Flood Retention
As Local Flood Retention is implemented through voluntary participation rather than compulsory measures, site selection must take into account farmers’ cultivation practices and willingness to participate.
The suitability of potential implementation sites may also be affected by factors such as connections to surrounding drainage facilities, crop types, fallow and cultivation periods, and farmers’ acceptance of potential crop losses. A systematic site-screening and implementation mechanism is therefore required to identify suitable areas.
Following a series of expert workshops, the Water Resources Planning Branch developed a screening methodology with reference to land use suitability analysis. Because Local Flood Retention site selection involves multiple spatial attributes and different levels of importance among individual assessment criteria, a weighted linear combination approach is applied to assess overall site suitability.
To establish the relative importance of the assessment criteria, the Analytic Hierarchy Process (AHP) is applied in conjunction with expert questionnaires, providing a more systematic and objective basis for identifying priority areas for Local Flood Retention.
Based on ongoing inventories and assessments of potential sites, high-priority catchments have been identified in several areas, including:
- Yunlin County: 9 high-priority catchments
- Chiayi County and Chiayi City: 8 high-priority catchments
- Kaohsiung City: 28 high-priority catchments
- Pingtung County: 8 high-priority catchments
Assessments for other counties and cities are currently ongoing.
The assessment results will provide an important basis for subsequent planning, identification of suitable land, and prioritization of Local Flood Retention implementation. They will also support local governments in progressively promoting Local Flood Retention measures and strengthening overall watershed flood resilience.