Hydraulic Engineering Office

The areas surrounding Sections 2 and 3 of Xinglong Road, Fuxing Road, and Xingde Road in Wenshan District are naturally low-lying. Compounding this, the main drainage system in the area—Xinglong Trunk Line—has limited capacity due to topographical constraints, making it one of the few places in Taipei City where the completed drainage infrastructure still falls short of originally planned flood capacity. The area has previously been listed as one of three key flood-prone zones in the city. As extreme weather events such as intense rainfall and typhoons become more frequent, localized flooding has become a persistent concern for residents. Guided by the principle of "midstream flood reduction," the city began exploring the use of detention basins to temporarily store excess rainwater, along with complementary diversion measures, to address the area's natural limitations. After coordination with the military, the city secured use of the parking area at a military police base for an underground detention basin. The surface level was later developed into Xinhai Eco Park (Wenmu No. 91 Park) by the Parks and Street Lights Office of the Public Works Department, with the park completed on December 31, 2020. To further enhance the region’s drainage capacity, HEO implemented two major projects, the Xinhai Eco Park Detention Basin and Wenshan Sports Center North-Side Detention Basin.

Flood-Prone Areas and Coverage along Xinglong Trunk Line

(1) Project Scope:

Section 4, Xinhai Road, Wenshan District

(2) Project Description:

To regulate peak flow from upstream Section 4 of Xinhai Road and Section 2 of Xinglong Road, an underground reinforced concrete (RC) detention basin was constructed beneath Xinhai Eco Park (Wenmu No. 91 Park), managed by the Parks and Street Lights Office of the Taipei City Public Works Department. Construction began on November 20, 2015, and was completed on August 25, 2017, providing an initial detention capacity of 39,000 cubic meters. An expansion on the east side was completed on January 23, 2019, increasing the total capacity to 46,000 cubic meters. The facility is equipped with four pump units, with a total discharge capacity of 1.375 cubic meters per second (cms).

Photographs of the Completed Xinhai Eco Park Detention Basin

Site Plan of Xinhai Eco Park Detention Basin

Schematic Diagram of Xinhai Eco Park Detention Basin Layout

(3) Inflow Mechanism:

During normal weather and low-flow conditions, stormwater continues to drain through the existing box culvert and bypass channel beneath Section 4 of Xinhai Road into the downstream drainage system, without entering the detention basin. Only during typhoons or heavy rain events, when the water level in the culvert exceeds the overflow weir height, does water begin to flow into the detention basin for storage.

(4) Project Benefits:

The stormwater drainage catchment area for Section 4 of Xinhai Road covers approximately 64 hectares. Located midstream within the Xinglong Trunk Line system, this detention basin serves as a key element in Wenshan District’s midstream flood mitigation plan. Before the installation, peak runoff flow was 18.57 cms. After construction, peak flow was reduced to 3.2 cms—an impressive 83% reduction in peak discharge.

Illustration of Detention Basin in Normal Conditions

Illustration of Detention Basin Operation During Typhoon/Flood (Within Design Standards)

Illustration of Detention Basin Operation During Typhoon/Flood (Exceeding Design Standards)

(5) Key Features of the Detention Basin:

This is an off-channel detention basin design, meaning stormwater only flows into the basin when water levels in the Xinhai Road culvert exceed the elevation of the overflow weir during typhoons or intense rainfall. After the storm subsides, the stored water is promptly pumped out. Notably, this facility is the first underground urban detention basin in Taiwan. The area above the basin has been transformed into Xinhai Eco Park (Wenmu No. 91 Park) by the Parks and Street Lights Office of the Public Works Department and opened on December 31, 2020. In addition to flood mitigation, the park now serves as a recreational and leisure space for the residents of Wenshan District.

Site Plan of Wenmu No. 91 Park

(1) Project Scope:

The detention basin is located on the north side of the Wenshan Sports Center site (north of No. 222, Section 3, Xinglong Road, Wenshan District). The sports center sits at the intersection of Section 3, Xinglong Road and Lane 8, Alley 192, diagonally across from the Taiwan Police College.

(2) Project Description:

To effectively address localized flooding in low-lying areas between Lane 115, Section 3 of Xinglong Road and Xingde Road, an underground reinforced concrete (RC) detention basin was constructed on the land north of the Wenshan Sports Center. Construction began on November 11, 2015, and was completed on July 13, 2017. The facility has a detention capacity of 6,000 cubic meters and is equipped with three pump units with a total discharge capacity of 0.375 cms.

Location of Wenshan Sports Center Detention Basin

Photograph of Completed Wenshan Sports Center Detention Basin

(3) Inflow Mechanism:

The upstream section of the Xinglong Trunk Line connects to the Wenshan Sports Center Detention Basin via an overflow junction near No. 222, Section 3, Xinglong Road. During typhoons or heavy rainfall, when the culvert’s water level exceeds the overflow weir height, stormwater flows into the basin and begins temporary detention.

(4) Project Benefits:

This underground detention basin forms part of the comprehensive midstream flood management plan for the Xinglong Trunk Line drainage system. With a total storage capacity of approximately 6,000 cubic meters, it helps reduce downstream flood volume by an estimated 5,100 cubic meters and decreases the potential flood-affected area by about 17,000 square meters. Prior to the basin’s construction, the peak flow in the Section 3 Xinglong Road stormwater system was 9.307 cms. After implementation, peak flow was reduced to 7.285 cms—representing a 21% reduction. The project has delivered significant flood mitigation results. When combined with the detention basin at the military police site and the Fuxing Road diversion project, the system effectively alleviates flooding issues, enhances flood protection standards, safeguards residents from flood threats, and improves the overall quality of the living environment.

Inflow Mechanism of the Detention Basin

(5) Key Features of the Detention Basin:

This is an off-channel basin design: stormwater only enters the basin when the water level in the Xinglong Road box culvert exceeds the elevation of the overflow weir during typhoons or heavy rainfall. After the event, water is promptly pumped out.

The green space above the detention basin has been developed into a barrier-free outdoor fitness and leisure park, featuring multiple pieces of fitness equipment and pavilions. This allows essential flood infrastructure to also serve as a welcoming public recreational space for the community.

Pavilion View

Outdoor Fitness Equipment