Standing atop the embankment patrol road of the second phase of the Beijing Daxing International Airport flood detention project, the reservoir area appears vast and orderly, with extensive greenery blanketing the floodplain and scattered sunflowers adorning the slope protection vegetation. A winding white maintenance pathway meanders through the heart of the reservoir, where hydraulic structures such as diversion sluices and drainage culverts lie quietly dormant. Should floodwaters surge during the rainy season, this expansive terrain will instantly transform into a "floodwater receptacle," regulating and storing excess runoff.

This newly operational flood detention zone serves as a vivid microcosm of Beijing's systematic efforts to reinforce its urban flood defense framework. According to the Beijing Water Authority, the city has concentrated on addressing flood control vulnerabilities in the Yongding River and North Canal basins, with eight flood detention zones newly constructed or upgraded across the region. Collectively, these projects add approximately 35 million cubic meters of flood storage capacity, equivalent to 17.5 times the volume of Kunming Lake.

Flood detention zones are a critical component of the flood control engineering system for major rivers, working in tandem with reservoirs, river channels, and levees to manage floodwaters. Often described as the "trump card" of river basin flood defense, their primary function is to temporarily receive and store excess stormwater runoff from the basin, thereby diverting surplus flood volume, attenuating peak flows, and minimizing overall flood damage.

In the southern section of the Daxing International Airport flood detention zone's second phase, vegetation is distributed in a patchwork pattern across the reservoir area, with a light-colored patrol trail tracing the contours of the low-lying terrain. In the distance, the diversion sluice and drainage gate structures are nestled among the trees. The low-lying areas are blanketed in greenery, and the irrigation channels still hold small amounts of rainwater from recent precipitation.

"The waterway connecting the first and second phases of the Daxing International Airport flood detention zone is the Yongxing River, which receives drainage from the entire Daxing New Town, Panggezhuang, and the Airport Economic Zone, flowing past the southeastern side of Daxing International Airport before eventually entering Langfang in Hebei Province. It is a typical cross-regional flood control river. Under the coordinated flood control dispatch mechanism for the Beijing-Tianjin-Hebei region, the discharge rate at the Donglianggezhuang sluice is strictly controlled within 110 cubic meters per second. If the flow exceeds this threshold, the first phase of the detention zone is activated, and only after it reaches capacity is the second phase engaged, enabling precise diversion of excess floodwater," explained Wang Xuepeng, deputy director of the Niantan Water Affairs Office under the Daxing District Water Authority.

Wang noted that the first phase of the Daxing International Airport flood detention zone was completed at the end of 2000, specifically to ensure flood safety for the airport area. "Construction of the second phase began in March 2024 and was completed in September of last year, and it now has the capacity to store floodwater."

The second phase of the Beijing Daxing International Airport flood detention project covers a total area of 1.14 million square meters with a total flood storage capacity of 2.9 million cubic meters. Built around the Yongxing River water system, the project is divided into southern and northern zones, with the southern zone capable of storing 550,000 cubic meters and the northern zone 2.35 million cubic meters. Together with the first phase's 3.3 million cubic meters of storage capacity, the two phases form a complementary dual flood defense barrier safeguarding the Daxing International Airport area.

Regarding the heavy rainfall brought by Typhoon "White Dolphin," Wang said the precipitation levels were insufficient to trigger the detention zone's activation. Beside the red observation corridor in the first-phase detention area stands a water level gauge, where a distinct red mark stands out among the blue indicators. "That marks the flood water level during the '23.7' event, when the storage level reached 22 meters, while the maximum design level for the first phase is 24 meters," Wang explained. "This is precisely why the second phase project was initiated."

According to the project manager, the second phase has established a mature closed-loop dispatch model. During flood season, floodwater enters the southern zone through the three-bay diversion sluice on the western side and then flows by gravity through a connecting culvert into the northern zone for storage. Once the rain subsides and water levels stabilize, the two-bay drainage gate on the eastern side serves as the primary outlet, supplemented by the diversion sluice, with all five bays operating in coordination to release water back into the Yongxing River in an orderly manner, minimizing flood risk to the greatest extent possible.

The project also adheres to the principle of ecological water management, preserving the original woodland landscape of the site. "The original site consisted of forestland, farmland, and villages. During construction, native trees such as oil pines and ginkgo were preserved in place, and transplanted trees were returned to the embankment slopes after completion, complemented by native vegetation to form ecological slope protection," the project manager said.

During the flood season, the detention zone remains open and empty, with only small amounts of rainwater retained in the irrigation channels to sustain vegetation, achieving the dual goal of "ensuring safety during floods while maintaining ecological beauty in normal times." "We are currently studying plans to open the second phase to the public, and it may become a recreational ecological space for residents in the future."

In fact, following the "23.7" flood event, Beijing began systematically planning eight major flood detention zones across the southern, western, and eastern key river basins, covering multiple dimensions including river channel management, sluice and dam construction, ecological restoration, and intelligent control systems. In addition to the Daxing International Airport flood detention project's second phase, the other seven zones are strategically positioned with distinct focuses to comprehensively address basin flood control deficiencies.

For example, the Mentougou Liushui Connectivity Flood Detention Zone has created 1 million cubic meters of storage capacity through dredging and retrofitting sand and gravel pits, while simultaneously implementing river recharge projects to revitalize regional water resources. The Nankou and Shagou River Flood Detention Zone is equipped with six control sluices and two culverts beneath roads, establishing a systematic water control framework through earthwork remediation, slope greening, and river channel connectivity. The Wenyu River Park Shunyi Phase II Flood Detention Zone covers approximately 109.4 hectares and integrates water ecological construction, intelligent electrical control, landscape services, and automated drainage facilities to deliver combined flood control, ecological, and public benefits. The Bahekou Flood Detention Zone has completed comprehensive management of 6.7 kilometers of river channels, creating two major storage nodes at Laowan and Bahekou with a combined capacity of nearly 3.47 million cubic meters. The Xiyuhe Flood Detention Zone occupies 85 hectares of land while simultaneously managing the river channel and water system.

Today, the eight flood detention zones are essentially complete and operational, with 35 million cubic meters of newly added storage capacity significantly expanding the capital's flood control buffer capacity and further consolidating its safety baseline.