Standing on the crest patrol road of the Beijing Daxing International Airport Flood Detention Project (Phase II), the reservoir area stretches out flat and open, with vast greenery blanketing the floodplain and scattered sunflowers dotting the slope protection vegetation. Winding white maintenance walkways meander through the heart of the reservoir, while hydraulic structures such as flood diversion sluices and drainage culverts lie quietly in wait. Should floodwaters strike during the rainy season, this expansive site will instantly transform into a "flood collection basin" to regulate and store excess inflow. This newly operational detention area serves as a vivid microcosm of Beijing's systematic efforts to strengthen its urban flood control system.

According to the Beijing Water Authority, the city has focused on addressing the weak links in flood control within the Yongding River and North Canal basins, centrally constructing and upgrading eight flood detention areas. These efforts have added approximately 35 million cubic meters of new flood storage capacity citywide, equivalent to 17.5 Kunming Lakes. The Phase II project of the Daxing Airport detention area has now been completed.

Flood detention areas are a vital component of the flood control engineering system for major rivers. Working in tandem with reservoirs, river channels, and levees to collectively manage floods, they are often referred to as the "trump card" of river basin flood defense. Their primary function is to temporarily receive and store excess storm floodwaters from the basin, thereby diverting surplus flood volume, reducing peak flows, and minimizing overall flood damage to the greatest extent possible.

In the southern section of the Phase II area of the Beijing Daxing International Airport Flood Detention Zone, vegetation is distributed in a staggered pattern across the reservoir. A light-colored patrol trail winds along the contours of the depression, with flood diversion sluices and water release structures faintly visible amidst the trees in the distance. The low-lying land is blanketed in greenery, and the irrigation channels still hold small amounts of rainwater accumulated from recent showers.

"The watercourse between Phase I and Phase II of the Daxing International Airport detention area is the Yongxing River, which drains the entire Daxing New City, Panggezhuang, and the Airport Economic Zone, flows past the southeast side of Daxing International Airport, and eventually empties into Langfang, Hebei Province. It is a typical cross-regional flood control river. Under the Beijing-Tianjin-Hebei coordinated flood control dispatch mechanism, the discharge from the Donglianggezhuang sluice is strictly controlled to within 110 cubic meters per second. Once the flow exceeds this threshold, Phase I detention is activated, and only after Phase I is fully filled does Phase II begin operating, precisely diverting excess floodwaters," explained Wang Xuepeng, Deputy Director of the Niantan Water Affairs Office under the Daxing District Water Authority.

Wang noted that the Phase I project of the Daxing International Airport detention area was completed at the end of 2000, specifically to ensure flood safety for the airport region. "Construction on Phase II began in March 2024 and was completed in September of last year, and it now has the capacity to store floodwaters." The Phase II project covers a total area of 1.14 million square meters with a total flood storage volume of 2.9 million cubic meters. Built around the Yongxing River system, it is divided into southern and northern zones, with the southern zone holding 550,000 cubic meters and the northern zone 2.35 million cubic meters. Together with Phase I's 3.3 million cubic meters of storage capacity, they form a dual flood defense barrier protecting the Daxing International Airport area.

Regarding the heavy rainfall brought by Typhoon "White Dolphin," Wang stated that the precipitation was insufficient to trigger the detention area's activation. Beside the red sightseeing corridor of Phase I stands a water level gauge, where a striking red mark is visible among various blue indicators. "That marks the flood level during the '23·7' event, when the water level reached 22 meters, while the maximum storage level for Phase I is 24 meters," Wang explained. "This is precisely why the Phase II project was initiated."

According to the project manager, Phase II has established a mature closed-loop dispatch model. During the flood season, floodwaters enter the southern zone through the three-bay flood diversion sluice on the west side and then flow by gravity through connecting culverts into the northern zone for storage. Once the rain subsides and water levels stabilize, the two-bay water release sluice on the east side serves as the primary outlet, supplemented by the diversion sluice, with all five bays operating in coordination to return water to the Yongxing River, minimizing flood risk to the greatest extent possible.

The project also adheres to ecological water management principles, preserving the original forest structure of the site. "The original site consisted of woodlands, farmland, and villages. During construction, native pine and ginkgo trees were preserved in place, and transplanted trees were replanted on the slopes after completion, complemented by native vegetation to form ecological slope protection," the manager said. During the flood season, the reservoir area remains open, with only irrigation channels retaining small amounts of rainwater to nourish vegetation, achieving "flood safety in the wet season, ecological beauty in the dry season." "Phase II is currently exploring plans for public opening and sharing, and it may become a recreational ecological space for citizens in the future."

In fact, following the "23·7" event, the city began systematically planning eight major flood detention areas across key river basins in southern, western, and eastern Beijing, covering multiple dimensions including river channel management, sluice and dam construction, ecological restoration, and intelligent control. Beyond the Daxing International Airport Phase II project, the other seven detention areas are strategically distributed with distinct focuses, comprehensively addressing basin flood control weaknesses.

For example, the Mentougou Six-River Interconnection Detention Area has created 1 million cubic meters of storage space through gravel pit dredging and renovation, while simultaneously implementing river recharge projects to revitalize regional water resources. The Nankou and Shagou River Detention Area is equipped with six control sluices and two culverts beneath roads, establishing a systematic water control system through earthwork grading, slope greening, and river connectivity. The Wenyu River Park Shunyi Phase II Detention Area covers approximately 109.4 hectares, integrating water ecological construction, intelligent electrical control, landscape services, and automated water release facilities to deliver multiple benefits in flood control, ecology, and public welfare. The Bahekou Detention Area has completed comprehensive treatment 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 Detention Area occupies 85 hectares and includes concurrent river system restoration.

Today, the eight detention areas are essentially complete and operational. The 35 million cubic meters of newly added storage capacity has significantly expanded the capital's flood control "buffer space," continuously reinforcing the safety baseline for river basin flood defense.