On the surging Yalong River, a decisive battle crucial to the success of the Mengdigou Hydropower Station project—the river closure—has entered its final sprint of preparations. The roar of machinery has replaced the roar of the river, and flickering lights illuminate the sleepless valley. All builders are working to the highest standards, with the most concrete measures and the most resolute conduct, to lay a solid foundation for that historic moment of "dragon-mouth closure."

The "rehearsal" closure in model tests

"In the battle of river closure, the plan comes first." The closure of the Mengdigou Hydropower Station is by no means an easy task.

The river channel at the Mengdigou Hydropower Station features steep mountains on both banks and a deeply incised valley, forming a typical "V" shape. The riverbed slope is extremely steep, and the river surges through the narrow valley at velocities reaching several meters per second, like an unbridled wild horse that is difficult to tame. Such turbulent flow carries enormous energy, so that the material dumped during closure may be instantly swept away by the fierce current the moment it enters the water, making the advance of the closure dike extremely difficult.

When the closure dike begins to advance, even more severe challenges follow. Due to the special river terrain and flow conditions, the front of the dike is directly exposed to the main current and bears the most violent impact of the river. At the dragon-mouth position during closure, the unit-width power is enormous, with each square meter bearing tens of thousands of units of energy impact. This imposes近乎苛刻 (near-exacting) requirements on the protection materials, construction techniques, and construction organization and coordination capabilities of the dragon-mouth section. The slightest error could lead to closure failure and the loss of all previous efforts.

The core technical weapon is the precise 1:50 movable-bed model. In the test hall, the river is miniaturized and time is accelerated. Technical experts, like commanders, rehearse various "battle formations" on the sand table.

"If we advance from the left bank, how will the flow respond?" "When the dragon mouth narrows to 30 meters, how large must the stones be to hold their ground?" "At the most dangerous moment, what kind of 'heavy weapon' should be deployed?" ... Every question seeks its answer in model tests. Through repeated adjustment, they ultimately pinpointed the core tactic of "single-dike vertical closure, one-way advance from the left bank to the right bank." This plan is like a highly skilled boxer concentrating all his strength at a single point to achieve a breakthrough.

However, facing the towering waves at the dragon mouth, the risk remains extremely high. The technical team turned its attention to the already-built diversion tunnel. How could more river water be made to "obey" and enter the diversion tunnel in advance, thereby "reducing the burden" on the main closure battlefield?

A creative idea that can be called a "stroke of genius" was born—building a flow-dividing spur dike downstream of the diversion tunnel. This spur dike, constructed from materials from cofferdam demolition, appears simple but is actually ingenious. Like an invisible hand, it cleverly raises the water level near the diversion tunnel entrance while the battle at the dragon mouth is at its height, as if opening a more attractive "side door" for the river, significantly increasing the diversion ratio. This move effectively "bleeds off" part of the energy at the dragon mouth, turning a head-on frontal assault into a clever containing assist, greatly reducing the final difficulty and risk of closure. The flow-dividing spur dike planned downstream of the diversion tunnel is like a masterful move of "using four ounces to deflect a thousand pounds," guiding more river water into the tunnel in advance and relieving enormous pressure on the main closure dike force facing the dragon mouth.

The "hardcore" stockpile built up in the material yard

If the technical plan is compared to the "art of war," then the mountain-like stockpile of closure materials is the "provisions and fodder for the troops." The material preparation yard on the left bank is the most solid rear base for this battle.

Looking around, various types of stone materials are piled up like mountains, reflecting a cold and resolute gleam in the sunlight. Reinforced gabions are neatly arranged like soldiers awaiting deployment; alloy mesh bags are tightly stacked, displaying tough protective strength; giant concrete tetrahedrons stand proudly like solid fortresses. Every piece of stone and every component speaks to the importance of the coming closure battle.

"The material reserve factor is set at 1.8." This decision is based on strict technical specifications and a deep understanding of the narrow valley in the dam site area of the Mengdigou Hydropower Station. Even more encouraging is that, thanks to the enormous advantage of integrated cascade hydropower development in the Yalong River basin, the upstream Lianghekou Hydropower Station and the Mengdigou Hydropower Station have formed an efficient joint dispatch system, with precise and orderly flow control, providing unprecedented stable hydraulic conditions for closure construction. This exemplary act of basin-wide coordination provides key insurance for the smooth progress of the project. And the ample material reserve is precisely to calmly meet any possible challenges during closure and ensure nothing goes wrong.

Look at that array: extra-large stone, large stone, medium stone, and stone debris—conventional forces classified by particle size, towering into mountains. They are the backbone for filling the main body and steadily advancing. The 540 reinforced gabions are like armored vehicles ready for action, and the 2,700 alloy mesh bags are like flexible armor—a special elite unit that will resist the scouring of the torrent with their bodies in the core area of the dragon mouth where flow velocity is highest. The decisive heavy weapons are the 150 concrete tetrahedrons weighing 10 to 20 tons each, like the ancient "water-suppressing divine beasts," which will be pushed into the river center at the final moment of closure to settle the outcome with a single blow.

Each material pile has an "identity card," with number, category, and volume clearly marked. This "material feast" ensures that once the battle begins, logistical supplies can flow continuously and reach the front line precisely.

Sleepless nights at the command center and the construction site

Plans and materials must ultimately be executed by people. At the forefront of closure preparations is an iron construction team with efficient command, clear division of labor, and rapid response.

At the intersection of Roads No. 1 and No. 5 on the left bank, the closure construction command center has long entered "wartime status." This is the "nerve center" of the entire battle. The command center is clearly divided into three levels, with six functional modules: dike closure, technical support, road traffic, material yard command, logistics support, and emergency rescue.

Here, wired telephones and wireless walkie-talkie signals intertwine, ensuring that the commander's decisions can instantly cross the valley and reach the ear of every dike-head operator. Every morning meeting is a "brainstorming session," summarizing the previous day's progress, analyzing the latest hydrological data, and deploying the day's attack rhythm. Decision-making, execution, and feedback form an efficient closed loop.

"If the roads are blocked, everything is lost." In the narrow and steep canyon, ensuring an unimpeded "lifeline" is the top priority. The road traffic group bears enormous pressure. They not only ensured that all newly built and reconstructed roads were completed and met the "two-lane" traffic standard, but also constantly inspect and maintain key sections.

One can imagine that at the critical moment of closure, thirty dump trucks carrying dozens of tons each will line up end to end on this mountain road, forming a steel dragon. Any traffic jam or breakdown could disrupt the entire attack rhythm. Therefore, they know every curve and every slope thoroughly and have formulated detailed vehicle diversion and emergency evacuation plans.

At the pre-advance section of the closure dike, which is about to become the main battlefield, there is a scene of bustling activity. Backhoes, bulldozers, and dump trucks have completed their final "pre-battle inspection," and drivers are rubbing their hands, full of confidence in the performance of these "old partners." The 2,000-square-meter construction platform formed during the left-bank pre-advance is particularly valuable at this moment. It is not only a "parking lot" for equipment dispatch, but also a "temporary ammunition depot" for special materials and a "field repair shop" for sudden equipment failures.

Meanwhile, the "wrapping-head" protection construction on the right bank is in its final stage. This is like putting gloves on a punching fist, ensuring that the dike head remains stable during advance and will not collapse under the impact of the river. As night falls, the construction site is as bright as day. The roar of machinery, the whistles of command, and the roar of the river intertwine into a powerful battlefield symphony. Builders work day and night, with people resting but machines never stopping, and everyone's eyes shine with the light of decisive victory.

From the meticulous rehearsal in the laboratory to the mountain-like "hardcore" stockpile in the material yard, and then to the efficient coordination between the command center and the front line, the preparations for the river closure of the Mengdigou Hydropower Station have spread out like an impenetrable giant net toward the surging Yalong River...