Gutang feet
cofferdam
The ancient seawall of Qiantang River, which has been in use for 300 years, has been upgraded and reinforced recently.
After six visits to the south of the Yangtze River, I once broke my heart for the construction of Qiantang River seawall. According to legend, the emperor of online celebrity also personally played a pile in Haining.
With the ebb and flow of the tide, most ancient seawalls have been relegated to the second line, but there are still about 40 kilometers of ancient seawalls in Haining and Haiyan, which bear the heavy responsibility of flood control and tide control. In 2019, the ancient seawalls in Haining section were listed as national cultural protection units.
How to improve and reinforce? Yesterday morning, the reporter of Qianbao Hour followed the staff of Qiantang River Basin Center in the province and came to the ancient seawall construction site in Haining section to find out.
The ancient seawall was originally “on stilts”
At the bottom is pine piling.
In the seawall section of Yanguan-Jianshan section of Haining, cofferdam has been laid in some river sections, and the river water has been drained to enter the construction stage.
On the construction site, trucks shuttled back and forth, and pile drivers clattered. At the construction site, the reporter was able to get a glimpse of the 300-year-old seawall.
The ancient seawall is roughly composed of the pond body and the pond foot, and the pond body is made of stones.
What material is used for the foot of the pond in the river? It’s countless upright wooden stakes.
Without reinforced concrete and mechanical equipment, how did our ancestors pile the seawall?
The staff of Qiantang River Basin Center in the province said, “In ancient times, piling was roughly like this. People fixed 4-6 meters of pine trees vertically on the beach, and then set up a piling frame. A group of strong men hoisted stone hammers on the frame with hemp ropes, hitting the pile head hard …”
Pine, rich in turpentine, is said to be immortal in water for thousands of years. The structure of the pond foot of ancient seawalls in Ming and Qing Dynasties was to lay a plum blossom pile along the coast, then a layer of horsetooth pile on the outside, and two rows of horsetooth piles were used to reinforce the outermost part near the river.
It’s hard to imagine that the rock-solid fish scale pond in Ming and Qing Dynasties was actually built on a wooden stake, and it felt like a “giant” stepping on wooden stilts.
Sticky rice mortar bonded bar stone
Also reinforced with a “stapler”
Historically, the Qiantang River has been at the mouth of the sea, and it once drifted all the way from the niche mountains in Xiaoshan on the south bank to Haining seawall on the north bank dozens of kilometers away.
If the unpredictable Qiantang River is not managed, if the tide invades both sides of the river, the people will be miserable, and the wild “Mother River” will even flush the tide all the way to Songjiang Prefecture (now in Shanghai), so that the people there will eat salty water.
Since ancient times, China has attached great importance to the regulation of Qiantang River. Stones are used to build seawalls, and the origin of stones is varied, ranging from granite to Taihu stone, which is transported to the riverside site by water for construction.
Up to now, the ancient seawall in Ming and Qing Dynasties has been built with countless stones. Apart from being glued and leveled with sticky rice mortar, there are also iron ingots and iron curbs with stapler-like structure inside, and the exquisite degree of the project is amazing.
However, such a delicate ancient seawall is only 6 meters high. On the 11th typhoon in 1997, the water level of Qiantang River was more than 1 meter higher than that of the ancient seawall. Seven executions occurred in the seawall in Haining section, and the sea water poured directly into the villages along the river.
Obviously, the construction standard of the ancient seawall is low, and its flood control standard is only about once every ten years.
Around 2000, Qiantang River Administration of Zhejiang Province built a new seawall about 10 meters high at the back of the ancient seawall of Ming and Qing Dynasties in Haining, which raised the flood control standard to the once-in-a-century event.
In recent years, during the safety assessment of ancient seawall, the Provincial Water Resources Department found that the toe of seawall about 16.5km from Yangtianmiao to Tashanba section was deeply brushed locally, and some sections of seawall were unstable, which needed to be reinforced urgently.
16.5km overhaul of ancient seawall
30,000 new piles will be hammered again.
Qiantang ancient seawall is a national cultural protection unit. It should be overhauled under the premise of protection, and the flood control standard at the foot of the seawall should be raised to once every 300 years. The scheme must be prudent and rigorous.
After several revisions, the current construction method was determined.
Yesterday, at the Daji River section of the ancient seawall, the reporter saw that the riverside beach 8 meters, 10 meters and 12 meters wide outside the foot of the ancient seawall became a “cement road”. Looking closely, this road is made up of pieces of reinforced concrete slabs. This winding “cement road” separates the pond foot of the ancient seawall from the river water and plays a role in protecting the pond foot.
On the Yingjiang side of the “Cement Road”, a row of deep piles were laid at the bottom, and each 12-meter or 15-meter-long reinforced concrete column was closely arranged. The weight of a concrete pile is close to 5 tons, and big trucks can only pull 3 piles to the construction site at a time.
After the concrete piles are hoisted by the pile driver, each pile has to “click” for more than one minute before it can be plunged into the riverside beach. If there is a stone in the mud that can’t be driven, pull it out, dig it away and pile it again.
More than 30,000 such concrete piles are needed for the 16.5-kilometer ancient seawall that is being overhauled and embedded in the bottom of the river to protect the inner foot of the ancient seawall.
Compared with the old pond foot with wooden stakes only 4-6 meters deep, the reinforced concrete piles arranged in a wall 12-15 meters deep on the outside are obviously much stronger, plus the 8-12 meter wide concrete apron on the outer upper cover of the pond foot. It can be said that this is a new set of moisture-proof “armor” for the old pond foot stepping on wooden stilts.
During the renovation period this year and next
The tidal observation in some sections of Haining River has an influence.
There are also ancient seawalls in Hangzhou. For example, there are ancient seawalls in Ming and Qing Dynasties buried under Hanghai Road and Qiutao Road. You can also see that the ancient seawall has become an inland river bank in Zhuantang, Qiantang New District and other places in Hangzhou.
After visiting the construction and reinforcement work at the scene, the reporter has a question: Will the foot of the new pond solidified by concrete go deep into the river, which will affect the tide?
The staff of Qiantang River Basin Center said, “The construction of Xintangjiao is basically flush with the original tanshui. After the construction, it will be 1.5-2m underwater, which will basically have no impact on the tidal bore of Qiantang River.”
However, the construction period of the seawall project from Yangtianmiao to Tashanba section on the north bank of Qiantang River is 3 years, and it is expected to be completed in early 2024. If you visit Haining section of Qiantang River during these 3 years, some sections of Qiantang River will still be affected.
“Take the flood season in August 18th as an example. During the spring tide this year, there will be a 500-meter river cofferdam construction at 1km upstream of Yanguan. During the spring tide in 2023, there will be some river cofferdam construction in Xincang section of Haining. During the closed construction period, it is not appropriate to watch the tide along the Yangtze River.” The staff of Qiantang River Basin Center reminded.
In addition to the reinforcement project at the foot of the pond, the scheme of cultural landscape construction and ecosystem building along the Qiantang River seawall is being further improved.
Considering the water conservancy, cultural and historical value of Qiantang River estuary regulation, Zhejiang is expected to build a new seawall museum in Haining section of Qiantang River.
Our reporter Shi Wen correspondent Xu Xianhong Wen/photo