Dozens of heavy-duty trucks were at work, busily transporting soil and rocks from an enormous pit. Just a few hundred meters away, where the debris had once lain, the land had not only been leveled, but crops had been planted, including oilseed rape and wheat.
Without prior knowledge, visitors would hardly know they were standing in a coal mine. No heaps of coal are visible, and the familiar black color can only be glimpsed occasionally at the pit's bottom because a large swath of the land is covered by crops.
Welcome to the Xiwan open pit coal mine, 60 kilometers from the Yellow River as it flows through Shaanxi province.
As China ramps up measures to harness the world's most heavily sediment-laden waterway, the mine, in Shenmu county, Yulin city, is just one example of efforts being made to improve soil and water conservation in the river basin.
A 250-hectare section that has been leveled and planted with crops accommodates surface soil removed to aid construction of the coal mine, which started in 2015.
"Covered by sand and dotted with a few patches of grass, the area was so barren it could hardly support any crops," said Lei Zhiyong, chief engineer of Shaanxi Shenyan Coal, the mine's operator.
Yulin is located in the area bordering the Mu Us Desert－one of China's four major deserts－and the Loess Plateau, which is blanketed by deep, fine, wind-blown soil. The Yellow River gets its name because of the amber water that appears as it picks up the sediment during its passage across the plateau.
In the river's lower reaches, sedimentary deposits have caused the riverbed to rise above the surrounding plain, making the section "a river above the ground".
Soil remediation measures－designed to cleanse and revitalize the land－were rolled out soon after construction of the mine started.
While leveling the area, Shaanxi Shenyan Coal invited experts from Northwest A& F University in Xianyang, Shaanxi, and the China University of Geosciences in Wuhan, capital of Hubei province, to analyze the soil's composition, Lei said.
Based on the analysis, crops were chosen for experimental cultivation, he added, pointing at a plot of oilseed rape. The plants are thinly scattered and mostly short, though some have blossomed, and Lei said efforts will be made to improve the soil and grow trees and crops.
Though the mine only went into production in July last year, remediation efforts have also been made across another 50-hectare site. So far, total investment in water and soil conservation at the mine has reached 170 million yuan ($26 million), he said.
Lei noted that soil and rocks dug out of the pit are used to fill mined areas, thus ensuring that the pit's size remains relatively unchanged.
Similar planting projects will be carried out in the newly filled band as operations continue in the 50-square-kilometer mine.
To promote sustainable use, the company has also changed the way it obtains land use rights.
Instead of buying the rights from farmers－a common practice nationwide－the company rents the land, paying 22,500 yuan per hectare annually.
"When all of the land has been leveled and the soil improved, we will return it to the farmers," Lei said.
"Through consistent efforts, we expect to transform the rough, sandy area into quality farmland that will support large-scale agricultural operations and guarantee handsome incomes for the farmers," he said.
He noted that a forest belt will be planted to anchor the sand and prevent the wind from eroding the soil, and added that all the wastewater generated in the mine is collected for concentrated processing before being reused.
Worst hit area
The water and soil conservation work at the mine is a microcosm of the efforts made by the industry in the resource-rich area that straddles the provinces of Shanxi, Shaanxi and the Inner Mongolia autonomous region, which is a major contributor to the river's high concentration of sediment.
Resource exploitation means the area is the place worst hit by water and soil loss in the river basin, according to the local soil and water conservation supervision bureau.
Established in 1992 to tackle the problem, the bureau is the country's only soil and water conservation governmental body overseeing an area that falls under the jurisdiction of different provincial-level governments.
"About 70 percent of the major zones that contribute coarse sediment to the river in the basin are located in the area," according to the bureau, an affiliate of the Yellow River Conservancy Commission.
Analysis of monitoring data shows that 120 million metric tons of soil and solid waste were discarded by local coal mines from 1986 to 1994, which raised the sediment density in rivers by almost 27 percent.
With four major coalfields, the area boasts proven reserves of 280 billion tons, the bureau said. Meanwhile, local authorities have said there are currently more than 200 coal mines in Yulin alone.
All new major construction projects in the area have to roll out water and soil conservation measures, said Yu Quangang, the bureau's head. He added that in recent years all conservation plans for new projects have been inspected and approved by the body.
Yu said satellite remote sensing can help monitor any work, operations or activity that result in disturbance of the earth in an area as small as 0.1 hectare－about the size of two basketball courts.
This has saved bureau officials from visiting mines frequently to supervise work, he said.
In addition to traditional approaches to soil conservation, such as tree planting, authorities have also worked to transform traditional mining operations to prevent water and soil loss.
At the Xiaobaodang underground coal mine, also in Shenmu, experiments have been carried out since August last year to identify an operating norm that would prevent leaks of shallow groundwater.
The efforts have borne fruit. Based on close monitoring of the leaks and underground fissures that can occur under a range of extraction methods, experts have formulated a preliminary operating norm. It provides specific suggestions about approaches under different conditions, including various thicknesses of impermeable layers of earth and rock that prevent water from penetrating the mining seams.
Xie Yongli, chief engineer of Xiaobaodang Coal, said the company drilled 23 observation wells to assist the monitoring work prompted by experiments.
As far as he is aware, prior to the experiments, there was no similar monitoring of the disturbance mining causes to underground water sources in China.
He said the company plans to apply the preliminary norm to new seams while carrying out more experiments and monitoring to further improve the system.
The company has also taken other measures to prevent soil erosion in the 220-sq-km mine.
For example, it has planted over 11,100 trees and invested 112.7 million yuan in water and soil conservation, a huge increase on the 32.2 million yuan cited in its initial plan.
Benefits to society
As the Xiaobaodang experiments continue, a series of trials have lasted for decades at the Xindiangou field research station in Yulin's Suide county.
Established in 1952, the station is dedicated to exploring potential solutions for water and soil conservation in the Loess Plateau.
While conducting experiments on construction work, such as silt arrestors－small dam-like structures that can help separate solids and suspended sediment and stop them from being carried by the runoff－it also operates experimental plantations to test the abilities of different plants to aid water and soil conservation across an area of 1.44 sq km.
As a result of the efforts, the vegetation coverage has risen from 3.5 percent in 1953 to about 75 percent today, while soil loss has been reduced by 80 percent, said Cui Le, the station's deputy head.
The lessons learned from the research have been promoted in other areas. For example, about 59,000 silt arrestors have been built across the Loess Plateau.
Thanks to the efforts of different regions and sectors, half of the area affected by water and soil loss in the plateau has been preliminarily treated. Meanwhile, various measures have resulted in the average annual volume of sediment entering the river from the plateau being reduced by 435 million tons in recent years, according to the Ministry of Water Resources.
As work continues at Xindiangou, researchers plan to introduce more water and soil conservation measures that will generate economic benefits.
"We have managed to transform barren slopes into lush mountains with lucid water (in the valleys). In the next step, we are going to make the lush mountains and lucid water into valuable assets," Cui said.
The concept of lucid waters and lush mountains as invaluable assets was introduced by President Xi Jinping during a 2005 visit to Anji, Zhejiang province, when he was provincial Party secretary.
"We plan to introduce more agricultural measures in the research field to seek potent solutions that will control water and soil loss while generating financial benefits for local people," Cui said.