Geographical knowledge problem

Preventing and controlling floods in the middle and lower reaches of the Yangtze River is the primary task of building the Three Gorges Project.

In ancient China, Yunmengze was always a natural place to store the Yangtze River flood. After Yunmengze disappeared, Dongting Lake replaced Yunmengze as another natural place to store floods in the Yangtze River. Therefore, in the middle and lower reaches of the Yangtze River at that time, "the flood process was not obvious and there were few river disasters". However, with the continuous deposition of sediment, the water surface area and volume of Dongting Lake are shrinking day by day, which greatly weakens its ability to regulate and store the Yangtze River flood. This forced a large number of floods to be directly discharged from Jingjiang River. However, so far, the safe flow of Jingjiang reach (including the flow discharged into Dongting Lake) is only 60,000 ~ 68,000 cubic meters per second. Therefore, every flood season, the flood level of Jingjiang reach is often 6 ~ 10 meters higher than the ground on both sides of the river, forming a "suspended river", which always threatens the lives and property of people in Dongting Lake area and Jianghan Plain150 thousand and the safety of 23 million mu of cultivated land.

It is necessary to build a reservoir that can store the flood of the Yangtze River, so that it can store flood detention like Yunmengze and Dongting Lake, and protect the middle and lower reaches of the Yangtze River from flood disasters. In the upper reaches of Jingjiang reach, through a lot of exploration, measurement and scientific research, and decades of search and demonstration, the ideal dam site has finally been found, which is the Three Gorges Water Control Project. Therefore, it can be said that the construction of the Three Gorges Project is a historical necessity, and flood control is the primary starting point for the construction of the Three Gorges Project.

The Last Pot of Clear Water

Pollution is also a problem that plagues these two lakes.

With the rapid development of economy, Dongting Lake has long been crystal clear. In 2006, according to the statistics of the State Environmental Protection Administration, the overall water quality was only five categories (the water quality was divided into six categories, the worst was five categories, followed by five categories; Five, five and four kinds of water are not suitable for drinking.

Maybe this is a painful lesson. From the end of that year, Hunan Province closed 234 small paper-making enterprises around Dongting Lake within six months. Not long ago, at the 2008 national meeting of environmental protection directors, Zhou Shengxian, director of the State Environmental Protection Administration, said that after various measures were taken, the local water quality of Dongting Lake had been improved from poor five categories and five categories to three categories.

However, Dongting Lake is far from being out of the haze of pollution. Nie, former deputy chief engineer of Hunan Provincial Water Resources Department and former director of Dongting Lake Water Conservancy Administration, said in an interview with Caijing that the excessive use of chemical fertilizers and pesticides in the whole lake area has caused serious pollution to water and soil. Especially in the dry season, the water level drops seriously, and the water quality is often difficult to guarantee.

According to the statistics of China National Environmental Monitoring Center, as of June, 2007 165438+ 10, the overall water quality of Dongting Lake was still classified into four categories. In June 2008, 5438+1October 1 1, the data released by Hunan Environmental Monitoring Center Station also showed that the ammonia nitrogen in the outlet section of Dongting Lake exceeded the standard, which belonged to the fourth water quality.

Among the four freshwater lakes in China, Poyang Lake was once considered as the only one without eutrophication, and it has the reputation of "the last basin of clear water" in China. When Caijing reporters visited Poyang Lake, some residents proudly said that the lake was not polluted.

However, all this has been quietly changing.

According to the data of Jiangxi Water Resources Bulletin, 200 1 Poyang Lake has no pollution, 80% of the water quality is better than Class III, and 20% belongs to Class III. Poyang Lake at this time can indeed be called "a basin of clear water". But by 2006, less than 60% of Poyang Lake was better than Class III, more than 20% belonged to Class III, and nearly 20% was worse than Class III. According to the statistics of the Ministry of Water Resources, by 2006, Poyang Lake as a whole was in a state of moderate eutrophication.

Facing the rapid decline of water quality in Poyang Lake, Jiangxi Provincial Water Resources Department began to issue a monthly report on dynamic monitoring of water quality and quantity in Poyang Lake from June 5, 2007 at 438+1October 8. According to the circular, the water quality of Poyang Lake was still deteriorating in 2007.

In September of that year, the water level of Poyang Lake was basically the same as in previous years. When the water surface area of the lake area was 3005 square kilometers, no Class I or II water was found in ten evaluation sections of the lake area. Three types of water account for 60%; Four types of water account for 40%. June 5438+February of that year, with the water level of Poyang Lake hitting a record low, the self-purification ability of the lake decreased obviously, and the water quality injected into the Yangtze River has become five kinds of heavily polluted water.

In addition to the wastewater discharged along the lake, all kinds of wastewater along the five major rivers in Jiangxi Province, such as Ganjiang River and Raohe River, will eventually flow into Poyang Lake, and the whole control task is bound to be very arduous. Xing Jiusheng, chief of water quality department of Jiangxi Hydrology Bureau and chief technology officer of Jiangxi Water Environment Monitoring Center, told Caijing that many industrial parks in the province have not really reached the discharge standard, and the construction of sewage treatment plants in several cities has just started, and Poyang Lake has entered the dry season ahead of schedule. "How can the water quality be good?"

With Guangdong, Zhejiang and other developed provinces constantly raising the threshold of environmental protection, many heavily polluting enterprises have moved to Jiangxi, where the economy is relatively backward, and the threat faced by Poyang Lake is likely to deteriorate further.

Take Ji 'an, an old revolutionary base area in Jiangxi as an example. Since 200 1, many papermaking enterprises in Fuyang, Zhejiang Province have been introduced to the local area, and the wastewater generated has been directly discharged into the Ganjiang River, causing water pollution accidents. In 2006, it was jointly inspected by the State Environmental Protection Administration and the State Administration for Industry and Commerce.

Influence of Three Gorges Project

In the middle and lower reaches of the Yangtze River, there are many lakes dotted around. But so far, only a few lakes such as Dongting Lake and Poyang Lake are still directly connected with the Yangtze River. Generally speaking, Dongting Lake has advantages and disadvantages for the Yangtze River, and Poyang Lake has advantages and disadvantages.

In Hunan Province, the rolling Yangtze River flows into Dongting Lake through four inlets-Songzi River, Hudu River, Ouchi River and Huarong River. Chenglingji in the lower reaches is the only exit from the lake to the Yangtze River. In Jiangxi Province, Poyang Lake receives water from five major rivers in the province, and then flows into the Yangtze River in Hukou County, Jiujiang City.

From the time point of view, since 2003, the water shortage problem of Dongting Lake and Poyang Lake in dry season has obviously intensified. Just in June 2003, the Three Gorges Project realized the second stage of water storage, and the water level in front of the dam increased from 90 meters to 135 meters.

The Yangtze River Water Conservancy Commission has repeatedly stated that the lack of water in these lakes is mainly due to the decrease of upstream inflow due to weather, which has nothing to do with the Three Gorges Project. However, there are various indications that the influence of the changes in the relationship between rivers and lakes (berths) caused by the Three Gorges Project may still not be ignored.

Tong, a professor-level senior engineer of Hunan Institute of Geology, told Caijing that after the Three Gorges Reservoir is in operation, the increased discharge before the flood season will raise the water level of Dongting Lake in the dry season, which is the original knowledge of Dongting Lake researchers. However, in June 2003, the observation data since the second impoundment of the Three Gorges Reservoir showed that the water level and groundwater level of Dongting Lake actually decreased during the dry season. "This is a huge contrast with the original understanding of the Dongting Lake environment."

The reason for this unexpected situation, he explained, is that after the impoundment of the Three Gorges Reservoir in June+10 every year, there will be a serious "loss" of water in the Yangtze River, which directly leads to the water level in Chenglingji being lower than before the operation of the reservoir in dry season, which in turn leads to the rapid inflow of Dongting Lake into the Yangtze River and the "loss" of water. Before the flood season of the following year, the discharge of diarrhea will increase. However, because the four estuaries of the Yangtze River into Dongting Lake have already been cut off, the increased discharge is not enough to enter Dongting Lake.

Tan, director of Jiangxi Hydrological Bureau, also said in an interview with Caijing that, similar to Dongting Lake, the impoundment of the Three Gorges Reservoir has a significant impact on the ebb and flow of Poyang Lake.

Observations show that at 0: 00 on September 25, 2007, the Three Gorges began to store water, ending the flood season. Within a few days, the flow of Poyang Lake from the mouth of the lake to the Yangtze River suddenly increased, reaching more than 6,000 cubic meters per second. At the same time, the flow of several major rivers into the lake was only 1000 cubic meters per second. In this case, on June 3rd1day, the water level of Hukou Hydrological Station dropped from above15m at the beginning of the month to below10m.

Of course, in addition to the Three Gorges, the dense reservoirs in the two lake basins also intercepted the incoming water of the upstream rivers during the dry season. In Jiangxi Province, the number of large and medium-sized reservoirs has exceeded 250. According to Tong, there are 223 large and medium-sized reservoirs in the upper reaches of the four major rivers in Ethan, an important channel for Dongting Lake to enter the lake, and several reservoirs are under construction.

Water shortage is not all the challenges brought by the Three Gorges Project to these two lakes. Xiong Da, a retired professor-level senior engineer of Jiangxi Institute of Water Resources Planning and Design, believes that within 30 years of the initial operation of the Three Gorges Project, siltation will occur in the Hukou reach, which may have disastrous consequences for flood control in Poyang Lake area.

According to Zhong, deputy director of Dongting Lake Water Conservancy Administration, the impact of the Three Gorges Project on flood control in Dongting Lake is more beneficial than harmful-in flood years, the water level in Chenglingji area can be lowered, thus greatly reducing the flood threat of Jingjiang reach to Dongting Lake area.

However, in Tong's view, the impact of the operation of the Three Gorges Reservoir on the flood control of Dongting Lake can only be said that the advantages outweigh the disadvantages.

Because of the siltation of Dongting Lake itself, it is expected to be greatly relieved after the operation of the Three Gorges, and the capacity of Dongting Lake will also increase; But at the same time, the sediment that should have been deposited in Dongting Lake will be seriously deposited at the only exit of Dongting Lake after being washed to Chenglingji-Hankou reach, which is not conducive to flood discharge in Dongting Lake during flood season.

However, Professor Liu Ying, deputy director of Poyang Lake Ecological Environment and Resources Research Office of Jiangxi Normal University, pointed out that due to the lack of in-depth systematic research and exact data, there is still controversy about the impact of the Three Gorges Project on the water level and flood control pattern of the two lakes in dry season.

Fortunately, this possible impact has attracted the attention of relevant departments. In September 2007, Cai Qihua, director of the Yangtze River Water Conservancy Committee of the Ministry of Water Resources, pointed out at the annual meeting of China Association for Science and Technology that the Three Gorges Project has great benefits in flood control and power generation. At the same time, "the huge water and sediment regulation after its operation will change the hydrological situation, river evolution, river-lake relationship and river flood discharge capacity in the middle and lower reaches of the Yangtze River, thus affecting the water environment and water ecology in the lower reaches of the dam, directly or indirectly affecting the ecological functions of important wetlands such as Dongting Lake, Poyang Lake and the Yangtze River estuary."

From June 5438 to February 25, 2007, the project "Study on the Impact of Three Gorges Project on Poyang Lake and Five Rivers in Jiangxi Province" led by Jiangxi Institute of Water Conservancy was also launched. As the largest scientific research project in the history of water conservancy in Jiangxi Province, the state finance will allocate 4.47 million yuan of special funds, and the Jiangxi Provincial Water Resources Department will also provide matching funds.

The Three Gorges Project will not have a great impact on the ecological environment, nor will it cause sediment deposition.

In terms of ecology, after the completion of the Three Gorges Project, the kinetic energy of rivers will be used to generate electricity, replacing huge amounts of coal for thermal power generation. Hydropower is a clean energy source, and the annual reduction of carbon dioxide emissions, coal combustion and other pollutants emissions is amazing.