Longjiang river regulation
Longjiang is the largest and longest river in the county, which originates from Puning County and flows into Huilai via Lu Fengxian, with a drainage area of 554.5 square kilometers and a total length of 88 kilometers. In the early days of the founding of New China, dikes on both sides of the main stream were scattered, low and incomplete. At high tide, the tide rushes in, which is harmful to farmland. During the rainstorm, flash floods and floods occurred, and the dam destroyed by Hong Chao has not been repaired yet. 1957 winter, the dike of the main stream of Longjiang River was fully restored. By February 1958, the downstream main dike was built for 25 kilometers. The right bank starts from Tangtian Village in Houshan Township and ends at Yang Xia Village in Nanhai Township. On the left bank, go fishing in Shi Cun from Bangshan Village. The width of the dam crest is 2 ~ 3m, the internal and external slopes are 1: 2 and 1:2.5, the elevation of the dam crest is18.2 ~ 22.5m (Huishui), there are 69 large and small buildings along the dike, and the national investment is1.2000 yuan, which makes the Longjiang dike reach 20 years.
Because the middle and lower reaches of Longjiang River belong to a plain river, the drainage capacity of the river is limited, and the original engineering standard is low. The dike body is mostly made of fine sand with poor strength and thin dike body, which leads to leakage of dike foundation, serious landslide and many dangerous sections of dike body. Originally, according to the design standard of 20-year return period, the flood peak flow of dike repair is 32 10 second cubic meter, but the actual safe flow is only 2300 second cubic meters, which is only close to the 10 year return period standard. Coupled with the flood discharge of large and medium-sized reservoirs such as Longtan and Xiangkou in the upper reaches of Lu Fengxian, the safety of Longjiang levee is seriously threatened. During the typhoon 1986 on July 7th, the water level at the bridgehead of Longjiang River reached 2 1.34 m (warning water level 19 m), and the peak flow was 2946 cubic meters. There are 47 breaches in the middle reaches of Junying and Luyang, the length of which is 1852 m, which has caused serious losses to agricultural production. From the winter of 1986, according to the actual situation of the main dangerous section at 16, the dike was strengthened and repaired in stages, so that the dike reached the flood control standard of once every 20 years. Through the maintenance and reinforcement of water conservancy in winter and spring of 2003, some dangerous sections of Longjiang levee have been eliminated, but many dangerous sections have not been eliminated in time due to the limitations of manpower, material resources and financial resources. The rainwater collection area of Longjiang County is 746.9 square kilometers, and the upstream reaches Shenquan Port 4 1.3 kilometers. From Changpu Village in Kuitan to Bangshan Bridge Gate in longjiang town, there are two tributaries in the upper reaches, Gaopu and Bengkan, and 17 small tributaries, which merge into the mainstream from the left and right banks. From Bangshan Bridge Gate to Shenquan Port, there are large tributaries such as Touliao Water, Luoxi Water, Nangou Water and Xixi Drainage River, which flow into the mainstream from the left and right banks, forming the central plain of the county, with cultivated land area of 1 1.9 million mu. After 1957, the main dike in the middle and lower reaches was built on a large scale, and the two tributaries of Ganneixi and Shuangxizui were blocked. Since then, the flood has returned to the main river, and the tide cannot directly enter the farmland, and the flood disaster has gradually decreased. Because the upstream tributaries all originate from high mountains, the vegetation condition is poor and the riverbed gradient is large. Whenever flash floods occur, a large amount of sediment is brought into the main channel, and the siltation is extremely serious. For more than 20 years, reservoirs have been built on the tributaries of the middle and upper reaches to control and weaken some flood peaks. However, in the dry season, the main flow decreases, leading to a surge in sedimentation in the middle and lower reaches. The maximum cross-section sediment concentration is 2722kg per cubic meter, and the riverbed is gradually silted. From Shi Cun in the lower reaches to Zhou Jindong near the estuary, the riverbed silts up to 1.5 meters, which affects the flood discharge capacity, the water level in the middle reaches is greatly extended, and the waterlogging on both sides of the middle and lower reaches is serious. Especially at the end of winter and the beginning of spring, the flow decreases, and the sediment brought by the tide floats in Shenquan Port, stretching for 2 kilometers to the southeast sandbar, and the navigation channel is blocked. Over the years, the measures of storage, blocking, interception, enclosure and drainage have achieved certain results, but with the passage of time, the siltation of Longjiang River has become more and more serious, and the jacking time of each drainage channel has also been greatly extended.
From May 27th to June 3rd, 1977, there was continuous rainstorm. The rainfall in three days is 643.2 mm, and the maximum discharge of Longjiang River is 14 10 cubic meter per second. Once in 20 years, the flood level of Shi Cun reached 16.39 meters, lasting for one week. The area affected by waterlogging in the middle and lower reaches (including the Leiling water system) is 60,000 mu, and the area affected by waterlogging is 35,000 mu. Therefore, the regulation of the lower reaches of the Longjiang River has become a top priority. After many explorations and studies, we have worked out the scheme of single flow in the main stream and flood diversion. In other words, give up stone fishing in a section of the river in Zhou Jindong and directly introduce the tail water of Longjiang River into the South China Sea. In September of the same year, the plan was reported to Shantou. With the approval of the district, the project started on1October 26th 10 in the same year. At the end of the year, the excavation project of the main trough "Longgou" will be completed, and the dike at the entrance section of 1.5km will be built. 3.5 km downstream of Xinhe River is a micro-sandy soil layer. Boil the dragon ditch first. The bottom of the ditch is 20m wide, with a slope of 1:3 and an elevation of13m. After the excavation of Longgou, a sand embankment was built to block the old estuary from Bangzhuang to Chicen, and the runoff regulated by Bangshan Bridge Gate was used to scour Longgou. From March to June, 1978, * * * was scoured for 6 times, and the scour width of the main ditch ranged from 20m to 100m, with an average scour depth of 0.5m 943,000 cubic meters of earth was washed away. On September 25th 1979, the flood flow of the new river channel was 2543 cubic meters per second, the lower section of the new river channel was 3.5 kilometers, and the width of the long ditch developed to 300 meters, with an average depth of 2 meters and the deepest point of 4 meters. The flood carried away about 5.54 million cubic meters of sediment.
From the observation of discharge and water level of Longjiang River, due to the separation of flood and waterlogging, the flood process is short and the flood discharge speed is fast, so that the flooded area of farmland is reduced, and the waterlogging time is less than two days, especially in Zongpuyang and East Long Yang. Although I soaked in Xixiwei, the soaking time was greatly shortened, no more than two days and two nights. This shows that the regulation project in the lower reaches of Longjiang River has achieved initial results in flood control and drainage. Due to lack of funds, the main dike in the upper reaches of the new river is only 1km, and the stone fence and flood diversion gate at the ocean bottom of the seawall are still not completed. After the main stream of Longjiang River was diverted from Chisenhai to Shenquan Port, only Luoxi River and Leiling River flowed through Shenquan Port, and the annual flow decreased from 654.38+09 billion cubic meters to 400 million cubic meters. Sedimentation and displacement at the entrance of Shenquan Port are accelerated. After the entrance of the old waterway was blocked by the bar sand at 1983, it turned to the southwest and developed into a long and narrow sea passage with a width of only 70 to 80 meters and a water depth of about 1 meter, and a water depth of only about 0.5 meters at low tide. The siltation of Shenquan Port not only seriously affected the transportation and fishery production, but also caused frequent floods due to poor flood discharge. In case of rainstorm or heavy rainstorm, the flood discharge speed is delayed by more than 20 hours.
1982, the leading group for comprehensive investigation of coastal zone and tidal flat resources in provinces and cities organized more than 38 experts and technicians from 38 units in the whole province 100, and spent two years investigating and demonstrating the reasons for sedimentation in Shenquan Port. The Design Case of Comprehensive Improvement Project of Shenquan Port in Huilai County was compiled by the Fourth Navigation Engineering Survey and Design Institute of the Ministry of Communications. The project is planned to be implemented in four phases, with a total investment of 380 yuan.
The first phase of the project started in March 1985, and the new passage was completed and opened to traffic in March 1986. In the actual construction period of 10 month, a new waterway is dug, with a length of1220m, a width of130m and a bottom width of 60m, with a designed low water depth of 3.22m and a high water depth of 4.55m.. The old entrance is blocked for 340m, and a wave-proof and sand-proof dike is built for 240m, a bank protection stone dike for the north-south channel is 24 12m, and a flood-proof and moisture-proof dike is 880m. The first phase of the project * * * invested 7.272 million yuan.
The second phase of the project started in February 1987 and was completed in April 1988. It is estimated that the masonry of the retaining wall of the north revetment of the extended waterway is 552m, the silt at the outlet of the dredged waterway is 654.38+10,000m3, the sand retaining dike is 380m (the length of the first phase project is 620m), and other ancillary reinforcement works. After final accounts, the project cost is * * * 4 137200 yuan.