As mentioned earlier, the total water resources in Meizhou (including water used by transit passengers) is 25.722 billion m3. However, when comparing regional water resources, we can only use the average water quantity of local river runoff for many years. According to the comparison of the same period 1993, the per capita water resources in Meizhou City is 2876m3, which is higher than the national average of 2630m3, but lower than the provincial average of 3077m3 [3], which is far from the world average of 8,840 m3 [4].
Uneven distribution in time and space
Water resources are transformed from atmospheric precipitation, so the temporal and spatial distribution characteristics of water resources are basically consistent with atmospheric precipitation. In terms of time distribution, Meizhou has a long rainy season and abundant rainfall, with an average annual rainy day of 150 days and an annual rainfall of 1400 ~ 2500mm. Rainfall in the year is mostly concentrated from April to September, accounting for 70% ~ 80% of the whole year, and it is more concentrated from May to June, forming a very obvious flood season; The dry period is from June 65438 to March of the following year, and the average rainfall in each month is less than100 mm. The rainfall in Meizhou also varies greatly from year to year. For example, the average annual rainfall in Fengshun Tangkeng Town is 1978mm, the longest is 3093mm( 196 1 year), and the youngest is 1262mm( 1956). Long-term Water Resources Supply and Demand Planning in Meizhou City (Meizhou Water Conservancy Bureau, 1956)
. The concentration of annual rainfall and the difference of annual rainfall make Meizhou prone to natural disasters such as drought and flood. In terms of spatial distribution, there are more mountains than plains, more windward than leeward, more rainfall in the north in spring than in the south, and less rainfall in summer. Judging from the regional distribution, Fengshun County, south of Lianhua Mountain, has a lot of rainfall, which belongs to the high-value area of the province's runoff depth isoline, and the isoline is1600 mm; ; Wuhua, Xingning and Meixian river basins (Meijiang District) to the north of Lianhua Mountain are few, belonging to the low-value area of annual runoff depth isoline in the whole province, with isoline of 600 ~ 800 mm, and Jiaoling, Plain and northern mountainous area of Meixian County to the south of Xiangshan Mountain have increased. This feature leads to the uneven distribution of total water resources in counties (districts and cities) in the city, and the per capita water resources are quite different (table 12.3). The uneven distribution of water resources in time and space is one of the unfavorable factors for the development and utilization of water resources in this area.
Table 12.3 Meizhou City Resource Distribution Table Unit: 100 million m3
12.3.3 Flood and low water are obvious.
The probability of Meijiang flood is 16% before 1950. After 1950, due to the serious destruction of forest vegetation, a large area of soil erosion was caused, and the confluence condition of the underlying surface deteriorated, which increased the flood probability to 36%[ 1]. The river floods in Meizhou usually occur from May to September, with the characteristics of relatively small peak height and rapid fluctuation, and the floods caused by typhoon and rainstorm in the later flood season have the characteristics of high water level. For example, at Hengshan Station in Meijiang, the six typhoon storms and floods from 1953 to 1980 all exceeded the warning water level by more than 5m (the warning water level at Hengshan Station was 52m), and the flood level of Typhoon No.6001reached 58.56m, the highest in history [1]. Then there were 8607 and 97 10 floods. /KOOC-0/997 Typhoon/KOOC-0/0 landed at the Pearl River Estuary at 20: 30 on August 2, and Meizhou was hit by heavy rain. The average rainfall in the city is 168.5mm, and the rainfall in some places exceeds 300mm, causing flash floods and the water level of the river soaring. More than 9,000 water storage projects in the city have reached or exceeded the flood limit water level. The flood caused the city's direct economic loss of1421000000 yuan, including water conservancy loss of 266 million yuan (Meizhou Yearbook Compilation Committee, 1988).
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Due to the influence of climatic factors, the low water in this area generally appears in the non-flood season (10 to March of the following year), with the lowest monthly average in 10 and February, but the historical dry flow appears in May, which is related to the abnormal weather system and the increase of agricultural water demand in severe drought years. The average low water modulus in the upper reaches of Hanjiang River is between1.95 and 4.88/s km2. The annual variation Cv of low water at each station is between 0.4 ~ 1.40, and the separation coefficient CS = 2 ~ 3cv, indicating that the annual variation of low water in this area is great. The once-in-a-century low flow of Meijiang Hengshan Station is 5m3/s, once-in-20 years1/m3/s, 10 once-in-a-decade 15m3/s[ 1].
12.3.4 The river has high sediment concentration.
Due to the long-term influence of soil erosion, the sediment concentration of rivers in Meizhou City is relatively high (the average sediment concentration of Wuhua Water for many years is 0.66kg/m3), and Meijiang River is listed as the river with the highest sediment concentration in the whole province [1]. Although the sediment concentration in the river channel has been alleviated after 10 years of soil erosion control, sediment deposition in the downstream riverbed and reservoir still exists in different degrees, which not only poses a threat to the flood, but also has an impact on the flood. For example, the storage capacity of combined water has accumulated to15.48 million m3 by the end of 1997, which is higher than the normal storage capacity of Meizhou 1997 Annual Report on Comprehensive Statistics of Water Resources13.
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12.3.5 is rich in water resources.
The steep river bed slope, large natural drop and abundant hydraulic resources in Meizhou mountain area are favorable conditions for developing small hydropower and promoting industrial and agricultural production. There are 20 rivers * * * with theoretical hydropower reserves above 654.38+1100,000 k W, namely Hanjiang River (Meijiang River, Qinjiang River), Jiaozhou River, Wuhua River, Ningjiang River, Chengjiang River, Grottoes River, Chagan River, Youshu River, Song Yuan River, Tingjiang River, Xihe Zhang River, Meitan River and Hexi River. The theoretical reserve of the city's hydraulic resources is 120.65k W, and the exploitable amount is123.93kw. By the end of 1997, the installed hydropower capacity of the city was 54.2k W, accounting for only 43.27% of the exploitable amount. Report on Revision of Hydropower Development Planning in Meizhou River Basin (Meizhou Hydropower Bureau, 1998).
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12.3.6 surface water is polluted to some extent.
The development of industrial and agricultural production and the continuous improvement of urban residents' living standards will inevitably lead to the gradual increase of domestic sewage and wastewater emissions from urban industrial and mining enterprises. At present, the urban management and industrial wastewater treatment in Meizhou still cannot keep up with the development of the situation. Most urban domestic sewage and industrial wastewater are directly discharged into rivers without purification treatment, causing different degrees of pollution of urban surface water bodies (rivers). Although most river sections can still reach Grade III or above in rainy season, the pollution degree is aggravated in dry season due to the sharp reduction of surface runoff, and the organic pollution is particularly prominent in the river sections with concentrated factories and little water on both sides of the river, such as the river sections of Butte and Ningjiang near Xingning in the plain (Table 12.4).
Table12.4 Summary of Water Quality of Major Rivers in Meizhou City in 2004
People pay more and more attention to the water quality protection in Meicheng section of Meijiang River. To this end, the municipal government set up a leading group for cleaning and pollution prevention in Meijiang and a supervision and management brigade for cleaning and pollution prevention on both sides of Meijiang, and also allocated funds to rebuild and expand garbage dumps and build a sewage treatment plant in Jiangnan. Overall, the water quality in Meicheng section of Meijiang River is good. However, with the social and economic development of Meizhou, the task of pollution prevention and control in the future is still very arduous.