Surface water is the general name of rivers, glaciers, lakes and swamps, also known as "land water". It is one of the important water sources for human life and the main component of water resources in various countries.

The total length of rivers in China is about 420,000 kilometers, and the total runoff reaches 27110.50 billion cubic meters, accounting for 5.8% of the world's runoff. Although there are many rivers in China, their regional distribution is uneven. 96% of the total runoff in China is concentrated in the outflow basin, accounting for 64% of the total area of the country, while the inland basin only accounts for 4%, accounting for 36% of the total area of the country. Winter is the dry season of river runoff in China, and summer is the wet season.

Glaciers in China have a total area of about 56,500 square kilometers, a total storage capacity of 2.964 billion cubic meters, and an annual melting water volume of 50.46 billion cubic meters, mostly distributed at the source of rivers. Glacier meltwater is an important water supply source for rivers in China, especially in arid areas of northwest China. Glaciers in China are all mountain glaciers, which can be divided into continental glaciers and marine glaciers, among which continental glaciers account for more than 80% of the national glacier area.

The distribution of lakes in China is very uneven. There are more than 2,800 lakes above 1 square kilometer, with a total area of about 80,000 square kilometers, mostly distributed in the Qinghai-Tibet Plateau and the plain areas in the middle and lower reaches of the Yangtze River. Among them, the freshwater lake covers an area of 36,000 square kilometers, accounting for about 45% of the total area. In addition, China has built more than 86,000 artificial lakes and various types of reservoirs.

There are only two types of swamps in China, namely peat swamp and latent swamp, with an area of 165438+3000 square kilometers. Sanjiang Plain and Zoige Plateau are the two areas with the most concentrated marshes in China. Most swamps in China are located in low-lying and water-rich areas with high potential fertility, which is an important target for China to further expand the cultivated land area.

Table 1 standard limit value of basic items of surface water environmental quality standard unit: mg/l

Serial number I Category II Category III Category IV Category V

Man-made variation of ambient water temperature at 1 (℃) should be limited to: weekly average maximum temperature rise ≤ 1, and weekly average maximum temperature drop ≤2.

2 p H value (dimensionless) 6-9

3 Dissolved oxygen ≥ saturation rate 90% (or 7.5) 6 5 3 2

4 permanganate index ≤ 2 4 6 10 15

5 chemical oxygen demand ≤ 15 15 20 30 40

6 Five-day biochemical oxygen demand (BOD5) ≤ 3 3 4 6 10

7 ammonia nitrogen ≤ 0.01.51.01.52.0

8 Total phosphorus (calculated as P) ≤ 0.02 (0.0 1) 0. 1 (0.025) 0.2 (0.05) 0.3 (0. 1) 0.4 (0.2) for lakes and reservoirs.

9 Total nitrogen (calculated as nitrogen in lakes and reservoirs) ≤ 0.2 0.5 1.0 1.5 2.0

10 copper ≤ 0.01.1.01.01.0.

1 1 zinc ≤ 0.051.01.02.02.0

12 fluoride (calculated as F-) ≤1.01.01.51.5.

13 selenium ≤ 0.01.01.01.01.020.02

14 arsenic ≤ 0.05 0.05 0. 1 0. 1

15 mercury ≤ 0.00005 0.00005 0.00010.0010.001.

16 cadmium ≤ 0.001.005 0.005 0.005 0.01

17 chromium (hexavalent) ≤ 0.0 1.05 0.05 0. 1

18 lead ≤ 0.01.01.050.050.1

19 cyanide ≤ 0.005 0.05 0.2 0.2 0.2

20 volatile phenol ≤ 0.002 0.002 0.005 0.010/

2 1 petroleum ≤ 0.05 0.05 0.05 0.5 1.0

22 anionic surfactant ≤ 0.2 0.2 0.2 0.3 0.3

23 sulfide ≤ 0.050. 1.20.5 1.0

24 fecal coliforms (per liter) ≤ 200 2000 10000 20000 40000

Table 2 Standard limit value unit of centralized drinking water surface water source supplement project: mg/L

Standard value of serial number item

1 sulfate (calculated by SO42-250)

2 Chloride (calculated as Cl-) 250

3 nitrate (containing nitrogen) 10

4 iron 0.3

5 Mn 0. 1

underground water

Groundwater is water that exists in cracks in the earth's crust or soil.

All kinds of water widely buried below the surface are collectively called groundwater. Atmospheric precipitation is the main source of groundwater.

According to different underground burial conditions, groundwater can be divided into three categories: upper stagnant water, diving and running water.

The upper stagnant water is a water storage body formed by local waterproofing, which makes the infiltrated atmospheric precipitation stay in shallow rock cracks or sedimentary layers.

Diving is the groundwater buried on the first stable aquiclude below the surface, and most of the groundwater usually seen is diving. Springs are formed when diving out of the ground.

Self-flowing water is groundwater which is buried deeply and flows between two aquicludes. This kind of groundwater often has a high water pressure, especially when the upper and lower aquicludes are inclined, the water in the interlayer will bear a high water pressure. When a well or borehole passes through the upper roof, strong pressure will make water gush out and form self-flowing water.

Groundwater can be divided into vadose zone water, phreatic water and confined water according to burial conditions.

The water in the vadose zone refers to the water in the vadose zone above the groundwater level, including adsorbed water, film water, capillary water, gaseous water and temporary gravity water. The water that exists seasonally on the local aquiclude in the vadose zone is called upper stagnant water.

Diving refers to the gravity water with free water surface that exists on the first stable aquiclude under the surface. Mainly supplied by precipitation and surface water infiltration.

Confined water is water filled in the aquifer between the upper and lower aquicludes. It bears pressure, and when the upper water-resisting layer is drilled through, water can rise or spray from the borehole. According to the types of water-bearing gaps, groundwater is divided into pore water, fissure water and karst water. Pore water is groundwater existing in rock and soil pores, such as groundwater in loose sand layer, gravel layer and sandstone layer. Fracture water is water that exists in the cracks of hard rocks and some clay layers. Karst water, also known as karst water, refers to groundwater existing in caves of soluble rocks (such as limestone and dolomite).

Groundwater is a huge family. It is estimated that the total amount of groundwater in the world is as high as 65.438+0.5 billion cubic kilometers, accounting for almost one-tenth of the total water volume of the earth and more than the whole Atlantic Ocean!

Groundwater is closely related to human beings. Well water and spring water are the most commonly used groundwater in our daily life. But groundwater can also cause some harm, such as too much groundwater, which will cause railways and highways to collapse, flood mining tunnels and form swamps. At the same time, it should be noted that there is an overall balance problem of groundwater, so we can't blindly overexploit it, otherwise it will easily form underground cavities, stratum subsidence and other problems.

Water in underground rock and soil gaps. Water-bearing rocks and soils can be divided into two zones. The upper layer is unsaturated zone, and there are gases besides water. The lower part is the saturated zone, that is, the saturated zone. The gaps between rocks and soil in the saturated zone are filled with water. Groundwater in a narrow sense refers to the water in the saturated zone. Groundwater can be developed and utilized as the source of domestic water, industrial water and farmland irrigation water. Groundwater has the advantages of stable water supply and less pollution. Groundwater with special chemical composition or high water temperature can also be used as raw materials for medical treatment, heat source, beverage and extraction of useful elements. In the excavation of mines and tunnels, there may be a large number of water gushing, which will bring harm to the project. In plains and basins with shallow groundwater level, phreatic evaporation may cause soil salinization; In areas where the groundwater level is high, the soil is too wet for a long time, and the surface water is stagnant, swamps may appear, causing harm to crops.

Potassium, sodium, magnesium, calcium, chlorine, sulfate and bicarbonate are the most widely distributed ions in groundwater. The total amount of various ions, molecules and compounds in groundwater is called total salinity. The total salinity less than 1g/L is called fresh water, 1g/L is called micro water, 3- 10g/L is called salt water, and 10g/L is called salt water. The content of dissolved salts such as calcium, magnesium, iron, manganese, strontium and aluminum in groundwater is called hardness. High content means high hardness, while low content means low hardness.

The movement of most groundwater belongs to laminar flow. In a wide gap, if the water velocity is high, turbulent motion is easy to occur. Groundwater mainly includes precipitation infiltration, irrigation water infiltration, surface water infiltration recharge, overflow recharge and artificial recharge. In some cases, there is horizontal supply. Groundwater discharge mainly includes spring, phreatic water evaporation, surface water discharge, overflow discharge and artificial discharge. Spring water is the main way of natural drainage of groundwater.