Sandstorm principle

Sandstorm is a general term for sandstorm and sandstorm, which refers to the weather phenomenon that strong winds drag a large amount of dust on the ground into the air, making the air particularly turbid and the horizontal visibility lower than 1 km, in which sandstorm refers to a sand-laden storm formed by strong winds blowing a large amount of dust near the ground; Sandstorm is a storm formed by strong winds, which brings a lot of dust and other particles into the sky. Generally, wind speed and visibility are used to classify the intensity grade of sandstorm. At present, the intensity of sandstorm is divided into four levels: level 4 ≤ wind speed ≤ 6,500 m ≤ visibility ≤ 1000m, which is called weak sandstorm; Grade 6 ≤ wind speed ≤ 8,200 meters ≤ visibility ≤500 meters, which is called medium-intensity sandstorm; The wind speed is ≥9 and the visibility is ≤200 meters, which is called a strong sandstorm. When it reaches its maximum intensity (instantaneous maximum wind speed ≥ 25m/s, visibility ≤ 50m, or even reduced to 0m), it is called extremely strong sandstorm (or black storm, commonly known as? Black Wind). ?

The hazards of sandstorms can be roughly divided into four categories: sand burial, wind erosion, strong wind attack and air pollution.

Due to the influence of sandstorm, the whole earth discharges 2~200 tons of dust into the air every square kilometer every year. It is observed that the dust in Central Asia can be transported to the Hawaiian Islands 10,000 kilometers away by the westerly airflow. These dusts contain many toxic minerals, which are harmful to human body, livestock, crops and trees, and can cause eye diseases and respiratory infections.

1On the afternoon of May 5, 993, a strong sandstorm occurred in northwest China. At first, a sandstorm wall appeared in the northwest of Jinchang. Ten minutes later, the city was dusty, dark and opaque. From time to time there was dull thunder, and a terrible scene appeared between heaven and earth. This state lasted for nearly three hours in Jinchang, and swept eastward to Wuwei, Baiyin, Alashan League, Inner Mongolia, and Yinchuan, Ningxia, wreaking havoc in Fiona Fang for 500 kilometers. It lasted for five hours, hundreds of people were killed, injured and missing, and the direct economic loss was 540 million yuan, which also caused many environmental problems.

1. Macro measures

(1) Carry out extensive and in-depth publicity and education on environmental awareness to improve the ideological level of the whole nation. Care and care for the environment, consciously participate in the transformation and construction of the environment, and form the fashion of the whole society.

② Improve laws and regulations, strengthen law enforcement supervision, protect the environment according to law, and promote desertification control.

③ Strictly implement the family planning policy, control the excessive population growth, and constantly improve the quality of the population.

④ Developing various scientific and educational undertakings in desertification areas. Cultivate grassroots scientific and technological forces, improve the rural scientific and technological market as soon as possible, do a good job in scientific and technological services, and improve the cultural and scientific quality of people in desertification areas.

⑤ Establish an effective investment mechanism and a management mechanism in line with the current national conditions.

⑥ Establish an advanced desertification dynamic monitoring and forecasting system, make good decisions, and do a good job in information management and service.

⑦ Carry out a lasting green revolution in desertification areas, accelerate the reversal of desertification process, and gradually improve the basic functions of agricultural ecosystems.

(8) Strengthen international exchanges and cooperation in combating desertification and strive for funds and foreign aid.

(9) Accelerate the adjustment of industrial structure, rationally allocate the proportion of agriculture, forestry and animal husbandry according to market requirements, actively develop aquaculture and processing industries, divert rural surplus labor force, and reduce the pressure of population on land.

(10) Optimize the energy structure in agricultural and pastoral areas, and vigorously advocate and encourage people to use unconventional energy sources such as wind energy and light energy to reduce the damage to forests, grasslands and other resources.

2. Technical measures

(1) biological measures

(1) Seal off sand forests to grow grass and restore natural vegetation.

Implement certain protective measures (fences), establish necessary protection organizations (forest protection stations), prohibit the damage to people and animals, give plants time to thrive and gradually restore natural vegetation. At the same time, the enclosure can be replanted and managed manually to accelerate the ecological reversal.

② Planting trees, grass and fixing sand by airplane.

Aerial seeding has the characteristics of high speed, less labor, low cost and good effect, and is especially suitable for vegetation restoration in remote and barren areas with vast land and sparse population, inconvenient transportation and barren hills. The key technical problems to be solved in aerial seeding are: predicting climate, selecting site conditions, determining suitable sowing area, determining suitable sowing amount, seed treatment technology, preventing and controlling livestock and poultry diseases and insect pests, and enclosure protection.

③ Fixing quicksand by sowing, cutting, raising seedlings and planting grass.

Direct seeding afforestation and sand fixation: Sow on grassland quicksand to ensure that the seedlings reach a certain density (15-20 plants /m2), a certain height (15-20 cm) and a certain area (> 1000m2), and wind erosion can turn into sand-burying plants and fix sand dunes. The successful direct seeding plant varieties are mainly two pioneer plants of sand, namely Huabao and Yangchai. Can be broadcast, can also be broadcast in strips or holes.

Afforestation and sand fixation: in the flowing sand of arid grassland, appropriate deep planting and reasonable close planting are adopted to fix the sand. For example, in Dingbian Changmaotan Forest Farm, Artemisia ordosica is densely planted on sand dunes in autumn to survive and form sand barriers.

Cutting afforestation and sand fixation: In quicksand areas of Shaanxi and Ningxia, sand dunes are directly fixed with Salix cuttings. Yulin people adopt the way of cluster planting, forming a pattern of alternating density and density, which not only resists wind erosion but also solves the problem of water shortage. The row spacing between clusters is 0.5m× 1.5m, and each cluster contains 4-5 cuttings.

(4) Establish a shelter forest system in sandstorm area.

Oasis protection system in arid area: first, fences, shrubs and sand-fixing belts around the oasis; second, backbone sand-prevention belts; third, farmland forest network and other related forest species inside the oasis. The actual situation is much more complicated than the typical introduction, so it should be used flexibly according to the actual situation.

Sandy farmland shelterbelt: Semi-humid areas have more rainfall and better conditions, which can be dominated by trees. The main belt distance is about 350m, and the eastern part of semi-arid areas is slightly better, while the western part is on the edge of dry farming, with poor conditions and the most serious desertification. Generally, sandy grassland will not be eroded by wind, but large-scale dry farming and wind erosion need forest protection very much. Trees in the east can still grow, the height can reach 10m, and the main belt distance is 200 ~ 300m；. In the vast arid areas in the west, arbor forests can be planted in areas with good conditions, while drought-tolerant shrubs are the main ones in other areas, with the main belt distance of only about 50 m, and there are many sandstorms in arid areas, so small grid narrow forest belts are used. The main belt distance in northern Xinjiang is 170 ~ 250 m, and the auxiliary belt distance is1000 m; South Xinjiang is windy and dusty, with a grid of 250 m× 500 m; The front of sandstorm adopts (120 m ~ 150 m) × 500 m grid, and there are many tree species to choose from, mainly trees.

⑤ Sandy grassland shelterbelt

Construction technology of grazing forest: the selection of tree species should pay attention to feeding value, with arbor as the main species in the east and irrigation as the main species in the west. The main belt distance depends on the degree of sandstorm damage. The maximum protection distance can be 25 hours for those who are not serious, 15h for those who are serious, and10h for the grazing land of sick young girls. Sub-band spacing depends on the actual situation, generally 400 ~ 800 m, and there is no sub-band in mowing land. The main shrub belts are about 50m apart, the main forest belt is 10 ~ 20m, and the auxiliary belt is 7 ~ 10~20m. Considering that the grassland Guang Lin is few, dry and windy, in order to form a forest environment, the forest belt can be wider, with 6-8 rows of forest belts in the east and 4-6 rows of trees, and one row on each side is sparse. It is a sparse structure or ventilation structure without shrubs, and the biological fence should be compact. Afforestation density depends on water conditions, which can be higher in good conditions and lower in bad conditions.

(2) Engineering measures

Sand-blocking and sand-fixing: Using branches, firewood, straw, gravel, clay, slats, plastic plates and other similar materials, various obstacles are set on the sand surface to control the direction, speed and structure of wind-blown sand flow, so as to achieve the purpose of sand-fixing, sand-blocking, wind prevention and terrain change. Sand barriers play an important role, which cannot be replaced by biological measures.

According to the different principles and setting methods of sand prevention, sand barriers can be divided into two types: plane sand barriers and vertical sand barriers. The tiled sand barrier is a sand barrier, which uses straw, pebbles, clay and so on. Pave the sand surface in an omni-directional or banded way to isolate the contact between the wind and the sand surface, resulting in the effect of no sand without wind. Fixing quicksand in situ can protect plant growth, but it has little effect on sand retention in sandstorm flow. This measure has played an important role in the eastern region, affecting the water content in the western region, but it is beneficial to the improvement of sandy soil. A vertical sand barrier is a sand barrier. When the wind-blown sand flow encounters any vertical sand barrier, the wind speed will drop, and some sand particles carried by the wind will be deposited before and after the sand barrier, thus reducing the sand transport. Multiple rows of vertical sand barriers can fix the sand surface between sand barriers and intercept quicksand. Because most of the moving sand particles are within 30cm near the surface and within 10cm, it is unnecessary to set too high sand barriers to fix sand, control sand flow and prevent sand damage.

Chemical sand fixation measures: the diluted chemicals with a certain glue structure are sprayed on the surface of quicksand, and the water quickly penetrates downwards, while the chemicals are left in the cracks of the sand layer with a certain thickness (1 ~ 5 mm) to form a hard protective shell, thus enhancing the wind erosion resistance of the sand surface and achieving the purpose of sand fixation. At present, dozens of chemical sand-fixing materials have been developed, but they have not been popularized because of their high cost.

Wind-driven sand control: it is a sand control measure based on output, which reduces roughness, strengthens wind power, makes sand flow unsaturated, and produces sand pulling and surface wind erosion.

Agricultural measures: first, develop water conservancy, expand irrigation area, increase fertilizer and improve soil; Second, measures to prevent wind erosion and dry farming, such as strip farming, intertillage and planting tall crops.