Present situation analysis and countermeasures of soil and water conservation in a city?

Chongqing has a total land area of 82,400 square kilometers? China, the largest and most populous municipality directly under the central government, is rich in resources and has a wide economic radiation. It is one of the centers of economic development in the western region and shoulders the heavy responsibility of driving and promoting the economic and social development in the southwest region. However, the relatively backward level of economic and social development and fragile ecological environment are incompatible with its position in the economic and social development of the western region. Soil erosion in Chongqing is serious. Although a series of soil and water conservation measures have been taken in recent years and the investment in ecological environment construction has been increased, soil erosion is still deteriorating and has become one of the factors that seriously restrict its economic and social development.

1 soil erosion in Chongqing

According to the Classification Standard for Soil Erosion of the Second National Remote Sensing Survey of Soil Erosion (sl 19096) formulated by the Soil and Water Conservation Monitoring Center of the Ministry of Water Resources, and according to the soil erosion modulus and other related indicators such as slope and vegetation coverage, the degree of soil erosion is divided into six grades: micro, mild, moderate, intensity, extreme intensity and severe erosion, and the soil erosion area above mild is usually regarded as the total area of soil erosion in this area. Soil erosion in Chongqing has a wide distribution range and great intensity. According to the survey results, the total area of soil erosion in Chongqing is 52 039.53 km? , accounting for 63. 15% of the total land area, and the average soil erosion modulus is 3548. 18t/akm? The total soil erosion in the whole year was 65.438+0.85 billion t, of which the area of moderate soil erosion was 39.021.97 km? , accounting for 47.36% of the city's total area, accounting for 75% of the soil erosion area; The sum of strength, ultimate strength and severely eroded area is 13 777.88 km? , accounting for 16.72% of the total area, accounting for 26.48% of the soil erosion area. That is to say, there is moderate soil erosion in nearly 1/2 area of the city, and the soil erosion area above intensity exceeds 1/4 of the total loss area, which shows the seriousness of soil erosion.

Serious soil erosion will directly lead to the decline of soil fertility, the elevation of riverbed siltation and the aggravation of flood disaster, which will affect social and economic development. Since 1980s, the state has strengthened land consolidation planning, and Chongqing has been listed as the key prevention and control area of soil and water conservation in the Yangtze River. With the construction of the Yangtze River shelterbelt system and the comprehensive management of small watersheds, Chongqing's ecological environment construction has made some progress. With the development of the western region and the implementation of the measures of returning farmland to forests, soil and water conservation has been widely valued. However, the research shows that the soil erosion in Chongqing is still deteriorating in recent ten years. According to the data provided by the Municipal Water Conservancy Bureau, since 1998, the area of soil erosion in Chongqing has increased by 42,000 hm? And only 1. 1 10,000 hm? .

2 factors affecting soil erosion in Chongqing

Soil erosion is the result of comprehensive action of natural factors and human activities. There are many natural factors affecting soil erosion, such as hydrology, meteorology, geology, landform, vegetation, soil and so on. Human activities include deforestation, steep slope reclamation, unreasonable farming, overgrazing, mining and road construction. The natural erosion process of soil is generally slow, and the amount of erosion is less than or close to the quality of substances formed in the process of soil formation. Soil erosion is compensated by the natural process of soil formation, which is in a relatively balanced state and generally harmless. Unreasonable human economic activities, especially the destruction of vegetation, lead to the imbalance of natural ecosystem and accelerate the process of soil erosion. The rate of artificial accelerated erosion is ten times or even hundreds times higher than that of natural erosion. Topsoil, which takes thousands of years to be removed under natural erosion, may be lost in a very short time, and improper economic activities of human beings are the root cause of soil erosion.

2. 1 Influence of geological and geomorphological conditions on soil erosion

Different kinds of rocks and their weathering products have different material composition and characteristics, and they leave different properties such as soil texture, mineral nutrients and water content, and have different effects on soil erosion. The interbeds of purple mudstone, sandy shale and mudstone sandstone are widely distributed in the central and western parts of Chongqing. This kind of rock is easily weathered, and the weathered products are rich in mineral nutrients, and most of them are reclaimed as cultivated land. The purple soil formed is sticky, with low water-holding capacity and serious soil erosion. Geomorphological factors mainly affect soil erosion by affecting the characteristics of slope runoff. Slope and slope length are the most basic geomorphological factors affecting soil erosion. The greater the slope, the greater the runoff velocity, the worse the soil stability, and the easier it is to cause soil erosion. Under the same slope condition, the greater the slope, the more runoff collected and the more serious soil erosion. The landform of Chongqing is dominated by mountains, with hills and middle-low mountains accounting for 94% of the total area, of which the mountains with a slope greater than 150 account for 85%. Zhongshan is mainly distributed in the north and southeast, with many low mountains in the central region and hills mainly distributed in the western region on the left bank of the Yangtze River. This topographic feature is easy to make rainfall form runoff and cause strong soil erosion. The area of platform and flat dam only accounts for 6% of the total area, and the soil erosion is relatively weak.

2.2 Impact of climatic factors on soil erosion

One of the effects of climate factors on soil erosion is precipitation, and precipitation and its temporal and spatial changes are directly related to soil erosion. Chongqing is located in the subtropical humid monsoon climate zone, with abundant precipitation and uneven distribution during the year. The annual precipitation is1100 ~1400 mm, and the most wet year in the reservoir area is1531.8 mm. The precipitation is mostly concentrated in summer, with the precipitation in July and August accounting for more than 50% of the whole year, and the precipitation in the second half of the year accounting for about 78% of the whole year. Another feature is that the rainfall intensity and primary rainfall are relatively large. According to the records, the maximum daily rainstorm is 278.9 mm, and Fuling Station is 308.9 mm.. Precipitation also increases with the elevation. The mountain is high and steep, and the heavy rain has produced great scouring force. Soil erosion caused by several heavy rains with heavy rainfall and high precipitation intensity often accounts for the vast majority of soil erosion in the whole year.

2.3 the influence of vegetation factors on soil erosion

Vegetation is a positive factor to prevent soil erosion. Vegetation can intercept rainfall through canopy, store water and protect soil by litter, and solidify soil by roots, which can slow down the intensity of surface runoff, improve soil erosion resistance and reduce soil erosion. The effect of soil and water conservation is very obvious in the area covered by trees, shrubs and grasses, and there is generally no obvious soil erosion. According to the data analysis, under the condition of constant rainfall, the runoff coefficient of cultivated land with coverage over 95% is 0.23, while that of agricultural land with coverage 15% is 0.59. In general, the loss of dense forests or areas with multi-layer structures of trees, shrubs and grasses is only11000 ~1of agricultural land. The forest coverage rate in Chongqing is relatively low. In the early 1990s, the average forest coverage rate in Chongqing was about 13%. In the past ten years, through the implementation of natural forest protection projects and returning farmland to forests, although the forest area has expanded, the current forest coverage rate is only about 25%. The mountain vegetation in the west, north and southwest is well protected, the forest coverage rate is over 30%, and the degree of soil erosion is obviously light.

2.4 the impact of unreasonable land use on soil erosion

Unreasonable land use, such as indiscriminate reclamation of farmland, excessive deforestation and overgrazing, will cause serious damage to natural vegetation, thus aggravating the occurrence of soil erosion. Chongqing is densely populated, with a per capita land area of only 0.27 hm? Is the per capita land area in China 0.78 hm? 34.6%, which is at a low level in China. The construction of the Three Gorges Project will also flood the area by 27,000 hm? Land, transportation, energy, urban construction and immigration will also occupy a lot of land. In 2002, the per capita cultivated land area in Chongqing was 0.044hm? , lower than the national average (0.098hm? ) 1/2, and the paddy field area is small and there are many dry slopes. Chongqing is one of the most serious areas of sloping farmland reclamation in China. According to the results of the national land resources survey, the area of sloping farmland with a slope greater than 25 in Chongqing accounts for 16. 12%, which is higher than the national average of 1 1.6 percentage points and the western average of 4. 1 percentage points. The area of sloping cultivated land with a slope greater than 15 accounts for nearly 1/2 of the total cultivated land area (table 1). Cultivated land resources in the Three Gorges reservoir area are even scarcer, with a per capita arable land of only 0.07hm? Among them, 66.3% is dry land, and sloping dry land accounts for 83. 1% of the dry land area. More people and less land lead to deforestation and land reclamation on steep slopes, and sloping farmland becomes the main source of river sediment.

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