Source: Worry-Free paper net Date of submission: [07-04-03 16:25:48] Author: unknown.
The dam project in the lower reaches of the Yellow River is eroded, and the poor surface soil quality and large exposed area are the basic factors, while raindrop attack, surface runoff, wind blowing and freezing and thawing are the inducing factors. It is an effective method to take good vegetation and biological protection measures for the project.
Dam projects in the lower reaches of the Yellow River are often eroded by natural forces such as water flow, wind blowing and human activities, resulting in earthwork loss, affecting the integrity of the project and reducing the intensity of the project, which is extremely unfavorable to flood control. Therefore, it is an important work of project management to explore and study the erosion factors of the Yellow River dam, take effective protective measures and maintain the integrity of the project.
1 erosion factors of the Yellow River dam
The dam in the lower reaches of the Yellow River is different from the natural slope: the designed slope of the dam is 1: 2.5 or 1: 3. Soil erosion mainly occurs on hilltops and slopes. According to the analysis and research, the poor quality and large exposed area of surface soil are important factors of soil erosion, and raindrop strike, surface runoff, wind blowing and freezing and thawing are inducing factors of surface soil instability. Slope erosion and soil loss are often the result of the interaction of many factors.
(1) Slope: The stability of the slope of the Yellow River Dam depends on whether the shear strength inside the soil exceeds its shear strength, and if it exceeds the shear strength, the soil will slide down. The reasons are: first, the shear strength increases; Secondly, the shear strength of the soil itself decreases. Under the condition of constant internal factors, the steeper the slope, the greater the runoff speed of rainwater, the longer the slope, the greater the accumulated runoff, and the more likely the soil will be eroded.
(2) Soil: The dikes in the lower reaches of the Yellow River are mostly sandy loam, and the surface is covered with cohesive clay, and the vertical thickness is generally 0.20-0.30m m. In the dike section with good cover quality, the turf of the protection project grows vigorously, and the topsoil is less exposed, so it is not easy to be eroded; On the other hand, the soil used to wrap the roof is sandy, the turf grows poorly, and the topsoil is exposed and easy to be eroded; In addition, with the passage of time, under the conditions of sun exposure, weathering and the increase of humus in plant growth, the properties of soil will also change, and the cohesion between aggregates will decrease and the corrosion resistance will decrease.
(3) Climate: The Yellow River in Shandong is located in the north temperate zone and belongs to monsoon climate. The Yellow River runs southwest-northeast, and the upper reaches of the estuary are cold. Under the conditions of frost heaving in winter, melting in spring and periodic freezing and thawing, it is easy to cause gravity erosion and soil erosion. The amount of soil erosion varies with the slope direction of the dam. In winter, the surface soil in Chaoyang has a thin frozen layer, which thaws early and the turf turns green quickly. In the growing season, there is sufficient sunlight, vigorous growth, dense slope coverage and less soil erosion. On the contrary, the backward slope soil is thick in winter, late in spring, slow to turn green, lack of light in growing season, and its growth is not as good as that of Chaoyang slope, with low coverage, serious wind erosion in spring and rainfall erosion in summer.
(4) Rainfall and vegetation: When rainfall falls directly on the topsoil, raindrops play the role of inhibition, filling and splashing, while inhibition is to disturb the topsoil, and runoff takes the soil away and becomes the main way of topsoil loss. The existing turf covers and buffers the influence of water droplets. According to the cohesive action of acid soil, the slope with high turf coverage has great water retention capacity, which plays a major role in conserving water, blocking surface runoff and preventing soil erosion. Relevant experiments show that the amount of soil loss in the area where rainwater suppression is blocked is only1100-1/200 of that in bare land.
(5) Wind: The Yellow River levee is higher than the surrounding ground, and the topsoil is seriously eroded by wind. Wind is the inducing factor of soil loss after rainfall, especially in winter and spring, when the soil is dry, the water content is low and the grass withers. It is observed that under the wind speed of 3m/s, all the scattered topsoil will be blown away. The movement mode of topsoil: one is sliding along the surface, the other is jumping, and the third is floating. If there is 0.5- 1.0m wide-band turf on both sides of the embankment, about 5- 10Lm thick or more topsoil can be retained every year, which shows that biological protection has played a good role in stabilizing the soil from erosion.
(6) Anti-corrosion measures: the methods of protecting topsoil can be summarized as engineering treatment method and biological protection method. Among the biological protection laws, the grass planting protection project is the most extensive one. The high coverage of turf on the engineering surface greatly reduces the possibility of soil erosion.
2 biological protection of dam projects in the lower Yellow River
The application of biological protection in dams in the lower reaches of the Yellow River has a long history. Since the Song Dynasty, there have been records of planting trees outside the dam to prevent waves from consolidating the dam. In the Ming Dynasty, Liu Tianhe summed up the experience of planting willow on the river bank and formulated the methods of planting willow, namely, lying willow, low willow, partial willow, floating willow, slow willow and high willow. Since the Yellow River was harnessed by the people, great achievements have been made in planting trees and grass, greening dikes, and preventing water waves.
Over the years, the Yellow River levee in Shandong Province has been mainly planted with kudzu grass, and other grasses such as iron bamboo shoots have cooperated with each other, which has achieved remarkable results in soil consolidation and scour prevention. However, due to the failure to regenerate in time, the original turf naturally aged and degraded, and cattle and sheep were destroyed, which greatly reduced the turf coverage rate. In some areas, tall grass grows, and the biological protection function is reduced. In addition, the drainage facilities are not perfect, and there are many gullies and waves in rainy season every year, which seriously affects the integrity and flood control ability of the project and increases the project funds and maintenance costs. Whether there is turf protection project or not, the earthwork loss varies greatly. Judging from the actual situation, soil erosion rarely occurs in places with high turf coverage and vigorous growth. However, in some areas with no turf coverage or low coverage and poor turf growth, a large amount of soil erosion often occurs when rainfall is concentrated, forming large gullies and waves. Starting from 1990, Shandong Bureau has carried out the work of "experimental research on introduction and cultivation of excellent grass seeds in protection engineering" and achieved great results. According to the basic requirements of the flood control project in the lower Yellow River, eight exotic grass species such as Manila, Bent and carpet grass were introduced, and a variety of grass species such as "iron bamboo shoots and Leymus chinensis" were cultivated, which created conditions for biological protection of dikes.
Biological protection not only has good economic, ecological and social benefits, but also greatly changes the project area, afforests and beautifies the project, improves the environment and climate, and provides a good place for local urban and rural residents to visit and rest.
3. Do a good job in biological protection to ensure the safety and integrity of flood control projects.
The turf on the slope of flood control project plays an important role in preventing rainwater gully erosion, wind and wave erosion, soil erosion, maintaining the integrity of the project and maintaining the flood resistance strength of the project.
3. 1 continuously renew the rejuvenated turf.
Take advantage of the good opportunity of the spring rain season to carry out external planting and replanting to consolidate and expand the results.
3.2 According to different river sections, climate, soil conditions and slope conditions, plant grass according to local conditions.
On the embankment slope, besides renewing and rejuvenating the original Geba grass, we should also vigorously expand the planting of iron shoots and Leymus chinensis, and plant Manila grass on the embankment shoulders, culverts, dangerous workers and control workers. Combined with greening and beautification, carpet grass, Manila and iron sprout grass should be planted.
3.3 Strengthen management and remove tall weeds in time.
For the road sections with high weeds, reeds, secondary forests and low bushes, manual removal is labor-consuming and time-consuming, and the road sections that need to be removed repeatedly every year to meet the requirements need to be removed with herbicides.
Then you can handle it yourself