Basic knowledge of flood control _ How to prevent flood (2)

1 1. What is a pipeline? Piping, also known as undercurrent and soil flow, refers to the backwater side of the dike under the condition of high water level in flood season. Flowing soil? And then what? Insufficient corrosion? A general term for two dangerous situations with different meanings. This kind of danger is generally called turning sand and drumming water in Hubei, and it is called soaking spring in Jiangxi.

The development of piping danger is the fastest with flowing soil. Its process is that with the rise of water level, the sand carried by water inflow increases, the water inflow increases, and the sand carried by water inflow increases. If the sand layer under the foundation of the nearby dike (sluice) is hollowed out, it will lead to the sudden collapse of the dike (sluice) and even the disaster of breaking the dike.

Generally speaking, the alluvial strata in the middle and lower reaches of the Yangtze River are covered with cohesive soil, followed by silty sand and fine sand. There are clayey soil interlayers between the sand layers, followed by strongly permeable layers such as gravel and pebbles, which are exposed in the river bed and connected with the river.

Because the pressure loss caused by seepage flowing through the strongly permeable layer is small, there may still be a large water pressure under the clay layer within hundreds of meters of the dike. If this water pressure breaks through the clay layer, the silt and fine sand below will flow out with the water (without the protection of the filter layer), so piping will occur.

12, pipeline grab protection principle

The practical experience of protecting piping danger in the middle and lower reaches of the Yangtze River proves that the principle of dealing with piping should be to stop sand gushing and leave a way out for seepage. In this way, silt, fine sand and so on. It can no longer be carried out by the current to cause soil damage, and the seepage pressure nearby can be reduced to stabilize the danger.

It is worthy of vigilance that piping is a common cause of dike breach, but there are still insufficient understanding of its danger, improper measures, or carelessness, which delays the opportunity. Some people failed to build a large well, or the high well collapsed, which caused the levee to burst and brought serious losses to the country and people. The painful lessons of history must be remembered.

Piping is a serious danger, but as long as we are vigilant, cautious, timely detection and timely treatment, we can get rid of the danger. The following are effective ways to protect pipelines over the years:

1, surround the low weir with soil bags around the water tunnel. Filling the hole with filter material, it is best to fill the coarse sand first, then fill the melon and rice gravel, and finally fill the stone, which can effectively prevent the sand from being taken out. However, due to water inrush, coarse sand can not be filled in, so gravel and stones can be filled first to prevent water inrush, and then filled according to grading, which is slightly higher than the original ground. If there is no suitable stone nearby, brick slag can be used instead. For example, once the sandstorm is not stopped. You can remove a part of the upper coarse filler, and then fill it according to the above gradation until the water seepage is smooth and no sand particles are brought out. After the filter material is filled, you still need to pay attention to defense. If the filler is found to be sinking, you can continue to fill a stone until it is stable.

2. The method is the same as above, except that the cofferdam is not built, and the filter material can be directly filled.

3, such as piping, embankment foundation soil loss is too much, resulting in cracks in the embankment, should be repaired and reinforced in time.

4. After getting out of danger, we should still strengthen our defense, observe the changes around us and the relationship between seepage and river fluctuation, so as to provide reference for post-flood treatment.

13, how is the flood frequency and grade specified?

Hydrological elements can be calculated according to their rarity according to observation and investigation data such as precipitation and peak flow, which is customarily called? Frequency? . ? Flood frequency? It is usually expressed in%. Generally, 0.0 1%, 0. 1%, 1%, 10% and 20% are used to measure floods of different magnitudes in hydrology. The smaller the flood frequency, the less likely it is that a flood exceeding a certain scale will occur. For example, if the flood frequency is 1%, it is a once-in-a-century flood.

In hydrology, besides using flood frequency to measure the size of flood, the return period (in years) is also commonly used. Return period refers to the concept that floods of a certain magnitude occur once every few years on average in a long period of time. For example, the return period of a flood of a certain magnitude is 100 years (commonly known as once in a hundred years), which means the possibility that a flood of this magnitude will occur once every 100 years on average for a long time, but it cannot be understood as once every 100 years. In fact, this kind of flood may occur more than once a year 100, or it may not happen at all.

Flood frequency and return period are actually a standard to measure flood magnitude and an important basis to determine the scale and grade of water conservancy projects and dike construction.

Combined with the flood control capacity of rivers in China, flood grades are generally divided as follows:

A flood with a return period less than 10 year is a general flood;

The flood with return period 10 to 20 years is a major flood;

The flood once every 20 to 50 years is a major flood;

Floods with a recurrence period of more than 50 years are catastrophic floods.

The flood grade of a river is approved and issued by the competent department after comprehensive consideration of various factors, and does not refer to the flood frequency or grade of a single station.

14. How to identify landslides and debris flow gullies?

Identification of landslide:

1. Geomorphic foundation: When round-backed chairs, horseshoe-shaped landforms or multi-level abnormal abutments appear on the slope, their shapes are obviously out of harmony with the surrounding slopes; There are depressions in the upper part of the slope, and the depth of the lower slope foot extending into the riverbed is greater than that on both sides; The sources of the two valleys turn and meet at the upper part of the slope; The above landforms indicate that landslides may have occurred in these areas. There are obvious cracks on the slope, which have been lengthened and widened recently; The house on the slope is cracked and tilted; There is soil squeezing at the foot of the slope, which often collapses; The above landforms may be the basis of landslide formation.

2. Stratigraphic basis: In areas where landslides have occurred, the types of rock strata or soil are often obviously different from the surrounding non-sliding slopes. Compared with non-sliding slope, sliding rock or soil is usually disordered in sequence and loose in structure.

3. Groundwater basis: Landslide will destroy the unity of the original slope aquifer, leading to the change of groundwater flow path and discharge position. When it is found that the distribution of local slope is not harmonious with the distribution of spring points and seepage zones on the whole slope, and many springs or original springs suddenly dry up in a short time, it can be combined with other evidence to judge whether there is a landslide.

4. Vegetation foundation: the trees on the slope are staggered, which is generally the performance that the slope has experienced violent sliding; On the slope, the trunk of the tree bends downward and the upper part of the trunk keeps growing vertically, which is generally the result of slow sliding of the slope for a long time.

Identification of debris flow gullies;

First, the source basis: the formation of debris flow must involve a certain amount of loose earth and stone. Therefore, there are a lot of broken and evacuated materials on both sides of the valley, and the landslides and collapses on both sides of the valley are obvious, and the vegetation is underdeveloped. Debris flow is easy to occur in valleys with strong soil erosion and slope erosion.

2. Topographic foundation: gullies that can collect a large amount of water and maintain a high water flow speed can accommodate and carry a large amount of earth and stone. The upper reaches of the valley are surrounded by mountains on three sides, with steep slopes. The plane shapes of the valley area are funnel-shaped, spoon-shaped and leaf-shaped. The middle reaches of the valley are narrow, the gullies in the lower reaches are wide, the height difference between the upper and lower reaches of the valley is more than 300 meters, and the slopes on both sides of the valley are more than 25 degrees, which is beneficial to the formation of debris flow.

3. Water source foundation: Water provides dynamic conditions for the formation of debris flow. Local rainstorm-prone areas, reservoirs in danger of dam failure, downstream of ponds and seasonal melting areas of ice and snow have conditions to produce a large amount of running water in a short time, which is conducive to the formation of debris flows. Among them, the frequency of debris flow in local rainstorm-prone areas is the highest.

If a ditch is conducive to the formation of debris flow in terms of material source, topography and water source, it must be a debris flow ditch. The frequency, scale and viscosity of debris flow will change with the above factors. Gullies where mudslides have occurred are still dangerous in the future.

15, how to deal with tornadoes?

When encountering a tornado, if you are at home, you must stay away from doors, windows and external walls of houses and hide in the wall or small room opposite the tornado.

The safest place to avoid a tornado is the basement or semi-basement. In case of emergency such as pole collapse and house collapse, the power supply should be cut off in time to prevent electric shock or fire.

When the tornado is outside the stadium, you should quickly escape in the opposite direction or vertical direction of the tornado and lie on the low-lying ground, but stay away from trees and telephone poles to avoid being hit, crushed or electrocuted. When driving out and encountering a tornado, don't drive to avoid it, let alone avoid it in the car. You should leave the car immediately and avoid low-lying areas.

16. What is a flood diversion and storage area?

Flood diversion refers to the planned diversion of excess flood when it will exceed the guaranteed water level or the flow will exceed the safe flow. Excess flood water is discharged into lakes and depressions, or into other rivers, or directly into the sea, or bypasses the protected area and returns to the original river downstream. Flood diversion is a measure to sacrifice part and save the whole situation.

Flood storage and detention area is the general name of flood storage and detention area. Flood discharge area refers to the natural river channel and its banks or between banks and dikes, which is used for discharge in the event of a major flood. Flood storage and detention area refers to the area where low-lying areas are used to store excess floods exceeding the safe discharge of rivers. The flood storage and detention area mainly plays the role of flood storage and peak clipping to reduce the pressure of flood on dikes on both sides of the river. Due to historical reasons, many flood storage and detention areas have residents reclaiming cultivated land.

17, how to avoid lightning strike

Thunderstorm, also known as thunderstorm, is a kind of rainfall phenomenon accompanied by lightning, and the discharge of lightning atmosphere often occurs in summer. Originated from charged clouds, it will discharge objects such as trees, tall buildings and telephone poles protruding from the ground, which will not only destroy tall buildings, but also kill people and animals near the protrusions, and sometimes cause forest fires.

Although lightning is dangerous, its harm can be avoided or reduced as long as protective measures are taken. (1) A lightning rod should be installed at the top of a high-rise building, which is used to guide lightning safely into the earth. (2) In thunderstorm weather, it is best to cut off the power supply of household appliances such as radios and televisions, and try not to use telephones and computers. The outdoor antenna of TV set should be equipped with grounding device. Don't touch gas pipes, tap water pipes and all kinds of live equipment. (3) When lightning strikes, the possibility of being struck by lightning indoors is much smaller than that of being struck outdoors. Therefore, try not to go out when a thunderstorm comes. (4) When there is a thunderstorm, if you are in the forest of Shan Ye, you can find a dry cave to shelter from the rain. Never stand on a wet rock wall or under a big tree to shelter from the rain, and don't get close to isolated tall buildings, telephone poles, chimneys and other towering objects. For example, in the wild, shovels or umbrellas with metal handles can't be held high. A better way is to stay away from conductive objects. Outdoor workers should not use walkie-talkies in thunderstorm weather. (5) During a thunderstorm, when walking on the road and there is nowhere to shelter from the rain in the field, attention should be paid to: the lower the body position, the better; The closer the human body is to the ground, the better; Stay as far away from rails and high-voltage lines as possible. The best emergency measure is to get down quickly.

It is particularly noteworthy that due to the extremely high sensitivity of VLSI such as computers, even if lightning rods are installed in buildings with computer facilities, electromagnetic induction caused by lightning strikes will form high-voltage shock waves and damage electronic equipment. What's the name of this thunder quilt? Induction lightning strike? Or? A second lightning strike? . It doesn't thunder like direct thunder, but it happens quietly, but it is very dangerous.

All users who use computer networks should establish lightning protection awareness to ensure that residential resources are not damaged by lightning. In order to avoid and reduce the loss of computer hardware caused by lightning, we should first pay attention to the regular inspection and detection of lightning protection devices in buildings, and strive to be foolproof.

Whenever a thunderstorm comes, it is best not to use the computer, unplug or cut off the power supply, or turn off the middle switch of the line. If it can't be stopped, in order to achieve the best lightning protection effect, the grounding wire of the machine and the grounding wire of the building can be kept independent, and there is enough safe insulation distance between them. If the two cannot be insulated safely, the two grounding systems should be connected into a unified grounding network through technical treatment.

Contents of pre-flood inspection 1. Whether the flood control organization (i.e., flood control leading institutions, flood control departments, rescue teams, etc.) is sound. Whether it is sound and whether the command and dispatch are smooth;

Two, flood control system, measures, flood control emergency plan formulation;

Three, whether there are related buildings (construction cofferdam, flood control wall, etc.). ) meet the requirements of flood control;

Four, electricity, communications, transportation, water supply, drainage, fire and other facilities are reliable; Whether emergency materials are ready;

5. Whether to evacuate personnel from the operation site that may induce landslides, mudslides, lightning strikes and other disasters, and formulate emergency measures;

6. Whether measures have been taken for camps and large-scale equipment affected by floods;

Seven, whether there are warning signs on the construction roads threatened by floods.

Work in flood season ① Grasp the water regime and weather conditions: timely release meteorological and hydrological conditions such as flood temperature, wind power, precipitation, ice and snow, water level, tidal level and flow rate, forecast possible flood peak, flood rise and flood volume, and issue an alarm when necessary.

(2) Flood dispatching: According to the water regime and engineering conditions, as well as the flood control dispatching scheme, all kinds of flood control projects that have been built are used for flood control dispatching. When flood diversion, flood storage and flood detention measures are needed, timely and decisive decisions shall be made, and flood storage shall be ordered on time and according to the quantity.

③ Engineering Guarding: Organize flood control personnel to patrol and guard dikes, dams, culverts and other projects without interruption, find dangerous situations in time, analyze reasons, make correct judgments, formulate emergency protection plans and organize emergency protection. Below the warning water level, it is generally defended by professionals, and above the warning water level, flood control personnel are organized to defend.

(4) Emergency measures: In case of over-standard flood and irresistible manpower, you should ask for permission from the superior, and implement emergency measures such as temporary flood diversion in time according to the approved emergency measures and prescribed procedures to minimize losses and avoid death. Resettlement of residents in flooded areas or areas that may be flooded.

⑤ Emergency rescue: Most dangerous situations develop from small to large, and there are many signs before going out. Frequent inspection, early detection, danger is easy to catch and protect. The principle of emergency protection of dike leakage danger is to stop the river from the back row; The protection of revetment is mainly to strengthen roots and prevent corrosion; The leakage on both sides of the dike-crossing building is also blocked before and then blocked, mainly to aggravate the sliding danger (see dike rescue).