August 12 Shanghai Urban Planning Institute Link:
0. 1 sponge city, schools of thought contend
0.2 sponge city is a basket?
1. 1 special planning index control
1.2 annual total runoff control rate?
The State Council Document No.75 requires that more than 20% in 2020, more than 80% in the built-up area in 2030, and 70% of rainwater will be absorbed locally. Can you do that?
There are too many arguments about the index of annual runoff control rate. This is the "Sponge Club Sponge City and Watershed Group" established by Professor Guo of the United States, and the debate in this group is the most intense.
Cheng Xiaotao is the deputy chief engineer of China Institute of Water Science. He is @ Che Wu, and he is "confused" about the annual runoff control rate. What he means is that some people don't know the basic knowledge of hydrology, and those who engage in municipal drainage don't know hydrology. Then he talked about "light rain stays, heavy rain is discharged quickly", which is a matter of concept. If 70% of the light rain stays, it may mean that the river has no confluence for more than 90% of the time.
The discussion was very intense. At 5: 30 in the morning of July 22nd, I got up so early to discuss. It was evening time in America at that time, because it was just 12 hour from now, that is, evening time.
Is it a problem that Xiaoyu didn't stay? I studied water conservancy, and later engaged in water work, closely combined with urban planning, and learned about water-related majors and relationships; Let me answer General Cheng's question:
In fact, it is no problem to keep the rain. The little sponge blocked the rain. Where do you say the rain is kept? In fact, most of them are infiltration, which increases the basic ecological flow. How can there be no basic ecological flow more than 90% of the time?
Secondly, retaining light rain will increase evaporation. Below I use a picture to illustrate that rain will return to the earth.
After the third light rain remained, even if it was used, where did the rain you used go? Didn't it excrete after use? There is no decrease in water, because matter does not go out.
I told him at that time that some water conservancy projects, such as large reservoirs, intercepted light rain and greatly reduced the ecological base flow. This is another issue, including the current debate about the Three Gorges Project and the South-to-North Water Transfer Project, which will not be discussed here today.
Can all the heavy rain be drained quickly? I asked this question in reverse. What is the reason for the serious waterlogging in Wuhan this year?
Citing some opinions of Wang Jiazhuo, director of China Law Institute, the waterlogging in Wuhan was first caused by continuous rainstorm.
Among them, from June 30th to July 6th, 1 week, the cumulative rainfall in Wuhan was 576mm, which was 539mm higher than that of 98 major floods:
Secondly, floods are caused by floods, because the water level of the Yangtze River has risen.
The water level in Hankou of the Yangtze River is 5-6 meters higher than that in Hangao.
The water in Wuhan can't be discharged, so it can only be discharged by pumping stations.
The third reason is that a large number of lakes are filled in Wuhan, which leads to a serious shortage of stagnant storage.
The fourth reason is poor drainage. The investment of Wuhan drainage three-year action plan released in 20 13 is 1300 million yuan, but only 4 billion yuan has been completed by the end of 20 15, and most of the planned pumping stations in Wuhan have not been built.
Cities in the middle and lower reaches of the Yangtze River suffered serious floods this year. Compared with the "98" flood, the maximum rainfall intensity in a week exceeds the 98 flood, but the total rainfall in a month is not as big as the 98 flood.
Why did the water level in the middle and lower reaches of the Yangtze River exceed the water level in the same period of 98 major floods this year? Natural disaster or man-made disaster?
Man-made disasters are greater than natural disasters. 1998 After the flood, the water and soil conservation in the upper reaches of the Yangtze River is still effective, so the main reason is that there are too many cement fields, and the towns along the Yangtze River are forced to discharge water upwards, which raises the water level in the middle and lower reaches of the Yangtze River. This is a problem in the whole Yangtze River basin, so it is necessary to build sponges in the whole Yangtze River basin.
On August 4th, the "Thousand Green Articles" in the column of Southern Weekend:
I quote the article "One Pot of Porridge":
"Even the most basic parameter, the control rate of annual runoff, is debated endlessly." Cheng's general view is that sponge city only solves the problem of "light rain without water" in a small scale, and can't solve the problems of "heavy rain without waterlogging" and "the water body is not black and smelly", but blocks the basic flow direction of urban rivers and causes them to dry up.
Various viewpoints are summarized as follows:
What did Professor Che Wu say?
Professor che is a little dismissive. He said that two years later, he is still struggling with this. I don't know how many times we told them face to face at the meeting and after. We are a little arrogant, but we didn't make it clear, otherwise we wouldn't be arguing now.
I agree with Professor Che that "sponges can store water, preserve water, replenish groundwater and provide necessary basic flow for rivers and lakes". This statement is correct, but he should make the whole situation clear.
I use the following picture of Mr. Che, who has been engaged in rainwater collection and utilization and rainwater management for twenty or thirty years and is really experienced.
This is teacher Che's water cycle diagram, which comes from his paper "Comparison of Natural Drainage, Grey Water Drainage and LID Water Cycle:
What are the consequences of traditional urbanization? When it rains, 55% of the rainwater is discharged, and black water is discharged. Only 15% seeps downward, and 30% evaporates back into the sky.
After the renovation of the sponge city cover, the emission can be reduced from 55% to 20%, and the water quality has improved.
Permeability increased from 15% to 35%; Evaporation increased from 30% to 45%, with an increase rate of 50%.
However, the transformation of sponge city is impossible to return to the pure natural water cycle:
Natural water circulation is that after rain, only 65,438+00% of rainwater produces runoff, 40% permeates downwards, 50% evaporates and circulates again.
When I talk about it, I mean that water conservancy and municipal drainage are not the same thing as urban planning.
So the first question is: have you thought about the goal of sponge city? Is the object a big sponge, a medium sponge or a small sponge?
In fact, due to professional restrictions, municipal drainage is considered as a small sponge, at most, it is a pipe network and a medium sponge.
Water conservancy is a big sponge concept, which is considered from the water cycle of the basin. In fact, the basin of water conservancy is not a complete basin, because the basin generally does not consider the urban sponge and the infiltration and evaporation of rainwater, and the ground and underground and even the atmosphere are a whole.
A professor of water conservancy in Tsinghua envisions: controlling and utilizing atmospheric water circulation and designing a "natural road" for water vapor transportation to replace "South-to-North Water Transfer Project" and "West-to-East Gas Transmission Project"!
The second problem is that the objectives of the three majors are unclear. What's our goal, whether it's a sponge city or a water conservancy project? Is it water? Water quality? Or ecology? The target is not clear.
The third question, the conditions are not clear. The boundary conditions of each family are different:
1 Is the conditional rainfall light rain or heavy rain? Is it a rainstorm or a rainstorm? Is the rainfall short or long? Didn't even make it clear.
The second condition, soil, how is the infiltration of soil? Is there saturation in the early stage? In fact, the key to sponge city is below. The soil under the rain garden should be changed, and the permeability is several times higher than that of the original soil. Therefore, the United States requires that the accumulated water in the rain garden must penetrate 24 hours, so the rain garden should be replaced with soil.
The third condition is vertical, and the most important thing for a sponge city is vertical design. In the first half, I quoted Xiaoguang as saying: "LID design without vertical professional depth will definitely fail".
If the object, goal and conditions of the sponge city are not clear, all families will not talk on the same platform and channel, and if the chicken talks to the duck, it will be a pot of porridge.
It is recommended to use big data virtual reality. Isn't it VR now? You can use the mathematical model of big data to simulate the whole water circulation process of the surface, underground and atmosphere completely, and then you can know the whole process by watching the virtual reality animation calculated by the model, just like I gave a lecture today, talking with pictures and numbers.
I use another picture to speak. This is the water cycle diagram of the earth, the water cycle of land and sea:
Of the 100 mm rainfall on land, 39 mm comes from the ocean, and the remaining 6 1 mm comes from the evaporation of land itself, including the evaporation and transpiration of plants and soil, so 6 1% rainfall is self-circulating.
Of course, the return to the ocean is 39 mm, because the water is balanced, of which 38 mm enters the sea through runoff, and 1mm returns to the ocean through groundwater, which is such a water cycle.
Source: Gleick, P.H., 1996: Encyclopedia of Water Resources, Weather and Climate, edited by S.H. Schneider, Harvard University Press, new york, Volume 2:
Only 3% of the earth's water is fresh water, while surface fresh water such as rivers, freshwater lakes and freshwater marshes only accounts for 0.3% of the earth's fresh water.
But 20% of the world's surface fresh water is concentrated in Lake Baikal, and 20% is stored in the Great Lakes of the United States (Lake Huron, Lake Michigan and Lake Superior).
Rivers only account for 0.006% of the global fresh water; It can be seen that life on earth only depends on the total water supply of the earth.
Why can rivers, which account for only 0.006% of the world's fresh water, feed billions of people around the world?
Because water is circulating!
We look at the water cycle from the river basin, which is the whole catchment area of the Yangtze River basin.
This is the distribution of annual average rainfall in different areas of the Yangtze River Basin. The place with the largest annual rainfall is Sichuan Basin, with an average annual rainfall of 1, 200 ~ 2000mm (gray, partially blue). Taihu Lake in Shanghai to the Yangtze River estuary is all green, and the annual rainfall is 1000 ~ 1200mm.
The average annual precipitation of the whole Yangtze River basin is1.067mm. Because the Yangtze River basin covers an area of 1.8 million square kilometers, the total rainfall is 1.92 trillion cubic meters.
What is the runoff from the Yangtze estuary into the East China Sea? It is 95 13 billion cubic meters, accounting for 49% of the total precipitation. What do you mean? According to the algorithm that rainwater can be absorbed by itself and not discharged, the annual runoff control rate of the whole Yangtze River basin is 5 1%?
This 5 1% is similar to the 50% proportion of evaporation in Mr. Che's natural water cycle diagram, because it is a global average and a large number of hydrometeorological data have been consulted. On average, 50% of rainwater evaporates back, because matter is immortal and water is constantly circulating.
Another example is the Yellow River Basin, which is cut off for several months a year, because the amount of water discharged into the sea is very small. Is the annual runoff control rate of the Yellow River above 90%?
So can the annual total runoff control rate index be applied to sponges?
Back to the discussion on the annual runoff control rate index of small and medium-sized sponges. 20 15, 1 1 October, Xiaoguang, who is engaged in water supply and drainage abroad, wrote an article, which aroused everyone's discussion. He believes that the annual runoff control rate is a misunderstanding, and the average natural runoff rate for many years cannot be used, because sponge cities are mainly aimed at small and medium-sized urban blocks.
The second is the adaptability of the index: it should be a water quality control index, not a water quantity control index, but now it is mainly aimed at water quantity in China.
The third is the scope of application of the index, which is mainly applicable to plots and building communities. , not applicable to urban areas with water systems.
Because the sponge city index system of the Ministry of Housing and Urban-Rural Development is not clearly defined, there are different opinions. For example, how about Shanghai? How to deal with the problem of annual runoff control rate reaching the standard?
Shanghai has also formulated a sponge city index system, which is compiled by seven units.
There are two fewer dragons in water control than in Kowloon, namely, housing management, construction, planning, development and reform, water supply, transportation, environmental protection and landscaping, and one dragon and seven dragons work together to control water.
If the total annual runoff control rate in Shanghai is controlled at 75% corresponding to 22 mm and 80% corresponding to 26.7 mm.
Shanghai's index system has a noun explanation, including rainwater stagnation:
Then Shanghai has a very interesting explanation: because according to the requirements, Shanghai can't reach 80% of the total annual runoff control rate. Why?
Because of the so-called "three highs and one low" in Shanghai: high groundwater level, high coverage, high development intensity and low permeability, your Ministry of Housing and Urban-Rural Development has an index assessment policy, so I have countermeasures in Shanghai. What countermeasures does Shanghai use? Using rivers to support the bottom:
If the annual runoff control rate in Shanghai is not up to standard, then I will adjust the storage through inland rivers or even through deep storage, as long as the river channel is adjusted. Last time, I told the person who set the 70% standard by the Ministry of Housing and Urban-Rural Development. I said that you didn't make it clear and there was nothing you could do. If you have policies, we in Shanghai will have countermeasures.
The debate shows that the definition of annual runoff control rate is unclear, and the scope of application is unclear, let alone why. On the contrary, it caused misunderstanding and made hydrologists mistakenly think that sponge city was cut off! In fact, foreign countries don't care much about water quantity, mainly water quality, and the water cycle mentioned above.
The Guide divides the annual runoff control rate. In Schedule F2- 1 of the Guide, the average 80% runoff control rate of four municipalities and provincial capitals in China corresponds to 24.9 mm, that is, 25 mm
According to the statistical analysis of tens of thousands of rainfalls in Shanghai in recent hundred years, controlling the rainfall of 26.7mm each time is equivalent to controlling 80% of the total annual rainfall runoff.
Let's go back to the water cycle diagram, which is the global water cycle diagram. The 25mm mentioned above has been discussed with foreign experts for several years. They have always said that foreign covers are designed to control rainfall runoff and pollution, generally 20mm to 30mm, with an average of 25mm an inch, so they control one inch of rainfall. At first, I didn't understand. I said why it's only one inch, not two inches, not half an inch. They say it's too difficult to control.
Now I have found the answer. This is an article in the Encyclopedia of Nature published by Harvard University. Do you know anything about the global water cycle? How much water is there in the earth's atmosphere? It is 12900 cubic kilometers, with 129 trillion tons of rain, which is water vapor in the atmosphere.
If water vapor falls to the ground once and is evenly distributed on the earth's surface, how much rain does it rain on average on the whole earth's surface?
25 mm, 2.5 cm, one inch! This is the law of nature, and this is the Tao. That is to say, the average water vapor in our air is 25mm in the world, so you can see that it is constantly circulating, and its average complete rainfall is 25 mm.
For example, Shanghai, because it is humid, is a little bigger than the average, 26.7 mm, corresponding to 80% control rate. So behind this inch number is the law of nature, that is, Tao, which is very interesting.
This is Shanghai, and Xujiahui weather station is here.
It is the earliest weather station in China with a meteorological record of 100 years.
According to the statistical analysis of tens of thousands of rainfalls in recent hundred years, the probability distribution of the number of rainfalls and the total rainfall at Xujiahui Station is as follows:
If you look at different rainfall, 5 mm, 10 mm and 27(26.7) mm, there is a statistical analysis of rainfall times, because there are many light rains, and the rainfall less than 27 mm accounts for almost 95%, because there are several heavy rains.
The cumulative rainfall is less than 27 mm, that is to say, how much is the cumulative rainfall controlled? Control 82% to 83% of the total rainfall. This value is based on the statistical analysis of tens of thousands of rainfalls in the past hundred years, but behind it is the law of natural water cycle.
So speaking, this is a water cycle problem. It can be seen that if we want to build a sponge city, we need to know astronomy and geography. Only by understanding these can we know what the internal laws are.
Let me talk about the circulation of groundwater in depth. This is a schematic diagram of groundwater circulation.
After rainwater permeates, there are water-resisting layers and pressure-bearing layers below the surface, which can be evaporated by plants and soil and returned to the atmosphere.
10% of water in the atmosphere comes from plant transpiration, and a big oak tree transpiration 15 1 ton of water a year;
On July 30th, in the training of "Planning, Design, Construction and Management of Sponge City" in Shanghai, I talked about "Zhouyi sticks to divination to see sponges":
Later, it was organized into Zhouyi sponge series:
Divination is thunder under the water,