Analysis on irrigation canal design of farmland water conservancy?

What is the specific content of irrigation and drainage design for farmland water conservancy? The following is the answer of Zhong Da Consulting Company.

In the design of irrigation channels, the determination of section size is mainly to reasonably select the slope of the channel section, the width b of the channel bottom, the water depth h in the channel and the superelevation Δ h, which are related to irrigation efficiency, project cost and other issues. Only by going deep into the site and fully understanding the original data can we calculate the accurate water diversion flow and carry out reasonable section design.

Farmland water conservancy construction is an important content of agricultural water conservancy system, and it is also the most direct livelihood project in agricultural water conservancy systems at all levels in Huize County, which is closely related to people's lives and rural economic development. Agricultural water conservancy projects play a vital role in storing rainwater, regulating water use, and ensuring and promoting agricultural production. The irrigation and drainage design of small-scale irrigation and water conservancy projects is described below.

To design a channel, we must first determine the diversion flow of the channel, and then carry out the cross-section design of the channel, including cross-section design and longitudinal section design. Then draw a cross section, calculate the engineering quantity, make a budget estimate, and finally write a preliminary report.

1 design standard for irrigation and water conservancy projects

Generally speaking, the irrigation design standard should be reasonably determined after comprehensive consideration according to the factors such as water supply, existing water conservancy facilities, agricultural development requirements and local economic conditions. Irrigation design standard refers to the guarantee degree of irrigation water source to irrigation water. High design standard means high guarantee of irrigation water. Therefore, it directly affects the scale of irrigation projects. Generally speaking, there are two standards for irrigation design: one is the guarantee rate of irrigation design, and the other is the number of drought-resistant days.

1. 1 irrigation design guarantee rate

The guarantee rate of irrigation design refers to the percentage of the number of years that an irrigation project can satisfy irrigation water in the long-term use process, which is represented by the symbol "P". For example, P=80%, which means that a project can meet the irrigation water demand of the whole irrigation area for 80 years in 100, and the remaining 20 years cannot be fully guaranteed, resulting in water shortage. P=80% is the irrigation design guarantee rate of this irrigation area. Therefore, when designing an irrigation project for farmland irrigation, the designer must determine the scale of the irrigation project according to the situation where the project is located, especially the local water source and crop type. Irrigation design guarantee rate can be 50% ~ 80% in water-deficient areas and areas dominated by dry crops; 70% ~ 95% can be used in areas rich in water resources and areas dominated by rice.

1.2 days to prevent premature delivery

The so-called drought-resistant days refer to the days when the water demand of crops can be met under the condition of continuous rainlessness according to the water supply capacity of irrigation facilities such as small reservoirs and ponds ("continuous rainlessness" does not mean that there is absolutely no rain during the drought-resistant period, but that there is little rainfall, and the daily rainfall is generally treated as rainlessness). For example, if the irrigation facilities can meet the irrigation water demand of crops for 80 consecutive days, the irrigation design standard of the irrigation facilities is drought resistance for 80 days. Drought resistance time should be defined as the irrigation period when the water demand of local main crops is urgent. The number of drought-resistant days should be determined according to the situation in different regions, and the design should be "specifically analyzed".

2 Determination of channel diversion flow

Channel drainage is the sum of net irrigation flow and channel loss flow in irrigation area. It is related to the water quantity at the source of the river, the internal water source conditions in the irrigation area, crop species, planting area, farmland soil quality, irrigation quota, irrigation climate, channel length and other factors. Calculation of canal water diversion: It should be calculated according to the irrigation system and controlled irrigation area of crops and the maximum water consumption of different crops at the same time. The calculation formula is as follows:

Q= irrigation quota (m3/ mu) × irrigation days per mu × seconds of day and night (86400)× channel effective utilization coefficient.

The effective utilization coefficient of canal system is a coefficient considering factors such as canal leakage and evaporation loss, and generally it can be 0.5 ~ 0.7 for main canal; The branch canal adopts 0.6 ~ 0.8; It can be increased to 0.8 ~ 0.9 when the canal is lined.

3-channel design

3. 1 Determination of channel water level elevation. The water level elevation of the canal is determined according to the elevation of the ground datum point in the irrigation area and the head loss at all levels along the canal. The head loss along the channel includes the slope loss of the channel and the head loss of the building passing through the channel.

3.2 Channel cross-sectional design. After the water diversion amount of the channel is determined, the channel section design can be carried out. When the flow rate is constant, the size of the channel cross section is related to factors such as speed and gradient.

3.3 Top width and structure of the canal embankment. The width of the canal embankment is determined by comprehensive analysis according to the requirements of traffic and operation management, construction and stability. In the excavation section, the top width of the embankment on the traffic side is 5.0m, and the top width of the embankment on the other side is 2.0m. In the filling section, the side with traffic requirements is set to 6.0m, and the other side is set to 4.0m. According to the actual situation of the main canal, the right canal embankment is treated according to the traffic requirements. The traffic-side canal embankment adopts the gravel pavement structure, with a width of 4.0m and a thickness of 15cm.

Considering the connection with existing roads, the Zuo Di width of the main canal on the west side of Huangyangtan Farm is adjusted to 6m at 54+625 ~ 55+449, and a 4.0m-wide gravel pavement is laid. The second-phase main canal must pass through the middle of Ningmin Town. In order to facilitate the residents on both sides of the canal embankment to travel, a gravel pavement with a thickness of 15cm was laid at the section with the pile number of 49+55 1 ~ 53+ 162 in Zuo Di.

In order to ensure the safety of residents and meet the requirements of building a new socialist countryside, railings were laid on both sides of the canal embankment. The layout range is 49+55 1 to 53+ 162. The railing is a reinforced concrete structure, which consists of railing columns and railings. The height of balustrade column is 1.2m, and the section size is 0. 15×0. 15m, and C20 concrete is used for cast-in-place. The lower part of the balustrade column is C 15 cast-in-place concrete foundation, with a height of 0.5m and a section size of 0.45×0.45m, and the top is the same height as the top of the canal embankment. Rails are set every 2m along the direction of water flow, which are symmetrical. The railing is connected by two railings; The railing is prefabricated with C20 concrete, with a single length of1.96m and a cross-sectional size of 0.11× 0.08m. ..

3.4 River bed roughness. The roughness of trough bed is related to soil, geological conditions, construction quality and channel maintenance, as well as the flow and sediment concentration through the channel. The riverbed roughness in this design is mainly determined according to the riverbed roughness table with different properties suggested in the Code for Design of Irrigation and Drainage Engineering and the design and operation experience of similar projects in Ningxia Yellow River Diversion Irrigation District. For the full-face concrete precast slab masonry channel, take n=0.0 17.

3.5 Channel gradient. The river slope is calculated according to the empirical formula and determined by comprehensive analysis of the present situation.

According to the slope calculation formula recommended in Code for Design of Irrigation and Drainage Engineering, the main canal is muddy water channel, and the slope calculation of the channel is as follows:

I = 0.275 N2(ω)3/5/qh 1/4

Where: ρ-sediment carrying capacity of muddy water channel, calculated as 13.94kg/m3;

Ω —— sediment settling speed, taking 0.384 mm/s;

N—— river bed roughness, taken as 0.017;

Qh-design flow of muddy water channel, qh =18.0 ~13.0m3/s.

According to the calculation, the particle size of the channel sediment is 0.025mm, and the calculated longitudinal gradient of the main channel is 1/9472 ~ 1/8732. Referring to the lining channel of the same scale, it is generally 1/8000 ~ 1/4000. This design adopts 1/.

4-channel longitudinal profile design

Generally speaking, the longitudinal section design of the channel is carried out at the same time as the cross section design. Include that elevation line along the canal ground, the normal water level line of the canal, the minimum wat level line of the canal, the elevation line at the bottom of the canal, the elevation line at the top of the canal embankment, the position of the water diversion outlet and the arrangement of the canal system buildings. In the design of the longitudinal section of the passage, firstly, according to the layout of the passage and the ground elevation corresponding to different mileage, the ground elevation line is drawn on the longitudinal section. Then refer to the water level elevation of the water source or the upper channel, the slope along the channel bottom and the water level elevation required by each water intake point, and draw the normal water level line according to a certain slope (referring to the slope at the channel bottom, which is the same as the hydraulic slope I used in hydraulic calculation). With the normal water level line, we can draw the elevation line at the bottom of the channel according to the normal situation of the channel, and then draw the lowest water level line, the increased water level line and the crest elevation line parallel to the channel bottom line according to the minimum water depth, increased water depth and superelevation of the channel. On the premise of meeting the water level elevation required by the diversion point of the next level channel, if the ground slope of the upper level channel is steep or steep, the falling water and steep slope can be specifically selected according to the needs of comprehensive utilization, and their height difference and position can be determined. When the upstream channel divides water to the side, it is necessary to ensure the smooth downward classification of the water flow under normal flow and meet the diversion requirements of the downstream channel under minimum flow, so it is often necessary to build a sluice. Head loss of canal water passing through sluices and other canal buildings (such as aqueducts, inverted siphon pipes and culverts) along the canal. ) must be estimated and represented on the longitudinal section.

5 concluding remarks

Small-scale irrigation and water conservancy construction is the most basic condition for agricultural development and the key to sustainable development of agriculture. A sound farmland water conservancy construction system and perfect management measures will greatly alleviate the inconvenience caused by natural disasters to people's lives and reduce the loss of agricultural production.

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