Analysis on the design of small farmland water conservancy projects?
1 Introduction
Water-saving transformation in irrigation areas is a need to ensure national food security and promote economic development in irrigation areas. Drought and water shortage are the biggest threat facing my country's agriculture and the main constraint on agricultural development. Under the premise that the population continues to grow, farmland gradually decreases, and reserve land resources are seriously insufficient, an important aspect of stabilizing and improving comprehensive grain production capacity is to stabilize and appropriately expand the area of water-saving irrigation. Water conservancy facilities are in disrepair and are seriously damaged, resulting in extremely serious water waste and losses. Every year, farmland is washed away and submerged due to channel diversion breaches. The engineering facilities in Fufeng County are seriously damaged, the integrity rate is low, the water delivery capacity of the channels is seriously insufficient, the water utilization rate is low, and water resources are wasted seriously. At the same time, motorized wells in small irrigation areas are seriously aging, farmland cannot be irrigated, and water transmission projects are not supported. Based on the above situation, it is necessary to plan and construct small-scale farmland water conservancy projects in Fufeng County. Water-saving renovation in the irrigation area is a need to ensure national food security and promote economic development in the irrigation area.
2 Project Overview and Current Situation of Farmland Water Conservancy Projects
2.1 Project Overview Fufeng County is located in the west of the Guanzhong Basin, in the middle section of Xibao Expressway and Xibao North Line, with a total land area of 745.8km2. The cultivated land area is 776,100 acres, and the per capita cultivated land of farmers is 1.59 acres. The farmland in the county is square, the roads are networked, and the transportation is relatively convenient. The county mainly grows food crops. The main food crops include wheat and corn. The annual sowing area is 1.006 million acres, and the average multiple cropping index is 150%. The main cash crops include peppers, apples, etc., and the agricultural industry is mainly animal husbandry. 2.2 Current status of water conservancy projects in the project area At present, the existing water conservancy projects in the project area mainly include small farmland water conservancy projects, backbone projects in large and medium-sized irrigation areas, and small reservoir projects. By the end of 2009, the county had 9 pit ponds, 343 small irrigation pumping stations, 2,843 agricultural irrigation wells, 810 water cellars, 291km of canals in small irrigation areas, 1,080km of large and medium-sized irrigation canals, and 117.3 irrigation canals in motor-well irrigation areas. km, and 112.8km of low-pressure water transmission hidden pipes. The facility irrigation area is 520,000 acres, the effective irrigation area is 450,000 acres, and the water-saving irrigation area is 234,000 acres. There are 122.8km of main and branch channels in the Baoji Gorge and Fengjiashan irrigation areas in the county. Since 2000, the county has invested 31 million yuan in projects such as the renovation of water conservancy backbone projects for comprehensive agricultural development and the renovation of irrigation areas with provincial financial special funds, and has completely relined 38km of main and branch canals. There are 11 county-managed reservoirs, all of which are small reservoirs. Taichuan Reservoir, Guanwu Reservoir, Baijiayao Reservoir and Wujungou Reservoir have a total irrigation area of 58,000 acres. Generally speaking, the water conservancy infrastructure in the irrigation area is weak, the canal buildings are severely damaged, the pumping stations are in disrepair, and the pumps are aging. Farmland irrigation is mainly based on earthen canals and flood irrigation. Groundwater resources are wasted seriously, and the control area of a single well is Small, irrigation guarantee rate is low. The irrigation needs cannot be met, which seriously hinders the economic development of the project area.
3 Water-saving renovation project design in the irrigation area
In order to improve the current status of the above-mentioned water conservancy projects in the Fufeng County irrigation area, the entire Fufeng County is divided into four project areas to design systematic water-saving renovation projects. . The typical design of the entire water-saving renovation project is described below. 3.1 The engineering design of the motorized well shall be based on local hydrogeological conditions and water consumption requirements, and the designed wellbore depth shall be 180m. There can be four layers of water within this depth, with a total thickness of 40m, a wellbore diameter of 550mm, and a cast iron well pipe material. The effective working length of the water filter pipe is 50m, the actual pipe length is 130m, and the total total length is 180m. The thickness of the gravel outside the pipe is 140mm, and the diameter of the gravel is 10mm to 20mm. The gravel material is standard gravel produced by the Fufeng County Sand Factory. The well wall pipe connection form adopts welding connection. The calculation parameters are determined based on the geological conditions of the wellbore design and the lithology of the aquifer. From the wellbore histogram, it is known that the total thickness of the aquifer is M = 40m. The lithology of the aquifer is mainly coarse and medium sand. Select the permeability of the aquifer. The coefficient K=15m/d, the effective working length of the water filter pipe is L=50m, the well hole diameter D=550mm, the outer diameter of the water filter pipe ds=0.288m, and the well pipe diameter d=0.25m. In order to ensure the service life of the tube well and avoid corrosion, scaling, blockage and other damage to the water filter pipe caused by excessive permeation flow rate, in the design we use a flow rate smaller than the allowable inlet flow rate for calculations. The calculation formula is: Q=Л×dg×L×n×Vg. Substituting the corresponding parameters into the formula, we can get Q=195m3/h.
The calculated theoretical water output represents the water inlet capacity of the water filter pipe, and the design flow rate should be less than the calculated theoretical value, so it should be multiplied by a safety factor of 0.3 to determine the design water output, that is, Q=58.6m3/h. 3.2 Water conveyance channel design A typical engineering design is based on the lining project of the eleventh branch and one bucket canal in the north of Qicun, Famen Town. The total length of the channel is 850m, which mainly irrigates part of the cultivated land in Qi Village. The controlled irrigation area is 650 acres, and the average controlled channel length per mu is 2.5m~3.1m. The design flow of the channel should be calculated based on the crop irrigation system and the controlled irrigation area, as well as the simultaneous water consumption of different crops in the same period. The calculated channel design flow is 0.1m3/s. The selection of the vertical gradient of the channel should be determined by the actual terrain conditions. Try to make the canal bottom gradient consistent with the ground slope. Under the condition of meeting the requirements of irrigation water diversion, try to choose a larger specific gradient, but the bucket canal is generally not larger than 1/500. Therefore, according to the terrain characteristics of the project area, the channel selection ratio is reduced to 1/600. In order to improve irrigation efficiency, save water and energy, save land space, and reduce water supply costs, and also for mechanized construction, the channel section is designed as a "U"-shaped concrete section, the channel design flow is 0.11m3/s, and the vertical ratio is reduced to 1/600 , the channel section is selected as D40 section, the lining thickness is 5cm, and C15 concrete is used for pouring. An expansion joint is set up every 5m in the channel. The joint shape is a mechanically cut half-slit with a width of 2.5cm. The joints are filled with tar plastic clay. 3.3 The design of pumping stations is based on the principle that the designed irrigation area, design flow rate, and supporting pump models of the original pumping stations remain unchanged. The 35 pumping stations in the project area will be renovated and designed, and 62 (sets) of new energy-saving units will be replaced. It exerts its original effectiveness. It is determined that the pumping station in Dahuai Village, Zhaogong Town, Fufeng County project area will be used as a typical design. The project is located 600m south of Xinyi Reservoir. The diversion water source is Meishui River water and the controlled irrigation area is 380 acres. According to the actual survey, the topographic lift of the pumping station is 8.23m. The design flow is calculated based on the controlled irrigation area, irrigation quota, number of irrigation days, daily irrigation time and canal water utilization coefficient. The water pump model is determined based on the design flow and pumping lift. After determining the flow rate and head of the water pump, you can use the "water pump performance table" to select the required water pump. 3.4 Low-pressure concealed pipe design This project plans to drill 1 reinforced concrete tube well with a depth of 180m. According to the hydrogeological data of the existing motorized well, the water output of the motorized well is 32m3/h, the static water level is 35m, and the dynamic water level is 95m. The land plot is rectangular and is long from east to west. 400m, 234m wide from north to south, and an area of about 140 acres. The machine shaft is located in the northwest corner of the plot. The crops grown in the plot are mainly wheat, corn, and pepper. The crop planting direction is east-west, with the plot slightly higher in the north and east and lower in the west. The design irrigation quota is calculated according to the formula m=1000Hγ(覻1-覻2)/η. According to the actual situation of the area, the irrigation quota for wheat and corn is calculated to be 40m3/mu, and the irrigation quota for pepper is 27m3/mu. The main crops in this area are wheat, corn, and pepper. The growth period of corn and pepper is in the rainy season. Appropriate supplementary irrigation can meet the requirements. The irrigation cycle is 12 days. The pipeline layout is in the shape of a comb. According to the technical specifications of pipe irrigation, combined with the shape of the plot, operation and management system, farming habits, water output from the well and other actual conditions, one main pipeline is laid out on the western boundary of the plot and three vertical main pipelines are laid out. Branch pipe, the length of the pipe is 720m, and a water outlet is installed on the pipe for irrigation. After the project is implemented, the wheat planting area in the area accounts for 90% of the cultivated land area. The daily start-up hours are 16 hours, and the irrigation water utilization coefficient is 0.8. Calculated based on the well control area, the results show that the design flow rate is less than the water output of a single well, so the single well outlet is used. The water volume is the design flow rate. The pipe diameter is determined using the economic flow rate method. Based on the calculated pipe diameter, a UPVC pipe with an outer diameter of 110mm and an inner diameter of 105.6mm is selected. After calculation, the head loss along the route is 5.77m, and the local head loss is calculated as 10% of the water head along the route, taking 0.57m. The design lift of the water pump is determined by the head loss of the pipeline system (h), the dynamic water level of the well (h net), the height difference from the well to the most unfavorable point of water supply (△h), etc., that is, H=hnet+h+△h+2.0 (output The required water head at the nozzle), the design lift of the water pump supporting the well is 95+5.77+0.33+2.0=103.1m. Pump selection is carried out according to the design flow rate and design head.
4 Project Economic Benefit Analysis
The Fufeng County Small Farmland Water Conservancy and Water-Saving Renovation Project Construction Project plans to line 82.1km of channels and reconstruct 639 canal buildings; in the well irrigation area, new construction There are 41 supporting wells; 28.16km of low-pressure pipelines have been laid; there are 981 water plugs; the irrigation area can be increased by 7,640 acres and the irrigation area can be improved by 26,222 acres. The irrigation water utilization coefficient in the well irrigation project area increased from 0.65 to 0.8; the irrigation water utilization coefficient in the pump irrigation area increased from 0.5 to 0.65; the county's comprehensive grain production capacity increased by 3.7942 million kg. We will vigorously develop farmers' water cooperatives and increase the irrigation area under their management by 13,000 acres. After the project is completed, the crop multiple cropping index will increase from 150% to 180%, and the annual grain production can be increased by 3.7942 million kg. Calculated based on the current market price of 1.8 yuan/kg, the income can be increased by 3.7942×1.8=6.8296 million yuan. The income increase of cash crops per mu is calculated based on 100 yuan, which can increase the income by 3.39×180%×0.4×100=2.4408 million yuan. After the completion of the project, 1.866 million m3 of water can be saved annually. Based on 0.1 yuan per cubic meter of water, 1.8666 million × 0.1 = 186,600 yuan can be saved. After the implementation of the entire project, *** can increase revenue by 9.457 million yuan, and the water allocation coefficient is 0.4, that is, the net income of the water conservancy project is 9.2554 million yuan × 0.4 = 3.7828 million yuan. Based on the above analysis and calculation of incremental benefits and incremental costs, and in accordance with the relevant evaluation index calculation regulations, the results are shown in Table 1. It can be seen from the economic evaluation analysis and calculation results that the economic internal rate of return of this project is 12.44065% greater than the economic benchmark rate of return of 8%; the economic net present value of 8.441 million yuan is greater than zero; the economic benefit-to-cost ratio is 1.27, greater than 1.0. Therefore, the project is economically reasonable.
5 Conclusions and Suggestions
Through the implementation of this project, the environment of the irrigation area will be fully improved, and the area of forest and grassland in the irrigation area will be further expanded, which will be conducive to the improvement of the ecological environment of the irrigation area. Ecological and environmental benefits are reflected in conserving water sources, maintaining soil and water, reducing sandstorm disasters, preventing sediment loss, regulating climate, improving the ecological environment, and purifying the air. The implementation plan of the key county construction project for small farmland water conservancy in Fufeng County can be selected based on the current situation and existing problems of small water projects in the project area. The options are correct, the layout is reasonable, the economic benefits are significant, and there are good social and ecological benefits.
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