Design of water distribution networks for on-demand irrigation

Three fundamental aspects are studied in the design and operating process of a water distribution network for on-demand irrigation. The first determines plot discharge as a function of the average application rate of system, A_rs, in sprinkler irrigation or of the equivalent discharge per unit of area in drip/micro irrigation, and according to plot size. The second determines the maximum and minimum demand curves, aspects which have not yet been published. These constitute the possible operating points of the surrounding irrigation network. The third is the dimensioning and regulation of the pumping plant that minimises the investment and operating costs according to usage conditions in the irrigated area, with operation in different hourly periods with different energy costs. The results show that the use of hydraulic valves with limiting flow controllers makes the design of the network easier. Moreover, the installation cost decreases when adjusting the hydrant discharge to the exact size of each plot, thus eliminating excess discharge. The determination of the maximum demand curve allows dimensioning of the pumping plant, as well as its regulation and control in real time after including it into the PID (proportional, integral and derivative) logic of a programmable controller. Moreover, a simplified method for evaluating the energy consumption during the irrigation season is presented, valid for electricity tariffs with different hourly costs.     

Soil-cement tiles for lining irrigation canals

Laboratory flume test was conducted to investigate the effect of flowing water an soil-cement canal tiles. For this purpose, soil-cement tiles were constructed from different soils at various cement contents. A flume, 3 metre long and 100 mm wide, was lined with the tiles and the lined bed was subjected to flow velocities of around 2 m/s for a period of 7 days. The tiles made from coarse-textured soil (sandy loam and silt loam) aggregates of 5 mm and from fine textured soil (clay loam) aggregates of 2 mm size were found to be intact and smooth even when constructed at a cement contents lower than that needed to meet the durability requirements.Attempts were also made to measure seepage losses of soil-cement tile linings. A channel section of approximately 1 metre length with a side slope of 1:1 was constructed in the laboratory with the tiles and seepage losses measured by the ponding method were found to be in the range of 0.00123–0.00343 m³/m²/day.The results clearly suggest that soil-cement tiles (irrespective of type of soil) made with 2 mm or less size of soil aggregates are erosion resistant and due to very little or negligible rates of seepage losses, the soil-cement tile lining of irrigation canals is expected to be very promising especially in the areas where irrigation water is costly.     

USBR canal lining experience

The US Bureau of Reclamation has been constructing irrigation water distribution systems since the early 1900s in the 17 Western United States. The advent of this construction soon necessitated a means for preventing excessive seepage from some canals or portions thereof. Numerous types of linings have been installed including concrete, asphalt, masonry, buried plastic membrane, exposed membrane, compacted earth, etc., with varying degrees of success. The three most commonly used at the present are concrete, buried plastic membrane, and compacted earth. Although not a type of lining, buried pipelines are also used extensively and among other advantages they reduce seepage losses very significantly.     

灌溉渠道防渗处理经济分析

通过实例分析，说明灌溉渠道防渗处理是一项投资少、见效快、效益好，且一举多得的具有发展前途的农业基础设施改造工程，在经济上是可行的。     

Simulation of nitrate distribution under drip irrigation using artificial neural networks

Accurate knowledge of nitrate distribution in the soil under fertigation through drip-irrigation systems is fundamentally important for system design and management. The determination of nitrate distribution through modeling represents a highly complex nonlinear problem that includes adsorption, transformation, convection, and dispersion. For this reason, an alternative methodology is proposed, which combines artificial neural networks (ANN) and laboratory experiments. Seventeen experiments with apparent discharge rates varying from 0.6 to 7.8 l/h, the apparent cylindrical applied volume from 6 to 15 l, and the input concentration from 100 to 700 mg/l were conducted to provide a database for establishing the ANN architecture. The model input parameters were initial soil water content, initial nitrate concentration in the soil, discharge rate, input concentration of fertilizer (NH₄NO₃), applied volume, and final soil water content. The model output was nitrate concentration in the soil after fertigation. A total of 298 vectors were used to train the ANN model, and 212 independent vectors were used to test the model. Results of the test show a good correspondence with a determination coefficient (r ²) of 0.83 between the model-estimated nitrate concentration in the soil and laboratory-measured nitrate concentration in the soil. These results show that the optimized ANN models are reasonably accurate and can provide an easy and efficient means of estimating nitrate distribution in the soil under fertigation through drip-irrigation systems.Communicated by J.E. Ayars     

大型灌区渠道闸门一体化测控系统

基于自动化控制、网络通信和测量等技术,设计并研发了能够实现信息采集-处理-决策-信息反馈-监控-共享一体化的灌区闸门测控设备,并在甘肃省景电灌区进行了应用和验证.结果表明:渠道闸门一体化测控系统实现了灌区流量数据自动监测、收集和计算分析,提高了计量精度;能够对数据进行存储、查询与展示,实现了数据的共享,形成了灌区水资源管理数据库;实现了渠道流量远程自动控制与调节,提高了管理水平和管理效率;实现了智能手机远程操作,提高了办公效率.灌区闸门测控一体化测控系统的实施减少了灌区现场维护的次数,降低了设备运行成本,极大地提高了灌区水资源管理效率.研究成果可为中国大型灌区水资源科学管理提供有力的技术支撑,对闸门量水测流技术进步进行了有益的探索.     

河套灌区渠系优化配水模型应用研究

优化渠系配水过程是缓解灌区水资源压力、实现农业高效节水的重要举措.以河套灌区总干渠、干渠两级渠系作为研究对象,将水流过渡平稳和渠道渗漏量最小作为优化目标,建立渠系优化配水模型,采用回溯搜索算法(BSA)、多目标粒子群算法(MOPSO)以及向量评估遗传算法(VEGA)进行求解.结果显示,BSA,MOPSO,VEGA这3种算法所求的配水时间分别为30.96,11.65,29.96 d; 3种算法所得的阀门开启时间点的偏态系数分别为-0.048,0.068,0.566,表明BSA和MOPSO更能保证灌溉水在渠道运输中的稳定性.考虑渠首水位季节性变化对灌区引水时间产生的限制作用,BSA和MOPSO分别更适用于渠首引水量较少、充足的情况.考虑配水时间的集中程度以及干渠的地理位置分布,BSA和MOPSO更有利于实施分区管理措施.     

大型灌溉管网配压式进排气阀排气特性

针对大型灌溉管网中气液相间工况下现有进排气阀无法连续排气的问题,结合配压原理,提出了一种新型配压式进排气阀结构设计方案,阐述了其结构组成和工作原理;采用数值模拟分析与物理模型试验相结合的方法对不同阀瓣开度、不同排气压差条件下阀门的排气过程及排气量进行了研究,探明了阀瓣开度和排气压差对主阀腔体内部气流流态以及阀门排气量的影响,对比实测值与数模结果偏差为0.08%~6.43%,验证了分析方法的合理性;试验测得了DN50新型进排气阀各压差工况的最大排气量,结果显示,其排气量分别高于相关行业标准中规定的该尺寸进排气阀在排气压差为0.035 MPa和0.070 MPa时应达到的排气量要求达27.31%和21.71%,排气性能良好.     

Simulation of automatic control of an irrigation canal

Improved water management and efficient investment in the modernization of irrigation schemes are essential measures in many countries to satisfy the increasing demand for water. Automatic control of the main canals is one method for increasing the efficiency and flexibility of irrigation systems. In 2005, one canal in the irrigation scheme ‘Sector B-XII del Bajo Guadalquivir’ was monitored. This canal is representative of irrigation schemes in Southern Spain; it is divided into four pools and supplies an area of 5154 ha. Ultrasonic sensors and pressure transducers were used to record the gate opening and water levels at the upstream and downstream ends of each canal pool. Using the recorded data and the SIC (Simulation of Irrigation Canals) hydraulic model, two canal control options (local upstream control and distant downstream control) were evaluated using a PI (Proportional-Integral) control algorithm. First, the SIC model was calibrated and validated under steady-state conditions. Then the proportional and integral gains of the PI algorithm were calibrated. The controllers were tested using theoretical demand changes (constant outflow followed by a sudden demand increase or decrease) and real demand changes generated on the basis of a spatially distributed crop water balance that included a number of sources of variability (random and not random) in the determination of field irrigation timing and depth. The results obtained show that only the distant downstream controller was able to adjust quickly and automatically the canal dynamics to the varying water demands; it achieved this efficiently and with few spills at the canal tail, even when there were sudden and significant flow variations.     

Flexibility analysis of irrigation outlet structures using simulation of irrigation canal hydrodynamic model

The Upper Swat Canal (USC) System became operational in 1917–1918 in North West Frontier Province (NWFP) of Pakistan. The rehabilitation and modernization of the USC was undertaken with a view to overcoming the shortage of water supplies for irrigation. The water allowance was enhanced from 0.39 to 0.77 Ls⁻¹ ha⁻¹ in the study area. Recently, the operation and management of a secondary canal or ‘distributary’ was transferred to the Farmers Organization (FO). This distributary named ‘Chowki’ offtakes from the Maira Branch of the USC. The cultivable command area (CCA) of this distributary is 4,306 ha and it serves 1,485 beneficiaries. A management committee on Chowki Distributary was formed in 2003. This distributary consists of one main and two minor channels having twenty-eight direct outlets. The Simulation of Irrigation Canal (SIC) hydrodynamic model was used to evaluate the flexibility of Chowki Distributary. The model was calibrated at 100, 80 and 70% of the design discharge (Q _d) and it was validated at 90, 85 and 60% of the design discharge. The observed and simulated water levels were in close agreement with each other for the calibration and validation periods. The statistical analysis and paired t-test indicate that the model results are not statistically different from the measured values at 1% significance level. The simulated results of the SIC model were applied to studying flexibility of the outlet structures along the Chowki Distributary. The flexibility analysis demonstrates that poor performance is inbuilt into the system due to inadequate control over the accuracy of the crest setting during the construction of the outlets.     

井灌工程优化规划方法的研究

以平原灌区旱、涝、碱综合治理为前提,以控制地下水位等为约束条件,进行灌溉水资源供需平衡计算;用供需平衡计算确定的最大开采量作为各种布井方案的标准,计算各种布井方案的投资、运行管理费用和能耗;进行各种井灌工程方案的优选。     

A model for equitable distribution of canal water

The equitable distribution of canal water is imperative to ensure social justice as well as crop productivity. In north-west India and Pakistan, water from the tertiary canal (watercourse) is distributed to the farmers through a rotational system of irrigation. In this system the duration of supply to each farmer is in proportion to his holding in the outlet (watercourse) command, without considering the seepage loss. The rate of seepage loss increases with increase in length of watercourse from head to tail. Thus, the farmers in the lower reaches get much less water per unit area than the farmers in the upper reaches. The farmers must be compensated for the seepage loss. Therefore, a model was developed to ensure equitable distribution of water to the farmers located on a watercourse in proportion to their land holdings giving due compensation for the seepage loss. The model is based on the assumption that soil throughout the length of flow is homogeneous and loss through evaporation is negligible. The model developed ensures an equitable distribution of water to the farmers according to their land holdings. A comparison of existing and revised time allocation reveals that the farmers located in the upper reaches were getting more time (up to 12.2 min per unit area), while the farmers located in the lower reaches have been getting less time (up to 28.1 min per unit area). The existing allocation of time of 0.75 h per unit area to all the farmers according to the old rules was revised to 0.546–1.219 h per unit area from head to tail. The conclusions drawn suggest that the strategy developed here should be adopted elsewhere in the existing system of irrigation for equitable distribution of canal water. Received: 21 December 1999     

重力给水输水管路优化设计

在分析影响重力输水管渠设计的主要因素基础上，以输水管渠系统投资最小为目标函数，建立了优化设计的数学模型。并推导出计算公式，应用这一公式，确定地压管渠与有压管道最优长度和有压管道最优管径。     

基于数值模拟的“适变断面”衬砌渠道抗冻胀机理探讨

能适应渠基冻胀变形的衬砌渠道简称“适变断面”渠道。为了探明其抗冻胀机理及削减冻胀效果,应用ADINA软件对混凝土衬砌“适变断面”渠道冻胀进行数值模拟,计算渠道冻胀的温度场、变形场和应力场,研究衬砌板应力和变形规律,并与弧形坡脚梯形渠道比较分析表明：“适变断面”渠道能降低最大法向冻胀量55.11%、最大法向冻胀力51.65%、最大切向冻结力56.85%;通过冻胀量均方差及冻胀力分析比较,“适变断面”使渠道受力状态得到显著改善,冻胀变形分布更加均匀;衬砌板法向错位值总计1.3 cm,纵向伸缩缝周向压缩值总计为9.7 cm,揭示了“适变断面”渠道利用宽纵缝既能释放衬砌板法向冻胀变位,又能吸收周向冻胀变位,从而适应渠基冻胀变形减轻冻害的抗冻胀机理。最后通过模拟计算了“适变断面”渠道冻胀量均方差对边坡系数的敏感性,指出边坡系数i约为1∶1.7～1∶1.4时,“适变断面”渠道抗冻胀效果很显著,为“适变断面”渠道的推广及优化设计提供了参考。     

Bonding of soil and of sediment cleaned from channels by cement into blocks for lining irrigation channels

Water diverted from rivers to canals and then to fields brings along a heavy sediment load. According to estimates, the elevation of irrigated fields in the Indus Basin has increased up to 8 cm due to deposition of sediment from irrigation water. The deposition of sediment in the canals, distributaries and watercourses is a common concern. Each year during the winter, the canals are closed for desilting the conveyance system. Sediment deposited in the farmer-managed watercourses is piled along the watercourse banks, which takes fertile land out of production. This study was conducted to evaluate the possibilities of preparing cement blocks with soils and with sediments removed from the watercourses and using them in low cost linings to decrease losses from watercourses. Soil–cement and sediment–cement blocks were prepared, and tested for strength, durability and ability to reduce losses from watercourses. Compositions of the soil and of the sediments removed from the channels were determined. Blocks mortared into walls lining the sides of these channels reduced losses to less than 20% of losses in unlined old channels. Plastering the inside of these walls reduced water losses to less than 1% of the losses occurring in old unlined channels. Sediment–cement blocks were easier to make and they develop greater strength than soil–cement blocks. Cost of channel lining, using these blocks, appears to be about 2/3 of costs using fired brick masonry.     

Low energy consumption seasonal calendar for sectoring operation in pressurized irrigation networks

Pressurized irrigation networks and organized on-demand are usually constrained by the high amounts of energy required for their operation. In this line, sectoring, where farmers are organized in turns, is one of the most efficient measures to reduce their energy consumption. In this work, a methodology for optimal sectoring is developed. Initially it groups similar hydrants in homogeneous groups according to the distance to the pumping station and their elevation, using cluster analysis techniques and certain dimensionless coordinates. Second, an algorithm based on the EPANET engine is implemented to search for the best monthly sectoring strategy that accomplish supplying the actual irrigation demand under minimum energy consumption conditions. This methodology is applied to two Spanish irrigation districts (Fuente Palmera and El Villar). Results showed that organizing the networks in sectors, annual energy savings of 8 and 5% were achieved for Fuente Palmera and El Villar when the theoretic irrigation needs were considered. However, these savings rose up to 27 and 9%, respectively when the local practices, deficit irrigation, were taken into account. Thus, they confirm that water and energy efficiency cannot be optimized independently and need to be considered together.     

Impacts of concrete lining of irrigation canals on availability of water for domestic use in southern Sri Lanka

Irrigation schemes have contributed to the availability of water not only for agriculture but also for domestic use by rural households. In the Uda Walawe irrigation scheme in southern Sri Lanka, irrigation canals are being lined with concrete to save water, meant to enable extension of the irrigated area. The effects of lining on the availability of water for multiple uses were investigated by field measurements of water levels and by an inventory of the perceptions of changed water availability by the population through focus group discussions. From the measurements it was determined that canal seepage provides an important contribution to groundwater recharge. It was estimated that after concrete lining the annual groundwater recharge in the irrigated areas will be reduced by approximately 50%. This saves a substantial amount of water that can be used to extend the irrigation area so more people can benefit from the available irrigation water. However, in the currently irrigated areas lining will have negative impacts by lowering groundwater levels due to a reduction in seepage from canals. This seepage contributes to the recharge of shallow wells used by the population to obtain water for drinking and cooking. The perception of the population was that enough water remains for domestic use. Other changes, such as reduced yields from home gardens were considered to be more important. Despite these negative impacts the expected positive impacts in the extension area justify, from a social equity point of view, concrete lining as a measure to redistribute the available water over the Uda Walawe area.