浅析渠道防渗工程中的几个问题

渠道防渗是输水和灌溉工程中节水的关键内容之一。本文分析了渠道防渗材料、防渗结构和防冻方面出现的问题，并提出了解决途径和措施。     

渠道防渗节水效果浅析

配合以节水为中心的大型灌区续建配套与节水改造,对奎屯灌区输水渠道进行了防渗处理,通过计算渠道防渗前后渠道水利用系数,并进行比较,认为渠道防渗节水效果明显,渠道防渗带来的是综合效益。     

渠道防渗工程技术

渠系输水损失占渠首总引水量的50％,渠道防渗是我国目前应用最广泛的节水工程技术。本文从渠道的断面形式、防渗结构及材料等方面作了探讨,并介绍了特种土基渠道对渠床的处理办法。     

混凝土防渗渠道施工技术

混凝土防渗渠道具有防渗好、糙率小、允许流速大、强度高及使用年限久等优点,可适应各种条件。而搞好施工,确保工程质量才能正常发挥其功能,延长其使用年限。l施H准备在工程开工前首先要搞好各方面的协调工作。一是规划设计,根据当地的地形、地貌、地质以及耕作习惯等搞好综合规划,确定最优方案、设计最佳断面;二是资金筹集,确保工程所需经费;三是施工队伍,有一流的队伍,才能做出一流的工程;四是施工材料,对工程所需材料如水泥、黄砂、石子等要准备充足货源,合理调配,以保证工程迸度、资金合理利用;五是施工场地做到四通一…     

渠道防渗工程问题的探讨

渠道防渗具有节水、节地、省工、省时等许多优点。自1990年以来,宿豫县渠道防渗工程建设得到飞速发展,到目前为止,已建成防渗渠道69．3km,受益农田面积约0．47万hm‘。1996年,宿豫县被国家列为全国300个节水增产重点县之一,渠道防渗工程将得到更快更好的建设。下面结合以     

水利工程渠道防渗技术探究

水利工程的渠道防渗可以提高水资源的利用率,可以促进农业生产的发展,可以减少渠道渗漏,扩大灌溉面积。此外,还可以防止次生盐渍化的发生,改善生态环境,调控地下水位,对沼泽地与盐碱地进行改良。渠道防渗同时还具有节约用地面积、降低渠道管理和维护费用等多方面益处。因此,水利工程渠道防渗技术具有大力推广的意义。     

渠道膜料防渗的有关技术问题

渠道膜料防渗在我国广泛应用,并已取得丰富的经验和显著的社会效益。文章根据调查了解和收集到的有关资料,对渠道膜料防渗的有关技术问题提出了探讨性意见,供在设计和施工膜料防渗渠道时参考。     

渠道防渗抗冻新材料与新技术

渠道防渗技术是目前中国应用最广泛的节水工程技术措施。本文论述了渠道防渗技术发展现状，介绍了渠道防渗抗冻新材料与新技术，提出目前渠道防渗技术由单一防渗材料向复合防渗材料，由单一防渗结构形式向复合防渗结构形式发展，指出必须加强跨学科研究和跨行业合作，加大渠道防渗抗冻新材料与新技术的研究和推广应用力度。     

Comparative evaluation of canal seepage investigation techniques

Various methods are used to estimate the canal seepage rate such as empirical formulae, analytical or analogue studies and the direct seepage measurement techniques, i.e. seepage meters, ponding tests and inflow–outflow tests. Considering significance of physical measurement techniques both ponding and inflow–outflow methods were used to evaluate the seepage losses. These methods have their merits, demerits and limitations which are well understood. However, while interpreting seepage loss evaluations, there can be independent random errors, like the fluctuations in flow conditions affecting different current meter positions, and systematic errors, like the use of different instruments or different methods to measure different terms in the balance. These errors have to be distinguished.The data from various studies in the region have been reviewed and analyzed. A statistical analysis of a number of replications of ponding and inflow–outflow test data of the seepage estimation work on various canals under the Fordwah Eastern Sadiqia (South) project, Bahawalnagar, Pakistan has been done to show the accuracy of results achieved through both the methods. It has been shown that the ponding method is more accurate than the inflow–outflow method as variability of various statistical parameters from the ponding tests is comparatively less. It is proved that inflow–outflow tests should not be used for seepage investigations where seepage rates are fairly small and there is no possibility to use sufficiently long reaches.     

模拟退火粒子群优化投影寻踪的渠道防渗模式评价

为了对渠道防渗工程的方案进行优选,采用模拟退火粒子群优化投影寻踪方法对渠道防渗模式进行优化评价.优化粒子群算法,使其在退火过程中接受优解,且还以一定的概率接受差解.同时利用模拟退火粒子群算法在搜索过程中具有概率突跳的能力,有效地避免搜索过程陷入局部极小解,提高了算法的收敛速度和精度.将该模拟退火粒子群算法与投影寻踪结合,建立了模拟退火粒子群优化投影寻踪模型,将该模型应用到灌区渠道防渗模式优化评价中,选取10个指标作为评判因子,提出适合该地区的干渠渠道防渗工程优化模式,其优劣排序依次为方案Ⅳ、方案Ⅱ、方案Ⅲ、方案Ⅴ、方案Ⅰ.研究表明模拟退火粒子群优化投影寻踪的评价模型对灌区渠道防渗模式进行综合评价是切实可行的,模拟退火粒子群优化投影寻踪的评价方法在解决实际问题中展示了其优越性,并取得了良好的应用效果.     

苏北平原区渠道防渗工程评价和方案优选方法

为了科学评估各渠道防渗方案,根据工程成本、生态环境效应和施工工艺等3个方面,构建了渠道防渗工程评价指标体系.以江苏省宿迁市船行灌区防渗渠道为例,借助超级决策软件,引入模糊集理论建立多属性决策模型,采用网络分析法和熵权模糊方法,结合实际情况对灌区4种渠道防渗方案进行了综合评价,并确定不同渠道防渗的最佳方案以对工程的方案进行优选.结果表明:一级指标体系中的施工工艺所占的权重最大,工程成本居次,生态环境效益的最低,各不同渠道防渗方案的优劣程度差异明显,最优的方案1其相对接近度值为0.65,方案2和3其次,方案4的相对接近度值最低,为0.37.评估结果较好地反映了平原区渠道防渗的特点并符合当地渠道的实际情况,可为苏北平原灌区的防渗工程的发展提供科学依据.     

Using an ADCP to determine canal seepage loss in an irrigation district

Seepage from earthen irrigation canals represents substantial water loss in irrigation districts. Historically, the determination of canal seepage was accomplished using the inflow-outflow method with propeller and electromagnetic type flow meters. This method was difficult, time consuming, and limited by measurement device accuracy. In recent years, advances in technology have lead to the widespread use of Acoustic Doppler Current Profilers (ADCP) for discharge measurements in streams and rivers. Even though ADCP use has become widespread for stream discharges, studies to determine canal seepage using this new technology are limited. Using an ADCP, extensive field measurements were conducted in the Middle Rio Grande Conservancy District. This paper describes the ADCP measurement protocol used to measure irrigation canal seepage and presents predictive equations for determining canal seepage based on flow rate and canal geometry.     

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.     

Inverse method for operational control of canal systems

A non-linear explicit inverse solution method for the operational control of remotely controlled canal systems is presented. The model accounts for canal seepage, turnout flows (point sink), control structures with steeply varying and/or discontinuous discharge characteristics. The governing unsteady flow equations are solved backward both in space and time. For each space interval, the use of finite difference approximations for the operational problem results in a system of two non-linear equations in two unknowns. These equations are solved using Newton's method. The method is extended to canal networks. The canal junctions are classified into three types. The controllability of flow for each type of canal junction and for the network as a whole are discussed. The model, though explicit, is found to be unconditionally stable. The model results are verified with the unsteady flow simulation model based on non- linear Preissmen's scheme. The applicability of the model to a canal system is demonstrated.     

Does genomics empower resource-poor farmers? Some critical questions and experiences

This article explores the possible impact of genomics on the relationship between resource-poor farmers and ‘formal’ agricultural research. It notes that regions of low-resource agriculture serve as reservoirs of genetic diversity and then outlines some ways in which advances in genomics are enabling agricultural researchers to make increased use of this kind of genetic material. The adoption of genomics-based tools by agricultural research programmes will, it suggests, increase the benefits they can obtain from initiatives that elicit germplasm selected by farmers. The interactions between these two processes are examined in two distinct (and contrasting) contexts: maize in China and rice in Vietnam. Both of these case studies confirm that indigenous genetic resources take on greater significance to research systems that are equipped with genomics-based tools. The paper concludes that the ability of resource-poor farmers to demand the provision of research services relevant to their situation may increase as the resources that they control take on greater value to agricultural research.