A Numerical Simulation Model for Conjunctive Water Use in Basin Irrigated Canal Command Areas

Basin irrigation is a common practice for growing water intensive crops like paddy. Irrigation water, when supplied through a network of canal, is often found to be inadequate to meet the crop water requirement uniformly throughout the irrigated command area. The most deprived are the cultivators of the lower end of the command, who resort to supplementing the crop water requirement by extractions from the ground. This practice is noticeable in irrigation system without a proper canal water distribution schedule and often result in water logging in the upper command regions contrasted with excessively depleted groundwater table in the lower commands. The present contribution attempts to model the conjunctive water use of such a canal irrigated command using physically based numerical sub-models for simulating surface flow, groundwater flow and the interlinking process of moisture movement through the unsaturated zone for a given quantum of supplied water and crop water demand. Individual models are validated to demonstrate their applicability in an integrated framework. Various plausible conjunctive water use scenarios are tested on a hypothetical command area practising basin irrigation to identify the best possible water distribution strategy under given constraints.     

Water resources utilization in an irrigation project in India

Quantitative information on the adequacy of current operating procedures and available water resources in a typical major irrigation project in India (the Mahi Right Bank Canal project in Gujarat, India) is provided by comparing monthly and seasonal irrigation demands with canal releases and groundwater draught over a four‐year period. A strategy based on water conservation and the use of groundwater in the monsoon season for the full exploitation of reservoir potential in the subsequent seasons is proposed.     

Seepage losses from canal irrigation schemes

The effects of surface and subsurface conditions on the recharge of leaky aquifers by seepage from irrigation canals are examined. Physical and geological data from the Mahi Right Bank Canal command area in Gujarat, India, are used. The implications for conjunctive use of canal water and groundwater in the project area are discussed.     

宁夏平罗县井渠结合灌区地下水盐运移规律研究

以综合治理井渠结合灌区土壤盐碱化为目标,针对宁夏平罗县井渠结合灌区下游灌水难、排水难和盐碱化严重等问题,采用渠灌井排、井沟联合使用等措施,对作物进行适量和适时灌溉,充分利用地下水资源,并监测井渠结合灌溉条件下田间土壤含盐量、地下水矿化度和水位埋深的变化情况,分析地下水埋深和矿化度对土壤含盐量的影响。结果表明:井渠结合灌溉对降低地下水位效果显著。以黄河水为主要灌溉水源的宁夏银北自流灌区,地下水矿化度变化幅度较小;灌溉后的土壤表层含盐量骤降,0~40 cm土层的盐分变化较大;土壤盐分与地下水矿化度具有较强的线性正相关性,与地下水埋深呈负相关。研究成果对干旱半干旱区灌区水资源优化配置、盐碱地改良具有参考价值。     

Assessing Options to Increase Water Productivity in Irrigated River Basins Using Remote Sensing and Modelling Tools

In regions where water is more scarce than land, the water productivity concept (e.g. crop yield per unit of water utilized) provides a useful framework to analyse crop production increase or water savings in irrigated agriculture. Generic crop and soil models were applied at field and regional scale, together with geographical and satellite data to analyse water productivity in Sirsa District (India). In this district certain parts show a serious decline in groundwater levels and water shortage, while other parts experience a serious rise of groundwater levels, causing waterlogging and salinization. The regional analysis showed a large spatial variability of water productivity, net groundwater recharge and salinization. Scenario analysis showed that improved crop husbandry, reallocation of canal water from fresh to saline groundwater areas and reduction of seepage losses in saline groundwater areas are effective measures to increase the overall water productivity and to attain sustainable irrigation in Sirsa District.     

Groundwater Exploitation and Its Impact on the Environment in the North China Plain

Abstract

The North China Plain (NCP) is one of China's most important social, economic, and agricultural regions. Currently, the Plain has 17,950 thousand ha of cultivated land, 71.1 percent of which is irrigated, consuming more than 70 percent of the total water supply. Increasing water demands associated with rapid urban and industrial development and expansion of irrigated land have led to overexploitation of both surface and the ratio of groundwater resources, particularly north of the Yellow River. In 1993, the ratio of groundwater exploitation to recharge in many parts of the NCP exceeded 1.0; in some areas, the ratio exceeded 1.5. Consequently, about 1.06 million ha of water-short irrigated areas in the NCP also have poor water quality. Persistent groundwater overexploitation in the northern parts of the NCP has resulted in water-level declines in both shallow and deep aquifers. According to data from 600 shallow groundwater observation wells in the Hebei Plain, the average depth to water increased from 7.23 m in 1983 to 11.52 m in 1993, indicating an average water-table decline of 0.425 m/year. Water table declines are not uniformly distributed throughout the area. Depletion rates are generally greatest beneath cities and intensively groundwater-irrigated areas. Water-table declines have also varied over time. With the continued decline of groundwater levels, large depression cones have formed both in unconfined and confined aquifers beneath the Hebei Plain. Groundwater depletion in the NCP has severely impacted the environment. Large tracts of land that overlie cones of depression have subsided, seawater has intruded into previously freshwater aquifers in coastal plains, and ground-water quality has deteriorated due to salinization, seawater intrusion, and untreated urban and industrial wastewater discharge. In order to balance groundwater exploitation with recharge, the major remedial measures suggested are to strengthen groundwater management, to raise water use efficiency, to adjust the water-consumed structure, and to increase water supply     

Positive externalities of irrigation from the Sardar Sarovar Project for farm production and domestic water supply

A detailed study was conducted in six districts of Gujarat, India, in gravity- and lift-irrigated commands of the Sardar Sarovar Project to assess the direct and indirect benefits of canal irrigation. Benefits such as savings in the cost of energy used to pump groundwater for irrigation, reduction in well failures, and increased income of well irrigators from farming (crops and dairy) were remarkable. Groundwater augmented by recharge from gravity irrigation resulted in large economic returns to the well irrigators in the command areas and reduced the cost of domestic water supply in villages and towns (through improved yield of agro-wells and drinking-water wells, respectively). Canal irrigation also raised wages for workers, through enhanced agricultural labour demand along with appreciation of land markets.     

节水兴源是解决运城地区灌溉缺水的根本出路

运城地区水资源可利用量８ ．４ 亿ｍ ３ ，其中地下水可开采量６ ．１ 亿ｍ ３ ，目前年开采量７ ．５ 亿ｍ３ ，超采１ ．４ 亿ｍ ３ 。２０００ 年全区缺水１１ ．７８ 亿ｍ ３ ，其中主要是灌溉缺水。解决缺水的根本出路在于开源与节流并举。节水工作范围广、投资大，应首先改变旧的灌溉习惯，推行沟畦灌溉。渠道防渗重点抓全面配套，提高水利用系数。田面节水新技术应先搞实验，再逐步推广。开源之路在于兴建黄河水源工程，近期先建浪店水源工程，长远方案是实施禹门口引水，远近结合，在保证灌溉用水同时向城市及工业供水。     

Groundwater overdraft reduction through agricultural energy policy: insights from India and Mexico

Rapid expansion of groundwater irrigation has transformed the rural economy in regions around the world, leading to significant increases in agricultural productivity and rising incomes. Farmer investment in wells and pumps has driven this expansion on the demand side; however, the supply of cheap agricultural energy—usually electrical power—is a critical though often overlooked driver of the groundwater boom. One serious outcome in numerous regions around the world has been groundwater overdraft; where pumping exceeds aquifer recharge, water tables have declined and water quality has deteriorated. India and Mexico are two of the largest users of groundwater in the world and both face critical overdraft challenges. The two countries are compared, given that electrical energy supply and pricing are primary driving forces behind groundwater pumping for irrigation in India and Mexico alike. Both countries have attempted regulatory measures to reduce groundwater overdraft. However, with low energy costs and readily available connections, there are few financial disincentives for farmers to limit pumping. The linkages between energy and irrigation are reviewed, comparing and contrasting India and Mexico. Examples of legal, regulatory and participatory approaches to groundwater management are assessed. Finally, the implications of linking electrical power pricing and supply with ongoing groundwater regulation efforts in both countries are explored.     

Intensive groundwater use: a silent revolution that cannot be ignored.

Over the last decades, agriculture in arid and semi-arid countries has experienced a true "silent revolution" of intensive groundwater use. Millions of independent farmers worldwide have chosen to become increasingly dependent on the reliability of groundwater resources, and as a result their countries have reaped abundant social and economic benefits. Data from several countries shows that groundwater irrigation presents a much greater efficiency, than surface water irrigation systems, thus contributing to fulfil the motto of "more crops and jobs per drop". If this situation is confirmed globally, the usual world water visions have to be reviewed. However, the "silent revolution" has been carried out with scarce control on the part of governmental water agencies, and thus a series of unwanted effects have developed in certain places. While these by no means justify the pervasive "hydromyths" and obsolete paradigms that voice the frailty of groundwater, appropriate management of groundwater resources remains a worldwide challenge. This paper provides an overview of these issues, and concludes with the necessity there is to educate all levels of society on the importance of groundwater and to create bottom-up user associations to manage aquifers as common pool resources.     

河北省地下水超采综合治理农业措施 压采效果与技术经济性分析

我国在河北开展地下水超采综合治理试点,为了掌握各项措施的实际压采效果与技术经济性,采用现场抽 水灌溉试验、入户走访调查等手段,通过治理区地块与非治理区地块治理前后地下水灌溉用水量的对比,分析总 结各项措施的压采效果与实施经验,并通过治理措施的投入成本与压采效果对比,研究剖析各项治理措施的技术 经济性。研究结果表明：治理措施较好地发挥了减少地下水开采的作用,种植结构调整措施和水源置换措施减少 地下水开采量超过 2?400?m3/hm2;高效节水灌溉措施、水源置换措施实施初期所需建设投资较大,导致单位压采量 所需投资较高,农业种植结构调整类措施实施初期的投资相对较低,但后期单位压采量所需投资逐年增加。从压 采效果、技术经济性、水源条件与超采类型及程度 4 个方面,对不同地区选择治理措施给出建议,为今后地下水 超采治理提供参考。     

Rational Pricing of Water as an Instrument of Improving Water Use Efficiency in the Agricultural Sector: A Case Study in Gujarat,India

The agricultural sector in India accounts for over 85% of the total water used for various purposes in the country. However, the efficiency of water use in agriculture is very low, approximately 40% for surface irrigation and 60% for groundwater irrigation. Part of the reason for the low efficiency is the highly subsidized price of irrigation water that encourages the excessive application of water to crops. This paper is based on a case study conducted in the command area of a public irrigation canal in the state of Gujarat, India. It attempts to explore the role of the rational pricing of canal irrigation water in motivating farmers to use water judiciously and thereby enhance the water use efficiency in irrigated agriculture. The paper contends that farmers are sensitive to an increase in irrigation water charges, but unless the administered price is increased to the level that would prevail in a free market, it will not have its intended effect on irrigators.     

宁夏引黄灌区渠道砌护对生态环境的影响分析

随着灌区节水工程的实施，渠道的渗漏水量减少，对地下水的补给水量也减少，针对是否会产生自然植被衰竭、湿地萎缩、生态退化等一系列生态环境问题，本文通过大量的试验观测数据，从生态系统的基本功能、生态与地下水位、渠道渗漏水量、地下水动态变化等角度，分析探讨了渠道砌护节水对自然植被、湖泊湿地、土壤盐溃化等方面的影响，为灌区渠道砌护节水工程的进一步实施提供决策依据。     

南水北调东线一期工程对梁济运河段地下水影响研究

南水北调东线一期工程建成后,输水期间抬高沿线河水位,河水与地下水补排关系必将发生变化,对河道两侧地下水水位和水量产生一定的影响。根据梁济运河段的地貌、地质和水文地质条件,应用地下水非稳定运动数学模型,研究河渠渗漏对地下水水位的变化,从而分析预测影响区盐渍化情况。梁济运河在南水北调通水后,减小了两岸地下水埋深,影响范围约在500～1000m,地下水埋深减小为1.0～3.0m,地下水埋深均大于适宜临界埋深,但还存在盐渍化的潜在可能性。     

基于神经网络的灌区退水量动态模型

采用相关分析的方法确定了灌区退水量的主要影响因素，将神经网络的在线学习功能与数据库技术相结合，建立了灌区退水量动态模型，实现了模型的在线学习，以动态的模型反映灌区退水系统的动态变化，保证了退水量模型使用的长期有效性。与实测资料对比表明，模型能够较好的模拟灌区退水系统的变化，利用灌区渠首的引水量、降水量和地下水埋深资料能够较准确的对灌区的退水量进行预测。     

The Pros and Cons of Encouraging Shallow Groundwater Use through Controlled Drainage in a Salt-Impacted Irrigation Area

Encouraging shallow groundwater use through water table management or controlled drainage in irrigated areas can relief crop water stress under water shortage condition. But substituting fresh irrigation water with saline groundwater may speed up salinity buildup in the crop root zone, and consequently increase water use for salt leaching. With a proposed analytical model, this paper presents a case study demonstrating the effect of encouraging shallow groundwater use through controlled drainage on salt and water management in a semi-arid irrigation area in northwestern China. Based on the average rainfall condition, the model assumes that salt accumulates in the crop root zone due to irrigation and shallow groundwater use; till the average soil salinity reaches the crop tolerance level, leaching irrigation is performed and the drainage outlet is lowered to discharge the salt-laden leaching water. For the relatively salt tolerant crop–cotton in the study area, the predicted leaching cycle was as long as 751 days using the fresh water (with salinity of 0.5 g/L) irrigation only; it was shortened to 268 days when the water table depth was controlled at 2 m and 23% of the crop water requirement was contributed from the saline groundwater (with salinity of 4.43 g/L). The predicted leaching cycle was 140 days when the water table depth was controlled at 1.5 m and groundwater contribution was 41% of the crop water requirement; it was shortened to 119 days when the water table depth was controlled at 1.2 m and the groundwater contribution was 67% of the crop water requirements. So the benefit from encouraged shallow groundwater use through controlled drainage is obtained at the expense of shortened leaching cycle; but the shallow groundwater use by crops consists of a significant portion of crop water requirements, and the leaching cycle remains long enough to provide a time window for scheduled leaching in the off season of irrigation. Weighing the pros and cons of the encouraged shallow groundwater use may help plan irrigation and drainage practices to achieve higher water use efficiency in saline agricultural areas.     

近30年来白洋淀流域平原区地下水位动态变化及原因分析

白洋淀流域平原区是华北平原的农业高产区域,灌溉用水主要靠开采地下水。近几十年来,白洋淀地下水位下降严重,在1974年-2007年。该区域地下水埋深以平均每年0．51m的速率下降,1980年以后下降速率明显加速,在2000年-2007年年均下降速率达到了0．99m。引起地下水位持续下降的主要原因是地下水超采严重,且用水高峰期遭遇枯水期,尤其体现在1980年以后年降水偏枯．同时社会经济用水量维持在高峰阶段。低效的农业用水模式及地下水超采已经严重制约了白洋淀地区水资源的可持续利用。     

开采条件下阜阳市深层孔隙水资源分析

阜阳市由于大量集中开采深层孔隙水导致了区域内地下水位不断下降,从而引发了一系列的环境地质问题,如地下水降落漏斗、地面沉降等。为了更合理地利用深层孔隙水以及开展地面沉降防治方面的工作,根据阜阳市1989~2008年20 a均衡期内的地下水开采量以及地面沉降的统计数据,利用水量均衡法对开采条件下深层孔隙水的水资源量进行了计算。计算结果表明:在20 a的均衡期内,开采的深层孔隙水为7.5×10~8m~3,黏性土压密释水量(Q_压)为3.88×10~8m~3,其占比为51.73%,可以看出这是产生地面沉降的直接原因;越流量(Q_越)为3.18×10~8m~3,其占比为42.40%;弹性释水量(Q_弹)为0.44×10~8m~3,占比为5.87%。与多年开采总量8.78×10~8m~3相比,差值为1.28×10~8m~3,误差为14.58%(其误差应为侧向补给量所导致)。根据计算结果,提出了应制定控制地面沉降等地质环境方面问题的管控措施,合理激发浅层地下水对深层地下水的越流补给;同时应增加越流量在地下水开采资源量中的所占份额。     

陡河流域地表水与地下水转化关系

通过对陡河流域地表水-地下水水样的氢氧同位素分布特征进行分析,发现研究区河岸带第Ⅰ含水层除了受大气降水、灌溉回归水入渗补给外,还接受河水早期的渗漏补给,第Ⅱ含水层对第Ⅲ含水层有越流补给,第Ⅱ含水层同时也受大气降水和灌溉回归水的影响,而远离河岸带的第Ⅳ含水层与上覆各含水层稳定同位素组成显著不同,河岸带水库附近的第Ⅳ含水层可能受地表水库渗漏影响。河岸带地下水与地表水水力联系的变迁严格受河岸带地下水水位变化控制,如景庄子剖面的地下水埋深为5m,雨季时河水补给地下水,旱季时地下水补给河水,而靠近地下水漏斗中心的越河乡剖面地下水水位埋深达25m,其常年受地表水补给。     

Simulation-Optimization Modeling for Conjunctive Use Management under Hydrological Uncertainty

The canal water supply, which is the only source of irrigation, in the rice-dominated cropping system of the Hirakud canal command (eastern India) is able to meet only 54 % of the irrigation demand at 90 % probability of exceedance. Hence, considering groundwater as the supplemental source of irrigation, conjunctive use management study by combined simulation-optimization modelling was undertaken in order to predict the maximum permissible groundwater pumpage from the command area. Further, optimal land and water resources allocation model was developed to determine the optimal cropping pattern for maximizing net annual return. The modelling results suggested that 2.0 and 2.3 million m³ of groundwater can be pumped from the bottom aquifer during monsoon and non-monsoon seasons, respectively, at 90 % probability of exceedance of rainfall and canal water availability (PERC). Optimal cropping patterns and pumping strategies can lead to about 51.3–12.5 % increase in net annual return from the area at 10–90 % PERC. The sensitivity analysis of the model indicates that the variation in the market price of crops has very high influence on the optimal solution followed by the cost of cultivation and cultivable area. Finally, different future scenarios of land and water use were formulated for the command area. The adoption of optimal cropping patterns and optimal pumping strategies is strongly recommended for sustainable management of available land and water resources of the canal command under hydrological uncertainties.