Review of water table depth planning for a multi objective water management system

In this paper, the concepts for planning and design of drainage depth will be reviewed in relation to the different requirements for maximizing crop production. The relationships of the drainage depth with other design parameters and their interdependency will be discussed. Reference will be made to the cost, cost/benefit ratio and economic returns of drainage systems with respect to the drainage depth. Some applications and practices in different countries will be highlighted.     

Discharge rates,salinities, and the performance of subsurface collector drains in Egypt

To evaluate the hydraulic performance of subsurface collector drains and to study the relationships between discharge rates, crop patterns, and the salinity of drainage water, subsurface drains were monitored in different parts of the Nile Delta and Valley.Actual discharges were much smaller than design discharges. Also, overpressure in the pipes occurred frequently, indicating too small a capacity in the design. From research in one pilot area, it was concluded that if construction methods and materials are not improved, the roughness factor in the design should be increased by 100% to allow sufficient capacity.The cultivation of rice increases discharges. Salinity of drainage water is higher in winter than in summer, and higher in the north of the Delta than in the south.     

Verification of impermeable barrier depth and effective radius for drain spacing using exact solution of the steady state flow to drains

The steady-state drainage equation ofHooghoudt (1940) has adrawback that tables for the determination of the so-calledequivalentlayer, d_e are needed. These calculations arecumbersome as d_e is dependenton the unknown spacing. Moreover, additional head islost due to theconvergence of stream lines towards the finite numberof perforations withinthe pipe wall. Therefore, corrections are required byreplacing the actualdrain radius by its effective radius. The designers inEgypt assume that thedepth of impermeable layer is infinity which resultsin an over estimationof drain spacing that will affect the ability of thedrainage system.Van der Molen and Wesseling (1991) have developed aseries solution toreplace the Hooghoudts approximation method for theequivalent depth by anexact solution. A comparison between this solution andthose of Lovell andYoungs (1984) and Hooghoudt (1940) showed that theexact solution proved tobe very accurate and efficient solution. The mainobjective of this study isto verify an accurate depth of the impermeable barrierand an effectiveradius of drain pipes which should be used in thedesign process using theexact solution.A field investigation was conducted in a study area of33,138 ha in theNorthern Delta of Egypt within Daqahliya Governorate.The results indicatethat a 5 m depth instead of infinity for theimpermeable layer in Nile Deltaand an effective radius of 90 mm should be used in thedesign process. Theuse of the exact solution for equivalent depth is acrucial issue especiallywith the high rate of on-going drainage projects inEgypt.     

河岸浸没预测及排水沟效果研究

针对浸没预测忽略上边界入渗补给和蒸发等问题的缺陷，利用Visual Modflow地下水模拟软件，建立了非稳定流数学模型，设定合理的边界条件，重点探讨了入渗系统和蒸发系统的确定方法和步骤。利用建立的数学模型，模拟计算浸没范围，并设置排水沟边界模拟排水效果。对多层地基，得出3.5m深排水沟可以将浸没范围控制在距堤脚100m范围内的结论。     

浅埋区地下水--土壤水资源动态过程及其调控

分析了冬小麦生长期地下水-地下水资源量动态过程和地下水、土壤水分变化特征.结果表明,在地下水浅埋区地下水对土壤水的补给为农田蒸散的重要的水分来源,现行的灌溉制度不考虑这一作用,过多的灌溉量不仅会消弱地下术对土壤水的补给,而且多余的土壤水分还会下渗补给地下水,造成水资源的无效损失和动力能源的损耗.为了提高作物水分利用效率,提出了相应的地下水-土壤水资源调控措施.     

The effect of salinity on water productivity of wheat under deficit irrigation above shallow groundwater

Saline groundwater is often found at shallow depth in irrigated areas of arid and semi-arid regions and is associated with problems of soil salinisation and land degradation. The conventional solution is to maintain a deeper water-table through provision of engineered drainage disposal systems, but the sustainability of such systems is disputed. This shallow groundwater should, however, be seen as a valuable resource, which can be utilised via capillary rise (i.e. sub-irrigation). In this way, it is possible to meet part of the crop water requirement, even where the groundwater is saline, thus decreasing the need for irrigation water and simultaneously alleviating the problem of disposing of saline drainage effluent. Management of conditions within the root zone can be achieved by means of a controlled drainage system.A series of lysimeter experiments have permitted a detailed investigation of capillary upward flow from a water-table controlled at shallow depth (1.0 m) under conditions of moderately high (5 mm/day) evaporative demand and with different levels of salinity. Experiments were conducted on a wheat crop grown in a sandy loam soil. Groundwater salinity was held at values from 2 to 8 dS/m while supplementary (deficit) irrigation was applied at the surface with salinity in the range 1-4 dS/m.Our experiments show that increased salinity decreased total water uptake by the crop, but in most treatments wheat still extracted 40% of its requirement from the groundwater, similar to the proportion reported for non-saline conditions. Yield depression was limited to 30% of maximum when the irrigation water was of relatively good quality (1 and 2 dS/m) even with saline groundwater (up to 6 dS/m). Crop water productivity (grain yield basis) was around 0.35 kg/m³ over a wide range of salinity conditions when calculated conventionally on the basis of total water use, but was generally above 1.0 kg/m³ if calculated on the basis of irrigation input only.     

农田不同排水措施地下排水效果模拟试验研究

在地下水位较高、地表易于形成积水的中国南方地区,通过农田排水措施可以及时排除多余地表积水,快速降低地下水位,以达到排涝降渍、协同调控的目的.文中基于室内砂槽试验,揭示暗管排水、明沟排水、不同反滤体高度的反滤体排水及改进暗管排水等措施的地下排水规律及效果.结果表明:将暗管周围土体置换为高渗透性土体介质的改进暗管排水可明显提高排水流量,当土体置换高度达2 cm时(对应于田间条件40 cm),其排水流量均高于相同埋深条件下的其他排水措施,达暗管排水的1.59~1.66倍;改进暗排在地表积水消失时仍保持较大的排水流量,可达相同埋深暗管流量的2倍以上,在积水层消失后,能迅速降低农田土壤水的渍害胁迫,将地下水位降低至暗管埋设高度;各种排水措施,在地表积水即将消失时,出现了流量与水头变化幅度较大的现象.相对于各种地下排水措施,改进暗管排水在除涝降渍中存在明显优势.研究结果可为涝渍灾害易发地区高效除涝降渍减灾工程设计和建设提供参考.     

暗管控制排水对棉田排水的影响

对几次较大规模降雨产生排水后排水量、排水氮素含量、地下水位等进行观测,结果发现暗管排水使得地表、地下排水量被重新分配,控制水位排水使地表排水量所占比例提高、而总排水量比常规排水减少36.4%～82.7%、地下排水峰值量较常规排水减少7.2%～85.4%。地表、地下排水硝氮质量浓度较低,一般低于4 mg/L;地表排水总氮质量浓度在2.3～11.5 mg/L之间,地下排水总氮质量浓度在0.6～9.1 mg/L之间。要减少氮素流失总量,减少排水量是关键。     

堤内地下水受河水位的影响规律及其排水研究

河水位对堤内地下水有重要的影响,且河水向二岸的侧渗常导致堤内排水困难,使农作物遭受渍害。针对汉江中下游典型的二元土壤结构,利用V isualM od flow建立地下水流数学模型,模拟分析堤内地下水位和沿程“向上补给”流量随河水位变化的规律。为了排水降压,将渗流模型简化,导出排水沟深度和间距的计算公式,并用数值法验证了该处理方法的正确性。研究成果可为河岸渍害的防控提供理论依据。     

土体冻胀与地下水关系的研究进展

地下水与冻胀之间的关系在各种工程的施工设计、冻害防治和农业灌溉中起着重要的作用。地下水位的高低直接影响着土体的冻胀。概述了近五十年来我国在这方面取得的成果。包括产生冻胀的地下水位临界深度，受地下水位影响的冻胀带的分布规律和冻胀性分类，冻胀与地下水位之间的定性定量关系以及他们之间的作用机理。今后的研究发展方向是加强冻胀机理的研究，建立健全冻胀预报模型的研究和对冻结过程中地下水位变化的研究。     

生态沟-湿地系统对稻田排水中氮素的去除效果

为研究灌排调控下生态沟-湿地系统对稻田排水中氮素的原位削减效果,探讨低碳氮比对于系统氮素去除效果的影响.依据大田试验观测资料,分析了控制灌排模式下生态沟-湿地系统水体中氮素质量浓度变化规律和碳氮比分布特征.结果表明,控制灌排模式下生态沟-湿地系统对稻田排水中氮素去除效果显著,施肥后排水中TN,NH4＋-N和NO3--N质量浓度出现峰值,在农沟拦蓄后质量浓度大幅下降,氮素平均去除率分别为63.9%,67.8%和83.2%.进入湿地再次净化后,氮素质量浓度进一步降低,平均去除率分别为47.7%,44.3%和82.0%.控制灌排模式下系统水体中有机质对水环境影响较小,水体碳氮比水平总体偏低.控制灌排模式下生态沟-湿地系统很好地实现了对氮素的原位削减,低碳氮比对于系统氮素去除效果的影响不大.     

外包滤料对暗管排水与土壤脱盐效果的影响

为了探究不同外包滤料条件下的暗管排水性能和土壤脱盐效果,基于室内试验研究成果,在田间设置4种暗管排水系统(各系统中暗管埋深均为80 cm,间距均为20 m),所用外包滤料分别为68 g/m²土工布(L)、砂滤料(S)、68 g/m²土工布+砂滤料(LS)和无外包滤料(W),以当地常规明沟排水(CK)作为对照,通过田间试验分析了春灌过程中各暗管系统的排水性能指标及土壤脱盐效率.结果表明:相比处理W,处理L,S和LS平均排水速率提升了7.44%,12.55%和15.75%,平均流量衰减度降低4.07%;处理S和LS累积排水量提高了5.11%和8.31%(P<0.05).各暗管处理春灌后平均土壤脱盐率均达47%以上,较CK提升显著,其中处理LS效果最优,为50.94%.综上,应优先选择处理LS作为河套灌区暗管排水系统外包滤料布设方案.该研究结果可为河套灌区暗管排盐技术的推广应用提供理论支撑和科学指导.     

基于SWAP模型的毛乌素沙地地下水埋深与天然植被关系研究

进行了基于SWAP模型模拟的毛乌素沙地不同水文年地下水埋深的预测研究。根据预测出的不同水文年的地下水埋深的动态变化,预测出试验区在该水文年的天然植被生长状况与地下水埋深的关系,即芦苇出现频率峰值所对应的地下水埋深为1.45 m;赖草出现频率峰值所对应的地下水埋深为1.90 m。并用2006年的实测资料进行了检验,得出SWAP模型可以用于推求该地区不同水文年条件下的天然植被生长状况。     

Verification of drainage design criteria in the Nile Delta,Egypt

A monitoring programme to verify the design criteria of subsurface drainage systems was conducted in a pilot area in the Nile Delta in Egypt. The programme, which covered a 9-year period, included the monitoring of the cropping pattern, crop yield, soil salinity, watertable, discharge and salinity of the drainage water and overpressure in the subsurface drainage system. The results showed that the yield of all crops (wheat, berseem, maize, rice and cotton) increased significantly after the installation of the subsurface drainage system. Optimum growing conditions for the combination of crops that are cultivated in rotation in the area required that the watertable midway between the drains had a average depth of 0.80 m. A corresponding drain discharge of 0.4 mm/d was sufficient to cope with the prevailing percolation losses of irrigation water and to maintain favourable soil-salinity levels. The additional natural drainage rate in the area was estimated at 0.5 mm/d. The most effective way to attain these favourable drainage conditions is to install drains at a depth between 1.20 to 1.40 m. For drain-pipe capacity the Manning equation can be used with a design rate of 1.2 mm/d, for collector drains this rate should be increased to 1.8 mm/d to compensate for the higher discharge rates from rice fields. These rates should be used in combination with a roughness coefficient (n) of 0.028 to take sedimentation and irregularities in the alignment into account. When this value of the roughness coefficient is used, no additional safety has to be incorporated in the other design factors (e.g. the design rate).     

暗管排水条件下微咸水灌溉对土壤盐分动态及夏玉米生长的影响

进行暗管排水条件下微咸水灌溉田间试验,设置3种暗管埋深,分别为80 cm(D1)、120 cm(D2)以及无暗管排水(D0),3种微咸水浓度,其电导率分别为0.78 dS/m(S1),3.75 dS/m(S2)和6.25 dS/m(S3),共9个处理,每个处理3组重复.试验结果表明:暗管排水措施可以有效排除微咸水灌溉过程中土壤中累积的盐分;在玉米全生育期内,暗管埋深D1条件下,3种浓度微咸水S1,S2和S3灌溉时根系土壤电导率分别下降了39.00%,31.56%和29.43%,暗管埋深D2条件下,根系土壤电导率则分别下降了31.91%,18.08%和7.44%;夏玉米干物质累积量、穗棒累积量和穗棒质量分配率及最终产量均随着微咸水浓度的升高而降低;在相同微咸水浓度下,不同暗管埋设条件下的夏玉米最终产量从大到小依次为D1,D2,D0;3种暗管埋设条件下的作物需水量从大到小依次为D0,D2,D1的规律;暗管埋深80 cm的处理(D1)下夏玉米水分利用效率最高,而未埋设暗管的处理(D0)水分利用效率最低;当暗管埋设条件一定时,夏玉米水分利用效率随微咸水浓度的升高呈逐渐降低的趋势.     

太阳能暗管排水对银北灌区油葵土壤环境及产量影响

针对土壤盐渍化严重影响了宁夏银北灌区土壤环境和作物产量的问题,通过太阳能暗管排水区和非暗管排水区对比试验方法,着重研究了2017和2018两年太阳能暗管长时间持续排水对土壤环境和油葵产量的影响。结果表明:太阳能暗管排水可以有效改善土壤环境,使两年的地下水平均埋深分别增加4.5%和6.4%,地下水平均矿化度分别降低7.9%和9.0%,两年土壤平均脱盐率分别为4.7%和8.2%,对表层土壤的脱盐效果最为明显。同时提高了油葵产量和水分生产效率,两年油葵产量分别提高13.8%和21.6%,灌溉水分生产效率分别增加13.3%和21.8%,作物水分生产效率分别增加16.4%和22.9%。综合试验结果和经济成本考虑,油葵生育期灌水2次、播前灌水1次、冬灌1次,生育期5-9月持续排水,这是适宜惠农当地太阳能暗管排水条件下油葵的灌排制度。     

新疆叶尔羌河平原绿洲洼地旱排作用的初步分析

通过对新疆叶尔羌河流域平原绿洲一个典型洼地水量平衡的观测和计算,分析了洼地在容泄绿洲排水、排盐方面的旱排作用及排水、排盐能力。提出在绿洲排水规划时,可将旱排（或内排水）作为一种重要的排水方式,选择合适的洼地作为主要的旱排规划区。     

水资源不均等分配及其影响分析以簸箕李灌区为例

以簸箕李灌区为例,分析了该灌区水资源不均等分配及其所带来的对水资源利用方式和效率的影响。结果表明,在灌区内部从上游到下游,水资源可利用量很不均等,上游享用更多的水资源,地下水起到了调节水资源可用量年内波动的作用。上游地区地下水调节了春季水资源可用量的变异性,下游汛期储存的地下水在来年春季被重新利用,年平均利用量达到降雨灌溉总量的40.7%。下游农民应对水资源短缺的另2种途径是进行排水管理和减少种植面积,平均排水再利用量达到40 mm,因此下游地区具有更高的水资源利用效率。在水资源配置中应注意配置方案对水资源利用方式和效率的影响,同时要兼顾效率和公平。     

典型草原区河谷带地下水位对水均衡要素变化的响应

近几年锡林河流域开始进入降水偏丰周期,但地下水“入不敷出”的情况愈加明显,过量的地下水开采需求只能通过消耗地下水储蓄量来实现。基于水均衡原理和统计学方法分析锡林河平原区地下水位对降水量和开采量间的响应程度。研究结果表明,各个观测井对降水时序变化的响应差异较大,其中饲草料基地井与农场三队井地下水位变幅对降水较为敏感;水位埋深与开采量之间存在明显的正相关关系,从水位-开采量关系曲线变化趋势来看,随着地下水开采量增加,农场三队、饲草料基地和奶牛场的水位响应最明显;农作物大棚种植区地下水位主要受降水量与开采量共同作用,响应程度为51.16%,而饲草料基地受开采量影响最大,达到60.71%,压减灌溉饲草料地规模、调整集中连片布局为分散式利用是缓解农灌区地下水超采、促进农牧业安全发展的主要途径。     

Evaluating the width of hydrological buffer zones between drained agricultural land and nature reserve areas

This paper presents the development of a practical tool to evaluate the required width of a hydrological buffer zone, in order to maintain the effects of subsurface drainage within reasonable limits. A simple mathematical formulation describing the lateral drawdown extent of a drained water table in unsteady flow conditions was used. Simulation results were worked out by introducing the concepts of protection level or threshold of tolerance for the vegetation of the protected area The latter are expressed in terms of an admissible drawdown combined with exceedance duration and/or frequency criteria. An application of this method to the protection of a peat bog system in the Swiss Jura region is presented.