暗管排水条件下微咸水灌溉对土壤水盐运移特征的影响

为探索高效节水控盐灌排技术,通过田间试验,以玉米为试材,研究了不同微咸水矿化度及暗管埋深对土壤水盐运移的影响。结果表明,微咸水矿化度和暗管埋深对土壤含水率和盐分均有影响,高矿化度处理灌后土壤含水率比低矿化度高,1.3m暗管埋深灌后土壤含水率要高于0.8m暗管埋深;微咸水灌后1d作物主要根系层(0~40cm)脱盐率受矿化度影响较大,矿化度越高,脱盐效果越差;灌后25d,淡水灌溉及暗管埋深0.8m、3g/L微咸水的处理土壤无积盐,其余各处理均发生积盐现象,灌溉水矿化度越大,0~80cm土层积盐越强烈,1.3m暗管埋深较0.8m埋深土壤积盐更加明显。建议同类型区种植玉米时暗管埋深为0.8m,灌溉使用微咸水矿化度不超过3g/L为宜。     

沿江圩区局部洼地排涝模数关联因子分析及应用

沿江圩区局部洼地涝灾频发,是目前圩区涝灾治理的重点.针对局部洼地排涝特点,以扬州江都沿江开发区为例,通过排涝水文分析计算得到排涝模数与排涝面积、水面率、调蓄水深、暴雨重现期4种关联因子之间的关系,选取典型区对局部洼地涝灾进行成因分析,并在此基础上提出圩区内局部洼地涝灾的防治措施.结果表明:排涝面积与排涝模数的偏相关系数为-0.905,相关性最大;局部洼地排涝面积小,洪水汇流速度快,洪峰径流模数和排涝模数较大;局部洼地区缺乏小型河网、河流间距过大、水系布置不合理和采用排涝模数较低,是涝灾频发的主要原因.以关联因子分析和成因分析为基础,提出了通过缩小河流间距、增加水面率、充分发挥河道的调蓄作用等措施以防治涝灾的产生,并且提出了符合圩区局部洼地水情特征的一种排水管网与河道布置模式.     

Modeling flow and transport in heterogeneous,dual-porosity drained soils

A finite element solution of the equations for coupled flow of water and transport of chemicals in slowly permeable soils containing macropores is presented. Two example solutions are presented for the condition of a horizontal soil profile with a drainage ditch. The first is for steady state saturated flow while the second is for transient water flow produced by time varying rainfall. Through these examples it is found that the characteristic leaching time of a chemical from the soil matrix is determined by the rate of transfer of chemical mass between the pore domains. When the rate of transfer is zero, the rate of leaching is greatly retarded compared to the case where the rate of transfer is nonzero. The chemical outflow from the macropore domain is very rapid when the rate of transfer is zero, while the chemical outflow is greatly delayed, but increased in magnitude when the rate of chemical transfer is nonzero.

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Résumé Une solution par éléments finis des équations régissant lécoulement de l'eau et son influence sur le transport des composés chimiques à l'intérieur de sols à perméabilité lente contenant des macropores est présentée.Deux solutions sont citées en exemple, traitant le cas d'un sol sans pente avec un fossé d'évacuation.La première solution est pour un écoulement saturé en régime permanent alors que la seconde traite de l'écoulement variable résultant de pluies d'intensités changeantes.Ces exemples ont permis de déterminer que le temps caractéristique nécessaire à la désorption d'un composé chimique donné de la matrice du sol est fonction du taux de transfert de ce composé entre les domaines de macropores.Lorsque le taux de transfert est nul, le taux de désorption est considérablement ralenti par rapport aux cas où le taux de transfert n'est pas nul.Le composé chimique s'évacue très rapidement des domaines des macropores lorsque le taux de transfert est nul, alors que l'évacuation est considérablement retardée mais beaucoup plus volumineuse lorsque le taux de transfert du composé chimique n'est pas nul.

     

Parameter sensitivity and field evaluation of SIDRA model

The simulation model SIDRA is based on a semi-analytical and semi-numerical solution to the Boussinesq equation. It has been developed on the ground of theoretical and field experimental results with the aim of a good prediction of both drainage peak and recession flow rates. Theoretical aspects and basic equations of the model are presented for the most general case where both soil physical properties and water table shapes are depth-dependent. The parameter sensitivity and field performances of the model are estimated in shallow loamy soils facing a seasonal waterlogging during winter season in France. Water table shape factors are the most sensitive parameters. Drainable porosity is slightly more sensitive than hydraulic conductivity for drainflow rate prediction whereas hydraulic conductivity is slightly more sensitive for water table elevation prediction. A comparison of experimental and simulated long term discharge and water table exceedance duration curves shows that the model could be a useful tool to assess the performances and control the relevance of a given subsurface drainage design.

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Résumé Le modèle de simulation SIDRA est basé sur une résolution semi-analytique et semi-numérique de l'équation de Boussinesq. Il a été développé à partir d'une approche théorique et de l'analyse de résultats d'expérimentations de terrain avec pour principal objectif d'atteindre une bonne prédiction des débits de pointe et de tarissement. Les principales équations du modèles sont présentées dans leur forme la plus générale qui permet de prendre en compte des propriétés hydrodynamiques et des formes de nappe dépendantes de la profondeur. L'étude de sensibilité aux paramètres et l'évaluation des performances du modèle sont réalisées dans le cas de sols limoneux peu profonds, sur la période hivernale où se manifeste l'engorgement des sols en France. Le modèle est très sensible aux variations des facteurs de forme de nappe. Concernant les paramètres hydrodynamiques, les débits simulés sont plus sensibles aux variations de la porosité de drainage qu'à celles de la conductivité hydraulique. A l'inverse les hauteurs de nappe simulées sont plus sensibles aux variations de conductivité hydraulique. Une comparaison sur une longue période des fréquences de dépassement de débits et hauteurs de nappe, simulées et observées, montre que le modèle peut constituer un bon outil de contrôle de l'efficacité d'un réseau de drainage et de son dimensionnement.

     

Flow resistance and hydraulic capacity of water courses with aquatic weed growth. Part 2

The flow resistance is generally derived from fieldmeasurements, using the total wetted area of the cross-section.Less attention has been paid to the aquatic weed growth stageand often different resistance have been derived. In this paperthe flow resistance required in the Manning formula wascalculated from laboratory experiments and field data. A goodsolution appeared to be using the unobstructed part of the cross-section only and excluding the part covered by weeds. Apractical solution was found using the relative weed obstructionin the water courses to represent the weed growth. Weedobstruction was measured throughout the growing season. Thedata were obtained from water courses without any weedcontrol and also in sections where weeds were cleared twiceduring the growing season.     

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.     

松弛参数的计算机识别

报道了松弛曲线各参数的识别理论，计算机解法及在物料力－流变学特性研究中的应用。     

围岩特性和衬砌厚度对衬砌混凝土在设置垫层下温控影响研究

基于有限元分析软件ANSYS,在溪洛渡泄洪洞有压段衬砌混凝土设置垫层的情况下,对不同围岩弹性模量和衬砌厚度进行仿真模拟。通过比较不同衬砌部位,不同点位的最高温度、最大内表温差、早期最大拉应力等,针对围岩弹性模量和衬砌混凝土厚度的变化对衬砌混凝土温度和温度应力的影响进行了分析。研究结果表明,①不同围岩弹性模量下,相同温控措施下衬砌混凝土温度场大致相同。较好围岩会增大早期衬砌混凝土的最大拉应力,减小最小抗裂安全系数,必须采取严格的温控防裂措施,防止早期裂缝。②相同温控措施下,衬砌混凝土越厚,最高温度越高,最大内表温差越大。较薄衬砌混凝土会增大早期衬砌混凝土的最大拉应力,减小最小抗裂安全系数,温控防裂措施要求严格。     

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.     

Water, nitrogen and yield losses for a nonhomogeneous furrow set

Water distribution can be nonuniform along the furrow length under surface irrigation. This “down field” nonuniformity is combined with “inter-row” non-uniformity which is a consequence of differences in infiltration characteristics across the plot. Global nonuniformity of application depth causes variation of yield, drainage and nitrogen leaching. In addition to that, due to year-to-year variability of climate, irrigation depths range significantly (from 0 to 360 mm/season). The objective of this paper is to study the impact of the nonuniformity of irrigation-water distribution within a furrow plot on yield, water and nitrogen losses when climate variation is taken into account. Six maize vegetation seasons on a Chromic Luvisol soil in the Sofia region with varying irrigation requirements are considered. Irrigation water is distributed in relative terms over the plot at different levels of nonuniformity (coefficient of variation C_v ranging from 13 to 66%) by the FURMOD model. Water and nitrogen cycle and crop growth are simulated then compared at 30 representative points in the set with various “climate-irrigation nonuniformity” combinations by the CERES-maize model. It was established that non-uniformity of irrigation is not important in wet vegetation periods. The drier the irrigation season, the higher the yield loss and risk to environment due to nonuniformity of irrigation water distribution. In moderate and dry irrigation seasons it causes yield losses of 2–14%, significant variation (30% < C_v < 200%) of drainage, nitrogen leaching and residual soil nitrate over the furrow set. Surface irrigation performances can be improved by reducing lateral nonuniformity of stream advance.