河套灌区排水工程管理的数值模拟研究

利用SWAP(Soil-Water-Atmosphere-Plant)模型对河套灌区的永联试验区进行了排水工程管理的数值模拟研究,分析了排水沟的间距和深度对田间水均衡要素的影响。结果显示,现有排水沟深度下的排水沟间距调整对区域排水和潜水埋深的影响不明显,但当排水沟深度增加时,排水沟排水量和控制区域的潜水埋深发生显著变化。根据模拟结果,认为永联试验区的排水沟间距取500 m,深度取2.5 m较为适宜。     

干旱区盐碱地防盐排水标准探讨

本文通过分析张掖盐碱区耕地的高地下水位降落速度与土壤积盐量之间的关系,确定了地下水位高于防盐临界深度的允许持续时间,可为排水沟(管)间距计算提供参数。     

网沟地块的布设计算

在四周均有排水沟的网沟地块内,地下水位受周围排水沟的影响而变化。这种情况属平面二维渗流运动,研究工作较少,且公式复杂,难以达到实用;而系列排水沟属一维渗流运动,其在稳定流或非稳定流条件下的排水计算,包括考虑地下水不同蒸发与埋深关系指数的排水计算在内,已有不少研究成果.本文以排水效果相同为基础,将平面渗流运动转变为一维渗流运动,用简单的几何关系即可求得网沟地块宽度与系列沟间距之关系,从而可使系列沟的研究成果亦能用于网沟地块的布设计算。     

基于遗传算法的田间排水系统优化设计

针对传统经验试算法的低效性,将遗传算法(GA)用于解决田间排水工程设计中的非线性优化问题.从田间排水系统的任务出发,分别介绍了田间排水沟的断面优化设计和间距优化设计方法,并运用遗传算法进行模型求解.实例表明,遗传算法能够有效解决田问排水沟的优化设计问题,并且能严格满足系统约束条件,操作简单,计算效率高.     

网沟地块的布设计算再探

在“网沟地块的布设计算”一文中,作者曾就地块四周沟水位相同时的近似计算进行了初步探讨,本文拟就对应沟(管)水位相同时两高两低的网沟布设问题作进一步探讨,所得结果亦可用于地块四周沟水位相同时的网沟布设计算. 对于已建或拟建的田间排水沟、管,如果由于经验不足而在运用中发现间距偏大,或者受当前经济条件等原因所限而有意识地采用了较大间距时,为了使排水效果达到要求的排水标准,就需要加设固定的或临时的     

东港地区稻田适宜排水沟距试验对比分析

通过对辽宁东港灌区稻田排水沟距的综合对比试验分析，探讨了该地区稻田不同排水沟距对控制地下水位、渗漏量、土壤Eh值及水稻产量的影响，初步提出该地区稻田适宜的排水沟距。为今后该地区及类似地区排水沟道的规划设计提供了借鉴和参考，对水田的增产增收具有重要意义。     

基于VBA的宁夏引黄灌区暗管排水间距计算方法研究

暗管排水工程是控制灌区地下水位,防治耕地盐碱化的主要技术手段。【目的】综合考虑排水条件、排水目的等因素,选择合适的计算方法计算暗管间距。【方法】对几种常用的暗管间距计算方法进行了理论分析并总结了其适用条件,编写了基于VBA的计算程序以实现不同计算方法的优选并确定相应的暗管间距。在此基础上,选取宁夏引黄灌区2个典型暗管排水工程案例进行了分析计算。【结果】稳定流状态下,当kH/q≤100时,宜选择阿维里扬诺夫-瞿兴业公式计算暗管间距,当kH/q>100时,宜选择Hooghoudt公式计算暗管间距;非稳定流状态下,以治渍为目的地区选择按地下水位下降速度计算暗管间距,以防治盐碱化为目的地区选择按排蒸比计算暗管间距。【结论】利用VBA开发的程序可以解决暗管间距计算过程中较繁琐的迭代、累加等计算问题,操作便捷,实用性强;非稳定流方法更适合于宁夏引黄灌区暗管排水间距的计算,银北灌区宜按排蒸比计算暗管间距,银南灌区宜按地下水位下降速度计算暗管间距。     

网沟地块的稳定与非稳定渗流排水计算

根据网沟地块内的地下水流向四周排水沟,而系列沟地段内的地下水流向两侧排水沟的特性,采用网沟地块与系列沟地段的渗流排水的向量关系,较简便地解决了网沟地块的布设计算问题,从而使广泛应用的系列沟研完成果也可用于网沟地块布设的排水计算。     

分维计算水田土壤强度最佳测量间距

对测量水田土壤强度并计算其分维时的测量间距和测点数进行探索，并根据回归分析得出水田土壤强度在分维计算中的最佳测量间距为６０ｃｍ。     

基于PSO-GRA耦合决策的排水沟系统多目标规划模型

排水沟系统承担排水蓄涝、环境保护等效能,多目标排水沟系统规划具有十分重要的现实意义。综合考虑工程费用、减污与产量效应构建排水沟系统多目标规划模型,运用粒子群算法(PSO)生成规划方案非劣解集,并耦合灰色关联投影法(GRA)优选非劣解集进行方案决策,将模型应用于上海松江高标准农田稻作区规划排水沟系统。结果显示,稻作区优选规划方案推荐排水历时5 d,农沟与支沟沟深1.3、1.7 m,间距77、270 m,优化水面率7.64%。与传统单目标规划方案相比,设计降水条件下,增加滞涝水量648.5 m~3/hm~2,总氮的单位面积削减能力4.22 kg/hm~2,削减率增加28.1%,水稻相对产量96.2%。该模型能客观权衡多目标的矛盾性进行科学决策。     

Subsurface drain flow and crop yield predictions for different drain spacings using DRAINMOD

DRAINMOD was run for 15 years to predict and compare drain flow for three drain spacings and crop yield for four drain spacings at the Southeastern Purdue Agricultural Center (SEPAC). Data from two continuous years of daily drain flow from one spacing were used to calibrate the eight most uncertain parameters using a multi-objective calibration function and an automatic calibration method. The model was tested using the remaining field data for the 5, 10, and 20 m drain spacings for drain flow and the additional 40 m spacing for yield predictions. Nash–Sutcliffe efficiency (EF) for daily drain flow simulations for the calibration years and drain spacing ranged from 0.62 to 0.79. The daily EF for model testing ranged from −0.66 to 0.81, with the average deviations of 0.01 to 0.07 cm/day and standard errors of 0.03–0.17 cm/day. On a monthly basis, 91% of plot years had EF values over 0.5 and 76% over 0.6 for years with on-site rainfall data. The total yearly drain flow was predicted within ±25% in 71% of plot years, and within ±50% in 93% of plot years with on-site rainfall data. Statistical tests of daily drain flow EF values for three spacings and percent errors of crop relative yield for four spacings indicated that the reliability of the model is not significantly different among different spacings, supporting the use of DRAINMOD to study the efficiencies of different drain spacings and to guide the drain spacing design for specific soils. In general, the model correctly predicted the pattern of yearly relative yield change. The relative corn (Zea mays L.) and soybean (Glycine max L.) yields were well predicted on average, with percent errors ranging from 1.3 to 9.7% for corn and from −3.3 to 10.3% for soybean.     

Entrance resistance of enveloped drainage pipes

The entrance resistance and the effective radius of corrugated PVC drain pipes without envelope and with six different prewrapped envelopes were evaluated in a sand tank experiment.By applying the theory of resistances, the entrance resistance of the naked pipe was found to be 0.0136 days/m. With envelopes, the values were 0.0024 to 0.0067 days/m, depending on the types of envelope.The effective radius of the naked pipe was found to be 0.47 cm for a drain pipe with an actual radius of 3.0 cm. This value increased to between 1.20 and 2.50 cm when envelope material was used. Then the values of the calculated entrance resistances were substituted in the steady state drainage equations under normal field conditions to evaluate the effect on drain spacing. In all equations, a tendency towards increasing the drain spacing was observed when envelope material was used.     

Nitrogen loss through subsurface drainage effluent in coastal rice field from India

Experiments were conducted to estimate nitrogen loss through drainage effluent in subsurface drained farmers’ field at a coastal site near Machilipatnam, Andhra Pradesh, India. The concentration of three forms of nitrogen, namely, NH₄–N, NO₂–N and NO₃–N in the subsurface drainage effluent from 15, 35 and 55 m drain spacing areas were measured in 1999 and 2000. The area with 15 m spacing was already reclaimed during 1986–1998 by the subsurface drainage system. The soil salinity of the root zone was brought down from an initial high of 35 to 4 dS m⁻¹. The subsurface drainage system with 35 and 55 m drain spacing was laid in the adjoining area and commissioned in 1998. Earlier raising of any crop in the area with 35 and 55 m spacings was not possible due to very high salinity, sodicity and poor drainage conditions. The nitrate-nitrogen loss dominated in reclaimed land with 15 m spacing whereas ammonium-nitrogen loss dominated in the land that was highly saline and in the initial stage of reclamation by the subsurface drainage technology with 35 and 55 m drain spacing. The total nitrogen loss of 3.75 kg per ha per year in 15 m drain spacing area was minimum and 23.53 kg per ha per year in 35 m drain spacing area was maximum. The nitrate-nitrogen loss contributed the maximum of 82% and ammonium- and nitrite-nitrogen contributed 11 and 7%, respectively, in 15 m drain spacing area whereas the ammonium losses contributed 93 and 82% in 35 and 55 m drain spacing areas, respectively. The losses in the form of nitrite and nitrate remained negligible in 35 m drain spacing area, but the losses to the tune of 8 and 15% in the form of nitrite and nitrate, respectively, occurred in 55 m drain spacing area.     

Numerical simulations of steady-state subsurface drainage with vertically decreasing hydraulic conductivity

Most subsurface drainage equations assume either homogeneous, two-layer or three-layer soil conditions. Finite difference simulations were performed to quantify the effect of gradually decreasing hydraulic conductivity on watertable depths for steady-state subsurface drainage. For vertically decreasing hydraulic conductivity, and for cases where drain spacing was based on effective hydraulic conductivity of the 0.5 to 2.0 m layer, mid-spacing watertable depth ranged from 0.282 to 0.900 m. The average value was 0.718 m, which is considerably shallower than the 0.9 m design value used for determining drain spacing. These higher watertables may have detrimental effects on crop yield, especially in arid areas where soil salinity is a problem. The importance of the difference between actual and design watertable depths was mostly related to the type of hydraulic conductivity decrease function, drain depth, and drainage rate. These differences are explained by the position of the drain within the soil profile and the effect of the spacing on the equivalent depth of flow. Using effective hydraulic conductivity of the 0.5 to 3.0 m layer for determining drain spacing reduced the error. For an effective hydraulic conductivity value of 0.3 m/d, the average watertable depth increased from 0.748 m for the 2.0 m auger hole to 0.829 m for the 3.0 m hole. The results presented can be used to estimate the error on watertable depth resulting from ignoring the vertical variations of hydraulic conductivity.     

Water table behaviour in drained lands: effect of evapotranspiration from the water table

Subsurface drain spacing is underestimated by the equations that do not account for evaporation-evapotranspiration (ET) lowering the water table in drained lands. An analytical solution is proposed to evaluate water table behaviour in subsurface drained lands in the presence of ET. A piecewise linear model is proposed and used to describe any realistic functional relation between ET and depth to water table. Characteristics of the solution have been highlighted with the help of numerical examples for which drainage parameters have been chosen from two actually operating drainage systems installed in semi-arid regions. The accuracy of the proposed solution has been verified with the existing numerical scheme as well as by comparing the water table behaviour with the observed field data. Application of the solution in subsurface drainage design has been illustrated which suggests that drain spacing at this particular site could be increased by 9 to 18% if the contribution of ET in lowering the water table is taken into account.     

Simulation of drainage water quality with DRAINMOD

The design and management of drainage systems should consider impacts on drainage water quality and receiving streams, as well as on agricultural productivity. Two simulation models that are being developed to predict these impacts are briefly described. DRAINMOD-N uses hydrologic predictions by DRAINMOD, including daily soil water fluxes, in numerical solutions to the advective-dispersive-reactive (ADR) equation to describe movement and fate of NO₃-N in shallow water table soils. DRAINMOD- CREAMS links DRAINMOD hydrology with submodels in CREAMS to predict effects of drainage treatment and controlled drainage losses of sediment and agricultural chemicals via surface runoff. The models were applied to analyze effects of drainage intensity on a Portsmouth sandy loam in eastern North Carolina. Depending on surface depressional storage, agricultural production objectives could be satisfied with drain spacings of 40 m or less. Predicted effects of drainage design and management on NO₃-N losses were substantial. Increasing drain spacing from 20 m to 40 m reduced predicted NO₃-N losses by over 45% for both good and poor surface drainage. Controlled drainage further decreases NO₃-N losses. For example, predicted average annual NO₃-N losses for a 30 m spacing were reduced 50% by controlled drainage. Splitting the application of nitrogen fertilizer, so that 100 kg/ha is applied at planting and 50 kg/ha is applied 37 days later, reduced average predicted NO₃-N losses but by only 5 to 6%. This practice was more effective in years when heavy rainfall occurred directly after planting. In contrast to effects on NO₃-N losses, reducing drainage intensity by increasing drain spacing or use of controlled drainage increased predicted losses of sediment and phosphorus (P). These losses were small for relatively flat conditions (0.2% slope), but may be large for even moderate slopes. For example, predicted sediment losses for a 2% slope exceeded 8000 kg/ha for a poorly drained condition (drain spacing of 100 m), but were reduced to 2100 kg/ha for a 20 m spacing. Agricultural production and water quality goals are sometimes in conflict. Our results indicate that simulation modeling can be used to examine the benefits of alternative designs and management strategies, from both production and environmental points-of-view. The utility of this methodology places additional emphasis on the need for field experiments to test the validity of the models over a range of soil, site and climatological conditions.     

Watercourse Pollution due to Surface Runoff following Slurry Spreading. Part I: Calibration of the Soil Water Simulation Model SOIL for Fields Prone to Surface Runoff

The Swedish soil water model SOIL has been calibrated for several drained fields in Scotland and Ireland. Drainage efficiency in these fields varies, with inefficient drainage systems leading to saturated profiles and large surface runoff flows. The model has been modified to represent drainflow in typical Scottish and Irish fields in which permeable backfill extending to the surface is present directly above plot drains. When the conductivity of the backfill material is low, surface runoff is shown to be enhanced in specific soil types. Overall, the predictions of the modified model are in reasonably good agreement (as shown by the efficiency factor values) with measured water table levels, drain and surface runoff flows in these fields. These calibrated fields are to be used in subsequent work on pollution from surface runoff following slurry spreading. A useful indicator of potential runoff risk in such systems is the total saturated hydraulic conductivity of the profile, defined here as arising from the combination of the saturated soil and drain conductivities. Fields are classified into high risk if the conductivity of the profile is lower than 6 mm/d, low risk if the conductivity is greater than 18 mm/d, and moderate risk for intermediate conductivities. A sensitivity analysis of the model with regard to drain and surface runoff flows, varying the drain spacing, a backfill resistance term, the soil matrix and macropore saturated hydraulic conductivities, soil porosity and the pore size distribution index, is also presented. This analysis shows that in order of increasing importance, backfill resistance, macropore saturated hydraulic conductivity and drain spacing, have the largest effect on the generation of surface runoff.     

Evaluation of two water table management models for Atlantic Canada

Two water-table management models, DRAINMOD and SWACROP, were compared and contrasted using the field measurements made at a 5.4 ha experimental site in Atlantic Canada. Three drainage treatments, consisting of 3, 6 and 12 m drain spacing, were used to measure the subsurface drain outflows and the corresponding midspan water-table depths during the summer months of 1990 and 1991. Several statistical parameters, i.e. the average mean of differences, the average absolute deviations, the standard errors of estimate and the standard deviation of the differences, were used to compare the measured values with the values simulated by the two models. Both models did a comparable job by yielding values close to the measured ones. They were quite sensitive to the rainfall events; the simulated drain outflow rates were usually higher than the measured values during and right after the rainfall events. The differences between the two models were quite obvious after the rainfall events, especially the ones after dry spells. On the whole, the two models were simulating water-table depths and drain outflow rates quite close to each other. Therefore, it can be stated that both DRAINMOD and SWACROP can be used to design subsurface drainage system in Atlantic Canada. However, improvements are needed in both models to simulate better under rainfall events, especially those following a prolonged dry spell. Keywords:     

Evaluating Drainage Design Parameters for the Fourth Drainage Project, Pakistan by using SWAP Model: Part II – Modeling Results

This paper presents the results of modelsimulations to evaluate drainage designparameters for the Fourth Drainage Project(FDP), Punjab, Pakistan. The SWAP model wasapplied to compute the effects of landdrainage (12 combinations of drain depthand spacing) on soil moisture conditions inthe root zone and their effect on cropyield and soil salinization. For theconditions considered, the selection ofdrain depth is found to be more criticalthan that of drain spacing. Deeper drainsperform technically better in relation tocrop growth and soil salinization. Theoptimum drain depth for the multiplecropping system of the FDP-area was foundto be 2.2 m. This drain depth will producereasonably good crop yields at rather lowdrainage intensity while keeping the rootzone salinity within acceptable limits.This drainage design also maintained thegroundwater table depth below the root zonethroughout the growing season. The outcomeof this study reveals that the drainagedesign criteria applied for the FDP israther conservative with high drainageintensity. The FDP-area can effectively bedrained with a 25 percent lower drainageintensity (q _drain/h)provided no operational or maintenanceconstraints are present. However, the finaldecision on the optimum combination ofdrain depth and drain spacing would requirea thorough economical analysis. Thenon-steady state approach proved successfulin analyzing the complex interactionsbetween irrigation and drainage components.It is a valuable tool to optimize thedesign of drainage systems against cropyields and soil salinization.