A preliminary study of an alternative controlled drainage strategy in surface drainage ditches: Low-grade weirs

This study examined hydrological characteristics of low-grade weirs, an alternative controlled drainage strategy in surface drainage ditches. Chemographs of vegetated and clear scraped (control) replicates of weir vs. non-weir treatments were compared to determine differences in time to peak (T_p) and time to base (T_b). Drainage ditches T_p and T_b were affected by both vegetation and weir presence. The order of treatment efficiency for T_p was observed to be: non-vegetated non-weir < vegetated non-weir < non-vegetated weir < vegetated weir. Furthermore, T_b for each ditch was the reverse relationship from T_p where vegetated weir > non-vegetated weir > vegetated non-weir > non-vegetated non-weir. Low-grade weirs increase chemical retention time (vegetated and clear scraped), the average time a molecule of contaminant remains in the system. Future research in water quality improvement and weir management will yield useful information for non-point source pollutant reduction.     

Salinity dynamics of wetland ditches receiving drainage from irrigated agricultural land in arid and semi-arid regions

Agricultural drainage ditches are considered as wetland ecosystems when they possess the characteristic hydrology, soil and vegetation of wetlands. In arid and semi-arid regions, wetlands receiving agricultural drainage have to cope with the conservative nature of salts leached from soils. Excessive accumulation of salts in wetlands may threaten the ecological functions of the system, thus endanger the sustainability of the drainage disposal system and the productivity of the farmlands. Based on the salt and water balance in a farmland drainage and wetland disposal system in arid regions, this paper presents a thorough investigation on salinity dynamics of wetland ditches receiving agricultural drainage. Theoretical equations were derived to describe salinity changes in water and soils of wetlands under both equilibrium and pre-equilibrium conditions; a case example was then used to display model predictions of salinity variations over time under different salinity management goals. The example wetlands are de facto drainage ditches that possess wetland characteristics, and the ditch to farmland area ratio is 9.1%. The results showed that salt as a conservative substance will eventually concentrate in the ditches to a very high level if there is little outflow discharge; but the salt accumulation process may develop over a relatively long time, which opens a time window for management practice, such as flushing the salts when fresh water is available. By assuming different threshold salinity levels in the ditches, the proposed analytical models were used to predict time intervals when fresh water recharge is needed to bring down the salinity level in the ditches. For the study area under current drainage practice, the predicted outflow to inflow ratio for salinity was 58.2% and reached an equilibrium level of 9.60 g L⁻¹ in the ditches; salinity levels in the ditches reached threshold values of 5, 7 and 9 g L⁻¹, in about 1, 4 and 12 years, respectively. Salinity analysis showed that the salt retention capacity of the ditch soil is limited, the soil salinity varied according to the ditch water; salt removal through plant uptake and harvest was insignificant. This study indicates that although salt concentration in wetlands receiving agricultural drainage may eventually build up to a critical level, timely recharge with fresh water may bring down salt content in the wetlands and sustain adequate environmental and ecological functions of such a drainage disposal system in arid and semi-arid regions.     

Sediment phosphorus dynamics for three tile fed drainage ditches in Northeast Indiana

Phosphorus (P) losses from agricultural lands degrade surface waters due to anthropogenic eutrophication. Previous studies focused on plot-to-field scale P loss and reductions from best management practices (BMP's), little information in intense agricultural catchments has been gathered on the dynamics influencing P beyond the edge of the field. This study was conducted to examine the phosphorus equilibrium between the water column and sediments in three tile fed drainage ditches in Northeast Indiana. Surface water and sediment samples were collected and analyzed for organic carbon (C), particle size and P from sites along three ditches with similar soils and land use at sites within each watershed draining approximately 300 and 1500 ha on each ditch. Organic C, silt and clay fractions of the bottom sediments decreased with increasing drainage area. Soluble P concentrations were low in Ditch A, but increased with increasing drainage area (0.02–0.05 mg P L⁻¹). Overall, the P concentrations were higher in the Ditches B and C (0.06–0.09 mg P L⁻¹). Exchangeable P, P partitioning index and equilibrium P concentrations (EPC_o) decreased with increasing drainage area by as much as 95, 93 and 100%, respectively, except in one catchment area with a confined animal feeding operation between sampling points, where ExP and EPC_o increased by 4 and 116%, respectively. Aluminum sulfate and calcium carbonate treatment of ditch sediments reduced exchangeable P and sediment EPC_o in this study. Results from this study indicated some watershed characteristics, as well as sediment physiochemical properties, affect ditch sediment and water P equilibrium and buffering capacity. Furthermore, this study demonstrated that managers could potentially use chemical treatment of the ditches to increase the temporary retention of P in ditches and maybe reducing sediment P availability.     

Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches

Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃-N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH₄⁺-N, and greater NO₃-N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO₃-N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters.     

农田排水沟水土流失成因与防治

黑龙江省本着改造中低产田,夺取农业高产的原则,对易受涝灾和渍害的田地进行了改造,其主要措施是沿地洼地带挖排水沟,进行排水,降低地下水位,改良土壤的物理性质。但经过一段时间应用后,部分排水沟受到破坏,造成水土流失。为此,分析了黑龙江省中低产田改造治理过程中开挖排水沟产生水土流失的原因,并在此基础上提出了切实可行的防治措施。     

农田排水系统分布特征对水质净化效果的影响研究

【目的】分析不同排水沟塘系统分布特点对农田排水污染物去除能力的影响。【方法】分别选择陕西省富平县卤泊滩和江苏省扬州市江都区为研究区,通过理论计算,比较了2种不同分布但农田面积比接近的排水沟塘系统的水质净化能力。【结果】①位于南方的江都研究区"小沟多塘"排水系统对于污染物的去除率比卤泊滩地区"大沟无塘"高出7%～36%;②在卤泊滩研究区,污染物降解的主要场所为排水农沟,而在江都研究区,则是面积较大的支沟和池塘;③2个研究区不同类型沟塘对污染物的去除效率都与其面积呈现良好的相关性。【结论】分布特征决定了沟塘水系的水力联系,"小沟多塘"类型分布的排水系统更有利于污染物的降解。     

生态灌区农田排水沟塘湿地系统的构建和运行管理

建设生态型灌区是灌区现代化发展的重要内容。针对传统灌区农业面源污染日益严重的现状,总结了当前利用农田排水沟渠塘堰系统去除农业面源污染的研究进展,探讨了减污型农田排水沟渠塘堰湿地系统的构建方法,其基本特征包括:水利工程属性(排渍排涝及水流的不冲不淤要求),沟塘末端修建控制排水闸(低坝),种植优势植被,生态护岸(护底)工程,排水闸(退水闸)等水工建筑物减污型工况设计。分析了该系统的运行管理方式。     

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.     

Determination of the variation of hydraulic conductivity with depth in drained lands and the design of drainage installations

For lands drained by ditches dug to a horizontal impermeable floor, the variation of the soil's hydraulic conductivity with depth may be obtained from the relationship between water-table height and drain-outflow rate. Some relationships obtained on an experimental plot on a clay soil, drained by tile drains with gravel backfill, and on another in the same field which was mole-drained, were analysed to give the variation of hydraulic conductivity with depth by assuming that their performances approximated to that of ditches. For the tile-drained plot, the hydraulic conductivity value increased by three orders of magnitude near the bottom of the plough layer; this was reduced in a subsequent year when the field was uncultivated under grass with consequent higher water tables. The mole-drained soil was more permeable than the tile-drained soil at a lower depth, and its hydraulic conductivity at this lower depth did not change in the subsequent year when the field was uncultivated. An assumed uniform hydraulic conductivity value, calculated using drainage theory and matching at one water-table height, gave relationships between water-table height and drain outflow which did not agree with observations.A general hydraulic approach to drainage design is suggested whereby the drainage from an investigational area may be used to measure the hydraulic conductivity variation with depth and to design the correct drainage scheme for a predicted stress period of rainfall. Even if the drainage rate from an area is not measured, the water-table recession alone in an area drained by ditches may give sufficient information to design a drainage system on a rational physical basis.     

傍河井取水与引黄河水之间的关系分析

以莘县为例,探讨傍河井抽取的地下水与引黄河水之间存在的关系。研究结果表明,引黄沟渠在抽水井影响半径2倍以外时,傍河井的数量或者抽水量足以引起引黄沟渠周围区域性地下水位下降,则引黄河水对该区域的地下水补给量就会增加,取水量越大,地下水位下降越大,补给量增加的也越多;当引黄沟渠在抽水影响半径2倍之内时,引黄河水就会直接补给水井,补给量与水井的单位时间出水量、水井与引黄沟渠的距离、抽水时间有关,出水量越大、距离越近、抽水时间越长,引黄河水的侧渗补给量越大,反之依然。     

盐碱地排水沟水体盐分变化规律

为了研究陕西卤泊滩盐碱地排水沟在排水出路受阻,上游灌区退水导致排水沟周期性较高水位运行条件下的水体盐分变化情况,选择研究区3条排水沟,进行野外水盐监测试验,测定了排水沟水体盐分随时间的变化规律.研究结果表明:在当前条件下影响研究区排水沟水量的主要因素为干旱蒸发和上游灌区退水.干旱期排水沟水量较少,上游灌区低含盐量的退水进入研究区排水沟内,致使水量显著增大,在研究区下游排水沟内水深达1.15 m;排水沟水体电导率值在干旱季节较高,盐分从上游至下游呈现出一定的富集现象;上游监测点位水体电导率基本维持在2~14 ms/cm,下游水体电导率值高达25.2 ms/cm;研究区上游灌区退水在排水沟内大量蓄积,使得排水沟水体电导率值降低至1.9 ms/cm,稀释率高达10倍,表明退水可以稀释排水沟中的盐分水平,维持排水沟水体盐分平衡,达到排盐效果.     

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。     

农田渠系工程景观生态格局

农田渠系工程作为土地整理中农田水利工程的主要构成部分,其生态功能评价有着重要意义。选择湖北省孝昌县白沙镇基本农田土地整理项目西区为研究区域,根据农田渠系的生态功能特性,将其分为两类:生态功能型和非生态功能型沟渠,通过运用景观格局分析方法,通过对比传统景观分析方法和考虑生态性的景观分析方法对研究区域的7种类型渠系进行测算。结果表明,研究区渠系在两种分析方法下,景观指数有较大差异;同时,研究区生态功能渠系形成了10个渠系孤立岛,对依赖渠系廊道进行迁移、生存和庇护等的生物影响大。      

Ontology-based simulation of water flow in organic soils applied to Florida sugarcane

An ontology-based simulation (OntoSim) is a unique data modeling environment where soil–plant-nutrient processes are represented as database objects and the user-defined relationships among objects are used to generate computer code (Java) for running the simulation. The aim of this study was to model hydrologic processes of sugarcane-grown organic soils utilizing OntoSim in the Everglades Agricultural Area (EAA) of South Florida. This OntoSim-Sugarcane model describes the complex hydrology of sub-irrigation and open ditch drainage commonly used on Florida farms.Model calibration was conducted by (i) selecting rectangular farm water management units (<12 ha), which are encompassed with farm ditches, from two farms in the EAA, (ii) assembling all relevant input data including water tables (WT) recorded at the monitoring farm well of each unit, and (iii) optimizing the fits between the simulated and observed daily WT during two consecutive water years (WY). By calibrating two site-specific parameters – lateral saturated hydraulic conductivities of soil profiles and vertical saturated hydraulic conductivity of the underlying limestone bedrock – good agreement between simulated and observed daily WT was obtained (Nash–Sutcliffe efficiency coefficient >0.65; coefficient of residual mass <1%) within the units during WY96–97 (May 1995–April 1997). The validation of the model during subsequent WY98–99 at both units also showed Nash–Sutcliffe efficiency >0.55 and coefficient of residual mass <3%. It indicated that OntoSim-Sugarcane is able to simulate daily fluctuations of WT within the farm units and estimate lateral drainage/sub-irrigation and deep seepage that significantly contribute to the water balance at farms in the EAA. Thus, it can be a promising management tool to provide farmers with accurate assessment of water movement in this agricultural area.     

入沟流量对灌水质量和水流特性的研究

通过垄作沟灌的田间灌水试验,用极差分析研究入沟流量、沟宽、沟深、沟底纵坡4个技术参数对灌水质量的影响和研究入沟流量对地面水流特性的影响。研究表明:入沟流量对灌水质量影响最大,其次为沟底纵坡、沟深和沟宽;水流推进时间随着入沟流量的增大逐渐减少,推进速度逐渐加快,水流推进距离与水流推进时间呈幂函数关系,相关程度都大于0.99;水流消退时间随入沟流量的增大逐渐增大,消退速度逐渐减小,尽管水流消退时间与距离也呈幂函数关系,但二者的相关性没有推进过程的好。研究成果对我国入沟流量的相关研究具有一定的参考价值。     

调控排水沟水位与利用地下水资源关系的初探

在自流灌溉区地下水位埋深大于3m的区域,采用排水沟上筑建地下水位调控闸调控沟水水位,能够调控农田地下水位的高度,使土壤毛细水管将地下水分补充到作物根系有效利用的土层,实现地下水资源的有效利用,达到节水的目的。把沟水位调控在2.5m左右时,土壤含水量最适宜农作物生长发育的需求,土壤肥力提高,土壤含盐较少,作物对地下水利用的效果最佳,节水量可达900m3/hm2。     

The effects of a weir on reducing acid flux from a drained coastal acid sulphate soil backswamp

A trial was conducted to examine the effects of retaining drain water with a weir on reducing acid flux from a drained coastal acid sulphate soil backswamp. Prior to weir construction, groundwater seepage to the ditch drain was the main hydrological pathway for acid flux. High hydraulic conductivity (>120 m per day) in the sulphuric horizons due to extensive macropores, combined with tidal modulation of drain water levels encouraged rapid seepage of acid groundwater. Most seepage occurred while the backswamp groundwater table was in a narrow elevation range, referred to as an ‘acid export window’. The acidity of drainage water was highly sensitive to the hydraulic gradient between the groundwater table and the adjacent drain water level. Acid flux rates from groundwater seepage were strongly positively correlated to effluent groundwater hydraulic gradients. The constructed weir was designed to reduce the magnitude of effluent groundwater gradients and retain shallow groundwater by maintaining high and stable drain water levels. This reduced groundwater seepage to the drain and increased the proportion of shallow groundwater lost from the system via evapotranspiration. The weir affected 60% of drainage network and observed and modelled data suggest acid flux from groundwater seepage was reduced by about 65–70%. Effluent groundwater gradients behind the weir were reduced by about 80%. The main effect of the weir was to reduce discharge volumes, although reductions in H⁺ and acidic metal cation concentrations were also observed. This study demonstrates that a weir can be an effective means of reducing acid flux in coastal acid sulphate soils where main hydrological pathway of acid export is groundwater seepage. However, this strategy may not prevent continued sulphide oxidation. Reduced acid export, but continued acid generation, combined with enhanced evaporative flux has the potential over the longer term to increase the net accumulation of acidic products in the backswamp soil and groundwater. Further monitoring is required to assess this possibility.     

基于平均农渠数量的斗渠流量确定方法

灌区内轮灌斗渠的流量一般根据灌水率和灌溉面积确定。对于灌区内斗渠控制灌溉面积大小不一的情况,斗渠的田间净流量应按各条渠道的灌溉面积占轮灌组灌溉面积的比例进行分配。通过计算每条斗渠控制的平均农渠数量来演算斗渠流量,方法较为简单和准确,并通过相关规范公式验算和实践检验,可作为斗渠规模确定的一种方法来运用。      

Cautionary notes on the use of pedotransfer functions for estimating soil hydraulic properties

The performance of published pedotransfer functions was evaluated in terms of predicted soil water content, pressure heads, and drainage fluxes for a layered profile. The pedotransfer functions developed by Vereecken et al. (1989), Vereecken et al. (1990) were used to determine parameters of the soil hydraulic functions θ(h) and K(h) which were then used as input to SWATRER, a transient one-dimensional finite difference soil water model with root uptake capability. The SWATRER model was used to simulate the hydraulic response of a multi-layered soil profile under natural climatic boundary conditions for a period of one year. The simulations were repeated by replacing the indirectly estimated water retention characteristic by (1) local-scale, and (2) field-scale mean observed θ(h) relationships. Soil moisture contents and pressure heads simulated at different depths in the soil profile were compared to measured values using these three different sets of hydraulic functions. Drainage fluxes at one meter below ground surface have also been simulated using the same three sets of hydraulic functions. Results show that simulations based on indirectly estimated moisture retention characteristics (obtained from pedotransfer functions) overpredict the observed moisture contents throughout the whole soil profile, but predict the pressure heads at shallow depths reasonably good. The results also show that the predicted drainage fluxes based on estimated retention functions are about four times as high compared to the drainage fluxes simulated using measured retention curves.     

自清洗网式过滤器水力性能试验

通过清水试验和浑水试验对自清洗网式过滤器的水力性能进行了试验研究．清水试验主要研究过滤器的局部水头损失随不同进口流量(0～230 m3／h)的变化情况．浑水试验分别对过滤器的过滤状态和排污状态进行研究:过滤状态主要研究在最大进水流量(230 m3／h)下改变不同进水含沙量时的局部水头损失变化,以及在保持相同进水含沙量(019 g／L)下改变不同进水流量时的局部水头损失变化;排污状态重点研究在不同预设压差值下最佳排污时间的变化规律．试验结果表明:对于清水过滤,进水口流量值在0～140 m3／h变化时,对应的过滤器初始局部水头损失变化缓慢;当流量在140～230 m3／h时,局部水头损失增加较快,并拟合出水头损失经验公式．对于浑水过滤,改变不同进水含沙量值,局部水头损失均在6～7 m出现拐点,之后迅速增大,确定其预设排污压差值为007 MPa;排污过程中,当排污时间达到20 s时,排污管出水含沙量趋于稳定,排污效果较好,确定其最佳排污时间段为20～30 s．