Drainage design practices in France

Subsurface drainage annual rate boomed in France in late 70s and reached a steady rate of 130 000 hectares in 1982. As a consequence, better knowledge of drainage requirements, techniques and effects on farm management is requested. Emphasis has been put on preliminary survey planning. First of all extension and location of areas to be drained is determined with the help of farmers and local representatives within so-called “local juries”. Secondly, drainage recommandations are derived using the so-called “soil reference area” method. Drainage criteria and design methods are discussed on the basis of recent field experimental results. Drain spacing computation is related to tail recession stage; soil hydraulic properties are measured in situ using Guyon's pumping test. Subsurface and arterial drainage design rate are related to discharge exceedance duration curves and annual level of protection.     

Cover crop effects on nitrogen load in tile drainage from Walnut Creek Iowa using root zone water quality (RZWQ) model

Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from artificial subsurface drainage (tile drains) in a subbasin of the Walnut Creek, Iowa (Story county) watershed using the hybrid RZWQ-DSSAT model for a maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] and maize-maize-soybean rotations in all phases with and without a winter wheat (Triticum aestivum L.) cover crop during a 25-year period from 1981 to 2005. Simulated cover crop dry matter (DM) and N uptake averaged 1854 and 36 kg ha⁻¹ in the spring in the maize-soybean phase of the 2-year rotation and 1895 and 36 kg ha⁻¹ in the soybean-maize phase during 1981-2005. In the 3-year rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha⁻¹ in the maize-maize-soybean phase, 2039 and 43 kg ha⁻¹ in the soybean-maize-maize phase, and 1963 and 43 kg ha⁻¹ in the maize-soybean-maize phase during the same period. Annual N loads to tile drains averaged 29 kg ha⁻¹ in the maize-soybean phase and 25 kg ha⁻¹ in the soybean-maize phase compared to 21 and 20 kg ha⁻¹ in the same phases with a cover crop. In the 3-year rotation, annual N loads averaged 46, 43, and 45 kg ha⁻¹ in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha⁻¹ with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 20-28% in the 2-year rotation and 19-22% in the 3-year rotation at the watershed subbasin scale over a 25-year period.     

排水工程对三江平原湿地流域的影响分析

在三江平原别拉洪河流域地形图、土地利用图和排水工程建设资料的基础上,利用地理信息系统进行流域景观制图,并根据排水工程建设量将该流域划分出4个排水分区。利用景观结构分析软件FRAGSTATS分别计算了各分区2个时期(1967年和2005年)的多种景观结构指标。结果表明:排水工程之前,除了旱地无排区的其它3个排水区域,自然湿地覆盖率均达到90%以上,且呈大块连续状分布,结构比较简单,自然状态保存完好;排水渠大量修建之后,沼泽地因排水基本消失,草甸及其它沼泽类型也大片被排干,取而代之的是以大面积的旱地和水田为基质,湿地以小的斑块体镶嵌其中的流域景观,景观结构破碎化严重并趋于复杂化。最后提出下一步的研究工作。     

Shallow subsurface drainage in an irrigated vertisol with a perched water table

Waterlogging and salinity are reducing the productivity of irrigated agriculture on clay soils in south east Australia. We compared five drainage treatments: (1) undrained control (Control); (2) mole drains (Mole); (3) mole drains formed beneath gypsum-enriched slots (GES) (Mole + GES); (4) shallow pipe drains installed beneath GES (Shallow Pipe); (5) deep pipe drains (Deep Pipe). The experiment was set out on a vertisol and our measurements were made during the growth of an irrigated onion crop.

Over the 3 months before the spring irrigations commenced, the perched water table on the Control was less than 400 mm below the soil surface for 27% of the time, whereas the shallow drainage treatments (Treatments 2, 3 and 4) reduced this time to less than 4%. During the irrigation season, the perched water table on the Mole + GES treatment rose above 400 mm for 3% of the time. The perched water table on the Mole treatment was above 400 mm for 14% of the time, compared with 19% of the time on the Control. The Deep Pipes were less effective in reducing the depth to the perched water table, both before and during the irrigation period.

Mole drains increased the gas-filled porosity above the drains. However, the gas-filled porosity remained below reported levels for optimum root growth. Although the drains effectively drained excess water, and lowered the water table, the hydraulic gradient was insufficient to remove all of water from the macropores. Gypsum enriched slots above the mole drains increased the gas-filled porosity in the slots but the drainable porosity in the undisturbed soil appeared to be inadequate for optimum root growth, even though some drainage occurred near the slots.

Discharge from the shallow drainage treatments averaged 58 mm for each irrigation, and was considerably more than the amount required to drain the macropores. The mole channels were in reasonably good condition at the end of the irrigation season, with at least 70% of the cross-sectional area of the channel open.

Shallow subsurface drains increased onion yield by about 38%. For each day the water table was above 400 mm, the yield declined by 0.23 tonnes per hectare. Farmer adoption of shallow subsurface drainage will depend on the long-term economic benefits (influenced by the longevity of the mole channels and yields response) and the need to develop more sustainable management practices.     

Effects of moling and cultivation on soil-water and runoff from a drained clay soil

Flow regimes of water draining from replicated mole drained and undrained plots under different cultivation systems were examined in a 10-year study. In 9 out of 10 years, winter cereals were grown with all residues removed by burning. One crop of oil-seed rape was sown in 1985. A 2 year uniformity trial at the start of the experiment, when all plots were tine cultivated, showed that a cultivation pan exerted an important influence on soil-drainage and water movement. Once removed, effective subsurface drainage increased the depth to the water-table by an average of 215 mm over the winter, with up to 90% of the flow occurring through the mole drains. Following the imposition of differential cultivations in 1980, no discernible change in runoff was observed on plots under ploughing compared to the previous tine cultivations. In contrast, direct drilling caused higher surface runoff than ploughing due to surface compaction, although better subsoil structure development led to more rapid vertical movement of water, and especially in the years following mole drainage an increased peak drain-flow of up to 30%. Although drainage decreased the overall flood risk by as much as 16% in a 10 year return period event, cultivations were of considerable importance and direct drilling increased peak runoff by at least 70% from both drained and undrained plots.     

Subsurface drainage to combat waterlogging and salinity in irrigated lands in India: Lessons learned in farmers’ fields

The introduction of irrigated agriculture in the arid and semi-arid regions of India has resulted in the development of the twin problem of waterlogging and soil salinization. It is estimated that nearly 8.4 million ha is affected by soil salinity and alkalinity, of which about 5.5 million ha is also waterlogged. Subsurface drainage is an effective tool to combat this twin problem of waterlogging and salinity and thus to protect capital investment in irrigated agriculture and increase its sustainability. In India, however, subsurface drainage has not been implemented on a large scale, in spite of numerous research activities that proved its potential. To develop strategies to implement subsurface drainage, applied research studies were set-up in five different agro-climatic sub-regions of India. Subsurface drainage systems, consisting of open and pipe drains with drain spacing varying between 45 and 150 m and drain depth between 0.90 and 1.20 m, were installed in farmers’ fields. The agro-climatic and soil conditions determine the most appropriate combination of drain depth and spacing, but the drain depths are considerably shallower than the 1.75 m traditionally recommended for the prevailing conditions in India. Crop yields in the drained fields increased significantly, e.g. rice with 69%, cotton with 64%, sugarcane with 54% and wheat with 136%. These increases were obtained because water table and soil salinity levels were, respectively, 25% and 50% lower than in the non-drained fields. An economic analysis shows that the subsurface drainage systems are highly cost-effective: cost-benefit ratios range from 1.2 to 3.2, internal rates of return from 20 to 58%, and the pay-back periods from 3 to 9 years. Despite these positive results, major challenges remain to introduce subsurface drainage at a larger scale. First of all, farmers, although they clearly see the benefits of drainage, are too poor to pay the full cost of drainage. Next, water users’ organisations, not only for drainage but also for irrigation, are not well established. Subsurface drainage in irrigated areas is a collective activity, thus appropriate institutional arrangements for farmers’ participation and organisation are needed. Thus, to assure that drainage gets the attention it deserves, policies have to be reformulated.     

Evaluation of the CERES-Maize water and nitrogen balances under tile-drained conditions

The CERES-Maize model was developed to investigate how variations in environmental conditions, management decisions, and genetics interact to affect crop development and growth. A tile drainage subroutine was incorporated into CERES-Maize to improve soil-water and nitrogen leaching under subsurface tile drainage conditions. The purpose of this work was to evaluate the soil-water, soil-nitrogen, tile drainage, and tile-nitrogen loss routines of CERES-Maize for tile-drained fields in Iowa. An analysis was conducted based on information collected from a study of 36 plots consisting of five management systems during a 4-year period from 1993 to 1996, at Nashua, IA. The model was calibrated for each plot using data from 1994 and 1995, and validated using data from 1993 and 1996. Temporal soil-water contents and water flow from tile drains were calibrated to an average root mean square error (RMSE) of 0.036 cm³ cm⁻³ and 2.62 cm, respectively, compared to measured values. Validation trials gave an average RMSE for soil-water and tile drainage of 0.046 cm³ cm⁻³ and 5.3 cm, respectively. Soil-nitrate and tile-nitrogen flows were calibrated, with an RMSE of 6.27 μg NO₃ g⁻¹ soil⁻¹ and 3.21 kg N ha⁻¹ soil⁻¹, respectively. For the validation trials, the RMSE for soil-nitrate content and cumulative tile-nitrate flow was 6.82 μg NO₃ g⁻¹ soil⁻¹ and 8.8 kg N ha⁻¹, respectively. These results indicate that the new tile drainage algorithms describe water and nitrate movement reasonably well, which will improve the performance of CERES-Maize for artificially drained fields.     

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.     

Evaluating a multi-level subsurface drainage system for improved drainage water quality

This paper describes a multi-level drainage system, designed to improve drainage water quality. Results are presented from a field scale land reclamation experiment implemented in the Murrumbidgee Irrigation Area of New South Wales, Australia. A traditional single level drainage system and a multi-level drainage system were compared in the experiment in an irrigated field setting. The single level drainage system consisted of 1.8 m deep drains at 20 m spacing. This configuration is typical of subsurface drainage system design used in the area. The multi-level drainage system consisted of shallow closely spaced drains (3.3 m spacing at 0.75 m depth) underlain by deeper widely spaced drains (20 m spacing at 1.8 m depth). Data on drainage flows and salinity, water table regime and soil salinity were collected over a 2-year period.     

圩垸内部排水沟网与二级泵站优化组合的计算机模拟模型

平原圩区排水干河以下存在众多圩垸，其中大量低洼圩垸内部涝水不能自排入干河，需靠二级泵站抽排。文章针对这类圩区特点，建立了包括排水沟网布置、沟道断面尺寸、湖泊和二级泵站规模的数学模拟模型，并提出了模型试验和多目标决策的方案优选方法。实例研究表明，模型仿真性能好，具有可操作性。     

Predicting effects of drainage water management in Iowa's subsurface drained landscapes

Long-term hydrologic simulations are presented predicting the effects of drainage water management on subsurface drainage, surface runoff and crop production in Iowa's subsurface drained landscapes. The deterministic hydrologic model, DRAINMOD was used to simulate Webster (fine-loamy, mixed, superactive, mesic) soil in a Continuous Corn rotation (WEBS_CC) with different drain depths from 0.75 to 1.20 m and drain spacing from 10 to 50 m in a combination of free and controlled drainage over a weather record of 60 (1945-2004) years. Shallow drainage is defined as drains installed at a drain depth of 0.75 m, and controlled drainage with a drain depth of 1.20 m restricts flow at the drain outlet to maintain a water table at 0.60 m below surface level during the winter (November-March) and summer (June-August) months. These drainage design and management modifications were evaluated against conventional drainage system installed at a drain depth of 1.20 m with free drainage at the drain outlet. The simulation results indicate the potential of a tradeoff between subsurface drainage and surface runoff as a pathway to remove excess water from the system. While a reduction of subsurface drainage may occur through the use of shallow and controlled drainage, these practices may increase surface runoff in Iowa's subsurface drained landscapes. The simulations also indicate that shallow and controlled drainage might increase the excess water stress on crop production, and thereby result in slightly lower relative yields. Field experiments are needed to examine the pathways of water movement, total water balance, and crop production under shallow and controlled drainage in Iowa's subsurface drained landscapes.     

Analysis of groundwater behaviour in a farmer controlled subsurface tile drainage system in Mardan, Pakistan

Extensive subsurface drainage system was installed in districtMardan in the North West Frontier Provinceof Pakistan in 1987 to control increasingwater logging and salinity problems due tocanal irrigation. Several recentlycompleted fields studies have indicatedthat subsurface drainage system hasenormously lowered watertable in certainareas due to extensive drainage network. Therefore, a study of controlled subsurfacedrainage technique was initiated in MardanScarp area to observe the temporal andspatial variations in water table depths ofthis specific case under various modes ofcanal irrigation and monsoon rains. Twoartificially drained areas, consisting of40 ha and 160 ha respectively, werecontrolled and selected for extensivemonitoring. A total of 98 observationswells (7.6 cm dia. and 4.1 m depth) wereinstalled in between lateral drains toobserve water table fluctuation. Theresults of this study are very interesting.Each of the two areas monitored in thestudy behaved differently. It was observedthat in one of the areas design water tabledepth at 1.1 m was maintained with properfunctioning of the controlled techniqueapplied to the subsurface drainage system. The results from this area showed that 25to 55% of the time throughout the yearachieved this objective whereas in thesecond area desired water table could notbe maintained and water table depth in thisarea remained between 2.0 to 2.7 m causingunnecessary water stress to plants. Alsoit was observed that watertable in theformer area is mostly controlled by thefunctional behavior of the irrigationcanal. In addition, the proper functioningof controlled techniques in subsurfacedrainage system supplemented veryefficiently to retain the groundwater levelto the optimal limits in dry season and tothe design ones in the others for timelyneeds of the crops. Also rainfalls havesignificant impact on the spatial andtemporal behaviors of water table depths inboth the areas during the monsoon season.     

Adaptability constraints of a technically and economically feasible subsurface drainage system in the low-lying acid sulphate soils of Kerala,India

This paper discusses the introduction of subsurface drainage as a tool to improve rice production in low land areas of acid sulphate soils. Pipe drains with 15 and 30 m spacing were installed in farmers fields in coastal lowlands of Kerala, India, at Kuttanad. Soil conditions improved within 2 years after the introduction of the subsurface drainage and significantly improved the crop yield. Data collected over a period of 14 years, showed a yield increase of 1.1 t/ha (43%) compared to non-drained areas. An economic analysis indicated that subsurface drainage is feasible with a benefit–cost ratio of 2.45, an internal rate of return of 47% and a net present value of Rs 5.17 million. The poor financial status of the farmers, however, is the main constraint for the large-scale adoption of the comparatively capital-intensive subsurface drainage systems in the acid sulphate soils of Kerala.     

Selecting the Drainage Method for Agricultural Land

To facilitate crop growth excess watershould be drained from the rooting zone toallow root development of the crop and fromthe soil surface to facilitate access tothe field. Basically, there are threedrainage methods from which the designercan select being; surface drains, pumpedtube wells and horizontal pipe drains.The selection between these techniques isnot very straightforward and depends to acertain extend on the preferences of thedesigner. Yet, guidance is given in thispaper on the basis of a set of questionsthat are grouped in a flowchart.Although the flowchart suggests sharpchoices between alternative drainagemethods, in reality the choice between therecommended methods overlaps. Partly thisis because the values in the selectioncriteria (questions) are indicative.Further overlap is caused by theconstruction and operation & maintenancecost of the drainage system under localconditions. These costs are not included inthe flowchart.     

Efficiency of controlled drainage and subirrigation in reducing nitrogen losses from agricultural fields

In northeast Italy, a regimen of controlled drainage in winter and subirrigation in summer was tested as a strategy for continuous water table management with the benefits of optimizing water use and reducing unnecessary drainage and nitrogen losses from agricultural fields.To study the feasibility and performance of water table management, an experimental facility was set up in 1996 to reproduce a hypothetical 6-ha agricultural basin with different land drainage systems existing in the region. Four treatments were compared: open ditches with free drainage and no irrigation (O), open ditches with controlled drainage and subirrigation (O-CI), subsurface corrugated drains with free drainage and no irrigation (S), subsurface corrugated drains with controlled drainage and subirrigation (S-CI). As typically in the region free drainage ditches were spaced 30 m apart, and subsurface corrugated drains were spaced 8 m apart.Data were collected from 1997 to 2003 on water table depth, drained volume, nitrate-nitrogen concentration in the drainage water, and nitrate-nitrogen concentration in the groundwater at various depths up to 3 m.Subsurface corrugated drains with free drainage (S) gave the highest measured drainage volume of the four regimes, discharging, on average, more than 50% of annual rainfall, the second-highest concentration of nitrate-nitrogen in the drainage water, and the highest nitrate-nitrogen losses at 236 k ha⁻¹.Open ditches with free drainage (O) showed 18% drainage return of rainfall, relatively low concentration of nitrate-nitrogen in the drainage water, the highest nitrate-nitrogen concentration in the shallow groundwater, and 51 kg ha⁻¹ nitrate-nitrogen losses.Both treatments with controlled drainage and subirrigation (O-CI and S-CI) showed annual rainfall drainage of approximately 10%. O-CI showed the lowest nitrate-nitrogen concentration in the drainage water, and the lowest nitrogen losses (15 kg ha⁻¹). S-CI showed the highest nitrate-nitrogen concentration in the drainage water, and 70 kg ha⁻¹ nitrate-nitrogen losses. Reduced drained volumes resulted from the combined effects of reduced peak flow and reduced number of days with drainage.A linear relationship between daily cumulative nitrate-nitrogen losses and daily cumulative drainage volumes was found, with slopes of 0.16, 0.12, 0.07, and 0.04 kg ha⁻¹ of nitrate-nitrogen lost per mm of drained water in S-CI, S, O, and O-CI respectively.These data suggest that controlled drainage and subirrigation can be applied at farm scale in northeast Italy, with advantages for water conservation.     

Enhancement of crop yields from subsurface drains with various envelopes

A field experiment was conducted for 10 years in the Nile Delta of Egypt to quantify the benefit of subsurface drainage on crop yield. During three crop rotations, subsurface drains at a spacing of 20 m and a depth of 1.5 m doubled the yield of cotton and rice and increased the yield of wheat and clover by 50%. No significant enhancement in crop yield was found from placing various envelope materials around the drains compared to no envelope. Drains of 75 mm diameter resulted in significantly lower yields (20% less) for cotton and rice than drains of 100 mm diameter but there were no yield differences for wheat and clover. Applying 10 Mg/ha of gypsum and deep plowing (25 cm deep) improved yields from 5 to 19% for all crops, cotton and clover having the largest yield improvement. Soil salinity to a depth of 1.5 m was reduced from an average 5.3–2.2 dS/m after 1 year of drainage without additional water being applied beyond the normal irrigation amounts and rainfall.     

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.     

Analysis of a two-component hydrograph separation model to predict herbicide runoff in drained soils

This paper evaluates the use of a two-component hydrograph separation model to predict the leaching of two relatively soluble herbicides, isoproturon and simazine, from an agricultural drained clay soil. The model successfully predicted the pattern and extent of herbicide leaching in drainflow at a 15-min time interval using electrical conductivity of rainfall and drainflow as the single chemical parameter. Analysis of the hydrological characteristics of individual rainfall events allowed current sources of uncertainty in the model to be identified and highlighted areas for further research. For example, future use of the model should incorporate the measurement of intra-event variations in electrical conductivity of rainfall as an input in order to improve model accuracy and precision. Repeated under-estimation of herbicide concentration in drainflow when suspended sediment concentrations were elevated indicated that desorption hysteresis may have occurred at the soil surface and during transport through the tile drain system. This resulted in the transport of a greater proportion of herbicide through preferential pathways in sediment-associated form than predicted by assuming an instantaneous desorption at the soil surface. The results of the research suggest that the nature and importance of sediment-associated herbicide transport through tile drains warrants further investigation.     

Response of wheat to saline irrigation and drainage

The response of wheat (Triticum aestiuum L.) to varying depths of irrigation, quantity of water applied and to the drainage conditions was studied in 2 m × 2 m × 2 m size lysimeters filled in with a sandy loam soil. Saline water with an electrical conductivity of 8.6 dS m⁻¹ was used for irrigation. The treatments included four irrigations of 5 cm depth, four irrigations of 7 cm, and three irrigations of 9 cm, scheduled on the basis of cumulative pan evaporation, while the drainage conditions were represented by the drained and undrained lysimeters. Another treatment, using good quality water for irrigation, represented the potential yield of the crop. The growth parameters, as well as the yield, showed an improvement with larger irrigation depth increments in the drained lysimeters. But, in contrast, in the undrained lysimeters, the yield was reduced with larger irrigation depth increments, mainly due to a sharp rise in water table depth during the irrigation cycles. The rise and fall in water table showed a high sensitivity and were also highly disproportionate to the irrigation and evapotranspiration events. The yield tended to be higher with a smaller depth of water applied more frequently in the undrained lysimeters. But, in view of the limitations of conventional surface irrigation to apply water in smaller depth increments, an improved drainage is imperative for cropping in shallow saline water table conditions.     

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.