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).     

Modeling subsurface drainage for salt load management in southeastern Australia

Subsurface drainage has been implemented in irrigation areas of South-eastern Australia to control water logging and land salinisation. Subsurface drainage has been identified as a major salt exporter from irrigated areas. The water table management simulation model DRAINMOD-S was evaluated to simulate daily water table depth, drain outflow, and salt loads by using experimental field data from a two year field trial was carried out in the Murrumbidgee Irrigation Area South-eastern Australia to study different options for subsurface drainage system design and management to reduce salt load export. Three subsurface drainage systems were modeled, deep widely spaced pipe drains, shallow closely spaced drains and deep pipe drains that were managed with weirs to prevent flow when the water table fell below 1.2 m. The reliability of the model has been evaluated by comparing observed and simulated values. Good agreement was found between the observed and simulated values. The model confirmed the field observations that shallow drains had the lowest salt load and that by managing deep drains with weirs salt loads could be significantly reduced. This work shows the value of the DRAINMOD-S model in being able to describe various drainage design and management strategies under the semi-arid conditions of South-eastern Australia. The model can now be used to investigate design and management options in detail for different site conditions. This will assist decision makers in providing appropriate subsurface drainage management policies to meet drainage disposal constraints within integrated water resources management planning.     

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.     

Time-dependent drainage from root zone and drainage coefficient under different irrigation management levels for subsurface drainage design in Egypt

Drainage water from the lower boundary of the root zone is an important factor in the irrigated agricultural lands for prediction of the water table behavior and understanding and modeling of water and chemical movement in the soil profile. The drainage coefficient is an important parameter for the design of subsurface drainage. On a 33,138 ha of the Nile Delta in Egypt, this study is conducted using 90 irrigation periods over a 3-year crop rotation to estimate the time-dependent drainage from the root zone and the design subsurface drainage coefficient with different cropping seasons and irrigation management levels.The results showed that the cropping seasons and the irrigation management levels as indicated by different irrigation efficiency are significantly affected the drainage rate from the root zone and the design value of subsurface drainage coefficient. Drainage rates from the root zone of 1.72 mm/d and 0.82 mm/d were estimated for summer and winter seasons, respectively. These rates significantly decreased in a range of 46% to 92% during summer season and 60% to 98% during winter season when the irrigation efficiency is increased in a range of 5% to 15%. The subsurface drainage coefficient was estimated to be 1.09 mm/d whereas the design drain pipe capacity was estimated to be 2.2 mm/d, based on the peak discharge of the most critical crop (maize), rather than 4.0 mm/d which is currently used. A significant decrease of the drainage coefficient and the drain pipe capacity ranges from 18% to 45% was found with the increase of irrigation efficiency in a range of 5% to 15%. The leaching requirement for each crop was also estimated.     

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.     

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.     

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.     

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.     

新疆内陆干旱重盐碱地区暗管排水技术的应用

用两个试验区六年试验资料进行分析，以明沟排水为对照，论述了内陆干旱重盐碱地区暗管排水改良盐碱地的效果及社会、经济效益。提出了暗管排水的设计标准及技术参数，为类似地区推广暗管排水技术提供了依据。     

A new approach to water management of tropical peatlands: a case study from Malaysia

The use of peatlands in the humid tropics requires drainage to remove excess rainfall. The design principles for the drainage systems currently being implemented on peatlands are the same as for mineral soils. The objective of such systems is the timely removal of excess rainfall by surface runoff. For peatlands, with their different soil-hydraulic characteristics, these systems have resulted in poor watertable control and high rates of irreversible subsidence. Concerns about this rate of subsidence and the level of sustainability of the present land use have prompted a study to develop a new water management system. This new system includes a shift from a drainage system that focuses on discharge of excess water towards a system that combines drainage and water conservation. In the new two-step design, the drain spacing and corresponding drain discharges are obtained with a steady-state approach. These outputs are used to calculate the capacity of the drains, including control structures, using an unsteady-state approach. The new system results in a shallower but more narrowly spaced drainage system and maintains a more constant but relatively high watertable and reduces subsidence. It should be remembered however, that even with the improved water management, subsidence cannot be arrested; it is the price one has to pay for the use of tropical peatlands.     

Analytical Approximation of Subsurface Total Drainage Quantity in Non-Steady State Drainage Flow, and its Verification in Heavy Soils

The subsurface total drainagequantity is one of the most importantindicators for the drainage policy of watermanagement. The methods of estimationof the subsurface total drainage quantityunder unsteady state drainage flow maybe different in consideration of the timeduration of the process and in relation tothe type, quality and quantity of the data used.Simple analytical approximation of thesubsurface total drainage quantity, whichwas developed by the operation of asubsurface pipe drainage system insaturated soil under unsteady statedrainage flow, is viewed in this paper.Derivation of the formula for subsurfacetotal drainage quantity is based onthe subsurface flow to drains with anapproximately horizontal impervious layer,where the Dupuit's assumptions and Darcy'slaw are applied. It is assumed that duringthe drainage process there will be no rechargeto the groundwater table.This analytical approximation of thesubsurface total drainage quantity at acertain time t was formed into a singleexponential equation. The correctness andapplicability of the analyticalapproximation of the subsurface totaldrainage quantity was verified with the help ofthe field measurements on the heavy soilsof an experimental watershed area of theResearch Institute for Soil and WaterConservation (RISWC) Prague-Zbraslav, CzechRepublic. The shape and the parameters ofthis subsurface total drainage quantityequation were also proved by nonlinearregression analysis, with application of themethod of Marquardt.This analytical approximation should serveas an elementary tool of water engineeringpractice for an immediate estimation of thevalues of subsurface total drainagequantities from field pipe drainagesystems in saturated soils. It shouldalso serve as a tool with only a minimumamount of information (the basic soilhydrology data and drainage system basicdesign parameters) and its application to awide range of drainage policies ispossible.     

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.     

Drainage Design in the Gharb Plain in Morocco

The Gharb plain in Morocco faces both problems of excesswinter rainfall and salinity hazards due to a shallow,permanent and saline groundwater. A large area of 80.000 hahas been equipped with subsurface drains out of a totalplanned area of 200.000 ha. This system has been designedwithout any local references and has encountered severalmaintenance problems mainly caused by high drain depths.A pilot experiment has been installed to provide drainagedesign criteria appropriate to the local conditions. Mainexperimental results based on water and salinity balance andon groundwater flow are presented in the paper. They show thatin the Gharb plain, drainage systems should be designed fromwinter drainage design criterion. The paper also stresses onthe particular attention to paid to the surface drainage whichremove about 40% of the excess water.     

岩溶山区泉渍低产田暗管排水试验研究

为配合联合国粮食计划署对湖南湘西援助的“W.F.P.中国3779项目”的实施,探索岩溶山区泉渍低产田治理工程技术措施和经验,我们从1989年起连续三年进行了以暗管排水为主要措施的治理试验。 本文对泉渍低产田暗管排水系统的规划设计进行了总结,对治理工程产生的环境和经济效益进行了分析,对岩溶山区泉渍低产田暗管排水标准及工程技术要素进行了总结和探索。     

改进暗管排水结构型式对排水性能的影响

提出一种占用耕地少、排水流量较常规暗排大且环境友好的改进暗排。基于室内土柱试验,分析改进暗排在地表积水、土体饱和条件下的排水除涝性能及其机理,提出地表积水土体饱和入渗条件下改进暗排排水流量的理论计算公式。结果表明,改进暗排可以有效提高暗管排水能力,试验条件下,反滤体宽度为2~6 cm的改进暗排在自由出流条件下的排水流量为常规暗排排水流量的2~3倍;积水层深度相同时,改进暗排排水性能随反滤体宽度的增加而增大,但增幅逐渐减小;土体介质和反滤体的渗透系数差别越大,改进暗排的排水作用越明显。理论方法计算结果与试验结果相吻合,证明提出的理论计算公式是合理可行的。     

The effect of standing water above drains on the water table height midway between drains

Wesseling (1964) stated that standing water above drains as a result of submerged outlets creates a radial flow in the vicinity of the drains which promotes flow conditions so that a smaller rise of the water table height midway between drains results. Wesseling (1979) concluded the same for standing water above drains as the result of too high entrance resistance. Standing water above drains may also be due to overpressure in the drains as a result of too small pipe diameter or to irregular drain slopes. With the exception of submerged outlets the resulting water table rise midway between drains is however in the same order of the water table rise above the drain as can be derived from theoretical analysis. This conclusion was confirmed by measurements at an experimental field where the standing water above drains, as a result of overpressure, and the water table midway between drains were monitored in a field located at the northwest of the Nile Delta. In spite of the low discharge rates, overpressure was observed in the drains. It was mainly attributed to irregular drain slopes. The analysis of field data showed that the water table midway between drains rises at least the same as the water table height above the drains. Since overpressure in drains causes a decrease of the dewatering zone, a careful and accurate installation is of utmost importance for the proper functioning of a drainage system.     

Review of the Egyptian experience in implementing land drainage projects

About 30 years have passed since the Government of Egypt embarked on implementing a series of large scale drainage projects. At present, about 3.8 million acres have been provided with drainage systems on the basis of systematic pre-drainage investigations and designs. The target is to provide drains in approximately 6.4 million acres in the Nile Valley and Delta.The implementation of the subsurface drainage system is carried out by the public sector and private contractors under direct supervision of governmental regional departments. The implementation process depends on many factors related to the drainage material, machinery, manpower, site requirements, farmers and organizations involved. Problems and constraints are sometimes challenging, however, the annual rate of implementation has gradually increased to 170,000 acre/year.This paper discusses the different aspects involved in the implementation process of drainage systems. The development in materials, machinery and construction technologies will be reviewed. Institutional and management factors are going to be also considered.     

农田“三暗”工程的试验与推广

嘉定县地处长江口太湖碟形洼地的东缘。1982年以来,逐步试验推广以除渍为重点的、兼有灌、排、降、控综合功能的农田“三暗”工程,为建设高产、稳产农田创造了良好的水利基础设施。     

Evaluation of impact of Khushab sub surface pipe drainage project in Pakistan

This paper describes the essential contents of research at a recently completed subsurface pipe drainage project located in the Khushab district of Pakistan. The paper explores the need and decision by Government of Pakistan to install a Sub Surface Pipe Drainage Project near Khushab where an old Surface Drainage System was already installed by the Provincial Irrigation and Power Department, Government of Punjab, Pakistan, since 1960. The new Sub Surface Pipe Drainage Project’s planning and executing agency M/S Euro-Consultant used existing Surface Drains with remodeling for to carry the additional drainage effluent of newly constructed sump pumps of the pipe drainage system connected to the old drains by means of small outfall drains. Until now the new system is working well in lowering the water table as well as increasing the agro-socio-economic status of the local population.