Showing papers in "Irrigation and Drainage Systems in 1997"
TL;DR: In this article, the performance indicators currently used in the Research Program on Irrigation Performance (RPIP) are summarised and compared to other performance indicators used in other research programs, including water delivery, water use efficiency, maintenance, sustainability of irrigation, environmental aspects, socioeconomics and management.
Abstract: This paper summarises the performance indicators currently used in the Research Program on Irrigation Performance (RPIP).Within this Program field data are measured and collected to quantify andtest about 40 multidisciplinary performance indicators. These indicatorscover water delivery, water use efficiency, maintenance, sustainability ofirrigation, environmental aspects, socio-economics and management. Theindicators now are sufficiently mature to be recommended for use inirrigation and drainage performance assessment.
133 citations
TL;DR: In this paper, a lack of understanding of the links between water scarcity, food production, food security, and environmental sustainability has been identified, and research to improve this understanding would have high payoffs.
Abstract: Global food projections indicate that food prices in the next threedecades will likely be stable or decline, but progress inreducing malnutrition in developing countries will be slow. Smallshortfalls in crop productivity growth would lead to rising foodprices and worsening malnutrition. Increased food production fromirrigation is essential, and will require expansion of irrigatedarea and water supplies, and improved efficiency of use of existingwater supplies. Neither of these growth factors will prove easy, andboth will require complex institutional and policy reforms. Failureto meet food production needs through efficient expansion andintensification of irrigated agriculture would increase pressure onland resources and hasten the process of environmental degradation.Irrigation and water development strategies have been hampered bya lack of understanding of the links between water scarcity, foodproduction, food security, and environmental sustainability.Research to improve this understanding would have high payoffs.
97 citations
TL;DR: In this article, the authors examine trends in the understanding and policies toward farmer participation in irrigation management over the past 20 years, with special attention toexperiences with induced participation and management transfer programs in the Philippines, Sri Lanka, Pakistan, Senegal, Columbia Basin USA, and Mexico.
Abstract: This article examines trends in the understandingof and policies toward farmer participation in irrigationmanagement over the past 20 years, with special attention toexperiences with induced participation and management transferprograms in the Philippines, Sri Lanka, Pakistan, Senegal,Columbia Basin USA, and Mexico. Key lessons relate to the valueof social organizers as catalysts; the role of the irrigationagency as partner; and the enabling conditions for participation.As levels of income and infrastructure rise, we can expect moreformal organizations that enable farmers to deal with bankaccounts, service contracts, water rights, water markets, andadvanced technology in irrigation systems. The impact ofparticipation on irrigation performance needs to be evaluated notjust in terms of reductions in government costs, but by whetherimprovement in physical structures and farmers‘ control overwater are great enough to offset the farmers‘ costs ofparticipating.
83 citations
TL;DR: In this paper, a case study on water management within a traditional, falaj irrigation system in northern Oman was conducted, where daily irrigation applications and crop water use was monitored during an 11-month period among 6 farm holdings at Falaj Hageer in Wilayat Al-Awabi.
Abstract: This paper reports on results from a case study on water management within a traditional, falaj irrigation system in northern Oman. In the planning and design of regional irrigation development programs, generalized assumptions are frequently made as to the efficiency of traditional surface irrigation systems. Although qualitative accounts abound, very little quantitative research has been conducted on on-farm water management within falaj systems. Daily irrigation applications and crop water use was monitored during an 11-month period among 6 farm holdings at Falaj Hageer in Wilayat Al-Awabi. Contrary to the frequent assumptions that all surface irrigation systems incur unnecessarily high water losses, on-farm ratios of crop water demand to irrigation supply were found to be relatively high. Based on actual crop water use, irrigation demand/supply ratios among monitored farms varied from 0.60 to 0.98, with a mean of 0.79. Examination of the soil moisture budget indicates that during most irrigations of wheat (cultivated in the low evapotranspiration months of October–March) sufficient water is applied for the shallow root zone to attain field capacity. With the exception of temporary periods of high falaj delivery flows or periods of rainfall, field capacity is usually not attained during irrigations within the more extensive root zones of date palm farms. The data presented in this paper should provide a better understanding of water use performance by farmers within traditional falaj systems. Moreover, these data should also serve to facilitate more effective development planning for irrigation water conservation programs in the region.
43 citations
TL;DR: Wang et al. as discussed by the authors reviewed the research and practice on the utilization of shallow saline groundwater in the part east of South GreatCanal in Haihe River Plain and found that using saline water for irrigation plays important role for overcoming the constraints and increasing crops yields.
Abstract: Drought and fresh water shortage are the main limiting factorsfor sustainable development of agriculture in North China Plain.Using saline water for irrigation plays important role forovercoming the constraints and increasing crops yields. Theexploitation and utilization of shallow saline groundwaterenables to regulate the groundwater depth and to promote thetransform of precipitation into available water resources.Thispaper reviews the research and practice on the utilization ofshallow saline groundwater in the part east of South GreatCanal in Haihe River Plain. Findings are presented on the useof saline water, cycling and blending of saline and fresh waterfor irrigation, indexing of crops salt tolerances, regulating forsoil salt-water regime, saline-alkali land reclamation andgroundwater quality freshening. These approaches help therational regulation and utilization of the local water resourcesfor comprehensive control of drought, waterlogging and salinity.
36 citations
TL;DR: In this article, the authors explore current dissatisfaction withpast irrigation improvement approaches and examine reasons such dissatisfaction is so widespread, and build on these themes to speculate on directions inwhich both public irrigation agencies and local level management institutions will evolve in the future.
Abstract: The paper explores current dissatisfaction withpast irrigation improvement approaches and examines reasonssuch dissatisfaction is so widespread. It reviews past andcurrent efforts to improve irrigation management in developingcountries and deduces themes with implications for the future. Finally it builds on these themes to speculate on directions inwhich both public irrigation agencies and local levelmanagement institutions will evolve in the future.
30 citations
TL;DR: In this paper, a model is presented in which the wilting point is a function of the soilsalt content, and the model was used to simulate several theoretical and experimentalsituations for forage corn and grain corn.
Abstract: In most cases, when calculating soil water availability, only thewater content is considered. The effect of salinity on the wiltingpoint is neglected. The objective of this work is to use asimulation model (CERES-maize) in order to predict cornyields as a function of water salinity under severalenvironmental, agrotechnical, and plant characteristics. A modelis presented in which the wilting point is a function of the soilsalt content. At high salinity, the water content at wilting pointis higher than at low salinity, resulting in an insufficient amountof available water and, therefore, a reduced yield. The modelwas used to simulate several theoretical and experimentalsituations for forage corn and grain corn. Simulation resultsshowed that nitrogen fertilization increases the salinity thresholdvalue and the yield sensitivity (rate of yield reduction per unitof salinity). The also showed that forage corn is more sensitiveto salinity than grain corn. If the soil is not leached, a heaviersoil texture has a higher salinity threshold value. On the otherhand, if the soil is leached, the soil texture has no influence onthe salinity threshold value and the yield is less sensitive tosalinity in sandy soils. The determination coefficient (r2= 0.75) indicated that the results of the simulations were in goodagreement with the field data.
27 citations
TL;DR: In this article, the authors present an overview of different options for reuse of drainage water and guidelines for its safe use. But they do not consider the use of the non-consumed fraction ('drainage water') of the irrigation water already diverted.
Abstract: Increasing competition for water of good quality and the expectation that at least half of the required increase in food production in the near-future decades must come from the world's irrigated land requires to produce more food by converting more of the diverted water into food. Reuse of the non-consumed fraction ('drainage water') of the irrigation water already diverted is a proven but risky option for better fresh water management. This paper presents an overview of different options for reuse of drainage water and guidelines for its safe use. Criteria for maximum irrigation water salinity to prevent soil deterioration and crop yield reduction, for the maximum concentration of toxic substances and limits for bacteriological water quality are given. Examples of sustainable reuse of drainage water in Egypt, India and the USA are presented. The usefullness of simulation models for the analysis of regional water and salt balances is demonstrated.
25 citations
TL;DR: In this article, the authors describe the functioning and organization of water markets, using information collected in sample watercourses of the Fordwah Branch irrigation system, South-Punjab, Pakistan.
Abstract: As a response to inadequacy in canal water supplies, farmers in Pakistan have invested in private tubewells to control irrigation water resources. Also, they participate in surface water and groundwater markets that take place within tertiary units of the irrigation system. The present paper describes the functioning and organization of these water markets, using information collected in sample watercourses of the Fordwah Branch irrigation system, South-Punjab, Pakistan. The variability in type and intensity of water markets is investigated with regard to access to water resources and farm production strategies and constraints.
24 citations
TL;DR: In this paper, a modelling system that combines the hydraulic simulations of the canal and hydrological simulation of the irrigated command is introduced, which is applied to the Mahanadi Reservoir Irrigation Scheme, a large irrigation project in Central India.
Abstract: A modelling system that combines the hydraulic simulations of the canal and hydrological simulations of the irrigated command is introduced. It uses MIKE 11 and MIKE SHE, two well-established modelling systems, for the hydraulic and hydrological simulations respectively. In addition, it also has an irrigation scheduling module and a crop growth module. The modelling system is applied to the Mahanadi Reservoir Irrigation Scheme, a large irrigation project in Central India. The results show that presently a significant amount of water is wasted in the command during the monsoon season. It is demonstrated that the minimization of this wastage could lead to a substantial crop production in the subsequent dry season. Furthermore, the simulations illustrate the versatility of the modelling system for planning and analysing the various aspects of an irrigation project.
23 citations
TL;DR: In this paper, the selection of operative furrow irrigation modelling for real-time applications is discussed Models derived from Horton and linear infiltration through the water balance equation (WBE) are preferred to those derived from the 2-term Philip's equation and to the solution of WBE involving both the power advance function and Kostiakov's extended equation.
Abstract: The complexity of physical phenomena in furrow irrigation,where numerous parameters vary with time and space, makeempirical models more operative than mechanistic models forimproving irrigation efficiency In addition, when theseempirical models are well adapted for real-time calibration onadvance trajectory, they can be considered an efficient toolto predict irrigation performanceIn the first section of this paper, the selection of operativefurrow irrigation modelling for real-time applications isdiscussed Models derived from Horton and linear infiltrationequations through the water balance equation (WBE) arepreferred to those derived from the 2-term Philip‘s equationand to the solution of WBE involving both the power advancefunction and Kostiakov‘s extended equationThe second section shows that simplified analytical modellingoptions can be added to the basic advance-infiltration modelfor improving irrigation efficiency The modelling optiondeveloped in this paper concerns the prediction of cutoff timeand irrigation performance for closed-end furrows (CEF)The simplified analytical model for CEF based on the massconservation principle is successfully compared to field testsand numerical simulations
TL;DR: In this article, the overall irrigation efficiency, ep, for the irrigation networks in the Thessaloniki plain, in Northern Greece, was estimated from historical data, spanning eight years.
Abstract: The overall irrigation efficiency, ep, for the irrigationnetworks in the Thessaloniki plain, in Northern Greece, wasestimated from historical data, spanning eight years. Irrigationnetworks differ regarding the method of water delivery and themethod of field application. Overall irrigation efficiency is theparameter which helps to adjust water supply to meet the actualcrop water requirements. A method is introduced which calculatesnetworks ep using spatially distributed data. Efficiencyvalues for all systems were calculated using the proposed method.Seasonally averaged ep values for eight years for 32(surface and sprinkler) irrigation networks ranged from 0.38 to0.81. Analysis of the time series ep values can identifyoperational factors that might affect network ep. Sprinklerand surface network irrigation efficiencies did not show anysignificant difference.
TL;DR: The quality of service provided by the provincial Irrigation Department (DGI) to the Water Users Associations (UA), and subsequently by the UA's to the related water users, is based on the provincial water law.
Abstract: The quality of service provided by the provincial Irrigation Department (DGI) to the Water Users Associations (UA), and subsequently by the UA's to the related water users, is based on the provincial water law. The intended volume of water being delivered per considered period further depends on the water availability and on the (crop irrigation) water requirements. The Service Level (SL) compares the intended water supply with the water supply that would be required to supply the entire irrigable area with sufficient water. As soon as the intended water delivery pattern is set, the measured actual delivery can be assessed against the intention. Several performance indicators are used in this context. Based on the assessment of the Water Delivery Performance Ratio and the Overall Consumed Ratio recommendations are made on changes which can be made to improve water use and reduce problems of waterlogging.
TL;DR: In this article, the authors used a hydro-dynamic model (SIC) to assess the impact of maintenance measures on water distribution in secondary canals in south-east Punjab and found that the main cause of present inequity in waterdistribution are deviations in dimensions of tertiaryoutlets.
Abstract: In secondary canals in Pakistan‘s Punjab, the waterdistribution depends on the hydraulic characteristicsof channels, cross-structures and tertiary outlets.Maintenance of channels and structures plays a crucialrole in upholding equitable distribution of water tothe tertiary units. In the past, maintenance has beenundertaken by irrigation managers based on experienceand observations. In the present study a hydro-dynamicmodel (SIC – Simulation of Irrigation Canals) is usedto assess a priori the impact of maintenance measureson water distribution. Maintenance measures can thusbe selected that remove existing bottlenecks in thewater distribution in the most cost-effective way. The methodology is applied to a secondary canal insouth-east Punjab. The simulation results show thatthe main cause of present inequity in waterdistribution are deviations in dimensions of tertiaryoutlets, which, if restored, would make the mosteffective contribution to improve the waterdistribution. Maintenance of the channel is necessaryif its capacity diminishes.
TL;DR: In this paper, the authors analyze the cost of irrigation water to the farmers in Mendoza Province consisting of three components; canal cleaning by the farmer, a water charge to their users Association (UA), and a water charges to the provincial Irrigation Department (DGI).
Abstract: The cost of irrigation water to the farmers in Mendoza Province consists of three components; canal cleaning by the farmer, a water charge to their Users Association (UA) and a water charge to the provincial Irrigation Department (DGI). The total cost of irrigation water shows large differences when the area of the UA is taken into consideration: farmers in smaller associations pay considerably more than those in large units. This is the case for all three groups of costs. The annual budgets of 31 UA's were analyzed with respect to 19 budget items prescribed by DGI. Several of these items contain a low percentage of the total budget. Further, they make participation of users during the annual meeting in which the budget is discussed and approved unnecessary difficult. We recommend to reduce the number of budget items to 7. Because of low collection levels (average 64%) the UA's spend a major part of their income on recurrent costs like salaries. As a result little is spent on maintenance and improvement of the system, creating dissatisfaction with the paying water users. Thus. a vicious circle needs to be broken about the deterioration of the system, dissatisfaction of users, less participation in the running of the Association and further deterioration. Recent experience shows that the discontinuation of flow to non-paying users in combination with improved water delivery services by the UA breaks the circle.
TL;DR: A survey has been carried out in three Regions of north-east Italy, Emilia Romagna, Veneto and Friuli Venezia Giulia, with four objectives: (a) to update the statistics on the use of pipedrainage; (b) to describe the farms that adopt this technique asa replacement of the traditional surface drainage methods; (c) to characterise the features of the drained soils and of the drainage systems; and (d) to assess their performance as mentioned in this paper.
Abstract: A survey has been carried out in three Regions of north-eastItaly, Emilia Romagna, Veneto and Friuli Venezia Giulia, withfour objectives: (a) to update the statistics on the use of pipedrainage; (b) to describe the farms that adopt this technique asa replacement of the traditional surface drainage methods;(c) to characterise the features of the drained soils and of thedrainage systems, and (d) to assess their performance Withalmost 70000 ha drained, the Regions present almost all of thepipe drained area in Italy Pipe drainage first saw applicationsin the last seventies and became increasingly popular during theeighties Most pipe drainage systems are installed in heavysoils, where the underground waterlogging is due to seasonalperched water table or to infiltrations from rivers or sea Due tothe pedoclimatic variability of the area, slightly differentsolutions in terms of design variables and installation criteriaare found, but the following features are quite common: drainspacing 11–13 m slope 01–03%, depth 09–1 m The pipe drains discharge in open collectors (single systems) Anincreasing interest for the use of the drainage systems forsubirrigation purposes has been observed, particularly inVeneto, requiring some adjustment in the drainage design Theperformance of drainage in terms of control of water tabledepth and maintenance requirements are considered satisfactoryin almost all the cases The most effective solutions forsuccessfully managing the subirrigation are also describedThe introduction of pipe drains allows to enlarge fields (to morethan 10 has) and to save time for carrying out the operations forcrop cultivation The crop yield in pipe drained fields is slightly higherto that obtained in the traditionally drained fields, withthe exception of winter wheat
TL;DR: In this article, the proposed improvements at mesqa level for the Bahr El Saidiarea, which is representative for the irrigation areas under IIP, are described and their effect on the irrigation practice; review, evaluation and refinement of three alternatives for mesqa improvement and appraisal from management, operation and social point of view.
Abstract: Irrigated agriculture has beenpractised in Egypt for thousands of years. Manyprojects have been implemented and new projects arestill needed to improve the existing irrigationnetworks to increase the agricultural productivity aswell as the area of cultivable land. Recently theMinistry of Public Works and Water Resources (MPWWR)in Egypt started the Irrigation Improvement Project(IIP) with the objective to increase the productionfrom the existing agricultural land. To achieve thisobjective IIP proposed the redesign of main and branchcanals, the improvement or replacement of existingtertiary canals (mesqas) and the establishment ofWater Users Associations (WUA's). IIP emphasizes thatfor an optimal effect of the proposed improvements achange from rotational supply to continuous supply,from upstream flow control to downstream flow controland from the existing Agricultural Extension Serviceto a new Irrigation Advisory Service (IAS) isnecessary. This paper mainly focuses on the proposedimprovements at mesqa level for the Bahr El Saidiarea, which is representative for the irrigation areasunder IIP. The aspects presented are:– description of the improvements and their effecton the irrigation practice;– review, evaluation and refinement of three alternatives for mesqa improvement and appraisal from management, operation and social point of view;– hydrodynamic modelling to assess the hydraulicperformance of the three alternatives.
TL;DR: In this article, the authors present a summary illustration showing several items in a typical stilling well and broad-crested weir that need attention, and offers suggestions for correcting the deficiencies.
Abstract: Practical technologies can encourage farmers to adopt practices that support sustainable irrigated agriculture. Important among these are convenient water measurement and control techniques. Many simple constructions or operating procedures are available that can bring considerable convenience to farmers and irrigation delivery system operators. Some are new technologies and some are improvements on older technologies. Many can be implemented with small expense. Some are superior replacements for current practices. The techniques and devices discussed included: (a) accurate and convenient zero setting for weirs and flumes (b) pressure-transducer field checks, (c) easy-to-use scales for orifice and Venturi meters, (d) flow-profile improvers to assist accurate meter operations in irrigation pipelines, (e) floor sills and wave suppressors for canals that usually flow at variable depths of flow, (f) water surface slope measurements–based on static-pressure tubes, and (g) field checks of flow velocity profiles to evaluate flow conditioning using rising-bubble techniques for flow-profile visualization. Many of the concepts are demonstrated in a summary illustration showing several items in a typical stilling well and broad-crested weir (long-throated flume) that need attention, and offers suggestions for correcting the deficiencies.
TL;DR: The legal-administrative setting for the use of water resources in Mendoza Province is founded on different legal rules as mentioned in this paper, including the National Constitution, the Argentine Civil Code, National Laws, the Constitution of the Provincial State, the General Water Law, (legal) administrative regulations of the General Department of Irrigation.
Abstract: The legal-administrative setting for the use of water resources in Mendoza Province is founded on different legal rules. This includes the National Constitution, the Argentine Civil Code, National Laws, the Constitution of the Provincial State, the General Water Law, (legal) administrative regulations of the General Department of Irrigation. The current water law is based on the roman law, on the Arab irrigation water rights which were brought to Argentina by the Spaniards and on the practices of the original American pre-Colombian 'intermediate law'. The latter is marked by a strong regional sense. As such, the water law is strongly influenced by the region's elements of nature and attempts to offer solutions to problems. The legal rules are discussed from a behavioral and organizational perspective. Examples from the Lower Tunuyan System are given to illustrate the day-to-day effects on irrigation water management.
TL;DR: In this article, a model RESBAL was coupled with the calibrated and validated on-farm water management model FAIDS and run for eight years to optimally design a series of connected reservoirs for the disposal of drainage effluent from an area provided with a subsurface drainage system.
Abstract: Nearly 60 per cent of the geographical area of Haryana state in Indian Union is underlain by saline ground water. The intra-basin transfer of surface water in the early sixties for irrigation has disturbed the hydrodynamic equilibrium resulting in waterlogging and salinization in large parts of the state. The existing inland drainage basin conditions did not permit the disposal of drainage effluent. The reuse system was therefore, integrated with the drainage system. A model RESBAL was coupled with the calibrated and validated on-farm water management model FAIDS and run for eight years to optimally design a series of connected reservoirs for the disposal of drainage effluent from an area provided with a subsurface drainage system. The possibility of the reuse of the disposed water for irrigation, aqua culture and salt harvesting was also studied comprehensively in order to maintain proper salt balance in the root zone.
TL;DR: In this article, a field investigation was conducted in a study area of33,138 ha in the Northern Delta of Egypt within Daqahliya Governorate, where an accurate depth of the impermeable barrier and an effectiveradius of drain pipes which should be used in the design process using the exact solution.
Abstract: The steady-state drainage equation ofHooghoudt (1940) has adrawback that tables for the determination of the so-called’’equivalentlayer, de‘‘ are needed. These calculations arecumbersome as de 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 Hooghoudt‘s 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.
TL;DR: In this article, the authors report on laboratory research on the sediment passage capability through long-throated flumes and broad-crested weirs with which the Froude number in the approach channel does not exceed 6 over a distance of about 20 times the water depth upstream of the structure.
Abstract: This paper reports on laboratory research on the sediment passagecapability through long-throated flumes and broad-crested weirs withwhich the Froude number in the approach channel does not exceed 06over a distance of about 20 times the water depth upstream of thestructure Design rules are given for any combination of flume or weirin combination with any channel
TL;DR: In this article, the flow resistance required in the Manning formula was calculated from laboratory experiments and field data, using the unobstructed part of the cross-section only and excluding the part covered by weeds.
Abstract: 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.
TL;DR: In this paper, a procedure is proposed to determine the frequency of weed control based on hydrological and hydraulic conditions, which can be used to calculate the permissible flow rate of a water course.
Abstract: In many parts of the Netherlands a dense network of water courses is necessary to drain the land. A related aspect is the changing transport capacity of the water courses due to the growth of aquatic plants in the growing season. In turn this phenomenon requires aquatic weeds to be controlled by water boards in order to maintain the water course's required capacity. The procedure outlined in this paper can be used to determine the frequency of weed control based on hydrological and hydraulic conditions. The drainage from groundwater gives an expected variation in discharge over the growing season. The permissible flow rate is governed by both the growth of weeds and the permissible water levels in the water course. Weed control is necessary during the growing season when the expected discharge is more than the permissible flow rate. This procedure has been incorporated in the model MWW (Maintenance of Water courses by Water boards). An example how to use MWW is given.
TL;DR: In this article, a methodology based on a groundwater-balance approach was developed and applied in Schedule I-B of the Fourth Drainage Project near Faisalabad in Pakistan to determine the seasonal net recharge in this area, anumerical groundwater model was run in inverse mode.
Abstract: To assess the drainable surplus of an irrigated area, a methodologybased on a groundwater-balance approach was developed and appliedin Schedule I-B of the Fourth Drainage Project near Faisalabad inPakistan. To determine the seasonal net recharge in this area, anumerical groundwater model was run in inverse mode. The data inputfor the model consisted of the geometry of the aquifer system, theaquifer parameters, and historical watertable elevations. The seasonalnet recharge values, calculated from the individual recharge anddischarge components, were “tuned” with the results of the inversemodelling. The advantage of such an integrated approach is that allthese components are linked. The design net recharge was estimatedfrom the historical net recharge of the wettest monsoon in the studyperiod. Its rainfall recharge values were then substituted for those of adesign monsoon. In this substitution procedure, the rainfall rechargemethodology and parameters were adopted from the tuning procedure.From this design net recharge, estimates could be made of the requireddrainable surplus, with and without drainage simulation.
TL;DR: In this article, a vertically adjustable flume for canal flow measurement is described, which allows control of the ponding restriction from nearly zero to just enough restriction to gain measurement control of flow at nearly all flow rates in the design range of a particular size.
Abstract: The utility of developing vertically-adjustable flumes for canal flow measurement systems, is important to several problems in field practice. One involves the perception by some canal water users that flumes and weirs significantly and harmfully restrict flow. These perceptions, correct only sometimes, occur often enough to cause resistance to flow measurements and impedance to proper irrigation management. Parshall flumes and Cutthroat flumes require ponding depths upstream equal to about 40% of head reading while long-throated flumes and the related broad-crested weirs require only 10 to 15%. The actual head drop through all of these flumes is greater than hydraulically necessary for all but the maximum design discharge. The highly obvious excessive ponding is often misunderstood as a harmful restriction to flow. Also, the velocities at the low flows are reduced by this excessive ponding, which can aggravate sediment accumulation. The system described herein allows control of the ponding restriction from nearly zero to just enough restriction to gain measurement control of the flow at nearly all flow rates in the design range of a particular size. This reduces the amount of visible restriction. For a small structure size, with a control section less than 1 m wide and flowing under a head of less than about 25 to 30 cm, this restriction is about 10% to 15% of the head reading, or about 3 to 5 cm at maximum head. This maintains relatively high velocities in the approach channel for assisting sediment movement. The device is applicable to measuring flow rates in unlined and lined canals. The system described permits adjustment of the canal flow levels, reduces the perception of ponding, and minimizes the induced sediment problems.