Search

Solar power development over canals is an emerging response to the energy–water–food nexus that can result in multiple benefits for water and energy infrastructure. Case studies of over-canal solar photovoltaic arrays have demonstrated enhanced photovoltaic performance due to the cooler microclimate next to the canal. In addition, shade from the photovoltaic panels has been shown to mitigate evaporation and potentially mitigate aquatic weed growth. However, the evaporation savings and financial co-benefits have not been quantified across major canal systems. Here we use regional hydrologic and techno-economic simulations of solar photovoltaic panels covering California’s 6,350 km canal network, which is the world’s largest conveyance system and covers a wide range of climates, insolation rates and water costs. We find that over-canal solar could reduce annual evaporation by an average of 39 ± 12 thousand m3 per km of canal. Furthermore, the financial benefits from shading the canals outweigh the added costs of the cable-support structures required to span the canals. The net present value of over-canal solar exceeds conventional overground solar by 20–50%, challenging the convention of leaving canals uncovered and calling into question our understanding of the most economic locations for solar power. Over-canal solar photovoltaic arrays are likely to reduce water evaporation and carry financial co-benefits, but estimates are lacking. With hydrologic and techno-economic simulations of solar panels covering California’s canal network, this study shows the advantages of covering canals with solar panels.

Nitrate pollution remains an unsolved issue worldwide, causing serious effects on water quality and eutrophication of freshwater and brackish water environments. Its economic costs are still underestimated. To reduce nitrogen excess, constructed wetlands are usually recognized as a solution but, in recent years, interest has been raised in the role of ditches and canals in nitrogen removal. In this study, we investigated the environmental and economical sustainability of nitrogen removal capacity, using as a model study a lowland agricultural sub-basin of the Po River (Northern Italy), where the role of aquatic vegetation and related microbial processes on the mitigation of nitrate pollution has been extensively studied. Based on the Life Cycle Assessment (LCA) approach and costs and benefits analysis (CBA), the effectiveness of two different scenarios of vegetation management, which differ for the timing of mowing, have been compared concerning the nitrogen removal via denitrification and other terms of environmental sustainability. The results highlighted that postponing the mowing to the end of the vegetative season would contribute to buffering up to 90% of the nitrogen load conveyed by the canal network during the irrigation period and would reduce by an order of magnitude the costs of eutrophication potential.

Decreasing nitrate concentrations is one of the most relevant Water Framework Directive (WFD) goals, which today is still unreached in several European countries. Vegetated canals have been recognized as effective filters to mitigate nitrate pollution, although rarely included in restoration programs aimed at improving water quality in agricultural watersheds. The Po di Volano basin (713 km2, Northern Italy) is a deltaic territory crossed by an extensive network of agricultural canals (~1300 km). The effectiveness in buffering nitrate loads via denitrification was assessed for different levels of in-stream emergent vegetation maintenance by employing an upscale model based on extensive datasets of field measurements. The scenarios differed for the canal network length (5%, 20%, 40%, and 60%) where conservative management practices were adopted by postponing the mowing operations from the middle of summer, as nowadays, to the early autumn, i.e., the vegetative season end. The scenario simulations demonstrated that the capacity to mitigate diffuse nitrate pollution would increase up to four times, compared to the current condition (5% scenario), by postponing the vegetation mowing to the end of the vegetative season in 60% of the canal network length. By preserving the in-stream vegetation in 20% of the canal network, its denitrification capacity would equal the nitrate load reduction target required for achieving, from May to September, the good ecological status according to the WFD in waters delivered to the coastal areas. Changing the timing of vegetation mowing may create a large potential for permanent nitrate removal via denitrification in agricultural landscapes, thus protecting the coastal areas when the eutrophication risk is higher. Conservative management practices of in-stream vegetation might be promoted as an effective low-cost tool to be included in the WFD implementation strategies.

This research proposes a novel generic method for irrigation scheduling in a canal network to optimize multiple objectives related to canal scheduling (e.g. maximizing water supply and minimizing imbalance of water distribution) within multiple hierarchical layers (e.g. the layers consisting of the main canal, distributaries) while utilizing traditional canal scheduling methods. It is based on modularizing the optimization process. The method is theoretically capable of optimizing an unlimited number of user-defined objectives within an unlimited number of hierarchical layers and only limited by resource availability (e.g. maximum canal capacity and water limitations) in the network. It allows flexible decision-making through quantification of the mutual effects of optimizing conflicting objectives and is adaptable to available multi-objective evolutionary algorithms. The method’s application is demonstrated using a hypothetical canal network example with six objectives and three hierarchical layers, and a real scenario with four objectives and two layers.

Dredging of the UK canal network is an imperative operation to maintain navigation and the ecological balance of the water course and to improve water quality to ensure that restoration works that have been carried out on the network since the 1960s continue to enrich the canal transport legacy for future generations. With this in mind, continual improvement and economic efficiencies are sought to ensure that more canal miles can be dredged to maintain and enhance the green corridors of Britain while providing value for money for each pound spent on canal maintenance. One such initiative is the innovative use of coastal dredging technology adapted for use on inland waterways in order to provide a system for specifically increasing production on spot dredging projects, resulting in a reduction in programme time and in turn increasing the number of miles dredged without an increase in expenditure.

This study estimates and compares the effects of small and large irrigation dams on cropland productivity in South Africa. To this end, a panel data set of South African river basins is constructed. The econometric analysis reveals that although large dams increase cropland productivity downstream, they have a negative effect on cropland within the vicinity. However, their existence can enhance the relatively small positive impact of local small dams. Although a cost-benefit analysis of irrigation benefits shows that small dams may be more viable than large ones, large dams can play a potentially important role within a system of both types of dams.

For development of irrigated agriculture in the Tapi basin, Ukai-Kakrapar Scheme, one of the biggest irrigation scheme in Gujarat, was taken up by the Government of Gujarat. Tapi is one of the largest rivers in central India which flows west-ward and discharges into the Arabian Sea. The present project work has been taken to study problems in existing unlined Kakrapar right bank canal of Kakrapar project. Kakrapar weir is located on river Tapi in village Kakrapar of Mandvi taluka of Surat district. As increased in demand-of food and fodder, demand of water for irrigation is also increasing In unlined canal high velocity cause erosion and heavy seepage loss leads to water logging problems in surrounding area. These problems can be solved by canal lining. Both these reasons have reduced the availability of water to the farmers. With modernization of canal one has to take into consideration the existing cross drainage or regulating structures on existing canal has also to be redesigned. Detail economic analysis is also done giving effective measures to reduce the cost. Thus to improve the efficiency of the canal network, modernizing existing canals has become need of the hour.

India plans to transfer water from the water surplus region of the north-east to the water scarce regions of western and southern India. The plan is called the National River Linking Project (NRLP). Sixteen links in the Himalayan region and 14 links in the Peninsular region are proposed that will transfer annually about 174 Billion m 3 (Bm 3 ) of water through a canal network of 14,900 km. It will involve connecting 37 rivers and construction of dams/storages in 3,000 places. It is estimated to cost US$ 120 Billion (in 2000 price). The projected benefits are additional irrigation to 34 million hectares of land, generation of 34,000 MW of electricity, reduction of floods, and social upliftment. Many prominent experts and personalities have criticized the project claiming that it will be a financial, social and environmental disaster. Both the proponents and opponents think that India will be doomed depending on whether the NRLP is implemented or not (Amarsinghe 2009). The International Water Management Institute (IWMI) in collaboration with the Challenge Program for Water & Food (CPWF) undertook a three year Strategic Analysis of the NRLP to evaluate the NRLP concept with a detailed analysis. This paper is a general description of the NRLP, and it summarizes the findings of the Strategic Analysis of this Project undertaken by IWMI-CPWF. Further, it explores the possible consequences to India's neighbors in general and Nepal in particular. Hydro Nepal; Journal of Water, Energy and Environment Vol. 12, 2013, January Page: 13-19 DOI: http://dx.doi.org/10.3126/hn.v12i0.9026 Uploaded Date : 10/28/2013

The canals are designed to transport water to meet irrigation and other water demands or to divert water from surplus basins to deficient basins to meet the ever increasing water demands. Though the positives of canal network are increase in agricultural output and improvement in quality of life, the negatives of canal introduction and irrigation, along its route, are inherent problems of water logging and salinity due to seepage from canals and the irrigation, when not managed properly. To plan strategies to prevent waterlogging and salinity, it is necessary to predict, in advance, the probable area which would be affected due to seepage. This paper presents a methodology to predict the area prone to water logging due to seepage from canal by using 2D seepage solutions to 3D field problem. The available analytical solutions for seepage from canals founded on pervious medium and asymmetrically placed drains, have been utilized. The area, prone to waterlogging, has been mapped using GIS.

The western part of India is hot desert, which is known as Thar Desert. The largest extent of this desert is spread over Rajasthan state. In order to increase agriculture potential of desertic soil Indira Gandhi Canal Project (IGCP) was introduced. The development of IGCP project has bought changes in the land use pattern in terms of increase in area under the agriculture. The increase in area under agriculture and under irrigation network has brought fluctuations in the groundwater level. This fluctuation in groundwater level is result of the seepage of water through the excessive irrigation and the seepage from the canal network. Thus the human impact in form of land-use pattern of a land is an important determinant of rise and fall in groundwater level. The spatial and temporal variation in groundwater level has been analysed Inverse Distance Weightage technique across different pentards for 128 observation wells of the Anupgarh, Vijayanagar and Suratgarh tehsil of Sriganganagar district of Rajasthan, which lies in the northwestern part of IGCP Stage I.

a b s t r a c t Objectives: MicroCT allows the complex canal network of teeth to be mapped but does not readily distinguish between structural tissue (dentine) and the debris generated during cleaning. The aim was to introduce a validated approach for identifying debris following routine instrumentation and disinfection. Methods: The mesial canals of 12 mandibular molars were instrumented, and irrigated with EDTA and NaOCl. MicroCT images before and after instrumentation and images were assessed qualitatively and quantitatively. Results: Debris in the canal space was identified through morphological image analysis and superimposition of the images before and after instrumentation. This revealed that the removal of debris is prohibited by protrusions and micro-canals within the tooth creating areas which are inaccessible to the irrigant. Although the results arising from the analytical methodology did provide measurements of debris produced, biological differences in the canals resulted in variances. Both irrigants reduced debris compared to the control which decreased with EDTA and further with NaOCl. However, anatomical variation did not allow definitive conclusions on which irrigant was best to use although both reduced debris build up. Conclusions: This work presents a new approach for distinguishing between debris and structural inorganic tissue in root canals of teeth. The application may prove useful in other calcified tissue shape determination. Clinical significance: Remaining debris may contain bacteria and obstruct the flow of irrigating solutions into lateral canal anatomy. This new approach for detecting the amount of remaining debris in canal systems following instrumentation provides a clearer methodology of the identification of such debris.

Manchester was a major centre of transport innovation in industrial Britain. Research has focused on the pioneer transport links with Liverpool, neglecting the town's extensive eastern canal network. This article analyses the commodities conveyed from 1800 to 1855 on the Rochdale Canal, the most heavily trafficked of the town's eastern waterways. It highlights the canal's importance in carrying corn to feed Lancashire's industrial work force as well as its role in transporting cotton textiles to east-coast ports and in supplying Manchester with building materials. The article also analyses the types of firm carrying goods on the canal and assesses the canal's importance in relation to Manchester's other major water routes.

During the last two decades micro-computed tomography has become the method of choice for the non-destructive assessment and quantitative morphometry of hard tissues in three dimensions. With the advent of third-generation synchrotron radiation sources, micro-computed tomography in the micrometer range has become feasible and has been employed to analyze local bone tissue properties. However, owing to limitations regarding the tradeoff between object size and spatial resolution, non-destructive conventional global computed tomography of hard tissues, such as bone, remains unachievable in the submicrometer domain so far. Here, we report on a post-processing technique for the assessment of hard tissues using local synchrotron radiation-based computed tomography, which overcomes this experimental limitation.

Most of the research on the design of feedback controllers for irrigation canals has been concentrated on single, in-line canals with no branches. Because the branches in a network are hydraulically coupled with each other, it may be difficult to automatically control a branching canal network by designing separate feedback controllers for each branch and then letting them run simultaneously. Thus feedback control of an entire branching canal system may be more efficient if the branching flow dynamics are explicitly taken into account during the feedback controller design process. This paper develops two different feedback controllers for branching canal networks. The first feedback controller was developed using linear quadratic regulator theory and the second using model predictive control. Both algorithms were able to effectively control a simple branching canal network example with relatively small flow changes.

There is a need for improvement in the operation and management of many irrigation and drainage systems worldwide. Computer models are used widely for better management. One of such models is HEC-RAS that was applied to Ordibehesht Canal at the Doroodzan irrigation network, northwest of Fars province in the southern Iran. The model was calibrated and validated for two irrigation seasons during 2001 and 2002. The present gate opening rules used to control the offtakes were simulated by the model and the discharge reductions were evaluated. Discharge reduction of offtakes due to discharge reductions at system source were evaluated by the model. Results show that the present rule is not appropriate for the present system. Fluctuations of discharge at the beginning of canal show considerable and nonuniform changes in discharge of offtakes along the Ordibehesht Canal. The head offtakes show more reductions in the water delivered than middle and tail offtakes. A new sensitivity indicator was defined and used to show the response of offtakes due to discharge changes at system source. The study also shows that HEC-RAS model can be used successfully for a large and complex irrigation system for evaluation of its performance in the absence of observed flow data and improvement of irrigation management plans.

The majority of Britain’s canal network dates from the late eighteenth and early nineteenth century and contains many examples of the vision and skills of the engineers of that period. One notable feature of the network is the hundreds of simple bridges that cross the canals. Constructed over 200 years ago, these bridges were designed to carry, at most, small-scale horse-drawn traffic. However, with both vehicle size and dependence on satellite navigation systems increasing, these historic structures are suffering impact damage that is eroding the historic fabric and costing British Waterways an estimated £2·5 million each year to repair. This paper considers the issue of bridge strikes on the Lancaster canal in the north west of England, and outlines how British Waterways are seeking to promote partnerships with communities and regulatory authorities to minimise damage. When such repairs are completed they are often required to be undertaken at short notice, in inclement weather and under pressure to secure reopening. The paper thus also details how British Waterways has worked to develop and trial processes and specifications that allow the sympathetic repair of such historic structures using traditional materials and methods under the constraints mentioned above.

The Oued Righ valley located in the south-east of Algeria consists of 50 palm groves containing 2 million palm trees. The drainage flows in a traditional canal 136 km to discharge into downstream in depressions. However, the rate of urban waste in the canal increased for over the past 20 years. The physico-chemical analyses of the canal waters showed that the quality of the water is poor. With the absence of a sewage network and poor quality of water in the canal network, the waters are polluted groundwater. This new situation has caused the death of more than 50% of the palm trees.

The adjustment of structures along irrigation free-surface systems aims to achieve, or maintain, a targeted status of the canal network. The interaction between structures and reaches is an important aspect of canal control and the process of the operation itself can generate perturbations. These perturbations depend on the frequency and mode of operation as well as the sensitivity to the setting of the structures. Highly sensitive structures generate relatively large changes in their outputs for small input changes. Therefore, highly sensitive structures should be operated with more precision than others to minimize deviations between the actual and targeted states. Knowing which are the sensitive structures along a canal and how to operate them is essential for a cost-effective operational procedure. This paper presents a set of sensitivity indicators that enable the identification of sensitive structures and an assessment of their operational tolerance.

Canals in the UK typically comprise artificial channels, with a wide range of embankments and cuttings. These structures often suffer from a range of problems unique to the canal environment including age, wide variation in construction methods and, in the case of embankments, a requirement to retain water. It is the responsibility of British Waterways to regularly inspect and evaluate these slopes with regard to long-term safety and identification of maintenance requirements. A system of slope inspection procedures has been developed which is tailored to aspects of slope stability related to canal structures. This is used in conjunction with a risk evaluation procedure to identify areas of concern on a proactive basis. The results are used to co-ordinate maintenance effort, and identify requirements for more detailed ground investigation.

Irrigation-water-delivery systems are designed and managed to receive water from a source and to distribute it among farmers in order to meet their agricultural requirements. High system performance can be achieved through rehabilitation of deteriorating and inadequate physical facilities and through improved system management. Various design decisions must be made in order to rehabilitate or develop irrigation-water-delivery systems, including those related to specification of the characteristics of hydraulic structures used to convey regulate, or divert water This study develops and applies a response surface methodology (RSM) for achieving optimal design for hydraulic structures in irrigation-water-delivery systems in canal networks. This approach provides a means of understanding system behavior through developing a response surface in terms of a mathematical expression representing system performance as affected by design decisions. Design decisions include pipe diameters for diversion and r...

A methodology is presented for optimal design of hydraulic structures in a branched irrigation canal network subject to parametric and objective uncertainty. Monte Carlo simulation of steady spatia...

In this paper, we propose a three-step algorithm based on Hessian matrix analysis to quantify local orientation in a 3D canal network image.

The paper presents the design, implementation and field tuning of a supervisory and control system of an irrigation canal network upstream controlled with AMIL radial gates and equipped with other Neyrpic devices such as automatic siphons and orifice modules. Besides the hydraulic system, the paper also presents the supervisory and control system architecture, including a few synoptics, and their remote terminal units (monitoring or control and monitoring units). The developed and field tuned manual and automatic controllers are also presented. The manual controllers – direct and gate position controllers (for the gates operation) and gate flow controllers - are defined for the main canals and main distributors intakes in order to permit a pre-defined flow value or a daily flow schedule achievement and also defined for a few gate controlled bottom canal orifices used to discharge the overflow to the drainage system. The automatic controllers - water depth controllers for a few gate controlled bottom canal orifices – are defined in order to prevent automatically canal overtopping. The supervisory and control system also monitor the outflows at the main canals and the main distributors - the most important canal top side weirs, canal terminal weirs and automatic Neyrpic siphons. The flow equations used in the computing of flow in real-time inside the developed controllers and the monitoring units were field tuned using collected data readings from a monostatic doppler current meter. The tuning parameters are also defined and presented.

Renewed interest in the role of delivery networks in farmlevel wateruse efficiency has prompted the development of a transient hydraulic simulation model for improving the operation and design of i...

Handling constraints in Evolutionary Algorithms (EAs) can be challenging, especially for highly constrained, complex optimization problems. Because constraints are not handled directly in an EA, heuristics must be carefully designed and applied to guide the search toward feasible, good-performing solutions. A common way to handle constraints in EAs is to use penalty functions. These penalty functions can have various formulations, and often require time-consuming finetuning of the penalty parameters to effectively search for feasible solutions with good objective function values. This paper investigates the performance of various constraint-handling techniques applied to an EA-based irrigation canal network management problem. The problem involves determining efficient network operations that minimize the water consumed while preventing problems such as water shortage and flooding. The case study is based upon a complex large-scale irrigation network in Egypt. The constraint-handling methods investigated include three penalty functions. The associated fine-tuning parameters for each constrainthandling method are varied to investigate the sensitivity of the solution quality (feasibility and objective function value) to these parameters. The solution quality and its sensitivity to the constraint-handling parameters are compared for the constraint-handling methods. This comparison is intended to help provide guidelines for better performing penalty function methods for an EA-based irrigation canal network management problem that can be successfully implemented without excessive fine-tuning requirements.

In 1991, the World Bank was forced to appoint a team to conduct an independent review of the human and environmental impact of a mega-dam and water-distribution project on the river Narmada in India. The review team asked us to help assess the problems caused by the 75,000-km canal network being built for the project. We combined spreadsheet modeling with insights gained from a rapid rural appraisal to prepare both quantitative and qualitative findings and recommendations, many of which have been vindicated by later research and events. The review team used all our findings in a damning report, which led to the World Bank withdrawing from the project. Taking into account the review team's report, the Supreme Court of India has put a ban on the continuation of the project until it is satisfied that the project authorities have taken care of all the human problems of rehabilitation and resettlement.

A generalised formulation of the mathematical model developed for the analysis of transients in a canal network, under subcritical flow, with any realistic combination of control structures and their multiple operations, has been presented. The model accounts for a large variety of control structures such as weirs, gates, notches etc. discharging under different conditions, namely submerged and unsubmerged. A numerical scheme to compute and approximate steady state flow condition as the initial condition has also been presented. The model can handle complex situations that may arise from multiple gate operations. This has been demonstrated with a problem wherein the boundary conditions change from a gate discharge equation to an energy equation and back to a gate discharge equation. In such a situation the wave strikes a fixed gate and leads to large and rapid fluctuations in both discharge and depth.

The system for scheduling and cleaning canal systems (SCCS) described in this paper serves for a proxi-optimal scheduling of cleaning operations for municipal canal systems. The ranking of the canal sections to be cleaned is provided in two independent ways and the plan is then established by an opportunistic compromise. The main characteristics of the expert system are its adaptability and capability for replacing lacking data in the data-base by default values. The paper reports on practical experience obtained with the SCCS system for a canal network of about 2000 sections.

France's canal age was largely the outgrowth of the plan proposed by François Becquey, the state administrator who orchestrated a successful campaign to convince influential Frenchmen that a nationwide canal network was one of the essential tasks of their generation. As Becquey originally conceived his plan, canal building would directly contribute to economic growth and help foster a spirit of business enterprise. In the end he had to settle for a scheme under which the government paid a steep price to a handful of financial consortia for the right to assume all the risks and costs of building and operating the system itself.

A collection of computer models is described which have been developed as aids to resource planning on the U.K. canal network. The first part of the paper describes the structure of this set of models, and the philosophy underlying their design and use. The individual models are then briefly described. British Waterways Board engineers have been closely involved throughout the development of the models, and are now using them operationally. Some examples of the use of the models are given in the final section of the paper.

In this paper a new methodology for estimating conveyance efficiency within irrigation systems is presented. Based on statistical analysis of daily water releases from the source of supply and deliveries to the farmers in an irrigation district in Mexico, a linear model is obtained for estimating conveyance efficiency and two component factors. One of these factors points out the relative importance of the operational losses (i.e., losses due to water management), and the second shows the importance of the fixed losses which can be attributed to the average flow through the canal network without variations. In the last part of this paper, an analysis of the expected benefits and costs accruing from system improvement permits derivation of a decision rule which may be used for analyzing the economic feasibility of lining in-place canals.

tural production since 1950. In the past decade, the West Punjab area of Pakistan has shown similar dynamism in agriculture. The region thus affords an opportunity for the examination of factors involved in rural economic development, useful theoretically, as well as for the lessons it may have for the rest of the subcontinent. This paper is an exploration of some of the social factors in Punj abi rural development, focusing on the interplay between village social stratification systems and conditions effecting development. Our discussion of social dynamics is based in part on field work in two Lahore District communities (Pakistan) two villages in Ambala District (India), and on visits to many other villages primarily in Central Punjab and Canal Colony Districts which are today in West Pakistan.' Since our information is obviously derived from a limited sample, we cannot suggest that the social patterns described are universal in this region, but we believe they are common enough to be important. Our analysis should be taken as directed toward the development of some interpretive ideas and hypotheses, and certainly not as an attempt to formulate definitively the nature of social dynamics throughout rural Punjab. In any attempt to deal with rural economy in the Punj ab, the history of public works, particularly canal irrigation, must be taken into account. With the extension of the canal network, culminating in the great canal colonies constructed from 1880 to 1930, Punj ab moved from one of the poorest agricultural regions to the most productive. The total area under cultivation increased sharply-50 per cent from 1868 to 1921-and the proportion of canal irrigated area, from around 6 per cent to 36 per cent.2 Up to the 1920's, the area under cultivation seems to have expanded more

French Provence has an irregular rainfall and a large need of water, both for urban use and for the irrigation of its fertile soil. Local needs, the general progress and the development of the Electricité de France (E.D.F.) have led to the formation of the Canal Society of Provence, from which important improvements in the existing canal network are to be expected, and also in the provision of new sources of water. As the number of works and reforms are large, the author has limited himself to a description of the more outstanding ones. In relation to the construction machinery used in these works, special mention should be made of a jumbo which drills and clears away the debris after firing the charges. This is a very important problem, which appears to be finally solved, so that in the near future the rate of drilling in galleries will be substantially improved. Another important feature, which could be usefully applied to hydraulic projects with shortage of water, is the use of pressurized irrigation networks and aspersion type watering., La Provenza francesa es una región de régimen pluvial irregular y muy necesitada de aguas, tanto para usos urbanos como para la irrigación de sus fértiles tierras. Las necesidades locales, la evolución de los tiempos y la aparición de Electricité de France (E.D.F.) en Francia se han conjugado para crear la Sociedad del Canal de Provenza, de la que se espera grandes mejoras de la red de canalizaciones existentes y nuevas aportaciones de agua. Como el número de obras y reformas es numeroso, el autor se ha limitado a describir las más destacadas. Merece particular atención la presencia, entre la maquinaria auxiliar de construcción, de un «jumbo» que perfora y limpia el escombro después de la pega, problema de sumo interés que, actualmente, parece se halla en vías de solución definitiva, con lo que, en un futuro próximo, se podrán mejorar los avances medios diarios en la perforación de galerías. También presenta interés para futuras ordenaciones hidráulicas, máxime donde escasea el agua, la introducción en la red de canalizaciones en carga y el empleo de la irrigación por aspersión.

The operation of the major irrigation canal systems gives occasion for many unsteady flow conditions, especially at the starting/stoping of the pumping devices placed along the canal network. As a consequence, the water depth may be a strongly time-dependent parameter. In some circumstances, certain undesired values may be attained at various cross-sections (e.g. -below the intake levels, above the embankment levels etc.). On the other hand, it is of great importance to assure an imposed irrigation schedule using the smallest energy consumption at the pumping station responsible for the water supply within the canals system.

Irrigation has always acted as a stimulus, because of its technical requirements, to the development of mathematics and surveying and, because its practice is conducive to disputes, to the evolution of common law.' Thus, it is not surprising that irrigation agriculture in medieval Valencia led to the creation of specialized categories of experts whose purpose was to provide for the smooth functioning of the system on the basis of traditional practice. The impact of irrigation was felt most palpably in two fields-technology and law-whose monuments are still visible today in the vast canal network of the Valencian huertas (irrigated areas) and in the complex body of customary water law epitomized by the renowned Tribunal of Waters. In medieval Valencia, water cases were frequently argued by lawyers who had become specialists in irrigation litigation. In a like way, the technical workings of the system were intrusted to a corps of expert surveyors-the livelladors, or levelers. Both groups had the same function: to insure the equitable distribution of an irregular supply of water. Today's surveyor works both as measurer and leveler. Thus, my translation of livellador by the general term "surveyor" may give grounds for misinterpretation. These medieval "levelers" did more than work just with the level; a great part of their energy was devoted both to general surveys of prospective canal routes and irrigation sites and to the actual construction of hydraulic works. But it must be stressed that, although the translation "surveyor" is justifiable, the livelladors were still not the same as, and had little in common with, the men who surveyed fields-the agrimensores (or, in medieval Valencian, soguejadors-those who worked with the soga, or "cord").2