User charges in irrigation: Potentials and limitations

Interest in systems of user charges for irrigation projects serving large numbers of small farmers has grown in recent years in response to concerns about

-the need to provide more adequate funding of O&M,

-distortions and inefficiencies induced by subsidies, and

-inadequate accountability of irrigation system managers to water users.

The effects that can be expected from a system of user charges depend on

-whether the charges are assessed as water prices or as area-based fees,

-whether the irrigation agency has a significant degree of financial autonomy, and

-the nature of the linkages between irrigation charges and investment decisions.

Other important considerations in establishing user charges are the ability of the users to pay irrigation fees; the cost-effectiveness of O&M activities; the costs of implementing the user charges; and whether charges are project-specific or uniform throughout a region or a nation.     

Boots on the ground: construction management of urbanizing irrigated farm land

Since its inception, in 1885 the Buckeye Irrigation Canal has delivered irrigation water in the Buckeye Valley, southwest of Phoenix, Arizona. Throughout its tenure the owners of the canal have consulted design professionals for its engineering needs. Early engineering in 1885 established canal alignments, delivery points and channel capacity. Until recently, the Buckeye Valley was a rural area relying on agricultural revenues to drive the local economy. Now, due to the recent housing market boom new homes started springing up like corn in September driving the existing open-channel laterals below grade into a patch work redesigned pipeline system. Because of these changes, professional construction managers are an enormous benefit to the Buckeye Water Conservation and Drainage District (BWCDD), the owner of the canal.As a result of this urbanization, contractors working for home developers are installing irrigation pipelines and systems with the focus of completing the project as quickly and economically as possible. Irrigation providers, on the other hand, focus on meeting the agricultural needs of their clients with consistent and uninterrupted water delivery. The services of a professional construction manager help both entities achieve their respective goals, shield BWCDD from construction of sub-par systems and risk, maintain uninterrupted service to growers and providing the technical expertise to communicate with both BWCDD and contractors.Construction managers provide a number of services to rural irrigation districts under-going urbanization. They team with an irrigation district by:

• Understanding irrigation design concepts;
• Understanding agricultural demands;
• Providing a thorough knowledge of construction practices and standards;
• Creating long-term design functionality;
• Reducing stress on and increasing productivity of personnel;
• Coordinating construction activities with water deliveries;
• Verifying constructed facilities perform as designed, which reduces maintenance costs.

Construction managers represent an irrigation district in the field by:

• Reviewing development plans for adherence to current construction standards and practices and coordinates construction schedules with water delivery needs;
• Observing construction for proper installation;
• Clarifying installers understanding of plans and specifications;
• Coordinating interruptions in service;
• Tracking multiple construction projects;
• Explaining agricultural practices to contractor personnel;
• Providing a single point of contact for construction related correspondence.

These “boots on the ground” create a local presence with a focus on the specific needs unique to an irrigation district. They provide a liaison while minimizing the impact to its growers.This paper will discuss the strain of urbanization on an irrigation district and the benefits of an engineering consulting firm to manage construction projects. The benefits include expertise, technical resources, design capability, coordination and inspection. Construction managers can help protect an irrigation district from being overwhelmed by rapid urbanization.     

The potential for farmer participation in irrigation system management

The management of most irrigation systems involves shared responsibility between one or more government agencies and farmers. Finding the optimal level of farmer management participation is an essential part of achieving optimal system performance. Two cases are discussed where farmers have been encouraged to play a more active management role with promising results. In the Gal Oya system in Sri Lanka, farmers manage the tertiary channels and also have a voice in managing the main system. In the Philippines, small systems have been turned over entirely to farmer management, while on large systems farmers manage the tertiary or secondary levels. A number of factors appear to be important in the management success of these irrigation systems including:

-the social environment,

-a manageable main system,

-a strong commitment by the irrigation agency,

-the use of community organizers, and

-construction tasks around which farmers can organize.

Greater farmer involvement in irrigation management can have both economic and social benefits. Economically there is evidence that farmers perform certain functions better than outside agencies can, and that both farmers and agencies perform their management tasks better when they feel a mutual responsibility for a common objective. Social benefits include the organizational skills that farmers learn and which may be useful in other activities, and a sense of self-respect and self-reliance. Though farmer participation requires a deliberate effort on the part of international and government agencies, as well as farmers, the benefits can be substantial.     

Development of the irrigation M&O learning process

A learning process has been developed, based on experiences in Thailand, Sri Lanka and Nepal, for improving the maintenance and operations practices of an irrigation project or system. This learning process has been designed to:

minimize the investment (O&M) costs so as to avoid rehabilitation;

increase credibility of irrigation project staff with central headquarters through improved financial management practices and accountability; and

develop more knowledge about what is occurring within the system in order to meet the needs of farmers.

     

Computerised irrigation scheduling using spreadsheet models

Microcomputers are increasingly being used to help in the management of smallholder irrigation schemes in Third World countries. In many cases, commercially available spreadsheet packages offer advantages over established scientific programming languages. The paper starts with a review of computer models which have been developed for irrigation scheduling. Two criteria are identified which must be considered when developing computer models for this purpose: realistic data requirements and programs which are easy to understand. Spreadsheet packages provide a good introduction to computing and macro programming techniques can be used to customise spreadsheet models to create refined yet simple management tools. Two practical examples are presented from current research projects:

-a small scale scheme in Zimbabwe, where a spreadsheet model is used to produce irrigation schedules for smallholder farmers;

-a 20,000 ha project in Thailand, where a spreadsheet model makes use of feedback to improve main system scheduling.

     

Salt tolerance analysis of chickpea,faba bean and durum wheat varieties: II. Durum wheat

Seven varieties of durum wheat (Triticum turgidum), provided by ICARDA, were tested in a greenhouse experiment for their salt tolerance. Afterwards two varieties, differing in salt tolerance, were irrigated with waters of three different salinity levels in a lysimeter experiment to analyse their salt tolerance.The characteristics of the salt tolerant variety compared to the salt sensitive variety are:

• -a shorter growing season and earlier senescence;
• -a higher pre-dawn leaf water potential;
• -a stronger osmotic adjustment;
• -a better maintenance of the number of productive stems per plant.

Salt tolerance of durum wheat corresponds with drought tolerance because the tolerance is caused by earlier senescence and stronger osmotic adjustment, both reducing the transpiration of the plant.     

Hydraulic model investigation of downstream erosion of large regulators: a case study

Flow conditions, which could not be explained, occurred in the stilling basin and outfall channel of the Feni Regulator sited at the western end of the Feni River closure dam. This regulator controls outflows from the upstream reservoir which supplies irrigation water to Muhuri Project in Bangladesh. Analysis of flood discharge data revealed that the design discharge for the structure was not exceeded; yet abnormal scour occurred in the outfall channel and the brick block rip-rap placed thereon was damaged. A model study was conducted to understand the causes of such unusual local erosion downstream of the stilling basin and to provide answers to two main questions:

-Is potential scour serious in terms of the stability of the structure?

-What protection measures could be taken to stabilize the scour at a safe level?

Using a 1:30 scale model, the probable maximum scour was simulated, and the performance of alternative rip-rap designs including that of the existing one were examined. The results of this study supplemented by field scour data collected during subsequent flood seasons indicated that even if the flow rate through the regulator approaches the design flood discharge, the downstream scour is not likely to extend up to an elevation of ? 10.7 m, a scour level observed in the previous year at a lower discharge. It also showed that the existing rip-rap blocks were marginally undersized and consequently the rip-rap was prone to failure if flow conditions departed from uniform. A suitable method of scour protection downstream of the stilling basin at the regulator exit also evolved from the study.     

A review of slurry aeration 3. Performance of aerators

The two previous papers in this series have examined the factors affecting the aeration, mixing and foam control aspects of aerator performance. In this final paper, existing designs are reviewed to provide some guidance for the selection of aerators for farm use.The various types are classified as follows:

• 1.(a) compressed air,
• 2.(b) mechanical surface,
• 3.(c) mechanical subsurface,
• 4.(d) combined compressed air/mechanical, and
• 5.(e) pumped liquid.

Each group is assessed in terms of its principles of operation, the main factors influencing performance, and reported effectiveness in various liquids (including agricultural slurries wherever possible).     

The Water Delivery Performance Within the Chivilcoy Tertiary Unit, Mendoza, Argentina

The 4th Chivilcoy tertiary unit (1630 ha)receives irrigation water from theMontecaseros canal. This canal and its 16tertiary units is managed by theMontecaseros Users Association (8531 ha),being one of the 13 UA's in the Rio TunuyanMedio irrigation system (81200 ha). The 4thChivilcoy unit was selected for performanceresearch because it is representative for amajor part of the Tunuyan system; itcontains (near abandoned) fields with waterlogging and salinity problems and fieldswith maximum attainable yields. This paperreports on performance indicatorsquantifying the water delivery to the 12quaternary units. Also the delivery ofwater to the 19 farms in the Los Saucesquaternary unit (109 ha) is quantified. Allflow data were measured with broad-crestedweirs fitted with pressure loggersmeasuring the head at 15 minutes intervals.Because of this short interval, the timingof water delivery could be monitored andcompared with the intended deliveryschedule.     

Assessing water stress in a hedgerow olive orchard from sap flow and trunk diameter measurements

We used sap flow and trunk diameter measurements for assessing water stress in a high-density ‘Arbequina’ olive orchard with control trees irrigated to replace 100 % of the crop water needs, and 60RDI and 30RDI trees, in which irrigation replaced ca. 60 and 30 % of the control, respectively. We calculated the daily difference for both tree water consumption ( $ D_{{E_{\text{p}} }} $ ) and maximum trunk diameter (D _MXTD) between RDI trees and control trees. The seasonal dynamics of $ D_{{E_{\text{p}} }} $ agreed reasonably well with that of the stem water potential. We identified peculiarities on the response $ D_{{E_{\text{p}} }} $ to changes in water stressing conditions, which must be taken into account when using the index. An analysis of the water stress variability in the orchard is required for choosing the instrumented trees. The reliability of the D _MXTD index was poorer than that of $ D_{{E_{\text{p}} }} $ . The maximum daily shrinkage (MDS) was not a reliable water stress indicator.     

On-demand canal operation: Optimally designed

The design of most canal systems requires that they be operated under rigid schedules, rather thanon-demand. Rigid schedule operation results in water wastage through spillage, or users taking their turn even when the water cannot be efficiently used. This paper develops a two step method for optimally designing a canal system so it can be operated effectively under user on-demand requests for water. The first step determines the cross-sectional dimensions of the canal to provide storage capabilities while minimizing costs, by solving an appropriate nonlinear optimization problem. In the second step a hydraulic simulation model finds a near-optimal storage capacity based on construction and right-of-way costs, penalties due to operational water losses, water over supplied to users and supply shortages. The performance is evaluated by a quality index that is defined as the ratio of volume of satisfied demands to total volume of water requested. Results of regression equations from hundreds of computer sensitivity analyses relating variables are summarized in tables.     

Salt tolerance analysis of chickpea,faba bean and durum wheat varieties: I. Chickpea and faba bean

Two varieties of chickpea (Cicer arietinum L.) and faba bean (Vicia faba), differing in drought tolerance according to the classification of the International Center for Agronomic Research in Dry Areas (ICARDA), were irrigated with waters of three different salinity levels in a lysimeter experiment to analyse their salt tolerance.The drought-sensitive varieties are more salt tolerant than the drought-tolerant varieties. Under saline conditions, the drought-sensitive varieties show a much higher yield up to a salinity threshold, corresponding with an electrical conductivity (EC_e) between 2.5 and 3 dS/m for chickpea and between 5.5 and 6 dS/m for faba bean.The drought-sensitive varieties are able to improve or maintain the water-use efficiency when irrigated with saline water. This ability can be ascribed to

• •the larger biomass production owing to the later senescence, which allows a better utilization of the irrigation water;
• •the late flowering of chickpea.

     

Analysis of several discharge rate–spacing–duration combinations in drip irrigation system

In order to study the use of water irrigation in a rational way, several combinations of discharge rate, irrigation duration and inter-emitter distances were tested. For instance, three dripper spacings of 30, 50 and 70 cm which delivered water volumes of 4, 8 and 16 l per dripper, respectively, and three discharge rates of 2, 4 and 8 l/h for each spacing, were applied.An overlapping of the wetted bulbs was observed at the end of the different irrigation experiments. The inter-dripper root-zone had an average water content of 45% and a coefficient of uniformity of 90%.The discharge rate of 2 l/h applied to a 70 cm dripper spacing was characterised by water losses of 15% due to the significant irrigation duration (8 h).From this study, we reach the following conclusions, specific to the soil type and practical culture.

• 1.The maximum irrigation duration does not exceed 4 h.
• 2.Two hours durations can be used for the different spacings, each of which was characterised by its own discharge rate.

     

The yield,quality and profitability of annual forage,perennial pasture and perennial forage systems under irrigation

Intensive fodder production systems were compared under irrigation in western New South Wales. The three basic systems studied were:

• 1.(1) Annual forages (Sorghum bicolor × S. sudanense plus Avena sativa).
• 2.(2) Perennial pasture (Paspalum dilatatum).
• 3.(3) Perennial forage (Medicago sativa).

The first two systems included nitrogen fertilizer or legume options, while the last had the option of including a perennial sorghum.Dry matter production was highest in the annual forage system (maximum of 30·5 tonnes ha⁻¹ year⁻¹), although annual establishment costs were higher than for perennial systems. The perennial pasture yielded 21·5 tonnes ha⁻¹ year⁻¹ but, like the annual forage system, 250 kg N ha⁻¹ year⁻¹ was required to obtain this yield. The perennial forage yielded 19·8 tonnes ha⁻¹ year⁻¹ without nitrogen fertilizer. Furthermore, it yielded more digestible dry matter and nitrogen than any other system.Although the annual forage system was the most profitable when based upon a set price for hay, the best system for grazing was difficult to determine; factors relating to grazing management are discussed.     

Conjunctive use of canal and groundwater in Punjab,Pakistan: management and policy options

Data from 41 watercourses commands in Pakistan show that, as expected, farmers in head end reaches of canals receive more canal water than those in tail end reaches. Contrary to conventional wisdom, however, these head end farmers also use more groundwater than those at the tail end. Overall, groundwater plays a more important role in irrigation than surface water, ranging from 65% dependence on pumped water in head end areas to over 90% in tail end areas. This means that groundwater is no longer supplemental to canal water, but is an integral part of the irrigated agricultural environment. However, the cropping choices of farmers appear to reflect the amount of good quality canal water they receive: head end farmers are able to grow more high value basmati rice in the summer and more vegetables in the winter, leaving tail enders to rely on less valuable crops such as fodder and wheat.Tail end areas are not only deprived of their fair share of surface water: they have to pump proportionately more groundwater which shows decreasing quality towards the tail. Typically, head end areas have groundwater with EC values of less than 1.0 dS/m, rising to over 2.0 dS/m in tail end areas. When the quality of both surface and groundwater used by farmers is examined, only the top 40% of the distributary gets water of adequate quality, the next 40% get below average quality, while the tail 20% of farmers irrigate with water that is classified as saline.Because of higher dependence on more expensive groundwater tail enders use less water per unit area, thereby reducing the leaching requirement. The result is a clear increase in soil salinity from head to tail along distributary canals, and there is some evidence of land abandonment in tail end watercourses due to excess salinity.The implications of these results are far reaching. Government policy includes plans to divert significant quantities of fresh canal water to areas underlain by saline groundwater on the basis that farmers already have adapted to pumping fresh groundwater. The results reported suggest that if this policy were implemented, there is a risk that over-dependence on fresh groundwater could lead to an intensification of the rate of soil salinization and deterioration of quality in areas currently classified as fresh groundwater zones.At present, the location and utilization of privately owned shallow tubewells is not monitored, and thus it is not possible for government agencies to determine just how much water of different qualities is being used. Further, canal water deliveries, public deep well monitoring, watercourse monitoring programs, soil salinity measurements, and agricultural performance monitoring are all scattered among different agencies and organizations, making the task of effective conjunctive management of surface and groundwater even more difficult.Conventional wisdom: Groundwater in Pakistan ... where it exists within the canal system ... is used to supplement surface water supplies to meet peaks in demand. (WAPDA, 1990)     

The Arizona Water Settlement Act and urban water supplies

The 2004 Arizona Water Settlements Act (AWSA 2004) when implemented will allocate to two Native American tribes, the Gila River Indian Community (GRIC) and the Tohono O’odham Nation (TON) almost ten percent of Arizona’s total developed water supply, which is 7.04 million acre-feet a year. The successful passage of AWSA, given the scale of the water rights settlement and competing uses for finite water supplies, is the topic of this paper. Key motivations for the settlement are that: (1) the 653,500 acre-feet a year allocation is around a third of the GRIC’s Gila River Adjudication 2001 claim; (2) the GRIC signed a number of water leases and exchanges providing water to municipalities and has not ruled out signing more; and (3) AWSA resolved more than tribal water claims; it also settled thorny issues of Central Arizona Project (CAP) debt repayment (for $2 billion in construction costs) and division of water allocation between federal (Indian) and state (non-Indian) uses including the reallocation of high priority uncontracted CAP water to cities.     

Constructional aspects of some heated concrete floors for greenhouses

The paper gives particular attention to the constructional aspects of concrete floors in greenhouses.In 1979 preliminary research was started in IMAG into the cultivation of vegetable seedlings on several floor materials, namely on ordinary concrete, porous concrete and asphalt. Overhead watering was provided, and the heating system was in the soil below the floor.These experiments revealed two problems. Uneven water distribution caused uneven growth and the mass of soil around and the concrete above the heating tubes caused a long response time for warming up and cooling down the concrete surface. For strength and wear resistance the ordinary concrete turned out to be the only suitable material.In 1981 IMAG made further trials with floors where heating and (flooded) watering system were integrated in the floor. These floors were made of reinforced concrete cast in situ, of asbestos cement and of concrete tiles. The 100 mm thick concrete floor cast in situ, turned out to be the most suitable because of the loading capacity and the good drainage of water. A standard specification was prepared for this floor type. At the end of 1985, applications of concrete floors in greenhouse, extended to 150 ha in the Netherlands for the production of vegetable seedlings, pot plants and cut flowers in pots or mats. If this trend continues there will be about 600 ha by 1990.Further development of the concrete floor has the objectives of improving thermal behaviour and easier removal or restoration of a floor. For that purpose two types of floor are under trial.

• 1.(1) An insulated concrete floor cast in situ that contains less concrete per square meter.
• 2.(2) A concrete floor built from removable concrete elements combined with a system for air movement between the plants.

     

Water distribution on a large distributary,Tungabhadra, India

Results are presented of field research on water distribution in the command area, covering 18,200 ha, of a secondary irrigation canal in the Tungabhadra Left Bank Scheme, Karnataka State, India.The official objective of the Scheme and the resulting implications for the water distribution are discussed first. An explanation of the planning and operation of the water distribution follows.The results are based on analyses of the water flows taken from the D36 secondary canal and distributed along the canal to the pipe outlets (inlet structures to the tertiary units), and of the canal section rotation practised along the canal. The analyses concentrate on three dimensions of the water supply:The design flows, according to the official Scheme objectives and criteria;The targets, as set by the system operators before every season;The actual distribution procedures and flows, as observed during the operation.The analyses, supported by flow measurement data, illustrate that the water distribution is not based on consistent and clear criteria and procedures, but that it is the outcome of varying compromises, decided upon pragmatically by the field staff, to bridge the gap between the farmers' demands and the upstream constraints to water availability. This paper explains the widespread phenomenon of head reaches taking too much water, leaving little or nothing for the tail end of the canal.     

Improving estimates of <Emphasis Type="Italic">N</Emphasis> and <Emphasis Type="Italic">P</Emphasis> loads in irrigation water from swine manure lagoons

The implementation of nutrient management plans for confined animal feeding operations requires recording N and P loads from land-applied manure, including nutrients applied in irrigation water from manure treatment lagoons. By regulation, lagoon irrigation water nutrient records in Mississippi must be based on at least one lagoon water nutrient analysis annually. Research in Mississippi has shown that N and P levels in lagoon water, and the N:P ratio, vary significantly through the year. Nutrient estimates based on one annual analysis do not account for this variability and may overestimate or underestimate N and P loads. The present study reports an improved method to more precisely estimate N and P loads in irrigation water from swine manure lagoons. The method is based on predictable annual cycles of N and P levels in lagoon water and employs simple curve-fitting of lagoon-specific formulas derived by analyses of historical data. Similarity of curves from analyses of Mississippi lagoons and other lagoon studies suggests that the method can be applied using the often limited nutrient data for a lagoon to more precisely estimate seasonal shifts of N and P and to improve the precision of estimates for N and P in irrigation water. Although the present study focused on swine manure lagoons in the southern US, recognition that the annual N cycle in lagoon water is temperature driven, suggests that additional research incorporating temperature into future models could extend these models to other types of waste treatment lagoons and climates.     

Groundwater modelling to assess the effect of interceptor drainage and lining

Recharge to the aquifer through seepage from irrigation canals is often quoted as one of the main causes for waterlogging in Pakistan. In the design of drainage systems to control this waterlogging, rules-of-thumb are often used to quantify the seepage from canals. This paper presents the option to use a groundwater model for a more detailed assessment. Groundwater models may assist in evaluating the effect of recharge reducing measures such as interceptor drains along irrigation canals and lining. These measures are commonly aimed at reducing the drainage requirement of adjacent agricultural lands. In this paper an example is given of the application of a numerical groundwater model, aimed at assessing the effect of interceptor drainage and canal lining in the Fordwah Eastern Sadiqia project, being a typical and well-monitored location in Pakistan. The paper also presents references to other conditions. The model was used to obtain a better insight in the key hydraulic parameters, such as the infiltration resistance of the bed and slopes of irrigation canals, the drain entry resistance of interceptor drains and the hydraulic conductivity of soil layers. The model was applied to assess the effectiveness and efficiency of interceptor drains under various conditions. The results of the study show that the net percentage of intercepted seepage is too low to have a significant effect on the drainage requirement of the adjacent agricultural lands. Besides, the operation of the system, with pumping required, is often an added headache for the institution responsible for operation of the system. The marginal effect of interceptor drains and lining on the drainage requirement of adjacent agricultural land does not always justify the large investments involved. It can be concluded that: