Search

Estimation of evaporation from three models namely: Penman, Priestley-Taylor, and Linacre for calculating evaporation rate were compared with the observed values of data collected from pan evaporimeter. Based on two years data, the most promising and reliable model for Algardabiya reservoir in Libya has been established. Various statistical measures such as RMSE, MBE, [R.sup.2] and t test have been chosen for performance evaluation of these models. The study revealed that the models resulted in reasonable accuracy. The errors in the model prediction were 2.95, 1.68, and 1.15 (mm/d) for Penman, Priestley-Taylor, and Linacre models, respectively. Linacre model, which requires only temperature data, was found to be the most reliable. Key words: semi-arid region, Algardabiya reservoir, evaporation, modeling, class A pan. L'estimation de l'evaporation a partir de trois modeles (Penman, Priestley-Taylor et Linacre) de calcul du taux d'evaporation a ete comparee aux (valeurs observees des) donnees colligees d'un bassin d'evaporation. En se basant sur deux annees de donnees, le modele le plus prometteur et le plus fiable pour le reservoir d'Algardabiya en Libye a ete determine. Diverses mesures statistiques, telles que l'ecart-type, l'erreur de justesse moyenne (MBE), [R.sup.2] et le test t, ont ete choisies pour evaluer le rendement de ces modeles. L'etude a montre que les modeles offraient une precision raisonnable. Les erreurs dans la prevision du modele etaient de 2,95, 1,68 et 1,15 (mm/j) respectivement pour les modeles Penman, Priestley-Taylor et Linacre. Le modele de Linacre, qui ne demande que des donnees de temperature, s' est avere le plus fiable. Mots-cles: region semi-aride, reservoir Algardabiya, evaporation, modelisation, bassin de classe A. [Traduit par la Redaction], 1. Introduction Evaporation is one of the major components of the hydrologic cycle and it describes the loss of water from water bodies to the air over a long period [...]

Competition for limited available water for crop production is an ever-increasing issue for farmers due to increasing demand of irrigation water worldwide. Due to high energy cost in operating pressurized irrigation systems, energy-efficient low-pressure wick irrigation systems can play important roles for smallholder greenhouse crop production by ensuring higher water use efficiency than most traditional approaches. The objectives of this study were to investigate HYDRUS 2D-simulated water distribution patterns in soil and soilless growing media, and to evaluate water balance in these media under capillary wick irrigation system. To accomplish these objectives, eggplants (Solanum melongena L.) were grown in potted peatgro and sandy clay loam in a greenhouse experiment, water distribution was simulated by using HYDRUS 2D software package and compared with the measured values, and water uptake by the plant roots was determined for water balance calculation. The wetting pattern was found axially symmetric in both growing media (peatgro and soil) under the wick emitters. The simulated water distribution in both growing media revealed dependency of spatial extent of the wetted zone on water application period and hydraulic properties of the media. The mean absolute error (MAE) in water content over depth varied from 0.04 to 0.10 m³ m-3 and the root mean square error (RMSE) varied from 0.04 to 0.11 m³ m-3. Deviations between the measured and simulated water contents in the peatgro medium were larger over depth than over lateral distance. In contrast, the model criteria matched well for the sandy clay loam and provided MAE of 0.01 to 0.02 m³ m-3 and RMSE of 0.01 to 0.03 m³ m-3, indicating good agreement between the measured and simulated water contents. [ABSTRACT FROM AUTHOR]

A GIS-based user-interface programme was developed to compute the geospatial Water Productivity Index (WPI) of a river-fed rice irrigation scheme in Northwest Selangor, Malaysia. The spatial analysis includes irrigation blocks with sizes ranging from 20 to 300 ha. The amount of daily water use for each irrigation block was determined using irrigation delivery model and stored in the database for both main season (August to December) and off season (February to May). After cut-off of the irrigation supply, a sub-module was used to compute the total water use including rainfall for each irrigation block. The rice yield data for both seasons were obtained from DOA (Department of Agriculture, Malaysia) of the scheme. Then, the Water Productivity Index (WPI) was computed for each irrigation block and spatial thematic map was also generated. ArcObjects and Visual Basic Application (VBA) programming languages were used to structure user-interface in the ArcGIS software. The WPI, expressed in terms of crop yield per unit amount of water used (irrigation and effective rainfall), ranged from 0.02 to 0.57 kg/m³ in the main season and 0.02 to 0.40 in off season among irrigation blocks, respectively. The development of the overall system and the procedure are illustrated using the data obtained from the study area. The approach could be used to depict the gaps between the existing and appropriate water management practices. Suitable interventions could be made to fill the gaps and enhance water use efficiency at the field level and also help in saving irrigation water through remedial measures in the season. The approach could be useful for irrigation managers to rectify and enhance decision-making in both the management and operation of the next irrigation season. [ABSTRACT FROM AUTHOR]

Deficit irrigation in the Gavkhuni River Basin (GRB), Iran, is an effective method for alleviation of drought impacts on crop yields. Whilst it saves considerable amounts of water, it has little effect on crop yields. The effects of deficit irrigation on grain yield and yield components of maize were studied using two factors [namely, the variety at two levels (704 maize variety with 9354 kg ha-1 yield, and 647 maize variety with 8822 kg ha-1 yield) and irrigation at four levels (control, 100, 80, and 60% of water level use)] for three consecutive years. Significant differences (P≤0.05) were noticeable in grain yield, as well as depth and column of kernel among the irrigation treatments. In addition, the effects ofcultivars on grain yield, 1000 kernel weight, number of kernel per ear row, number of kernel per column, and depth of kernels were insignificant. Nevertheless, the effects of irrigation treatments on 1000 kernel weight and number of kernel per ear row were not significant. Based on the results and considering the quantitative characteristics of the crop, it was established that for the deficit irrigating of maize, the 80% irrigation level (i.e. 80% of crop evapotranspiration) is the most advantageous treatment when water is not limited. However, when higher water productivity and the possibility of using the water saved are taken into consideration during severe drought conditions, 60% irrigation level treatment is recommended. [ABSTRACT FROM AUTHOR]

One of the mosi interesting water management case studies in Iran is the case of Zayandehrud River, the main river that supplies water to Isfahan Province which is located in Gavkhuni River Basin (GRB). This paper examines the present and future demands for water and determines the extent to which water will be available for agricultural use by the year 2020. Although demand and supply conditions in 2000 were more or less in balance, there was an increase in the supply of some 28% by 2010 due to the completion of the third trans-basin diversion and the development of other local water sources. However, the demand exceeded its supply in 2010 and the basin fell into severe deficit. In this condition, the only way to keep supply and demand in balance is to reduce allocations to agriculture. By 2020, agriculture would only have 5% more water than the present and water supply is only 90% that of the normal, and this would then shrink from 2025 onwards. In other words, agriculture would have to be sacrificed in order to ensure full supplies of water for the other sectors. The scenarios examined reveal that a sustainable agriculture can only be accomplished by water saving practices and management measures, which may further lead to reduced demand, control supplies, and improve the efficiency of water use. [ABSTRACT FROM AUTHOR]

In the present study, an assessment of water quality from 20 randomly selected shallow wells inside poultry farms in Minna, north-central Nigeria, was carried out in order to establish the effects of a poultry waste dump located close to the wells by determining some physico-chemical and microbiological parameters of the groundwater samples. Samples of water were collected from the shallow wells between November 2011 and January 2013, and analyzed for physical, chemical, and bacteriological parameters. Sampling was carried out during the dry and wet seasons to find out if the water quality changes with the season. Analysis of variance was used to analyze the results and the means obtained were compared with the New Duncan Multiple Range Test. The results of the bacteriological parameters showed that the water quality is very poor; highly contaminated with faecal matter. Only 15% of the water samples satisfy the WHO guideline of 0 cfu/100 ml in dry season but reduced to 5% in the wet season. For total coliform, 10% satisfy the WHO guideline value in the dry season but none of the wells sampled was totally coliform-free in the wet season. About 25% were free from faecal streptococci during the dry season, but only 5% was free from these bacteria in the wet season. Statistics (p> 0.05) shows significant difference between coliform values in the wet and dry seasons. Generally the wells are polluted with coliforms, which may have migrated from poultry waste dumps into the wells. The difference in physical parameter values was also statistically (p>0.05) significant between seasons, with 55% of the water samples satisfying WHO 5NTU turbidity value in the dry season but the reducing to 30% in the wet season. Lower values were recorded for TDS and EC in the wet season than in the dry season. For chemical tests, 50% of the water met up with WHO 50 mg/L nitrate guideline in the dry season and were reduced to 35% in the wet season. Statistics (p>0.05) show no significant difference in the phosphate values for wet and dry seasons. It is clear from these results that water from the shallow wells is more contaminated in the wet season than the dry season. [ABSTRACT FROM AUTHOR]

Equitable water allocation is essential in an irrigation scheme for obtaining potential crop yields from the entire scheme, especially when water supply is inadequate. An optimization model achieved this goal by coupling an optimal water allocation model with available water supply and irrigation water demand for a river-fed rice irrigation system in Malaysia. This model consists of a paddy field water balance module and an optimization module. The outputs from the module are daily irrigation demand and surface runoff, if there is any. The optimization module consists of an objective function, which minimizes water shortage across the scheme area while maintaining equity in water allocation. This model performs optimization subject to several system constraints, and the decision variable of the model is daily releases or supply to the tertiary canals. Performance of this model remained unaffected under different water supply conditions, and the optimization model reliably examined the effects of alternate water allocation and management rules with field information. It improves efficiency and equity in water allocation with respect to crop growth stages and water shortages rather than simply cutting irrigation supply on a proportional basis to overcome water shortages. [ABSTRACT FROM AUTHOR]