Abstract. The availability of the actual water use from agricultural crops is considered as the key factor for irrigation water management, water resources planning, and water allocation. Traditionally, evapotranspiration (ET) has been calculated in the Gezira scheme as the point of reference with evapotranspiration (ET o ) and crop coefficients (k c ) being derived from actual measurements of soil-water balance. Recently developed, advanced energy balance models assisted in estimating the ET through the remotely sensed data. In this study Enhanced Thematic Mapper Plus (ETM+) and MODerate Resolution Imaging Spectroradiometer (MODIS) images were used to estimate the spatial distribution of the daily, monthly and seasonal ET for irrigated sorghum in the Gezira scheme, Sudan. The daily ET maps were also used to estimate k c over time and space. Results of the energy balance, based on being remotely sensed, were compared to actual measurements conducted during 2004/05 season. The seasonal actual ET values, obtained from the seven MODIS images for irrigated sorghum, were estimated at 579 mm. The values for remotely sensed k c , derived during the initial mid-season and late-season crop development stages, were 0.62, 0.85, 1.15, and 0.48, respectively. On the other hand, the values for the experimental k c during the pervious mention stages were 0.55, 0.94, 1.21 and 0.65, respectively. The estimated seasonal ET of the sorghum, derived by remotely sensed k c , was 674 mm. The Landsat data and the Free MODIS provided reliable, exhaustive, and consistent information on the water use, relevant for decision support in the Gezira scheme.

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Abstract:Estimates of the amount of recession flow can be derived from streamflow records. Such estimates are critical in the assessment of low flow characteristics for the Blue Nile River, from which about two-thirds of the irrigation requirements in Sudan are satisfied. The recession flow hydrograph can be estimated by fitting the conceptual nonlinear storage outflow model using an iterative algorithm. An analytical model to forecast the Blue Nile recession flow is developed and the performance of the model is compared to the previous Blue Nile recession flow model. In the proposed model, a simple linear regression equation is introduced to illustrate the effect of antecedent flow on the recession parameter. Results indicate that the model can provide a simple and reliable method to predict the recession flow of the Blue Nile River.

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ABSTRACT. Current methods for estimating evapotranspiration (ET), the essential variable in irrigation performance and water management, largely neglect the spatial and temporal variations in ET. Accurate regional ET maps would provide valuable information on actual crop water use. The objective of this study was mainly to evaluate a Pilot Project (PP) supported by the Food and Agriculture Organization of the United Nations (FAO). In this study, Surface Energy Balance Algorithm for Land (SEBAL) model was used to assist the evaluation attempt. The performance of the ET model was evaluated by comparing the predicted daily ET with values derived by conventional methods based on ground measurements and meteorological data on 6 Sepetmber, 25 Sepetmber, 28 November and 11 December. The ET values from SEBAL showed good agreement with the actual values measured in the field. The amount of water required to satisfy the irrigation needs at canal level was monitored and successfully estimated. However, during November the daily estimated water demand ranged from 15667 m 3 for Tereifi minor to 28954 m 3 for Heleiwa west minor canal. The average values of relative irrigation supply (RIS) were determined as 0.73 which indicates improvements in operational performance of minor canals. The results of this study demonstrate that remote sensing measurements and limited ground data can be used to successfully estimate ET and assess irrigation performance in areas of poor infrastructure. Results achieved support previous opinion that repeatedly recommended the PP as a crucial step for water management in the Gezira scheme, Sudan.

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An accurate estimation method for seasonal, annual, or decadal riverine constituent loads, which are the masses that pass through a river cross-section into a receiving water body during target periods, has been investigated on the premise of high-frequency discharge and infrequent water quality (WQ) observations (e.g., Philips et al., 1999; Webb et al., 1997) due to the high cost and labor of WQ monitoring and analysis (Horowitz, 2013; Verma et al., 2012). Load estimation studies have targeted the WQ parameters related to water pollution or erosion, such as nutrients or suspended sediments (SS), from catchments or watersheds with various land uses. Among the load estimation methods (LEMs), the rating curve (RC) method (RCM) is very common, whereas the river load estimates of nutrients and SS by this method can contain large biases and variances (e.g., Lee et al., 2016; Walling & Webb, 1981). Load estimation studies have also retrospectively evaluated the uncertainty in the load estimates by several LEMs, including the RCM using the Monte Carlo method based on high-frequency WQ data sets, daily data sets (

Abstract. The Gash Delta Spate Irrigation System (GDSIS), located in eastern Sudan with a net command area of 100 000 ha (an area currently equipped with irrigation structures), was established in 1924. The land is irrigated every 3 years (3-year rotation) or every 2 years (2-year rotation) so that about 33 000 or 50 000 ha respectively can be cultivated annually. This study deals with assessing the performance of the 3-and 2-year rotation systems using the Monte Carlo simulation. Reliability, which is a measure of how frequently the irrigation water supply satisfies the demand, and vulnerability, which is a measure of the magnitude of failure, were selected as the performance criteria. Combinations of five levels of intake ratio and five levels of irrigation efficiency for the irrigation water supply of each rotation system were analysed. Historical annual flow data of the Gash River for 107 years were fit to several frequency distributions. The Weibull distribution was the best on the basis of the Akaike information criteria and was used for simulating the ensembles of annual river flow. The reliabilities and vulnerabilities of both rotation systems were evaluated at typical values of intake ratio and irrigation efficiency. The results show that (i) the 3-year rotation is more reliable in water supply than the 2-year rotation, (ii) the vulnerability of the 3-year rotation is lower than that of the 2-year rotation and (iii) therefore the 3-year rotation is preferable in the GDSIS. The sensitivities of reliability and vulnerability to changes in intake ratio and irrigation efficiency were also examined.