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:Stream-flow recessions are commonly characterized by the exponential equation or in the alternative power form equation of a single linear reservoir. The most common measure of recession is the recession constant K, which relates to the power function form of the recession equation for a linear reservoir. However, in reality it can be seen that the groundwater dynamics of even the simplest of aquifers may behave in a non-linear fashion. In this study three different storage-outflow algorithms; single linear, non-linear and multiple linear reservoir were considered to model the stream-flow recession of the upper Blue Nile. The recession parameters for the linear and non-linear models were derived by the use of least-squares regression procedures. Whereas, for the multiple linear reservoir model, a second-order autoregressive AR (2) model was applied first in order to determine the parameters by the least-squares method. The modelling of the upper Blue Nile recession flow performed shortly after the wet season, when interflow and bank storage may be contributing considerably to the river flow, showed that the non-linear reservoir model simulates well with the observed counterparts. The variation related to preceding flow on a recession parameter of the non-linear reservoir remains significant, which was obtained by stratification of the recession curves. Although a similar stratification did not show any systematic variation on the recession parameters for the linear and multiple linear reservoir models.

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.

A simple water balance model was used to generate monthly water surplus for 0.5° grid cells of the Upper Blue Nile basin. An application of a spatially distributed unit hydrograph method is presented to route generated runoff from the grid cells. The work differs from previous modelling work on the basin in that it accounts the spatial variability of the flow parameters. The study illustrates that velocity is a more significant parameter in determining the response of the basin. The key inference from the simulation with spatially variable parameters is that, if variable velocity zones exist in a basin, then it is important to consider the effect of non-uniform dispersion coefficients as well. The study also demonstrated the successful simulation of the hydrological cycle for a local/national data-poor basin using data sets mainly from global archives.

An analytical model for the forecasting of the Blue Nile River low flow is developed and compared with the current modified similar year method. The model is based on the general non-linear reservoir equation and the historical flow of the river for the calibration period 1912-1961. The comparison is made after the year 1961 for 6 different years in terms of the temporal 10-day flows and for the period 1962-1996 in terms of the standard error of estimates (SEE). The model and the modified similar year forecasted 10-day flows were also compared with the actual temporal 10-day flows during the driest and the wettest year of the whole record between 1912-1998. Results showed that the model temporal distribution of flows is more close to the actual ones compared with the modified similar year method. The model has less SEE in 31 years out of 38 compared with the modified similar year method.

Since its establishment in 1925 decisions in the Sudan's Gezira irrigated scheme have been top-down from the central headquarters of the Sudan Gezira Board (SGB). The irrigation system is divided into the upper system (US) that includes the dam, main, branch and major canals and the lower system that comprises the minor, tertiary and field channels. The Ministry of Irrigation and Water Resources (MOIWR) is responsible for the O&M of the US in addition to the maintenance of the Minor canals. The operation of the minor canals is handled by the SGB. The maintenance of the minor canals was given to the SGB in 1999, thus unifying O&M for the first time in 75 years. This opened the door for the O&M to be handed to tenants in a pilot project (PP) supported by the FAO during [2000][2001][2002]. Crop yields in the PP outyielded the neighboring blocks as well as the scheme average during the two years of the project. The PP is to be extended to at least one block in each of the 18 Gezira administrative groups. The PP established the base of legalization and institutional arrangements that govern the water users' activities and resulted in a great change in tenants' attitudes towards water management. Copyright supérieurs à ceux des parcelles voisines ainsi que le rendement moyen du programme durant les deux années que le projet a duré. Le PP sera étendu d'au moins un bloc de parcelles dans chacun des 18 secteurs administratifs de Gezira. Le PP a établi la base pour la légalisation et les dispositions institutionnelles qui réglementent les activités des utilisateurs de l'eau et a entraîné un profond changement de l'attitude des exploitants à l'égard de la gestion des ressources en eau.

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