Introduction:

Khartoum plains and the flood plains of Atbara and the Main Nile were severely flooded during August-September 1988. As a result of that a Flood Early Warning System (FEWS) was installed in the Nile Waters Directorate of the Minstry of Irrigation and Waters Resources in Khartoum, some in the main river gauging stations on the Blue Nile and Atbara river system. The FEWS model is used to enable more advanced warning for future floods from the Nile.

FEWS consists of three main components:

1. A Primary Data User Station (PDUS) with relevant software for receiving and processing of METEOSAT thermal infra-red images on a half-hourly basis (AUTOSAT\ARCS). These data are used for the estimation of daily rainfall quantities from cold cloud duration and the coverage data over the catchment of the Blue Nile and Atbara River.
2. A communication system for real-time transimission of water levels in the Blue Nile, Atbara river, and the Main Nile in Sudan to the Flood Waning Centre in Khartoum (MOIWR).
3. A computerized flood forecasting system, consisting of set of mathematical models (SAMFIL\NETFL), and temporary data base embeded in an appropriate user interface.

Daily Rainfall Estimation Models:

In the absence of real-time information about rainfall over the Ethiopian Plateau, TAMSAT Group at the University of Reading (UK) developed a method (Model) for real-time rainfall estimation. The presence of cold clouds with temperature lower than some predetermined threshold is taken as indication of rain. Rainfall total within a period is associated with the cold cloud duration (CCD) and the portion of the catchment area covered or cold cloud cover (CCC).

Rainfall- Runoff Model

SAMFIL is an upgraded version of the well known Sacremento model, extended with kalman filter data assimilation algorithm. The model is used for the real-time forecasting of the inflow from the Blue Nile and Atbara catchments into the main river basin in Sudan.

Rainfall Forecasting Model

In order to increase the lead time, rain forecast is derived from statistics. Wet, average and dry scenarios have been derived for the months July, August & Septmber from the CCD for the years 1987-1990 using rainfall frequency curve. For the remaining months the scenrio was derived from the monthly data of the nearby point rainfall statistics.

Flow Routing Model

Water and Environmental Dynamics (WENDY) model extended with kalman filter is used for real-time forecasting of water levels and flows in the Blue Nile, Atbara River and the main Nile down to Dongola. The model is a one-dimensional flow model based on the numerical solution of st. Venant equation using finite difference method.

Flood forecasting

Forecasts are made for a period of ten days . This is approximately the lead-time between rainfall events over Ethiopia and the rise of water level at Dongola in the Main Nile. The lead-time for Khartoum is approximately six days. by using remote sensing and rainfall runoff modelling three days are gained by runoff forecasting for the Ethipian catchments of the Blue nile and Atbara river at the Sudanese Border.

Conclusions

Sudan FEWS is in operation since August 1992, providing an advanced operational tool that gives three days ahead at El Deim in the lead-time, using remote sensing and hydrologic modelling techniques.

The results achieved so far are promissing, although further studies are required to improve the system efficiency.

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