Osman, A.R. 
The area seems to be a river fluvial formation such as flood plain, delta and alluvial landform. 
Flood plains are formed when sediments carried by the Blue Nile and its tributaries and deposited long ago during flood 
periods in the Gezira area when the velocity was low. 
The alluvial landform seems to be formed by continental alluvial deposits which is a system occurring where stream 
systems originating in mountains wash down large amount of sediments onto the adjacent plains. The Blue Nile is 
originating in Ethiopian high lands and is washing down large amount of sediments on the Gezira plain. 
6. DRAINAGE 
The drainage system of the study area is a meandering system. The texture density is medium south of latitude 14° 10° N 
and coarse north of 14° 10° N down to Khartoum town. 
6.1 The Old Stage (Map A) 
This map represent a part of the old stage of the Blue Nile, the whole part is meandering about five meanders could be 
observed on this part. The straight-line distance from the southern end to the northern point calculated as 20km. Within 
these 20 km the Blue Nile is meandering continuously forming some point bars and oxbow lakes. These point bars and 
oxbow lakes are by the helical flow which localize the erosion on the outside bends of the meanders and deposit on the 
inside bends to form the point bars. There are two clear oxbow lakes on the sample map shown. 
The measurements of the meander wave length is ranging from about 8 km as a lower reading and 10 km for the higher 
wavelength found in the portion. The meander wide is ranging from about 8.5 km as the lower reading and 10 km as the 
higher measurement. The lower amplitude is 8 km. Where as the higher one measured is 10 km. The surface width 
dimensions are also ranging from 800m where it is narrow to 1400m where it is covering about 240 km. 
The channel length is the line running at the middle of the stream and it is about 44.7 km for this part of the sample area. 
It is the longest channel length of the three samples because it has more meanders than the other two samples. The 
talweg length of part (A) is measured as 46 km and it is the longest tawleg of the three samples. The meander belt axis 
of this site is 20.2 km. This measurement and the length of the channel are used in this study to measure the sinuosity 
index (Si) using the formula of BRICE (1964). 
SI= Length of channel 
Length of Meander Belt Axis 
No islands could be observed in this portion of the Blue Nile. 
6.2 The Mature Stage (Map B) 
Map (B) represent the mature part ofthe Blue Nile mapped from the satellite image. This part is sinuous, having less 
meander than the map (A). The straight-line distance of this map is also 20 km same as the previous one. No oxbow 
lakes could be observed along this channel and the meanders are smaller. The meander wavelength is about 7.5 km. The 
meander width is a most about half of map (A), it is only 5 km, the amplitude is 4.5 km which is also half of the old 
stage meander. The surface width is ranging between 400 meters for the narrows part and 1500 meters for the wide part 
of the map (B). The meander belt is calculated as 120 km?. 
The channel length is about 29.8 km, it is lower than map (A) and higher than map (C). The talweg is also higher than 
(C) and lower than (A). It is 31.6 km. The meander belt axis is 20.4 km. This belt axis and the length of the channel are 
used for the calculation ofthe (SI). Only one island could be observed and the Rahad River is joining from the eastern 
side. 
6.3 The Young Stage (Map C) 
Map (C) is a sample of the young part of the Blue Nile mapped from satellite image. It starts from 15 km south of 
Hasaheisa town. The only meander created along the young portion of the Blue Nile is shown as part of the left bank and 
Rofaa town on the right bank of the Blue Nile. The straight-line distance of this part from the south to the north is the 
same as (A) and (B). 20 km. The meander wavelength is 4.5 km just more than half of the mature map (B) meander 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1091