Lake Victoria water levels provide an important indicator of climate; since 1954 these levels have been maintained natural by agreement, but after recent increased releases require adjustment to retain a naturalised series. It is possible to compute the impact of recent over-abstraction on declining water levels. This impact has been significant: of the order of 0.6 m.

An analysis of the vast wetland of the Sudd swamps in southern Sudan was designed to assess and describe interdependencies between morphology and hydrology. Findings based on field survey and remote sensing data include an assessment of the effect of ground slopes and morphological features on spill and flooding of the seasonally flooded grasslands. Through bathymetric surveys and analysis of Landsat images, depth profiles and cross-sectional depth and flow distributions were established. Data from remote sensing, field survey and historical sources were correlated and correction factors established; the SRTM was found to be partly unsuitable for further assessments. Further analysis of remote sensing data was used to investigate the Sudd's inland delta as well as the question of spill into the Bahr el Ghazal basin. Figure 1. Overview of project area in southern Sudan with detailed core area of interest.Figure 3. Water level (WL) time series of Burakok (within the Swamp) and at the tails of Khor Adwar and Khor Baidit, showing surface level fluctuations in correlation to the wet and dry season. (Note that the station at Khor Adwar is not cut off but located just to the west of the road dam.) Morphological analysis of the Sudd region 1715 Figure 5. SRTM DEM of the area between Bor and Shambe, showing an inland delta formation. The transition from incised trough in the south to elevated channels in the north is clearly visible. Morphological analysis from SRTM Digital Elevation Model (DEM)Evaluating the DEM in Figures 5 and 6 on a coarse scale, varying slope directions can be identified along the course of the Bahr el Jebel. From Bor northwards, where the incised and restricting trough disappears in the east, the ground slopes in a north-northwesterly direction, like the flow direction of the river. After reaching Shambe, the ground slope changes into a westerly direction towards the Bahr el Ghazal basin, while the river, bound by alluvial banks, is heading oblique to this slope towards the north until it reaches Lake No. Slope gradients can be estimated as 0·1 m/ km, with very limited local undulations, the only pronounced features being the incised river trough south of Bor with banks disappearing further north. The system changes to another formation visible from the DEM, the pronounced inland delta between Baidit/Padak and Shambe, as shown in Figure 5. Here the channel flows at higher elevation than the surrounding plains, with level differences between the river and the surrounding plains about 2-3 m. Further north, the inland delta becomes less defined, but can still be observed running obliquely to the general westerly slope of the area towards the north. A series of cross-sections derived from the DEM at locations perpendicular to the river is shown in Figure 7, illustrating the transition from incised trough to elevated inland delta.Cross-sections from JIT (1954) have been digitized and compared with SRTM DEM extracted cross-sections, as shown in Figure 8. While qualitatively the cross-sections are very sim...

Abstract. An assessment to describe and quantify the extent of changes in the channel and lagoon system of the Sudd was carried out using Landsat satellite images of 1973, 1979, 1997 and 2002. Using supervised classification and visual interpretation after referencing the images, the water bodies for a representative area between Bor and Shambe (a stretch of 150 km) were delineated. The resulting files were compared to establish and quantify changes in-between the years and as well compared to Lake Victoria outflow data to assess a likely correlation which was found for the largely water level dependent lagoon system. Changes in the channel system were interpreted to happen in a certain pattern but the extent of changes could not be correlated to the outflow data as they are influenced by other, here not considered factors like wind drift and channel blockages by vegetation.

Somalia has frequently been affected by droughts, famines and water-related humanitarian crises. Water is scarce and the only perennial streams, the Juba and Shabelle rivers, are trans-boundary with river flows mainly originating from the Ethiopian highlands. In both riparian countries water demands are projected to increase. This paper reveals the impact of rising regional water abstractions on stream flows by illustrating sectoral demands and joining them into scenarios of medium and high population and economic growth. These scenarios are associated to the time horizons of 2035 and 2055, respectively. The scenarios disclose alarming trends especially for the Shabelle River: in the medium and high growth scenarios, water demands surpass the available river flows by 200 and 3500 hm 3 , respectively. The calculated deficits partly derive from conflicting assumptions about river flows by the two main riparian countries, an obstacle to any integrated planning efforts and sustained regional development.

The flooding and drying mechanisms of the seasonal flood plains of the Sudd swamps in southern Sudan are, while dependent on the river levels, influenced by a complex interaction between soil, vegetation, topography and seasonal trends in rainfall and evapotranspiration. Based on field measurements, these components have been assessed in detail and evaluated regarding their function in the seasonal cycle of flooding and drying. A detailed analysis of soil and evapotranspiration conditions, as well as the interaction with vegetation and meteorological conditions, has been conducted using field and laboratory experiments. Sources, processes, flow directions and the fate of the floodwaters on both the river-fed seasonal flood plains and the rain-fed grasslands have been established. The results show that river spill is responsible for flooding these areas while no return flow occurs, and drying is caused by evapotranspiration. Rainfall can only cause temporary flooding in extreme events.