Spatio-temporal water body and vegetation changes in the Nile swamps of southern Sudan

Hydrological Sciences Journal

2010

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A two-dimensional (2D) hydrodynamic assessment of the Nile swamps in southern Sudan has been carried out using DHI MIKE 21 software based on a ground referenced and corrected Shuttle Radar Topography Mission (SRTM) digital elevation model. The model was set up and calibrated using available historical information as well as newly measured data. The results show the model capable of representing the hydraulic conditions in the swamps, allowing the assessment of different flow conditions and their effects on the swamp. The study has established water-level gradients, flow directions and velocities in the swamp, as well as on the seasonal flood plains, and describes the importance of evapotranspiration for losses in the system. Key words swamp model; Sudd; flood plain; 2D hydrodynamic model Etude numérique bidimensionnelle de l'hydrodynamique des marais du Nil dans le sud du SoudanRésumé Une étude bidimensionnelle (2D) du fonctionnement hydrodynamique des marais du Nil dans le sud du Soudan a été réalisée en utilisant le logiciel DHI MIKE 21, basée sur un modèle numérique de terrain fourni par le projet SRTM (Shuttle Radar Topography Mission), référencé au sol et corrigé. Le modèle a été établi et calé à partir de données historiques et de mesures récentes. Les résultats montrent que le modèle est capable de représenter le fonctionnement hydrodynamique des marais, et permet de simuler différentes conditions hydrauliques ainsi que leurs impacts sur les marais. L'étude a permis de définir les gradients hydrauliques, les directions et les vitesses des écoulements dans les marais, ainsi que dans les plaines d'inondation saisonnière, et décrit l'importance de l'évapotranspiration en tant que perte dans le système.

Section: Model Performancementioning

confidence: 99%

Section: The Study Sitementioning

confidence: 99%

Section: Model Set-up Sensitivity and Calibrationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Two-dimensional numerical assessment of the hydrodynamics of the Nile swamps in southern Sudan

Petersen¹,

Hydrological Sciences Journal

2010

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“…Wright, in JIT (1954) gave initial hints on soil water recharge values of between 300 and 800 mm, assuming that the latter was overestimated. Sutcliffe (1974) described the vegetation distribution of different species in the swamps and Petersen et al (2007) described the vegetation dynamics with regard to changes in the permanent swamps. Hurst & Phillips (1938) and Migahid (1948Migahid ( , 1952 reported outcomes of different evapotranspiration experiments.…”

Section: Introductionmentioning

confidence: 99%

Flooding and drying mechanisms of the seasonal Sudd flood plains along the Bahr el Jebel in southern Sudan

Petersen¹,

Hydrological Sciences Journal

2010

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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.

Morphological analysis of the Sudd region using land survey and remote sensing data

Petersen

Sutcliffe

Earth Surf Processes Landf

2008

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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...