Impacts of large dams on downstream flow conditions of rivers: Aggradation and reduction of the Medjerda channel capacity downstream of the Sidi Salem dam (Tunisia)

Zahar, Yadh; Ghorbel, Abdelmajid; Albergel, Jean

doi:10.1016/j.jhydrol.2007.12.019

Cited by 108 publications

(64 citation statements)

References 14 publications

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“…2004), the Medjerda River in North Africa (Zahar et al, 2008), the Tana River in Kenya (Maingi and Marsh, 2002) and the Hadejia-Jama'are floodplains in Nigeria (Barbier and Thompson, 1998), while many others are threatened such as the Okavango Delta in Botswana (Milzow et al, 2009) and the Rufiji Delta (Duvail and Hamerlynck, 2007).…”

Section: Leauthaud Et Al: Flood Characterization In the Tana Rivementioning

confidence: 99%

Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Léauthaud

Belaud

Duvail

et al. 2013

Hydrol. Earth Syst. Sci.

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Abstract. Wetlands, such as those of the Tana River Delta in Kenya, are vital but threatened ecosystems. The flooding characteristics of wetlands largely determine their physical, chemical and biological properties, so their quantification is crucial for wetland management. This quantification can be achieved through hydrological modelling. In addition, the analysis of satellite imagery provides essential hydrological data to monitor floods in poorly gauged zones.The objective of this study was to quantify the main water fluxes and flooding characteristics (extent, duration and number of floods) in the poorly gauged Tana River Delta in East Africa during 2002-2011. To do so, we constructed a lumped hydrological model (the Tana Inundation Model, TIM) that was calibrated and validated with MODIS data. Further analysis of the MYD09A1 500 m composite product provided a map of the empirical probability of flooded state. In non-extreme years and for the current topology of the delta, the flood extent exceeded 300 km 2 . Floods over 200 km 2 occurred on average once a year, with a mean duration of 18 days. River discharge from the upper basin counted for over 95 % of the total water inflow. The results are discussed in the light of possible improvements of the models and wetland management issues.This study provides the first known quantification of spatial and temporal flooding characteristics in the Tana River Delta. As such, it is essential for the water and natural resource management of the Tana River basin. The water balance approach was pertinent to the study of this system, for which information on its internal properties and processes is limited. The methodology, a combination of hydrological modelling and flood mapping using MODIS products, should be applicable to other areas, including those for which data are scarce and cloud cover may be high, and where a medium spatial resolution is required.

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Section: Leauthaud Et Al: Flood Characterization In the Tana Rivementioning

confidence: 99%

Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Léauthaud

Belaud

Duvail

et al. 2013

Hydrol. Earth Syst. Sci.

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“…Two rock drawings illustrating war ships from archaic times (620 BC) were found in northwest Tunisia, in the continental part of Numidia, indicating navigation. Navigation on Wadi Mejerda appears very likely, owing to its morphology and especially its width, which varies from 35 to 170 m (Niox 1890, Abidi 2007, Zahar et al 2008. This suggests that navigation by Carthaginian trade ships (max.…”

Section: Navigation Through Mejerdamentioning

confidence: 99%

Historical aspects of soil erosion in the Mejerda catchment, Tunisia

Jebari

Berndtsson

Lebdi

et al. 2012

Hydrological Sciences Journal

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Agricultural use and related water erosion may lead to significant changes in the sedimentological and hydrological characteristics of watersheds, and therefore negative consequences for rural development. This research aimed to put present-day soil erosion of the important Mejerda catchment into a historical context. The catchment of Wadi Mejerda in northern Tunisia has experienced soil erosion due to weather and human impacts for thousands of years. We used historical texts and results from archaeological research that go back to 1000 BC, as well as data collected during the last century. Soil erosion from different types of agricultural landscape management was analysed together with information on the soils' production potential, the hydrographic network and flood frequency. The results showed that water erosion has increased the hydrographic network by 65 km and increased the deltaic plain by as much as 15 km 2 /century. However, soil productivity has decreased significantly. Moreover, due to in channel sedimentation and river choking, the number of flooding occurrences has multiplied over the last century. Finally, it is shown that water erosion follows a specific cycle of degradation throughout the watershed. These findings should be considered for better water and soil management in the context of semi-arid areas.Key words agricultural landscape; deltaic plain; farmland management; historical background; hydrographic network; Mejerda Wadi; semi-arid; temporal degradation pattern; Tunisia; water erosion Evolution temporelle de l'érosion hydrique sur le bassin versant de l'oued MedjerdahRésumé L'activité agricole est généralement liée à l'érosion hydrique qui entraîne des changements au niveau des caractéristiques sédimentologiques et hydrologiques des bassins versants. Elle a par conséquent des répercus-sions négatives sur le développement rural. Le présent travail est une étude de l'évolution temporelle de l'érosion hydrique dans un contexte historique. Le site de recherche concerne le bassin versant de l'oued Medjerdah situé au nord de la Tunisie. Ce bassin est soumis au phénomène de l'érosion hydrique qui s'est déclenché initialement sous la contrainte de facteurs climatiques et anthropiques. Nous nous sommes référés à cet effet aux études historiques et archéologiques remontant à plus de 1000 ans av. J.-C., ainsi qu'aux archives relatives au siècle dernier. La relation avec la gestion du paysage agricole a été commentée en fonction du potentiel de production des sols, du transport solide, du développement du réseau hydrographique et, finalement, de la fréquence des inondations. Les résultats enregistrés ont montré que l'érosion hydrique est à l'origine d'une baisse de fertilité importante des sols, d'une évolution du réseau hydrographique de 65 km et d'une progression de la plaine deltaïque de 15 km 2 /siècle. Finalement, il a été révélé que le phénomène érosif suit un cycle spécifique de dégradation à travers le bassin versant étudié. Ces acquis pourraient être considérés pour une meilleure ...

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“…River channel scour occurs frequently immediately below dams after their construction, and has been well documented over the last 80 years (Lawson, 1925;Shulits, 1934;Andrews, 1986;Kondolf, 1997;Magilligan and Nislow, 2005;Graf, 2006;Chen et al, 2010). By contrast, channel aggradation downstream of dams has also been observed (Arroyo, 1925;Malhotra, 1951;Petts, 1979Petts, , 1980Zahar et al, 2008), whereas Magilligan et al (2008) found no significant difference between pre-and postdam channel morphology in the forested upland watersheds in the Connecticut River basin, USA.…”

Section: Introductionmentioning

confidence: 98%

“…However, the downstream changes of flow and sediment regime caused by dams can vary significantly between river reaches and over time. The influence of dams on flow and sediment regime and subsequent channel morphology has long been a concern of fluvial geomorphologists and hydraulic engineers (Arroyo, 1925;Malhotra, 1951;Gregory and Park, 1974;Petts, 1979Petts, , 1980Graf, 1980Graf, , 1999Graf, , 2006Williams and Wolman, 1984;Chien, 1985;Andrews, 1986;Gregory, 1987;Carling, 1988;Xu, 1990;Phillips, 2003, Magilligan andNislow, 2005;Petts and Gurnell, 2005;Phillips et al, 2005;Pan et al, 2006;Singer, 2007;Magilligan et al 2008;Zahar et al, 2008;Chen et al, 2010;Fu et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Channel adjustments in response to the operation of large dams: The upper reach of the lower Yellow River

et al. 2012

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The Yellow River in China carries an extremely large sediment load. River channel-form and lateral shifting in a dynamic, partly meandering and partly braided reach of the lower Yellow River, have been significantly influenced by construction of Sanmenxia Dam in 1960, Liujiaxia Dam in 1968, Longyangxia Dam in 1985 and Xiaolangdi Dam in 1997 Using observations from Huayuankou Station, 128 km downstream of Xiaolangdi Dam, this study examines changes in the river before and after construction of the dams. The temporal changes in the mean annual flow discharge and mean annual suspended sediment concentration have been strongly influenced by operation of theses dams. Observations of sediment transport coefficient (ratio of sediment concentration to flow discharge), at-a-station hydraulic geometry and bankfull channel form observed from 1951 to 2006 have shown that, although variations in flow and sediment load correspond to different periods of dam operation, changes in channel form are not entirely synchronous with these. The channel has been subject to substantial deposition due to the flushing of sediment from Sanmenxia Dam, resulting in a marked reduction in bankfull cross-sectional area. Flows below bankfull had a greater impact on channel form than higher flows because of very high sediment load. At-a-station hydraulic geometry shows that the variation of channel cross-sectional area below bankfull in this wide and relatively shallow system largely depends on changes in width. Such at-a-station changes are significantly influenced by (1) events below bankfull and (2) overbank floods. Bankfull depth is the main component of channel adjustment in that depth adjusts synchronously with channel area. The channel adjusts its size by relatively uniform changes in depth and width since 1981. Channel morphology is not the product of single channelforming flow frequency. It is determined by the combination of relatively low flows that play an important role in fine sediment transport and bed configuration as with relatively high flows that are effective at modifying the channel's morphology. The sediment transport coefficient is a useful index for efficiently guiding the operation of the dams in a way that would minimize channel changes downstream. Sedimentation over the nearly 60 years of study period caused the lower Yellow River to aggrade progressively, the only significant exception being the two years following completion of Sanmenxia Dam.

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Impacts of large dams on downstream flow conditions of rivers: Aggradation and reduction of the Medjerda channel capacity downstream of the Sidi Salem dam (Tunisia)

Cited by 108 publications

References 14 publications

Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Characterizing floods in the poorly gauged wetlands of the Tana River Delta, Kenya, using a water balance model and satellite data

Historical aspects of soil erosion in the Mejerda catchment, Tunisia

Channel adjustments in response to the operation of large dams: The upper reach of the lower Yellow River

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