Etudes diverses

Documents

Trier par : Titre | Date | Clics | [ Croissant ]

The Economic and Ecological Effects of Water Management Choices in the Upper Niger River The Economic and Ecological Effects of Water Management Choices in the Upper Niger River

Date de mise en ligne: 30/10/2009
Date de modification: 22/11/2012
Taille du fichier: 821.41 KB
Téléchargements: 4951
THE ECONOMIC AND ECOLOGICAL EFFECTS OF WATER MANAGEMENT CHOICES IN THE UPPER NIGER RIVER : DEVELOPMENT OF DECISION SUPPORT METHODS

The major aim of the three-year study was to develop a decision-support system for river management in the Upper Niger, in which ecological and socio-economical impacts and benefits of dams and irrigation systems can be analysed in relation to different water management scenarios. The study involves various components: hydrology, arable farming, livestock, fisheries, ecology and socio-economics. An economic analysis has been conducted to determine the role of dams in the economy of the Inner Niger Delta and the Upper Niger region. By innovatively combining the above information on hydrology, ecology, fisheries, and agriculture, the study shows that building new dams is not an efficient way to increase economic growth and reduce poverty in the region.

	The Distributional Impact of Dams : Evidence from Cropland Productivity in Africa The Distributional Impact of Dams : Evidence from Cropland Productivity in Africa

Date de mise en ligne: 30/10/2009
Date de modification: 22/11/2012
Taille du fichier: 1.94 MB
Téléchargements: 4814
THE DISTRIBUTIONAL IMPACT OF DAMS : EVIDENCE FROM CROPLAND PRODUCTIVITY IN AFRICA

We examine the distributional impact of major dams on cropland productivity in Africa. As our unit of analysis we use a scientifically based spatial breakdown of the continent that allows one to exactly define regions in terms of their upstream/downstream relationship at a highly disaggregated level. We then use satellite data to derive measures of cropland productivity within these areas. Our econometric analysis shows that while regions downstream benefit from large dams, cropland within the vicinity tends to suffer productivity losses during droughts. Overall our results suggest that because of rainfall shortages dams in Africa caused a net loss of 0.96 per cent in productivity over our sample period (1981-2000). However, further dam construction in appropriate areas could potentially lead to large increases in productivity even if rainfall is not plenty.

Land clearance and hydrological change in the Sahel: SW Niger Land clearance and hydrological change in the Sahel: SW Niger

Date de mise en ligne: 17/11/2009
Date de modification: 22/11/2012
Taille du fichier: 1.98 MB
Téléchargements: 4621
LAND CLEARANCE AND HYDROLOGICAL CHANGE IN THE SAHEL: SW NIGER
 
In the West African semiarid belt of the Sahel, for the second half of the XXth century, lasting droughts (1970s–1980s) and one of the World's highest population growths have resulted in major land cover and hydrological changes that can be quantified using aerial photographs. This paper aims to provide one of the longest combined observations of land cover and hydrological changes for semiarid areas using a time series of normalised mosaics of aerial photographs dating back from 1950, field inquiries, and updated groundwater data. The 500 km2 study area in southwest Niger was chosen (i) for its rural environment representative of the rain-fed agriculture belt of the Sahel and (ii) to encompass the main hydrological study sites investigated in this region over the past two decades (Hapex-Sahel and AMMA experiments, 1990–2000s). Results have significant implications for future freshwater availability and food security in the Sahel.

	Analyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et Bénin) Analyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et Bénin)

Date de mise en ligne: 05/10/2009
Date de modification: 22/11/2012
Taille du fichier: 439.85 KB
Téléchargements: 4423
ANALYSE DES INONDATIONS EN AVAL DU BARRAGE DE NANGBETO SUR LE FLEUVE MONO (TOGO ET BÉNIN)


L'analyse des risques d'inondation en aval du barrage hydroélectrique de Nangbéto sur le fleuve Mono a porté sur les variabilités interannuelles des précipitations et débits de 1955 à 1999, la vulnérabilité des populations, les modifications hydrologiques et les effets en aval au Togo et au Bénin du barrage construit en 1987. L'analyse des modules annuels n'a révélé aucune tendance, montrant ainsi que les changements intervenus dans l'affectation du sol, l'accroissement des surfaces imperméables et même le fonctionnement du barrage n'ont pas modifié de manière significative la variation interannuelle des débits annuels.
Outre le retour à l'amélioration des pluviométries dès la fin des années 80, les pressions anthropiques et la poussée démographique expliquent mieux l'ampleur et la fréquence élevée des inondations en aval du barrage hydroélectrique de Nangbéto. La dégradation des sols, le déboisement des berges du fleuve et des zones inondables, l'augmentation des habitations dans le lit majeur même du fleuve ne font que fragiliser les populations riveraines et accroître leur vulnérabilité face aux inondations.

Effects of river regulation on aquatic macrophyte growth and floods in the HADEJIA-NGURU Effects of river regulation on aquatic macrophyte growth and floods in the HADEJIA-NGURU

Date de mise en ligne: 15/10/2009
Date de modification: 22/11/2012
Taille du fichier: 452.87 KB
Téléchargements: 4219

EFFECTS OF RIVER REGULATION ON AQUATIC MACROPHYTE GROWTH AND FLOODS IN THE HADEJIA-NGURU WETLANDS AND FLOW IN THE YOBE RIVER, NORTHERN NIGERIA; IMPLICATIONS FOR FUTURE WATER MANAGEMENT

The Hadejia River is a tributary of the Yobe River in semi-arid northern Nigeria and is regulated by two major dams. The other main tributary is uncontrolled. Comparison of the discharge data for the controlled and uncontrolled rivers shows an average decrease of 33% in annual flow in the upstream part of the Hadejia River. The total annual flow and the peak flow in the Hadejia River further downstream, just above the Hadejia-Nguru Wetlands (HNW), however, did not show a significant reduction in discharge. This is related to a relatively small river flow reduction at lower flows in the upstream part of the Hadejia River and the fact that the formal large upstream water users are not (yet) working at full capacity. The major impact of the dams on the downstream part of the river is the change in regime from ephemeral to perennial. The introduced dry season flows created favourable circumstances for the development of aquatic macrophyte blockages in the HNW. Owing to these blockages, the Hadejia River stopped contributing to the flow in the Yobe River for much of the year. Furthermore, after the completion of the dams, the timing of the floods in the HNW became less predictable.
Suggestions for improvement of water management are made. These comprise engineering structures, including a flow diversion structure to regulate flows in the HNW, implementation of environmentally acceptable river flow strategies and water allocation management. Copyright © 2002 John Wiley & Sons, Ltd.