The Morila Gold mine, a joint venture between AngloGold Ashanti and Randgold Resources, is one of the 10 operating mines in Mali. The mine is located at 180 km southeast of Bamako, Mali, and has been operating since 2001. With the depletion of the orebody, a closure plan was established by the government and shareholders since 2012, and rehabilitation strategies are currently operating. The concentration of major, minor and traces elements were analyzed in 90 water samples (45 water supply boreholes, 13 shallow wells, 20 piezometers of the mine and 12 surface water), 46 stream sediment samples, 10 mine soil samples and 57 plant samples. All the samples were collected from June 2015 to December 2016 in three study areas: Morila mine, an intermittent stream at downstream of the mine and a controlled geochemical background area free of mining activities (located 15 to 20 km upstream of the mine). Chemical water analyses show that arsenic (As: 0.8 to 132 ppb), manganese (Mn: 2.52 to 5200 ppb) and total iron (Fe: 0.462 to 78 ppm) are present at high levels. The ANOVA tests demonstrate significant differences between the three sites for most major ions and trace metals in water, stream sediments and mine soils. The mean concentrations within the mine were significantly higher than those outside mine boundaries. Factor analysis and cluster analysis show a geogenic and pollution factors influencing the soils and the water quality in the study area. Arsenic values were mostly found in groundwater of the village of Sanso (the nearest village to the Morila mine), where 7 of the 10 sources of drinking water boreholes had arsenic contents higher than the standard value of 10 ppb. This arsenic contamination in groundwater and those located in background area could not be linked to mining activities, and attributed to geogenic influences. In stream sediments and soil samples, the values of the analyzed elements were ranged bellow the maximum allowed concentration except for As, Fe, Al and S. Mine soils have high Fe (similar to 10 wt%) and high Al (similar to 3 wt%) concentrations, likely derived from naturally sources. Sulfur contents in soil and stream sediments were high only in the mining environment, and derive from sulfide mineral oxidation. Arsenic contents were elevated in most plant species samples, and concentrations of samples located within the mine were higher than those of the background area. This study indicates that most of the metals and toxic contaminations were from geogenic origin, but mining activities likely also play a substantial role by increasing the level of these contaminants in water, soil and plants within the mining environment.

The objectives of this study. realized essentially from spatial and temporal statistical analyses. is to give a global outline of dams in the basin of the River Niger. The capacities of the dams is between 0.04 Mm(3) and 15 x 10(3) Mm(3). Two out of nine countries. Burkina Faso and Nigeria. concentrate 47% of the water in 94% of the dams built in the lower and mean parts of the basin. The future dam projects concern instead the upper Dart of the basin and should have a positive effect on the mobilization of water resources (light reduction of flood peaks and support of important low-water mark) and should also reduce flooded surfaces in the Interior Delta of Niger in Mali. More than half of the dams (60%) were built in the 1970 and 1980 decades: more than 70% of these dams were built during the 1980 decade. The classification of these dams by periods of five years indicates that 12 were built between 1970 and 1974. 21 between 1975 and 1979. 38 between 1980 and 1984, and 45 between 1985 and 1989. The increment of water stored matches this evolution. The years in which most dams were built correspond to the important period of drought in western Africa. We could therefore conclude that drought significantly induced the construction of dams, which could be interpreted as one of the adaptation strategies.

Resume L’objectif de cette étude, réalisée essentiellement à partir d’analyses statistiques spatiales et temporelles, est de donner un aperçu global des barrages de retenues d’eau construits sur le bassin du fleuve Niger. La capacité des barrages est comprise entre 0,04 Mm 3 et 15 10 3 Mm 3 . Deux des neuf pays, Burkina Faso et Nigéria, concentrent dans les parties moyennes et inférieures du bassin 94% de barrages inventoriés, qui retiennent 47% du volume d’eau stockée. Les prochains projets de barrage concernent plutôt la partie amont du bassin qui devrait avoir un effet positif pour la mobilisation des ressources en eau (légère réduction du pic de crue et soutien d’étiage important) mais qui réduiraient aussi les surfaces inondées dans le Delta Intérieur du Niger au Mali. Plus de la moitié (60%) des barrages ont été construits pendant les décennies 1970 et 1980 avec plus de 70% d’entre eux mis en eau durant la décennie 1980. Le dénombrement par période de cinq ans des barrages mis en eau au cours de ces deux décennies indique 12 constructions entre 1970 et 1974, 21 entre 1975 et 1979, 38 entre 1980 et 1984 et 45 entre 1985 et 1989. Les quantités d’eau stockées ont suivi la même évolution. Les années pendant lesquelles un plus grand nombre de barrage est construit correspondent à celles pendant lesquelles la sécheresse a été plus importe en Afrique de l’ouest. On pourrait penser que la sécheresse a induit un engouement à la construction des barrages, qui pourrait être interprété comme une des stratégies d’adaptation.

In this paper, we study the impact of climate change on river regimes in several parts of Africa, and we look at the most probable causes of these changes either climatically or anthropogenically driven. We study time series of updated monthly and annual runoff of rivers of North Africa, West Africa (Sahelian and humid tropical regions) and Central Africa, including the largest river basins: Niger and Volta rivers in West Africa, and Congo and Ogooue rivers in Central Africa. The recent years are studied in the perspective of multi-decadal variability. In West Africa and in a part of Central Africa, the climate has changed since 1970, and rainfall has not returned to previous annual amounts, except in Equatorial Africa. The consequences of the long-lasting drought are, depending on the area concerned, the modification of seasonal regimes (Equatorial area), the groundwater table decrease (Tropical humid area) and the land cover degradation (Sahelian area). The increasing number of dams and of agricultural areas also plays a major role on the modification of river regimes. The population increase will continue to impact on the environment: land cover change, deforestation, agriculture and increasing number of dams will be associated with a reduction of water and sediment discharges to the sea, and major impacts on downstream ecosystems and coastal areas. It seems necessary to share with stakeholders a comprehensive approach of the water cycle from the basin to the sea, to prevent long-lasting damages to ecosystems and infrastructures. Copyright (c) 2013 John Wiley & Sons, Ltd.

The Niger River basin covers 1.2 million km(2) and extends over nine countries in West Africa. Its average discharge to the sea is about 6000 m(3) s(-1) .The main upstream flood is produced during the 6-7 months of the tropical rainy season. The hydrological regime has been modified due to climatic and anthropogenic changes. There are only a few major dams on the River Niger, and future development plans will modify its regime and the flooded areas. The goal of this study is to provide a comprehensive overview of the hydrological changes of the Niger regime in its different sub-basins, in order to assess the impacts of future changes. The time series at Koulikoro and for the upstream basins show a high interannual flow variability since 1907, and a strong decrease since 1970. The runoff deficit in the Bani River after 1970 is greater than the rainfall deficit, due to a decrease in the groundwater level. NOAA images for 1990-2000 indicate that the flooded surfaces have decreased in the Inner Delta. The Sahelian flood from rivers in Burkina-Faso and Niger, and from the Sokoto River in Nigeria, has increased due to land degradation, despite the reduced rainfall. Now, more than half of the water of the Lower Niger comes from the Benue River. For the Sahelian basins, the increase in runoff can be closely related to the deforestation, but the dramatic decrease of the groundwater levels seems to be related to climate change. In the future, large changes will come from the proposed dams, which will reduce the flood peaks and the flooded surface areas, but will also have positive effects on the management of water resources.

The River Niger is the third longest river in Africa, with a stream length of 4200 km, a drainage basin of 2 170 500 km (of which 1 500 000km(2) is an active basin), and an average discharge of about 6000 m(3)/s. The natural variability of its rainfall and discharge are analysed for several major sub-basins, in the context of the West African drought, which has lasted for nearly 40 years. Two paradoxes are shown: the increase of Sahelian runoff since the beginning of the drought due to land degradation, and the steep decrease of Sudanian runoff over the same period, substantiated by the long-lasting decrease of the groundwater tables. The cooperation between the nine countries sharing the basin is organized through the Niger Basin Authority (NBA), which needs to propose and administer plans to meet objectives for all development projects throughout the basin. Much information about the water resources available in the basin is collected and analysed by the NBA, which is summarized in this paper, including surface and groundwater resources, rainfall and evaporation over the basin, existing and projected dams and water consumption for irrigation. From the standpoint of water resources, the Niger basin can be divided into four zones with different physical and geographical characteristics: (i) the Upper Niger basin, in Mali, Guinea, and Ivory Coast, covering a surface of 257 000 km(2), with only one large dam in Mali (Selingue, 1.7 MMm(3)); (ii) the inner delta, in Mali, which seasonally flooded surface can reach 35 000 km(2), and where the water losses vary between 24% and 48%; (iii) the Middle Niger basin, in Mali, Niger and Benin, where local flows from Sahelian and Sudanian areas join the residual outflow from the inner delta; and (iv) the Lower Niger basin, between Cameroon, Nigeria and Chad, where high rainfall increases the River discharge, and where large dams for hydro-electric power production and irrigation are built. The River Niger is deficient in dams to control water, especially in its upper and middle basins. Nigeria has many dams, including large dams, while Burkina-Faso has many small dams, but there are only a few dams upstream of the River Niger in Mali/Guinea/Ivory Coast. It is therefore likely that several dams will be built in the Niger basin in the coming years, and several are in the project phase: among which three are large ones in Guinea (Fomi), Mali (Tossaye) and Niger (Kandadji). All of these will have a large impact on the River Niger regime and the environment, especially the Fomi dam, which will significantly change the river regime upstream of the inner delta, inducing an important reduction of the flooded area, and the Tossaye dam on the Saharan border of Mali, which could promote a very significant level of evaporation, while the Kandadji dam will have less impact downstream. It is very important before building these dams to take into account the past years variability of climate and river regime. It is particularly important to take into account the very large runoff decrease in the tropical humid sub-basins, and the runoff increase in the Sahelian sub-basins.

The inner delta of the River Niger receives runoff from both the River Niger and the River Bani (249 000 km2) and is divided into a northern part (15 000 km2) and a southern part (58 000 km2). The average input and output discharges are approximately 1490 and 900 m3 s−1 (1955/1996), respectively. The annual average water loss is approximately 40% (24‐48%). The losses are greater in the northern (10·5 km3) than in the southern delta (8·2 km3), but this situation was reversed in 1984. The correlation between the output and input discharges is high for the northern part of the delta, but very low for the southern part, where the change in flooded area is likely to be limited. The average flooded area, calculated using a method based on the hydrological balance, is estimated to be about 10 000 km2 (north) and 14 000 km2 (south), which is consistent with the estimates provided by the previous authors. Copyright © 2009 John Wiley & Sons, Ltd.

Dans le contexte pluviométrique déficitaire de l'Afrique intertropicale, l'hydraulicité des fleuves soudano-sahéliens a beaucoup diminué depuis 25 ans. Les fleuves des régions humides, relativement épargnés jusqu'en 1980, montrent aussi, avec un retard de plusieurs années une hydraulicité qui baisse dans des proportions importantes, alors qu'un retour à la normale du régime des pluies paraît amorcé. Le déficit des apports est pour l'Afrique humide de 16% pour la décennie 80 (365 km3 an-1), contre 7% pour la décennie 70, et pour l'Afrique sèche de 27% (65 km3 an-1) pour la décennie 80 contre 13% pour la décennie 70. Les maximums annuels de crue sont systématiquement plus faibles dans la période récente. En régime équatorial, la crue de printemps est la plus affectée par le déficit hydrologique et la différence entre crue de printemps et crue d'automne a triplé entre les années 1950-1960 et les années 1980. L'ensemble de la région connaît des étiages exceptionnels répétés. En zone soudano-sahélienne, le tarissement s'est considérablement accéléré et montre une vidange des écoulements de base deux fois plus rapide dans la période récente. Le phénomène est également sensible en Afrique humide et traduit un amenuisement des réserves souterraines dû aux effets cumulés des déficits pluviométriques et décalé dans le temps, que l'on retrouve dans la baisse du niveau piezométrique des nappes phréatiques. Un effet mémoire est donc observé sur les écoulements de base, avec pour conséquence un un appauvrissement durable des ressources hydriques. Celui-ci restera indépendant, pour un temps, d'une éventuelle amélioration des conditions climatiques, comme le montrent les observations des années les plus récentes.

The annual average of rile groundwater levels in 27 wells is connected to the annual climate impact on the groundwater resources in the Bani river basin (Douna, 101 600 square kilometers). The groundwater level variations are well correlated to rainfall variations, and for the lowest levels of groundwater, the runoff stops in the dry season at Douna. The humid year of 1994 caused a rise in the groundwater level to the same level as 1981, together with a reduction of the depletion coefficient. But the runoff is still weak, showing that the rainfall-runoff relationships are modified over the long term. (C) 2000 Academic des sciences/Editions scientifiques et medicales Elsevier SAS.

Les chroniques hydrologiques du Niger superieur et de sa cuvette lacustre montrent un appauvrissement de la ressource en eau depuis deux decennies lie aux deficits pluviometriques et a l'amenuisement des ressources souterraines. La cuvette lacustre-delta central du Niger-constitue un hydrosysteme particulier de lacs et de plaines d'inondation ou les pertes annuelles, dues essentiellement a l'evaporation, sont extremement importantes. Les mesures de flux fluviaux de matieres particulaires, entreprises depuis 1990 sur le Niger amont et son delta, ont montre une perte globale de matieres en suspension a l'interieur du delta central. Les variations saisonnieres de la charge solide, en amont et en aval du delta central, permettent une premiere approche du fonctionnement de cet hydrosysteme. La forte hydraulicite de l'annee 1994/1995 a mis en evidence la complexite du phenomene de transport fluvial de matiere a l'interieur du delta.

Les chroniques hydrologiques du Niger superieur et de sa cuvette lacustre montrent un appauvrissement de la ressource en eau depuis deux decennies lie aux deficits pluviometriques et a l'amenuisement des ressources souterraines. La cuvette lacustre-delta central du Niger-constitue un hydrosysteme particulier de lacs et de plaines d'inondation ou les pertes annuelles, dues essentiellement a l'evaporation, sont extremement importantes. Les mesures de flux fluviaux de matieres particulaires, entreprises depuis 1990 sur le Niger amont et son delta, ont montre une perte globale de matieres en suspension a l'interieur du delta central. Les variations saisonnieres de la charge solide, en amont et en aval du delta central, permettent une premiere approche du fonctionnement de cet hydrosysteme. La forte hydraulicite de l'annee 1994/1995 a mis en evidence la complexite du phenomene de transport fluvial de matiere a l'interieur du delta.

Resume Depuis une vingtaine d'annees, le bassin du fleuve Niger et ceux des principaux cours d'eau africains sont soumis a un deficit pluvio­ metrique important. La chronique des debits enregistres a Koulikoro (120000 krrr') montre une decroissance persistante des ecoulements. Cependant la baisse des pluies n'est que de 20% en valeur moyenne decennale entre 195111960et 198111989, alors que celle des ecoulements est de 55 %. Si les conditions du ruissellement superficiel ont ete peu modifiees durant la secheresse, l'ecoulement souterrain a lui fortement diminue comme l'indique l'augmentation du coefficient de tarissement. La reduction des modules annuels et des maximums de crue peut etre logiquement reliee a la diminution des apports souterrains. Cette hypothese est confirmee en 1994: des pluies de 15% superieures a la moyenne 1951-1989 (frequence vicennale) ne produisent qu'une crue moyenne tant en pointe qu'en module. Par rapport a la moyenne de cinq annees de pluies equivalentes sur le bassin versant, la lame ecoulee est plus faible de 28% en 1994/1995, tandis que le coefficient de tarissement reste eleve, et superieur a la normale. Recent climatic changes and modification of the hydrological regime of the Niger river at Koulikoro (Mali)

Résumé Depuis une vingtaine d'années, le bassin du fleuve Niger et ceux des principaux cours d'eau africains sont soumis à un déficit pluvio- métrique important. La chronique des débits enregistrés à Koulikoro (120 000 km2) montre une décroissance persistante des écoulements. Cependant la baisse des pluies n'est que de 20% en valeur moyenne décennale entre 1951/1960 et 1981/1989, alors que celle des écoulements est de 55 %. Si les conditions du ruissellement superficiel ont été peu modifiées durant la sécheresse, l'écoulement souterrain a lui fortement diminué comme l'indique l'augmentation du coefficient de tarissement. La réduction des modules annuels et des maximums de crue peut être logiquement reliée à la diminution des apports souterrains. Cette hypothèse est confirmée en 1994: des pluies de 15% supérieures à la moyenne 1951-1989 (fréquence vicennale) ne produisent qu'une crue moyenne tant en pointe qu'en module. Par rapport à la moyenne de cinq années de pluies équivalentes sur le bassin versant, la lame écoulée est plus faible de 28% en 1994/1995, tandis que le coefficient de tarissement reste élevé, et supérieur à la normale. Recent climatic changes and modification of the hydrological regime of the Niger river at Koulikoro (Mali) Abstract Over the last 20 years, the Niger river basin as well as all the other African rivers has experienced a serious shortage of rainfall. For the Niger river at the station of Koulikoro (120 000 km2) the time series of runoff shows a continuing diminution. However, considering the decadal mean values, precipitation was reduced by 20% between 1951/1960 and 1981/1989, while the runoff decrease was 55% during the same period. The flood flows were not altered during the recent drought, but the baseflows strongly decreased as indicated by the increase of the recession coefficient. The reduction both the of mean annual discharges and of the values of the maximum peak flows can be assumed to be a result of the reduction of the baseflow. That hypothesis was verified in 1994: 15% higher rainfalls, compared to the 1951-1989 mean (return period of 20 years), only produced a mean level annual discharge and maximum peak flood. In comparison with the mean value calculated for the past five years for the same annual rainfall, the depth of runoff was 30% lower in 1994/1995, and the recession coefficient remained high, above the inter-annual mean.