Water Availability and Access

BFP Niger WP2 Water availability and access

Gil Mahé, IRD Montpellier, France

Gaston Liénou, Université de Yaoundé, Cameroun

Olusegun Adeaga, University of Lagos, Lagos, Nigeria

Introduction Goals of this workpackage

The West African drought has now been lasting for more than 30 years. It has tragic consequences in the Sahel countries, such as desertification. This drought, which is notably characterized by a decrease of rainfall, global surface-water flows and by a change in the rainy season characteristics, contributes to reduce the water availability in the Niger River Basin. This climate shift must be born in mind if one wants to understand the present hydrology and water uses in the basin. Approach and literature review A careful review of the literature has already been performed by the IRD scientists who have in the past and recently published papers on the hydrology and water uses of the Niger basin and more generally of West Africa (see some references at the end). These reviews deal with observed climate changes in the region, climatic variability and climate change impact on water resources, relationships between rainfall and runoff (Lubès-Niel et al., 2003), river discharge, water quality and sediment transport in the River Niger and in the Inner delta, groundwater, land use change, flooding, river modeling, socio-economics, integrated river management, etc. Using available data, together with a recent update with NBA services, the report provides an up- to-date analysis of the temporal and spatial variability of rainfall in the basin, including possible scenarii from Global Climate Models applied to the region. We consider that the water availability corresponds to the physical availability of the resource, whereas the water access is defined by this physical availability and infrastructures and social rules that allow the access to the resource. Rapid assessment of status and trends The identification and the characterization of the water resources and uses will be realized by (i) a bibliographical analysis (ii) a collection of available data. Water availability Rainfall HSM has already developed an intensive analysis of the variability of rainfall with time series (Lubès et al., 1994; Paturel et al., 1997; L’Hôte et al., 2002) indicators of the characteristics of variation ranging from the inter-annual and seasonal variation (including monthly variation, daily distribution, rain season time shift…) to the evolution of the number of rainy days. Rainfall is important for the evaluation of water productivity which is dominated by rain fed agriculture in the basin. Variability of rainfall is one of the key factors in the vulnerability of farmers.

Surface water The hydrological regime of the main Niger tributaries (annual flows, low and high water levels, flow distribution and recession phenomena) will be characterized in a synthetic analysis at the basin scale (Servat et al., 1998). Groundwater The aquifer main characteristics will be described (type of aquifer, deepness, primary and secondary porosity, quality, recharge...). The Niger River Basin has a high hydrogeological diversity: underflow conduit, cracked aquifer and great porous sedimentary systems. The groundwater recharge is very low (a few millimetres per year), but the over-abstraction risk does not exist in the traditional conditions of exploitation (traditional agriculture, low population density…). The anthropized areas (large dams for instance) may have crucial impact on groundwater, either positive or negative: in the Iullemeden basin, the groundwater recharge has been multiplied by ten when farmers have cultivated millet instead of natural savannah (GEF, 2003). Water uses In 2025, the Niger River Basin will face an economic water scarcity (predicted by IWMI, http://www.iwmi.cgiar.org/home/wsmap.htm). This means that the lack of infrastructures will be preponderant; hence the particular importance of the inventory of the main existing and planned water infrastructures. The data available Numerous data on rainfall, groundwater, surface water hydrology and hydraulics have been collected in the Niger River Basin, including the Benue, in the past by IRD (formerly ORSTOM), and later by its partner hydrological services. These data have already contributed to some databases and programmes on water resources with the collaboration of HSM-IRD: - SIEREM database “Environmental information system on water resources” (hosted by IRD- HSM) www.hydrosciences.fr/sierem - Program ECCO “Continental Ecosphere, processes and modelling” (2001- 2002 and 2005- 2007) http://www.recherche.gouv.fr/recherche/fns/ecco.htm - International Programme AMMA “African Monsoon Multidisciplinary Analysis” (2002-2010) Program CORUS “Cooperation for scientific and academic research” (2004-2006)

- SIGMA & SIGNER (hydro-geological SIG for Mali and Niger, initiated by PNUDDTCD in the late 80s’) - Program EQUANIS, which monitored the quality of the waters in the central lacustrine basin - The national departments for hydrology - International institutes: 2IE (ex-EIER/ETSHER) Ouagadougou, NBA, with the help of the basin coordinator, will also contribute to access to other important data sources. Program FRIEND/UNESCO “Flow Regimes from International Experimental and Network Data” will provide a very important network of contacts (the Western and Central Africa database is hosted by the University Cheikh Anta Diop of Dakar, correspondent: Raymond Malou and Soussou Sambou). CRH (Yaoundé) and University of Lagos will be an important source of information concerning the Benue River Basin and Nigeria. Water assessment and accounting at basin level A hydrologic model is used in order to simulate and understand the impacts of some scenarii on the basin hydrology, interannual runoff variability, monthly river regime variability, for a number of basins. Scenarii The last years have seen a growing interest for the studies on the impacts of climate change on water resources (Ardoin-Bardin et al., 2005). According to IPCC (http://www.ipcc.ch/), long term climatic forecasts of different general circulation models show a global planet warming. However the results of models differ when focussing on a given region. Climatic forecast scenarios will be built by IPCC climatic models (including HadCM3, and the regional MM5). Simulations will be carried on at 2 time scales (2025 and 2050).

Chapter one General facts about the Basin

The River Niger is the 3rd longest river in Africa, the 4th in the world, covering a distance of 4200 km and the 9th in terms of its drainage basin covering a surface area of 2 170 500 km2 of which 1 500 000 km2 is an active basin. It takes its rise from the Futa Jallon Highlands in Guinea with an average altitude of 1 100 meters. It flows north east and during the rainy season it forms a vast flood plain in Mali known as the inland Delta. Away from the inland Delta it meanders in Mali then flows majestically south east right to Nigeria where it is joined by the Benoue and empties itself into the Atlantic Ocean. Its geographical basin made up of vast desert areas, flood plains and marshy zones, is characterized by large valleys which are gradually drying up. With Algeria, leaving out the member countries of the Niger Basin Authority (NBA), ten countries make use of it, nine of whom are members of the NBA: Benin, Burkina Faso, Cameroon, Guinea, Ivory Coast, Mali, Nigeria and Niger.

From the stand point of water resources, the Niger Basin can diagrammatically be divided into four (4) zones with more or less homogenous physical and geographical characteristics (map 1.1):

The Upper Niger Basin ; it is found in Mali, Guinea, and Ivory Coast. It covers a surface area of 257 000 km2 out of which 140 000 km2 are situated in Guinea, serving as the watershed and is seen as the portion which can be used to partially regulate water flow through out the length of the river.

The Inland Delta ; Entirely situated in Mali, it covers a rectangular area facing south west and north east with a length of 420 km and a width of 125 km between Ke-Macina and San in the south and Timbuktu in the north. It has a surface area of 84 000 km2 and comprises four agro- ecological zones: the living delta, the middle Bani-Niger, the dead delta and the lacustrine zone between Gao and Timbuktu. It accounts for almost all of the rice cultivation which is the staple food in Mali. This is done thanks to the Markala Dam.

The Middle Niger Basin. It lies within Mali, Niger, Benin. It stretches from Timbuktu to Benin, covering an area of 900 000 km2, 230 000 km2 of which are inactive. It is made up of a series of

7 irrigated terraces. Water flow in this basin largely depends on additional influx from the Inland Delta and navigation is hampered by waterfalls.

The Lower Niger Basin: It lies between Cameroon, Nigeria and Chad. It is characterized by big dams for hydro-electric power production, irrigation and by industrial activities on the rest of the basin. Energy production is mainly derived from the Kainji, Lagdo and Jebba dams which supply 68% of Nigeria’s electricity needs and 22% of her total energy needs.

Inland delta Middle Niger basin

Upper Niger basin

Lower Niger basin

Map1.1: Niger River Basin: the Different countries Involved (ABN, 2007 a)

The relief of the Niger Basin, though small, can play a role in influencing the local climate. The altitude increases in a significant way the local rainfall whereas the slopes have an impact through the underground water production (map 1.2).

Map 1.2: Relief of the Niger Basin (ABN, 2007 a)

From a geological stand point, the Niger Basin is made up of the following elements (map 1.3):

- a granitoid Precambrian layer whose crystalline rocks can undergo an alteration leading to the formation of quartz sand and capable of containing water bearing beds in some areas.

- old sandy sedimentary rocks more or less metamorphosed and hardened laying on the substratum and favourable for the formation of arenas.

- more recent sedimentary rocks formed as a result of marine invasion or due to lacustrine sedimentation leaving behind varying deposits which are often sandy. It is the presence of geological forms that account for the great underground water resources of the Niger Basin.

- basic volcanic intrusions whose bed-vein can contain sheets of fissures. The physical and chemical composition of the geological layer of the Niger Basin appears favourable for the formation of quartz sand and this at a continental scale also propitious for the formation of water-

9 bearing beds. It also favours the production of detritic elements which when transported by water or air and then deposited can cause silting.

Map 1.3: Niger Basin and Geology (ABN, 2007 a)

Soil cover: Vegetal formations on the north of the basin follow a stretch of layout in a latitude manner, showing a degradation of their cover towards the northern Sahelian regions (map 1.4). The open forest in the southern part is gradually being replaced by anthropic formations interspersed by marginal soils occupying the better part of the area. The Sahelian region is dominated by sand and no vegetation.

Generally speaking, population density nowadays is small (about 55 inhabitants per km2 and has only a limited impact on the vegetation cover and water resources. But within the context of marked drought, population growth (3% per annum, 70 inhabitants per km2 by 2020), and the absence of forest and soil conservation techniques can lead to ecological disruptions at both local and regional levels.

Map 1.4: Niger Basin and soil occupation (ABN, 2007 b)

Chapter Two

Methodological Approach and Data Collection

1. Review of Documentation

The documentary approach was given pride of place in which priority was accorded mainly to scientific research results realized on the Niger basin on issues pertaining to water resources and its users. This data were completed with information gathered by experts sponsored by the Niger Basin Authority and carried out by national and international research and development bureau in Niamey, headquarters of the NBA and in other member countries of this association.

2. Inventory of hydrometric and pluviometric data

These inventories were realized by consulting the data base of the NBA, the SIEREM base of HydroSciences Montpellier.

Hydrometric data on the River Niger and its tributaries exist both in the data banks of the Niger Basin Authority and Hydrosciences Montpellier. However, that of Montpellier is much more important in terms of number of stations whereas that of the NBA has only a few stations with updated data (table 2.1).

The hydrometric data in Nigeria (table 2.2) exist almost exclusively on the data base of the NBA. The pluviometric data we got the inventory belong to the data base of SIEREM, Hydrosciences Montpellier. A synthesis of the various stations and their data is shown in table 2.3. There also exists an environmental data base concerning member countries of CILSS, set up in Agrhymet and which is of interest to the River Niger Basin.

Table 2.1: Stations of hydrometric data on NBA excluding Nigeria

Date the Percentage of ID_SIEREM ID_ORSTOM HN_Code Name of the station Source1 Date the end beginning gap SIEREM ABN IVORY COAST CIQ0174 1091601403 BEREDOUGOU S 01/01/1962 31/12/1977 20.6 CIQ0186 1091604803 DEBETE A-S 20/07/1975 31/12/1991 9.9 CIQ0187 1091605003 DEMBASSO A-S 01/08/1960 31/12/1978 14.4 CIQ0180 1091604003 DIOLALA S 01/05/1975 31/12/1991 16.7 CIQ0175 1091601406 DJIRILA A-S 05/09/1962 16/11/1991 12.4 CIQ0166 1091601203 GUINGUERINI A-S 15/03/1955 07/11/1991 30.1 CIQ0154 1091504003 IRADOUGOU A-S 06/07/1962 31/12/1996 4.7 CIQ0167 1091601206 1091500078 KOUTO AVAL 9512 A-S 15/06/1960 12/08/1999 2006 12.9 CIQ0181 1091604006 MANANKORO S 24/06/1975 31/12/1991 13.5 CIQ0194 1091607006 NIMBRINI S 25/01/1976 29/04/1991 26.7 CIQ0169 1091601208 PAPARA S 01/01/1976 04/05/1991 18.9 CIQ0185 1091604556 POINT 398 (LMNG) S 30/05/1975 07/11/1991 27.6 CIQ0190 1091605503 PONONDOUGOU A-S 22/03/1955 31/12/1985 26.6 CIQ0176 1091601409 1091500076 SAMATIGUILA 9513 A-S 16/01/1962 31/12/1993 2001 7.9 CIQ0155 1091504006 SIRANA D'ODIENNE A-S 01/01/1962 31/12/1993 5.4 CIQ0171 1091601210 TOMBOUGOU 2 SAMOROSSO S 01/01/1963 31/12/1977 35.7 CIQ0197 1091608006 WAHIRE 1 rivière (mahandiabani) S 01/01/1976 30/06/1991 17.8 CIQ0193 1091606206 WAHIRE 2 S 01/01/1976 29/06/1991 15.0 CIQ0179 1091603503 ZIEMOUGOULA A-S 11/07/1962 31/10/1993 3.8 CAMEROON CMQ0011 1051700121 1051500022 RIAO A-S 01/05/1950 25/08/1999 9.0 CMQ0013 1051701215 SAFAIE A-S 26/07/1954 30/06/1971 14.6 CMQ0014 1051701803 1051500021 COSSI A-S 14/07/1954 30/08/1999 2002 8.3 CMQ5006 1051700103 1051500023 BUFFLE NOIR A-S 06/10/1955 19/10/1995 14.8

CMQ5007 1051700106 1051500020 GAROUA A-S 07/08/1930 06/04/1995 2000 24.8 CMQ5009 1051701206 1051500019 DJELEPO A-S 26/07/1954 16/05/1995 2000 21.7 CMQ5012 1051704503 GOURI A-S 01/01/1964 30/12/1980 15.1 GUINEA GNQ0019 1171501510 BARANAMA S 01/12/1970 01/07/2001 20.3 GNQ0026 1171501705 1171500096 BARO A-S 01/05/1947 01/05/2001 2006 9.3 GNQ0033 1171501808 DABOLA A-S 01/02/1964 01/12/1999 2005 8.5 GNQ0034 1171501810 DIALAKORO S 14/05/1954 31/12/1980 25.3 GNQ0036 1171502005 DIALAWA S 01/06/1994 26/02/2000 22.6 GNQ0038 1171502007 DIAMARADOU S 24/11/1986 01/09/2000 18.3 GNQ0045 1171502405 1171500093 DINGUIRAYE S 01/01/1979 31/12/1995 30.7 GNQ0051 1171502508 1171500098 FARANAH A-S 01/06/1955 01/12/2001 2006 15.7 GNQ2000 1171500112 1171500094 KANKAN A-S 01/05/1938 01/12/2001 2006 6.4 GNQ2004 1171501512 1171500095 KEROUANE A-S 01/08/1970 01/08/2001 13.4 GNQ2008 1171501808 KISSIDOUGOU (NIANDAN SCIERIE) A-S 01/07/1957 01/04/2001 13.2 GNQ2011 1171502007 KONSANKORO S 01/03/1955 30/08/1987 28.9 GNQ2015 1171502510 1171500097 KOUROUSSA A-S 13/07/1947 26/02/2000 2006 25.1 GNQ4002 1171501705 11715000102 MANDIANA A-S 01/06/1954 01/08/2001 2006 10.9 GNQ4010 1171500115 OUARAN S 20/05/1954 30/05/1986 16.1 GNQ4100 1171501705 1171500092 TIGUIBERY (Siguiri) A-S 01/05/1952 01/12/2001 11.7 GNQ4101 1171501707 TINKISSO A-S 01/06/1955 30/08/1999 10.8 MALI MLQ0001 1271500103 1271500067 AKA A-S 01/01/1975 26/01/1998 2005 20.8 MLQ0002 1271500106 1271500058 ANSONGO A-S 19/10/1950 31/10/1983 2006 19.0 MLQ0006 1271500110 AWOYE S 27/06/1975 22/01/1994 38.9 MLQ0009 1271500118 1271500091 BANANKORO A-S 01/09/1967 28/07/1999 2006 23.9 MLQ0015 1271500136 1271500070 BENENY KEGNY A-S 26/07/1951 15/12/1982 2005 19.8 MLQ0017 1271500138 1271500074 BOUGOUNI 9528 A-S 09/03/1956 31/12/1979 2006 7.6 MLQ0019 1271500142 1271500073 DIOILA 9542 A-S 10/05/1953 31/12/1979 2006 8.8 MLQ0022 1271500145 1271500064 DIRE A-S 01/01/1924 30/11/2003 2006 7.5

MLQ0033 1271500176 1271500071 DOUNA A-S 01/05/1922 30/08/1999 2006 14.2 MLQ0037 1271502005 GOUALA S 01/01/1955 30/04/1979 62.5 MLQ0038 1271502007 1271500063 GOUNDAM A-S 01/07/1931 31/12/1983 2003 26.3 MLQ0039 1271502010 1271500090 GUELELINKORO S 01/06/1971 31/12/1979 8.3 MLQ0042 1271503002 KARA S 19/05/1952 28/12/1993 28.9 MLQ0044 1271509105 1271500080 KE MACINA A-S 01/01/1953 31/12/1997 2006 14.8 MLQ0047 1271509203 KENIEROBA S 08/05/1952 29/06/1994 16.9 MLQ0052 1271509406 1271500081 KIRANGO AVAL (DIAMARABOUGOU) A-S 01/01/1925 31/12/1983 2003 14.1 MLQ0086 1271600105 KOLONDIEBA- Tiénaga S 01/01/1972 23/12/1979 48.8 MLQ0088 1271600108 KORIENTZE S 04/01/1975 27/12/1993 45.4 MLQ0091 1271600111 1271500081 KORIOUME A-S 17/08/1963 30/08/1999 2003 38.5 MLQ0097 1271601506 1271500084 KOULIKORO A-S 01/01/1907 30/11/2003 2006 2.7 MLQ0103 1271602005 1271500072 KOUORO 2 A-S 19/06/1975 30/09/1979 2005 3.9 MLQ0104 1271602010 MADINA DIASSA S 01/11/1971 31/12/1979 36.5 MLQ0106 1271602020 MOPTI A-S 21/05/1922 30/09/1998 2006 18.5 MLQ2000 1271500110 1271500077 PANKOUROU A-S 08/03/1956 31/12/1979 2002 6.3 MLQ2001 1271500118 SARAFERE S 03/07/1954 28/12/1992 27.0 MLQ2004 1271500138 1271500087 SELINGUE BARRAGE AVAL A-S 01/01/1979 31/12/1995 21.9 MLQ2005 1271500142 SOFARA S 03/01/1952 28/12/1993 9.3 MLQ2006 1271500145 TILEMBEYA S 21/06/1922 30/07/1994 12.5 MLQ2007 1271502010 TONKA S 12/01/1974 19/12/1992 39.8 MLQ2008 1271600108 1271500060 TOSSAYE A-S 01/06/1954 29/10/1996 17.9 MLQ4100 1271502011 YANFOLILA S 01/01/1972 31/12/1979 75.0 NIGER NEQ0007 1321501803 1321500054 ALCONGUI A-S 01/01/1961 01/11/1982 2003 9.7 NEQ0016 1321502103 1321500041 BAROU IDENTIFIEE AU BENIN A-S 01/03/1961 12/01/1979 2001 17.1 NEQ0010 1321502703 1321500044 CAMPEMENT DU DOUBLE VE A-S 20/05/1963 10/11/1980 2003 7.9 NEQ0006 1321501603 DIONGORE A-S 09/08/1962 04/11/1981 22.8 NEQ0008 1321501806 DOLBEL A-S 01/01/1961 16/09/1980 4.4 NEQ0009 1321502403 1321500050 GARBE KOUROU A-S 01/01/1956 10/07/1998 13.3 16

NEQ0003 1321501203 1321500051 KAKASSI A-S 01/01/1957 31/10/1982 2003 9.2 NEQ0001 1321500117 1321500053 KANDADJI A-S 01/01/1975 31/12/1982 2004 0.9 NEQ2000 1321500127 1321500001 NIAMEY A-S 01/01/1929 30/11/2003 9.8 NEQ0015 1321506710 NIELLOUA S 01/01/1957 31/12/1977 9.6 NEQ0005 1321501403 1321500045 TAMOU A-S 07/08/1962 09/11/1981 14.5 NEQ0004 1321501206 TERA A-S 01/01/1961 31/12/1979 0.5 BENIN BJQ0009 1111501503 COUBERI A-S 20/05/1953 27/02/1997 16.9 BJQ0007 1111501306 KOMPONGOU ANCIENNE STATION A-S 01/01/1960 19/11/1986 20.5 BJQ0054 1111504003 KOUTAKROUKROU RTE KANDI-SEGBANA S 15/05/1953 29/01/1997 32.6 BJQ2000 1111500104 11111500038 MALANVILLE A-S 25/06/1952 08/01/2000 17.0 BJQ0003 1111501104 11111500100 ROUTE KANDI-BANIKOARA (AVAL) A-S 01/01/1962 31/03/1992 23.1 BJQ0002 1111501103 11111500039 ROUTE KANDI-BANIKOARA AMONT S 01/07/1952 12/10/1965 10.3 BJQ0050 1111501506 RTE KANDI-SEGBANA AMONT S 25/06/1952 30/12/1992 19.0 BURKINA FASO BFQ0016 1201501803 KORIZIENA A-S 01/01/1970 31/08/1999 2005 22.6 BFQ0015 1201501710 LIPTOUGOU A-S 01/01/1990 02/07/1998 2004 7.0 1201509003 TIN AKOF A 1968 2006 0.0 1201508030 MANNI A 1973 2003 0.0

Table 2.2: Stations and hydrometric data on the NBA in Nigeria

Station Code_HN ID_ORSTOM Debut 1e donnée

1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 avant ONITSHA 1331500002 1331500103 1914 1955 LOKOJA 1331500004 1331500109 1914 1914 UMAISHA 1331500005 1331700101 1955 1955 MAKURDI 1331500007 1331700103 1914 1955 KATSINA-ALA 1331500008 1331700203 1955 1955 IBI 1331500009 1331700104 1915 1916 GASSOL 1331500012 1331700701 1955 1989 LAU 1331500014 1331700106 1955 1955 WURO BOKKI 1331500018 1331700110 1954 1954 BARO 1331500026 1331500111 1914 1980 JEBBA (aval) 1331500029 1331500114 1914 1914 KAINJI DAM (amont) 1331500032 1331500119 1986 1990 JIDERE BODE 1331500034 1331500123 1967 1989 KENDE 1331500104 1331501701 1959 1989 AGWAN TARU 1331500013 1331700105 1955 BARE 1955 DADIN-KOWA (aval) 1942 DONG 1959 DONGA 1955 IDAH 1331500003 1331500105 1914 KADUNA SOUTH 1960 KAINJI AVAL 1331500031 1331500118 1966 KIRI * (=KIRI DAM ?) 1331500015 1331700108 1970 X X X KONTAGORA (ou KOMI) 1959 NIGERIA SEVAV 1955 SHINTAKU 1957 WUYA * 1331500028 1331501001 1948 YOLA 1331500017 1331700109 1914 1960 BAKALORI 1331500136 1972 M M M M M M M M M M M M M M GORONYO 1331500842 1960 M M M M M M M M M M M M M M M M M M M M M M M M M M JIBIYA 1331500842 1960 M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M KUBLI 1954 M M M M M M M M M M M M M M M M M M M M M M M M MALENDO BRIDGE 1331501044 1982 M M M M M M M M SHIRORO DAM 1984 M M M M M M SHIRORO HP 1331500037 1990 MRMRMRMRMRMRMRMRMRMRMRMRMRMRMRMRMR ZOBE 1970 M M M M M M M M BELI 1955 GARKIDA 1955 ISSARA/ABOH 1331500001 1954 KOJI 1963 MALABU 1914 NAFADA 1959 NGURORE EAST 1959 NGURORE WEST 1973 NUMAN 1955 Légende : Legend : données exploitables usable data données inexploitables unusable data données non numérisées non digitalised data M données mensuelles M Monthly values * : H seulement (pas de courbes de tarage) * : Only water levels (no rating curve)

Station Code_HN ID_ORSTOM Debut 1e donnée

1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 avant ADANI BRIDGE * 1962 ADANI DIVERSION * 1963 AGENEBODE * 1973 AJAOKUTA * 1975 AJERE * 1973 ALLOMA * 1963 AMANSEE * 1963 ANAKU * 1963 ASHAKA * 1960 AWUN * 1966 AZARA * 1960 BAJIBO * 1331500030 1960 BUNSA 1331500035 DINDIMA * 1959 EDIBA * 1973 EGABADA * 1963 EGBOM * 1331500027 1331500112 1963 EPENTI * 1973 FOKKU * 1962 GBAJA * 1962 GERINYA * 1960 GOMBE ABBA * 1959 IFITE * 1964 IKUN BEACH * 1973 ITU * 1935 IZON 1331500025 JAMATA * 1955

NIGERIA JATO AKA * 1960 KONI * 1331600120 1331500120 1961 KOWARA * 1967 KPADA * 1957 LAFIA OKURA * 1963 LESU * 1331600401 1331501401 1959 LOKO * 1331500006 1331700102 1955 LUKUSHI 1331500010 MALENDO * 1959 MOSHI * 1959 NYANKWOLA * 1331500011 1331700501 1956 NYIVU * 1959 OBIGBO * 1959 OFOFADIM * 1973 OGUTA I (UMUAMAM) * 1960 OGUTA II * 1960 OGUTA III * 1960 OKOROBA * 1961 RABBA * 1964 SABONGARI * 1331500036 1331500124 1963 SHELLEM * 1331500016 1331700903 1965 SUNTAI * 1959 TAPORE * 1331500103 1331700502 1975 TYULEN * 1974 VELWA * 1331500033 1331500121 1949 Légende : Legend : données exploitables usable data données inexploitables unusable data données non numérisées non digitalised data M données mensuelles M Monthly values * : H seulement (pas de courbes de tarage) * : Only water levels (no rating curve)

Table 2.3: Synthesis of stations and pluviometric data in the NBA

Contry Type of station Number of stations Total by country by type Agro-bio-climatologic 2 Climatological 3 Cameroon 39 Pluviometric 32 Synoptic 2 Agro-bio-climatologic 0 Climatological 1 Ivory Coast 15 Pluviometric 14 Synoptic 0 Agro-bio-climatologic 1 Climatological 2 Benin 13 Pluviometric 9 Synoptic 1 Agro-bio-climatologic 1 Climatological 2 Guinea 9 Pluviometric 2 Synoptic 4 Agro-bio-climatologic 0 Climatological 4 Burkina Faso 28 Pluviometric 22 Synoptic 2 Agro-bio-climatologic 5 Climatological 22 Mali 213 Pluviometric 173 Synoptic 13 Agro-bio-climatologic 3 Niger Climatological 19 141 Pluviometric 112

Synoptic 7 Agro-bio-climatologic 0 Climatological 0 Nigeria 51 Pluviometric 36 Synoptic 15 Agro-bio-climatologic 0 Climatological 2 Tchad 18 Pluviometric 15 Synoptic 1

Chapter Three

Water resources in the basin and their variability

Direct observation of surface water flow on the topographic slope of the Niger enables us to realize that some parts are not hydraulically linked to the river. These include the Algerian section of the basin (the Tassir Oua Ahaggar region) and those of Tamesna and Tahoua found in Mali and Niger. Great tributaries of the Niger which used to drain these regions at humid times, at moment can only subsist in dry valleys covered by great thickness of sand. Even the Continental Terminal aquifer found in the Iullemeden Sedimentary Basin is cut off from the hydrological system of the River Niger. It is the same situation with the Gando and the Liptako regions at the boundary between Mali and Burkina Faso.

The active hydrological section of the basin ( the contributory basin) is presented in the form of a clock with two parts linked between Dire and Tossaye by a bay in which the basin only limited to the canal formed by the river bed (map 3.1).

Zone where the flows do not reach any more the course of the river Niger Contributory basin

Map 3.1: Contours of the Niger Basin . In dark grey, the inactive basin.

1. Rainfall and climatology

The rainfall regime of the Niger River depends on the fluctuations of the Atlantic Monsoon which generally occurs between May and November. The intensity of the phenomenon is relatively homogenous on the east-west axis but experiences a serious gradient on the north- south axis following the scale of the basin.

An observation network of climatic parameters has gradually been put into place in the member countries of the Niger Basin since the beginning of the 20th century first by national meteorological services and secondly during research and development programmes. The length of observation is very inconstant, ranging from a few years to hundreds of years. Map 3.2 illustrates the situation of 530 rainfall stations and 105 climatic stations with at least 20 years of observations. Worthy of note is the unequal density of stations on the basin, with a great concentration in Mali and Niger which can be justified by greater interest vested in the acquisition of knowledge in water resources due to its vulnerability and also as result of difficulty of accessibility data (the case of Nigeria).

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                                                                                                                                                                                                                                                                                                                                                                                                                                                             Synoptic station               Climatological station         Rainfal station                      

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Map 3.2: The situation of rainfall observation stations (Source: SIEREM/ HSM)

The tracing of isohyets shows that the Niger traverses several agro-climatic zones, giving it a peculiar and complex character. The whole basin is characterized by pluviometric degradation of a generalized manner from north to south and which natural resources depend.

The average annual rainfall rises to 2000 mm in portions further south; in Guinea along the mouth of the river in Nigeria and in the south-west of Cameroon and eight out of eight months of rainfall between March, April, and October (map 3.3). Annual rainfall varies between 700 to 1000 mm spread 3 to 4 months only at latitudes closer to Bamako and Niamey. The Sahelian zones of the basin experience low rainfall lower than 400 mm between July and September.

300 730 520 200 300 700 100 200 450

0 100 J M M J S N 0 J M M J S N 300 400 1050 1700 900 300 1350 200 300 200 1200 100 200 1100 100 0 100 J M M J S N 0 J M M J S N 0 J M M J S N

Map 3.3: Niger River Basin: climatic zones and monthly rainfall illustrations

The nearness of the Niger River Basin (NRB) to the Sahel exposes the area to high evaporation rates. This constitutes a non negligible parameter in hydrological inventories. In this light the potential evapotranspiration (PE) exerts a great influence on the availability of water notably on free water plains (inland drainage and large water reservoirs) the calculated values of the slopes of the Niger River Basin according to the wet and dry seasons helped in the drawing up of map 3.4. PE data is derived from CRU data (University of East Anglia, UK). The spatial PE division shows latitude strips varying in the opposite direction of the rainfall. The lowest values are found in the southern part of the basin while the highest are in the North.

Map 3.4: Basin Slope of the Niger: Annual ETP: Humid year 1955 and Dry year 1984.

The inventories done on rainfall and compared with the potential evapotranspiration will determine the availability of water to infiltrate the soils towards the underground sheets .This monthly inventory evaluation defines the agricultural calendar.

When rainfall is lower than ETP, (P - ETP < 0), the water reserves in the soil are very low or even absent. In this case there is neither streaming nor infiltration .This is the state of affairs experienced in the basin between November and April. (Map 3.5)

On the contrary when rainfall is above the ETP (P - ETP > 0) water reserves in the soil are much more important therefore favouring agriculture. The monthly variations in the differences between rainfall and ETP will define the agricultural calendar as well as the start of streaming which start in the humid parts of the Basin (Guinea, Cameroon and Nigeria) between May and June .The Sahel regions of the basin are only involved between July and September.

Map 3.5a: Month by month comparison between rainfall and potential evapotranspiration (P - ETP) 1994.

Map 3.5b: Month by month comparison between potential evapotranspiration (P - ETP) 1984. 30

II. FLOWS

2.1. Data and Observations Network.

The hydrologic follow up of the Niger began in 1907 with the installations of stations in Koulikoro (Mali) and Jebba (Nigeria). The present hydrologic observation is estimated at 250 stations including the specific network meant to check the river flow within the framework of the Hydroniger Programme.

Information on stations and flows were obtained mainly from the data base of SIEREM, Hydrosciences Montpellier. The duration of observations varies at least from one year to 100 years. But about 43% of the stations were observed at least during ten years. (Fig. 3.1)

30 % 20

0 0-9 10- 20- 30- 40- 50- 60- 70- 80 et 19 29 39 49 59 69 79 plus Year of observation

Figure 3.1: Duration of observation in Hydrometric stations in the Niger Basin

Added to this diversity in the duration of observation are gaps which vary in the different data collected. In this regard, less than 5% of stations show gaps in the data series which goes beyond 40% and about 87% of flow series have gaps whose percentages vary between 0 and 30% (Fig. 3.2).

40 35 30 25 % 20 15 10 5 0 0-9 10-19 20-29 30-39 40-49 50 et plus year of deficiency

Figure 3.2: Percentages of gaps in the data series

# # # # # # # # # #

# # # # # ## # # # # # # # # # # # # # # # # # ## # ## # # ### # # # # # # # ## # # ## # # ## # # # # # # # # # # ## ## # # ## # # ## # # # # # # # # ##

# # # #

# #

Map 3.6: Hydrometric stations with at least 10 years flow data

Considering the duration of observation and the rate of flow chronicles, only stations with at least ten years of chronicle observations were retained. They contained less than 40% of gaps, (map 3.6). As shown on this map, only little information was obtained in the Nigerian territory.

However, some reports from the Niger Basin Authority sharing data inventories on the slope of the NBA indicate several stations in the Nigerian territory.

II.2 - Flow regimes, past volumes and variability

Thanks to data gathered across the network, we are more and more aware of the regime and the hydrologic characteristics of the river and its main tributaries. To go by Rodier’s classification (1964) quoted in the ICCARE Programme, the regime of the Niger and its tributaries is of the tropical type with only one season of high waters and one of low waters, each very distinct from the other, except for the lower part of the Benue River and for the tributaries to the River Niger in Nigeria. But the general layout showing the seasons corresponding to high water and low water is gradually being deformed from one climatic zone to the other and also with the morphology of the basin. In this connection, flow in the different parts of the river during a hydrologic year spanning from May to June in the following year (map 3.7).

- marked water mass at Tiguibery but especially in Koulikoro (reference station of upper Niger) from September to October.

- runoff cushioned and spread out in the inland delta (October-February) with significant water losses through evaporation and infiltration in the delta (the Dire station).

- two run-offs seen in the middle Niger:

o the first said to be local occurs in September or October mainly provoked by influx from the right bank which include Gorouol, Dargol, Sirba, Diamangou, Tapoa which upper basins are in Burkina Faso and Mali, and others like Mekrou, Alibori and Sota which drain northern Benin, o the second known as the Sudanian, which appears in February or March whose maximum is above the local water mass following the years.

- maximum runoff are observed in the lower Niger in September thanks to influx from the Benoue and other tributaries on the left bank. 33

Map 3.7: Hydrologic regimes of the Niger and its tributaries (humid year 1962/63 in blue and dry year 1993/1994 in red)

One of the major characteristics of the Niger and its tributaries during the last three decades has been its variability due to drought. Most of the surface water is presented in the form of a flow (Niger itself) and therefore is found to be directly dependent on climate and more specifically on the pluviometry. It is for this reason that on the one hand it presents high seasonal variations and on the other hand fairly high interannual variations. The interannual variability of flows decreases from the upper basin in Mali to Onitsha in Nigeria near the mouth of the basin: the ratio between wet and dry years average discharges is of 2.7 for Ke Macina, and of 1.4 for Onitsha (table 3.1).

Nevertheless, some surface waters (notably in the north and in the north-east of the inland delta of Niger) are lakes which are filled up during floods. In these cases, the relation between rainfall and surface water resources is less immediate. In effect, situated below and a good distance from the river, these inland lakes are fed by flood water and other canals. When the water levels decrease, these lakes do not empty themselves into the river thereby maintaining their water levels. In addition they have a bowl-like form. This explains why such lakes stay for 2 or 3 years though losing most of its water contents through evaporation.

Map 3.8: Monthly average volumes (in billion of m3) (1960-1990). 36

Table 3.1: Monthly volumes and annual flows (in billion m3)

Janu Febr Marc Apri May Jun July Augu Sept Octo Nove Dece Year Bani at Douna 0,8 0,4 0,3 0,2 0,1 0,2 0,8 5,6 7,1 6,8 3,5 1,4 27,2 Niger at Ke Macina 1,7 0,7 0,5 0,3 0,3 1,1 5,4 10,2 14,4 14,6 6,7 3,6 59,6 Niger at Diré 6,8 5,2 4,4 2,4 1,0 0,5 1,6 3,5 4,6 5,7 6,2 7,0 48,9 Niger at Ansongo 5,9 5,5 5,7 4,4 2,4 0,9 0,9 2,4 3,3 4,2 4,7 5,3 45,5 Wet year Niger at Malanville 5,0 5,0 5,6 4,7 3,1 1,3 1,2 4,0 5,6 6,6 4,5 4,7 51,3 Bénoué at Garoua 0,1 0,1 0,0 0,0 0,0 0,3 1,0 3,7 6,1 4,2 0,9 0,4 16,8 Bénoué at Makurdi 1,5 0,8 0,8 1,2 2,5 5,6 12,8 22,3 26,8 40,1 16,5 4,1 134,9 Niger at Onistha 8,3 6,6 6,8 6,4 6,9 8,6 20,2 38,8 50,8 69,1 38,1 12,1 272,7 Bani at Douna 0,2 0,1 0,1 0,0 0,0 0,1 0,3 1,6 3,6 3,2 1,2 0,4 10,8 Niger at Ke Macina 0,8 0,3 0,2 0,1 0,1 0,4 2,2 6,3 9,9 8,8 4,1 1,7 35,0 Niger at Diré 3,5 1,9 1,0 0,3 0,1 0,1 0,6 2,2 3,8 4,8 4,8 4,5 27,7 Niger at Ansongo 4,1 2,7 2,0 1,0 0,3 0,2 0,4 1,4 2,7 3,8 4,1 4,3 27,0 Average year Niger at Malanville 3,9 3,1 2,5 1,1 0,3 0,2 0,4 1,8 3,8 3,8 3,5 3,9 28,4 Bénoué at Garoua 0,1 0,1 0,1 0,1 0,1 0,2 0,8 2,6 3,5 1,4 0,3 0,1 9,3 Bénoué at Makurdi 1,4 0,8 0,8 0,9 1,5 3,6 8,7 16,8 26,1 24,9 7,9 2,5 95,9 Niger at Onistha 5,5 4,4 4,2 3,7 4,0 6,6 14,2 25,9 39,9 44,2 18,2 7,4 178,2 Bani at Douna 0,0 0,0 0,0 0,0 0,0 0,2 0,1 0,3 0,6 0,7 0,2 0,1 2,2 Niger at Ke Macina 0,3 0,2 0,2 0,1 0,2 0,4 1,0 3,9 3,7 4,4 1,2 0,7 16,3 Niger at Diré 1,0 0,4 0,2 0,1 0,1 0,1 0,5 1,6 2,7 3,2 2,9 1,7 14,4 Niger at Ansongo 1,4 0,5 0,3 0,2 0,2 0,2 0,4 1,0 2,1 2,7 3,1 2,6 14,9 Dry year Niger at Malanville 1,3 0,4 0,1 0,0 0,0 0,0 0,4 2,0 3,5 3,2 3,2 3,7 18,0 Bénoué at Garoua 0,2 0,2 0,2 0,2 0,2 0,2 0,9 1,2 0,9 0,5 0,3 0,2 5,3 Bénoué at Makurdi 0,6 0,5 0,5 0,5 0,9 2,0 7,2 12,9 16,7 12,9 3,9 1,0 59,6 Niger at Onistha 2,0 1,6 1,3 1,8 2,6 6,0 12,9 19,3 27,5 23,4 8,3 3,9 110,6

II.2.1 Rainfall-runoff variability

For selected parts of the basin, rainfall-runoff relationships studies have already been carried out, leading to preliminary results showing the spatio-temporal variability of rainfall and runoff. The 80s is the driest decade since the beginning of the 1900’s century.

20.00 1950 20.00 1960

15.00 15.00

10.00 10.00

ORSTOM - programme FRIEND AOC ORSTOM - programme FRIEND AOC 5.00 5.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00

20.00 1970 20.00 1980

15.00 15.00

10.00 10.00

ORSTOM - programme FRIEND AOC ORSTOM - programme FRIEND AOC 5.00 5.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00

------0 0 0 0 0 1 1 1

1 1 0 0 0 0 0

......

1 3 5 7 9 1 3 5

......

3 1 9 7 5 3 1

déficit excédent Figure 3.3: Rainfall index over the River Niger basin (Paturel et al., 1997).

The figure 3.3 shows how rainfall has decreased over the Niger basin since the 50s. The index represented is calculated according to the following formula:

[Xi - Average(Xi)] / Standard deviation(Xi) where Xi is the annual rainfall amount for the year i.

The rainfall deficit is less strong in the southern part of the basin, mainly over the Benue river basin.

Déficit sur les modules annuels bassin du NIGER 60 à 70% (2) Mali 50 à 60% (1) 40 à 50% (3) Niger30 à 40% (6) Mauritanie 20 à 30% (3) 10 à 20% (0) Tossaye bassin pas de rupture (2) Diré fossile Bassin actif

zones dépressionnaires Koulikoro Niamey Douna Couberi Malanville Baro Siguiri Rte Kandi-Banikoara Yola Garoua Kankan Niger Iradougou Bénoué Makurdi Riao

Onitsha Golfe de Guinée

Figure 3.4: Runoff index over the River Niger basin (Paturel et al., 1997).

The change in rainfall regime around 1970 led to a rapid change in runoff regime around the same year, as shown in figure 3.4. The upper Niger river basin in Guinea shows only a limited runoff reduction, while the Bani river basin experiences a very deep 70% runoff reduction (Figure 3.6), mainly due to a deep fall of the aquifer (figures 3.8, 3.9). The lowest runoff reduction is observed on the southern part of the bassin and over the Benue basin (figure 3.7). In Sahelian parts of the basin runoff coefficients have seriously increased, which lead to higher flood peaks, erosion, sediment transport and dam silting (fig 3.5). This is linked partly to the climate change-related rainfall reduction, but mainly to the increase of the cultivated surfaces, and the related disappearance of the natural vegetation (Mahe et al., 2005). In Soudano-guinean parts of the Niger River basin, the runoff decrease has been much deeper than that of the rainfall, due to the cumulative (memory) effect of the rainfall lasting shortage on the groundwater levels (Mahe, 2009).

Débit 30 dev st and runoff Rainfall Pluie 2 iation 25

20 1

15 0

b ofstations b 10 N - d 5 1 0 - 1958 1963 1968 1973 1978 1983 1988 1993 2

Year Rainfall Runoff

Figure 3.5: Rainfall-runoff relationships in Sahelian tributaries of the River Niger.

Niger à Koulikoro

1.00

0.50

0.00 Ecarts

-0.50

-1.00

1905 1914 1923 1932 1941 1950 1959 1968 1977 1986 1995 Années

Figure 3.6: Rainfall-runoff in the Soudano Guinean part of the River Niger in Mali

Figure 3.7: Rainfall-discharge modeling for Niger River at Onitsha, Nigeria (Olusegun et al., 2009 preliminary report)

The River Niger basin has been submitted to a strong rainfall deficit since 1970, which occurred over the whole basin. All the sub-basins experienced a reduction of runoff. But the Niger basin can be divided into three main areas: the upper basin of the River Niger in Guinea, Mali and Ivory Coast, where the runoff deficit is very strong; the lower River Niger basin, including the Benue river, where the runoff deficit is limited; and the Sahelian tributaries, mainly in Mali, Burkina-Faso and Niger, where the runoff has increased, due to changes in land- use (Mahe et al., 2003).

III - Groundwater resources a) Discontinuous water-bearing aquifers are of two types: they may be semi- continuous or entirely discontinuous, depending on the density, on the extension and the degree of intercalation of fissure network affecting the mother rock on the hydraulic relations with the sheets situated in their. This category of aquifer is common compact geologic formations poorly or non permeable but locally having secondary permeability. This could be either as a result of physical and chemical alteration or as a result of cracks. These discontinuous aquifers are mainly found on the right bank in the Niger (Guinea, Mali, Ivory Coast, Burkina Faso and Niger) in the Guinea Sudanian zones and the Sudano-sahelian zone. Pipe borne water projects in these villages make use of such aquifers. Specific flows and the rates of failure in bore-hole realization are very unsteady (between 30 to 70%). b) Generalized aquifers can be found in large sedimentary forms, especially on the right bank of the Niger River (Mali, Niger, Chad, Nigeria and Cameroon). In spite of differences between various aquifers as a result of the heterogeneous composition of each layer and changes related to their thickness, there nevertheless are common characteristics that run through them, on alluvial and colluvial tracts of land and on alterites . c) On plateau surfaces, superficial aquifers are superimposed seated aquifers. The outer aquifers can be partly continuous thereby forming a hydraulic link with the deeper layer or it can be discontinuous. These will depend on their thickness and the local rainfall. Their characteristics equally vary but are distinctly favorable if compared to the discontinuous aquifers with flows which can reach over 200m3/h and the possibility of artesian wells springing out in the Niger. 41 d) The figure 3.8 shows the importance of the baseflow in the annual runoff. This is for the Bani at Douna, but this is representative of most of the River Niger tributaries, from Guinea, Mali, Ivory Coast and Cameroon, under Soudano-guinean Climate. The figure 3.9 shows how surface flow and baseflow vary each years over a twelve years period (after Mahe, 2009). This is due to the nature of the aquifers, mostly in metamorphic cracked layers, either from granitic or from sedimentary substratum.

800 Total discharge Base flow 600 Surface flow

400

200 Discharges m3.s-1 . 0 1 31 61 91 121 151 181 211 241 271 301 331 361 Days from January 1st

Figure 3.8: Annual hydrograph for the Bani River at Douna. Total Runoff (bold line) / Surface runoff (thin line) / Base flow (dashed). Average 1984-1996.

1600 Annual rainfall 160 Surface runoff Base flow 1200 Total discharge 120

800 80

400 40 Rainfall mm.a-1 .

0 0 Baseflow/runoff mm.a-1 . 1984 1986 1988 1990 1992 1994 1996

Figure 3.9: Annual surface flows, base flows and total discharge for the Bani River at Douna, compared to annual rainfall. 42

Chapter four

Accessibility to water and its uses

Inventories on the measurements of water in the Niger Basin have been carried out in many reports. This involves a synthesis reflecting the scale of the Basin and the countries benefiting from the resources. This inventory does not claim to be exhaustive in its achievement, considering other works that have also been carried out in other countries. Other identified works mainly concern dams and irrigation canals.

IV.1: Reservoirs as far as reservoirs are concerned the inventory makes mention of a number of projects which can be classified following several criteria; existing projects or those under construction, their goals, year of realization and the country to which they belong. Giant dams have as main goal the generation of hydro electricity power and food production. Smaller ones are meant for small scale agriculture. Some works are under the project phase with feasibility studies already carried out or nearing completion. Others have been envisaged though no studies have been carried out on them. In the subsequent analysis, dams will be classified in two main groups: the existing ones and those still in project form.

IV.1.1: The existing dams

260 dams have been identified in the Niger basin (map 4.1). Their distribution is not regular and there are concentrations of installations on some sections of the basin.

The upper Niger basin : In its Guinea section, the upper Niger has a hydroelectric dam in Dabola on the river Tinkisso and on its Malian section three large scale hydraulic projects: the dam of Sotuba on Niger, which was adapted for the hydro power, the dam of diversion of Markala on Niger and the dam of Sélingué on Sankarani. Still on the Guinea side ; mention should be made of the Fomi Dam whose studies have been reactivated and are nearing completion.

The middle Niger basin : No major dam was built on this part, but it is necessary to mention both dams in project Taoussa in Mali and Kandadji in Niger, as well as project for the hydroelectric dam of Mékrou envisaged by Niger and Benin.

The Lawer Niger basin : 95% of the dams are on this section of the Niger. Four major projects were carried out in the Lower Niger, which three were built in Nigeria (Kainji and Jebba on the

Niger and Shiroro on the Kaduna) and one in Cameroon (Lagdo on the Benue). Many other small scale dams were built on the Niger tributaries in Nigeria.

$ Capacité non connue # V < 1 million # 1 million < V < 250 millions

# 250 millions < V < 1 milliard # # 1 milliard < V #

### ##### ## ######## ### ## ### ## # ## ### ### #### ### # ## # #$## ## $ # ### ## # # # # # # ## # # ######## # # # #### # # # # $ ###### # # ##### # # ######## # $ ## # ## # # ### ## #### # # ####### ### # # # # # # $# # # # ### # # # # # ## # # # # ## ## # #$ # $ # $### ## ### # ## # # # # # $# # # $ ## # # # # # # # # ## ## # $ $ # $ # # # $ $$

Map 4.1: Niger River Basin: Situation of existing dams.

Carrying capacity varies between 25.10-3 million m3 (Camp de chasse, Tapoa, Niger) to 16 billion m3 (Kainji, Nigeria). Fig. 4.1 shows the class distribution of the carrying capacity of all the identified dams. From this distribution, it is clear that 50 % of them are made up of small dams of less than 1million m3 and that among the giant dams (more than 10 million m3) those between the capacities of 20 million and 50 million are the highest in number.

Figure 4.1: Class Distribution of the Capacity of Dams (percentage)

An evaluation of the capacity of the existing dams places the global volume at 42 billion m3 which represents 27% of the water influx from the Nigerian Onitsha between the dry periods of 1971 and 2001; and 22% of the same influx in the same station during the rainy seasons between 1929 and 1970. All this reflect well enough the weak control of the water ressources of the river Niger and of its tributaries.

IV.1.2 - Projected dams

Seventy dams have been projected in the basin slope of the River Niger. On the sidelines of existing dams, two sub-basins are principally concerned with harnessing and pipe-borne water development. There include the upper and lower Niger (map 4.2). The only projected sites for construction works in the lower Niger are those of Makurdi, Lokoja and Onitsha.

$ Capacité non connue # V < 1 million # 1 million < V < 250 millions # 250 millions < V < 1 milliard # 1 milliard < V # #

# $ # # # # # # # # # # # # ## # # # # # # # # $ # # # # # #$# # # # # # # $ # # # $## # # ## # # $ # # ## #$ # ## # # # #$ # # # $ $

Map 4.2: Niger River Basin: situation of projected dams

Harnessing capacities vary from 25.10-3 million m3 (Tgueleguel on the Keita, Niger) to 6 billion m3 (Fomi site on the Niandan in Guinea). The capacity of the projected dams on the entire basin is about 48 billion m3 as against 42 billion m3 for the existing ones. More than 80% (39 billion m3) have been previewed to be stored in the Upper Niger and 20% only (9 billion m3) to be kept in the Middle Niger.

Considering the existing and projected dams in the Upper Niger, the volume of water stored will slightly could be above 41 billion m3 if all projects are realized. If this figure is compared to the discharged volume at the entry point of the Inland Delta (Ke-Macina and Douna) with respectively 75 billion m3 in a humid year and 21 billion m3 in a dry year, then it means that more than 55% of all flows could be stored in a humid year, and in a dry year flows in the upper basin would be insufficient to fill all the reservoirs. The situation which has been worsened by drought will have drastic consequences of the Lower Delta.

IV.2. Down-stream depletion

Apart from water lost to the dams, there are many down stream depletions on the Niger and its tributaries. These stoppages are destined mainly for agriculture, rearing and supply of drinking water to big towns.

IV.2.1 - Depletion for purposes of irrigation

171 retention points for irrigation purposes have been identified on map 4.3 along the Niger and its tributaries. 5412 billion m3 are deducted annually to irrigate a surface area of 264550 per inhabitant, giving an average of approximately 20 000 m3 per inhabitant. The retained volume from each country depends on the surface of the basin slope of the country concerned (table 4.1). In this connection the largest volume is kept aside in Mali, followed by Nigeria and Niger.

G G

## G ## G### ### # ## # G # ## # # # # # # G # G # G ## ### # # G# G # G # # ## # # ## # # ## # # # # # ## # # ## ## # # G# # # G# # # # # G#G G## ### G # ## # # # ## # # # # G # G# # # # # # # ### ## ## G# # # # ### # V < 1million # 1million < V < 5 millions # 5 millions < V < 20 millions G 20 millions < V < 1 milliard G 1 milliard < V Map 4.3: Niger River Basin: Retention sites for irrigation

Table 4.1: Retained volumes and irrigated surface area per country

Number of Total surface Annual total takings irrigated in volume taken in 2005 (ha) 2005 (Million of m3) Benin 2 1006 23

Burkina Faso 3 1482 9 Cameroon 3 5300 107 Ivory Coast 10 2495 46 Guinea 8 8984 104 Mali 8 117348 3825 Niger 43 43315 454 Nigeria 94 82620 847 Total 171 264550 5412

IV.2.2 - Retention for potable water supply

Various water catchments areas have been set up on the Niger and its tributaries to supply many towns with potable water. These include: - real retentions served by a network in which the volumes of water are indicated. - retentions in which volumes are estimated on the bases of hypothetical needs for water multiplied by the estimated population of people living along the river and its tributaries; the selected hypotheses were done for 2005 based on 20 litres per inhabitants per day for the rural areas and 40 for the urban agglomerations. Sites concerned by this experiment are represented on map 4.4.

 V < 1million  1 million < V < 10millions  10 millions < V < 100millions

 

                                            

Map 4.4: Niger River Basin ; retention sites for potable water supply

IV.2.3 - Water Retentions for Livestock Breeding

The estimate of reserved volumes for livestock was rendered difficult by its diffused nature. The real reserves meant to supply animals with drinking water are almost unknown. Quantities of water estimated in this case on the basis of hypothetical needs for water multiplied by the available livestock are done following the methods stated below. - Collection of data on the livestock per type of animal. - Summing up by units of tropical livestock. - Calculation of water needs associated with livestock on the basis of a need in 30 units per day. - The reserve sites for livestock shown on map 4.5 are all virtual points grouping reserve zones for each climatic area.

# V < 1 million # 1 million < V < 5 millions # 5 millions < V < 10 millions P 20 millions < V < 50 millions #

# # # # # P # # # ## # # # # # # ## # # ## P # # # # # # ## # # # # # # # # # # # # # P ## ## # # # # # # # #

Map 4.5: Niger River Basin, Retention Sites For Livestock Breeding.

Estimates show in 2005, about 223,6 million m3 of water was used in the basin slope of the Niger, for about 27 71 000 U.B.T. The distribution per every country is indicated in table 4.2. The largest 50 reserved volumes are found in those countries with the largest areas of land within the Basin (Nigeria, Niger). Mali is noted for its livestock numbering 8640000 U.B.T. However, reserved water for livestock is small (14,2 million m3)

Table 4.2: Livestock per Country and Quantities of Reserved Water in the Niger Basin.

Livestock in 2005 Total annual volume Equivalent in UBT uptaken in 2005 (Million of m3) Benin 666 000 7,3 Burkina Faso 3 115 000 34,10 Cameroon 2 665 000 29,2 Ivory Coast 535 000 6 Guinea 978 000 10,7 Mali 8 640 000 14,2 Niger 4 109 000 45 Nigeria 6 941 000 76 Tchad 102 000 1,1 Total 27 751 000 223,6

IV.2.4 - Important Remark

In all our estimations, it was accepted that all the livestock were fed with water from the Basin and its tributaries. Nevertheless, it should be noted that part of the riverine population gets its water from the water-bearing beds of the river. In this connection, the results of the many estimates, represents the maximum level of understanding without taking into account the pipe-borne water needs of the communities. The true needs of the people cannot be adequately assessed due to lack of information on certain aspects such as, infrastructural problems and the people’s reliance on wells and bore-holes.

IV.3 – Water use account

The basin water use accounting method has already been applied on the Niger River basin by Mainuddin et al. (2009). This approach enables to describe where the available water goes, its uses, analyse trade-offs, and provide a quick first order estimate of the water balance and uncommitted

51 water resources. These first results might be improved if needed, by incorporating recent available hydroclimatic data. Map 4.6 (after Mainuddin et al., 2009) shows the major water uses over the River Niger basin. This approach, combined with the Water Use Account Model, will be useful to determine areas where water can be reallocated to benefit the poors.

Map 4.6: Summary of major water uses in catchments of the Niger Basin (Mainuddin et al, 2009)

IV.4 - Water Transport

Water transport potentials exist on the Niger Basin but are under exploited. Before the construction of important road network, much of trade in the Basin region was carried out thanks to water 52

transport. But the river is not navigable through out its whole length. Two waterfalls, one in Sotuba in Southern Mali and the other in Labezanga around the border between Mali and Niger have hampered smooth water transport in the Basin. Water transport in the Basin can be broken into 3 navigable parts (Diarra, 2001): - From Kouroussa in Guinea to Mali. - From Koulikoro in Mali to Ansongo in Mali. - From Niamey (Niger) to the Gulf of Guinea in Nigeria as well as all of the Benue from down stream right up to Garoua.

Upstream from Bamako, small fishing boats can go upstream to Siguiri between August and November.

During the same period, navigation is possible on some tributaries in this area, particularly on the Milo and Tinkisso. Lots of goods are therefore transported between Mali and Guinea.

An important section of the river between Koulikoro and Koryoume covering a distance of 160 km is navigable between September and December. It is possible for small fishing boats to navigate in the inland Delta all year round. The Delta tributaries are also navigable when the water volume of the Delta is high. Mopti is the main port of the inland Delta. Large boats can sail up to Koulikoro from August to January.

Between Timbuktu and Taoussa (327 km) navigation is possible almost all year round. From Taoussa to Fafa, (270 km) boats of average sizes can sail during periods of high water volumes. From Fafa to Meana (123 km) navigation is limited except in periods of high tides. This is due to waterfalls and rocks. Between Meana and Tillabeny (170 km), navigation is possible between August and February. During this period, the river is navigable between Niamey and the Frontier with Nigeria. From the border to Lake Kainji (336 km) the river is only navigable during high water volumes. Lake Kainji is navigable on 130 km. Navigation is possible even with light boats from Jebba to the Atlantic Ocean (144 km), though some obstacles exist between Jebba and Onitsha.

The Benue is navigable from its Confluence with the Niger right up to Markurdi between June and December and up to Garoua between August and November. About 3000 km of coastal lagoon and channels linked to the Basin in Nigeria are navigable.

Map 4.7: Navigability of the River Niger (ABN, 2007 b)

As a result of the inter-annual variability of the flows and the increase in sand accumulation and not leaving out the man-made depletion of the waters for human use, the navigability of the river has significantly been affected from year to year.

IV.5 – Changes in water availability

IV.5.1 – Application of climatic scenarii

The recent years have seen a growing interest for the studies on the impacts of climate change on water resources (e.g. Ardoin-Bardin et al., 2004, 2005, 2009; Hulme et al., 2001). According to IPCC (http://www.ipcc.ch/), long term climatic forecasts of different general circulation models show a global planet warming. However the results about precipitation differ when focussing on a given region (Casenave, 2004). Climatic forecast scenarios has been built according to IPCC climatic models issues, including HadCM3 and ECHAM4, with the usual A2 greenhouse gas emission scenario (IPCC TAR, 2001 ; Nakicenovic et al., 2000). As part of the water availability and access analysis, we study the spatio-temporal variability of rainfall and discharges notably combining the influence of IPPC Global Climate Models scenarios to 2050.

Simulations have been carried out for the horizon 2050 with the HadCM3 model and A2 scenario. Figure 4.7 shows the changes in runoff in 2050 compared to the 1966-1995 average in West Africa. According to this GCM/scenario, there would be a slight increase in runoff over most of the upper Niger river basins in West Africa, but not over the upper Benue river basins. The situation would worsen in 2080 following a general rainfall reduction over West Africa. This is only one model and one scenario. After a comparison of several GCM outputs for the region, Ardoin et al. (2009) conclude that most of the recent GCM outputs for the region show lower rainfall predictions than the HadCM3 model.

Figure 4.7: Percentage of variation in runoff in West Africa between (1966-1995) and 2050, using the IPCC HadCM3 A2 scenario (Mahe et al., 2005)

IV.5.2 – The case of the Niger River inner delta in Mali

For the Niger Inner Delta (a key focus for the BFP Niger), an integrated model of the Niger inner delta called MIDIN has been developed (Kuper et al., 2002). Based on a simple scheme of the hydrosystem taken from Poncet et al. (2001 and 2002), the MIDIN model integrates several relationships between water, biology and human activities along the different hydrological entities like channels, lakes and floodplains. We must note that the central part of the delta is particular, as all the different streams diverging at the entry of the delta, converge toward an area of great natural lakes (Débo, Wallado, Korientze), which gather all the waters before the flood spreads again in the northern part of the delta, also inundating several other lakes on the right and left banks of the river. The Niger river unifies its different streams at Korioumé (Timbuktu), the very end of the inner delta. In the figure 4.8 (adapted from Mariko et al., 2003), is presented the correlation between the flooded surfaces, as depicted by NOAA images between 1990 and 2000 (Mariko et al., 2002; 55

Mariko, 2003), and the water heights at the main gauging station of Mopti in the delta. This correlations allows to determine the flooded area of the upper delta area according to the Mopti wter level. Results are also available for the main subregions of the Inner Delta (Mariko, 2002). This will result for instance in being able to predict one month in advance from the water height at Mopti the water height in the Northern part of the delta (North of the central lakes).

Delta amont (Juilet à octobre 1995) Surface 15000 inondée 2 (km ) 0,0093x 10000 y = 36,637e R2 = 0,9629

5000

0 0 200 400 600 800 Hauteur d'eau à la station de Mopti (cm)

Figure 4.8: Correlation between water height and flooded area in upstream part of the Inner Delta, Mali (after Mariko et al., 2003)

But, the flooded area is modified in area upstream of Mopti, since some years the Talo dam between San and Douna allows water to be distributed within new –or former but unused- irrigated areas. Consequences on the hydrological regime are negligible during the flood peak, and low flows are maintained at a minimum level during dry season, which is appreciated by many people. But as a negative consequence, it seems that the flood recession is quicker than before, and people are wondering whether the increasing demand of water for irrigation will not lead to a shortage of the minimum discharge allowed downstream. The MIDIN model has been used to test several scenarios of water usage and consumption (including dams and irrigation areas) in the upper basin and their impact on the river regime, the water height and the flooded surfaces (Kuper et al., 2002). The flooded surface has direct repercussions on livelihoods, as fish stocks, bourgou stocks on which livestock feeds and recession farming all depend on the height of the flood.

Chapter five

Conclusion

The River Niger basin is one the largest in Africa, spread over 9 countries. It has a very complex hydrological regime, due to very different climatic influences: dry tropical in the upper Niger and Benue basins, humid tropical up to sub-equatorial in the southern Niger and Benue streams, Sahelian in the northern area. The Niger River basin also contains an inner delta in Mali, which is a unique place in the world of about 40 000 km² of seasonally flooded area. There are only a few dams upstream of the Niger river in Mali/Guinea/Ivory Coast. Nigeria has a lot more dams, including big dams, while Burkina-Faso has a lot of small dams (map 5.1). The Niger Basin Authority (NBA) in Niamey is mandated by the 9 countries to coordinate all the development studies and realizations over the basin, to benefit all of the countries. This is a major task, very difficult due to contradictory interests of the countries according to their geographic location on the stream and to their socio-economic development needs.

Map 5.1: Dams of more than 100 millions m3 in West Africa (Barbier et al., 2009)

It is likely that several dams (big or small ones) will be built over the Niger basin in the coming years. It is very important before building them to take into account the past years variability of climate and river regime. It is particularly important to take into account the very deep runoff decrease in the tropical humid sub-basins, and the runoff increase in the Sahelian ones. It is also noticeable that most of the GCM outputs predict a rainfall reduction still to come during the next decades of the XX1st century. 58

This natural water resource variability is to be compared to the population increase, together with the increase of the water demand, either in urban or rural areas. For a great part of the population, riverine of the Niger river or of its tributaries, the water resource will be decreasing, and water access will become harder, and more expensive, either directly (setting of the new water policies and need to buy water), or indirectly (water deeper of more remote). More than ever there is a need for the 9 countries to work together to a harmonious development of the water resources use. Several tools such as WEAP, MIDIN and rainfall/runoff modelling which has been already used for the Niger basin, should be implemented at NBA, where people could use them as predicting tools.

References

General hydrological topics on West Africa

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Servat, E., Najem, W., Leduc, C., Shakeel, A. (2003) Hydrology in Mediterranean and Semiarid Regions. IAHS Publ. 278 (Sci. Eds.). Reports and others ABN (2007) a ; Etude d’élaboration du schéma directeur de lutte contre l’ensablement dans le bassin du Niger, rapport final. ABN (2007) b ; Elaboration du plan d’action de développement durable du bassin du Niger ; phase I : bilan-diagnostic, rapport définitif. Ardoin-Bardin, S. (2004) Variabilité hydroclimatique et impacts sur les ressources en eau de grands bassins hydrographiques en zone soudano-sahélienne. PhD, USTL-UM II, Montpellier, France. Casenave, L. (2004) Hydro-climatic variability: comparison of different global circulation models in western Africa. Master’s thesis. University of Chalmers, Sweden. Oyebande, L., Amani, A., Mahé, G., Niang-Diop, I. (2002) Climate Change, Water and Wetlands in West Africa: Building linkages for their Integrated Management. IUCN-BRAO Working Paper. Ouagadougou, Burkina-Faso. Rescan, M. (2005) Prévision des ressources en eau en Afrique de l’Ouest et Centrale jusqu’en 2099 par application des sorties du modèle d’évolution du climat HadCM3 à un modèle hydrologique. Master UM2 Montpellier. Servat, E. (1994) ICCARE. Identification et Conséquences d'une variabilité du Climat en AfRique de l'ouest non sahElienne. Présentation du programme". Programme ICCARE. Rapport n°1. ORSTOM, Abidjan, Côte d'Ivoire. Sighomnou, D. (2004) Variabilité du climat : implication sur les ressources en eau du Cameroun. Thèse d’Etat, Université de Yaoundé.

Sediment transport Papers Lienou, G., Mahé, G., Servat, E., Tégofack, R., Sahagu, J., Nwalal, J., Issa, Olivry, J.C., Ekodeck, G.E. (2005) Transport de matières en suspension au Cameroun dans un contexte hydroclimatique déficitaire. IAHS Publ. 291, 161-171.

Land use change Papers Mahé, G., Paturel, J.E., Servat, E., Conway, D., Dezetter, A. (2005) Impact of land use change on soil water holding capacity and river modelling of the Nakambe River in Burkina-Faso. Journal of Hydrology, 300, 1-4, 33-43. Maps and Books Reich, P. F., Numbem, S. T., Almaraz, R.A., Eswaran, H. (2001) Land resource stresses and desertification in Africa. In: Bridges, E.M., I.D. Hannam, L.R. Oldeman, F.W.T. Pening de Vries, S.J. Scherr, and S. Sompatpanit (eds.). Responses to Land Degradation. Proc. 2nd. International Conference on Land Degradation and Desertification, Khon Kaen, Thailand. Oxford Press, New Delhi, India.

River modeling Papers Lubès-Niel, H., Paturel, J.E., Servat, E. (2003) Study of parameter stability of a lumped hydrologic model in a context of climatic variability. Journal of Hydrology, 2003, 278: 213-230. Paturel, J.E., Ouedraogo, M., Mahé, G., Servat, E., Dezetter, A., Ardoin, S. (2003a) Influence of the spatialization of data on the modelling of monthly river regimes in West Africa. Hydrological Sciences Journal. 48, 6, 881-890. Paturel, J.E., Ouedraogo, M., Servat, E., Mahé, G., Dezetter, A., Boyer, J.F. (2003b) The concept of hydropluviometric normal in West and central Africa in a context of climatic variability. Hydrological Sciences Journal, 48, 1, 125-137. Conferences Dieulin, C., Boyer, J.F., Ardoin-Bardin, S., Dezetter, A. (2006) Calcul de la variable «capacité en eau du sol (WHC)» à partir d’un SIG, pour la modélisation hydrologique. GIRE3D Gestion Intégrée des Ressources en Eau Défi pour le Développement Durable. Marrakech Mai 2006. Actes sur CD. Maps and Books Gustard, A., Blazkova, S., Brilly, M., Demuth, S., Dixon, J., van Lanen, H., Llasat, C., Mkhandi, S., Servat, E. (1997) FRIEND’97—Regional Hydrology: Concepts and Models for Sustainable Water Resource Management. IAHS Publ. 246 (Sci. Eds.). Reports and others 62

Ouedraogo, M. (2001) Contribution à l’étude de l’impact de la variabilité climatique sur les ressources en eau de l’Afrique de l’Ouest – Analyse des conséquences d’une sécheresse persistante : normes hydrologiques et modélisation régionale. PhD Science de l’eau dans l’environnement continental, Université de Montpellier

Niger River

Climatic variability and climate change impact on water resources Papers Bamba, F., Diabate, M., Mahé, G., Diarra, M. (1997) Bilans hydrologiques pour des affluents majeurs du fleuve Niger : le Bani, le Sankarani, le Tinkisso et le Milo. Atelier Scientifique FRIEND-AOC UNESCO/PHI, Cotonou, 14-15 déc. 1995, Documents Techniques en Hydrologie, UNESCO PHI-V, n°16, pp. 65-82. Bricquet, J.P., Bamba, F., Mahé, G., Touré, M., Olivry, J.C. (1997) Evolution récente des ressources en eau de l’Afrique atlantique. Revue des Sciences de l’eau, 3, 321-337. Bricquet, J.P., Mahé, G., Bamba, F., Olivry, J.C. (1996) Changements climatiques récents et modification du régime hydrologique du fleuve Niger à Koulikoro (Mali). IAHS, Publ. 238, 157-166. Mahé, G. (2009). Surface/groundwater relationships in two great river basins in West Africa, Niger and Volta. Hydrological Sciences Journal, 54, 704-712. Mahé, G., Bamba, F., Orange,D., Fofana, L., Kuper, M., Marieu, B., Soumaguel, A., Cissé, N. (2002) Dynamique hydrologique du delta intérieur du Niger (au Mali). In: Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 179-195. Mahé, G., Bricquet, J.P., Soumaguel, A., Bamba, F., Diabate, M., Diarra, M., Henry Des Tureaux, T., Kondé, C., Leroux, J.F., Olivry, J.C., Mahieux, A., Orange, D., Picouet, C. (1997) Bilan hydrologique du Niger à Koulikoro depuis le début du siècle. Acta Hydrotechnica 15/18, Ljublana, Slovénie, 191- 200. Mahé, G., Leduc, C., Amani, A., Paturel, J.E., Girard, S., Servat, E., Dezetter, A. (2003) Augmentation récente du ruissellement de surface en région soudano-sahélienne et impact sur les ressources en eau. IAHS Publ. 278, 215-222. Olivry J.C., Bricquet J.P., Mahé G. (1998). Variabilité de la puissance des crues des grands cours d’eau d’Afrique intertropicale et incidence de la baisse des écoulements de base au cours des deux dernières décennies. IAHS Publ. 252, 189-197. Paturel, J.E., Servat, E., Mahé, G., Bricquet, J.P., Lubès-Niel, H., Olivry, J.C. (1997) Variations hydroclimatiques sur le bassin du Niger. Acta Hydrotechnica 15/19, Ljublana, Slovénie, 169-173. Sangaré, S., Mahé, G., Paturel, J.E., Bangoura, Y. (2002) Bilan hydrologique du fleuve Niger en Guinée de 1950 à 2000. Sud Sciences et Technologies, EIER, Ouagadougou, 9, 21-33. Conferences Bamba, F., Diabate, M., Mahé, G., Diarra, M. (1996) Rainfall and runoff decrease of five river basins of the tropical upstream part of the Niger river over the period 1951-1989. In: Roald L.A. (Ed.): Global hydrological change, EGS XXIth Gen. Ass., La Haye, Pays Bas, 6-10 mai 1996, 16 p. Conway, D., Mahé, G. (1999) Riverflow modelling in two large river basins: the Parana (subtropical) and the Niger (tropical). In: Hydrological and Geochemical Processes in large river basins, Symposium International IAHS, Manaus, Brazil, 16-19 nov. 1999, CD-Rom Manaus’99-HiBAm, 8p. Mahé, G., Bamba, F., Diabate, M., Diarra, A., Diarra, M. (1997) The reduction of the water resources on upper basins of the Niger river: hydrological balances and analysis of the depletion curves (1951- 1989). Poster proceedings, Sustainability of water resources under increasing uncertainty, 5th IAHS Assembly, Rabat, Maroc, April 23-May 3, p.9-12. Reports and others Adeaga O., Mahe G., Servat E. (2009). Analysis of Water Resources Availability and Variability in Lower Niger Basin. Interim report. HydroSciences Montpellier Laboratory. BFP Niger Project. French Embassy in Lagos. Dec. 2008. Bamba, F., Fofana, M.L., Mahé, G. (1999)I Spatialisation des données hydrologiques dans le Delta Intérieur du Niger. Rapport d’étude, projet GIHREX, IRD-ENI-Météorologie Nationale, IRD Bamako, 61 p. Mahé, G. (1996) Annuaire des précipitations mensuelles et annuelles de la Guinée Konakry de l’origine des stations à 1995. ORSTOM Bamako. Projet FRIEND-AOC, 62 p. Mahé, G., Dicko-Biga, H. (1997) Rapport de mission à Tossaye du 06 au 09 janvier 1997, ORSTOM Bamako, 14 p. Mahé, G., Henry Des Tureaux, T., Koumaré, K. (1996) Rapport de mission Delta Central 30-01/16-02 1996. Programme Equanis/PEGI-GBF, ORSTOM Bamako 49 p. 63

Mahé, G., Marieu, B., Picouet, C. (1997) Rapport de mission Delta Intérieur du fleuve Niger. 8 au 25 août. ORSTOM, LECOM, 22 p. Manga, M. (2000) Essai de détermination des influences climatiques naturelles et anthropiques dans la variabilité des régimes hydrologiques des rivières Nakambé à Wayen et Gorouol à Koriziena, Mémoire d’ingénieur, EIER, Ouagadougou Marieu, B., Bamba, F., Bricquet, J.P., Cissé, N., Gréard, M., Henry Des Tureaux, T., Mahé, G., Mahieux, A., Olivry, J.C., Orange, D., Picouet, C., Sidibé, M., Touré, M. (1998) Actualisation des donnees hydrometriques du fleuve Niger au Mali pour EQUANIS. Rapport final EQUANIS. Programme PEGI/GBF/EQUANIS, ORSTOM/LECOM-CNRST-DNHE, Bamako, Mali, 82 p. Marieu, B., Mahé, G. (1997) Rapport de mission Douna-Macina-Mopti, du 13 au 17 novembre. ORSTOM/ Lecom, Bamako, 7 p. Ould, M. (2001) Détermination de ruptures statistiques dans les séries chronologiques des paramètres météorologiques – application aux bassins des Voltas et du Niger. Mémoire d’ingénieur, EIER, Ouagadougou Soumaguel, A., Mahé, G., Diarra, M., Camara, A. (1996) Annuaire des précipitations mensuelles et annuelles de l’origine des stations à 1995 au Mali. Tome 1 (A à K) 77p., tome 2 (L à Z) 58 p., tome 3 (postes récents ou projets) 22 p. ORSTOM et Météorologie Nationale du Mali, Bamako. Soumaguel, A. (1996) Elaboration des fichiers Opérationnels pour le calcul Régionalisé des pluies par la méthode du vecteur Régional (MVR) sur le bassin versant du Niger. Rapport d’activité FRIEND- AOC, Bamako, ORSTOM, Laboratoire d’hydrologie, 35 p.

Water quality, Sediment transport Papers Bricquet, J.P., Gourcy, L., Mahé, G., Orange, D., Picouet, C., Olivry, J.C. (1998) Dissolved matter fluxes in the Niger river’s inner Delta. IAHS Publ. 253, 435-446. Bricquet, J.P., Mahé, G., Bamba, F., Diarra, M., Mahieux, A., Des Tureaux, T., Orange, D., Picouet, C., Olivry, J.C. (1997) Erosion et transport particulaire par le Niger : du bassin supérieur à l’exutoire du delta intérieur (bilan de cinq années d’observations). IAHS Publ. 246, 335-346. Lienou, G., Mahé, G., Olivry, J.C., Naah, E., Servat, E., Sigha-Nkamdjou, L., Sighomnou, D., Ndam Ngoupayou, J., Ekodeck G.E., Paturel, J.E. (2005) Régimes des flux des matières solides en suspension au Cameroun : revue et synthèse à l’échelle des principaux écosystèmes ; diversité climatique et actions anthropiques. Hydrological Sciences Journal, 50, 1, 111-124. Lienou, G., Sighomnou, D., Sigha-Nkamdjou, L., Mahé, G., Ecodeck, G.E., Tchoua, F. (2003) Système hydrologique du Yaéré (Extrême-Nord Cameroun), changements climatiques et actions anthropiques : conséquences sur le bilan des transferts. IAHS Publ. 278, 403-409. Liénou, G., G. Mahé, J.E. Paturel, E. Servat, G.E. Ekodeck, F. Tchoua (2009). Variabilité climatique et transport de matières en suspension sur le bassin de Mayo Tsanaga : Extrême-Nord Cameroun. Sécheresse, 20, 1, 139-144. Picouet, C., Orange, D., Mahé, G., Olivry, J.C. (2002) Rôle du delta intérieur du fleuve Niger dans la régulation des bilans de l’eau et de sédiments. In : Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 245-258. Sigha-Nkamdjou, L., Sighomnou, D., Lienou, G., Ndam, J.R., Bello, M., Kamgang, R., Ekodeck, G.E., Ouafo, M.R., Mahe, G., Paturel, J.E., Servat, E. (2005) Impact des modifications climatiques et anthropiques sur les flux de matières de quelques bassins fluviaux du Cameroun. IAHS Publ. 292, 291-300. Conferences Bricquet, J.P., Mahé, G., Olivry, J.C., Gourcy, L. (1997) Dissolved matter fluxes in the Niger river’s inner delta. Poster proceedings, Hydrochemistry, 5th IAHS Assembly, Rabat, Maroc, April 23-May 3. Reports and others Bassirou, A. (2007) Impact des rejets de la ville de Niamey (Niger) sur la qualité des eaux du fleuve Niger. PhD thesis, Faculté Universitaire Notre Dame de la Paix, Namur, Belgium. 299p. Kondé, C., Orange, D., Mahé, G., Gourcy, L. (1997) Première quantification des flux de méthane produits dans le delta intérieur du fleuve Niger. Rapport interne, ORSTOM, Laboratoire d’Hydrologie Bamako, CNRST, 25 p. Picouet, C. (1999).Géodynamique d’un hydrosystème tropical peu anthropisé : le bassin supérieur du Niger et son delta intérieur. PhD Sciences (Hydrologie-Hydrochimie), Université Montpellier, 454 p.

Groundwater Papers

Favreau, G., Leduc, C., Marlin C. (2001) Increase of groundwater recharge induced by a change in land- use: comparison of hydrodynamic and isotopic estimates in semi-arid Niger. Impact of human activity on groundwater dynamics. IAHS Publ. 269, 67-73. Favreau, G., Leduc, C., Marlin, C., Dray, A., Taupin, J.D., Massault, M., Le Gal La Salle, C., Babic, M. (2002) Estimate of recharge of a rising water-table in semi-arid Niger from 3H and 14C modeling. Ground Water, 40, 2, 144-151. Favreau, G., Leduc, C., Seidel, J.L., Ousmane, S.D., Mariotti, A. (2003) Land clearance and nitrate-rich groundwater in a Sahelian aquifer, Niger. IAHS Publ. 278, 163-167. Leduc, C., Favreau, G., Schroeter, P. (2001) Long-term rise in a Sahelian water-table: the Continental Terminal in South-West Niger. Journal of Hydrology, 243, 1-2, 43-54. Leduc, C., Favreau, G., Guero, A., Daddy, Gaoh, A. (2006) Comment on “Estimating groundwater mixing ratios and their uncertainties using a statistical multi parameter approach” by Rueedi J., Purtschert R., Beyerle U., Alberich C., Kipfer R., J. Hydrol. 2005, 305:1-14. Journal of Hydrology, 318, 3-6. Mahé, G., Dessouassi, R., Cissoko, B., Olivry, J.C. (1998) Comparaison des fluctuations interannuelles de piézometrie, precipitation et débit sur le bassin versant du Bani a Douna. IAHS Publ. 252, 289-295. Mahé, G., Olivry, J.C., Dessouassi, R., Orange, D., Bamba, F., Servat, E. (2000) Surface water groundwater relationships in a tropical river in Mali. Comptes rendus de l’Académie des Sciences, Série IIa, 330, 689-692. Savané, I., Sangaré, Y. (1997) Evolution climatique de la région nord-ouest de la Côte d’Ivoire de 1935 à 1992 et son influence sur la réserve d’eau souterraine et sur l’agriculture. Technical Documents in Hydrology, UNESCO Ed., 16, 127-146.

Reports and others GEF (2003) Managing hydrogeological risk in the Iullemeden aquifer system. UNEP Project, Mali, Niger, Nigeria. JICA -Japan International Cooperation Agency (1995) The study on the national Water resources master plan. Abstract, 11p. UNDP (1990) Synthèse hydrogéologique du Mali. 328p.

Land use change, flooding Papers Mahé G. (2006) The impacts of land use/land cover change and climate variability on the hydrology of the Sahel. AISH Publ. 308, 679-684. Mahé G., Bamba F., Soumaguel A., Orange D., Olivry J.C. (2009). Water losses in the Niger River inner delta: water balance and flooded surfaces. Hydrological Processes, 23, 3157-3160. Mariko, A., Mahé, G., Orange, D., Royer, A., Nonguierma, A., Amani, A., Servat, E. (2002) Suivi des zones d’inondation du delta intérieur du Niger : perspectives avec les données basse résolution NOAA/AVHRR. In : Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 231-244. Mariko, A., Mahé, G., Servat, E. (2003).Les surfaces inondées dans le delta intérieur du fleuve Niger au Mali par NOAA/AVHRR. Bulletin SFPT, 172, 61-68. Conferences Mariko, A., Mahé, G., Servat, E. (2005) Impact de la variabilité hydroclimatique sur la dynamique spatio- temporelle de l’inondation en zone lacustre sahélienne par NOAA/AVHRR sur la période 1990-2000 : cas du Delta intérieur du Niger au Mali. Communication orale. Abstracts book. First International AMMA conference, Dakar. Reports and others Diarra, S., Kuper, M., Mahé, G. (2003) Flood management in the Niger river inland Delta in Mali. Prospect paper. WMO/GWP Associated Programme on Flood Management. DNH. Bamako Mali, 25 p. Koné, F. (2000) Suivi piézométrique au Burkina Faso – Bilan de 20 années d’observation. Mémoire d’ingénieur, EIER, Ouagadougou Mariko, A. (2004) Caractérisation et Suivi de la Dynamique de l'Inondation et du Couvert Végétal dans le Delta Intérieur du Niger (Mali) par Télédétection. PhD Science de l’eau dans l’environnement continental, Université de Montpellier 2.

River modelling Papers Conway, D., Mahé, G. (2009) Riverflow modelling in two large river basins: the Parana (subtropical) and the Niger (tropical). Hydrological Processes, 23, 3186-3192.

Paturel, J.E., Barrau, C., Mahé, G., Dezetter, A., Servat, E. (2007) Modelling the impact of climatic variability on water resources in West and Central Africa from a non-calibrated hydrological model. Hydrological Sciences Journal, Vol. 52(1), 38-48. Dezetter, A., S. Girard, J. E. Paturel, G. Mahé, S. Ardoin-Bardin, E. Servat (2008). Simulation of runoff in West Africa: Is there a single data-model combination that produces the best simulation results ? Journal of Hydrology 354: 203-212.

Socio-economics, integrated river management Papers Kuper, M., Mullon, C., Poncet, Y., Benga, E., Morand, P., Orange, D., Mahé, G., Arfi, R., Bamba, F. (2002) La modélisation intégrée d’un écosystème inondable : le cas du delta intérieur du Niger. In: Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 773-798. Laë, R., Mahé, G. (2000) Crue, inondation et production halieutique dans le Delta Central du Niger : Un modèle prédictif des captures en poisson. In: Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 865-882. Orange, D., Mahé, G., Dembélé, L., Diakité, C.H., Kuper, M., Olivry, J.C. (2002) Hydrologie, agro- écologie et superficies d’inondation dans le delta intérieur du Niger. In: Séminaire International GIRN-ZIT, Colloques et séminaires, IRD, 209-229. Yates, D., Purkey, D., Sieber, J., Huber Lee, A., Galbraith, H., West, J., Herrod, S. (2007) A physically- based, water resource planning model of the Sacramento Basin, California USA. ASCE Journal of Water Resources Planning and Management, in press. Yates, D., Sieber, J., Purkey, D., Huber Lee, A. (2005) WEAP21-A Demand- Priority and Preference- Driven Water Planning Model: Part 1, Model Characteristics. Water International, 30, pp. 487-500. Conferences Blanchet, F., Denon, K., Diarra, D., Mahé, G., Paturel, J.E. (2002) Possibility of improvement of rice growing under controlled submersion in Mali (Office Riz Segou) using «real time» hydrological data. In: FRIEND 2002 Regional Hydrology: Bridging the gap between research and practice (H. Van Lannen and S. Demuth Sci. Eds.), Proc. Friend Conf., Cape Town, South Africa, CD Poster Paper Proceedings. Poncet, Y., Kuper, M., Mullon, C., Morand,P., Orange, D., Mahé, G., Benga, E. (2002) Modelling a large tropical flooded area: a transdisciplinary approach. Third International Conference on Water Resources and Environment Research (ICWER). July 22-26, Dresden, Germany. Maps and Books Andersen, I., Dione, O., Jarosewich-Holder, M., Olivry, J.C. (2006) Le bassin du fleuve Niger. Vers une vision de développement durable. Banque Mondiale, Washington DC. Marie, J., Morand, P., N’Djim, H., Olivry J.C. (à paraître) La gestion des ressources du fleuve Niger au Mali. Expertise collégiale IRD/Institut d’Economie Rurale, Bamako-Paris, IRD Ed.. Orange, D., De Noray, M.-L., Coulon, G. (2000) Vivre et travailler dans le delta intérieur du fleuve Niger au Mali. IRD Ed., Paris. Quensière, J. (1994) La pêche dans le delta central du Niger – Approche pluridisciplinaire d’un système de production halieutique. IRD Ed. Reports and others Comprehensive Assessment of Water Management in Agriculture (2007) Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture. London: Earthscan, and Colombo: International Water Management Institute. De Noray, M.L., Mahé, G. (2004) Le Delta intérieur du fleuve Niger. Diaporama. Centre Culturel Français de Bamako, 16 min. Mainuddin, M., Eastham, J., and Kirby, M. (2009). Water-use accounts in CPWF basins: 7. Simple water-use accounting of the Niger Basin. CPWF Working Paper. Colombo, Sri Lanka: CGAIR Program for Water and Food. Orange, D., Arfi, R., Bénech, V., Mahé, G., Morand, P., Olivry, J.C., Poncet, Y. (1997) Projet GIHREX, Gestion intégrée, hydrologie, ressources et systèmes d’exploitation du Delta Intérieur du Niger. Doc. de projet, programme 621/UR2 « Grands Bassins Tropicaux : Dynamiques et Usages », ORSTOM, Paris. Thareau, E. (1997) Dynamique du système agraire et impact socio-économique de la retenue collinaire de Ntonimba. Mémoire de DESS Développement Agricole.IEDES, Paris I Sorbonne, ORSTOM/Lecom Bamako, 114 p.

BFP Niger - WP2 Water availability and access Abstract

1 Introduction

The West African drought has now been lasting for nearly 40 years. It has tragic consequences in the Sahel countries, such as desertification. This drought, which is notably characterized by a decrease of rainfall, global surface-water flows and by a change in the rainy season characteristics, contributes to reduce the water availability in the Niger River Basin. This climate shift must be born in mind if one wants to understand the present hydrology and water uses in the basin. The River Niger is the 3rd longest river in Africa, covering a distance of 4200 km and the 9th in terms of its drainage basin covering a surface area of 2170500 km2 of which 1500 000km2 is an active basin. It takes its rise from the Futa Jallon Highlands in Guinea with an average altitude of 1100 meters. It flows north east and during the raining season it forms a vast flood plain in Mali known as the inland Delta. Away from the inland Delta it meanders in Mali then flows south east right to Nigeria where it is joined by the River Benue and empties itself into the Atlantic Ocean. Nine countries sharing the active basin are member of the Niger Basin Authority (NBA): Benin, Burkina Faso, Cameroon, Guinea, Ivory Coast, Mali, Nigeria, Chad and Niger. Algeria has an important part of the inactive desertic basin. From the stand point of water resources, the Niger Basin can diagrammatically be divided into four zones with more or less homogenous physical and geographical characteristics (fig 1): The Upper Niger Basin ; it is found in Mali, Guinea, and Ivory Coast. It covers a surface area of 257000 km2 out of which 140 000km2 are situated in Guinea, serving as the watershed and is seen as the portion which can be used to partially regulate water flow through out the length of the river. The Inland Delta ; Entirely situated in Mali, it covers a rectangular area facing south west and north east with a length of 420 km and a width of 125 km between Ke-Macina and San in the south and Timbuktu in the north. It has a surface area of 84000 km2 and comprises four agro-ecological zones: the living delta, the middle Bani-Niger, the dead delta and the lacustrine zone between Gao and Timbuktu. It accounts for almost all of the rice cultivation which is the staple food in Mali. This is done thanks to the Markala Dam. The Middle Niger Basin. It lies within Mali, Niger, Benin and Ivory Coast. It stretches from Timbuktu to Benin, covering an area of 900.000 km2, 230 000 km2 of which are inactive. It is made up of a series of irrigated terraces. Water flow in this basin largely depends on additional influx from the Inland Delta and navigation is hampered by waterfalls. The Lower Niger Basin: It lies between Cameroon, Nigeria and Chad. It is characterized by big dams for hydro-electric power production, irrigation and by industrial activities on the rest of the basin. Energy production is mainly derived from the Kainji, Lagdo and Jebba dams which supply 68% of Nigeria’s electricity needs and 22% of her total energy needs.

2 Water resources in the basin and their variability

Inventories of data are available by consulting the data base of the NBA and the SIEREM base from HydroSciences Montpellier Laboratory. Direct observation of surface water flow on the topographic slope of the Niger enables us to realize that some parts are not hydraulically linked to the river. These include the Algerian section of the basin (the Tassir Oua Ahaggar region) and those of Tamesna and Tahoua found in Mali and Niger. Great tributaries of the Niger which used to drain these regions at humid times, at moment can only subsist in dry valleys covered by great thickness of sand. Even the Continental Terminal aquifer 67 found in the Iullemeden Sedimentary Basin is cut off from the hydrological system of the River Niger. It is the same situation with the Gando and the Liptako regions at the boundary between Mali and Burkina Faso.

Inland delta Middle Niger basin

Upper Niger basin

Lower Niger basin

Figure 1: Niger River Basin: the different countries involved, and main regions. The active hydrological section of the basin (the contributory basin) is presented in the form of a clock with two parts linked between Dire and Tossaye by a bay in which the basin only limited to the canal formed by the river bed (Fig 2).

Zone where the flows do not reach any more the course of the river Niger Contributory basin Figure 2: Contours of the Niger Basin

Rainfall and climatology The rainfall regime of the Niger River depends on the fluctuations of the Atlantic Monsoon which generally occurs between May and November. The intensity of the phenomenon is relatively homogenous on the east-west axis but experiences a serious gradient on the north- south axis following the scale of the basin. There are 530 rainfall stations and 105 climatic stations with at least 20 years of observations. Data from Nigeria and Guinea are difficult to recover. The average annual rainfall rises to 2000 mm in portions further south in the basin, while it decreases to less than 400 mm in the north under Sahelian and semi-desertic climate (fig 3). 68

300 730 520 200 300 700 200 450 100

100 0 J M M J S N 400 0 300 1700 J M M J S N 1050 1350 900 300 300 200 1200 200 1100 200 100 100 100 0 0 J M M J S N J M M J S N 0 J M M J S N

Figure 3: Niger River Basin: climatic zones and monthly rainfall illustrations A great part of the basin experiences a high evaporation due to the vicinity of the Sahara. This has a great influence on the availability of water notably on free water plains (inland drainage and large water reservoirs). Potential evaporation is lower in the southern part of the basin and higher in the North (fig. 4). The difference between rainfall and PE determines the availability of water for infiltration. This monthly inventory evaluation defines the agricultural calendar (fig. 5).

Figure 4: Annual PE: Humid year 1955, in mm.

The inventories done on rainfall and compared with the evapotranspiration potential will determine the availability of water to infiltrate the soils towards the underground sheets .This monthly inventory evaluation defines the agricultural calendar. When rainfall is lower than ETP, (p- E.T.P<0), the water reserves in the soil are very low or even absent. In this case there is neither streaming nor infiltration .This is the state of affairs experienced in the basin between November and April. (fig. 5)

On the contrary when rainfall is above the ETP (P-E.T.P>0) water reserves in the soil are much more important therefore favouring agriculture. The monthly variations in the differences between rainfall and ETP will define the agricultural calendar as well as the start of streaming which start in 69 the humid parts of the Basin (Guinea, Cameroon and Nigeria) between May and June .The Sahel regions of the basin are only involved between July and September.

Figure 5: Monthly difference between rainfall (P) and potential evapotranspiration (ETP) in 1994, for half degree squares. Light blue: PE>P; dark blue: P>PE.

Flows Rainfall-runoff variability The hydrologic times series for the Niger began in 1907 with the installations of stations in Koulikoro (Mali) and Jebba (Nigeria). The present hydrologic observation is estimated at 250 stations including the specific network meant to check the river flow within the framework of the Hydroniger Programme. The volumes discharged are lower in the upper basins, and increase strongly when entering Nigeria where rainfall are heavy over the Niger basin (fig. 6). The hydrological regimes strongly changes for the upper Niger when passing through the inland delta, where he flood is delayed by two to three months, and is reduced from 24 to 48% during extremely dry or wet years. The River Niger basin has been submitted to a strong rainfall deficit since 1970, which occurred over the whole basin. All the sub-basins experienced a reduction of runoff. The 80s are the driest decade since the beginning of the 1900’s century (fig. 7). The rainfall deficit is less strong in the southern part of the basin, mainly over the Benue river basin. But the Niger basin can be divided into three main areas: the upper basin of the River Niger in Guinea, Mali and Ivory Coast, where the runoff deficit is very strong (fig. 8); the lower River Niger basin, including the Benue river, where the runoff deficit is limited; and the Sahelian tributaries, mainly in Mali, Burkina-Faso and Niger, where the runoff has increased, due to changes in land-use (fig. 9).

Figure 6: Monthly average volumes (in billion of m3) (1960-1990).

20.00 1950 20.00 1960

15.00 15.00

10.00 10.00

ORSTOM - programme FRIEND AOC ORSTOM - programme FRIEND AOC 5.00 5.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00

20.00 1970 20.00 1980

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ORSTOM - programme FRIEND AOC ORSTOM - programme FRIEND AOC 5.00 5.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00 -15.00 -10.00 -5.00 0.00 5.00 10.00 15.00 20.00

------0 0 0 0 0 1 1 1

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......

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déficit excédent Figure 7: Rainfall index over the River Niger basin (Paturel et al., 1997).

In Sahelian parts of the basin runoff coefficients have seriously increased, which lead to higher flood peaks, erosion, sediment transport and dam silting (fig. 9). This is linked partly to the climate change-related rainfall reduction, but mainly to the increase of the cultivated surfaces, and the related disappearance of the natural vegetation . In Soudano-guinean parts of the Niger River basin, the runoff decrease has been much deeper than that of the rainfall, due to the cumulative (memory) effect of the rainfall lasting shortage on the groundwater levels. 71

Niger à Koulikoro

1.00

0.50

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1905 1914 1923 1932 1941 1950 1959 1968 1977 1986 1995 Années

Figure 8: Rainfall-runoff in the Soudano Guinean part of the River Niger in Mali and Guinea.

30 dev st and runoff Rainfall 2

iation 25

20 1

15 0

b ofstations b 10 N

- d 5 1 0 - 2 1958 1963 1968 1973 1978 1983 1988 1993 Rainfall Year Runoff

Figure 9: Rainfall-runoff relationships in Sahelian tributaries of the River Niger.

Groundwater resources Discontinuous aquifers are mainly found on the right bank in the Niger (Guinea, Mali, Ivory Coast, Burkina Faso and Niger) in the Guineo-sudanian zones and the Sudano- sahelian zone. Pipe borne water projects in these villages make use of such aquifers. Specific flows and the rates of failure in bore-hole realization are very unsteady (between 30 to 70%). Generalized aquifers can be found in large sedimentary forms, especially on the right bank of the Niger River (Mali, Niger, Chad, Nigeria and Cameroon).

800 Total discharge Base flow 600 Surface flow

400

200 Discharges m3.s-1 . 0 1 31 61 91 121 151 181 211 241 271 301 331 361 Days from January 1st

Figure 10: Annual hydrograph for the Bani River at Douna. Total Runoff (bold line) / Surface runoff (thin line) / Base flow (dashed). Average 1984-1996.

On plateau surfaces, superficial aquifers are superimposed to deeper aquifers. The outer aquifers can be partly continuous thereby forming a hydraulic link with the deeper layer or it can be discontinuous. The figure 10 shows the importance of the baseflow in the annual runoff. This is for the Bani at Douna, but this is representative of most of the River Niger tributaries, from Guinea, Mali, Ivory Coast and Cameroon, under Soudano-guinean climate.

3 Accessibility to water and its uses

Reservoirs Dams will be classified in two main groups: the existing ones and those still in project form. The existing dams 260 dams have been identified on the basin slope of the Niger (fig. 11). Their distribution is not regular and there is the concentration of installations on some sections of the basin, in Burkina-Faso (mainly small dams) and in Nigeria (all sizes including big dams).

$ Capacité non connue # V < 1 million # 1 million < V < 250 millions

# 250 millions < V < 1 milliard # # 1 milliard < V #

Figure 11: Niger River Basin: Situation of existing dams.

Carrying capacity varies between 25.10-3 million m3 (Camp de chasse, Tapoa, Niger) to 16 billion m3 (Kainji, Nigeria). Figure 12 shows the class distribution of the carrying capacity of all the identified dams. From this distribution 50 % of them are small dams of less than 1 million m3, and there are only 4 “giant” dams (more than 1 billion m3): 1 in Mali and Cameroon and 4 in Nigeria.

Figure 12: Class Distribution of the Capacity of Dams

An evaluation of the capacity of the existing dams places the global volume at 42 billion m3 which represents 22% of the water influx from the Nigerian Onitsha between the dry periods of 1971 and 2001; and 27% of the same influx in the same station during the rainy seasons between 1929 and 1970. This situation reflects the poor mastery of water resources in the Niger and its tributaries.

Projected dams Seventy dams have been projected in the basin of the River Niger, mainly on the middle and upper Niger valley, in Niger, Burkina-Faso, Mali and Guinea. The only projected sites for construction works in the lower Niger are those of Makurdi, Lokoja and Onitsha.

$ Capacité non connue # V < 1 million # 1 million < V < 250 millions # 250 millions < V < 1 milliard # 1 milliard < V # #

# $ # # # # # # # # # # # # ## # # # # # # # # $ # # # # # #$# # # # # # # $ # # # $## # # ## # # $ # # ## #$ # ## # # # #$ # # # $ $

Figure 13: Niger River Basin, situation of projected dams.

Projected capacities reach 6 billion m3 (Fomi site on the Niandan in Guinea). The capacity of the projected dams on the entire basin is about 48 billion m3 as against 42 billion m3 for the harnessing of existing ones. More than 80% (39 billion m3) have been previewed to be stored in the Upper Niger and 20% only (9 billion m3) to be kept in the Middle Niger. Considering the existing and projected dams in the Upper Niger, the volume of water stored will slightly be above 41 billion m3. If this figure is compared to the discharged volume at the entry point of the Inland Delta (Ke-Macina and Douna) which respectively measure 75 billion m3 in a humid year and 21 billion m3 in a dry year, then it means that more than 55% of all flows will be stored in a humid year and flows in the upper basin will be insufficient to fill all the reservoirs. The situation which has been worsened by drought will have drastic consequences of the Lower Delta.

Down-stream depletion Depletion for purposes of irrigation 171 retention points for irrigation purposes have been identified along the Niger and its tributaries. Approximately 5412 billion m3 have deducted annually to irrigate a surface area of 264550 per inhabitant, giving an average of 20 000 m3 per inhabitant. The retained volume from each country depends on the surface of the basin slope of the country concerned (table 1). In this connection the largest volume is kept aside in Mali, followed by Nigeria and Niger. Retention for potable water supply Various water catchments areas have been set up on the Niger and its tributaries to supply many towns with potable water. The hypotheses are for 2005 based on 20 inhabitants per day for the rural areas and 40 for the urban agglomerations. Potable Water Retentions for Livestock Breeding The estimate of reserved volumes for livestock is difficult by its diffused nature. Calculation of water needs associated with livestock is

74 based on a need in 30 units per day. Estimates show in 2005, about 223,6 million m3 of water was used for about 2771000 U.B.T. The largest reserved volumes are found in those countries with the largest areas of land within the basin (Nigeria, Niger). Mali is noted for its livestock numbering 8640000 U.B.T. However, reserved water for livestock is small (14,2 million m3).

Table 1: Retained volumes and irrigated surface area per country Number of Total surface irrigated in Annual total volume taken in uptakes 2005 (ha) 2005 (Million of m3) Benin 2 1006 23 Burkina Faso 3 1482 9 Cameroon 3 5300 107 Ivory Coast 10 2495 46 Guinea 8 8984 104 Mali 8 117348 3825 Niger 43 43315 454 Nigeria 94 82620 847 Total 171 264550 5412

But it should be noted that part of the riverine population gets its water from the water-bearing beds of the river. The results of the many estimates, represents the maximum level of uptaking without taking into account other sources of water.

Water use account Figure 14 (after Mainuddin et al, 2009) shows the major water uses over the River Niger basin. This approach, combined with the WEAP model, could be useful to determine areas where water can be reallocated to benefit the poors.

Figure 14: Summary of major water uses in Niger Basin catchments (Mainuddin et al, 2009)

4 Changes in water availability

Application of climatic scenarii Simulations have been carried out for the horizon 2050 with the HadCM3 model and A2 scenario. Figure 15 shows the changes in runoff in 2050 compared to the 1966-1995 average in West Africa. According to this GCM/scenario, there would be a slight increase in runoff over most of the upper Niger river basins in West Africa, but not over the upper Benue river basins. The situation would worsen in 2080 following a general rainfall reduction over West Africa. This is only one model and one scenario. After a comparison of several GCM outputs for the region, Ardoin et al. (2009) conclude that most of the recent GCM outputs for the region show lower rainfall predictions than the HadCM3 model.

Figure 15: Percentage of variation in runoff in West Africa between (1966-1995) and 2050, using the IPCC HadCM3 A2 scenario.

The case of the Niger River inner delta in Mali For the Niger Inner Delta (a key focus for the BFP Niger), an integrated model of the Niger inner delta called MIDIN has been developed. It integrates several relationships between water, biology and human activities along the different hydrological entities like channels, lakes and floodplains. The figure 16 shows the correlation between the flooded surfaces, as depicted by NOAA images between 1990 and 2000, and the water heights at the main gauging station of Mopti in the delta. This correlations allows to determine the flooded area of the upper delta area according to the Mopti water level. This will result for instance in being able to predict one month in advance from the water height at Mopti the water height in the Northern part of the delta (North of the central lakes).

Delta amont (Juilet à octobre 1995) Surface 15000 inondée 2 (km ) 0,0093x 10000 y = 36,637e R2 = 0,9629

5000

0 0 200 400 600 800 Hauteur d'eau à la station de Mopti (cm) Figure 16: Correlation between water height and flooded area in the upper inner delta, Mali

5 Conclusion

Nigeria has a lot of dams, including big dams, while Burkina-Faso has a lot of 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 (including a few very big ones like in Fomi in Guinea) will be built over the Niger basin in the coming years. It is very important before building them to take into account the past years variability of climate and river regime. It is particularly important to take into account the very deep runoff decrease in the tropical humid sub-basins, and the runoff increase in the Sahelian ones. It is also noticeable that most of the GCM outputs predict a rainfall reduction still to come during the next decades of the XX1st century. Several tools such as Water Use Account, MIDIN and rainfall/runoff modelling should be implemented at NBA, to be used as predicting tools.