Hydroelectric production in Akosombo, and the development of irrigated agriculture upstream, a fair balance to be found to reconcile regional energy and food security.-Challenges of the Volta Basin Water Charter

The Volta River is a West African river that flows from Burkina Faso to Ghana where it empties into the Atlantic Ocean. It basin extends over six countries: Benin, Burkina Faso, Côte d’Ivoire, Ghana, Mali and Togo. These states, members of the Volta Basin Authority, have committed themselves to drawing up a Water Charter. One of the challenges of this international agreement is to agree on a reasonable level of abstraction to reconcile food and energy security for the populations, while guaranteeing the minimum needs of the ecosystems. Supported by an appropriation of the needs-resources balance through the use of Lego® bricks, their reflection was supported by a hydro-economic analysis. This analysis consisted in comparing the added value associated with an agricultural abstraction which leads to a definitive consumption of water upstream of the basin, for example in Bagré in Burkina Faso and the one associated with the same quantity of water if it had been allowed to flow and turbined in one of the hydroelectric facilities located further downstream, for example in the large Akosombo dam in Ghana. The results show that the agricultural valorisation of a continuous abstraction of one m3/s, i.e. 30 Mm3 per year, allows to irrigate 1,500 ha and generates an added value of 1,300 M FCFA per year, i.e. 44 FCFA/m3. This volume of 30 Mm3, taken upstream of the dam would induce a loss of hydroelectric production of 6 GWh/year, worth 297 M FCFA, i.e. 10 FCFA/m3. The economic value of each m3 withdrawn to develop irrigated agriculture upstream of the basin is thus higher than that of each m3 turbined in the Akosombo-Kpong complex. Within the limit of an acceptable reduction of hydropower production, the economic development of the basin as a whole would thus benefit from the development of irrigated agriculture. 2 E3S Web of Conferences 346, 03002 (2022) https://doi.org/10.1051/e3sconf/202234603002 Sharing Water: Multi-Purpose of Reservoirs and Innovations

Abstract. The Volta River is a West African river that flows from Burkina Faso to Ghana where it empties into the Atlantic Ocean. It basin extends over six countries: Benin, Burkina Faso, Côte d'Ivoire, Ghana, Mali and Togo. These states, members of the Volta Basin Authority, have committed themselves to drawing up a Water Charter. One of the challenges of this international agreement is to agree on a reasonable level of abstraction to reconcile food and energy security for the populations, while guaranteeing the minimum needs of the ecosystems. Supported by an appropriation of the needs-resources balance through the use of Lego® bricks, their reflection was supported by a hydro-economic analysis. This analysis consisted in comparing the added value associated with an agricultural abstraction -which leads to a definitive consumption of water upstream of the basin, for example in Bagré in Burkina Faso -and the one associated with the same quantity of water if it had been allowed to flow and turbined in one of the hydroelectric facilities located further downstream, for example in the large Akosombo dam in Ghana. The results show that the agricultural valorisation of a continuous abstraction of one m 3 /s, i.e. 30 Mm 3 per year, allows to irrigate 1,500 ha and generates an added value of 1,300 M FCFA per year, i.e. 44 FCFA/m 3 . This volume of 30 Mm 3 , taken upstream of the dam would induce a loss of hydroelectric production of 6 GWh/year, worth 297 M FCFA, i.e. 10 FCFA/m 3 . The economic value of each m 3 withdrawn to develop irrigated agriculture upstream of the basin is thus higher than that of each m 3 turbined in the Akosombo-Kpong complex. Within the limit of an acceptable reduction of hydropower production, the economic development of the basin as a whole would thus benefit from the development of irrigated agriculture.
Si les outils présentés n'ont pas permis à la Charte de l'eau de la Volta d'atteindre l'ambition d  Hydroelectric production in Akosombo, and the development of irrigated agriculture upstream, a fair balance to be found to reconcile regional energy and food security. Abstract. The Volta River is a West African river that flows from Burkina Faso to Ghana where it empties into the Atlantic Ocean. It basin extends over six countries: Benin, Burkina Faso, Côte d'Ivoire, Ghana, Mali and Togo. These states, members of the Volta Basin Authority, have committed themselves to drawing up a Water Charter. One of the challenges of this international agreement is to agree on a reasonable level of abstraction to reconcile food and energy security for the populations, while guaranteeing the minimum needs of the ecosystems. Supported by an appropriation of the needs-resources balance through the use of Lego® bricks, their reflection was supported by a hydro-economic analysis. This analysis consisted in comparing the added value associated with an agricultural abstraction -which leads to a definitive consumption of water upstream of the basin, for example in Bagré in Burkina Faso -and the one associated with the same quantity of water if it had been allowed to flow and turbined in one of the hydroelectric facilities located further downstream, for example in the large Akosombo dam in Ghana. The results show that the agricultural valorisation of a continuous abstraction of one m 3 /s, i.e. 30 Mm 3 per year, allows to irrigate 1,500 ha and generates an added value of 1,300 M FCFA per year, i.e. 44 FCFA/m 3 . This volume of 30 Mm 3 , taken upstream of the dam would induce a loss of hydroelectric production of 6 GWh/year, worth 297 M FCFA, i.e. 10 FCFA/m 3 . The economic value of each m 3 withdrawn to develop irrigated agriculture upstream of the basin is thus higher than that of each m 3 turbined in the Akosombo-Kpong complex. Within the limit of an acceptable reduction of hydropower production, the economic development of the basin as a whole would thus benefit from the development of irrigated agriculture.

Challenges of the Volta Basin Water Charter
1 The Volta River, a fast-growing basin whose development must be coordinated to guarantee the availability of water resources on the different sections of the river 1.1 The Volta river, a transboundary development axis shared by six countries Covering an area of more than 400,000 km² [1], the Volta River basin is shared by six West African states. Burkina Faso, to the north and upstream, and Ghana, to the south and downstream, share equally 82% of its surface area. The basin also extends to Benin, Côte d'Ivoire, Mali and Togo (Figure 1).

More rainfall in the southern part of the basin
The Volta River basin is characterised by a strong north-south rainfall gradient, with heavier rainfall in the south of the basin. Average interannual rainfall ranges from 500-600 mm/year in the north of the basin to 1,100-1,300 mm/year in the Lower Volta system ( [2], based on CRU data -1901-2014). These accumulations are spread over a shorter period in the north, where 3 months show accumulations above 100 mm, compared to 6 to 7 months in the south.

Under natural conditions, 95% of run-off is spread over 6 months of the year
Hydrologically, the rake-shaped basin is divided into three main sub-basins: the Mouhoun / Black Volta, the Nakanbé / White Volta and the Oti / Pendjari, together covering 85% of the basin [2]. These three tributaries feed Lake Volta in Ghana and form the Volta River downstream of the Akosombo Dam, located at the extreme south of the basin. With similar surface areas, their contributions amount to, on average, 6,700 million m 3 per year (Mm3/year), 5,800 Mm 3 /year and 8,500 Mm 3 /year respectively, with the Volta River having at its outlet about 33,000 Mm 3 [2]. The spatial variability of rainfall and the variability of its temporal distribution is reflected in the hydrological regime of the river and its three main tributaries, marked by a strong north-south flow gradient. Moreover, under natural conditions -excluding the influence of storage facilities -95% of runoff is spread over 6 months of the year. This is characterised by severe low-water levels, which can go as far as several months of dryness in the most upstream sub-basins, and very powerful high waters, regularly generating major floods. The river and its tributaries are a strategic resource for Burkina Faso and Ghana.
1.4 A hydro-agricultural potential that is globally little exploited but which covers very contrasting situations and is developing strongly in the upstream parts of the basin With a potential theoretical development, all types of practices taken together and estimated on the basis of agronomic, hydrological and economic factors at nearly 600,000 ha basinwide [3,4,5,6,7], irrigated agriculture seems for the moment to be underdeveloped. Currently, the large irrigation schemes cover a little more than 24,000 ha [2]. Irrigation as a whole, including private or community irrigation and informal irrigation, represents about 45,000 ha, mainly located in the upstream Sudano-Sahelian zone. This represents gross abstractions from surface water resources in the order of 845 Mm 3 /year [2]. With more than 70% of the population living on less than €1 per day [8] and a population that could double in 30 years [9], the development of irrigated agriculture in the basin is of twofold importance, contributing both to socio-economic development and to strengthening food security. In this context, irrigation is the primary focus in the upstream part of the basin. However, the development potential is not uniformly exploited in this part of the basin. Irrigation is poorly developed in the Northern Region of Ghana. In Burkina Faso, on the contrary, large irrigated areas are already being developed, including Samendeni (21,000 ha), Noumbiel (7,800 ha), the Bagré agropole (13,000 ha), and Kompienga. If the entire potential of 600,000 ha were to be watered, the demand for irrigation water would then represent more than 10,000 Mm3/year [2].
Three large multi-purpose structures, which are however mainly used for irrigation storage, Bagré (1,720 Mm3), Kompienga (2,025 Mm3) and Samendeni (1,050 Mm3), were built to support the development of agriculture in the Nakanbé, Oti and Mouhoun valleys [2]. They complement Léry (603 Mm3), which enabled the development of the Sourou valley. Burkina Faso also has a large number of small hillside reservoirs, mostly located in the lowlands. These reservoirs, between 1,000 and 1,200 in the Burkinabe portion of the basin, have made it possible to develop informal and small-scale private irrigation. Northern Ghana is also equipped with about 200 such small reservoirs. All of these small dams are locally vital for subsistence agriculture, but they represent only a small volume of storage at the scale of the basin as a whole: about 300 Mm3 [10,11,12]. Moreover, major development programmes are planned for 2050 in the upstream parts of the basin: the Noumbiel (11,300 MW), Juale (1,200 MW) and Pwalugu (3,260 MW) projects and the SADA programme (24 facilities) [5] being the most emblematic. These development programmes aim to supply water to major irrigation projects and, more generally, meet the national strategic objectives of strengthening food security and adapting to climate change [13].
1.5 Hydropower, a pillar of regional energy security, is produced downstream of the basin Hydroelectric production is a major strategic issue in the Volta Basin. Ghana, with 1,580 MW installed, representing 97% of the installed capacity in the basin, is the main producer of hydropower in the basin. In 2013 and 2014, the country's hydroelectric facilities produced 8,387 GWh, representing 65% of the national electricity production (12,963 GWh) [14]. Ghana has made hydropower production the priority sector for the use of its water resources. About 7% of the country's hydropower production -mainly from the Akosombo plant -is exported to Benin and Togo. For Ghana, Togo and Benin, and to a lesser extent for Côte d'Ivoire, the basin is thus of strategic importance in that it provides a significant part of their energy supply for the needs of their population and their industries. Ghana does not supply Burkina Faso, which to date has wished to maintain its energy independence and has turned to alternative means of production (solar, thermal). However, this does not rule out the possibility that in the future Ghana will also supply the northwestern part of Côte d'Ivoire and Burkina Faso. An interconnection project between Côte d'Ivoire, Burkina Faso and Ghana is indeed envisaged [15]. This would further reinforce the strategic importance of the basin's water resources in the energy security of the countries of the sub-region.
Most of the hydroelectric production comes from the Bui dam (400 MW) and the Akosombo-Kpong complex (1,190 MW). These two facilities are located completely downstream of the basin and benefit from almost all the contributions of the Black Volta for the first and the basin as a whole for the second. Consequently, the abstractions upstream of these structures were very limited in the Ghanaian portion of the basin and closely monitored in those of other countries. This strategy explains the low level of development of irrigation schemes in the northern half of the country, although upstream abstractions are currently (2017) negligible in the balance of hydrological inputs. The combined historical analysis of the hydrological balance and hydropower production at the Akosombo dam (Figure 2) shows that the interannual variability of the hydrological inputs and the production objectives at the Akosombo-Kpong complex are the factors determining the management of Lake Volta. The prospect of a drastic increase in upstream abstractions, as envisaged by 2050, would however have a significant impact on hydrological inputs to the lake and consequently on energy production. 1.6 A level of resource mobilisation that is currently reasonable but difficult to sustain in the long term On an annual scale, the balance between needs and resources is assessed on the basis of the ratio "abstractions / average flows". This indicator reflects the level of pressure exerted by abstractions (current and possible future) on surface water resources at the level of each sub-basin. Given the very limited hydrological data available in the Volta basin, the assessment is carried out over an average hydrological period, at 7 reference stations at the outlets of the main sub-basins. However, for some stations, it was only possible to carry out this assessment for a dry hydrological period (1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984), such as the one the basin has known up to now. This analysis gives an indicative overview of the pressure of abstractions on the resources in the current situation and on a 2050 horizon (Figure 3).
The current level (2017) of water resource mobilisation, at 5% of the dry five-year annual inflow, is sustainable and has a low impact on the management of the Akosombo dam and its reservoir, Lake Volta. However, population growth will, in the medium term, lead to a strong increase in the demand for water to supply drinking water to the population. The development programmes planned to meet this demand will require a very large storage capacity, over 8,000 Mm 3 , and will put pressure on water resources that will be difficult to sustain in the long term (38% of the average supply and 50% of the dry fiveyear supply by 2050) [2]. The effects of climate change, which have not been assessed, could amplify this pressure if they were to have a negative impact on the availability of water resources in the basin, leading to dry episodes such as those experienced in West Africa in the 1970s and 1980s or in the early 2000s. Fig. 3: Annual balance of current (2017) and 2050 abstractions, and of mean annual and 5year dry hydrological inflows to Lake Volta (statistics for water resources calculated over the period 1950-1984 for stations whose hydrological series allow it, otherwise over the period 1970-1984).

A Water Charter as a tool for reconciling energy security, food security and the proper functioning of ecosystems
In 2007, the six basin states established the Volta Basin Authority (VBA) to manage the water resources of this international river in a concerted manner [16]. In order to operationalise the mandate of the VBA, the six States committed themselves in 2017 to draw up a Water Charter. This is an international agreement aimed at establishing the principles and modalities for an equitable, concerted and sustainable use of the shared water resources of the Volta Basin, with a view to contributing to the sustainable development of the Volta Basin. The Charter was adopted by the Council of Ministers on 14 December 2018 [17].
As the pressure on water resources in the Volta river basin is increasing, the development of abstractions in its upstream and downstream parts must be coordinated in order to guarantee resource availability in its various sections.
The aim is to strive for a balance that maximises the fundamental uses upstream and minimises the impacts on downstream uses in order to support economic development and improve the well-being of the populations of the basin as a whole. One of the challenges of this international agreement was to agree on the definition of a reasonable level of abstraction to reconcile food and energy security for the populations, while guaranteeing the proper functioning of the associated ecosystems.
The representatives of the six States were accompanied throughout the process of drawing up the Charter to agree on this commitment and to define its values. This support took the form of hydro-economic modelling of the major balances of water resource management in the basin. The indicators thus produced provided an objective basis on which a multi-stage consultation process was built, at national and then regional level, using innovative participation methods. During this process, the values considered, resulting from the hydro-economic analyses, were the subject of exchanges and compromises.

A simplified approach to hydro-economic modelling
The available hydrological series were criticized in order to define a common reference period, with a minimum length of 30 years, where the reliability of the data is best, and on which to calculate and compare hydrological statistics and indicators at different points in the basin. The reference period chosen is the period 1950-1984. From the 1980s onwards, the hydrological series show numerous derating shifts and calibration problems in low waters, the calibration curves having for the most part not been revised since [18].
Agricultural water demand was estimated using the Penman-Monteith method [19] and climate statistics of temperature and evapotranspiration calculated from CRU data, over the same reference period as that of the hydrological series   [20]. An irrigation scheme sown with rice on 100% of its surface in winter and 50% in the off-season, with an abstraction and distribution system with a 40% efficiency, was considered representative of the large schemes of the Sudano-Sahelian zone of the basin. This is equivalent to a gross abstraction of 20,000 m 3 /ha/year. The gross abstractions were considered definitive, without any return to the river or the accompanying groundwater, which is a strong simplifying assumption.
The annual hydropower production was estimated based on the average efficiency of the Akosombo hydropower plant (0.18 GWh/Mm 3 ) on the basis of the annual reports of its manager, the Volta River Authority [21]. The average and five-year average dry output for the current situation are thus 6,600 and 5,000 GWh/year respectively.
The range of values of the maximum abstractable volumes envisaged on the scale of the basin ranges from 2,500 Mm 3 (current demand + domestic and livestock needs by 2050, without irrigation development) to 12,500 Mm 3 (current demand + domestic and livestock needs + total irrigation development by 2050), in increments of +1,000 Mm 3 .
The proposed socio-economic approach is very simplified. It aims to identify trends in order to raise awareness and guide stakeholders in the consultation process. It consists in estimating the direct economic value of hydropower and agricultural products without taking into account positive and negative externalities. The analysis is based on the example of a continuous abstraction of 1 m 3 /s upstream of the basin in Burkina Faso which represents 30 Mm 3 /year. This volume is then converted into irrigated area or hydropower production, according to the hypotheses presented above, which are in turn converted into economic added value. Hydroelectricity production is converted into added value by subtracting the unit production cost (FCFA 5.5/kWh) from the VRA 2014 selling price (FCFA 55/kWh) [21], which is then reduced to a unit value per m 3 . As a reference, the unit production costs of thermal power are estimated at about FCFA 20/kWh. Irrigated areas are converted into added value from average yields and gross added values per hectare. It was not possible to access figures from agricultural programmes in the upstream part of the basin. The analysis is therefore based on the hypotheses of the hydro-agricultural development programme of the Office du Niger in Mali, also located in the Sudano-Sahelian climatic zone and in a comparable socio-economic context (production: 5,900 kg/ha for winter rice and 4,500 kg/ha for off-season rice; added value: FCFA 642,000/ha and FCFA 467,000/ha respectively; employment: 132 and 142 person.days/ha/year respectively in direct employment and 80% in indirect employment). [22] 2.2 An ambitious process of consultation, concertation and co-development The consultation process that structured the drafting of the Water Charter consisted of two iterations in the following sequence: individual consultations of local stakeholders, consultations at national level, and consultations at regional level. The first was for the establishment of a diagnosis of the transboundary issues that the Charter will have to address. A second time to identify, harmonise and agree on proposals for concrete commitments to be included in the Charter and their implementation procedures. In order for stakeholders to understand the quantitative water resource management issues that the Water Charter aims to frame, the "Leg'eau" § facilitation method was proposed in a regional workshop (Figure 4). This method uses Lego® bricks to represent water resources and their uses. A map in A0 format representing the hydrological network, the main sub-basins, uses and existing structures was made available to stakeholders, as well as a set of Lego® bricks symbolising water resources and their uses (see legend in Figure 4). With the help of a guide and the correspondence between Lego® bricks and volumes of water, the stakeholders were invited to symbolise the needs-resources balances of the current situation and of different scenarios for the management and development of water resources. This approach makes it possible to visualise the relative share of abstractions for irrigation or turbined flows in relation to available resources. It also shows what the implementation of reserved flows represents in relation to the storage capacity in the basin and its impact on downstream production, or the usefulness of the volumes stored to satisfy uses in periods of low water levels. This consultation method positions the stakeholders as actors in the definition of the quantitative management methods of the basin. It enables them to take ownership of the results of hydrological and socio-economic analyses and to work collectively to reach a compromise acceptable to all. It is in this sense that it has guided the exchanges around the definition of the maximum abstractable volumes.
3 Greater use of upstream irrigation reduces hydropower production but increases the socio-economic development of the basin as a whole 3.1 Hydrological analysis In order to guide stakeholders in defining maximum abstraction volumes, an analysis of the basin's main quantitative balances was conducted. Figure 5 shows the direct relationship between the development of irrigated areas in the basin and the hydropower production differential at the Akosombo-Kpong complex. Thus, with the development of 100,000 ha of new irrigated areas in the basin, the production of Akosombo would decrease by 10% in an average year and by 15% in a dry five-year year (-700 GWh). In order to facilitate the positioning of the abstraction ceiling, the evolution of the irrigated areas at the basin scale and of the hydropower production at the Akosombo-Kpong complex as a function of the defined level of maximum abstraction volumes is presented in Figure 6. The two green curves show the irrigated areas that it is theoretically possible to develop in an average year and in a dry year as a function of the level of abstractable volume defined on an annual scale. The two blue curves show the impact of these abstractions on hydroelectric production at the Akosombo-Kpong complex. The estimate of the hydropower production does not take into account head height or losses from infiltration and evaporation on the level of the Volta Lake. This figure provides an objective support for exchanges and consultations between stakeholders that will lead to the definition of abstractable volumes. For example, by "moving" on these curves, it is possible to have an order of magnitude of agricultural benefits and impacts on downstream uses as a function of the level of maximum abstractable volumes envisaged, in increments of +1000 Mm 3 .
Due to the strong demographic growth, and potentially the effects of climate change, the increase in abstractions for basic needs by 2050 (Current Situation CS + Drinking Water

Socio-economic analysis
The conclusions of the hydrological analysis were supported by an economic analysis of the added value linked to the use of an abstraction according to the purpose for which it is reserved. The proposed approach aims to compare the added value associated with an agricultural abstraction -which leads to definitive consumption -and the wealth associated with the same quantity of water if it had been allowed to flow downstream and turbinedinstead of being consumed. This simplified approach aims to identify orders of magnitude in order to guide consultation between the stakeholders involved in defining the provisions of the Water Charter in terms of maximum abstraction volumes.

Potential agricultural added value associated with a levy in the Sahelian zone
In the Sudano-Sahelian climatic zone of Burkina Faso, the water needs to irrigate 1 hectare of wet-season rice and 0.5 hectare of off-season rice are estimated at around 20,000 m 3 /ha/year. An abstraction of 1 m 3 /s during one year can therefore develop up to 1,500 ha. On the basis of the hypotheses used for the hydro-agricultural development programme of the Office du Niger in Mali [22], the production of this irrigation scheme would generate an added value of about FCFA 1,300 million per year, and thus enhance the value of the cubic metre abstracted by FCFA 44. In addition to its economic added value, this levy would also contribute significantly to the food security of the region's populations and would generate a significant number of direct and indirect jobs -1,250 direct jobs and 1,000 indirect jobs according to the hypotheses of the same report.

Loss of hydroelectric added value associated with the same levy
According to the operating accounts of the Volta River Authority, the Akosombo and Bui hydroelectric plants produce 65% of the energy sold. The remainder of the production is provided by a set of conventional thermal units. As Akosombo and Kpong allow for the production of approximately 0.18 kWh/m 3 , 30 Mm 3 taken from upstream of the dam would result in a loss of production of 6 GWh at these two facilities. According to the average VRA tariffs, this loss of production would represent a loss of added value of about FCFA 297 million (i.e. a loss of FCFA 10/m3). The energy security of Ghana and the subregion would also be negatively impacted. In this scenario, a significant number of direct and indirect jobs could be lost. The analysis of the latter was outside the scope of the study and could not be estimated.
It can also be assumed that the energy that could not be produced by the Akosombo plant because of the 30 Mm 3 abstraction will be produced by a conventional thermal unit, in Tema for example, so as not to impact on the energy security of Ghana and the sub-region. This means that an additional 6 GWh will have to be produced by the Tema thermal plant. This adjustment of the energy mix will therefore generate a loss of turnover of about FCFA 85 million -a loss of FCFA 3/m 3 .
In the simplified approach presented above, the economic value of each cubic metre taken to develop irrigated agriculture thus seems to be higher than that of each cubic metre turbined in the Akosombo-Kpong complex. Figure 7 thus shows that the economic development of the basin as a whole would greatly benefit from the development of irrigated agriculture. However, agricultural development and hydropower production contribute to the food and energy security of the basin respectively, benefits that are ultimately difficult to oppose. This is why this hydro-economic analysis only aims to provide orders of magnitude, making it possible to raise awareness and guide the actors involved in the process of drawing up the Charter. It is up to these stakeholders to come up with a choice based on exchanges and consultation to achieve a fair balance between energy and irrigated agricultural production. The estimation of the added value offers only a partial vision of the issues at stake.

Prospects for further analysis
It would be interesting to complete the analysis with a geographical dimension, in order to integrate the location of these productions. Including the greenhouse gas emissions also, through a carbon balance sheet, induced by reservoirs, alternative energy production and the transport of agricultural inputs and products, as well as the social impacts, such as a finer estimation of the impact on employment and the maintenance of activities in rural areas, would allow a more transversal vision of these complex issues. All of these conclusions should finally be subjected to a detailed analysis of climate change. Their effects on temperature, evaporation, and precipitation will indeed impact all the parameters of these analyses. The availability of water resources, the demand for domestic and agricultural water, energy production needs, agricultural yields, as well as all the environmental services provided by the river and its ecosystem will be affected. VBA plans to further investigate these issues through the development of a set of hydrological, water resource allocation and socio-economic models. IUCN, UNEP and GEF have decided to support the financing of this work. In the medium term, these tools will allow to deepen the analyses in order to feed the elaboration of the Master Plan for Water Development and Management (SDAGE) of the basin, which will constitute the reference planning document.

Conclusion and recommendations
Aware of the very significant impacts that an uncontrolled increase in abstractions could have, the six States have undertaken to limit the total volume of water consumed annually in the bodies of water upstream of Lake Volta to a ceiling. The consultation process made it possible to envisage the definition of this ceiling at 6,500 Mm 3 , i.e. an increase of 5,000 Mm 3 compared to current abstractions, without a definitive consensus being reached. The six States considered that it was not acceptable to define the level of maximum abstractable volume on the basis of hydrological series dating back several decades . They undertook to invest in water resource monitoring and statistical processing of the series of measurements in order to establish robust hydrological series, with a reference period of at least 30 years, over the recent period.
Although the tools presented did not enable the Volta Water Charter to achieve the ambition of a clear and quantified framework for uses in the basin, they will nevertheless have enabled the stakeholders to adopt the concepts of coordinated and sustainable management of water resources and solidarity between upstream and downstream users in the same transboundary basin. They will also have provided an objective basis for establishing in-depth exchanges between the stakeholders on a sensitive and strategic subject at international level. While the States of the basin have been able to maintain indepth cooperation and establish mechanisms for coordinated flood management in order to anticipate and avoid damage, which is recurrent in the Volta basin, the issue of quantitative management is subject to tension. Evaluating the take-up of these tools by the stakeholders of the basin and identifying the means of sustaining their use in order to facilitate a permanent dialogue and contribute to lifting these tensions is a line of thought to be submitted to the VBA and its partners, and more generally to be proposed to transboundary basin organisations with similar issues in quantitative water resource management.