**4. Some impacts of developments in the catchment area**

Since water is an economic good [18, 19], dams have contributed significantly to socio-economic development through their benefits as long as they are technically,

## *Water Control, Impacts and Sub-Regional Cooperation around a Transboundary Hydrological… DOI: http://dx.doi.org/10.5772/intechopen.105698*

economically and financially feasible [20]. It is a given [21] that dam development at the national and regional scale is the main factor of economic development, while basins with dams have an increased economic activity by 25% over those that have no dams [22]. In [23], it is seen that reservoir construction, groundwater exploitation and cropland irrigation are prime optimization instruments for water resource utilisation with particular success in Africa where dam construction balanced out water shortage.

However, the general picture of population increase for the three countries is as below (Base year 2022).

As dams are connected with social development, which includes population [25, 26]. **Table 2** shows that existing dam utilisation in these countries will come under rapidly increasing pressure. According to the World Bank Report [27], Senegal is classified as water-stressed country, as despite the fact that resources are plentiful there is high annual variability [28] with extreme precipitation [29] occurrences [30] and projections for 2035 show a withdrawal increase of 30−60%, the upper limit correlated with population increase. In the case of Guinea-Bissau, water resources are under pressure [31] from changing and variable climate, abstraction, the methodology for the disposal of wastewater and urbanisation rate while water stock depletion and water resource pollution are seen as being the major threats. Threats in Guinea are seen to materialise at the end of the century [32] where rainfall will be reduced by 26% in the Fouta Djallon Highlands, and the Konkouré River may see its flow reduced up to 50% while the Milo by up to 70%.

Although they are essential for development, dams must satisfy additional requirements, those of environmental, political, institutional and social acceptance [33]. Before dam construction resettlement costs and methodology play an important role as seen in [34] where a four-step method is described; and in a study of the Narmada Valley in India where cost-benefit analysis was applied including the assessment of the costs of displaced people [35]. Dams, '*the most cataclysmic event in the life of a riverine ecosystem*' [36], have environmental impact on water quality [37] which include the release of excessive sediment, eutrophication leading to anoxic conditions at the bottom [38] that reduces sulphate to acidic hydrogen [39], flooded [40] and pre-impoundment reduction of biomass which usually is burned, evaporation induced salt built-up [41] plus salt carried over by the rain due to proximity to an ocean [42]. As seen in [43], biophysical systems are impacted by dams primarily via the hydrograph change and river system fragmentation [44]. This leads [45] to changes in both sediment load and the morphology of the riverbed, as seen in [46] to the riparian areas' species composition and to aquatic biota in terms of both health and viability [47]. This is what the now extinct WCD [21] called double-edged developments. In this paper, only negative impacts affecting all or part of the basin are considered.


### **Table 2.**

*Population increase in Guinea-Bissau, Guinea and Senegal [24].*

From a hydrological point of view, the study of flows at the Wassadou and Sonaco downstream hydrometric stations showed a considerable decrease in flows which partly reflects the variability of rainfall [4]. River flow [48, 49] is one of the most determining factors of riverine ecosystems as seen in [50]. Regarding the effects of dams on flows, they alter flow quantity as well as water quality, and in terms of specific flow events, they impact all their main variables i.e., their change rate, seasonal timing as well as magnitude and duration [51, 52]. Moreover, the ecological instream flow is not respected despite the fact that it is very important [53] and according to Ennesser [54], there is, in fact, no instream flow. The analysis of the hydraulic distance separating the stations of the reservoir dams, using indices formulated by Payan [55], made it possible to deduce that the Confluent dam, the most downstream, is close to the Wassadou station. In other words, the surface of the intermediate zone acts more on the transfer of the flow than on the generation of flows. Thus, the flows are reduced by the dam. **Figure 2**, taken in the immediate surroundings of the Confluent dam, shows the small flow of water escaping from the structure. The lateritic track (red arrow) crossing the river just downstream of this dam is a shortcut to Pakour in the dry season. The stone in the middle makes it easier for pedestrians and people on bicycles to cross. In the rainy season, on the contrary, it is impracticable because of the significant flows that pass through the dam and possibly the spillway in case of spillage. At the Sonaco downstream station, there is a considerable distance between the reservoir and this station. The surface area of the intermediate zone being large, it is very likely that the phenomena linked to the generation of flows (lateral contributions, exchange with the aquifer, the contribution of rainfall on the intermediate zone, etc.) significantly support the flow [4]. A good monitoring of the hydrometric network and an in-depth analysis will make it possible to confirm or disconfirm the impact of the reservoirs on the flows downstream.

Moreover, on several occasions, the Guinea-Bissau authorities have complained to their Senegalese counterparts, and then to the OMVG, about the low quantities of water that arrive downstream because of the upstream reservoirs. Already in 1993 [56], before the put-in water of the Niandouba dam-reservoir in 1997, the French Society of Studies and Consultancy (SOFRECO in French), in the study of the Master Plan for the integrated management and development of the Kayanga/ Geba and Koliba/Corubal river basins, pointed out that the river behaves like a lake downstream from the Sonaco Downstream station. From this station, a few dozen kilometres away, the riverbed is without water until the village of Fasse, where water is only found in the form of a lake. This situation is verified as far as the village of

**Figure 2.** *Weak flow downstream of the Confluence dam, June 2013 [4].*

*Water Control, Impacts and Sub-Regional Cooperation around a Transboundary Hydrological… DOI: http://dx.doi.org/10.5772/intechopen.105698*

Sincha-Kagna. The little amount of water you see in these places comes from the aquifer that is outcropping.

From an ecosystem point of view, the vegetation formations of the Anambe watershed have disappeared, giving way to a mono-specific vegetation (rice cultivation). The pastoral space around the developed perimeters is reduced, in addition to the difficulty of access to certain water points by livestock. Unlike the Confluence reservoir, in the Niandouba reservoir, the standing timber was not fully recovered before the put-in water. Also, some plant species inside the reservoir have died of asphyxiation due to permanent submersion (**Figure 3**). These dead feet still present in the reservoir constitute an obstacle to fishing activity and are an integral part of the main objectives [4].

In some parts of the basin, there is a proliferation of invasive aquatic plants, such as Nymphea spp., Salvinia molesta, Typha australis and other unidentified species, linked to the lentic character of the waters. This proliferation will induce a modification of the environmental conditions: the formation of sandbanks caused by the root system and reduction of the oxygen available in the water. According to STUDI International [10], aquatic plants constitute microcosms where many vectors of waterborne diseases (bilharzia, filariasis, malaria, and onchocerciasis) live and feed.

Also, the decrease of the flow speed in the downstream part of the basin (Guinea-Bissau) has the effect of creating favourable conditions for sand deposits in the major river bed [17], as illustrated in **Figure 4**. The penetration of the tide over a length of more than 150 kilometres inland and the rising of the salty surface water are the cause of the salinisation of several rice fields in Guinea-Bissau [17].

The developments have caused an increase in conflicts related to access to water. The most frequent ones are related to livestock wandering, particularly in the developed areas. Indeed, in these perimeters, which more or less form a belt, there is no provision for grazing in accordance with the requirements of pastoralism [57] for livestock access to the confluence reservoir. In the dry season, when the water points dry up, herders are forced to make tracks through the irrigated areas to give their herds water. The ensuing conflicts may be reported to the gendarmerie or, more often, settled out of court. However, since the arrival of farmers from the groundnut basin of Senegal, relations with the breeders have become more strained, and complaints to the gendarmerie and impoundments have increased [57].

Land conflicts are most often between indigenous and non-indigenous people. The latter is considered by the natives as privileged competitors of SODAGRI, which was in charge of the exclusive distribution of developed plots. Between 2005 and

**Figure 3.** *Asphyxiated vegetation upstream of the Niandouba dam, June 2013 [4].*

**Figure 4.** *Silting in the major bed of the Kayanga/Geba River downstream [17].*

2009, due to the resurgence of conflicts, a forum on land management enabled the municipal councils to regain their prerogatives and to take charge of the allocation and decommissioning of developed plots of land under the approval of the Sub-Prefect and the technical assistance of SODAGRI [58].

In 2018, a conflict opposed the inhabitants of villages along the river in the commune of Pakour to a private promoter. At the origin of this conflict, the municipal council granted 1000 ha to the promoter for the establishment of a banana plantation. After about 10 hectares were cleared, the inhabitants of these villages mobilised to demonstrate their refusal. The establishment of this banana plantation would prevent a tenth of villages from accessing the river; their only source of life (fishing to meet their needs, market gardening, rice growing, and watering places for their cattle) and the loss of their production fields.1 The event resulted in the arrest of 10 young people from the commune who were held in custody, referred to the prosecutor's office in Kolda and finally tried and sentenced to 2 months in prison.<sup>2</sup>

From a health point of view, the stagnant water has created conditions favourable to the development of numerous pathologies that affect the populations living in the Anambe basin. According to CSE [59], there are water-related vector diseases (malaria, onchocerciasis), water-borne diseases (diarrhoea, dysentery, typhoid fever) and water-borne diseases (urinary or intestinal bilharzia). Malaria is the primary reason for consultation in all health posts, both during the rainy and dry seasons. Urinary bilharzia is increasingly becoming a serious concern with cases detected in Kounkane, Wassadou and Medina Dianguette [59]. The cases of diarrhoeal diseases (dysentery and diarrhoea) detected in Kounkane over the period 2004−2009 include 801 cases in 2004, 993 in 2005, 1132 in 2008 and 1087 in 2009. This upward trend is observed at the Sare Coly Salle and Diaobe health posts. Dermatoses were diagnosed at the Kounkane health post, rising from 95 cases in 2004 to 125 in 2009, with a peak of 163 in 2007 [57].

The use of fertilisers and plant protection products in the irrigated areas of the Anambe zone risks polluting surface and groundwater in the long term. Indeed, the water taken from the Lake Waima in the Anambe basin for the irrigation of the

<sup>1</sup> https://www.koldanews.com/2018/03/29/pakour-velingara-les-populations-du-kayanga-contre-limplantation-dune-bananeraie-a820953.html

<sup>2</sup> http://www.enqueteplus.com/content/kolda-litige-foncier-dans-la-commune-de-pakour-10-jeunesmanifestants-arrêtés-seront-jugés

*Water Control, Impacts and Sub-Regional Cooperation around a Transboundary Hydrological… DOI: http://dx.doi.org/10.5772/intechopen.105698*

### **Figure 5.**

*Circuit schema of the irrigation water in Lake Waima (inspired by SODAGRI).*

perimeters is returned directly to it via the drainage channels, without any treatment. This constitutes a closed circuit as illustrated in **Figure 5**. However, a study carried out by the CSE over the period 2004−2008 showed that, from a physicochemical point of view, surface water is poorly mineralised, given the chemical parameters measured, the levels of which are below the usual standards [57]. Therefore, the analyses do not reveal any pollution likely to alter the quality and suitability of the water. Concerning groundwater, nitrate levels that were limiting the probability of occurrence have increased significantly with a maximum value of 130.94 mg.1-1 in June 2008. The traditional wells most affected by the presence of nitrates are in the villages of Maoude (130.94 mg.1-1), Dialakegny (97.57 mg.1-1), Kandia (62.43 mg.1-1) and Sare Koutayel (58.94 mg.1-1) [57]. These excessive concentrations constitute risks for the populations that use the water from these wells without any pre-treatment. Also, the populations of the bordering villages complain about the resurgence of intoxications that affect them and their livestock [57, 60].
