**3. Water control in the basin**

Water control generally involves the construction of dams, if necessary, which make it possible to compensate for the irregularity of seasonal or interannual water supplies by accumulating reserves. Dams are artificial structures built across the bed of a river to retain water or provide an artificial reservoir [11]. Thus, the benefits of an agricultural dam will be felt very gradually, as cultivation processes evolve, which we know are slow [12].

During the first phase of the development of the Anambe basin (Senegal), the Confluent dam-reservoir was built 300 m downstream from the Kayanga/Geba and the Anambe confluence. With a storage capacity of 59 million cubic meters, it was built in 1984 and diverts the flow of the river to fill the Anambe basin and irrigate 1365 ha [13]. In the non-rainy season, the water is blocked by the Kounkane weir. After more than a decade of exploitation, it was found that the additional water provided by this dam was not sufficient to achieve the objective of double cropping, due to rainfall deficits, coupled with significant water leakage downstream of the system, estimated at more than 50% of the runoff. These water leaks resulting from errors in the construction of the dam (defective retaining dyke), considerably reduce the possibilities of storing water [14]. It is in this context that the second phase was started with the construction of the Niandouba dam-reservoir in 1997, in addition to the development of new perimeters covering an area of 2805 ha. Located 10 km upstream of the Confluence reservoir, with a storage capacity of 85 million cubic metres, it provides a backup to this buffer reservoir. The main objectives are: to store water during the rainy season in order to provide the necessary complement to secure offseason crops in the Anambe basin; to allow the development of continental fishing in the reservoir in all seasons; and to contribute to the recharging of the underground water for human and animal water supply. This has resulted in improved hydrological conditions with over 100 million cubic metres of water available, allowing for relative water control in the Anambe-Kayanga/Geba system [13].

In 2012, PAPIL built the Velingara-Pakane dam-reservoir upstream of the Niandouba dam-reservoir to irrigate areas on the right bank of the river. The storage capacity is 1.5 million cubic metres.

Despite these dams, water control in this part of the basin is low, because development and production objectives have not yet been achieved due to, firstly, the rainfall deficit and, secondly, the production factors. However, a new dam project is envisaged at the confluence of the Niokolo-Koba and Koulountou rivers, tributaries of the Gambia River. It is expected to divert water from these tributaries, via a connecting channel, to reinforce existing reservoirs in order to expand the area cultivated and increase the production [15].

In Guinea-Bissau, on the contrary, there is no water control proper, because no hydro-agricultural development has been carried out, even though the country has a very old rice-growing tradition that is highly dependent on rainfall. According to STUDI International [10], rice production in mangrove and lowland areas is facilitated by the provision of salt dikes and water reservoirs. In the non-rainy season, small areas are irrigated from the river using motor pumps placed along the riverbanks. But irrigated agriculture is still in its embryonic stage. Enormous potential in developable lowlands has so far been little used for rice cultivation [16]. Today, despite the low level of development of the agricultural potential, the agricultural activities developed on the riverbanks are affected by the difficult climatic conditions combined with the hydraulic dams built in the Senegalese part of the basin. The difficulties in supplying drinking water to households are noted, and the strong degradation of ecosystems and the rise of the salt tongue are severely felt by the local populations [17].
