## Stations

A network of hydrolometric stations has been set up in Mali and Guinea. At some of these stations data are collected on a daily basis already more than a century. The monitoring of water quantity and quality in Mali and Guinea is managed by the Direction National Hydraulique. The operational monitoring on a local level is organised by the regional administrative levels of DNH in both countries. Water levels are measured daily using gauges; telemetric measurement is in study and development but not operational yet. The principal parameter monitored is the daily water level; discharge is derived from existing information on the bathymetry of the river at the cross section of the hydrometric stations.

In the table below the hydrometric stations are listed per country and tributary, and the year is given from which the first data are available. For most of the stations, the data are incomplete for the decennia in the first half of the 20^{th} century.

Station |
tributary |
Country |
data since |

Baro | Niandan | Guinea | 1947 |

Kankan | Milo | Guinea | 1938 |

Mandiana | Sankarani | Guinea | 1954 |

Kouroussa | NIger | Guinea | 1970 |

Dialakoro | Niger | Guinea | 1954 |

Faranah | Niger | Guinea | 1955 |

Sélingué | Sankarani | Mali | 1964 |

Banankoro | Niger | Mali | 1967 |

Koulikoro | Niger | Mali | 1907 |

Bamako | Niger | Mali | 1949 |

Niger | Mali | 1952 | |

Kirango | Niger | Mali | 1925 |

Douna | Bani | Mali | 1922 |

Bénény-Kegni | Bani | Mali | 1951 |

Sofara | Bani | Mali | 1953 |

Ké-Macina | Inner Niger Delta | Mali | 1953 |

Mopti | Inner Niger Delta | Mali | 1922 |

Akka | Inner Niger Delta | Mali | 1907 |

Niafunké | Inner Niger Delta | Mali | 1933 |

Goundam | Inner Niger Delta | Mali | 1931 |

Diré | Inner Niger Delta | Mali | 1931 |

Kouroumié | Inner NIger Delta | Mali | 1975 |

## Water levels Niger and tributaries

The water levels in the catchment of the Niger and tributaries is monitored at 6 hydrometric stations in Guinea and 15 stations in Mali. In each of the tributaries there are two or more stations. The available data for Guinea are given in five interactive graphs, three tributaries in the Upper Niger Basin: the Niandan at Baro, the Milo at Kankan and the Sankarani at Mandiana, and two stations along the Niger: Kourassa and Dialakoro. The graphs are shown below. The measurements are daily, but in some cases interpolated for periods during which there were no data. The latter data have been deleted as far as possible. To show that these interpolation may produce wrong results, one has not been removed (see straight blue line in the Mandiana graph between 1-8 and 1-11.

*The daily variation in water level (cm) in Baro (Niandan River) since 1970 between 1 April and 1 April the next year.*

*The daily variation in water level (cm) in Kankan (Milo River) since 1970 between 1 April and 1 April the next year.*

*The daily variation in water level (cm) in Mandiana (Sankarani River) since 1955 between 1 April and 1 April the next year.*

*The daily variation in water level (cm) in Dialakoro (Niger River) since 1954 between 1 April and 1 April the next year.*

*The daily variation in water level (cm) in Kouroussa (Niger River) since 1954 between 1 April and 1 April the next year.*

The data on water levels are presented below in interactive graps, the first graph shows the water levels per station per month, the second the water levels per station per year. Interpolated data in the interactive graphs are still present (visible as straight lines).

The data from Baro, Kankan and Mandiana represent the water levels in the upper reaches of the Niger, respectively in its tributaries Niandan, Milo and Sankarani. The other stations represent the water level further downstream. Koulikouro, Kirango and Ké-Macina give the water levels in the Niger proper. Ké-Macina is situated at the entrance of the Inner Niger Delta. The data of the latter station is used to assess the inflow of the Niger into the Inner Niger Delta; see below

*The daily variation in water level (cm) in Macina (Niger River) since 1953 between 1 June and 1 June the next year.*

## Water levels Bani

There are three hydrometric station in the Bani: Douna, Bénény-Kegni and Sofara. In the past, Douna was used as main hydrometric station to capture the flow of the Bani, but since the construction of the Talo dam (2007) the stations of Bénény-Kegni and Sofara gives a better picture of the flow of the Bani. At a high flood, part of the Bani flows directly to the Niger River along the Manga tributary, from Djenné to Kouakarou. This shortcut between the Bani and the Niger is situated downstream of Bénény-Kegni and upstream of Sofara.

*The daily variation in water level (cm) in Bénény-Kegni (Bani River) since 1952 between 1 June and 1 June the next year.*

## Seasonal variation of the flood level

When the first rains arrive in May in the upper reaches of basin in Guinea, the water level in the Inner Niger Delta is nearly at its lowest level. Then, the floodplain is desiccated apart from the river proper and some permanent water bodies. As rainfall progresses, the discharge of the Niger and Bani increases and gradually flooding starts in the most southern parts of the Inner Niger Delta. The seasonal flood pulse enters the delta at Ké-Macina (Niger) and Sofara (Bani) and inundates a huge part of the floodplains between Djenné in the south and Tombouctou in the north.

The seasonal flood pulse is illustrated by the water levels at the stations in Mopti and Dire. The flood moves as a wave through the delta, which means that in the same year not all floodplains of the delta are flooded at the same time. Flooding starts in the south in August and in most years the peak in Mopti is reached in the first half of October. The water level in the centre and north of the delta is still rising at that time. In the centre of the delta the flood peak and maximal flooding in most years is reached in the second half of October or November, and in Dire about a week later. The southern floodplains already run dry at the time.

*The daily variation in water level (cm) in Mopti since 1923 between 1 June and 1 June the next year**. When the flood is low, the peak is reached in early October, but in wet years, the peak is more than a month later. Data DNH.*

*The daily variation in water level (cm) in Diré since 1922 between 1 June and 1 June the next year. When the flood is low, the peak is reached in early November, but in wet years, the peak is two months later. Data DNH.*

The data on water levels are presented below in interactive graps, the first graph shows the water levels per station per month, the second the water levels per station per year.

**Annual variation of the flood level **

The graph below shows the annual variation in the highest flood level, as measured in Mopti, Akka and Diré. The water level has been measured daily on the gauge of Mopti since 1923, Akka since 1955 and Diré since 1931. Lacking years could be reconstructed using the annual peak levels measured in other hydrometric stations, which are highly correlated (see graphs below showing the relationship between Mopti and Akka and between Diré and Akka). The peak flood levels before 1923 have been derived from the relationship between the monthly average flow at Koulikoro in september and the maximal flood level in the Inner Niger Delta in the same year.

*Annual peak flood levels in Mopti, Akka and Diré since 2007.*

*The relationship between the peak flood level in Mopti as a function of the peak level reached in Akka in the same year.*

*The relationship between the peak flood level in Diré as a function of the peak level reached in Akka in the same year.*

## Annual inflow into the Inner Niger Delta

The Inner Niger Delta is flooded due to the large discharge of the Niger and the Bani during and after the rainy season. To estimate the annual inflow into the Inner Niger Delta, the daily measurements of the water level (measured in cm on the local gauge) have to be converted into daily discharge (m^{3}/s) using measurements at a wide range of water levels. The relationship between water level and river flow is not linear and DNH uses third-degree polynomials to get a good fit (Brunet-Moret *et al*. 1986; Zwarts & Diallo 2002).

The maximal flood level in the Inner Niger Delta is due to the discharge of the Niger and the Bani in the months before the peak is reached, thus still during incoming water which is for the Inner Niger Delta, on average, about 15 November. The annual variation of the inflow during incoming water is shown for three stations in the Bani.

*The total annual flow of the Bani during incoming water (1 June – 15 November) measured at three stations.*

Douna which was always the main hydrological stations for the Bani cannot be used anymore since the construction of the Talo dam downstream of Douna. Béneny-Kegni can be used very well instead, however, given the close relationship between the annual inflow for both stations:

*Bénény-Kegni (km ^{3}/year) = 0.9135 * Douna (R^{2}=0.989, n=52, calculated for the years 1952-2005). *

In contrast, Sofara deviates from Douna and Bénény-Kegni. As the graph shows the discharge is the same for both stations in dry years when the total discharge of the Bani is lower than 7 km^{3}.

*The annual discharge in Sofara as a function of the discharge in Bénény-Kegni in the same year, both calculated for the same period (1 June – 15 November). The straight line gives the expected relationship if both would be equal. If the total discharge of the Bani is larger than 7 km ^{3}, an increasing fraction of the water does not reach Sofara, because more and more water from the Bani River flows before Sofara to the Niger River, from Djenné to Kouakourou along the Manga tributary.*

The total annual inflow of Bani and Niger into the Inner Niger Delta equals the sum of the flow as measured at Macina for the Niger and at Bénény-Kegni for the Bani (see graph below).The flow of the Niger is, on average, four times larger than those of the Bani.

*The total annual flow at incoming water (1 June – 15 November) of the Niger (Macina) and the Bani (Bénény-Kegni).*

The Bani flows just before Mopti into the Niger. Thus, the gauge at Mopti measures the combined flow of Niger and Bani. Indeed, the trend at Mopti resembles those at Macina and Bénény-Kegni, with high flows in the 1950s, declining flows until 1990s and partial recover since then. However, the total flow at Mopti is lower than Macina and Bénény-Kegni and even lower than Macina alone.

*The total annual flow at incoming water (1 June – 15 November) of the Niger and BVani combined at Mopti.*

A separate graph shows the relationship between Mopti and Macina + Bénény-Kegni. In dry years, 68% of the flow of the Niger and Bani combined passes Mopti in dry years (13 km^{3} from the total flow of 20 km^{3}), but this fraction declines to 45% in wet years (30 km^{3} from the total flow of 65 km^{3}). The explanation is that a part of the water flows between Macina and Mopti directly into the Inner Niger Delta, primarily along the Diaka at Diafarabé, and further downstream, to a lesser degree, also along the Mayo Dipouli, Sogano, Mayo Moura, Mayo Kotaba and Mayo Dongue. The higher the river discharge, the larger the fraction flowing into the Inner Niger Delta upstream of Mopti.

*The total annual flow at incoming water measured in Mopti as a function of combined flow of the Niger (Macina) and the Bani (Bénény-Kegni) measured further upstream. The straight **line gives the expected relationship if both would be equal. At higher river discharge, an increasing fraction of the water does not reach Mopti, because more water from the Niger River flows after Macina, and before Mopti, directly into the Inner Niger Delta.*

## Annual river flow and peak water level

The annual peak flood level in the Inner Niger Delta, such as measured in Mopti, Akka and Diré, is determined by the flow of the Niger and the Bani. The three graphs show that the relationships are close, but not linear. Hence that third-degree polynomials were calculated to fit the relationships.

It is important to know these relationships and also that the relationships are so strong. Using these data, it is possible to indicate precisely what would be the impact on the flooding of an upstream infrastructure when it is known how much water is taken from the river during incoming water.

*The maximum annual flood level in Mopti as a function of the annual discharge of the Niger (measured at Macina) and the Bani (measured at Bénény-Kegni) during incoming water (1 June – 15 November).*

*The maximum annual flood level in Akka as a function of the annual discharge of the Niger (measured at Macina) and the Bani (measured at Bénény-Kegni) during incoming water (1 June – 15 November).*

*The maximum annual flood level in Diré as a function of the annual discharge of the Niger (measured at Macina) and the Bani (measured at Bénény-Kegni) during incoming water (1 June – 15 November).*