Flood vulnerability assessment of donstream area in Mono basin in Yoto district, south-eastern Togo
par Abravi Essenam KISSI
University of Lome - Master 2014
Mono River system is the largest river system in Togo with catchments area of 21500 km2; it serves as eastern boundary between the Yoto district and the Republic of Benin. The district is located in South-Eastern Togo, North-East of the Maritime region. It is geographically bound by latitude 6°30` and 6°60`N, longitude 1°20` and 1°35`E. It is bordered by the Haho district to the north, Bas-Mono and the Vo districts to the south, the Zio districts to the west and Republic of Benin to the east. The study was conducted in the downstream area of the Mono River basin in eight villages of Sedome (Mawussou, Djrekpon, Batoe), Esse-Godjin (Tofakope, Atikpatafo), and Tokpli (Kpodji, Tchakponou-kondji and Logokpo) counties, in the Yoto district "Map 1" .The selected villages fall under the hazard prone area, where populations have been affected, especially during 2010 flood event, providing then a better study population who can help us to generate a better view on the assessment conducted.
The study area is formed by hydromorphous soils which are rapidly saturates of water. The sand contents decreases, depending on the closeness of the area to the river. The geology consists of the continental shelf called the terminal plate which extends from Kouvé area to the north-western of Sedome.
The vegetation is a savannah and is composed of the classified and gallery forests and various grassland grasses.
The fauna consists of mammals (buffalo, warthogs, monkeys, deer, agouti etc.) and various birds of prey, aquatic life, crocodiles and hippos.
Map 1: Map showing the targeted villages
The study area, which is at an altitude that ranges from 17 to 55 meters above sea level, has Guinean sub-equatorial climate with two distinct rainy seasons separated by dry periods which are influenced by the movement of two (2) types of winds at different times of the year. The mean annual temperature ranges from 22°C to 30°C and precipitation varies between 800mm and 1200 mm/year; this usually peaks in May-June and September-October. The Mono River has a pluvial law which has changed in the downstream part of the basin due to the construction of Nangbéto dam in 1987 for hydroelectric purposes. Thus, it passed from the irregular to a relatively regular flow due to the release of water of the dam. Before the construction of the Nangbéto dam, the Mono River presented the phases of low water with null flow and height from mid-December to the third week of May, whereas from May until December the river experienced high flow with average maximum of (450 m3/s) in September. This is changed after the construction of the dam with a relatively permanent out-flow at the downstream part ( Ago et al 2005).
The study area is made up of three counties (Sedome, Esse-Godjin and Tokpli). According to the Togo Population and Housing Census Report in 2010, the total population of the three counties was estimated at about 34918 with 10803 in Sedome, 9261 in Esse-Godjin and 14854 in Tokpli. The majority of the population is located in the River floodplains. Agriculture is the most important activity being carried out in the area with a majority of the people living practising subsistence farming.