A GIS based flood risk mapping along the Niger-Benue river basin in Nigeria using watershed approach

Abstract

Floods are water induced disasters that lead to temporary inundation of dry land and cause serious damages in the affected location such as loss of lives and properties and destruction of infrastructures. They have become common occurrences in every part Nigeria and the recorded impacts of flooding on the inhabitants are alarming, causing hundreds of deaths and rendering thousands homeless. The impact of floods on people globally has led to the development of mitigation measures that could reduce the associated risk of floods to a manageable point. The management of flood risk begins with identification of areas prone to flood. This study used the scientific technique of GIS to identify flood risk areas along the River Niger-Benue basin. Satellite imageries SRTM DEM that covers the study area was used in this research. Monthly rainfall data was used to generate maps of standardized precipitation index (SPI) for thirty years (1978 to 2007). The SPI maps were used to determine the degree of precipitation condition across Nigeria and also to identify the locations where flood events are being triggered. The SRTM DEM was used to generate the flow direction and flow accumulation maps. Flow direction and Flow accumulation were used to generate the watershed and flood risk map. The flood risk map shows that 45% of Nigeria towns and villages are within the flood risk zone. Finally, some recommendations were made which will help the policy makers improve on flood management in the country.

Hydroclimatology of the Kaduna River Basin

“…Mean annual P, PET, ET a , and R in mm, P-PET in mm, and ratios of PET/P, ET a /P, R/P and ET a /PET for the ten locations across KRB. is enough R generated during the rainy season of every year, a perfect characteristics of tropical climate (Oguntunde & Abiodun, 2013;Ologunorisa & Durowoju, 2014;Oguntunde et al, 2014Oguntunde et al, , 2016Akinbobola et al, 2015;. Additionally, for all the locations, the ratio of hydrological-year ET a to hydrological-year P ranges from 0.65 (Location 9) to 0.95 (Location 1), and the runoff efficiency (hydrological-year R/hydrological-year P) ranges from 0.27 (Location 1) to 0.44 (Location 7) (Table 1).…”

Global Sustainable Development Report 2019

“…In Africa, satellite images have been used to identify flood risk areas in Namibia, 837 Senegal (Box 8-9) and Sudan (Box 8-7); and data from satellite imagery has been combined with GIS and precipitation data to produce a flood risk map along the Niger-Benue river. 838 Nigeria is participating with UK, Spain and China, in the Disaster Monitoring Constellation (DMC), 839 the first Earth observation constellation of low cost small satellites providing daily images for applications including global disaster monitoring. The Disaster Monitoring Constellation aims at providing both commercial and free satellite imagery for humanitarian use in the event of major international disasters.…”

Applications of Open-Access Remotely Sensed Data for Flood Modelling and Mapping in Developing Regions

“…Nigeria, used as the case study for this review is located downstream of the Niger Basin ( Figure 4) which collects run-off from a 2,156,000 km 2 area and passes this through the Niger and Benue rivers [165]. Thus, Nigeria is prone to fluvial flooding, which exposes floodplain dwellers to diverse negative consequences [166][167][168][169]. Nigeria recently experienced unprecedented levels of flooding attributed to poor dam water release management and risk communication, linked to data unavailability for informed and prompt decision making [165].…”

“…RS has been applied in seven sub-categories of flood management in Nigeria: (i) vulnerability assessment: integrating socio-economic and biophysical factors to ascertain a regions' coping capacity in relation to flood exposure [186][187][188]; (ii) flood frequency analysis: estimating expected flood magnitudes by fitting historic flood time series to a suitable probability distribution or combining hydrological data from regions of physiographic similarity [179,189,190]; (iii) rainfall intensity-duration-Frequency: applying rainfall data to gives an idea on return period of rainfall intensity which can be expected for a defined period [191,192]; (iv) hydrodynamic modelling: once flood estimates are determined, the outcomes are routed in 1/2 dimensional models in combination with terrain data to derive flood hazard information such as inundation extent, depths and /or velocity [193]; (v) flood risk mapping: other than hydraulically modelling flood hazard, flood depths and inundation extent for a particular point in time can be directly determined using satellite images and digital elevations models [21,167]; (vi) floodplain encroachment analysis: the increasing development of industries and settlements within the floodplain increases exposure and vulnerability [188,194]; (vii) rainfall varibility assemment: understanding the degree to which the amount of rainfall across an area varies through time and space [195,196]; and RS and GIS approaches are used to monitor floodplain encroachment, to ensure adherence to, and enforcement of flood management policies [197,198]; and (viii) water resource management: adoption of GIS and RS for sustainable water resource management [199]. Figure 7 shows the flood studies application areas in Nigeria, revealing vulnerability mapping, flood frequency assessment and risk assessment are the main areas of interest.…”