Analysis of Urban Floodplain Encroachment: Strategic Approach to Flood and Floodplain Management in Kaduna Metropolis, Nigeria

Abstract

This study was aimed at monitoring, mapping and characterisation of floodplain encroachment patterns on the River Kaduna floodplain in Kaduna metropolis, Nigeria,as part of the approach to flood hazard evaluation, flood risk assessment and effective flood and floodplain management. A Topomap of 1967 was used to extract the base built-up layer, while Landsat.TM, 1987, Spot.XS, 1995, Landsat.ETM, 2001 and Quickbird, 2006 were used to generate other built-up layers, which were extracted by digitization and converted to polygon shape files and later used for overlay analysis. A Digital Elevation Map (DEM) of the area was used for delineation of floodplain boundary. ArcGIS sorfware 9.0 operational tools was highly robust and flexible for mapping and analysis of urban growth patterns and characterisation of floodplain encroachment by communities. From the results, it was observed that the highest extents and rates of encroachment are recorded by communities in the proximity of the Central Business District (CBD) such as T/Wada, Ung. Rimi, Barnawa, Doka and the industrial layouts of Kakuri and Kudenda. These areas are the centers of highest socio-economic infrastructure which implies greater flood risk and damage potential in the event of flooding. Results also showed that about 52.83% of the urban segment of the River Kaduna total floodplain area of 48.55km², has been encroached by built-up. As a result of this pattern of encroachment, strong institutional framework and investment towards effective floodplain management is recommended

Characterization of Sprawling in Kaduna Metropolitan Area

“…Erdas imagine 8.5 image processing software was used for classification of images, while ArcGIS software was used for the cartographic or spatial modeling of urban growth using over-lay analysis of vector layers of urban built-up layers extracted by digitization. The multi-temporal satellite data sets which transforms LULC by means of "Change detection" techniques executable on satellite data that are heterogeneous for spatial and spectral resolution with homogenization and registration in a unique digital information environment [4]. Kaduna urban growth map was composed and used in the measurement and monitoring and analysis of spatio-temporal dynamics of Kaduna urban spatial growth patterns.…”

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

“…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.…”

Managing Infrastructure in the Stream Environment

“…Riparian buffer protection, revegetation, and removal of bank armoring is necessary to reestablish natural wood recruitment (Abbe and Brooks 2011) Floodplain encroachment occurs with development and earthen fill in the floodplains and bridge and roadway embankments that cross or parallel a river Infrastructure within floodplains is exposed to flood hazards including inundation and fluvial scour or deposition. Floodplain encroachment reduces a floodplain's ability to naturally store and convey floodwaters, which can increase flooding downstream, resulting in local and downstream channel instability and impacting sensitive riparian habitat (Jordan et al 2010;Ndabula et al 2012) Floodplain development should first be avoided by removing obsolete infrastructure, relocating old or damaged infrastructure, and siting new infrastructure outside of the floodplain (Pottier et al 2005). Infrastructure within the floodplain should be designed for flood resiliency (Lennon et al 2014…”