A multi-method approach to analyze changes in gully characteristics
between 2009 and 2018 in southeast Nigeria
Abstract
Gully erosion is the dominant environmental problem in southeast Nigeria
and has led to loss of human and material resources. In this study, we
evaluated changes in gully characteristics in southeast Nigeria between
2009 and 2018 using a multi-method approach including geotechnical
investigations, analysis of high-resolution satellite imagery (2 – 5 m)
and focus group discussions. Gully numbers increased from 26 to 39 and
mean gully length increased from 0.39 to 0.43 km. We found that the
soils in the study area have low cohesion and high sand content which
make them susceptible to dispersal by erosive forces. Land adjacent to
rivers had the highest concentration of gullies, and there was a sharp
rise in slope from 10 – 58.2% within a distance less than 500 m from
the river. Regarding potential gully-drivers, land-use changes were
observed. Non-vegetated lands increased from 58.6 km2 to 144.7 km2
between 2009 and 2018, while reductions in fallowed lands from 281.2 km2
to 57.8 km2 were observed. Results from focus group meetings indicate
there was no gullying in the area before the Nigerian civil war.
Although war-time activities which led to initiation of oldest gullies
have ceased, land-use changes likely increase volume of surface runoff.
We infer that interactions between soil conditions which potentially
enhance seepage erosion and higher surface runoff resulting from
land-use changes have propagated gullying in the study area post-civil
war.