Gis-based digital soil map for gully erosion management in anambra, South Eastern Nigeria

Digital soil maps offer solutions to several environmental issues, for example; gully erosion hazard, and flooding. The availability and production of such maps have been fundamental to recent advances in GIS and other related technologies. This paper describes the production of a digital soil map for Anambra, south eastern Nigeria, using GIS technology. Sheets 7 and 8 of hardcopy soil map of Nigeria each at a scale of 1: 650,000 were scanned and spatially referenced to WGS 1984 coordinate system. In a GIS, these images were subset, mosaicked and vectorized on-screen. A non-spatial database was created, by means of soil properties, for example; geology, slope, topography, and soil pH values, and linked to the vectorized data. Queries were built into the database, to simplify extraction of soil information to users of the digital soil map. Other soil thematic maps were produced. The results of the study tend to show that the soil distribution of the study area, is consisted of seven different soil mapping units (2a, 2c, 5c, 5d, 6a, 9a and 17a), occupying about 37.38%, 14.60%, 1.05%, 8.84%, 3.99%, 27.81% and 4.35% of the area respectively. Mapping units 2a and 9a appear to be dominant in the area and their characteristics seem to substantially contribute to the phenomenal gully erosion in the area.