While different parts of the region have some minor erosion issues, one exception is the Wither Hills where previous investigations have shown severe tunnel gully erosion has occurred and is still occurring in some of the loess soils. This is despite of extensive historic remedial works i.e. contour chisel ploughing and gully infilling on parts of the hills.
Current soil mapping indicates that these same loess soil types are also present in the hill soils to the southeast of Blenheim, suggesting that the erosion risk may also be present elsewhere in the area. However, current soil mapping is at a scale (i.e. 1: 250 000) that makes it difficult to accurately differentiate between different soil types and estimate the true extent and distribution of these potentially unstable soils. These hills are viewed as a desirable location for residential development. Hence it is important that we have reliable information about the location and erosion risk of these soils.
The aim of this study was to map the spatial distribution of soils in the hills southeast of Blenheim that have the potential for erosion, and to determine what risks they pose to infrastructure and buildings.
More than 470 soil observations were made across an area of approximately 1600 ha of the Wither and Redwood Pass Hills south and southeast of Blenheim. The details recorded at each soil observation included identification of the soil series, the location, altitude, slope angle and aspect; the landform type; the slope length; the nature of the soil materials; extent of site erosion; type of site erosion and depth of gully. Soil data recorded included brief descriptions of the horizon sequences, soil colours, textures, mottles and stone presence.
A report summarising the findings has been compiled.