Mapping soil moisture as an indicator of transport corridor slope instability using remotely sensed data

Much of the world's transport networks are located on cuttings and embankments. In the UK many of these earthwork structures were constructed in the mid-19th Century and are therefore susceptible to slope instability. Instability in transport corridors tends to manifest itself through shallow slope failures. The trigger for such failures is an increase in pore water pressure which is directly affected by an increase in soil moisture. Transport network operators carry out appraisals of their earthworks by making crude observations of soil moisture conditions in the absence of an efficient technique for making in situ measurements. Remote sensing offers the potential to monitor long stretches of transport corridor but currently there is no method for characterising soil moisture that can be considered operational or cost effective. This study explores the use of airborne Light Detection and Ranging (LiDAR) to map soil moisture distribution for a transport corridor near Haltwhistle, Northumberland. Terrain analysis calculations, namely potential solar radiation and a topographic wetness index, are applied to a fine scale DEM interpolated from the LiDAR point data using the AnuDEM routine which ensures consideration of hydrological flow. The relationships between soil moisture and the terrain analysis calculations are explored using both global and local (geographically weighted) regression analysis. It was found that a combination of the potential solar radiation calculation and the topographic wetness index, expressed by the natural logarithm, provided the best results (R2 = 0.65).