Volume estimation of soil stored in agricultural terrace systems: A geomorphometric approach

High-resolution topographic (HRT) techniques allow the mapping and characterization of geomorphological
features with wide-ranging perspectives at multiple scales. We can exploit geomorphometric information in the
study of the most extensive and common landforms that humans have ever produced: agricultural terraces. We
can only develop an understanding of these historical landform through in-depth knowledge of their origin,
evolution and current state in the landscape. These factors can ultimately assist in the future preservation of such
landforms in a world increasingly affected by anthropogenic activities. From HRT surveys, it is possible to
produce high-resolution Digital Terrain Models (DTMs) from which important geomorphometric parameters
such as topographic curvature, to identify terrace edges can be extracted, even if abandoned or covered by
uncontrolled vegetation. By using riser bases as well as terrace edges (riser tops) and through the computation of
minimum curvature, it is possible to obtain environmentally useful information on these agricultural systems
such as terrace soil thickness and volumes. The quantification of terrace volumes can provide new benchmarks
for soil erosion models, new perspectives to stakeholders for terrace management in terms of natural hazard and
offer a measure of the effect of these agricultural systems on soil organic carbon sequestration. This paper
presents the realization and testing of an innovative and rapid methodological workflow to estimate the
anthropogenic reworked and moved soil of terrace systems in different landscapes. We start with remote terrace
mapping at large scale and then utilize more detailed HRT surveys to extract geomorphological features, from
which the original theoretical slope-surface of terrace systems were derived. These last elements were compared
with sub-surface information obtained from the excavations across the study sites that confirm the reliability of
the methodology used. The results of this work have produced accurate DTMs of Difference (DoD) for three
terrace sites in central Europe in Italy and Belgium. Differences between actual and theoretical terraces from
DTM and excavation evidence have been used to estimate the soil volumes and masses used to remould slopes.
The utilization of terrace and lynchet volumetric data, enriched by geomorphometric analysis through indices
such as sediment conductivity provides a unique and efficient methodology for the greater understanding of
these globally important landforms, in a period of increasing land pressure.