| Rills are narrow and shallow watercourses that usually form on recently cultivated soils after an intense rainfall. Rills appear in natural environments, unaffected by human disturbance where highly erodible lithological materials, unprotected by vegetation, occur in combination with steep slopes, and with intense runoff generation. The primary objective of this thesis is to examine a number of natural rill systems on different lithological materials, in attempt to identify the key properties and processes which control their geometric characteristics. To ensure a range of lithologies and climatic and seasonal conditions, the study was carried out in, and with materials from, three badland areas in Ontario and Alberta, Canada, and Tuscany in Italy. In each badland area, well developed rill networks were selected for detailed measurements of geometric characteristics. Surface and subsurface samples were collected from rills and interrills and tested for mineralogy and chemical properties. Large bulk samples of unweathered materials were collected from each site for laboratory weathering experiments.; Based on the amount and type of clay minerals, the lithologies tested can be grouped into three categories: sandstones and siltstones (clay minerals ∼20%), smectite-rich mudrocks and smectite-poor mudrocks. Even though indices for geometric characterisation of larger drainage systems showed that rill systems have different properties on different lithologies, they did not identify more subtle differences in rill properties within one lithological unit. The main reason is the scale difference between rill systems and fluvial systems. Smaller rill systems are more sensitive to changes in microtopography than larger drainage systems for which these geometric indices were designed. The second reason is the high number of lithological varieties in each unit.; Research has shown that rill system geometric characteristics changed between years 2001 and 2003 on mudrock slopes. Smectite-rich materials proved to be extremely sensitive to limited water inputs, which cause swelling, and sufficient water to cause saturation and total liquefaction with collapse of structure. Other materials did not prove to be sensitive to moisture input changes. |
