Evaluating the role of inherited structural discontinuities in badland erosional processes with landscape evolution modelling

Catchment-wide erosion and sedimentation behaviour is influenced by variety of controls. One of these controls is erodibility, which may be determined by the lithological properties (e.g. texture, porosity) or the (density of) structural discontinuities (e.g. faults, fractures). In this study, the potential role of different erodibility of lithology and faults in spatio-temporal erosion and sedimentation behaviour was evaluated using the landscape evolution model, Landscape Process Modelling at Multi-dimensions and Scales (LAPSUS). The study area, Kula Badlands (western Turkey), is known for dense badland gully networks, incised into fine-grained sediments in one of the tributaries of the Gediz River, the Geren catchment. An earlier field-based study demonstrated the fault-controlled net erosion and consequent sedimentation in these badlands. Here, we test the role of lithology and faults in landscape development with scenario-based modelling. A reconstructed PalaeoDEM, representing a 30-ka-old landscape, was used as an input. Scenario simulations were conducted with lithology- and fault-related erodibility and sedimentability factors. Simulation results demonstrate a significant difference in spatial erodibility and sedimentability and catchment erosion and sedimentation behaviour. Incorporating higher erodibility factors for fault zones caused not only a considerable amount of within-catchment erosion in fault-determined erosion zones, but also a decrease in overall catchment sediment export. In addition, high constant sedimentability lowers the sediment export considerably whilst slightly increasing total erosion rates. These outcomes indicate that fault zones with higher erodibility can increase accommodation spaces, producing temporary (re)sedimentation locations, which decrease overall sediment delivery from its catchment on the long run. The model simulations suggest that fault-related higher erodibility and sedimentability can be important factors in controlling landscape dynamics at the local and catchment scale.