Search

Wildfires can affect agroforest-ecosystems generating several cascade effects on the soil-water continuum, among which erosion is one of the most important. Even so, few field studies analyse post-fire soil erosion at watershed scale, especially in the Mediterranean Basin, although here wildfires are particularly frequent.The present work analyses the impact of the first rain events following one severe wildfire in the Pisan Mountains, Tuscany region, Italy, with the aim to quantify and characterize the post-fire impact in terms of soil erosion and sediment yield at watershed scale.The study site is characterized by olive groves, maquis, maritime pine and chestnut forest, depending on the elevation. The area was affected by a fire involving an area of about 1000 ha in September 2018. Fire severity was assessed by remote sensing imagery, while fire impact on soil properties and sediment yield was assessed by field experiments, and sampling and lab analysis. Finally, a hydrological model was implemented in HEC-HMS environment for exploring the relationship between the erosion-deposition events monitored in a sample watershed, and the hydrological processes induced by the rainfall events.Experimental analysis revealed that the organic fraction of topsoil dramatically declined after the wildfire, together with the saturated hydraulic conductivity. Fire occurrence also generated a shift in the soil water repellency. The analysis of sediment deposited at the outlet of the catchment revealed that the first two rainfall-induced erosion-deposition events transported a larger amount of non-organic sediments, probably already close to the riverbed before the fire, while the other four events analyzed corresponded to deposited material much richer in organic matter, produced by the fire event. Overall, at watershed scale, soil erosion amounted to 7.85 t/ha, a relatively moderate rate considering the large fire impact on soil. This could be partly explained by the shallow soil depth of the study area (around 50 cm on average) and the high stoniness of soil, which would lead to preferential infiltration pathways for water, reducing runoff and erosion.

The present work describes a transferability analysis for soil and water bioengineering techniques as an instrument for sustainable erosion control in Central and South America based on an empirical data base from the last decades. In total, 31 case studies in Mexico, Nicaragua, Guatemala, Colombia, Ecuador and Brazil generated a database from an area where soil and water bioengineering techniques are not commonly used. The Transferability Analysis is structured in seven steps: (1) Objectives of the procedure, (2) Impacts of the measure, (3) Identification of up-scaling/down-scaling needs (4) Identification of the main phases and its components, (5) Identification of the level of importance of the components, (6) Assessment of the components in the context of the Take-Up Site and (7) Conclusions. For the assessment of soil and water bioengineering via the Transferability Analysis, in step 4 the following main phases have been identified from the data base: (a) Planning Phase, (b) Construction Phase, (c) Use Phase, as well as (d) End of Life Phase of a construction. Within these categories, 14 components have been defined: (a) know-how of soil and water bioengineering techniques, local climate conditions, botany, hydraulics, pedology, (b) materials, qualified labor, equipment and mechanical instruments, economic resources, (c) monitoring, efficiency, sustainability, maintenance, (d) replicability. The following assessment of the components allowed to determine key barriers, as well as key support factors for the transfer of soil and water bioengineering. As a result, barriers appeared to be the components qualified labor, equipment/mechanical instruments, hydraulics, know-how in soil and water bioengineering and pedology. Neither barriers, nor supporting key factors resulted to be the components local climate conditions, economic resources and efficiency. Supporting key factors for the transfer were materials, monitoring, sustainability, maintenance and replicability. The most important key factor of success was assessed to be botany, as various plant species with important characteristics for soil and water bioengineering are available in Central and South America, able to compensate the constraints through barriers in certain cases.

An experimental campaign was implemented along a 300 m stretch of a drainage channel, with the purpose of estimating the roughness coefficients of vegetated channels at the real scale for different management scenarios. The study was carried out in an agricultural area where the ordinary vegetation management consists in the total removal of natural vegetation along the whole wetted perimeter; thus, significantly impacting the aquatic ecosystem. To determine the sustainability of a less-impactful management, three scenarios were tested: a full-vegetated scenario, a partial removal, and the traditional total removal. The vegetation distribution and the channel morphology were determined for modelling purposes. Four increasing discharges were controlled by a pumping system up to the bankfull conditions, while hydraulic parameters were being monitored. Measuring the flow characteristics on three cross-sections, roughness coefficients were obtained by inverting the 1D equation of gradually varied steady flow. Results show how the presence of an undisturbed vegetation community significantly rises the water levels, thus possibly increasing the flood risk. The flow resistance resulted decreasing for increasing velocities, suggesting a considerable effect of plants reconfiguration due to drag. The intermediate scenario, represented by the preservation of an untouched vegetated buffer on one bank, resulted to be less impactful on flow and not far from the total removal scenario. The experimental results represent a reference for flow resistance models development and validation. Moreover, the findings of the present work provide useful information for a more focused drainage channel management, supporting the reduction of the ecological impact on aquatic communities.