Velio Coviello

A Semi-quantitative Model to Assess the Costeffectiveness of Soil and Water Conservation Measures

Soil and Water Conservation (SWC) measures have been regularly employed in the Sahelian area to reduce soil erosion and reservoir siltation. However, a proper cost-effectiveness analysis of the impact of SWC interventions on the catchment sediment budget is rarely carried out. In this paper, a semi-quantitative model is proposed to evaluate the cost-effectiveness of SWC measures at a catchment scale. Focusing on a case study located in Burkina Faso, the catchment sediment budget was estimated for an hypothetical SWC intervention by means of morphological and pedologic parameters and dam sedimentation rates. The proposed methodology showed interesting potentials for land and water management in the Sahelian region. In particular, where data for model calibration and validation are scarce, and when financial resources are limited, the proposed methodology can provide a diagnostic on sediment transport processes and reservoir capacity loss in order to design and implement suitable SWC actions.

Shear-Wave Velocity Reconstruction via Unconventional Joint Analysis of Surface Waves: A Case Study in the Light of Some Theoretical Aspects

In site characterisation studies, the unambiguous determination of the shear-wave velocity (VS) vertical profile is a crucial point often accomplished via surface-wave analysis. The determination of the dispersive properties eventually inverted for the determination of the VS vertical profile, can be performed both via active and passive methodologies and, for land data, while considering both Rayleigh and/or Love waves. Because of its constitutive equations, Rayleigh-wave propagation is often characterized by a complex phenomenology determining non-trivial mode excitement (thus complex velocity spectra), while Love waves typically result so-to-speak simpler. These aspects logically suggest the use of a joint approach capable of reducing the non-uniqueness of the solution and solving possible interpretative issues particularly problematic when the inversion is performed according to the classical approach (picking of interpreted dispersion curves and successive inversion). After the presentation of a synthetic dataset shown to put in evidence the above-mentioned problematic aspects, a case study solved while adopting a non-ordinary approach (the joint inversion of the whole Rayleigh- and Love-wave velocity spectra accomplished by considering the Full Velocity Spectrum approach) is presented.

Designing and Building Gabion Check Dams in Burkina Faso

Gabion check dams (GCDs) are among the most diffused soil and water conservation practices in Burkina Faso, used to cope with soil loss and reservoir siltation. Specifically, CGDs are flexible, permeable structures built in gullies to create a sedimentation bench that decreases the average upstream slope. The consequent slowing-down of the flowing water limits flood-wave sediment transport capacity reducing soil loss upstream, reduces the amount of trapped sediment in reservoirs and promotes water infiltration into the soil. The present work provides concise guidelines for the design and implementation of GCDs in Burkina Faso. This was achieved gathering the experience developed in the frame of several cooperation and development projects led by the Italian non-governmental organization. The theoretical elements and procedural steps to perform an appropriate design and implementation of GCDs are described and discussed, including hydrological and hydraulic methods to assess stream flow characteristics, spillway functioning, siltation rate, dimensions and stability of the structure.