Stefano Ferraris

Peat land oxidation enhances subsidence in the Venice watershed

The southernmost part of the Venice Lagoon catchment was progressively reclaimed from marshland starting from the end of the 19th century and finishing in the late 1930s (Figure 1). As a major result, the area was turned into a fertile farmland. At present, the area is kept dry by a distributed drainage system that collects the water from a capillary network of ditches, and pumps it into the lagoon or the sea. By its very origin, this area lies below sea level and progressively sinks mainly because of bio-oxidation of the histosols (soils with high organic content) that represent a large fraction of the outcropping soil in the area. The bio-oxidation process occurs in close connection with the agricultural practices and is currently responsible for a subsidence rate of between 1.5 and 2 cm/yr.

An iterative particle filter approach for coupled hydro-geophysical inversion of a controlled infiltration experiment

The modeling of unsaturated groundwater flow is affected by a high degree of uncertainty related to both measurement and model errors. Geophysical methods such as Electrical Resistivity Tomography (ERT) can provide useful indirect information on the hydrological processes occurring in the vadose zone. In this paper, we propose and test an iterated particle filter method to solve the coupled hydrogeophysical inverse problem. We focus on an infiltration test monitored by time-lapse ERT and modeled using Richards equation. The goal is to identify hydrological model parameters from ERT electrical potential measurements. Traditional uncoupled inversion relies on the solution of two sequential inverse problems, the first one applied to the ERT measurements, the second one to Richards equation. This approach does not ensure an accurate quantitative description of the physical state, typically violating mass balance. To avoid one of these two inversions and incorporate in the process more physical simulation constraints, we cast the problem within the framework of a SIR (Sequential Importance Resampling) data assimilation approach that uses a Richards equation solver to model the hydrological dynamics and a forward ERT simulator combined with Archies law to serve as measurement model. ERT observations are then used to update the state of the system as well as to estimate the model parameters and their posterior distribution. The limitations of the traditional sequential Bayesian approach are investigated and an innovative iterative approach is proposed to estimate the model parameters with high accuracy. The numerical properties of the developed algorithm are verified on both homogeneous and heterogeneous synthetic test cases based on a real-world field experiment.

Evaluation of Stemflow Effects on the Spatial Distribution of Soil Moisture Using TDR Monitoring and an Infiltration Model

AbstractThe partitioning of crop canopy water may affect soil water distribution and this may in turn affect sprinkler irrigation application efficiency. The aim of this work was to develop a methodology to evaluate spatial and temporal soil water content distribution in the case of sprinkler irrigation application efficiency considering stemflow. Time domain reflectometry (TDR) soil moisture monitoring was carried out on eight soil water sensor locations for both center pivot and traveling big gun irrigation in different phenological and tillage cases. The two case studies were chosen because they show the two opposite limits of the methodology’s application. Two water distribution estimation methods were employed: raw measured soil moisture and model simulation of the infiltration process. The infiltration process was modeled by means of the two-dimensional (2D) Richard’s equation. The simulations were calibrated on the data measured at eight soil water sensor locations. The stemflow and surface runoff ...

The Finite Volume Formulation for 2D Second-Order EllipticProblems with Discontinuous Diffusion/Dispersion Coefficients

We propose a finite volume method for the numerical resolution of two-dimensional steady diffusion problems with possibly discontinuous coefficients on unstructured polygonal meshes. Our numerical method is cellcentered, secondorder accurate on smooth solutions and based on a special numerical treatment of the diffusion/dispersion coefficients that makes its application possible also when such coefficients are discontinuous. Numerical experiments confirm the convergence of the numerical approximation and show a good behavior on a set of benchmark problems in two space dimensions.

Effects of Soil Management on Long-Term Runoff and Soil Erosion Rates in Sloping Vineyards

Runoff and soil losses caused by natural rainfall events were monitored over a 12-year period in an experimental vineyard located in Alto Monferrato, a vine-growing area of Piedmont (NW Italy). The measurements were carried out on three plots, each of which was managed with a different inter-row soil management practice: conventional tillage (CT), reduced tillage (RT) and controlled grass cover (GC), respectively. The annual average runoff coefficients were 17.4 % in CT and 15.3 % in RT, while in the GC plot it was limited to 10.3 %. The highest soil losses were observed for the tilled plots, with average yearly erosion rates of 10.4 and 24.8 Mg ha−1year−1 in the CT and RT plots. Only 2.3 Mg ha−1year−1 were recorded for GC treatment. The protective role of grass cover will be more and more relevant, taking in account climate changes that predict increase in rainfall intensity and erosivity. The evaluation of the effect of different conservation measures on the runoff and soil erosion, in relation with future climate scenarios, would be a useful to support soil management decisions in vineyards.