A Numerical Study of the Critical Threshold for Landslide Dam Formation Considering Landslide and River Dynamics

Landslide dam formation can be influenced by the erosive capacity of river flow and the dynamic characteristics of the landslide. When the deposition rate of a landslide that reaches a river is higher than the erosion rate of river flow, the landslide can form a dam by blocking the channel. Hence, in this paper, a dimensionless discharge threshold for landslide dam formation considering landslide and river dynamics is established and studied numerically. A two-layer depth-averaged model coupled with an erosion term is presented to simulate river and landslide movements and their interactions. Several numerical cases are simulated to study the influence of landslide and river dynamics on the critical threshold for dam formation by considering some key factors, such as landslide velocity and the angle between the river and landslide transport directions. Through the simulations, three types of landslide intrusion into river can be reflected: a dam forms quickly, a dam forms or does not form close to a critical state, and no dam forms. The results show that these factors together affect the process of dam formation if the difference between the landslide and river discharges is relatively small. All results are helpful to further clarify the formation of such dams for natural hazard prevention under future climate change conditions.

The coastal wetland systems of northern Tuscany: Massaciuccoli Lake and ex Porta Lake. State of knowledge and new opportunities for multidisciplinary approach

The Massaciuccoli lake of and the ex Porta Lake have been selected as Sites of Importance of the European Community for the particular biocommunities that they host. These areas have a complex history that has seen man intervening constantly over the centuries with reclamation operations, so that the landscape we see today is the result of a natural environment strongly shaped by man. Recent studies, conducted using a sequential stratigraphic approach, show that the depositional architecture of the Versilia Plain is determined by the variation in relative sea level, the amount of sedimentary input and the erosive capacity of the main watercourses, which have led to the formation of engraved paleovalleys. By using the stratigraphies collected in the IGGDATABASE, an attempt of stratigraphic reconstruction of the subsurface has been carried out in this work, underling that multidisciplinary detailed studies are necessary to better define the recent palaeoenvironmental evolution (Pleistocene-Holocene) and the depositional architecture of the subsurface of these areas. Moreover, a detailed monitoring of these systems both for abiotic and biotic parameters is needed as essential mean for their protection and preservation.

Intensity and distribution in the space-time of the rain erosivity in Goias and Federal District states

The ability of rainfall to promote soil disaggregation and transport depends on its intensity and distribution over time, allowing proper soil and water management practices in order to minimize their effects in and outside food production fields. The objective of this study was to verify the intensity of the spatial and temporal distribution of rainfall erosivity in Goias and Federal District states using historical series of rainfall data available at the National Institute of Meteorology (Inmet) from 1986 to 2017. Rainfall erosivity (EI) for Goias and Federal District were estimated using the modified Fournier index. Annual average for factor R were obtained by the sum of the EI in the 12 months of the year. Data were placed to descriptive analysis and classification according to their erosive capacity. The annual mean of the factor R for the study region was 8,834±5.2 MJ mm ha-1 h-1 ano-1, being classified as a strong erosive potential. However, considering the territory, its intensity in Goiás and DF varied from very strong to moderate throughout the year, indicating the need to adopt a conservationist practice that protects the soil from the kinetic energy of rainfall. It is concluded, therefore, that the intensity and distribution of the rainfall erosivity fluctuate both between the municipalities of Goiás (from 4.514±2.5 to 11.215±1.8 MJ mm ha-1 h-1 year-1), and throughout the year (from 180±1.5 to 1.519±4.4 MJ mm ha-1 h-1 month-1).

Downward seepage effects on dynamics of scour depth and migrating dune-like bedforms at tandem piers

The present study focuses on multi-scale statistical characterization of scour depth at tandem piers and migrating dune-like bedforms forming behind the piers in downward seepage affected alluvial channel, using an experimental approach. Experiments were conducted using two circular piers arranged in a tandem manner for no seepage, 10% seepage, and 15% seepage condition. The erosive capacity of reversal flow is hindered with downward seepage, which results in reducing velocity and Reynolds stress near the bed at upstream of piers in case of seepage runs. The bed elevation of the scoured region is decreasing with the increasing seepage percentage and the growth in scour depth is diminishing with time. The celerity of scour depth is decreasing with time as well as decreasing with increasing downward seepage. Probability density function of bedform elevation has positive tail slightly thicker than the Gaussian.

Spatial distribution of the daily precipitation concentration index in Algeria

In this paper, the spatial and temporal distribution of the daily precipitation concentration index (CI) in Algeria (south Mediterranean Sea) has been assessed. CI is an index related to the rainfall intensity and erosive capacity; therefore, this index is of great interest for studies on torrential rainfall and floods. Forty-two daily rainfall series based on high-quality and fairly regular rainfall records for the period from 1970 to 2008 were used. The daily precipitation CI results allowed the identification of three climate zones: the northern country, characterized by coastal regions with CI values between 0.59 and 0.63; the highlands, with values between 0.57 and 0.62, except for the region of Biskra (CI = 0.70); and the southern region of the country, with high rainfall concentrations with values between 0.62 and 0.69.

Erosivity of rainfall in Lages, Santa Catarina, Brazil

The erosive capacity of rainfall can be expressed by an index and knowing it allows recommendation of soil management and conservation practices to reduce water erosion. The objective of this study was to calculate various indices of rainfall erosivity in Lages, Santa Catarina, Brazil, identify the best one, and discover its temporal distribution. The study was conducted at the Center of Agricultural and Veterinary Sciences, Lages, Santa Catarina, using daily rainfall charts from 1989 to 2012. Using the computer program Chuveros , 107 erosivity indices were obtained, which were based on maximum intensity in 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, 120, 135, 150, 165, 180, 210, and 240 min of duration and on the combination of these intensities with the kinetic energy obtained by the equations of Brown & Foster, Wagner & Massambani, and Wischmeier & Smith. The indices of the time period from 1993 to 2012 were correlated with the respective soil losses from the standard plot of the Universal Soil Loss Equation (USLE) in order to select the erosivity index for the region. Erosive rainfall accounted for 83 % of the mean annual total volume of 1,533 mm. The erosivity index (R factor) of rainfall recommended for Lages is the EI30, whose mean annual value is 5,033 MJ mm ha-1 h-1, and of this value, 66 % occurs from September to February. Mean annual erosivity has a return period estimated at two years with a 50 % probability of occurrence.