Raindrop‐impact‐induced erosion processes and prediction: a review

Raindrop‐impact‐induced erosion is initiated when detachment of soil particles from the surface of the soil results from an expenditure of raindrop energy. Once detachment by raindrop impact has taken place, particles are transported away from the site of the impact by one or more of the following transport processes: drop splash, raindrop‐induced flow transport, or transport by flow without stimulation by drop impact. These transport processes exhibit varying efficiencies. Particles that fall back to the surface as a result of gravity produce a layer of pre‐detached particles that provides a degree of protection against the detachment of particles from the underlying soil. This, in turn, influences the erodibility of the eroding surface. Good understanding of rainfall erosion processes is necessary if the results of erosion experiments are to be properly interpreted. Current process‐based erosion prediction models do not deal with the issue of temporal variations in erodibility during a rainfall event or variabilities in erodibility associated with spatial changes in dominance of the transport processes that follow detachment by drop impact. Although more complex erosion models may deal with issues like this, their complexity and high data requirement may make them unsuitable for use as general prediction tools. Copyright © 2005 John Wiley & Sons, Ltd.     

Underwater acoustic noise measurement in test tanks

The range capability of underwater acoustic equipment installed onboard underwater vehicles is limited by the noise generated by propellers, hydraulic pumps.... Measuring this noise at sea is quite expensive. Here is described a procedure allowing the measurement of the radiated noise in test tanks. This method is derived from techniques previously developed in aerial acoustics and in electromagnetism     

An attempt to evaluate seismic hazard in Central-Southern Italy

A method for the evaluation of seismic hazard in a given zone, taking into account both the spreading of macroseismic effects and seismic catalogue information, is applied. A data-bank of some 500 digitized isoseisms of earthquakes having occurred in Italy between 1542 and 1986 is used. The isoseismical maps are digitized considering for each degree of intensity the length of 24 spreading rays starting from the macroseismic epicenter or barycentre of the megaseismic area. These rays are separated from each other by the same angle, i.e. every isoseism is divided into 24 equal circular sectors. The year 1542 is taken as the beginning of the time span, since this is when the first seismic event occurred for which reliable isoseismal maps are available. The epicentral intensities considered lie between theVI andXI degrees of the Mercalli-Cancani-Sieberg scale (MCS). This digitized data-bank is analyzed to achieve, for each homogeneous seismogenetic zone that has been recognized, the mean azimuthal spreadings of effects for each degree of intensity as a function of the epicentral intensity. Once a mean propagation model is obtained for each zone, this is applied to seismic events of the same zone, the isoseismal maps of which are not available. A geographic grid is defined to cover the analyzed area, and for each cell of this grid it is then possible to count the number of felt events and their degree. These effects have been evaluated either on the basis of the isoseismal maps (when available) or on the basis of the mean propagations of the zone in which the single event occurred. Moreover, an index summarizing the seismic information was computed for each cell of the previous grid. All the events producing effects and their provenance are stored on files, allowing the main seismogenic zones influencing this cell to be identified. This methodology has been applied to central and southern Italy in an area between the latitudes 40.6 and 43.3 N. In particular, attention is focussed on the sample areas of Rome (given the historical and political importance of the city) and of the Sannio-Matese and Irpinia zone (in which some of the strongest earthquakes of the Apennine chain have occurred). Finally, in order to evaluate the maximum expected magnitude, extreme value statistics (Gumbel III-type) are applied to the Colli Albani area, which represents the seismogenic zone nearest to Rome. For the Sannio-Matese and Irpinia area, considering the more dangerous zone as a ‘unicum’, theWeibull distribution has been hypothesized to determine the mean return time for events with an intensity greater than or equal to IX.     

Consideration of the interaction between dam and bedrock in a coupled mechanic-hydraulic FE-program

Summary The behaviour of existing dams and some accidents have shown the great importance of the interaction between dam and bedrock with respect to mechanic and hydraulic effects.The mechanic and hydraulic properties of a fissured rock mass are mainly determined by the discontinuities. When their opening widths change due to stresses, the permeability is affected. This causes alterations in the piezometric head distribution which again affect the state of stress.The paper presents a new concept to take into account the mechanic-hydraulic interaction in a 3-dimensional Finite-Element-program. The concept is illustrated by an example (gravity dam).     

Algorithmic techniques of identifying discriminative ocean areas in oceanology problems

A problem of locating and comprehensively investigating ocean areas that exercise a significant influence over the migration dynamics of fishing ranks among important problems of fisheries oceanology. Among all the environment factors affecting various fishery situations, factors should be chosen that are constantly logged on large water areas for a long time comparable with fishery observation time. As described in a number of works, the most suitable information for these purposes is data on the distribution of surface temperature fields. The problem of locating discriminative areas can then be stated as follows. For a particular fishery situation (e.g., for the period of maximum catch in fishing season), temperature values or thermostructural features should be singled out that are suitable to define the situation, using hydrological charts of surface temperature fields. Correlating the feature with the areas where they were observed, we will obtain discriminative areas. The important problem is then to develop techniques and means for algorithmically identifying areas. This relates to a vast volume of information and complex structure. Logical-mathematical models of locating discriminative areas are being developed at the Pacific Oceanological Institute for some years. These models are to be for forecasting fishery situations in the NW Pacific. Techniques for representing isotherm fields in a computer have been developed. Formal operations of comparing the fields have been proposed which aid in distinguishing significant differences in their structure. A software for analyzing isotherm fields has been developed based on threshold logic models. This approach allows one not only to identify discriminative areas for relatively stable fishery situations but also to trace their dynamics. This has been achieved due to multiple-alternative computations and the presentations of data obtained in the form suitable for their interpretation. Some components of proposed models have been used in the system of short-term forecasting saira and sardine fishery in the South-Kuril area.     

Influence of different air pollutants on the structure of needle wax of spruce (Picea abies [L.] Karsten)

With the help of the scanning electron microscope surface structures of spruces exposed to different sorts of air pollutants are examined. On the surface of unexposed spruce needles crystalline wax structures — hollow tubes — are visible covering the stomata rows on all sides of the needle and filling the stomatal antechamber with a close-knit mesh. Non-reactive dusts only mechanically disturb the wax structures; MgO-containing fine dusts influence the wax tubes in a more serious way: the wax tubes fuse and the crystalline structure is lost. X-ray-analysis of the deposited particles reveals Mg to be the dominating element. SO₂ also causes severe alterations of the wax structures; with oxidants as the main emission component the wax structures are nearly unaffected.