Quantification of in-channel large wood recruitment through a 3-D probabilistic approach

Large wood (LW) is a relevant factor in physical, chemical, environmental and biological aspects of low order mountain streams system. LW recruitment, in turn, is affected by many physical processes, such as debris flows, shallow landslides, bank erosion, snow- and wind throw, and increases the potential hazard for downstream human population and infrastructures during intense flood events. In spite of that, the LW recruitment quantification and the modelling of related processes are receiving attention only since few years ago, with particular reference to hillslope instabilities which are the dominant source of LW recruitment in mountainous terrains at regional scale. Actually, models based on the infinite slope approach, commonly adopted for slope stability analysis, can be used for estimating probable LW volume and for identifying the most hazardous areas of wood input, transport and deposition. Such models, however, generally request a robust calibration on landslide inventory and tend to overestimate unstable areas and then LW recruitment volumes. On this background, this work proposes a new LW estimation procedure which combines the forest stand characteristics of the entire catchment and a three-dimensional probabilistic slope stability model. The slope stability model overcomes the limits of the infinite slope approach and considers the spatial variability and uncertainty of the model input parameters through a Monte Carlo analysis. The forest stands characteristics allow including the root reinforcement into the stability model as stochastic input parameter, and provide the necessary information to evaluate the forest wood volume prone to be recruited as LW and its position on the hillslopes. The procedure was tested on a small mountainous headwater catchment in the Eastern Italian Alps, covered with pasture and coniferous forest and prone to shallow landslide and debris flow phenomena, especially during the late spring and the early autumn. The results showed how the proposed procedure is very promising. In fact, the estimated LW volume is comparable with the one measured by field surveys. As the procedure used data commonly available, it is of great interest as a tool for forest planning and management, and to predict the effects of forest alterations, both of natural and of anthropic origin (e.g. diseases, fire, clear-cutting or clearing), as well as helping in-channel wood retention structures positioning

Evaluation of short-term geomorphic changes in differently impacted gravel-bed rivers using improved dems of difference

The evaluation of the morphological dynamics of rivers is increasingly focusing, in recent years, on the achievement of quantitative estimates of change in order to identify geomorphic trends and forecast targeted restoration actions. Thanks to the development of more effective and reliable survey technologies, more accurate Digital Elevation Models (DEM) can be produced and, through their consequent differencing (DoD), extremely useful geomorphic analyses can be carried out. In this situation, a major role is played by uncertainty, especially in the final volumetric rates of erosion and deposition processes, that may lead to misinterpretation of spatial and temporal changes. This paper aims at achieving precise geomorphic estimates derived from subsequent hybrid (LiDAR and bathymetric points) surface representations. The study areas consist of gravel-bed reaches of two differently impacted fluvial environments, Piave and Tagliamento rivers, that were affected by two severe flood events (Piave, R.I. of 7 and 10 years and Tagliamento, R.I. of 15 and 12 years) in the inter-surveys period. The basic Hybrid Digital Elevation Models (HDTM) were processed accounting for spatially variable uncertainty and considering, beside slope and point density input variables, a novel component measuring the quality of the bathymetric derived points. In fact, since the major changes occur within river channels, the integration of this variable evaluating the precision of the bathymetric channel elevations in the HDTMs, has allowed, through the creation of targeted FIS (Fuzzy Inference System) rules, to obtain reliable geomorphic estimates of change. Volumes and erosion and deposition patterns were then analyzed and compared to outline the different dynamics among the sub-reaches and the two river systems

Tracking log displacement during floods in the Tagliamento River using RFID and GPS tracker devices

Large pieces of in-channel wood can exert an important role on the ecological and morphological properties of gravel-bed rivers. On the other side, when transported during flood events, large wood can become a source of risk for sensitive structures such as bridges. However, wood displacement and velocity in river systems are still poorly understood, especially in large gravel-bed rivers. This study focuses on log transport in a valley reach of Tagliamento River (Italy). Log displacement during flood events of different magnitudes recorded from June 2010 to October 2011 has been analysed thanks to the installation of 113 radio frequency identification (RFID) tags and 42 GPS tracker devices in logs of different dimensions. Recovery rates of logs equipped with RFID and GPS trackers were about 43% and 42%, respectively. The GPS devices allowed us to analyse in details the log displacement and transport overtime, indicating a higher log entrainment during rising limb of hydrographs. The threshold for the entrainment of logs from low bars is around 40% of bankfull water stage. No clear relationship was found between the peak of flood and log displacement length and velocity. However, log displacement length and velocity appear significantly correlated to the ratio between the peak of flow and the water stage exceeding the flow duration curve for 25% of time (i.e. the ratio hmax/h25 ratio). Log deposition was observed to occur at the peak flow, and logs transported during ordinary events are preferably deposited on low bars. This study reveals the potentials of GPS tracker devices to monitor the entrainment and movements of logs in large gravel-bed rivers during floods. These observations could be useful for better planning of river management practices and strategies involving the use of large wood pieces and could help for calibrating wood budgets at the reach scale

Transition rates and nuclear structure changes in mirror nuclei 47Cr and 47V

Lifetime measurements in the mirror nuclei 47Cr and 47V were performed by means of the Doppler-shift attenuation method using the multidetector array EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron Wall. The determined transition strengths in the yrast cascades are well described by full pf shell model calculations.Comment: Latex2e, 11 pages, 3 figure

Medium and short term riparian vegetation, island and channel evolution in response to human pressure in a regulated gravel bed river (Piave River, Italy)

During the last decades, several Italian gravel-bed rivers suffered from different types and levels of human pressures that changed their morphological and vegetation patterns. This study aims to analyze the medium- and short-term evolution of vegetation cover, fluvial islands and main channel characteristics along a gravel-bed reach of the Piave River (North-eastern Italy), with special emphasis on the changes in the vegetation cover type and structure. The Piave River experienced different types of human disturbance such as gravel mining, hydropower schemes, and land use changes. A sequence of aerial photographs (1960, 1970, 1982, 1991, 1999, 2006, 2010 and 2012) have been analyzed to detect the medium-term (about 50 yr) evolution of riparian vegetation along a reach about 30 km-long in the middle course of the Piave River. In addition, LiDAR data (2003) and seven repeated topographic surveys (done between 2007 and 2011) have been used to quantify changes in three cross sections on a sub-reach about 2 km-long, in order to analyze the channel evolution over a short period (1–8 yr). The medium-term analysis revealed that changes in the river evolutionary trend depended on the variations in human activities both in the main channel and at basin scale. In fact, during the last five decades there has been a consistent and continuous increase of riparian vegetation within the river corridor, from around 50% up to 68%, which corresponds to a continuous decrease from around 46% to 29% in the area of exposed gravel and low flow channels. Considering the different vegetation cover types, there was a predominant increase of stable and tall vegetation from around 34% up to a maximum of around 67% (1999), then a slight decrease to around 62% (2010 and 2012). After a slight recovery phase subsequent to the cessation of gravel mining in the late 1990s and associated to flood events in the early 2000s, the Piave River appears to have been in an equilibrium phase in terms of bed elevation, planform morphology and areas of vegetation, which is becoming taller and more mature, as a result of the combination of flow regulation, reduced bedload input from upstream and lack of relevant flood events. These results suggest that in highly regulated — in terms of flow and sediment fluxes — rivers the cessation of gravel mining alone is not sufficient to revert a degradation trend and thus restore prior morphological patterns

Short-term geomorphic analysis in a disturbed fluvial environment by fusion of LiDAR, colour bathymetry and dGPS surveys

Objective Estimating river's underwater bed elevations is a necessary but challenging task. The objective of this study is to develop a revised approach to generate accurate and detailed Digital Terrain Models (DTMs) of a river reach by merging LiDAR data for the dry area, with water depth indirectly derived from aerial imagery for wet areas. Methods This approach was applied along three sub-reaches of the Brenta River (Italy) before and after two major flood events. A regression model relating water depth and intensity of the three colour bands derived from aerial photos, was implemented. More than 2400 in-channel depth calibration points were taken using a differential Global Positioning System (dGPS) along a wide range of underwater bed forms. Results The resulting DTMs closely matched the field-surveyed bed surface, and allowed to assess that a 10-year recurrence interval flood generated a predominance of erosion processes. Erosion dominated in the upper part of the study segment (− 104,082 m3), whereas a near-equilibrium is featured on the lower reach (− 45,232 m3). The DTMs allowed the detection of processes such as riffle–pool downstream migration, and the progressive scour of a pool located near a rip-rap. Conclusion The presented approach provides an adequate topographical description of the river bed to explore channel adjustments due to flood events. Practice Combining colour bathymetry and dGPS surveys proved to represent a useful tool for many fluvial engineering, ecology, and management purposes. Implications The proposed approach represents a valuable tool for river topography description, river management, ecology and restoration purposes, when bathymetric data are not available

Environmental influences on the physiological and behavioural growth responses in salmonids : with reference to the growth-dip phenomenon

Photoperiod manipulations are widely used throughout the Atlantic salmon (Salmo salar) farming industry as a means of producing a product of uniform quality all-year round. However, farmers still remain sceptical over their effectiveness to regulate growth and maturation during the on-growing stage. Furthermore, reports of a characteristic growth-dip following light exposure suggest that light may negatively affect the physiological performance of fish in the short-term. Thus, this thesis investigates the effects of light characteristics (spectral quality, intensity and photoperiod) on growth and maturation of salmonid fish and addresses some of the uncertainties surrounding photoperiod use currently reported within the industry. Rainbow trout (Oncorhynchus mykiss) are seemingly an ideal model species for examining photoperiod effects on growth. Consequently, the application of constant light exposure (LL) at two different intensities (28W and 16W) during two different thermal conditions (summer and winter) was examined on individually tagged fish. Feed intake and growth appeared to be related to the ambient water temperature and did not appear to be affected by intensity or photoperiod, although the onset of constant light did appear to initially affect growth rate. This may indicate that LL has a limiting effect on the growth of trout or that the prevailing water temperature at which light is applied may override the photoperiodic effect. Furthermore, the lack of enhanced growth in trout exposed to LL, unlike that demonstrated for other salmonids, suggest that there may be a species-specific response to environmental variables. Thus, questions regarding photoperiod effects should be limited to the species in question. The main source of variation in results observed under photoperiod manipulations stems from the salmon industry. Atlantic salmon post-smolts were reared in seawater tanks and either maintained under a natural photoperiod (NP) or exposed to a simulated natural photoperiod (SNP), constant light superimposed on the natural light (NPLL) or constant light only (LL). Artificial light onset, irrespective of photoperiod, resulted in an apparent trend for a reduced appetite lasting up to 60 days. Furthermore, the onset of constant light resulted in a significant chronic elevation of plasma cortisol levels and changes to growth and thyroid hormone levels, providing direct evidence that constant light exposure induces stress. In addition, fish exposed to SNP failed to exhibit a stress response despite a low feed intake. However, differences in the plasma melatonin levels during twilight times, as compared to NP, suggest that gradual changes in the natural light intensity throughout the day, particularly around dawn and dusk, may be important for synchronizing daily events. No differences in growth were observed between the NP and NPLL regimes, although fish reared in an enclosed regime (SNP and LL) exhibited a significantly lower weight gain than fish in an open environment (NP and NPLL). This further highlights the impact that the rearing environment has on the growth performances of fish and the need for commercially run trials. Advances in lighting technologies and a greater understanding of how light is transformed through the water column have focussed research on the spectral sensitivity of fish. Therefore the lighting efficiency of novel blue narrow bandwidth LED lighting units through the water column and their effects on growth and maturation performances of salmon reared in commercial production cages were compared against the standard metal halide units currently utilized throughout the industry. LL application, irrespective of intensity or spectrum, reduced the numbers of fish maturing as compared to fish reared under a natural photoperiod. However, this was greatest under the standard metal halide units reflecting a greater light penetration and perception as determined by plasma melatonin levels. The metal halide groups exhibited the greatest relative weight gain over the trial period as compared to control fish. No evidence was observed for a growth-dip under metal halide light, although blue lit treatments exhibited an initial significant reduction in food consumption, suggesting a possible welfare issue. Nevertheless, the prototype blue LED units showed possible potential for commercial application by penetrating the water depth at half the distance of the metal halide units for only one eighth the power and one fifth the brightness. However, further tests of these prototype spectral units are required to examine the potential welfare and physiological growth and reproductive effects. These studies have shown that the efficacy of artificial light regimes is largely dependent upon the effectiveness of the light source through the underwater environment and its perception by fish, providing a sufficient intensity is emitted exceeding the physiological threshold level for the species cultured. Moreover, whilst the onset of artificial light may elicit a stress response and demonstrate a trend for a suppression of appetite for salmon reared in experimental tanks, no compelling evidence for a suppression of appetite or growth was found under normal commercial cage conditions. This suggests that the growth-dip observed within the industry may in part be a combination of a physiological response to the onset of light further exaggerated by the farmer’s perception and altered judgement in feeding. In addition, the results obtained from this study have helped to standardize the use of light regimes within the industry. Nevertheless, further studies are necessary to fully elucidate the underlying mechanisms which may govern growth and maturation in fish following the onset of light exposure.EThOS - Electronic Theses Online ServiceNutreco Aquaculture Research centre/Marine Harvest (Stavenger, Norway)University of StirlingFisheries Society of the British IslesGBUnited Kingdo