Morfología y estabilidad de las secuencias en escalones (step pool) en los torrentes alpinos de elevada pendiente

[ES] Abrahams y otros (1995) han demostrado que la morfología de tramos de cauce en escalones se aproxima a una condición de maximización de la resistencia al flujo y de elevada estabilidad. Para verificar esta teoría ha sido realizado un levantamiento de campo en 5 torrentes con estructuras escalón-remanso, obteniéndose una muestra de 49 secuencias a las cuales corresponden más de 250 escalones. Los resultados muestran que la validez de la inecuación de máxima resistencia : S 30-50 años la relación entre (H/Ls) y S puede ser menor de uno, alejándose de la condición de máxima resistencia. En una de las 5 cuencas estudiadas (Rio Cordon) funciona, desde el año 1986, una estación experimental para la medición continua de los caudales líquidos y sólidos. En este torrente ha sido analizada la analogía entre la longitud de onda de las antidunas y la distancia entre los escalones, y evaluada la transformación que han experimentado las secuencias después del pasaje de una crecida con Tr> 30-50 años. El mecanismo evolutivo predominante es el de la migración aguas abajo de las estructuras y la modificación de los escalones se produce por socavación y desestabilización de la base de apoyo.Se agradece el Centro Sperimentale Valanghe e Difesa Idrogeologica de Arabba (Regione Veneto) por el apoyo logístico. Un particular agradecimiento está dirigido a los Drs. Fabio Da Re y Diego Sonda por la asistencia brindada en los relevamientos de campo. Las investigaciones han sido promovidas y financiadas por la Unión Europea (DGXII) en el ámbito del Proyecto EROSLO-PEII (Contrato ENV4-CT96-0247).Aristide Lenzi, M. (1999). Morfología y estabilidad de las secuencias en escalones (step pool) en los torrentes alpinos de elevada pendiente. Ingeniería del Agua. 6(2):151-162. https://doi.org/10.4995/ia.1999.2786SWORD15116262Abrahams A.D., Li G. and Atkinson J.F., (1995) Step-pool streams: adjustment to maximum flow resistance. Water Resources Research, vol. 31, pp. 2593-2602.Allen J.R.L., (1982) Sedimentary structures, Vol I, Elsevier, Amsterdam, 593 pp.Ashida K., Egashira S., Ando N., (1984) Generation and geometric features of steep-pool bed forms, Bulletin of the Disaster Prevention Research Institute, Kyoto University, 27 (B-2), 341-353.Chin A., (1989) Step pools in stream channels. Progress in Physical Geography, 13, 391-403.D'Agostino V. (1996) La rinaturalizzazione dei torrenti montani. Quaderni del Dipartimento Territorio e Sistemi Agroforestali, Università di Padova, 33, 7 pp.D'Agostino V., Lenzi M.A. (1996) La valutazione del trasporto solido di fondo net bacino attrezzato del Rio Cordon. L'Acqua, vol. 4, 23-40.D'Agostino V., Lenzi M.A. (1997) Origine e dinamica della morfologia a gradinata (step pool) nei torrenti alpini ad elevata pendenza. Dendronatura, 2, 7-38.D'Agostino V., Lenzi M.A. (1998) La massimizzazione della resistenza al flusso nei torrenti con morfologia a step pool. XXVI Convegno Nazionale di Idraulica, Catania, Settembre 1998, Vol I, pp.281-293.Davis T.R., Sutherland A.J., (1980) Resistance to flow past deformable boundaries. Earth Surface Processes, vol. 5, 175-179.Fattorelli S., Keller H.M., Lenzi M.A., Marchi L., (1988) An experimental station for the automatic recording of water and sediment discharge in a small alpine watershed. Hydrol. Sciences Journal, 33 :607-617.Grant G.E., Mizuyama T., (1991) Origin of step-pool sequences in high gradient streams: a flume experiment. In Tominaga M. (ed.) Proceedings of the Japan-U.S. Workshop on Snow Avalanche, Landslides, and Debris flow Prediction and Control, Jpn. Sci. And Technol. Agency, Natl. Res. Inst. for Earth Sci. and Disaster Prev., Tsubuka, pp. 523-532.Grant G.E., Swanson F.J., Wolman M.G., (1990) Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon. Geological Society of America Bulletin, vol. 102:340-352.Grant G.E., (1994) Hydraulics and sediment transport dynamics controlling step-pool formation in high gradient streams: a flume experiment. In Ergenzinger, P. and Schmidt, K.H. Dynamics and Geomorphology of Mountain Rivers. Lecture Notes in Earth Sciences, Springer Verlag, Berlin-Heidelberg, 52:241-250.Hayward J.A., (1980) Hydrology and Steam Sediment from Torlesse Stream Catchment. Special Pubblication n. 17, Tussok Grasslands and Mountain Lands Institute, Lincoln College, Canterbury, New Zealand, 236 pp.Heede B.H., (1981) Dynamics of selected mountain streams in the western U. S. of America. Zetschrift fur Geomorphologie, 25: 17-32.Judd H.E., Peterson D.F., (1969) Hydraulics of large bed element channels. Utah Water Research Lab., College of Engineering, Utah State University, Logan, Report PRWG 17-6, 115 pp.Keller E.A., (1971) A real sorting of bed load material: the hypothesis of velocity reversal. Geological Society of American Bulletin, 88, 753-756.Keller E.A., Melhorn W.N., (1978) Rhythmic spacing and origin of pools and riffle. Geological Society of America Bulletin. 82 :753-756.Leopold L.B., Wolman M.G., Miller J.P., (1964) Fluvial processes in geomorphology. Freeman, San Francisco, California, 522 pp.Lenzi M. A., (1997) Measurements and assessments of bedload trasport in the Rio Cordon (Italy). Atti del Corso Rischi torrentizi: erosione e inondazioni, Università Europea d'estate sui rischi naturali, St. Niklaus (Valais, Suisse), 8-13 settembre 1997, 16 pp.Lenzi M. A., (1998) Criteri di classificazione dei sistemi fluviali. Quaderni del Dipartimento Territorio e Sistemi Agroforestali, Università di Padova, 50, 31 pp.Lenzi M. A., D'Agostino, (1998) Dinamica dei torrenti con morfologia a gradinata e interventi di sistemazione dell'alveo. En: Le sistemazioni idraulico-forestali, tra revisione e sviluppo. Quaderni di Idronomia Montana, 17, Editoriale Bios, pp. 31-56.Lenzi M.A., Marchi L., Scussel G.R., (1990) Measurement of coarse sediment transport in a small alpine stream. In: Lang H. and Musy A., Hydrology in Mountainous Regions, I Hydrological Measurements, the Water Cycle, IAHS Publ. no. 193: 283-290.Lenzi M. A., Marchi L., Tecca P.R., (1996) Field studies on sediment transport and debris flows in small basins of the Italian Alps. En: Hydrological problems and environmental management in highlands and headwaters: Krecek, Rajwar y Haigh (Eds.), pp.71-79.Lenzi M. A., Billi P., D'Agostino V., (1997) Effects of an extremely large flood on the bed of a steep mountain stream. Proc. of the conference on Management of Landscapes Disturbed by Channel Incision: Stabilization, Rehabilitation, Restoration;Wang, Langendoen, Shields (eds.), Oxford, Mississippi, USA; May 19-22, 1997; pp. 1061-1066.Milne J. A., (1982) Bed-material size and the riffle-pool sequence, Sedimentology. 29, 267-278.Montgomery D., Buffington J. (1997) Channel reach morphology in mountain drainage basins, Geological Society of American Bulletin. 109, n.5, 596,611.Richards K. S., (1976) The morphology of riffle-pool sequences, Earth Surface Processes. 1, 71-88.Richards K.S., (1978) Simulation of flow geometry in a riffle-pool stream, Earth Surface Processes. 3, 345-354.Rosport M., (1994) Stability of torrent beds characterised by step pool texture. Journal of Sed. Res., Vol 9, 3:124-132.Rosport M., Dittrich A., (1995) Step Pool Formation ad Stability -a Flume Study- . Proc. 6th International Symposium on River Sedimentation, pp. 525-532; Nov 1995, New Delhi, India.Whittaker J.G., (1982) Flow and sediment movement in steeped channels. Ph.D. thesis, Lincoln College, University of Canterbury, Christchurch, New Zealand.Whittaker J.G., Jaeggi M.N.R., (1982) Origen of step-pool systems in mountain streams. ASCE, J. of Hydraulic Division. 108: 758-773.Whittaker J.G., (1987) Sediment transport in step-pool streams. In: Thome, C.R., Bathurst, J.C. and Hey, R.D. Sediment transport in Gravel-Bed Rivers. Wiley, Chichester, pp. 545-579.Wohl E.E., Grodek T., (1994) Channel bed-steps along Nahal Yael, Negev desert, Israel. Geomorphology, vol. 9: 117-126.Yang C. T., (1971) Formation of Riffle and Pool. Water resources Research. 7, n. 6: 1567-1574.Yang C.T., Song C.C.S., Woldengerg M.J. (1981) Hydraulic geometry and minimum rate of energy dissipation. Water Resources Research. 7, n.6, 1567, 1574

Exploring the multiple effects of the invasive alien robinia tree: a PhD project presentation

The poster explains the background, research questions and objectives and methods of the PhD study on black locust (Robinia pseudoacacia) funded by the Linda Scattolin J:ROBIN project (2016-2019)

3_D modeling using TLS and GPR techniques to characterize above and below-ground wood distribution in pyroclastic deposits along the Blanco River (Chilean Patagonia)

To date, the study of in-stream wood in rivers has been focused mainly on quantifying wood pieces deposited above the ground. However, in some particular river systems, the presence of buried dead wood can also represent an important component of wood recruitment and budgeting dynamics. This is the case of the Blanco River (Southern Chile) severely affected by the eruption of Chait\ue9n Volcano occurred between 2008 and 2009. The high pyroclastic sediment deposition and transport affected the channel and the adjacent forest, burying wood logs and standing trees. The aim of this contribution is to assess the presence and distribution of wood in two study areas (483 m2 and 1989 m2, respectively) located along the lower streambank of the Blanco River, and covered by thick pyroclastic deposition up to 5 m. The study areas were surveyed using two different devices, a Terrestrial Laser Scanner (TLS) and a Ground Penetrating Radar (GPR). The first was used to scan the above surface achieving a high point cloud density ( 48 2000 points m-2) which allowed us to identify and measure the wood volume. The second, was used to characterize the internal morphology of the volcanic deposits and to detect the presence and spatial distribution of buried wood up to a depth of 4 m. Preliminary results have demonstrated differences in the numerousness and volume of above wood between the two study areas. In the first one, there were 43 wood elements, 33 standing trees and 10 logs, with a total volume of 2.96 m3 (109.47 m3 km-1), whereas the second one was characterized by the presence of just 7 standing trees and 11 wood pieces, for a total amount of 0.77 m3 (7.73 m3 km-1). The dimensions of the wood elements vary greatly according to the typology, standing trees show the higher median values in diameter and length (0.15 m and 2.91 m, respectively), whereas the wood logs were smaller (0.06 m and 1.12 m, respectively). The low dimensions of deposited wood can be probably connected to their origin, suggesting that these elements were generated by toppling and breaking of surrounding dead trees. Results obtained with the GPR confirm the ability of this instrument to localize the presence and distribution of buried wood. From the 3- D analysis it was possible to assess the spatial distribution and to estimate, as first approach, the volume of the buried wood which represents approximately 0.04% of the entire volcanic deposit. Further analysis will focus on additional GPR calibration with different wood sizes for a more accurate estimation of the volume. The knowledge of the overall wood amount stored in a fluvial system that can be remobilized over time, represent an essential factor to ensure better forest and river management actions

bank erosion and large wood recruitment along a gravel bed river

Riverine environments can be very dynamic and complex systems, particularly because of the interaction between active channel and riparian land during flood events of different magnitude. In recent years increasing attention has been paid to large wood (LW), focusing on its role and impact along riverine systems and fluvial landscapes. This research aims to analyze the characteristics of LW recruitment as a consequence of a flood event along a reach of a gravel-bed river. The study was conducted on a 3 km-long reach located in the middle course of the Piave River (north-eastern Italian Alps). A 20 m-wide buffer zone was considered along the floodplains and islands. Every standing tree in this buffer with diameter ≥0.10 m was measured manually (diameter breast height; height), whereas shrubs were not considered. The most common species in the study area are: Populus sp., Salix sp., Alnus sp., Carpinus sp., Fraxinus sp., Pinus sylvestris and Robinia pseudoacacia. An over bankfull flood (Q=1329 m3s–1; recurrence interval=6 years) in November 2014 caused erosions along the floodplain (15,565.5 m2), pioneer islands (25.2 m2) and building islands (2085.6 m2), recruiting 690 trees. Four of these trees were recruited from the pioneer islands (0.16 tree m–2), 79 from building islands (0.04 tree m–2) and 607 from floodplains (0.04 tree m–2). Accurate dendrometric measurements were used to define the input volume of LW from the floodplains (86.25 m3), pioneer islands (0.14 m3) and building islands (6.62 m3). The maximum distance traveled by LW recruited from the floodplain, pioneer and building islands was 8927, 1021 and 3727 m, respectively. Statistical analysis showed no significant relationship between the displacement and LW characteristics considered (diameter, length, volume, density). These results demonstrate that the recruitment and subsequent transport of LW is a complex mechanism that requires further study. To better characterize these mechanisms, it appears clear that it is important to consider not only the LW characteristics but also the connection between LW, morphological settings, and flood event characteristics

Using a terrestrial laser scanner to detect wood characteristics in gravel-bed rivers

The possibility of analysing the characteristics and volume of inchannel large wood (LW) is of importance for river management but the traditional manual field activities are usually time-consuming and not easy to apply at a larger spatial scale. This paper presents an alternative and faster method to detect the characteristics and measurements of large wood in rivers by using the terrestrial laser scanner (TLS) technology. Field-measurements data and TLS scans were collected in August 2013 along 14 ha of the Piave River (Italy) analysing 230 and 208 woody elements for the manual method and the TLS one, respectively. TLS data were processed using the Cyclone 7 software and the LW measurements were extracted adopting two specific tools. The resulting low margin of error in the comparison between field data and those derived from TLS surveys confirmed the ability of TLS in the detection of large wood and wood jams characteristics. The greatest deviations were found for wood jams height which the TLS showed a tendency to overestimate (+24.37%) and LW length with a slight underestimation (–19.76%). Considering the wood volume, the relative difference between the TLS and manual method was within a negligible margin of error of ±7%. Characteristics and measurements of LW in rivers can be obtained from TLS surveys, but some progress in this technique is still needed to allow a better management of the 3D point cloud and a faster extraction of the wood measurements. The proposed method represents an alternative tool for faster and repeated surveys of wood characteristics in a complex river environment, ensuring a reliable quantification of spatial and temporal variation of wood volume

integration of colour bathymetry lidar and dgps surveys for assessing fluvial changes after flood events in the tagliamento river italy

The estimation of underwater features of channel bed surfaces without the use of bathymetric sensors results in very high levels of uncertainty. A revised approach enabling an automatic extraction of the wet areas to create more accurate and detailed Digital Terrain Models (DTMs) is here presented. LiDAR-derived elevations of dry surfaces, water depths of wetted areas derived from aerial photos and a predictive depth-colour relationship were adopted. This methodology was applied at two different reaches of a northeastern Italian gravel-bed river (Tagliamento) before and after two flood events occurred in November and December 2010. In-channel dGPS survey points were performed taking different depth levels and different colour scales of the river bed. More than 10,473 control points were acquired, 1107 in 2010 and 9366 in 2011 respectively. A regression model that calculates channel depths using the correct intensity of three colour bands (RGB) was implemented. LiDAR and water depth points were merged and interpolated into DTMs which features an average error, for the wet areas, of ±14 cm. The different number of calibration points obtained for 2010 and 2011 showed that the bathymetric error is also sensitive to the number of acquired calibration points. The morphological evolution calculated through a difference of DTMs shows a prevalence of deposition and erosion areas into the wet areas

Evaluation of the morphological quality index in the Cordevole river (Bl, Italy)

The European Union (EU) Water Framework Directive (WFD, 2000/60/EC), which came into force in Italy under Decree Law no. 152 of 3rd April 2006, has as its objectives the protection and improvement of aquatic ecosystem status, promoting the sustainable use of water resources and mitigating the effects of floods and droughts. According to this Directive, the ecological classification of a watercourse should be considered in addition to physical-chemical and biological aspects of its hydromorphological condition, in order to define the deviation of the present condition from a pre-defined reference state. The Italian National Institute for Environmental Protection and Research has promoted a methodology called IDRAIM for the hydromorphological analysis of streams. This is an integrated approach aimed at implementing both WFD and EU Flood Directives (2007/60/EC). In this paper, we describe the application of the morphological quality index (MQI) protocol, which is part of the IDRAIM, used for evaluating the morphological quality of the Cordevole River, Province of Belluno, northeastern Italy. General settings and segmentation of the water network through the use of semi-automatic GIS techniques were presented. The MQI data derived from the application of 28 indicators in 42 reaches were then analysed. Most (48%) of the analysed reaches have a good quality status; 38% have a moderate quality status and poor morphological conditions (14%) are due to the presence of artificial elements and to the limited connectivity between hill-slopes and the river corridor

Acumulaciones de detritos leñosos en un cauce de montaña de Tierra del Fuego: análisis de la movilidad y de los efectos hidromorfológicos

This work reports on the geomorphic role of large wood pieces and jams in a third order mountain stream located in Southern Tierra del Fuego (Argentina), and draining an old-growth nothofagus forested basin not influenced by beaver damming activity. Even if the in-stream number of wood pieces (2,300) is comparable to that observed in other climatic areas, the slow growth of the nothofagus forest causes a lower wood abundance in terms of volumetric load (121 m3 ha–1). Due to the relatively small dimensions of the large wood pieces located inside bankfull edges (83% of the total surveyed pieces), almost the 70% of them demonstrated to have been transported by runoff and 6% derived from bank erosion or landslides. Wood jams exert a significant influence on the channel morphology, being responsible for the creation of 30% of pools. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity (about 1,750 m3). The LW-forced pool volume is strongly and positively correlated to the height of the LW jam. The results confirm that dead wood pieces, especially when organized in jams, play an important geomorphic role also in sub-Antarctic streams. The amount of large wood pieces quantified in the study site represents reference values for the assessment of the geomorphic effects of beaver activity in other Tierra del Fuego streams

Medium- and short-term channel and island evolution in a disturbed gravel bed river (Brenta River, Italy)

The timing and extent of the morphological and island changes that have occurred in the last thirty years in a gravel bed river that has been heavily impacted by human activities were analysed by nine sets of aerial photographs, repeated topographical measurements and morphological- vegetation surveys. Dam operations and gravel mining activities have produced modifications in the natural sediment regime that have generated important morphological responses in the channel. Large areas of the formerly active channel were colonised by riparian forest, both as islands and as marginal woodlands. The cessation of gravel extraction in the late 1990s seems to be causing incipient reversion of this pattern, with evidence of vegetation erosion/channel widening. Alteration of sediment regime has played a major role in the medium- and short-term channel evolution. However, only relevant flood events (recurrence interval >10 years) appear to determine substantial island erosion and, therefore, the proportion of islands versus channel fluctuates depending on flood history. Smaller scale analysis (sub-reach level) was more effective in describing morphological responses and relationships with the sediment dynamics within the 20 km study reach

An update of the sediment fluxes investigation in the Rio Cordon (Italy) after 25 years of monitoring

Quantification of bed-load transport in high-gradient mountain streams is important, but the field data needed to test transport models are scarce and difficult to obtain. In the present study, we describe the experimental station for monitoring water and sediment fluxes built in 1985 on the Rio Cordon, a small step-pool channel in the eastern Italian Alps. The measuring station consists of an inclined frame that separates fine from coarse sediments (D>20 mm), which are continuously measured by a series of ultrasonic sensors fitted above a storage area. The acquired 25-year dataset, which comprises a high-magnitude/ low-recurrence flood event, has allowed a magnitude-frequency analysis of bed-load volumes to be performed. Results from a combined frequency analysis of peak water discharge and total bed-load volumes are presented. In addition, the integration between the sediment transport dataset and the repeated surveys of sediment sources and of channel changes allowed us to assess the geomorphological effectiveness of different flood events. Despite the importance of the experimental station for making these bed-load observations possible, its maintenance costs are not low and these may have an impact on its future existence. At the same time, improving current instrumentation and future installations with novel technology would make the station an ideal location for calibrating surrogate techniques for sediment transport monitoring