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

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

analysis of morphological processes in a disturbed gravel bed river piave river integration of lidar data and colour bathymetry

The magnitude of river morphological changes are better analyzed through the use of quantitative approaches, wherein resolution accuracy and uncertainty assessment are treated as crucial key-factors. In this sense, the creation of precise DEMs (Digital Elevation Models) of rivers represents an affordable tool to analyze geomorphic variations and budgets, except for wetted areas, where reliable channel digitalization can normally be obtained only using expensive bathymetric surveys. The proposed work aims at improving channel surface models without having available bathymetric sensors, by deriving dry areas elevations from LiDAR data and water depth of wetted areas from aerial photos through a predictive depth-colour relationship. The methodology was applied to two different sub-reaches of the Piave River, a gravel-bed river which suffered severe flood events in 2010. Erosion and deposition patterns were identified through DEM differencing, showing a predominance of scour processes which can lead to channel instability situations. The bathymetric output was compared to other previously-derived models confirming the accuracy of the in-channel elevation estimates. Finally, a discussion on the role played by longitudinal protections during the studied flood events is proposed, focusing the attention on the incidence of two major bank erosions that removed significant volumes of stable areas

A mechanistic ecohydrological model to investigate complex interactions in cold and warm water‐controlled environments: 1. Theoretical framework and plot‐scale analysis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95321/1/jame60.pd

Il legname in alveo nei torrenti alpini: analisi quantitativa e modellazione GIS

The present work analyzes the wood presences in Dolomites streams. The processes that contribute to the formation, input, and transfer of such material in network channel have been investigated. Main task is to assess for guidance planning risk management in mountain areas. The study sites are represented by 13 mountain basins (drainage area ranging from 1 to 70 Km2), located in the upper part of Cordevole watershed basin (Province of Belluno). More than 9,000 wood elements were counted during the field survey. Wood storage is highly variable (8-106 m3 per hectare of streambed area), but a significant inverse relationship with drainage area is evident, as well as with occurrence of hillslope instabilities. Median log diameters do not vary considerably among the study basins (0.08 – 0.13 m), whereas large differences exist with regard to log length (0.79 – 3,75 m). The ratio between log length and the average channel width remains close to 1 for channels < 3rd order (A<10 km2), and drops for higher-order basins (down to 0.2-0.3). Therefore, a much higher mobility of wood elements might be envisaged for such channels, and this could be a reason for their lower wood load per unit of bed area. However, these larger basins present also higher degrees of human impact (roads, towns, control works) which are presumed to contribute to diminish the presence of in-channel wood. The second part of the research has been directed to develop a forecast tool able to assess the in-channel wood (LW). A GIS based model was chosen to create a spatial analyst in order to reproducing three main processes: 1) recruiting LW 2) slope transfer, 3) in-channel wood translation. For the first processes the areas of likely LW have been identified, through the intersection of the forest map and the hydrogeological instability susceptibility map (obtained by the means of the method of Weight of Evidence). The simulation of input and transfer along streams was obtained by applying the functions of LW propagation and decay, related to the soil morphology, the flow distance from network channel and stream power function. The model results are satisfactory: the simulated volume of LW are on the same order of magnitude as observed in the field surveys (Relative error = 0,04-4,9; average relative error = 1.2). Finally, different maps are presented to show the stream reach who are at highest risk of LW storage.Il presente lavoro analizza la presenza del materiale legnoso in corsi d’acqua delle Dolomiti. Sono stati studiati i processi che concorrono alla formazione, all’immissione e alla traslazione di tale materiale nelle reti idrografiche. Lo scopo finale è quello di dare delle indicazioni nella pianificazione della gestione del rischio idraulico in territorio montano. La ricerca ha riguardato 13 bacini montani di diversa grandezza (da circa 1 a 70 Km2) all’interno dell’Alto Cordevole (Provincia di Belluno). Lungo i collettori analizzati sono stati rinvenuti più di 9000 elementi legnosi. La quantità di legname presente nei collettori è risultata molto variabile (8-106 m3 per ettaro di superficie d’alveo), ma con una significativa correlazione inversa tra volume legnoso ed area drenata, ed una chiara associazione alla presenza di versanti instabili. Le dimensioni mediane dei tronchi rilevati presentano diametri abbastanza simili fra i diversi bacini (0,08-0,13 m), mentre la lunghezza risulta più differenziata (varia da 0,79 a 3,75 m). E’ stato calcolato che il rapporto tra la lunghezza dei tronchi e larghezza del canale è maggiore per i bacini con area drenata inferiore ai 30-40 km2, con valori prossimi all’unità nei bacini fino al 3° ordine, e coefficienti pari a 0,2 0,3 in quelli di 4° e 5° ordine. Si può quindi affermare che nei torrenti di ordine maggiore c’è una maggiore mobilitazione del legname. Questo aspetto, può essere una delle cause possibili della relazione inversa che sussiste tra volume areale di legname ed area drenata del bacino; tuttavia, la forte riduzione dei volumi legnosi nei corsi d’acqua più grandi è sicuramente ascrivibile al loro elevato grado di antropizzazione, (abitati, strade) che comporta frequenti interventi di sistemazione idraulico-forestale e di rimozione della vegetazione e del “detrito” vegetale in alveo. La seconda parte dell’attività di ricerca è stata indirizzata alla messa a punto di uno strumento previsionale per la quantificazione del legname in alveo (LW). Si è scelto di creare un modello di analisi spaziale su base GIS che simula distintamente i tre principali processi: 1) reclutamento di LW; 2) trasferimento lungo i versanti; 3) movimentazione del legname lungo la rete idrografica. Per il primo punto sono state individuate le aree sorgenti di legname potenzialmente reclutabile attraverso l’intersezione della carta dei particellari forestali e la carta della suscettibilità ai dissesti (ottenuta attraverso il metodo del Weight of Evidence). La simulazione dell’immissione in alveo e della successiva traslazione è stata ottenuta applicando delle funzioni di propagazione e decadimento legate alla morfologia del territorio, alla flow distance dalla rete idrografica ed alla stream power. Il modello ha restituito dei risultati soddisfacenti, simulando un volume di LW entro lo stesso ordine di grandezza di quello rilevato in campo. (errore relativo = 0,04-4,9; errore relativo medio = 1,2). Infine sono state redatte delle mappe in cui si evidenziano i tratti di torrente maggiormente a rischio di deposito eccessivo di legname

Large wood storage in streams of the Eastearn Italian Alps and the relevance of hillslope processes

An understanding of the dynamics of large wood (LW) in mountain channels provides the basis for evaluating natural morphological patterns as well as managing potentially hazardous wood transport during flood events. Few studies have investigated the distribution of LW in managed streams of the Alps across a wide spatial scale. This paper presents extensive field measurements of LW storage and channel morphology carried out in 13 channels of the Eastern Italian Alps with drainage areas ranging from 1.2 to 70 km2, mean bed slope between 0.03 and 0.38, and channel width between 2 and 20 m. More than 9000 LW elements were measured in the 33 reaches surveyed. A geostatistical, geographic information system (GIS)-based model for wood recruitment from hillslope instabilities was also developed and applied to the study basin. LW storage in the study channels results as being much lower than in seminatural basins of comparable size and climate, and only basins characterized by extensive mass wasting processes contain high wood loads with relevant morphological consequences. The statistical analysis of LW storage at the reach scale indicates that unit stream power is apparently the most significant hydromorphological factor influencing LW storage, in agreement with studies in other world regions. However, we argue that the effect of unit stream power on LW storage is not only linked to flow transport capacity but also derives from its association with LW supply and valley morphology. Both the GIS model and statistical tests on field data indicate that hillslope instabilities connected to the channel network dominate the LW recruitment volume and the distribution of in-channel wood storage