Multiscale structure of meanders

This is the final version of the article. Available from the publisher via the DOI in this record..River meander planforms can be described based on wavelet analysis, but an objective method to identify the main characteristics of a meander planform over all spatial scales is yet to be found. Here we show how a set of simple metrics representing meander shape can be retrieved from a continuous wavelet transform of a planform geometry. We construct a synoptic multiple looping tree to establish the meander structure, revealing the embedding of dominant meander scales in larger-scale loops. The method can be applied beyond the case of rivers to unravel the meandering structure of lava flows, turbidity currents, tidal channels, rivulets, supraglacial streams, and extraterrestrial flows.This research was supported by the Royal Netherlands Academy of Arts and Sciences (KNAW), project SPIN3-JRP-29, and by NWO-WOTRO Science for Global Development, project WT76-269. We thank Meinhard Bayani Cardenas, the Associate Editor, Efi Foufoula-Georgiou, Jon Schwenk, and one anonymous reviewer for their comments and suggestions. The data used in this study can be obtained by contacting the corresponding author. The processing routines can be downloaded at https://github.com/bartverm/ meanderscribe.git

Quantifying shape and multiscale structure of meanders with wavelets

features in the landscape, but the processes shaping them, act on a wide range of spatial and temporal scales. This results in meanders that curve at several spatial scales with smaller scale curves embedded in larger scale curves. Here, we show how to quantify the multi-scale structure of meanders from the valley scale until the sub-meander scale based on continuous wavelet transforms of the planform curvature. The zero crossings and maximum lines of the wavelet transform capture the main characteristics of the meander shape and their structure is quantified in a scale-space tree (Figure 1). The tree is used to identify meander wavelength and how meanders are embedded in larger scale features. The submeander structure determines meander shape, which is quantified with two parameters: skewness and fattening. The method is applied to the Mahakam River planform, which features very sharp, angular bends. Strong negative fattening is found for this river which corresponds to angular non-harmonic meanders which are characterized by strong flow recirculation and deep scouring

Assessment of “Carbopeaking” in a hydropeaking-impacted river in the Italian Alpine area

Hydropeaking (i.e., rapid and frequent artificial flow fluctuations caused by reservoir-operated hydropower production) is a much-investigated river stressor, and has been associated, among others, to sudden changes in temperature (“thermopeaking”), underwater soundscape (“soundpeaking”), total dissolved gas saturation (“saturopeaking”). We have recently started investigating the “carbopeaking”, i.e., variations of greenhouse gas (mainly CO2) concentrations and evasion fluxes through the water-air interface associated with hydropeaks. Here we report on the methodology and preliminary results from a field-measurement campaign conducted in a single-thread Alpine river (River Noce, Italy) during multiple hydropeaking events. The analysis of water samples collected in the upstream reservoir showed CO2 oversaturation in the hypolimnion, around the depth of the hydropower intake system. In the Noce reach upstream of the hydropower plant outlet (i.e., in a residual flow stretch), the CO2 concentrations displayed diel fluctuations around the atmospheric equilibrium concentration, likely driven by diurnal primary production. Conversely, water released at the hydropower outlet during hydropeaking were consistently oversaturated in CO2 relative to the atmosphere, in agreement with the concentrations in the reservoir’s hypolimnetic water. As a result, hydropeaking events were associated with an alteration of the sub-daily patterns of CO2 concentration downstream of the hydropower outlet which, combined with higher gas exchange velocities occurring during higher flow rates, can cause periods of enhanced CO2 emissions. The results highlight the potential impact of hydropeaking on greenhouse gas emissions, demonstrating the need to account for sub-daily variations of flow and gas concentration to accurately quantify carbon balances in rivers impacted by hydropower

Coastal vulnerability assessment: through regional to local downscaling of wave characteristics along the Bay of Lalzit (Albania)

Coastal vulnerability is evaluated against inundation risk triggered by wave run-up through the evaluation of vulnerability levels (referred to as VLs) introduced by Bosom and Jiménez (2011). VLs are assessed through different wave climate characterizations, referring to regional (offshore wave climate) or local (nearshore wave climate) scales. The study is set along the Bay of Lalzit, a coastal area near Durrës (Albania). The analysis reveals that the results vary due to uncertainties inherent in the run-up estimation, showing that the computational procedure should be developed by taking into account detailed information about the local wave climate. Different approaches in choosing wave characteristics for run-up estimation significantly affect the estimate of shoreline vulnerability. The analysis also shows the feasibility and challenges of applying VL estimates in contexts characterized by limited data availability through targeted field measurements of the coast geomorphology and an overall understanding of the recent coastal dynamics and related controlling factors.</p

Ground motion models for Molise region (Southern Italy)

On October 31st and November 1st, 2002 two moderate earthquakes of moment magnitude Mw=5.7 (INGV-Harvard European-Mediterranean Regional Centroid-Moment tensor project) occurred in southern Italy. After the mainshocks, felt in many municipalities of the Molise and Puglia region, a strong motion and a seismic temporary network were installed in the epicentral area and surrounding regions. The strong motion network was composed by 9 stations, integrating the accelerometers of the permanent Rete Accelerometrica Nazionale (RAN network), and operated until December 2003. The strong motion data set is composed by 195 recordings from 51 earthquakes (2.5<Ml<5.4) recorded by 29 accelerometers (Dipartimento della Protezione Civile et al., 2004). In addition to the strong motion network, several Italian research institutions (Istituto Nazionale di Geofisica e Vulcanologia, INGV; Istituto Nazionale di Oceanografia e Geofisica, INOGS; Dipartimento per lo studio del Territorio e delle sue Risorse, University of Genoa, Dip.Te.Ris) installed a temporary regional network, composed by 35 seismic stations. This network aimed at monitoring and studying the evolution in time and space of the seismic sequence. More than 1900 aftershocks were recorded in the period November 1st - December 5th, 2002 (Chiarabba et al., 2005). The unified velocity-acceleration data set has been considered to derive ground motion models for peak ground acceleration and peak ground velocity for both maximum horizontal and vertical components. The results obtained for the Molise area have been compared with the attenuation pattern of the Umbria-Marche region (central Italy), that was recently investigated by Bindi et al. (2006). The remarkable differences observed indicate the need of a regional attenuation relation for the area and the need of further investigations, to better identify the role of source characteristics, anelastic and geometric attenuation and site effects in the evaluation of peak ground motion values

Exploring the role of trees in the evolution of meander bends: The Tagliamento River, Italy

To date, the role of riparian trees in the formation of scroll bars, ridges, and swales during the evolution of meandering channels has been inferred largely from field observations with support from air photographs. In situ field observations are usually limited to relatively short periods of time, whereas the evolution of these morphological features may take decades. By combining field observations of inner bank morphology and overlying riparian woodland structure with a detailed historical analysis of airborne LiDAR data, panchromatic, and color images, we reconstruct the spatial and temporal evolution of the morphology and vegetation across four meander bends of the Tagliamento River, Italy. Specifically we reveal (i) the appearance of deposited trees and elongated vegetated patches on the inner bank of meander bends following flood events; (ii) temporal progression from deposited trees, through small to larger elongated vegetated patches (pioneer islands), to their coalescence into long, linear vegetated features that eventually become absorbed into the continuous vegetation cover of the riparian forest; and (iii) a spatial correspondence between the resulting scrolls and ridge and swale topography, and tree cover development and persistence. We provide a conceptual model of the mechanisms by which vegetation can contribute to the formation of sequence of ridges and swales on the convex bank of meander bends. We discuss how these insights into the biomorphological processes that control meander bends advance can inform modeling activities that aim to describe the lateral and vertical accretion of the floodplain during the evolution of vegetated river meanders

Task 3 - Molise - Deliverable D7: Validation shaking scenarios.

The main goal of this report is the computation of the bedrock seismic motion at 5 municipalities located in the Molise area (Bonefro, S.Giuliano, Colletorto, S.Croce di Magliano, Ripabottoni, hereafter referred to as sites BNF, SGI, CLT, SCM and RPB, respectively). This area represents one of the validation case studies, planned in the framework of Project S3 which aim is the production of ground shaking scenarios for moderate magnitude earthquakes. Indeed, the recently occurred Molise earthquake represents a proper opportunity to compare synthetic simulations with real data. Acceleration time series were recorded during the October 31, 2002 and November 1, 2002 main shocks by analog and digital instruments managed by the Italian Civil Protection Department [DPC-SSN, 2004] while acceleration and velocity records were collected during the first month of seismic activity by DPC, INGV, INOGS, Dip.Te.Ris.(Genoa) (see §2.1 and Deliverable D6). Both strong and weak motion data were employed to infer regional ground motion prediction equations and spectral attenuation models (§2.3 and §2.4) while acceleration time series recorded during the first main shock by nearby stations were used to constrain the seismogenic sources of the October 31 and November 1, 2002 twin earthquakes (§4.1). Bedrock shaking scenarios at different level of complexity were produced by ground motion prediction equations (scenarios of level 0, §4.2), high frequency (f>1Hz) simulations (scenarios of level I, §4.3) and broad band (0-12 Hz) simulations (scenarios of level II, §4.4). Comparison of results obtained with different simulations methods confirms the complexity of the Molise area as regard to both seismogenic and attenuation properties of the crust. Especially for this area the ground motion prediction is constrained by the demand of simulations reproducing different features of the seismic wavefield. In particular, the input motion for site effect modelling, performed at sites located in the epicentral area, was computed with a broad band technique able to reproduce the complete wave field in the frequency band 0-10 Hz in terms of acceleration time series (scenarios of level II scenarios)

An ecosystem service approach to license new run of the river hydropower plants

Freshwater ecosystems provide several services (ES) to society. Hydropower production is one of the most relevant ES supported by Alpine rivers, and it is often in conflict with other river uses and services. Recently, the demand by local authorities, public or private agencies for new small hydropower plants have been increasing, and new conflicts have been arousing. We propose an approach to model the alterations of selected ES which integrates hydrological and habitat models and evaluates possible variations of the selected ES under different withdrawal scenarios. The case-study is the Noce River, a gravel-bed river in the Italian Alps (Trentino, North East Italy) which is subject to hydropeaking. We selected four ES: habitat for juvenile and adult marble trout as biodiversity proxy, rafting as recreational services, and small hydropower production as provisioning service. We evaluated the variations of these services for maximum and no hydropower production, chosen as different boundary conditions. Moreover, we simulated the presence of four new different small hydropower plants with increasing withdrawals. Large hydropower is the key driver, affecting all the selected ES. Small hydropower decreases the potential for rafting up to 64%, while it is often negligible for other services