529 research outputs found
Reply to Reviewer#1 on "Assessing rating-curve uncertainty and its effects on hydraulic model calibration" by A. Domeneghetti et al.
No full textEffects of minor drainage networks on flood hazard evaluation
No full textScientific literature reports a plethora of numerical tools of different complexity (e.g. 1D, 2D raster-based or full 2D models) for flood hazard and flood risk evaluation. The correct identification of the appropriate model still represents a key aspect in the overall flood hazard process even though the potential of these modelling instruments are increased by the availability of high computational resources and by the amount of high-resolution topographic data provided by recent survey techniques. Given this context the present analysis investigates the effects of minor drainage networks on the estimation of flood hazard in a flood-prone area along the Enza River, close to the village of Sorbolo a Levante (RE, northern Italy). By means of a full 2D hydraulic model (Telemac-2D), the effects of the drainage system is analysed using three unstructured meshes with different degrees of complexity: (1) the minor drainage system allows the possibility to convey water outside the study area (REF); (2) the drainage system is reproduced only in terms of preferential flow-paths (REF-noFlow); (3) the drainage network is completely neglected (REF-noDN). The analysis indicates that the maximum flood extent seems not to be influenced by the mesh schematization, while water depths and the total volume are significantly related to the model schematization. Even if this analysis refers to a specific case study and further investigations are needed, it shows the fundamental role of the drainage network in controlling water depth distribution and the duration of the inundation, which should be accurately reproduced by numerical models
Flow duration curves from surface reflectance in the near infrared band
No full textFlow duration curve (FDC) is a cumulative frequency curve that shows the percent of time a specific discharge has been equaled or exceeded during a particular period of time at a given river location, providing a comprehensive description of the hydrological regime of a catchment. Thus, relying on historical streamflow records, FDCs are typically constrained to gauged and updated ground stations. Earth Observations can support our monitoring capability and be considered as a valuable and additional source for the observation of the Earth’s physical parameters. Here, we investigated the potential of the surface reflectance in the Near Infrared (NIR) band of the MODIS 500 m and eight-day product, in providing reliable FDCs along the Mississippi River. Results highlight the capability of NIR bands to estimate the FDCs, enabling a realistic reconstruction of the flow regimes at different locations. Apart from a few exceptions, the relative Root Mean Square Error, rRMSE, of the discharge value in validation period ranges from 27–58% with higher error experienced for extremely high flows (low duration), mainly due to the limit of the sensor to penetrate the clouds during the flood events. Due to the spatial resolution of the satellite product higher errors are found at the stations where the river is narrow. In general, good performances are obtained for medium flows, encouraging the use of the satellite for the water resources management at ungauged river sites
Assessing rating-curve uncertainty and its effects on hydraulic model calibration
No full textThis study considers the overall uncertainty affecting river flow measurements and proposes a framework for analysing the uncertainty of rating-curves and its effects on the calibration of numerical hydraulic models. The uncertainty associated with rating-curves is often considered negligible relative to other approximations affecting hydraulic studies, even though recent studies point out that rating-curves uncertainty may be significant. This study refers to a ~240 km reach of River Po and simulates ten different historical flood events by means of a quasi-twodimensional (quasi-2-D) hydraulic model in order to generate 50 synthetic measurement campaigns (5 campaigns per event) at the gauged cross-section of interest (i.e. Cremona streamgauge). For each synthetic campaign, two different procedures for rating-curve estimation are applied after corrupting simulated discharges according to the indications reported in the literature on accuracy of discharge measurements, and the uncertainty associated with each procedure is then quantified. To investigate the propagation of rating-curve uncertainty on the calibration of Manning's roughness coefficients further model simulations are run downstream Cremona's cross-section. Results highlight the significant role of extrapolation errors and how rating-curve uncertainty may be responsible for estimating unrealistic roughness coefficients. Finally, the uncertainty of these coefficients is analysed and discussed relative to the variability of Manning's coefficient reported in the literature for large natural streams
On the use of SRTM and altimetry data for flood modeling in data-sparse regions
No full textThe growing availability of remotely sensed data has fostered the implementation of hydraulic modeling in poorly gauged regions. However, these applications suffer the lack of knowledge of river bathymetry, which cannot be directly inferred from satellite instruments. This study explores the possibility to set up, calibrate, and validate a hydrodynamic model which geometry is based on global and freely available satellite data. First, the study tests two different procedures for inferring the river bathymetry under the water surface level. Second, focusing on a Po River stretch of ∼140 km (Northern Italy), the study further assesses the suitability of spaceborne topographic and remotely sensed altimetry data (i.e.; ERS-2 and ENVISAT) for implementing and calibrating hydrodynamic models. Referring to 90 m SRTM (Shuttle Radar Topography Mission) digital elevation model for the representation of the riverbed morphology, the work analyzes the performances of different 1-D numerical models which cross sections are modified according to two approaches: (1) Channel Bankfull depth (CB) and (2) Slope-Break (SB) approach. The calibration and validation processes are performed by referring to extended altimetry time series (∼16 years of data), while the accuracy and trustworthiness of 1-D models are tested with reference to a quasi-2-D model based on detailed geometry data. Results show that both CB and SB approaches enhance the performance of SRTM-based models. In particular, the SB approach is completely based on satelliteborne data and shows Nash-Sutcliffe efficiency, MAE, and RMSE values similar to those obtained with the benchmark model
Preface: Remote sensing for flood mapping and monitoring of flood dynamics
No full textThis Special Issue is a collection of papers that focus on the use of remote sensing data and describe methods for flood monitoring and mapping. These articles span a wide range of topics; present novel processing techniques and review methods; and discuss limitations and challenges. This preface provides a brief overview of the content
Identifying robust large-scale flood risk mitigation strategies: a quasi-2D hydraulic model as a tool for the Po river
No full textThis paper focuses on the identification of large-scale flood risk mitigation strategies for the middle-lower
reach of River Po, the longest Italian river and the largest in terms of streamflow. This study develops and
tests the applicability of a quasi-2D hydraulic model to aid the identification of large-scale flood risk mitigation
strategies relative to a 500-year flood event other than levee heightening, which is not technically
viable nor economically conceivable for the case study. Different geometrical configurations of the
embankment system are considered and modelled in the study: no overtopping; overtopping and levee
breaching; overtopping without levee breaching. The quasi-2D model resulted in being a very useful tool
for (1) addressing the problem of flood risk mitigation from a global - perspective (i.e., entire middlelower
reach of River Po), (2) identifying critical reaches, inundation areas and corresponding overflow
volumes, and (3) generating reliable boundary conditions for smaller scale studies aimed at further analyzing
the hypothesized flood mitigation strategies using more complex modelling tools (e.g., fully 2D
approaches). These are crucial tasks for institutions and public bodies in charge of formulating robust
flood risk management strategies for large European rivers, in the light of the recent Directive 2007/
60/EC on the assessment and management of flood risks (European Parliament, 2007)
Thermal history of nakhlites: A comparison between MIL 03346 and its terrestrial analogue Theo’s flow
No full textHigh resolution single-crystal X-ray diffraction (HR-SCXRD) and Mössbauer spectroscopy of the intracrystalline cation distribution have been performed on augitic core-crystals from a Miller Range nakhlite (sample MIL 03346,13) with approximate composition of En36Fs24Wo40. The Mössbauer data on the single-crystal yielded a very low Fe3+ content [Fe3+/Fetotal - 0.033(23)a.p.f.u.] that, together with the Electron microprobe analysis (EMPA) and the X-ray structural data allowed us to obtain the accurate cation site distribution and the Fe2+-Mg degree of order. This leads to a closure temperature (Tc) of 500 with a standard deviation of ±100°C that would correspond to a slow cooling rate, which is in disagreement with petrologic evidence that indicates that this sample originates from a fast cooled (~3-6°C/h) lava flow.In order to clarify this discrepancy we undertook (i) a SC-XRD study of an augite (~En49Fs9 Wo42) from a pyroxenite (TS7) of Theo's flow, a 120-m-thick lava flow regarded as a terrestrial analogue of MIL 03346; (ii) an annealing experiment at 600°C on a crystal from exactly the same fragment of MIL 03346. SC-XRD data from TS7 augite yields a Tc=600(20)°C, consistent with the cooling rate expected at 85m below the surface. This Tc is higher, although similar within error, to the Tc=500(100)°C obtained for MIL 03346; thus suggesting relatively slower cooling for MIL 03346 with respect to TS7. The annealing experiment on the MIL 03346 crystal clearly showed that the degree of order remained unchanged, further confirming that the actual Tc is close to 600°C.This result appears inconsistent with the shallow depth of origin (~<2m) assumed for MIL 03346, further supporting the discrepancy between MIL 03346 textural and petrologic evidence of fast cooling and the abovementioned Tc results obtained for augite. Therefore, a tentative scenario is that, soon after eruption and initial quench and while still at relatively high-T (~600°C), MIL 03346 was blanketed with subsequent lava flows that slowed down the cooling rate and allowed the augite Fe2+-Mg exchange reaction to proceed
Flow duration curve from satellite: Potential of a lifetime SWOT mission
No full textA flow duration curve (FDC) provides a comprehensive description of the hydrological regime of a catchment and its knowledge is fundamental for many water-related applications (e.g., water management and supply, human and irrigation purposes, etc.). However, relying on historical streamflow records, FDCs are constrained to gauged stations and, thus, typically available for a small portion of the world's rivers. The upcoming Surface Water and Ocean Topography satellite (SWOT; in orbit from 2021) will monitor, worldwide, all rivers larger than 100 m in width (with a goal to observe rivers as small as 50 m) for a period of at least three years, representing a potential groundbreaking source of hydrological data, especially in remote areas. This study refers to the 130 km stretch of the Po River (Northern Italy) to investigate SWOT potential in providing discharge estimation for the construction of FDCs. In particular, this work considers the mission lifetime (three years) and the three satellite orbits (i.e., 211, 489, 560) that will monitor the Po River. The aim is to test the ability to observe the river hydrological regime, which is, for this test case, synthetically reproduced by means of a quasi-2D hydraulic model. We consider different river segmentation lengths for discharge estimation and we build the FDCs at four gauging stations placed along the study area referring to available satellite overpasses (nearly 52 revisits within the mission lifetime). Discharge assessment is performed using the Manning equation, under the assumption of a trapezoidal section, known bathymetry, and roughness coefficient. SWOT observables (i.e., water level, water extent, etc.) are estimated by corrupting the values simulated with the quasi-2D model according to the mission requirements. Remotely-sensed FDCs are compared with those obtained with extended (e.g., 20-70 years) gauge datasets. Results highlight the potential of the mission to provide a realistic reconstruction of the flow regimes at different locations. Higher errors are obtained at the FDC tails, where very low or high flows have lower likelihood of being observed, or might not occur during the mission lifetime period. Among the tested discretizations, 20 km stretches provided the best performances, with root mean absolute errors, on average, lower than 13.3%
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