Publication Date:
2022-05-06
Description:
The Versilia plain, a well-known and populated tourist area in northwestern Tuscany,
is historically subject to floods. The last hydrogeological disaster of 1996 resulted in 13 deaths and in
loss worth hundreds of millions of euros. A valid management of the hydraulic and flooding risks
of this territory is therefore mandatory. A 7.5 km-long stretch of the Versilia River was simulated
in one-dimension using river cross-sections with the FLO-2D Basic model. Simulations of the
channel flow and of its maximum flow rate under di erent input conditions highlight the key role of
topography: uncertainties in the topography introduce much larger errors than the uncertainties in
roughness. The best digital elevation model (DEM) available for the area, a 1-m light detection and
ranging (LiDAR) DEM dating back to 2008–2010, does not reveal all the hydraulic structures (e.g.,
the 40 cm thick embankment walls), lowering the maximum flow rate to only 150 m3/s, much lower
than the expected value of 400 m3/s. In order to improve the already existing input topography,
three di erent possibilities were considered: (1) to add the embankment walls to the LiDAR data
with a targeted Di erential GPS (DGPS) survey, (2) to acquire the cross section profiles necessary for
simulation with a targeted DGPS survey, and (3) to achieve a very high resolution topography using
structure from motion techniques (SfM) from images acquired using an unmanned aerial vehicle
(UAV). The simulations based on all these options deliver maximum flow rates in agreement with
estimated values. Resampling of the 10 cm cell size SfM-DSM allowed us to investigate the influence
of topographic resolution on hydraulic channel flow, demonstrating that a change in the resolution
from 30 to 50 cm alone introduced a 10% loss in the maximum flow rate. UAV-SfM-derived DEMs are
low cost, relatively fast, very accurate, and they allow for the monitoring of the channel morphology
variations in real time and to keep the hydraulic models updated, thus providing an excellent tool for
managing hydraulic and flooding risks.
Description:
This work was supported by the Fondazione Cassa di Risparmio di Lucca, within the Project “Clima
e eventi alluvionali estremi in Versilia: integrazione di nuove tecniche geoarcheologiche, geomorfologiche,
geochimiche e simulazioni numeriche”, 2016-18 (Principal Investigator M. Bini), and by the University of Pisa,
within the Project PRA_2018_41 “Georisorse e Ambiente”.
Description:
Published
Description:
id 1630
Description:
7A. Geofisica per il monitoraggio ambientale
Description:
JCR Journal
Keywords:
DEM
;
structure from motion
;
unmanned aerial vehicle
;
FLO2D
;
Versilia Plain
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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