SIMULATIONS
OF BANK EROSION PROCESSES |
Massimo RINALDI - Department of Civil Engineering, University of Florence
SIEVE RIVER PROJECT
Pore
water pressures (positive and negative) were monitored for four years (1996-1999)
using a series of tensiometer-piezometers at increasing depths in a riverbank
of the Sieve River, Tuscany (Central Italy), with the overall objective of investigating
pore pressure changes in response to flow events and their effects on bank stability.
The saturated/unsaturated flow was modelled using a finite element seepage analysis,
for the main flow events occurring during the four year monitoring period. Modelling
results were validated by comparing measured with computed pore water pressure
values for a series of representative events.
| SIMULATION 1: Role of pore water pressures |
| River
bank:
Sieve River at Fornacina |
| Methods
of analysis:
Pore water pressure changes are modelled by SEEP/W in transient conditions
(using the hydrograph and rainfall as boundary conditions); bank stability
is modelled by SLOPE/W. The simulation is with ‘constant geometry’ (bank
deformation due to fluvial erosion is not taken into account, but bank
geometry changes only after the bank failure). |
| Author: S.Dapporto |
| Main references:
Rinaldi et al. (2001); Rinaldi et al. (2004) |
| SIMULATION 2: Seepage and stability analysis with deforming bank profile |
| River
bank:
Sieve River at Fornacina |
| Methods
of analysis:
Modelling of the riverbank retreat during the 19/11/1999 flow event includes
for each step the following components (see Flow
chart): a) fluvial erosion and consequent changes in bank geometry;
b) finite element seepage analysis; c) stability analysis by limit equilibrium
method. |
| Author: S.Dapporto |
| Main references: Dapporto (2003); Dapporto & Rinaldi (2003) |
Research
Project: “Modelling
hydraulic and geotechnical river bank erosion processes interactions”, funded
by the Royal Society (UK) (European Science Exchange Programme) - Dr. S.Darby
(Department of Geography, University of Southampton, UK) & Dr. M.Rinaldi
(University of Florence, Italy).
The
general aim of the project is to apply hydraulic & geotechnical modelling
techniques to investigate the interaction between two bank erosion processes:
(1) the erosive action of the flow & (2) mass failure of banks undermined
by fluvial erosion.
The
research was undertaken at two diverse study sites (Cecina River, Central Italy,
and the River Asker, Southern UK), representing end-members in a spectrum ranging
from very active (Cecina bank erosion rate ~ 7-17 m/yr) to mildly active (Asker
bank erosion rate ~ 0.2 m/yr) eroding river meanders. We have devised a new
methodological approach that involves undertaking a combination of monitoring
and hydraulic modelling investigations. Our rationale is to employ Computational
Fluid Dynamics (CFD) techniques to obtain simulated high-resolution near-bank
boundary shear stress data as a substitute for empirical data.
Main references: Rossi Romanelli et al. (2004); Darby & Rinaldi (2004 a, b); Darby et al. (2004 a, b)
| SIMULATION
3: Seepage
and stability with ‘constant geometry’ |
| River
bank:
Cecina River at Sterza confluence |
| Methods
of analysis:
Pore water pressure changes are modelled by SEEP/W in transient conditions
(using the hydrograph and rainfall as boundary conditions); bank stability
is modelled by SLOPE/W. The simulation with ‘constant geometry’ (similarly
to simulation 1) represents the ‘control simulation scenario’ in which
the bank is not deformed. Comparison with the scenario of bank deformation
by fluvial erosion will enable the effect of bank deformation on bank
stability to be isolated. |
| Author: L.Luppi |
| Main references: Luppi (2004); Rossi Romanelli et al. (2004) |
| SIMULATION
4: Seepage
and stability with deforming bank profile |
| River
bank:
Cecina River at Sterza confluence |
| Methods
of analysis:
In this preliminary analysis, near-bank boundary shear stress distribution
have also been evaluated at low resolution by applying a 1-dimensional
HEC-RAS model (simulation).
The near-bank shear stress distribution is then estimated using the Simons
& Senturk (1977) distribution. Water table position is assumed from
simulation 3 (SEEP with constant geometry) while a simplified pore water
pressure distribution is assumed above the water table. Safety factor
for slide and cantilever failures is calculated for each time step (see
Flow
chart). |
| Author: L.Nardi |
| Main references: Nardi (2004); Canovaro et al. (2004) |
| SIMULATION
5: Hydrodynamic
- Seepage - Stability modelling with deforming bank profile |
| River
bank:
Cecina River at Sterza confluence |
| Methods of analysis: Near-bank boundary shear stresses are computed by a hydrodynamic simulation using DELFT3D (2D depth averaged simulation) (Author: Beatrice Mengoni, University of Florence; Supervisor: Erik Mosselman, WL|Delft Hydraulics, NL). Near-bank shear stresses are used to deform the bank toe by using existing excess shear stress model for fluvial erosion. Pore water pressure changes are modelled by SEEP/W in transient conditions (using the hydrograph and rainfall as boundary conditions). Safety factor for slide and cantilever failures is then calculated for each time step. |
| Author: L.Luppi & F.Agresti |
| Main references: Mengoni (2004); Agresti (2005) |
Agresti
F. (2005) - Modellazione dei processi di arretramento di una sponda
del Fiume Cecina. Unpublished thesis, University of Florence, Faculty of
Engineering.
Attardo
S. (2007) - Influenza della vegetazione sulla stabilità
di sponde fluviali. Unpublished
thesis, University of Florence, Faculty of Engineering.
Canovaro F., Luppi L., Mengoni B., Nardi L., Rossi Romanelli L. & Teruggi L.B. (2004) – Monitoraggio e modellazione dei processi di arretramento di sponde fluviali. 29° Convegno di Idraulica e Costruzioni Idrauliche, Trento, 7-10 Settembre 2004, Editoriale Bios, Cosenza, 421-427.
Coppi
L. (2006) - Modellazione dei processi di erosione di sponda in
fiumi della Toscana. Unpublished
thesis, University of Florence, Faculty of Engineering.
Dapporto
S. (2003) – Processi di erosione e meccanismi di instabilità
di sponde fluviali: monitoraggio, modellazione e analisi. PhD
Thesis, University of Florence.
Darby S.E. & Rinaldi M. (2004b) -
The influence of fluvial bank erosion as a triggering mechanism for mass-wasting.
Abstracts Joint International Geomorphology Conference, Glasgow, August 2004.
Darby S.D., Rinaldi
M., Spyropoulos E., Bressloff N. & Teruggi L.B. (2004b) – Fluvial
bank erosion rates in meander bends: insights from a monitoring and modelling
study in the UK and Italy. Abstracts 32nd International
Geological Congress, Firenze, 20-28 August 2004.
Francalanci
S., Rinaldi M., Solari L., Nardi L. (2010)
– Modelling bank retreat in a single river bend. In: Vionnet C., García
M.H., Latrubesse E.M., Perillo G.M.E. (Eds), River, Coastal and Estuarine Morphodynamics:
RCEM 2009, Proceedings RCEM 2009 Symposium, 21-25 September 2009, Santa Fe,
Argentina, Taylor & Francis Group, London, 97-102.
Luppi
L., Rinaldi M., Teruggi L.B., Darby S.E., Nardi L. (2009) – Monitoring
and numerical modelling of riverbank erosion processes: a case study along the
Cecina River (Central Italy). Earth Surface Processes and Landforms. DOI:
10.1002/esp.1754, Vol.34 (4), 530-546.
Mengoni
B. (2004) –
Nardi
L. (2004) - Monitoraggio e modellazione dell'erosione e della stabilità
di una sponda del Fiume Cecina. Unpublished
thesis, University of Florence, Faculty of Engineering.
Nardi L., Francalanci S., Mengoni B., Rinaldi M., Solari L. & Lanzoni S. (2008) – Indagini preliminari sui processi di arretramento delle sponde nei corsi d’acqua in ghiaia. Atti IDRA 2008, 31° Convegno di Idraulica e Costruzioni Idrauliche, Perugia, 9-12 Settembre 2008, CD ROM, 8 pp.
Nardi L., Rinaldi M., Solari L. (2010) – Experimental observations on the retreat of non-cohesive river banks. In: Vionnet C., García M.H., Latrubesse E.M., Perillo G.M.E. (Eds), River, Coastal and Estuarine Morphodynamics: RCEM 2009, Proceedings RCEM 2009 Symposium, 21-25 September 2009, Santa Fe, Argentina, Taylor & Francis Group, London, 89-95.
Rinaldi M. & Darby S.E. (2008) - Modelling river-bank-erosion processes and mass failure mechanisms: progress towards fully coupled simulations. In: Habersack H., Piégay H. & Rinaldi M. (Eds), Gravel-Bed Rivers 6 - From Process Understanding to River Restoration. Series Developments in Earth Surface Processes, 11, Elsevier, Netherlands, 213-239.
