Monitoring and modelling of pore water pressure changes and riverbank stability during flow events
Article first published online: 4 FEB 2004
Copyright © 2004 John Wiley & Sons, Ltd.
Earth Surface Processes and Landforms
Volume 29, Issue 2, pages 237–254, February 2004
How to Cite
Rinaldi, M., Casagli, N., Dapporto, S. and Gargini, A. (2004), Monitoring and modelling of pore water pressure changes and riverbank stability during flow events. Earth Surf. Process. Landforms, 29: 237–254. doi: 10.1002/esp.1042
- Issue published online: 4 FEB 2004
- Article first published online: 4 FEB 2004
- Manuscript Accepted: 4 MAR 2003
- Manuscript Revised: 16 JAN 2003
- Manuscript Received: 5 APR 2002
- pore water pressures;
- saturated and unsaturated ﬂow;
- riverbank stability;
- riverbank failure;
- Sieve River, Italy
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. Riverbank stability analysis was conducted by applying the limit equilibrium method (Morgenstern-Price), using pore water pressure distributions obtained by the seepage analysis.
The simulation of the 14 December 1996 event, during which a bank failure occurred, is reported in detail to illustrate the relations between the water table and river stage during the various phases of the hydrograph and their effects on bank stability. The simulation, according to monitored data, shows that the failure occurred three hours after the peak stage, during the inversion of ﬂow (from the bank towards the river). A relatively limited development of positive pore pressures, reducing the effective stress and annulling the shear strength term due to the matric suction, and the sudden loss of the conﬁning pressure of the river during the initial drawdown were responsible for triggering the mass failure.
Results deriving from the seepage and stability analysis of nine selected ﬂow events were then used to investigate the role of the ﬂow event characteristics (in terms of peak stages and hydrograph characteristics) and of changes in bank geometry. Besides the peak river stage, which mainly controls the occurrence of conditions of instability, an important role is played by the hydrograph characteristics, in particular by the presence of one or more minor peaks in the river stage preceding the main one. Copyright © 2004 John Wiley & Sons, Ltd.