The effects of water-table position on accretion/erosion of a beach have been well documented in the literature. A lower groundwater-table facilitates deposition of the sand transported by waves since it reduces flow velocities during backwash and prolongs laminar flow. On the contrary, a high water-tableresults in a condition favoring beach erosion. Beach dewatering (BD), i.e. the artificial lowering of the water-table within beaches by a systems of drains, has been studied and applied over the last few decades as a possible methodology of shore stabilization. However, the installations carried out worldwide do not provide a convincing demonstration of the system capability. The initial position of the drain respect to the beach profile and the flow rates through the drain system are the key design parameters. A BD system has been installed on the Ravenna coastline in 2004. A 100 m long drain has been stablished on the beach just north of the Fiumi Uniti river mouth, a portion of the Adriatic Sea coastline characterized over the last decades by significant erosion due to land subsidence, of both natural and anthropogenic origin, and a decrease of sediment supply from the river. A finite element variably-saturated groundwater flow model is implemented to the actual vertical litho-stratigraphy of the beach and BD configuration. The drain effect on the beach groundwater table is simulated using the results by a Boussinesq wave propagation model as external boundary condition. The results show that the presence of a shallow relatively low-permeable layer, originated from the sedimentation in a marsh environment occurred till 25 years ago, significantly decreases the water volume drained by the system, thus being responsible for a relatively-low efficiency of the BD strategy. The study allows to conclude that an advanced modeling approach is very useful to support the BD system design that, by contrast, has been usually based mainly on empirical criteria up to date.
Piccini, M.F., Gonella, M., Teatini, P., Gabbianelli, G. (2006). Modeling Groundwater Response to Beach Dewatering at Ravenna Shoreline. LA VALLETTA : University of Malta.
Modeling Groundwater Response to Beach Dewatering at Ravenna Shoreline
GONELLA, MARCO;GABBIANELLI, GIOVANNI
2006
Abstract
The effects of water-table position on accretion/erosion of a beach have been well documented in the literature. A lower groundwater-table facilitates deposition of the sand transported by waves since it reduces flow velocities during backwash and prolongs laminar flow. On the contrary, a high water-tableresults in a condition favoring beach erosion. Beach dewatering (BD), i.e. the artificial lowering of the water-table within beaches by a systems of drains, has been studied and applied over the last few decades as a possible methodology of shore stabilization. However, the installations carried out worldwide do not provide a convincing demonstration of the system capability. The initial position of the drain respect to the beach profile and the flow rates through the drain system are the key design parameters. A BD system has been installed on the Ravenna coastline in 2004. A 100 m long drain has been stablished on the beach just north of the Fiumi Uniti river mouth, a portion of the Adriatic Sea coastline characterized over the last decades by significant erosion due to land subsidence, of both natural and anthropogenic origin, and a decrease of sediment supply from the river. A finite element variably-saturated groundwater flow model is implemented to the actual vertical litho-stratigraphy of the beach and BD configuration. The drain effect on the beach groundwater table is simulated using the results by a Boussinesq wave propagation model as external boundary condition. The results show that the presence of a shallow relatively low-permeable layer, originated from the sedimentation in a marsh environment occurred till 25 years ago, significantly decreases the water volume drained by the system, thus being responsible for a relatively-low efficiency of the BD strategy. The study allows to conclude that an advanced modeling approach is very useful to support the BD system design that, by contrast, has been usually based mainly on empirical criteria up to date.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
