Natural-based solution to mitigate flood risk due to SAND BOILS reactivations along the Po River

PROJECT DESCRIPTION

BACKGROUND

The occurrence of sand boils on river embankments during high water events is a common sign of backward erosion piping (BEP), an internal erosion process caused by seepage into the sandy aquifer beneath a river embankment. The resulting upward seepage pressures lead locally to sand fluidisation as if the sand is boiling.

The ejection of sand grains mixed with water from the exit hole is considered to be the onset of erosion, which may progress in the upstream direction and give rise to shallow pipes in the sandy aquifer. The eroded sand particles usually form a ring around the fluidised zone, like a volcano crater. The progression and widening of the pipes may result in a collapse of the riverbank, with catastrophic consequences.

The activation or reactivation of a sand boil is triggered by high water events, such as flooding that has become more common and intense, and longer lasting in recent decades due to climate change. The risk of riverbank instability, including failure mechanisms triggered by BEP, is thus growing. In Italy, sand boils are observed in some 130 sites along the Po river. At present, flood management actions taken by the local authority are limited to maintaining control of the sand volcanos during reactivation. Traditional engineering measures consist of landside berms or impermeable diaphragm walls, but these actions are costly and often ineffective.

OBJECTIVES

The main objective of the LIFE SandBoil project is to mitigate the risk of BEP by means of an innovative, sustainable, natural-based and cost-effective engineering solution. The intervention is devised to stop the progression of piping beneath the riverbank, which might lead to severe erosion and to the collapse of the structure. Reducing the risk of a riverbank collapsing also decreases the risk of flooding.

The project aims to scale up the prototype by demonstrating the technology along a segment of a riverbank. A long-term goal is to apply the intervention to the 130 catalogued Po river segments affected by sand boils. The technology will also be replicated in Hungary along the Danube river.

The project actions aim to promote safer land use with a strong socio-economic impact; costly emergency management and restorations will be avoided. A further objective is to produce guidelines for the design of an effective and sustainable engineering solution to mitigate the flood risk from BEP worldwide.

The project aims to contribute toEUlegislation on water and flood risk management:

Communication on flood risk management, flood prevention, protection and mitigation (COM/2004/0472 final), promoting cooperation among Member States to implement a co-ordinated flood prevention, protection and mitigation action programme;

Directive 2007/60/EC on the assessment and management of flood risks, to reduce and manage risks caused by floods for human health, environment, economic activity and cultural heritage;

Note by DG Environment, Towards Better Environmental Options for Flood risk management (DG ENV D.1 (2011) 236452);

Water Framework Directive 2000/60/EC, given that the new technique respects the natural groundwater flow and makes use of natural materials and eco-friendly products, thus ensuring good water quality.

At national level, the project contributes to the Italian Directive Piano di gestione del rischio di alluvioni (PGRA), developed by the Po river basin District Authority (AdbPO) in application of the EU Directive 2007/60/EC.

RESULTS

Expected results:

Implementation of the BOilDown prototype;

Preparation of a universal prototype to be applied on a large scale as a protection measure against floods. In Italy, around 130 potential sites are found along the Po river. In Hungary, the technology could be further applied to areas along the Danube which experience recurrent piping;

Cost benefits of technique demonstrated, with the average cost for a single application estimated to be less than 200k , significantly less than the 2M cost of current less-effective technology, while also eliminating the cost of the emergency management (In the Po river basin these costs are incurred by Interregional Agency for the Po River (AIPO), which spends about 20k for everyreactivation, with an expected annual budget of 500k, dedicated to emergencies);

A 5 to 6% improvement in resilience to flooding with respect to population, corresponding to an area of around 1% of the entire basin potentially affected by piping the intervention significantly reduces the risk of failure due to piping by stopping erosion and thus preventing damage of around 200M , according to AIPO estimates;

Reduced environmental impact relating to reduced need for emergency restoration requiring the use of vehicles and excavators giving rise to an estimated 0.5 tonnes of CO2 emissions a year; and

Production of guidelines for design, installation and maintenance, fostering the technologys replication across Europe.