Massive mining of sand from the middle and lower shoreface (depths of 10 to 30 m) in large-scale mining and borrow pits/areas will be required in future in many European countries. For example, around the North Sea and the Mediterranean Sea, mining of sand will be required to nourish beaches and coastal dunes in response to increased coastal erosion due to the expected sea level rise. This will be one of the most important environmental problems of the coming decades. Furthermore, the large-scale reclamation of land and the construction of large-scale artificial islands (for industrial purposes; ports and airports) in coastal seas which are presently being considered, will also require huge amounts of sand as building material.

Given the scale of these undertakings, the volume of sand required in the near future (10 to 20 years) will be of the order of 100 to 1000 million m³ per country surrounding the North Sea.

To meet these demands, the existing areas for mining of sand need to be extended considerably and new potentially attractive areas should be explored and exploited. Massive mining of sand may take place by dredging in artificial sand pits or channels (also navigation channels) or by removal (dredging) of existing large-scale sand banks/shoals in the offshore zone (middle and lower shoreface).

Large-scale mining pits will have a significant impact on the near-field and far-field (up to the coast) flow and wave patterns; the flow velocities inside the pit will be reduced and the wave heights may also be reduced, depending on the depth of the pit. As a consequence, the sand transport capacity inside the pit will decrease and sediments will settle in the pit area, resulting in deposition. Thus, the pit will act as a sink for sediments originating from the surrounding areas and depending on the local flow and wave patterns. Hence, erosion of the sea floor will take place in the (immediate) surrounding of the pit.

Considering the massive scale of future mining of sand and hence the large spatial scales that will be affected by the mining activities, the mining areas need to be situated in the offshore shoreface zone to minimise the effects of nearshore coastal erosion. On the other hand the mining of sand will be progressively more expensive at greater distances from the shore. Research is required to find the optimum solution between the effect on the coast and the costs of mining.

The most important questions to be addressed are:

• what are the most optimum dimensions of the sand mining pits/areas (small and deep areas or wide and less deep areas) in terms of effects on the coast and mining costs?

• what are the most attractive locations of sand mining in terms of effects on the coast and the mining costs?

• what are the sand infill rates of mining pits/areas after completion?

• what are the migration rates and directions of the side slopes of the mining pit/areas after completion?

• what is the effect of massive long-term sand mining on the surrounding shoreface and the coastline (coastal sand budgets)?

• what is the effect of removal (by dredging) of offshore sand banks/shoals on the surrounding shoreface and coastline?

• what is the effect of massive long-term sand mining on the ecological structure of the seabed?

The proposed SAND PIT project will address these questions. Research of sand transport and morphology under offshore conditions will be a major topic in the present SAND PIT proposal. New laboratory and field measurements are required to extend existing data bases. A large-scale test pit to be dredged in the North Sea and associated field measurements will be an important element of the proposed SAND PIT project to explore and analyse the impact of large-scale sand mining on the surrounding environment. The test pit data on hydrodynamics (current and wave patterns) and on morphodynamics (infill rates and bed slope migration rates of the pits) will be of utmost importance for the improvement of the existing predictive models and tools. The knowledge of shoreface processes generated through these experiments and research will also be very useful for the assessment of other activities on the shoreface such as:

• the construction of artificial islands;

• the dredging of deep navigation channels;

• the positioning of pipelines and telecom-cables at or in the sea bed;

• the development of windmill parks.

The participants of the SANDPIT project are: WL | Delft Hydraulics (coordinator, NL), University of Twente (NL), Rijkswaterstaat/RIKZ (NL),, University of Utrecht (NL), Hydraulic Research Wallingford (UK), University of East Anglia (UK), University of Aberdeen (UK), University of Wales, Bangor (UK), DHI-Institute of Water and Environment (DK), Norwegian Applied Mathematics Sintef (NO), Norwegian Univ. of Science and Technology (NO), SOGREAH (FR), University of Caen (FR), CETMEF (FR), University of Genova (IT), University of Catania (IT), University of Coimbra (PT).