Sand Losses from an Artificially Nourished Beach Stabilized by Groynes

Kunz, Hans; ,

Sand Losses from an Artificially Nourished Beach Stabilized by Groynes

by Hans Kunz, Coastal Research Station, Norderney, Germany,

Document Type: Proceeding Paper

Part of: Beach Nourishment Engineering and Management Considerations

Abstract:

Norderney is one of the East Frisian barrier Islands in Germany. Severe dune erosion jeopardized the settlement and neccessitated the use of seawalls and groynes after 1850. Even though they were successful in preventing further dune erosion, they were not able to stabilize the beaches. Thus, the first large scale beach nourishment project in Europe was initiated on Norderney in 1951/52. Up to now, six further beach fills were neccessary. The scouring of the replenished groyne fields and adjacent areas has been monitored since 1951; the beach restoration of 1989 has been affiliated with an interdisziplinary research project. It has been proven, that on Norderney beach nourishment is an appropriate solution to protect the existing structures from failure during severe storm surges. Calculations of beach volumes led to functions, which describe the sand losses out of groyne fields for different situations. Simple exponential functions do not fit; this can partly be explained by the impact of groynes. The results of field data on wave induced currents give the impression that the effectiveness of the groynes depends primarily on the relative reduction of the total water column due to the groyne elevation above the beach. There is a strong correlation between losses and the volume of nourished sand in the groyne fields. To lower the amount of losses, beach replenishment should not be higher than neccessary to achieve the protection goals. Above a 'critical beach profile' the losses of replenished material out of the groyne-fields increases considerably with height. Instead of exceeding heights of profiles, the material should be deposited on the shore face. The aspects of sand losses and nourishment techniques have to be combined with respect to cost-benefit optimation.

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