European Coasts - An Introductory Survey Chapter 4: Coastal structures 4.2 Groynes |
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As previously described, long shore sediment transport which increases in the downdrift direction induces beach erosion. A possible protection against such erosion is the construction of a series of groynes which reduces the sediment transport and hence stabilizes the coast.
The construction of a particular groyne field depends on the desired level of reduction of the long shore sediment transport. Complete blockage requires an impermeable, high groyne which extends through the complete surf zone. Commonly, a partial reduction in sediment transport is sufficient to achieve stabilization of the coast. A choice can be made between permeable or impermeable groynes, low (with overflow during high water) or high groynes, and short or long groynes. Another important aspect is the spacing between the groynes. All these factors, together with different available materials, result in many possible configurations. The choice depends on the specific local conditions.
A possible configuration is a groyne which has been built from stone layers of different sizes (see Fig. 78). It is similar to a rubble mound breakwater (see Fig. 72). This form of construction can be made impermeable by pouring asphalt over the top layer. A cheaper approach (but one with a shorter life-span) is to use a row of closely-spaced wooden piles or wooden piles and timber planks (see Fig. 79). Another possibility is a groyne built from steel sheet piles (see Fig. 80).
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This page is from the book "European Coasts", produced in the framework of the Erasmus project under EC contract ICP 92-G-2013 and placed on the Internet in the framework of the PIANC-MarCom initiative on Education. |