# How long is a groyne?

### How long is a groyne?

The length of the groyne is designed in order to trap a fraction of the transport. The northern groyne, 40 m long, is therefore extended of 80 m. Also the Southern groyne is extended, just 40 m, with the aim of stabilising the coast orientation.

### How much is a groyne?

In the Netherlands, groynes are estimated to cost about EUR 3,000 to 15,000 per running meter. Breakwaters are estimated to cost about EUR 10,000 to 50,000 per running meter. Artificial reefs are estimated cost around EUR 15,000 to 35,000 per running meter of structure (Deltares, 2014).

### How tall is a groyne?

Generally, groynes are designed to stick out about hs=0.

### How far apart are beach groynes?

three long groynes with a spacing of 600 m, i.e. 1.

### What do groynes look like?

Groynes are generally straight line but could be of various plan view shapes, permeable or impermeable, built from various materials such as wood, sand, stone rubble, or gabion, etc. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation.

### What wood is used in groynes?

The type of tropical hardwoods used in groynes (Greenheart, Ekki) has strengths twice that of European hardwoods such as Oak.

### Are groynes working?

Groynes cannot prevent the significant cross-shore erosion that typically occurs during storms. Nevertheless they have an indirect effect in that by having trapped sand on their updrift side, they have created a wider beach and an enhanced erosion buffer on that section of foreshore.

### How is the height of a groyne related to its effectiveness?

The difference in height of the beach either side of the groyne will give an indication of the effectiveness of groynes in trapping material being transported by longshore drift. The more effective the groyne the greater the distance between beach levels either side of the groyne. To do this:

### How is the life of a groyne determined?

The length and spacing between the groynes is determined by the force of the waves, the strength of the longshore drift, and the amount of sediment engineers want to capture. A typical wooden groyne has a life expectancy of around 25 years.

### How are the length and spacing of groynes determined?

Simple to construct, and reasonably cheap for a form of hard engineering, they are normally installed as groups rather than as a single groyne. The length and spacing between the groynes is determined by the force of the waves, the strength of the longshore drift, and the amount of sediment engineers want to capture.

### What should be the length of a groyne berm?

The groyne berm length should equal the intended crest width of the updrift beach. The groyne should extend down the beach at a level of about 1m above the anticipated updrift shingle beach, normally at a slope of about 1:5 to 1:10. The groyne head should extend down into the sand beach, allowing for some future erosion.