Groyne

About: Groyne is a research topic. Over the lifetime, 397 publications have been published within this topic receiving 4549 citations. The topic is also known as: groin & Breakwater.

Protection by means of offshore breakwaters

Abstract: The coast of Tel-Aviv is characterised by a narrow sandy beach, and the seabed is the nearshore shallow waters is strewn with rocky ledges and outcrops. These rocks are of a marine conglomerate type and are covered with layers of fine to medium grained sand of various thickness. At depths greater than 5 m the seabed is predominantly sandy. During the summer season, when waves and swells seldom exceed 2 m in amplitude, the sandy strip of the beach maintains its minimum width of about 20 m. However, winter storms reduce the width of the beach in some places to zero, and there is a marked tendency to erosion and scour of the beach in front of the retaining walls of the alongshore promenade or in front of the coastal bluff. In order to prevent this erosion and at the same time to enlarge the sandy beach area, we have proposed to erect in front of the beach a series of offshore breakwaters, either detached or groyne-connected. (Fig. 1) The first of the series was erected off the Tel-Baruch beach just north of Tel-Aviv. There beach sand was practically non-existent, and in order to enable bathers to enter the water, a breach in the shallow rocky belt had to be blasted. The Tel-Baruch breadwater is of a rubble-mound type, 200 m long and connected with the shore by a 100 m long groyne. It is founded on a rocky seabed at -3.0 m below M.S.L. and consists of a quarry-run core (0.5 to 250 kg units), protected on its seaward slope by a rock armour (2-6 tons units) laid on a 1:3 grade, and on its landward slope by a secondary armour (1-2 tons units) laid on a 1:1.5 grade. Its crown is topped by R.C. 0.25 thick slabs to a level of +1.0 m above M.S.L. Shortly after its erection in 1965, a sandy tombolo has formed at both sides of the groyne, increasing in area until a permanent equilibrium has been achieved. Erosion of the beach on both sides of the breakwater was avoided, owing to a belt of beach rock which protects the foreshore to the south and to the north of the breakwater.

Human impact on large rivers: the influence of groynes of the River Oder on larval assemblages of caddisflies (Trichoptera)

Abstract: The influence of groynes in large rivers on caddisflies has been poorly studied in the literature. Therefore, we carried out an investigation on the 420-km stretch of the River Oder equipped with groynes. At 29 stations, we caught caddisflies in four habitats: current sites, groyne fields, riverine control sites without groynes and in the river’s oxbows. We found that groyne construction increased species richness, diversity, evenness, and altered the structure of functional groups into more diversified and sustainable ones compared to the control sites. The groyne field fauna is similar to that of natural lentic habitats, but its composition is largely governed by the presence of potential colonists in the nearby oxbows. We distinguished three of the river’s caddisfly assemblages. The distribution of Trichoptera was governed inter alia by the plant cover and the amount of detritus, and consequently, the food resources. Oxygen, nitrates, phosphates and electrolytic conductivity were important as well. Groynes have had positive effects for caddisflies—not only those in the river itself, but also those in its valley. They can therefore be of significance in river restoration (although originally they served other purposes), especially with respect to the radically transformed ecosystems of large rivers.

Long term morphological modelling

Abstract: A morphological modelling concept for long term nearshore morphology is proposed and examples of its application are presented and discussed. The model concept combines parameterised representations of the cross-shore morphology, with a 2DH area model for waves, currents and sediment transport in the surf zone. Two parameterization schemes are tested for two different morphological phenomena: 1) Shoreline changes due to the presence of coastal structures and 2) alongshore migration of a nearshore nourishment and a bar by-passing a harbour. In the case of the shoreline evolution calculations, a concept often used in one-line modelling of cross-shore shifting of an otherwise constant shape cross-shore profile is applied for the case of a groyne and a detached breakwater. In the case of alongshore bar/nourishment migration an alternative parameterization is adopted. All examples are presented, analysed and discussed with respect to the question of realistic representation, time scale and general applicability of the model concept.