![]() ![]() Dissolved micronutrients such as nitrite, nitrate, ammonia, silicate, and phosphate along with TN and TP were estimated by the spectrophotometric method following standard procedures ( Parsons et al., 1984 Grasshoff et al., 1983). Samples for nutrient analysis were filtered through 0.45μ millipore filter paper and preserved at − 20☌ analyses were carried out within 2–3 days of collection. pH measurement was carried out by a pH meter (CyberScan PCD 5500) with ± 0.01 accuracy. The turbidity meter CyberScan IR TB 100 (± 0.1 NTU accuracy) was used for measuring the turbidity of the water sample shaving. Knudsen's method ( Grasshoff et al., 1983) was followed for salinity estimation. Dissolved oxygen (DO) was estimated by Winkler's titrimetric method ( Grasshoff et al., 1983). Precleaned polythene bottles were used for sample collection. Samples were collected monthly at the MAPS jetty (about 450 m away from the shore) during the study. Panigrahy, in Coastal Management, 2019 3.1 Material and Methods Sumer and Fredsøe’s (1997a,b,c) Sumer and Fredsøe (1997a) Sumer and Fredsøe (1997b) Sumer and Fredsøe (1997c) test results show: when KC = 1 and the dike head is the vertical structure, the maximum shear force amplification coefficient near the jetty is 6 while it is the gentle slope, the maximum value is less than 4 ( Fig. 8.35) the dike head with acute angle has the scour depth two times bigger than the dike with circular head. ![]() ![]() Dike head shape may also have an effect on the scour hole pattern and depth. When KC ≥ Cn the flow pattern is similar with the pile structure, which forms the horseshoe vortex at the bottom of dike head, the flow pattern at the cover side is separated to form the wake vortex when 1 ≤ KC ≤ C is similar with the pile structure, which forms the horseshoe vortex at the cover side when KC ≤ C is similar with the pile structure, which forms the horseshoe vortex at the cover side when d, the flow pattern at the cover side is separated to form the wake vortex when 1 ≤ r to the coastline and deep in the s KC number of the jetty structure is usually relatively small, only under the extreme wave it may produce vortex scour, therefore its scour features can refer to the pier structure. Under the action of wave, the influence of KC number on the water flow around jetty structures is similar to the isolated structures (here KC number is calculated based on the dike body width B according to D in Eq. Sumer and Fredsøe (1997a,b,c) Sumer and Fredsøe (1997a) Sumer and Fredsøe (1997b) Sumer and Fredsøe (1997c) studied the dike head scour of breakwater under the action of wave. Because the jetty is perpendicular to the coastline and deep in the sea, the wave will generate wave amplitude accumulation effect at the dike head, and thus is more likely to cause scour damage. In the estuarine marine environment, jetty structures in addition to suffering from water scour also suffer from the shock of wave. (2001a), Yang and Wang (2001) carried out the physical model test for the local scour and protection engineer effects of spur dike head on the strong tidal estuary. (2005) used the physical model test to research the local scour on spur dike head caused by the regulation project of deep water channel of Yangtze River Yang et al. With the management of estuarine coastal area and construction of port, it is very important to study the jetty scour under the action of currents and waves. Study of jetty structure scour began in the 1950s originally it was study on the local scour of spur dike under the action of steady flow, which had some valuable research results. Because of this, for the sake of safety, generally the jetty structure design regulates that the weight of protection stone on dike section should be larger than the weight of dike block, and when there are conditions, the gradient at both sides of dike head section can be slowed down to reduce scour. Jetty structures are generally perpendicular to the shoreline layout, with dike head into the sea, and at this time the influence of structures on the water flow is mainly two aspects: (1) dike truncates coast currents flow and other water flow, which will make the dike head flow velocity increase, resulting in the dike head scour and (2) wave will have amplitude accumulation on the dike head, which enhances the turbulent flow at dike head, and it will also exacerbate the dike head scour. Their scour mechanism and characteristics are similar with alongshore structures and pier structures, but there are some differences. Here the jetty scour refers to the dike scour damage on the top end of marine structure such as spur dike, jetty, abutment, breakwater or offshore breakwater due to their water restrain effect, and wave amplitude accumulation effect. Ye Yincan et al, in Marine Geo-Hazards in China, 2017 2.5 Scour of Jetty ![]()
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