Jetty design at Rio Araranguá

Master project report. The hydraulic efficiency of the river Ararangua will be increased by the construction of jetties at the mouth of the river. The river tends to migrate from south to north which decreases the hydraulic efficiency and causes flooding upstream during events of high discharge. To stop the migration the construction of jetties at the mouth of river Ararangua is proposed. A design for a jetty system is available (INHP, 1993), but should be updated. Due to the construction of a jetty system longshore sediment transport will be interrupted and this will cause morphological changes. At Ararangua river a large and highly varying longshore sediment transport is present with a high energy wave climate and micro tidal range. These conditions cause increased morphological changes when constructing a jetty system. The objective of this research is to design a jetty system that prevents flooding upstream and induces as less morphological changes as possible. The jetty should be designed at the specified location, using available datasets from previous research and according to modern design standards. Also navigation through the channel should be possible. The channel width and depth are determined by navigational and morphological purposes and are 120 m and 6 m respectively. A weir jetty, which has been implemented in the SW arm of the design, was considered the best sediment bypass system after a multi criteria analysis. Because of the placing of the deposition basin waves could penetrate much further in the jetty channel and lengthening the NE arm to 630 m and a depth of 6,6 m was necessary. The length of the SW arm of the jetty from the previous is kept at 650 meter to a depth of 7,2 meter. The final result of the structural design is a statically stable rubble mound breakwater with granite as construction material. Rock has been applied in the range of 0,4 m (170 kg) to 1,0 m (2,7 tons) in diameter, with a core of quarry run material. In sections where the required rock mass exceeded the threshold value for economical construction (2,7 t), tetrapods have been applied to stabilize the slope. Tetrapods have been applied of 6,6 and 9,7 tons. The total use of material is about 42.000 tons of tetrapods and 490.000 tons of granite rocks. Overtopping requirements determine the crest freeboard and 0,3 meter is added for post construction settlement. The crest width depends on construction considerations. All other dimensions are directly related to the stone size and weight, which are dependent on the design wave heights.