Flood inundation and shoreline erosion have long occurred in Sayung, Demak area, the northern coast of Central Java Province, Indonesia. The people of Sayung planted mangroves to reduce the flood inundation and shoreline erosion in that area. They built the bamboo array to protect the juvenile mangroves from incoming waves. The bamboo acts as a breakwater and is considered an environmentally friendly permeable structure to reduce wave energy and stimulate sedimentation. This paper discusses three bamboo arrays’ effectiveness in wave reduction using Numerical Wave Tank (NWT). The interaction of regular waves with a permeable structure comprising a single row of vertical circular poles was conducted based on the Smoothed Particle Hydrodynamics (SPH) method. The effect of different waves and structural dimensions on the permeable structure was investigated based on the structure’s transmission coefficient (Kt) performance. The investigations have revealed that structures with the combination of Vertical-Horizontal formation (VH) attenuate more wave energy than Vertical Only (VO) and the combination of Vertical-Diagonal formation (VD). As the wave steepness increases, the transmission coefficient decreases. Likewise, the transmission coefficient (Kt) is decreasing when the wave height is increasing. On the other hand, the transmission coefficient (Kt) increases as the wave period increases. As the structure spacing ratio between end-to-end and center-to-center spacing (e/S) rises, the transmission coefficient (Kt) also increases. The diameter (D) has a slight effect on the transmission coefficient (Kt). However, the center-to-center spacing (S) has a more significant impact than the diameter on the transmission coefficient, affecting an inclination on the transmission coefficient (Kt) when center-to-center spacing (S) goes up.

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This study reports distribution of water quality parameters, i.e. salinity, nitrite, nitrate, and phosphate of the Kalibuntung estuary in the southeastern Surabaya coastal area. The study was conducted over 34 sampling points in the river channel, river mouth, and in the coastal water of the Kalibuntung estuary. The result shows that the minimum salinity of (2-4 ppt) reached 3,000 m far from the coastline to upper strem. The maximum salinity of 28.60 ppt found in the coastal water, about 1,000 m seaward from coastline. Based on the numerical modeling analyses, distribution of salinity followed the water movement of eeb-flood currents cycles due to tidal fluctuation. The result obviously revealed that during flood current, water mass from the sea moves to the upper river, on the other hand, during eeb current more volume of river water flows to the sea. It is indicated by salinity values in the river mouth, which reached 27 ppt during high tide and < 20 ppt during low tide. Concentration of ammonia ranging from 0.42 mg/l in the lower part close to the river mouth, up to 6.13 mg/l in the uppermost of the river. This indicated that the river is heavily polluted by organic waste. Concentration of phosphate range from 0.06 to 0.43 mg/l. Its concentration decrease seaward, it is distributed to a distance of 3,000 m fom the river mouth. The river water of Kalibuntung estuary is not permitted to be used as a drinking water, and also it is not feasible for coastal aquaculture. Only in the lower part of the study area where it close to the rivermouth, its water can be used as a source of the coastal aquaculture. This research also found that the river water of the study area has already heavily polluted by organic waste, which it might come from domestic waste, agriculture or fertilizer for fishpond, or industrial organic waste.

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