Numerical Simulation of Ocean Wave Using High-Order Spectral Modeling Techniques: Its Influence on Transport Sediment in Benoa Bay, Bali, Indonesia

Ulung Jantama Wisha,Agus Maryono,Semeidi Husrin,Try Al Tanto,Gunardi Kusumah,Widodo Pranowo

doi:10.20884/1.oa.2019.15.2.554

Abstract

Benoa Bay is threatened by sedimentation issue within the bay. It impairs the water mass circulation, influencing scour, mixing, and turbulence as well as sediment transport processes. This study focuses on the wave characteristic and its relation to sediment transport within Benoa Bay. Spectral wave modeling techniques were employed. The equation was discretized based on the condition of winds, tidal, and currents. Total sediment transported was calculated according to the wave model result. Total suspended sediment (TSS) model was simulated which the simulation considers bed load and suspended load transport. Significant wave height (Hs) ranged 0-0.48 m and 0-0.44 m during high tidal condition and low tidal condition respectively. Wave undulation propagates toward the West and Northwest within Bay. The wave period (Ts) ranged 2-6.5 second. Total sediment transport ranged 2828.16 - 86235.66 m3/year. TSS concentration ranged 1-100 mg/L and 1-155 mg/L during high tidal condition and low tidal condition respectively. Those conditions indicate that the sedimentation has been extremely occurred within the bay. The areas around Benoa peninsula, Benoa harbor, and Serangan Island are heavily polluted by suspended sediment. Bottom sediment is stirred by hydraulic jump off wave propagation. The first wave crest induces scour, which its train carries the stirred sediment entering the bay. If ongoing, this condition will exacerbate the existing ecosystem. Benoa Bay development has a big role evoking the level of TSS and turbidity. The more the sedimentation occurs, the more the ecological problem takes place.

Highlights

Benoa Coastal Bay, located in the southern Bali Island, is severely strategic and potential to be developed in improving marine tourism in Bali Province
Waves propagation predominantly moves toward Benoa Bay with a constant value of significant wave height and wave period, triggering transport mechanism within the bay
The higher bed load sediment in the swell region is stirred due to the hydraulic jump off wave propagation

Summary

Introduction

Benoa Coastal Bay, located in the southern Bali Island, is severely strategic and potential to be developed in improving marine tourism in Bali Province. Benoa Bay has become the center of coastal development, tourism zone, and transportation for domestic and international interests. Benoa Bay is directly bordered by Lombok Strait and the Indian Ocean in the east and south, respectively whereby Lombok Strait is one of Indonesian throughflow (ITF) gates (Ningsih and Al Azhar, 2013). Some climatic variabilities such as El Nino Southern Oscillation (ENSO) and monsoons influence on hydrodynamic conditions in the surrounding Benoa Bay, in the generation of wind wave and its propagation from swell zone towards the coast. The changes in hydrodynamic conditions are gradually caused by morphological alteration recently occurred in Benoa Bay (Wisha et al, 2017)

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