I Gede Hendrawan

Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia

A three-dimensional (3-D) finite volume coastal ocean model (FVCOM) was used for the study of water circulation and seawater exchange in the Benoa Bay, Bali Island. The M2 tidal component was forced in open boundary and discharge from six rivers was included in the numerical calculation. The M2 tidal elevation produced by the FVCOM has a good agreement with the observation data. The M2 tidal current is also successfully calculated under the ebb tide and flood tide conditions. The non-linear M2 tidal residual current was produced by the coastline geometry, especially surrounding the narrow strait between the Serangan Island and the Benoa Peninsula. The tidal residual current also generated two small eddies within the bay and one small eddy in the bay mouth. The salinity distribution influenced by river discharge could be successfully calculated, where the numerical calculation and the observation results have a good correlation (r2) of 0.75. Finally in order to examine the seawater exchange in the Benoa Bay, the Lagrangian particle tracking method and calculation of residence time are applied. The mechanism of particle transport to the flushing of seawater is depicted clearly by both methods.

Pendugaan Kejadian Pemutihan Karang Berdasarkan Analisis Suhu Permukaan Laut (SPL) Tahun 2015-2016 di Perairan Bali

National Ocean Atmospheric Administrations (NOAA) by the program coral reef Watch (CRW) has developed a method to estimate the potential of coral bleaching using Sea Surface Temperature (SST). The products are hot spot (HS) and degree heating week (DHW). HS is the SST 1°C (SSTL≥1) above normal and DHW is the length of HS inhabits a place. The CRW product do not provided detail informations because it has a lower resolution. It is need a satellite image with a higher resolution to provide better informations. One of the satellite images that can be used is Moderate Resolution Imaging Spectroradiometer (MODIS) with a spatial resolution of 1 km. The purpose of this study was to know HS and DHW distribution patterns and status of coral bleaching in Bali waters seen from the analysis of HS and DHW. MODIS data is used daily, then do mosaicing process to get a weekly SPL (8 daily) and the monthly SST. Monthly SPL normally used to get maximum montly mean (MMM). HS obtained from the difference between 8 daily weekly SST and SST normal (MMM).).Location bleaching based on data Coral Triangle Center (CTC) and coralwatch.org. SST results revealed difference of SPL in 2015 and 2016 amounted to 1.48°C. Highest DHW in Bali Hai, Nusa Penida is 10 465° C-weeks in April 2016. Based on the value HS and DHW coral reefs in Bali waters threatened bleaching level Alert 1 and Alert level 2.

Distribusi Nitrat dan Fosfat Secara Spasial dan Temporal Saat Musim Barat Di Permukaan Perairan Teluk Benoa, Bali

Benoa Bay is an estuary that effected by pollutan from river and human activity. Reasearch on spatial and temporal distribution of nitrate and phosphate has been conducted in Benoa Bay. Data was collected at water surface during ebb from December 2016 to Februari 2017. There were19 Sampling pointlocated in Benoa Bay and 6 pointslocated in rivers around Benoa Bay. Nitrate was analysed using Brucine method and phosphate was analysed using AmmMolybdat method. The concentration of nitrate from December 2016 to February 2017 ranged from 0,036 mg/L to 1,154 mg/L and the concentration of phosphate ranged from undetectedto 0,739 mg/L. The concentration of nitrate at rivers ranged from undetectedto 3,584 mg/L andthe concentration of phosphate ranged from undetectedto2,405 mg/L. The concentration of nitrate and phosphate from December 2016 to February 2017 was fluctuating and the highest average concentration of nitrat and phosphate was found in February 2017. These was due to high rainfall in February 2017 and cause a lot of organic matters carried by the rivers into Benoa Bay. The highest distribution concentration of nitrate and phosphate was found around estuary. These due to input of organic matters from mainland through the rivers. Based on water quality standards of Bali Goverment, the concentration of nitrate and phosphate was exceeds the seawater quality standart.

THE VULNERABILITY STUDY OF LEMURU (SARDINELLA LEMURU) FISH RESOURCES SUSTAINABILITY IN BALI STRAIT IN CORELLATION WITH ENSO AND IOD

THE VULNERABILITY STUDY OF LEMURU (SARDINELLA LEMURU) FISH RESOURCES SUSTAINABILITY IN BALI STRAIT IN CORELLATION WITH ENSO AND IOD The aim of this research is to know the relationship between lemuru fish catch to Sea Surface Temperature (SST), El-Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) phenomenon in Bali Strait. The results showed, that in the period 2007 – 2016. fluctuations of catches lemuru tends to decline. Sea Surface Temperature (SST)distribution with the lowest temperature 25,28C at 24,53C 27,16C and the highest temperature is 29,31C in the range of 28,73C – 30,49C. The lowest temperature occurred in July September while the highest temperature occurred in January April.Based on the calculation there is a linkage and relationship between catch and SST as shown on the value of determination and correlation reached 50,0% and 70,73%. Most of the catches occurred in the west season and then the transition II, transition I and East Season. The relationship of ENSO phenomenon to the catch during the El-Nino phase of lemuru catch will increase while in the phase of La-Nina the catch of lemuru will decrease,because time of El-Nino phase of the sea surface temperature (SST) relative low which results in the chlorophyll-a mean case which is a food sources of lemuru fish. Based on Trenberth’s theory, (1997), the rise and fall of the ENSO Index of less than six months is not stated in ENSO. From the calculation results during the research of 2007 2016 happened three times ENSO phenomenon that is in 2009, 2010 and 2015.At the time of the IOD phenomenon, the IOD (+) phase will result in a decrease in catch while the normal IOD phase and (-) will increase the catch. From the results of this study can also be observed, in the year 2007 2011 phenomenon ENSO and IOD have a strong influence on the catch while in the year 2012 2016 the influence of the phenomenon of ENSO and IOD has no strong influence caused by the quantity of lemuru fish that have been over exploitation that resulted in the current Bali Strait on Over Fishing status.

Model Hidrodinamika Pasang Surut di Perairan Pesisir Barat Kabupaten Badung, Bali

Finite Volume Coastal Ocean Model (FVCOM) is using for numerical modeling of hydrodynamic tidal water in west coast of Badung regency, Bali. The model result is validation with field observations data in the area using the equation Root Mean Square Error (RMSE). Field tidal data elevation of sea level elevation measurements were obtained by using the palm of tidal. Field data speed and direction of sea currents obtained using Lagrangian method. Excellent results obtained with RMSE values tidal elevation of sea level by 0.24 m dan RMSE values for sea current is 0.125 m/s. The results of model simulations show sea current patterns in the waters of the west coast of Badung regency, Bali relatively the same at the spring tide and neap tide conditions. The pattern of sea currents at high tide shows current vector that moves in toward the water of the west coast of Badung regency area from Bali Strait and the Indian Ocean. At the time of low tide sea current vector movement towards Bali Strait and the India Ocean. Sea current velocity in the eastern waters of the west coast of Badung regency (longitude of 115,05°– 115,17°) is higher than the sea current velocity in western waters area (longitude of 114,95°– 115,05°). Sea current velocity in the waters of the west coast of Badung regency on the condition of the spring tide range from 0.005 to 0.025 m/s, on the other side the sea current velocity on the neap tide conditions range from 0.005 to 0.012 m/s.