Hydrodynamics and physical properties of seawater in Darvel Bay, Sabah

• Main Author: Ejria Saleh
• Format: Thesis
• Language: English; English
• Published: 2007
• Subjects: VM1-989 Naval architecture. Shipbuilding. Marine engineering
• Online Access: https://eprints.ums.edu.my/id/eprint/43796/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/43796/2/FULLTEXT.pdf

This study covers the hydrodynamic characteristics, wave climate and physical properties of seawater in Darvel Bay, Sabah , Malaysia. Water circulation and current patterns of approximately 17,150 km2 were studied by generating and simulating the water current in the bay waters using Mike 21 HD module in two monsoons. The numerical simulation for northeast monsoon (NEM) was generated for the period of 03- 05 December 2003 and the southwest monsoon (SWM) was generated for the period of 22-23 September 2005. Numerical model consists of bathymetric database set-up, calibration and validation of the models. Water current measurements were conducted by using two holy sock drogues tracking and current meter at the northern part of the study area. Holy sock drogues were deployed at 1 m below the water surface on 29 September 2003 and 03 December 2003 to represent the SWM and the NEM, respectively. Current velocity measurements using Aquadropp Profiler during 03-05 December 2003 was used to calibrate and verify the hydrodynamic simulation. Longterm wave climate in the study area was investigated through the model development using JONSWAP spectral analysis. Wind measurements for 5.25 years from the nearest wind station at Tawau were used for wave hindcasting. Extreme wave events for 20 years return period were calculated. Extensive field measurements were conducted in different monsoons to identify effects of hydrodynamic changes on physical properties of seawater. Temperature, salinity, pH and dissolved oxygen (DO) were measured on 05 March, 28 September and 17 December 1999 using Hydrolab. Seawater parameters were measured down to a depth of 30 m in 16 sampling stations. Vertical and horizontal profiles of measured parameters were discussed. Average current speed during ebb and flood tides from the holey sock drogues during September was 0.11 m/s and 0.12 mIs, respectively. It was reduced to 0.07 m/s during ebb tide and 0.09 m/s during flood tide in December. Both monsoon seasons showed that the holey sock drogues moved towards open sea during ebb tides and opposite direction during flood tides. The current velocity near the sea surface measured by Aquadopp Profile was almost 2 times higher than current velocity near the sea bottom. The range of current velocity during ebb tides was from 0.014 m/s to 0.18 m/s with average direction of 134°. During the flood tides current velocity ranged from of 0.011 m/s to 0.13 m/s during with average current direction of 250°. Currents simulation of 675 m resolution showed that strong current ranging from 0.05 to 0.20 m/s was detected along the northeast coastal area and moved towards Sakar Island before it turned towards Silam and Kunak areas with decreasing speed during the flood tides. Strong current were clearly shown at small passages within the islands in 75 m resolution. Wave hindcasting from the wind data showed strong wave activity from the east direction with maximum wave height of 1.58 m and wave period of 5.59 s, respectively. The impact of wave energy along the Darvel Bay coast is greatest during the SWM period. Seawater temperature is found to be varied at sea surface but slowly decreased towards 30 m of measurement. Salinity in September and December were higher compared to salinity in March. Variations of DO from surface to 30 m depth were found to be small but varied at different stations and months of sampling. Field measurement on pH depicted mostly constant value. Seasonal effects on water parameters in the study area. The findings of this research will be useful for seaweed farming, fisheries activities and coastal infrastructures development and management planning for the entire area of the Darvel Bay.