National Ports Development Strategy Study in the Sultanate of Oman 4.1.5 Duqm Port A consultant named Haskoning is carrying out the Master Plan and Feasibility Study for the development of the port. At the beginning of the study, Duqm Port had been planned to be fishery port, which was shown in Hydrographic Survey Report by MOAF in 1989 and site investigation report by Fugro in 1990. As GOS was setting the policy that Duqm Port would play a role in the development of middle area of Oman, the development plan of Duqm Port was enlarged to facilitate dry dock for repairing large vessels. Photo 4.1-3 shows the site situation around Duqm Port. The platform was on land, because it was taking refuge from severe waves during the SW monsoon. Photo 4.1-3 Site Situation around Duqm Port (1) Wave Condition The wave hindcasting was carried out by Haskoning. Based on the result of estimated offshore waves, wave deformation at shallow water area was examined. The design wave at the breakwater with a return period of 100 years was determined as shown below. As the wave period at Dupm is shorter than that at Qaboos and Sohar, it had better to confirm by the site investigation. Wave Direction; E Wave Height (H1/3); 5.8 m (return period: 100 years) Mean Wave Period (T1/3); 10.0 s (2) Tidal Levels As the parameters of tidal levels by Royal Navy of Oman in 2003 are available, they have been applied for this study as shown below. 4 - 9 Final Report MHHW +2.36 m CD MLHW +2.29 m CD MHLW +1.48 m CD MLLW +0.70 m CD LAT ±0.00 m CD (3) Tidal Current According to the Draft Final Report of the Feasibility Study (Haskoning, 2002), the average velocity of tidal current was 0.25 m/s during the SW monsoon with its prevailing direction of NE, and 0.125 m/s during NE monsoon with its prevailing direction of SW. (4) Geological Condition There are some boring results around the cliff of the eastern side of the port planning area. It shows that the soils are represented by marine deposits (3-5m thick beneath the seabed), mudstone and siltstone (below marine deposits). In the site investigation, weak mudstone has been found in the eastern cliff, and sandstone has been in the western side. Soil investigations were conducted by Haskoning in 2004, which includes 48 offshore and 7 onland boreholes. Its results are in line with the existing results of soil investigations. Photo 4.1-3 shows the platform applied for offshore borings, which was onland to avoid the severe wave condition during the SW monsoon. (5) Seismic Condition The significant earthquake has never experienced in the area around Duqm. Kh, horizontal seismic coefficient, has been calculated at less than 0.01 G with using the earthquake data of National Earthquake Information Center. As this figure is quite small, it has been decided that the seismic condition is not taken into consideration in the structural design of this study for Duqm Port. (6) Sedimentation The effect of littoral drift at Duqm was simulated by Haskoning. The result shows that net volume toward the north was estimated at 500,000 m3/ year approximately. The maximum difference between the original and dredged depths around the port entrance will be 2.0 m. However, soil materials, clay or silt, lying around the port are very sticky. The cliff in the eastern of the port can also provide such materials. Therefore, it is necessary for the discussion of sedimentation to grasp the characteristics of soil materials further at the detailed design stage. 4.1.6 Shinas Port The available data on natural conditions for Shinas Port is quite few, and Geotechnical Investigation Report by Fugro 1993 is the only available information. As Shinas Port is, however, located to the north of 50 km from Sohar Port, natural conditions at Shinas Port except geological condition are expected to be similar to those at Sohar Port. The study in Shinas Port has been carried out based on such assumption. 4 - 10 National Ports Development Strategy Study in the Sultanate of Oman (1) Geological Condition According to the Geotechnical Investigation Report (Fugro, 1993), the soil condition of the port is represented by marine deposits (1-2 m thick beneath the seabed), loose sand layer (5-7 m thick below marine deposits) and stiff sand layer (below a loose sand layer). 4.2 Engineering Aspects of the On-going Infrastructure Development Projects 4.2.1 Sultan Qaboos Port As mentioned above, Halcrow is preparing feasibility study for the port expansion which includes the construction of breakwater at a depth of -40 m outside the existing breakwater. With taking consideration of available rock materials with large quantity around the port and necessity of few dredging volume at turning basin and access channel as well, the anticipated project cost might be considerably small. If the compressive strength of rock at rocky hill behind the port is very high and difficult to explore and blast the rock located beside the port, it will be reasonable to transport rock materials from another quarry. A significant wave height at a depth of -40 m has been calculated at 6.0 m based on the information provided in the Master Plan Study (JICA, 1990). Judging from the wave height of 6.0 m, a suitable weight of armour concrete block will be 15-20 tons if CORE-LOC is used as for armour concrete block. Berth No.6 is suffering from the water surge from November to March, especially in February, because northeast wind is predominant. Therefore, the layout of breakwater should be examined carefully to ensure sufficient calmness inside the port in securing safe port operation. In order to keep the effect of breaking waves and relieve the surge problem, it is better to replace the existing armour concrete blocks protecting revetment to the eastern part of the existing breakwater. As the access road to/from the port will be of great importance for the port activities, its route alignment should be carefully studied in consideration of future highway plan, environmental matters and so on. 4.2.2 Salalah Port CES is preparing a detailed design for Berth No.5&6 and extended breakwater based on the Master Plan Study (JICA, 2000). At present, there are two problems encountered about wave characteristics. One is surge problem at Berth No.4 and 30, which disturb the port operation for three or four days in a year. It is presumed that the waves reflected by concrete wall at Berth No.30&31 are synchronized with incident long-period waves, and amplify vessel’s motion. The calmness inside the port area was examined with using a numerical simulation by JICA Study Team in 2000. The results show the calmness after construction of Berth No.5&6 and extended breakwater will be better than that of present condition. The calmness inside the port area has been 4 - 11 Final Report checked again by diffraction diagrams based on the assumption that wave period is 7 seconds and Smax, which is a parameter that represents the degree of directional spreading of wave energy, is 25. The result of examination by diffraction diagrams is in line with that by the numerical simulation. Moreover, by increasing the depth of the access channel from -16.5 m to -18.5 m, fewer waves will intrude into the port area due to the wave refraction. On the other hand, if the calmness inside the port area becomes worse after the construction of Berth No.5&6 and extended breakwater, as for remedial measures, it is considerable that the incident waves should be restricted to enter into the port area by the further extension of breakwater as a remedial plan, or the detached pier in front of Berth No.30&31 should be constructed, where more wave energy could be dissipated. Another problem is the damage of the existing breakwater. According to the Project Definition Study (CES, 2004), there has been scouring of the seabed and inadequacy of the armour units, resulting in the sliding/dislodging of Dolos having a weight of 20 tons as a primary cover layer and that of 15 tons as a secondary cover layer. The present condition of the existing breakwater is shown in Photo 4.2-1. Photo 4.2-1 Present Condition of Existing Breakwater Shore Protection Manual allows to reduce weight of armour concrete blocks in primary cover layer below a depth equivalent to twice of wave height. The design documents of the existing breakwater reveal that armour concrete blocks, which are less than required weight, had been placed above a depth of twice of wave height. That is the reason why sliding of amour blocks was taken place. Thus, it is acceptable that MOTC has a plan to apply 30-ton CORE-LOC from top to toe of the breakwater. The severe stress of concrete may occur in a part of both Dolos and CORE-LOC due to its shape. If these blocks do not contain enough reinforcement bars to meet the stress, it is probable that concrete blocks will be broken by wave forces. 4 - 12 National Ports Development Strategy Study in the Sultanate of Oman Regarding the beach erosion in the northern side of Salalah Port, it will be accelerated by the extension of breakwater because of the obstruction of the drift sand movement. It is necessary for the dredging work to dredge the port area without disturbing the current port operation.