INVESTIGATION OF WAVE AGITATION INSIDE THE NEW FISHERY PORT (CASE STUDY: NEW MRZOUKA FISHERY PORT, LIBYA) Abdelazim M. Ali Researcher, The Hydraulics Research Institute, National Water Research Center, Ministry of Water Resources and Irrigation, P.O. Box 13621, Delta Barrages, Egypt E-mail: abdelazim@hri-egypt.org ABSTRACT This paper presents the physical modeling of a new fishing port required to be constructed at Mrzouka, Libya along the Mediterranean coast. The modeling was set and the experimental work was carried out. The aim of the experiments was to check the proposed design of the protecting elements (two breakwaters) of the new port in order to ensure that the wave heights (0.30m), currents and water levels do not exceed the permissible values. A fixed bed model with a scale of 1:60 was constructed in the wave basin of the Hydraulics Research Institute, Delta Barrages, Egypt. The designed significant wave height H s (3.5m) was used in the model tests and the JONSWAP spectrum was prescribed in the physical model operation. The original design of the new port was tested. It was found that the wave heights inside the new port exceeded the permissible values. Three modified layouts (I, II and III) for the two breakwaters were designed and tested. For each case, the wave heights, currents and the water levels were measured. The results were analyzed and plotted, from which the third layout (III) produced wave heights, currents and water levels within the permissible range. Keywords: new port, waves, water level, currents, physical model, wave basin. 1. INTRODUCTION In order to increase the fish production capacity in Libyan Arab Jamahiriya, several new fishing ports along the Mediterranean Sea are planned to be constructed. One of these ports is Mrzouka Port. The proposed port is located at the western side of the Gulf of Sirt, at Mrzouka area, 50 km East of Misratah City, Figure (1). Along this reach the coast is North West to South East oriented. The coast is almost straight with some headlands. The new port location is completely protected from the North Western waves. The coastal length of the project is 1.5 km and the South
boundary of the new port is a steep hill of a maximum height of 2.0m. The North boundary of the new port is relatively flat with an average slope of 1:1000. The beach slope ranges between 1:30 and 1:75 up to depth 7m after which the slope flattens to be 1:250. The new port is protected by two offshore breakwaters one located at the North with a length of 770m and the second is located at the South with a length of 578m. The new port consists of three fishing basins for different types of fishing boats with water depths of 6m, 4m and 2m. The maximum permissible wave heights inside the fishing ports (according to the types of the fishing boats) should not exceed 0.3m and the water level inside the port should not exceed the crest level of the quay walls. Figure 1 Location of Mrzouka Port along the Mediterranean Coast of Libya Also, the mid depth and surface currents, inside the port, should be investigated in order to ensure safe maneuvering for fishing boats. At the location of the port, the predominant wave height is NEE with an angle of 22.5º to the East. The 50 years return period significant height H s is 3.5m. Breakwaters provide protection to the interior channels, moorage areas, and other basin elements. The permissible wave heights within these elements differ from one place to another (for example a 60 cm wave height is acceptable in the moorage areas for large fishing vessels while a 30 cm wave height should not to be exceeded for small fishing boats. Breakwater layout and its associated cost are usually needed to indicate the optimum arrangement. From the literature, it was found that the acceptable wave heights, within a port basin, depend on the vessel size, type and its moorage (piers or anchorage).
Model studies are thus required to investigate the expected wave conditions that could result from refraction, diffraction and breakwater overtopping and/or transmission in the different basin areas. They are also required in order to determine the optimum entrance configuration and wave heights inside the basin. Consequently, a physical model (1:60) was tooled to simulate the fishing port of Mrzouka. The model was constructed in the Hydraulics Research Institute (HRI) laboratory. It was meant by the model construction to test and optimize the alignment of the proposed design of Mrzouka port. Figure 2 shows the bathymetric map of the site and the original design of the new port with the two proposed breakwaters together with the internal fishing basins arrangements. Figure 2 The bathymetric map and the new port layout 2. PHYSICAL MODEL A physical model was constructed with a scale ratio of 1:60. The scale of the model was determined based on the available wave basin space and the limitation of the wave generator. This scale allows simulating the required area of 1.4km parallel to the shoreline and 1.0km offshore (area of the port). Froude criterion model similarity was adopted in the physical model as inertia and gravity forces are dominant. This implies that Froude number in the physical model is equal to that of the prototype, i.e. Froude number ratio equals unity.
in which: ( F ) = ( F ) r V gh P P = r m V gh m F r = Froude number V = average flow velocity (m/s) h = local characteristic water depth (m) g = acceleration of gravity (m/s 2 ) m = denotes the model p = denotes the prototype (1) This implies that the scale ratios of the different parameters are as follows: Length (horizontal and vertical) scale ratio = L r = 60 Velocity scale ratio = V r = (L r ) 0.5 = 7.75 Time scale ratio = T r = (L r ) 0.5 = 7.75 3. WAVE BASIN FACILITIES The experimental facilities, made available to the present investigation, were the wave basin; wave generator and measuring instruments. They are described as follows: 3.1. Wave basin The existing wave basin of the HRI is 34m x 31m measured from the external boundaries. The maximum water depth in front of the wave generator is 0.80 m. Rip rap is placed at the two boundary walls behind and in front of the wave generator to absorb the waves and minimize the wave reflection. The floor is made of isolated plain concrete to avoid seepage. 3.2. Wave generator A 25 m long hydraulic-type wave generator is installed in the wave basin. It is manufactured by Delft Hydraulics, Holland. The wave generator consists of 96 paddles (26.5 cm wide and 40 cm high). These paddles are connected with joints to the hydraulic-type piston. The wave generator comprises of an electric control and switch unit control panel. The signal for the wave generator is controlled by a PC and the CED 1401 converter control interface. The wave generator could generate 2.0 cm to 15.0 cm wave heights. The wave generator produces unidirectional regular or irregular waves, Fig. (3).
Figure 3 The wave generator used in this study 4. MEASURING DEVICES The measuring devices, made available to the present study, were the wave height meter (Whm) and the electromagnetic current meter (EMS). As for the wave height meter (Whm), it was designed for dynamic fluid level measurements, e.g. wave-height measurements in hydraulic models. Also, Electro- Magnetic Current meter (EMS) is used to measure continuously the average velocity components in the x- and the y-direction. Both devices Whm and EMS are manufactured by Delft Hydraulics, Holland. The accuracy of the current meter is ± 0.01 m/s ± 1 % of the measured value provided that tilts angle < 10 degree. Figure 4 shows the measuring devices. Figure 4 The Electro-magnetic Currentmeter (Left) and the Wave Height Meter (Right)
5. MODEL CONSTRUCTION AND SETUP The fishing port was modeled to a scale ratio of 1:60. The model construction and the undertaken measurements were carried out within a period of four months. The model was constructed in steps as follows: Step 1 The coastal area was divided into a series of parallel cross shore profiles. Step 2 For each cross shore profile, the distance from the shoreline and the water depth along its entire length were determined and scaled to the model scale. Step 3 The cross shore profiles were sent to the workshop to be manufactured. Step 4 The cross shore profiles were installed using the positioning device (Total Station) and were adjusted using a leveling device to level each point along the entire cross shore profile. Step 5 The cross shore profiles were filled with sand covered by a thin layer (5cm) of cement mortar. Step 6 The port (including the two breakwaters and the internal basins) was constructed according to the designed plan. Step 7 The measuring devices were placed inside the model after their calibration. Step 8 the basin was filled with water to the required water level. 6. MODEL OPERATION A test program was designed and the model was run. Each model run comprises three stages. These were preparation, steering/wave generation and data processing stages. In the preparation stage, all instruments (Whm, EMS) were connected to the data logger and were calibrated to produce the reference values for wave heights and current velocities. This was achieved in order to ascertain the allowed tolerance of each instrument. The required wave characteristics (significant wave height, type of wave spectrum and peak wave period) were also prescribed. This information is prearranged as input and output files. In the steering stage, the wave generation was set to be operated via a combination of software, hardware and intermediate files (created by the software). The prescribed wave spectrum is converted to a random voltage signal that is transferred to the amplifier and then to the piston to generate waves. In the present study, a JONSWAP spectrum was prescribed in the physical model operation. As for the data processing, the collected data was transferred via the data logger and stored in the computer automatically. Using a complete set of programs, these data were processed and presented as graphs and tables.
Figure (5) shows the model layout inside the wave basin and the location of the instruments. Two wave height meters (Whm1) and (Whm2) were placed in front of the wave generator in order to measure the incoming waves at deep water. In addition, four wave height meters were installed inside the port, (Whm3) at the mooring area, (Whm4), (Whm5) and (Whm6) at each basin. Moreover, the electromagnetic current meters (EMS) were installed inside the port as shown in Figure (5). The EMS1 was installed at the mooring area and the other two currentmeters were installed at the entrance of the basins with water depths of 4m and 2m. Figure 6 shows the model after completion. N EMS2&3 Vx Vy Southen Breakwater Whm6 EMS3 Whm5 EMS2 EMS1 Vy Vx Access Channel EMS1 Whm3 Whm4 Northern Breakwater Whm1 Whm1 Figure 5 Model layout and locations of the instruments
Figure 6 Model layout and Wave Basin 7. TEST PROGRAMME The study went through two phases. The first was to test the original design of Mrzouka fishery Port and the second was to test the suggested modification to the breakwaters alignment of new port. The following are the proposed alternatives, waves, and sea water level conditions that were applied during the two phases. 7.1 The proposed alternatives Three alternatives were proposed for the alignment of the two breakwaters of the new fishing port in order to ensure safe wave conditions inside the port. Figures 7 and 8 show the alignment of the proposed breakwater alternatives. The first alternative (I), the length of the North breakwater was increased by 60m and the South breakwater was reoriented to protect the two basins of small boats. In the second alternative (II), the length of the North breakwater was kept the same as alternative (I) but the last 200m was reoriented and the South breakwater was kept as alternative (I).In the third alternative (III), the North breakwater was increased by 108m, its head was reoriented and the South breakwater was not changed.
Figure 7 Alternatives (I) and (II) Figure 8 Alternative (III) 7.2 Wave Condition and water level The wave height was modeled to propagate from NEE with an angle of 22.5º to the East with a significant height H s of 3.5m. This is equivalent to 50 years return period. The wave heights in the model were taken as 40%, 60%, 80% and 100% of the significant wave height (H s ) at deep water. The peak period for each wave height was calculated using the following formula: T p = 4.5 H s (2) in which: T p : the peak period, (s) H s : the significant wave height, (m) The water level of the model was varied from (0.0) m+msl to (0.70) m+msl.
During the first phase, the total tests were six. In addition, 18 tests were applied to the three modified designs. Table (1) represents the model test program during the first and second phases. Test Number Table (1) Model Test Program Significant Wave Height at Deep Water H s (m) Peak Period T p (s) Sea Water Level (m)+msl 1 1.4 5.32 0.0 2 2.1 6.52 0.0 3 2.8 7.53 0.0 4 3.5 8.42 0.0 5 2.8 7.53 0.7 6 3.5 8.42 0.7 8. EXECUTED MEASUREMENTS In order to test and optimize the proposed design of Mrzouka fishery port the wave heights, mid depth currents, surface currents were measured. Also, particle tracking and visual observations were carried out for all the executed tests. Wave height The wave heights were measured in the model at different locations. Two wave height meters (Whm1 and Whm2) were installed in front of the wave generator to measure the incoming waves at deep water. One wave height meter (Whm3) was installed at the location of the mooring area at the entrance of the port. The other three wave height meters (Whm4, Whm5 and Whm6) were installed inside the port, one in each basin. Mid depth current The mid depth currents were measured inside the port in two directions using an electromagnetic current meter. The currents were measured at three stations; one station was at the mooring area and the other two stations were in the two basins with water depths 4 and 2 meters, respectively. Surface currents The surface currents were observed using small pieces of papers. Their movements were recorded by a photo camera with ten second time period for each photo. This method shows the area of circulation inside the port and the direction of the surface currents at the mooring area and in the three basins.
Particle Tracking Particle tracking technique was used in order to investigate the surface currents at a certain locations inside the port.their directions were defined so as their area of circulation. This technique was carried out using circular floating pieces of wood with diameter of 7cm that were recorded using a photo camera and a video camera, as well. Visual Observation During each test run, the wave height, water level, the area of circulation and the wave transmission were monitored visually. 9. RESULTS AND ANALYSIS In this section, the results of both study phases are displayed. The results cover the wave heights, mid depth currents, particle tracking and visual observations. 9.1 Results of First Phase (Testing the Original Design) Prior to the executed test program, comprehensive tests were conducted to determine waves and currents conditions for the original design of the new port. It was found that after testing the proposed design of Mrzouka fishery port the wave heights inside the port (1.43m) were higher than the permissible wave height (0.3m), Table (2). In addition, the water surface inside the port was found to be extremely fluctuating where the water level exceeded the crest level of the quay wall, Figure 9. Also, the mid depth current, at the mooring area, was found to range between 1.13m/s and 1.34 m/s, Table (3). These values are higher than the permissible values. Based on the measured results, it was clear that there is a need to modify the alignment of the two breakwaters in order to reach a safe condition inside the port. Table (2) Measured Wave Heights during the First Phase Test No. Sign. Wave Height at Sign. Wave Height inside the Port Deep Water (m) (m) Whm1 Whm2 Whm3 Whm4 Whm5 Whm6 Test 1 1.10 1.02 0.20 0.15 0.40 0.17 Test 2 2.41 2.23 0.52 0.35 0.94 0.43 Test 3 2.99 2.77 0.70 0.45 1.37 0.58 Test 4 3.49 3.30 0.79 0.51 1.41 0.67 Test 5 3.11 2.88 0.78 0.47 1.38 0.63 Test 6 3.65 3.33 0.92 0.58 1.43 0.75
Table (3) Mid Depth Currents during the First Phase Test Number 5 6 Current Index Current at Station one Current at Station two Current at Station three Vx Vy Vx Vy Vx Vy Max. Negative (m/s) -1.10-1.13-0.09-0.12-0.59-0.13 Max. Positive (m/s) 0.56 0.92 0.11 0.01 0.43 0.29 Average Negative (m/s) -0.18-0.29-0.02-0.05-0.15-0.05 Average Positive (m/s) 0.12 0.27 0.03 0.00 0.12 0.05 Max. Negative (m/s) -1.24-1.34-0.13-0.12-0.59-0.13 Max. Positive (m/s) 0.82 1.27 0.13 0.02 0.43 0.29 Average Negative (m/s) -0.22-0.37-0.03-0.05-0.15-0.05 Average Positive (m/s) 0.14 0.28 0.03 0.00 0.12 0.05 Figure 9 the surface currents at the Port entrance (Left) and inside the Port (Right) 9.2 Results of Second Phase (Testing the Alternatives) During the second phase, three alternatives were tested in order to fulfill safe conditions inside the new port. The obtained wave height at the mooring area and inside the port using alternative (I) was found to be 0.51m and 0.48m, respectively. During testing alternative (II), the wave height was found to be 0.33m and 0.32m at the mooring area and inside the port, respectively. At the mooring area, the reduction percentage of the wave height using alternatives (I) and (II) were found to be 45% and 65%, respectively. Also, the reduction percentage in the mid depth currents at the mooring area was found to be 60%.In addition, circulation zones were formed inside the port. Moreover, the water level fluctuated and exceeded the quay wall crest. Alternative three (III) was tested and the wave height at the mooring area and inside the port was found to be within the permissible value (0.30m). Table (4) shows the measured wave heights at the different location inside the new port.
The wave height was reduced by 70% with respect to the original design. In addition, the mid depth current at the mooring area and inside the port was reduced by 75% compared to the original design, Figure (10). Table (5) shows the obtained mid depth currents inside the new port. Also, it was found that the circulation zones were considerably reduced and the water level was calm. Table (4) Measured Wave Heights, First Phase, Alternative III Test No. Sign. Wave Height at Deep Water (m) Sign. Wave Height inside the Port (m) Whm1 Whm2 Whm3 Whm4 Whm5 Whm6 Test 1 1.11 1.02 0.06 0.05 0.05 0.03 Test 2 2.49 2.23 0.13 0.11 0.11 0.08 Test 3 3.04 2.80 0.23 0.17 0.18 0.11 Test 4 3.58 3.30 0.26 0.25 0.24 0.15 Test 5 3.17 2.86 0.26 0.19 0.20 0.13 Test 6 3.67 3.31 0.28 0.26 0.29 0.17 Table (5) Measured Mid Depth Currents, Second Phase, Alternative III Test No. 5 6 Current Index Current at Station one Current at Station two Current at Station three Vx Vy Vx Vy Vx Vy Max. Negative (m/s) -0.13-0.13-0.20-0.12-0.44-0.13 Max. Positive (m/s) 0.21 0.19 0.23 0.18 0.53 0.20 Average Negative (m/s) -0.03-0.05-0.03-0.03-0.11-0.03 Average Positive (m/s) 0.07 0.05 0.06 0.04 0.14 0.04 Max. Negative (m/s) -0.22-0.16-0.19-0.15-0.86-0.21 Max. Positive (m/s) 0.28 0.21 0.30 0.18 0.76 0.55 Average Negative (m/s) -0.05-0.05-0.04-0.05-0.18-0.04 Average Positive (m/s) 0.08 0.05 0.08 0.05 0.20 0.08 Figure 10 the surface currents at the Port entrance (Left) and inside the Port (Right), Alternative III
10. CONCLUSIONS AND RECOMMENDATIONS 10.1 Conclusions Based on the obtained results, alternative (III) proved to satisfy the required safe conditions and was therefore chosen to be the layout of the new fishing port at Mrzouka, Libya. It fulfilled the following: The wave heights at the mooring area and inside the port did not exceed the permissible wave height (0.30m). The average mid depth currents at the port entrance was found to be safe for boats navigation in and out of the port. The surface currents and circulation zones were reduced and were found to be safe for boats maneuvering. The water levels inside the port did not exceed the crest level of the quay wall. No overtopping was observed. 10.2 Recommendations The following recommendations are suggested for optimizing the design of the new port. Alternative (III) is recommended to be the final design for the new fishing port. The entrance width of the third basin for small boats should be widened to reduce the mid depth currents. The access channel should be tested qualitatively against sedimentation. Stability tests for the armour layer of the Northern and Southern breakwaters are required to be executed Bathymetrical surveys should be executed periodically in order to execute any remedial action in the proper time. REFERENCES 1. Lesser, G., De Vroeg, J.H., Roelvink, J.A., Geroloni, M., Ardone, V., 2003 Modelling the orphological impact of submerged offshore breakwaters, Proc. 5th Internat. Symposium on Coastal Engineering and Science of Coastal sediment Processes, May 1823, Florida, USA 2. Physical Model Tests for Coastal Protection Works at Rosetta and Damietta Promontories, Denmark, 1996. 3. Hydraulics Research Institute Integrated Development of Egypt's Northern Coastal Zone "Hydraulic Model Study of Protection Scheme for Pilot Area 1&2" HRI, Egypt 2003.
4. WL Delft Hydraulics, Integrated Development of Egypt's Northwestern Coastal Zone, Development of nearshore water condition, interim report 1, February 2002. 5. Engineer Manual EM 1110-2-1615 Hydraulic Design of Small Boat Harbors U.S. Army Corps of engineers, 1984. 6. USACE. 1986. Engineering and Design, Design of Breakwaters and Jetties, EM 1110-2-2904. 7. USACE. 2002. Engineering and Design, Coastal Engineering Manual, EM 1110-2-1100.