SEDIMINTATION CHALLENGES IN UMM QASR PORT, IRAQ

Transcription

1 Paper No: P021 SEDIMINTATION CHALLENGES IN UMM QASR PORT, IRAQ by C. Jürgensen 1, A.A. Samir 2, S. Salim 3, J.B. Abild 4, M. Hassan 5, H.J. Vested 6, L. Dall 7 and N. Arndal 8 ABSTRACT The paper describes the hydraulic investigations carried out, the sediment models established to simulate the complex sedimentation processes in the Umm Qasr New Port and proposals made to remedy the sedimentation problem in the port. Moreover, it describes the site surveys and data collection carried out as a prerequisite for a better understanding of the sedimentation processes and for verification of the numerical modelling. The sediment modelling was supplemented by real-time navigation simulations of relevant ship types calling at the port. A breakwater concept at the entrance to the New Port was developed to remedy the sedimentation and hence reduce the demand for maintenance dredging, while still ensuring safe approach and departure to the port. This will save resources and promote efficient port operation. 1. INTRODUCTION The recovery of the Iraq economy after decades of warfare and sanctions is dependant on the revival of the Iraqi transport infrastructure in order to facilitate the important reconstruction process. Imports to Iraq have in many years been diverted through ports in neighbouring countries with increased transportation cost, loss of revenue and job opportunities in Iraq as a result. The strategic objective of the Government of Iraq is to secure, that a larger share of these imports is directed through the Iraqi ports in the south of the country, thus making the country more self reliant. Khor Az Zubair Shatt Al Arab Khor Abdallah Umm Qasr Port River No. 1 Khor Az Zubair Figure 1: Iraqi ports in the south of Iraq with the main commercial port of Umm Qasr. 1 Dr., Senior Environmental Engineer, COWI A/S, crj@cowi.dk 2 Head of Hydrographic Survey, General Company for Ports of Iraq, ummqasrsurvey@yahoo.co.uk 3 Assist. Prof, Basrah Maritime Science Centre, Basrah University, sadiqsalimunibasrah@yahoo.com 4 Chief Project Manager, COWI A/S, jba@cowi.dk 5 Project Coordinator, COWI A/S, mha@cowi.dk 6 Head of Projects, DHI, hjv@dhigroup.com 7 Senior Hydrographic Surveyor, EIVA a/s, lda@eiva.dk 8 Senior Project Manager, FORCE Technology, nia@force.dk 1

2 The Danish Foreign Ministry (Danida) has assisted the Government of Iraq in this effort by funding a study of the Iraq Transport Corridor Study (ITCS) from Umm Qasr via Basrah to Baghdad, Iraq. The study is part of a more comprehensive Iraq Transportation Master Plan study (ITMP) for the whole Iraqi transport sector. The objective of the ITCS has been to identify existing bottlenecks in the transport infrastructure with focus on Ports, Waterways and Roads and the inter-modal exchange of goods between the different transport modes and to analyse and propose short, medium and long term improvements to the infrastructure in the southern transport corridor with the purpose to guide investments. The study and survey activities started in 2005 and activities are still ongoing. The project is carried out by the lead consultant COWI of Denmark who, for the port part of the study, has worked in a close cooperation with the Iraqi port authorities: General Company of Ports in Iraq (GCPI), Maritime Science Centre (MSC), Basrah University and Engineering Consultancy Bureau (ECB), Basrah - acting as local consultant. DHI Water and Environment, FORCE Technology and EIVA, all from Denmark have acted as sub-consultants to COWI. 2. BACKGROUND The ports of Iraq are all located in the Basrah Governorate in the south of Iraq see Figure 1. The main commercial port of Umm Qasr is located at the mouth of Khor Az Zubair. Khor Az Zubair was in the early 80ties linked to Shatt Al Arab through the Al Basrah Channel, but the sluice gates have been blocked since the Gulf War in The Umm Qasr Port comprises two ports: the old port located along the Khor Az Zubair and the New Port located in the dredged channel denoted River No. 1. The two ports have almost 3.5 km of quays for bulk and container cargo imports and have been designed to accommodate Panmax and large feeders with draft up to 12.5m. SEDIMENTATION PROBLEMS The waters of the upper parts of the Gulf have high concentration of sediments, partly due to the sediments carried with the rivers that have outlets in the area and partly due to the wind borne particles from the prevalent north-westerly Shamal. The sediment rich water of the Gulf is carried into the port approaches and ports with the tidal movements and deposited in areas with calm waters like River No. 1 see Figure 2. Figure 2: Satellite image shows inflow of sediment in the mouth of River No. 1 at rising tide. The bathymetric survey shows a pronounced sedimentation at the port entrance. Experience shows that the deposition of sediments in the Iraqi ports and approaches is substantial and amounting to approximately 10 million m 3 per year. River No. 1 constitutes a specific problem with 2

3 regard to sedimentation as this short approach - roughly 1 nautical mile - will require a yearly maintenance dredging in the order of 2 million m 3. As a consequence of the need for dredging of the sediment deposited in the Umm Qasr New Port, there is a need for extra dumping areas and breakwaters to contain the dredged material. Therefore, the money to be spent on dredging works and the logistics involved herein are substantial; annually in the order of USD 10 mio and will require a lot of resources to control the operations in different areas of the channels. Finding new economical and practical ways to reduce the sedimentation problem has therefore high priority for GCPI. 3. METHOD The methods applied to analyse and simulate the sedimentation processes and the remedial actions proposed to reduce the sedimentation in the Umm Qasr New Port are described in the following. FIELD MEASUREMENTS PURPOSE The main purpose of the present field survey programme is to establish basis for and verification of the hydrographic and sedimentation modelling carried out as a key element of the study. Iraqi experts within GCPI and in the scientific community at the Basrah University have been responsible for the data collection and have taken active part in the data analysis. Another important purpose of the study has been capacity building of the concerned authorities and institutions e.g. by supply and training in the use of state-of-the-art marine surveying equipment, methodologies and related software. PROGRAMME The programme for the field measurements have involved: Preparatory activities o o Procurement and supply of survey vessel "Al Salam" and miscellaneous marine survey equipment (single beam echo sounder, RTK, ADCP, tidal gauges, water and sediment sampling equipment) Training of Iraqi staff in the use and maintenance of the equipment by Danish experts (in Denmark and Kuwait). Survey activities in Iraq Analysis and reporting SCOPE The survey works have comprised: Bathymetric survey Ship borne single beam echo sounder, advanced GPS positioning Water level recordings Pressure cells, digital display Flow measurements Ship borne Acoustic Doppler Current Meter (ADCP) Suspended matter Several water samplers Sedimentation Core bottom sampler, haps sampler, Van Veen sampler 3

4 Sediment characteristics Application of the geo-lab at Basrah University MODELLING A conceptual understanding of the hydraulic conditions was developed by the hydraulic experts of COWI in co-operation with the experts H.J. Vested (DHI), L. Dall (EIVA) and J. Fredsøe (The Technical University, Denmark). The results were discussed with experts from GCPI and Basrah University in order to keep all involved parties on the same level of understanding of the status and the direction of the project. Figure 3: The conceptual sketch shows that sedimentation is due to two mechanisms: Tidal induced siltation and eddy induced siltation. The initial hydraulic assessment of the flow situation identified an exchange eddy at the entrance of Umm Qasr New Port that contributes significantly to the sedimentation in the Umm Qasr New Port, see Figure 3. By narrowing the entrance to the port by breakwaters the siltation contribution due to the exchange eddy can potentially be reduced. However, these breakwaters must be designed in such a way that they do not jeopardize the navigation to the port. Alternative layouts and alignments of the breakwaters were modelled by means of state-of-the-art numerical modelling of the complex hydraulic flows and sedimentation conditions at the port entrance. The modelling was carried out by DHI based on the field data that were collected by GCPI (Umm Qasr) and MSC (Basrah University). Since a significant reduction of sedimentation can be achieved by narrowing of the port entrance, the effect of the breakwaters on the navigational conditions had to be investigated in detail. Alternative breakwater layouts and different wind and current conditions were simulated for representative ships using real-time navigation simulators at FORCE Technology in Copenhagen. Port pilots from Umm Qasr took active part in the simulations. 4. RESULTS This chapter describes in brief the results from the field measuring by the staff of GCPI and MSC, the numerical modelling of hydrodynamics and sediment transport as well as the ship simulations. FIELD DATA A comprehensive field measurement campaign was initiated during 2007 to collect the information and data required for the subsequent modelling and verifications. Training of Iraqi staff and personnel was 4

5 carried out by Danish Experts either in Denmark or in Kuwait. Once the field campaign was started and ongoing in Iraq, required additional support was provided via telephone and or through supplementary training. The supply of the equipment and the subsequent training of the Iraqi survey staff were carried out with assistance from expert personnel from EIVA A/S, Denmark. BATHYMETRI The bathymetric survey was carried out in early 2007 using the fully equipped survey vessel "Al Salam". The resulting mapping of the data for Umm Qasr is shown in Figure 4 below. The data are plotted onto a satellite picture in order to give the correct understanding and overview. The survey results indicate that considerable sedimentation takes place at the entrance to the port. This is in line with experience as GCPI has a dredger placed here more or less permanently for maintenance dredging. This new bathymetry is important key information necessary to determine the net changes of the water depths since the earlier survey carried out by UNDP in Figure 4: GCPI survey in February 2007 carried out with the new survey vessel "Al Salam". 5

6 WATER LEVEL Water level gauges have been installed at the inner and the outer part of Umm Qasr New Port. The recordings are mainly used for port operation purposes, but were also used for calibration of the hydraulic models employed to investigate the sedimentation processes. An illustration of the recorded water levels is provided in Figure 5, where the measurements are compared with tidal forecast for Umm Qasr port. 6 5 Forecast Pressure cell Water level (m) CD aug aug aug aug aug-07 Figure 5: Water level recordings by pressure cell compared with tidal predictions from tidal constituents. CURRENT MEASUREMENTS Current measurements were conducted from the survey vessel "Al Salam" with the ADCP equipment. The data was analysed with the provided software systems and the measurements was subsequently used to verify the mathematical modelling of the complex flow pattern at the entrance to the New Port. An example of the automatic current profiling along a transect at the port entrance is shown in Figure 6. Figure 6: Results of an ADCP velocity profile transect (screen dump). Upper left panel: vertical profile; Upper right panel: Velocity vectors along the transect. Lower panel: Lateral velocity distribution. 6

7 Figure 6 shows high current speeds in the surface of the central flow (red colours) and low current speeds on the area of the New Port (dark blue area far left in the lower panel). This is in agreement with the expected and the modelled currents. Figure 7: Overview of depth averaged current measurements at falling tide. Figure 7 presents an overview of the depth averaged ADCP measurements at falling tide. The measurements show clearly the division between the main river flow and the calmer out flowing port water. SEDIMENT CHARACTERISTICS Sediment characteristics were investigated at different sampling campaigns in The density and the grain size distribution of the sediments in suspension were determined as well as the surface sediments at different locations. It is found that the sediment is well sorted and very fine silt with a typical d 50 grain size of about 10µm. The content of suspended sediment in different heights in the water column and at different phases in the tidal cycle was measured and illustrated in Figure 8 below. The sampling location is in the Umm Qasr New Port, fairly close to the port entrance. It is seen that the concentration of suspended matter is closely correlated to the tidal cycle. Further, there is no clear indication that the bottom water is significantly more turbid than the surface water. 7

8 Figure 8: Suspended matter measurements in three levels at a station close to the entrance. The water level is included for comparison. NUMERICAL MODELLING The Danish Hydraulic Institute (DHI) numerical model MIKE21 was applied. The model solves the governing equations for conservation of momentum and mass integrated over the vertical. The applied MIKE21 set-up consists of the Hydrodynamic (HD) module that describes water levels and velocities and the Mud Transport (MT) module for simulation of cohesive sediments. The bathymetry was represented in the model by a flexible mesh in order to describe the local flow field in the entrance and around breakwaters and breakwaters with a high resolution. In order to provide realistic boundary conditions for the MIKE21 model, the entire Arabian Gulf was modelled with a hydraulic model. This was done for a one-month period with forecasted forcing at the Strait of Hormuz. This model fed a river model (MIKE11) for the entire Khor Az Zubair and this model provided the boundary conditions, in form of river discharge and water levels, for the detailed high resolution MIKE21 model of Umm Qasr New Port. The detailed model was simulated for a 5 days tidal period. Figure 9 shows a comparison between simulated currents and ADCP measurements at ebb tide. As it is seen from Figure 9 the measurements verify the simulations. Measurements and simulations are compared for the same tidal phase (approximate), but the dates are different (for practical reasons). However, it is obvious that the simulated current speeds correspond very well with the measurements. Figure 10 compares the simulated sediment transport with satellite image (Google Earth). The tidal situation is low water and the flow is rising. Sediment rich water (grey) from the Khor Az Zubair is entering the New port at the south and the sediment poor water (blue) is leaving the port at the north. The comparison shows that the simulation captures the observed phenomenon of the sediment inflow at start of rising tide. 8

9 Figure 9: Current measurements compared with modelling. The measured velocities (yellow arrows) are compared with simulated velocities (black arrows). Figure 10: Comparison between satellite image and simulated sediment transport around the time of start of rising tide. The red colour indicates highest turbidity whereas the blue colour indicates lowest turbidity. The model was applied to assess a number of different breakwater layouts at the port entrance. The total sedimentation in the berth areas and navigation channel was calculated and the reduction determined relative to the existing situation. The layouts were evaluated from a navigation point of view until an optimal layout was determined taking both sedimentation and navigational aspects into consideration. Figure 11 shows the change in bed mass of sediments for the preferred breakwater layout at the entrance to the New Port (after 5 days of simulation). It is evident that sediments will accumulate at the south side of the New Port as is the case also at present without breakwaters. However, the total 9

10 sedimentation rate is lower and the area of sedimentation is smaller than found for the existing situation and the entrance itself will be more or less self cleansing. The result of the sediment modelling shows that the preferred layout of the breakwaters will reduce the net sedimentation in the Umm Qasr New Port by approximately 20% :00: Time Step 672 of 672. Total bed mass change [kg/m^2] Above Below 0 Undefined Value Figure 11: Total bed mass change for the preferred breakwater layout at the entrance to the Umm Qasr New Port. NAVIGATIONAL SIMULATION Navigational conditions for different ship types were simulated with different breakwater layouts, current flows and wind conditions. The final position of the entrance with a 240 m opening relatively far at the north side is a results of the navigational simulations. Figure 12 shows the preferred breakwater layout with a bulk carrier of DWT entering the port during high tide (north going currents and southerly winds). 5. DISCUSSION AND CONCLUSION Extensive sedimentation represents one of the major obstacles for efficient operation of the Iraqi ports and in particular for the Umm Qasr New Port. Several breakwater layouts that reduce the entrance width to the port were studied with respect to their potential for reducing the sedimentation rate in the port and their impact on navigation. The analysis of the complex hydraulics and sedimentation processes in Umm Qasr New port revealed that a substantial reduction of the annual sedimentation can be achieved by narrowing the port entrance. The sedimentation pattern is relatively complex over the tidal cycle. The resulting net effect is sensitive to the physical properties of the settling velocities of the sediment, occurrence of fluid mud and also to the local flow pattern in the opening of the New Port. The measurements assisted in reducing this uncertainty. The sedimentation modelling indicates a possible reduction of the maintenance dredging in Umm Qasr New Port of about 20% out of an annual dredging amount of about 2 million m 3. 10

11 Figure 12: Simulation of navigational conditions. Major ship entering the port. A process of interactions between the findings from the sediment modelling and the navigation simulations was necessary to develop an optimised layout. This layout is illustrated in Figure 12 and shows an opening relatively far to the north and two breakwaters that have a slight angle inward into the New port. Economic estimates for construction of the breakwaters and the savings in dredging indicate a pay back time of about 5 years, which is considered to be favourable. It is therefore concluded that feasible options exist that can remedy the sedimentation problems in the Umm Qasr New Port by substantially reducing the yearly maintenance dredging requirements. By providing state-of-the-art marine survey equipment and subsequent training of the Iraqi experts in the use of this equipment and related software, the Iraqi port authority now has the capability to monitor the hydraulic regime and sedimentation in the ports and approaches. GCPI and MSC participation in the data analysis and modelling activities has enhanced the understanding of the complex hydraulic and sedimentation processes in the Iraqi ports and approaches, which will enable GCPI to assess and venture into future developments of the Iraqi ports with due consideration to the sedimentation challenge. 11