The Panama Canal consists of 17 artificial lakes, several improved and artificial channels and two sets of locks. A typical passage through takes around nine hours, but it is presently handling more vessel traffic than had ever been envisioned by its builders and the proportion of large ships transiting it is increasing steadily.
The canal is one of the most important shipping routes in the world, handling an estimated 5 per cent of total world trade. Since its opening in 1914, the canal has provided a swift passage between the Atlantic and Pacific Oceans for ships ranging in size from small pleasure craft to 965-foot long Panamax cargo vessels.
An increasing number of ships, however, are too large to fit through the canal, requiring longer and wider locks. Therefore, the Panama Canal Authority (ACP) has proposed the third Set of Locks Project to install new locks and upgrade the canal to allow passage for Post-Panamax vessels. This project is a monumental geotechnical effort that is estimated to require eight years of construction at a cost of US$5.25 billion. On 22nd October, 2006, the Panamanian people overwhelmingly approved the project in a nationwide referendum.
In the summer of 2006, ACP retained Technos to carry out a geophysical investigation along critical portions of the expansion route. The investigation included over 27 km of sub-bottom seismic reflection data within the canal to map stratigraphy and to identify faults. In addition to the marine data, over 15 km of seismic refraction and multi-channel analysis of surface waves (MASW) data were acquired on land. The main objective of the land-based geophysical survey was to provide the physical properties of subsurface strata and show how they relate to stratigraphy, structure, and anomalous conditions. The investigation took place over a three-month timeframe and provided an integral set of data for the geologic characterisation of the new Panama Canal.
The Panama Canal is 77 kilometres long and extends southeast from the Atlantic Ocean, through a system of locks, to the Pacific Ocean. The locks raise ships to an elevation of approximately 26 meters (85 feet) above sea level. The Third Set of Locks Project will add new locks on the Pacific and Atlantic sides of the canal capable of handling longer and wider ships. The new locks will require new navigational channels that will join into the existing canal. The new locks will utilise water recycling basins to minimise fresh water loss through the lock cycle. The navigable depth of the canal will also be increased to allow for deeper draft ships.
Panama is located in a young and complex tectonic setting surrounded by four plate boundaries. The Isthmus of Panama is part of a volcanic arc that started developing in the Cretaceous Period, with deformation and faulting shaping the landforms through present time. Bedrock includes intrusive and extrusive volcanic rocks, pyroclastic rocks, and sedimentary rocks. The northern canal region is composed of Miocene to Holocene sedimentary sequences deposited on eroded pre-Tertiary volcanic rocks. The southern canal region is composed of Miocene-age sedimentary and volcanic rocks covered by residuum overburden or fill from recent excavations of the canal. Numerous faults and shear zones bisect much of the Panama Canal area, although active seismicity is surprisingly low.
Over 11 kilometres of new navigation channels will be cut through the soil and rock as part of the project. A portion of the new channels transect relatively steep hills with hard basalt cores and clay overburden. Existing boring data show that the geology is highly variable. In this investigation, the geophysical data were integrated with existing geologic data, such as boring logs, providing a more complete characterisation of subsurface conditions, the complex structural features and their physical properties.
Excellent data quality was obtained throughout the geophysical survey, allowing reliable models and interpretations to be developed. The models correlate well with each other and with existing borings. The results of the survey identify anomalous zones that may be related to faults, characterise the P-wave and S-wave velocity of the geologic units, and map the lateral continuity of structural features. The results will be used to guide further characterisation efforts and to properly design the new canal structures.
The sub-bottom seismic reflection survey covered widely-spaced survey lines in a reconnaissance level of effort within Miraflores and Gatun Lakes, which are part of the 77 km long Panama Canal. ACP provided a modern survey vessel equipped with a differential GPS navigation system and an experienced boat crew. An Applied Acoustics AA-300 boomer system was used as the seismic source with an energy level of 200 to 350 Joules. An 8-element single-channel hydrophone was towed behind the survey vessel to receive the acoustic signals. The shot (ping) rate was set at 0.5 seconds, which produced a sample at approximately 0.4-metre intervals. The processed marine seismic records contain good quality data to depths of up to 150 meters that show reflections due to stratigraphy and structure.
Technos are continuing with their survey and are now up to 81 line-miles of marine data. This data is crucial to the next engineering decisions – the building of the two new sets of single-lane, three step locks; two new navigational channels to connect the new locks to existing channels; and deeper, wider versions of existing shipping lanes.
The Third Set of Locks project is expected to be complete and open for traffic in 2015. The first land work, the dry excavation of a wide trench connecting Culebra Cut with the Pacific Coast, began in September this year.
Ronald D Kaufmann is vice-president of Technos Inc, Doral, Florida, USA. www.technos-inc.com. He served as a senior geophysicist from 1996 to 2005.
Mix and match
Applied Acoustics manufactures a variety of sub-bottom profiling products based on a component system configuration, so that the optimum package can be tailored for any particular application. Both the seismic energy source units, the CSP range, and the seismic energy sound source products, Boomer plates and Sparker assemblies, are manufactured at the Great Yarmouth, UK, plant where all research, sales and service also takes place.
The company has been manufacturing equipment for this market for almost two decades with products constantly being up-graded and fine tuned. Products launched in 2007 include the 6000 Joule Delta Sparker, the most powerful in the range and the versatile CSP-D energy source with a unique dual voltage output. By adjusting this output, switchable on the front panel, better penetration can be achieved from the boomer plate sound source, a feature previously only obtainable to the same extent with sparkers.
Many of the CSP products also operate with the benefit of a ‘slow start’, a means of gradually increasing power output to ease the load on the generator and help to avoid potential interference with marine mammals.
Applied Acoustic Engineering Ltd is based in Great Yarmouth, Norfolk, UK. www.appliedacoustics.com