Management of port infrastructure
Quality hydrographic survey data is essential for efficient maritime development
N R Raut
India has long coastline of 7517 kms with 12 major ports and 187 minor & intermediary ports. Major ports all together handled 423 million tones traffic & non–major ports all together handled 519 million tones traffic during the year 2006-07. Traffic at Indian ports has been growing at the rate of over 11% during last 5 years and with continuing rapid growth in trade, port traffic is expected to grow further. Lack of port infrastructure has been one of the major problems (i.e. low draught & inadequate back up services) in our maritime development. Shippers prefer shipments by large size & deeper draughts vessels, which is more economical in cost of operation. So, to accommodate such bigger vessels, the required depths should be available. Accordingly there is huge demand for dredging & quality hydrographic services at the Indian Ports as the channels to be widened & deepened to accommodate bigger vessels. Almost all the major ports in India have plans to widening & deepening their approach channels in order to accommodate bigger ships. Further, the maintenance-dredging requirement of ports is substantial considering the siltation problem at the ports.
International regulation for hydrographic services
A completely new situation has risen after the total revision of chapter V of the annex to SOLAS that maintains that hydrographic services are binding to Governments under international law.
– For the first time, international law makes it mandatory to operate hydrographic services. This obligation applies to all states that are parties to SOLAS.
International standards for port surveys
IHO published the 4th edition of special publication No.44 in April 1998 of IHO standards for hydrographic surveys. The principal aim of this publication is to specify minimum standards for hydrographic surveys in order that hydrographic data collected according to these standards is sufficiently accurate and that the certainty of data has to be adequately quantified to be safely used by mariners.
The new edition of IHO standards for hydrographic surveys describes a very important change. The accuracy of a survey is no longer dependent on the scale of the analogue chart. The accuracy as well as resolution of a survey depends on the type of the area to be surveyed. The preface of IHO standards recognises that hydrographic data is also important for coastal zone management, environment monitoring, resource development, legal and jurisdictional issues and coastal engineering works etc.
1) To calculate the error limits for depth accuracy the corresponding values of ‘a’ and ‘b’ listed in above table to be introduced into the formula ±√[a2+(b∗d)2] With ‘a’ = constant depth error, i.e. the sum of all constant depth error ‘b∗d ’ = depth dependent error, i.e. the sum of all depth dependent errors ‘ b’ = factor of depth dependent error ‘ d’ = depth
2) For safety of navigation purposes, the use of an accurately specified mechanical sweep to guarantee a minimum safe clearance depth throughout an area may be considered sufficient for above order surveys.
3) The value of 40 m has been chosen considering the maximum expected draught of vessels.
4) The line spacing can be expanded if procedures for ensuring an adequate sounding density are used.
For ports & harbours, and especially for those where the underkeel clearance is small, 100 % coverage of the seafloor is required during the sounding process in order to make sure that all potential hazards are mapped. It is not possible by single beam echosounder alone. So alternative technologies available are as follows:
• Mechanical sweeping is best but time consuming and therefore expensive. •
Towing side scan sonar is often impractical in confined areas such as ports.
• Compact high frequency multibeam echosounders, probably most viable alternative for the future, which can comply with the requirement of SP-44.
Minimum underkeel clearance implications on hydrography in port
Most ports have restriction on the depth available for navigation. This depth is referred to as ‘declared depth’ and is determined from hydrographic information from recent hydrographic survey. Ports which operate with minimum underkeel clearance for shipping use this declared depth in determining the loaded draught of vessels using the port.
Minimum underkeel clearance can be determined from the following factors.
• The vessel squat and settlement (related to speed)
• The vessel manoeuvring characteristics • Increase in draught of vessel due to vessels roll, pitch & heave movement
• Accuracy in the predicted or measured tide
• Accuracy of declared depth
• Allowance for possible siltation since last survey.
• Information about wave heights, direction & tidal stream
The hydrographic surveyor contributes to the measurement of factors of tidal height, accuracy of declared depth and frequency of hydrographic surveys and he may contribute to the measurement of vessels squat and roll, pitch & heave movement.
With increase in competition to attract business towards the ports and reduce the operating costs, the stakeholders are questioning the allowance factors in the determination of underkeel clearance. Some ports have developed a dynamic underkeel clearance that measures wave heights, wave direction and actual accurate tide heights to determine the maximum draught in which the vessel can load.
The technologies that available to hydrographic surveyor now have greatly increased the surveyor’s ability to provide highly accurate depth & position. These includes motion sensors, multibeam echo sounders, radio tide gauges, RTK GPS, Survey software for on-line data logging, computing, huge data managing power & processing the result in required format. Because of this available technology, the surveys could be made repeatable. With this degree of repeatability it is then possible to place a high degree of accuracy of depth on the published chart.
If surveys are carried out at a suitable frequency to determine the underkeel clearance for the port, it would then be possible to eliminate allowance for siltation from underkeel clearance.
Port dredging survey
The National Maritime Development envisages the capital dredging of major ports and navy to the tune of Rs.6,304 crores in addition to maintenance-dredging requirement.
To select suitable dredgers, equipment, methodology for dredging, quantity to be dredged and cost estimation, it is very much essential to carry out pre-dredging hydrographic, geo-technical & seismic survey in order to know the precise seabed profiles as well as sub-surface strata which is supposed to be dredged out.
In order for optimum deployment of costly dredgers, it is very essential to provide on-line progress of dredging works to dredgers by means of providing them dredging monitoring sounding charts.
Port authorities should adopt existing internationally accepted standards for surveying as set out above referred publication SP-44 and produce charts, which confirms IHO chart specifications for pre & post dredging survey so that cost of dredging can be worked out precisely as well as make it possible to declare a dredged route/ channel ‘cleared’ to required depth.
The hydrographic survey and other associated tasks shall be carried out by or be directly supervised by suitably qualified and experienced hydrographic surveyors. The resulting information shall be certified by this surveyor and shall state the order to which the information can be assigned.
Port management using ECDIS technology
ECDIS, or Electronic Chart Display and Information system, has been developed for navigational purposes but is in reality a full-fledged Marine Information System (MIS). Its data structure makes it useful for GIS, Port or Coastal Management.
The web-based port management package developed by Port Of San Diego offers new possibilities through real-time navigational & environmental data inputs and access to the land-based databases for ECDIS presentation through Internet. The data is presented on top of ENC in the form of thematic overlays using ECDIS technology. The real time information from environmental sensors includes weather, tidal stream and tidal heights above CD. Tidal height data is used to provide the dynamic underkeel clearance information in the ship manoeuvring area. The data is supported by web-camera images with zooming and panning capability. Updated ship movement information included together with static data show the relevant regulatory information, emergency response information, list of facilities, fees, and marine events etc.
To make all Indian ports more competitive & safe, it is very much essential that Port authorities should adopt the existing internationally accepted standards for surveying as set out in the above-referred publication SP-44 and produce charts that confirm IHO chart specifications
In order to comply with the IHO minimum standards for hydrographic surveys in Ports/Harbours/Harbour approach channels in India, the National Hydrographic Office, which is the national authority for hydrographic surveying, and the Ministry Of Shipping should address the following issues:
• Regulation for strict compliance of SP-44 & SP-57
• National Hydrographic Office should arrange courses on QA/ QC & international standards for Hydrographic surveys in Ports/Harbours for Port Hydrographic Surveyor.
• Set up a central certification agency for this work. That may be the National Hydrographic Office or other dedicated survey organisations, such as Minor Ports Survey Organisation
• Creation of quality resources required for this work.
• Regulation for hydrographic survey and other associated tasks shall be carried out by or directly supervised by a suitably qualified and experienced hydrographic surveyor.
1) IHO standards for Hydrographic Surveys special publication no-44
2) Technical paper on Hydrography in Port- Rod rIdley, Maneger HS, Queensland Dept. Of Transport presented in Australian Surveyors Congress.
3) Technical paper on hydrographic survey for dredging of harbour & harbour approach channel by N.R.Raut, AHS, MPSO
4) Theme paper on Indian Maritime Transport Services-Global opportunities and challenges –presented on 44th National Maritime day celebration-2007
5) Extending the ECDIS Technology towards port & coastal zone management-Hydro 2000
6) Technology for efficient mapping of ports and port entrances-Hydro1999.