The Department of Hydrography and Channel Management is responsible for guarding and mapping the depths of all rivers of Suriname and their estuaries in so far as this is relevant for the shipping industry. This department collects information on the tides of various rivers. The collection of data takes place with the aid of a tidal data logger. Furthermore, depth measurements are carried out in various rivers. During a depth measurement, visual tidal measurements are also made. Various positions and silt densities are also determined on the rivers. All these measurements are processed with the final result: the drafting of depth maps and the composition of tide tables. The final map should be a complete, accurate, legible and reliable representation of the entire area it represents.
Measuring and collecting tidal data
The tide is caused by the gravitational force of the celestial bodies such as the sun and the moon that bring about a tidal wave. A tidal wave indicates high tide and low tide. Measuring and collecting tidal data is realized with the aid of a water level gauging net. This gauging net consists of five tidal stations on which the water level at the estuary of the rivers is measured 24 hours a day, 365 days a year. The instrument recording the water level is called a tidal data logger. This is an instrument that consists of a pressure sensor and an internal memory. The pressure sensor is placed into the water in a pipe at sufficient depth. Via water pressure differences it indicates the level of the water column present. The water level is calculated against the height datum. The height datum in Suriname is the level of low water spring tide. The energy consumption of this instrument is very low and this makes it easy to use a battery with a solar panel. The water levels from the height datum are stored in the computer memory of the measuring station. This data is downloaded regularly via a laptop. The five tidal stations are located on a platform in the estuary at the access channel of the Suriname River, on the pier at Nieuw-Amsterdam, on the pier at the MAS, on the pier at Domburg and at the pier at Nieuw-Nickerie. The data of the tide is used to determine the water depths of the rivers at the moment of observation, to make forecasts with regard to water movements in the future and, also, for loading ore carriers (bauxite). This results in the so-called tide tables issued annually by the MAS.
Collecting and processing depth measurements
Based on depth measurements, data is provided to the pilots so that they can safely pilot their vessels. Furthermore, it is important to keep hydrographic data up-to-date for the improvement of nautical charts. The depth measurement is carried out with the aid of an echo sounder of which the positions are determined with the aid of a RTK (Real Time Kinematic) connected to the onboard computer. These hydrographic instruments are placed onboard the Multipurpose Marwina and the survey vessel, the Pasisi.
The work areas of the Department of Hydrography are:
|The rivers:||– Suriname River|
|– Commewijne River|
|– Nickerie River|
|– Corantyne River|
|Piers in the Suriname River:||– Nieuwe Haven|
|– Oil pier|
|– Shell, SUHOZA|
|– Staatsolie, Tout Lui Faut|
|Piers in the Nickerie River:||– Nieuw-Nickerie|
|Piers in the Corantyne River:||– Apoera|
The areas to be measured are divided into sections. These sections are given a number. Furthermore, these sections are subdivided in lines of direction at 50 m apart (standard is 25 m). The lines of direction serve to indicate the navigation lines. During navigation, the shipmaster can follow the lines of direction on a monitor. On the monitor, the position of the ship and the position of the lines of direction are clearly visible.
How the echo sounder works
The echo sounder is an instrument that emits sound signals to the bottom at a frequency of 38 KHz and a frequency of 200 KHz (the used frequency is 38 KHz). The signals are reflected back by the bottom. With the aid of a receiver, the signals are received. With the aid of calculations, the instrument determines the distance between the bottom of the river and the bottom of the ship. A GPS connected to the onboard computer sees to it that the measured depths are recorded. This data is stored on discs and printed for inspection purposes. An example of an echo sounder registration is provided in annex 6.
Processing raw data
In processing raw data, a computer program is used especially designed for port, dredging and sounding. This is the PDS 1000.
Raw data is the data stored on the discs (this consists of time, position and depths of the measurement). The raw data is imported into the memory of the computer. Then, the data is corrected with the occurring tide (reduction) and the draught of the vessel is added. The occurring tide is observed visually (Braamspunt). In doing so, the water level is read every ten minutes against the height datum. After the correction, the data is called processed data. Now, the depths can be mapped. On the map, the depth contours, shorelines and the positions of the buoys are indicated. The map is printed and then the depth contours are marked so that the channel becomes visible. An example of such a map is included in annex 7. The department is currently in a phase of switching to Hypack, another survey program.
Silt density gauge
Measuring the silt density is important because the channels of the Nickerie River and the Suriname River are not deep enough. The depth of the channel is maintained by the loaded ships themselves, in other words, to prevent the channel from silting up, the ships are loaded in such a way that they have a draught whereby the vessels just barely skim the bottom of the channel and the rotating propeller loosens the muddy river bottom (agitation dredging). The vessels have a capacity to be able to navigate through a silt bottom with a density lower than 1,200 kg/m3. It is, therefore, essential to gain insight in this matter. The instrument that measures the silt density is called a silt density gauge. This instrument can be used to measure absolute silt densities. The instrument is lowered into the silt from a gauging vessel and will as such carry out a point measurement. The instrument is, therefore, not suitable for dragging. All electronics used for determining the density are installed on the instrument. The data is transmitted to the onboard computer via an RS232 connection. The MAS uses the tonometric method. With the help of a software (Densi Tune), the density is determined. A photo of a density gauge is included in annex 8.
This department is divided in the subdepartments hydrography and channel management, and waterway marking. The task of the subdepartment hydrography and channel management is to conduct periodic hydrographic surveys in the rivers that provide access to the ports, this means mapping these rivers and indicating the route with the largest draught (the channel). The tidal movements are automatically registered by a tidal gauging net.
The task of the subdepartment waterway marking is the marking or signposting of the waterways to guide the shipping traffic in the safe and right direction. This is important because the channel of, among others, the Suriname River is shallow due to mud and silt and only at high tide can shipping traffic with some draught be guided into the ports of Suriname. For the marking and signposting of vessels buoys and beacons are used. They are also used to mark special objects such as wrecks, construction of bridges and piers.
The marking of the waterways can be subdivided into: