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SERVICES - SURVEY

ENGINEERING AND TOPOGRAPHIC SURVEYS

This comprises the following surveys.

  • Dam Deflection surveys

  • Control Surveys

  • Topographic and Engineering Surveys

Dam Deflection Surveys

 

Dam Deflection Surveys entails the monitoring of large dams to determine the movement or displacement of the structures. Monitoring is done for the following reasons:

  • Diagnostic – to provide scientific information to the Civil Engineering for design verification

  • Research – to establish the long term behaviour of the dam

  • Prediction – to monitor the safety of the structure.


The most accurate and modern electronic survey instruments and sophisticated software are used to determine co-ordinates and heights of stable reference pillars around the structure as well as monitoring points on, in and around the structure to 1 millimeter accuracy.

 

Control Surveys

Control Surveys entail the establishment of control beacons for larger water related projects which include control beacons for tunnels and dams. The control beacons serve as reference beacons for construction and are done to a very high standard of accuracy. A combination of GPS and terrestrial observations are employed in the process.

 

Topographic and Engineering Surveys

Topographic surveys provide plans for planning, design and as-built requirements. Plans are produced either by conventional ground survey methods or photo control points are fixed for photogrammetric processing. Engineering surveys are done for the design and construction of various water related infrastructure, which include dams, reservoirs, pipelines, pump stations, canals and access roads. Apart from conventional survey instruments, GPS using post processing techniques, as well as RTK (Real Time Kinematic), are used extensively in all these surveys.

 

HYDROGRAPHIC SURVEYS – FIELD SURVEYS AND DATA PROCESSING

 

The results of hydrographic surveys are used to calculate the amount of sedimentation in a dam, to show where the sediment is collecting in the dam and to calculate a revised capacity table. This information is used by the Department of Water Affairs to manage available storage water, floods and planning for the future.

To determine sediment deposits a sophisticated, automated measuring and calculating method is used. The original dam basin is divided into a number of compartmentalised areas bounded by accurately measured cross-sections taken between permanent silt beacons. The positions of permanent silts beacons are determined beforehand. A capacity table of volume is then drawn up for each compartment. Areas and volumes of every compartment for each contour interval are determined.

To determine the volume of silt deposited, only the end areas (sections) of the compartments need to be resurveyed. This is done electronically. The boat is equipped with an echo sounder for measuring accurate depths. GPS is used to obtain accurate position data and this data is used for calculation purposes.

The Hydrographic Section consists of a field team fully equipped with a boat, echo sounder, GPS and survey instruments. All the data processing is done at Head Office.

 

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