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ENGINEERING AND TOPOGRAPHIC SURVEYS
This comprises the following 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 and Sanitation 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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