A12. Topographic Survey

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1. Objectives

  • Topographic surveys or land surveys, are concerned with the height of the ground above a datum point
  • Surveying the landscape allows elevation data to be recorded in order to illustrate the terrain and features of the environment, including infrastructure, buildings and natural features

2. Method summary

Surveys should be recorded at regular (predefined) intervals along a transect. The transect can be along the river bed (i.e. a bed level survey) or across the channel (i.e. a cross section survey). Cross section surveys can include just the channel (i.e. from bank top to bank top) or might also include the floodplain. A Topographic survey can also be done in a grid pattern.

Several transects can be taken along or across a channel, and compared spatially or temporally, with similar river types, or at different time periods. GPS is a satellite- based positioning system that can offer 24-hour, 3D information depending on the hardware and software used to capture information and coverage. Data from a topographic survey is captured using a GPS which allows the position of a ‘receiver’ on the ground to be determined through the connection to satellites of known position (Brasington et al., 2000).

3. Advantages

  • Visually demonstrate terrain of the landscape
  • Scaled drawings before & after restoration can be compared for major land changes, floodplain reconnections, naturalisation of channel dimensions, and stream realignment
  • Plans show infrastructure and physical features which may hinder or alter a restoration project. Recording this at the early-stage of a project helps identify suitable restoration options
  • Identify, record and map specific features & how they change over time
  • Depending on GPS quality, topographic survey allows ‘high resolution ground-based capture of terrain data in complex fluvial systems’ (Brasington et al., 2000)

4. Limitations

  • Expensive
  • Equipment needed

5. Costs

The charge of a land surveyor will depend on the size of the area to be surveyed, and hence the length of time needed to hire the equipment or labour.

6. Data analysis

Topographic Survey produces a 3D survey drawing, drawn to scale. Elevation data captured during topographic survey can be used in Digital Elevation Models (DEM) to view the terrain of the landscape and compare spatially.

7. References

  1. Bangen, S. G., Wheaton, J. M., Bouwes, N., Bouwes, B. & Jordan. C. (2014) ‘A methodological intercomparison of topographic survey techniques for characterising wadeable streams and rivers’, Geomorphology, 206, pp 343-361. Available at : https://www.sciencedirect.com/science/article/abs/pii/S0169555X13005230
  2. Brasington, J., Rumsby, B. T. & McVey, R. A. (2000) ‘Monitoring and modelling morphological change in a braided gravel-bed river using high resolution GPS-based survey’, Earth Surface Processes & Landforms, 25(9). Available at : https://onlinelibrary.wiley.com/doi/abs/10.1002/1096-9837(200008)25:9%3C973::AID-ESP111%3E3.0.CO;2-Y?casa_token=UHbKX9nx17UAAAAA:RgjMeHAHrWslzy1Zg7SataX2af-qQXRpDcuxsLUXmFuqadDlIeTkz0INxWb9CXbE9hOQ9FsYzOyKPYzo
  3. Downward, S. R. (1995) Information from topographic survey, in Gurnell, A. M. and Petts, G. E. (eds.), Changing River Channels, John Wiley and Sons, 303-323.
  4. Kinzel, P. J. (2008) ‘River Channel Topographic Surveys Collected Prior to and Following Elevated Flows in the Central Platte River, Nebraska, Spring 2008’, US Geological Survey, Data Series 380. Available at : https://pubs.usgs.gov/ds/380/pdf/DS380_508.pdf
  5. Wheaton, J. M., Brasington, J., Darby, S. E. & Sear, D. A. (2010) ‘Accounting for uncertainty in DEMs from repeat topographic surveys : improved sediment budgets’, Earth Surface Processes & Landforms’, 35(2), 136-156. Available at : https://onlinelibrary.wiley.com/doi/10.1002/esp.1886
  6. Landscape survey example, Source : Laser Surveys https://www.lasersurveys.co.uk/services/land-building/topographical-surveys/