Topographical/Hydrographical Survey

Job Information:

The main goal of the project was to conduct a detailed topographical and hydrographical survey of two lakes located in the Garw Valley. Over time, these lakes had become heavily silted, leading to a drastic reduction in their water-holding capacity.

The scope, along with producing the standard topographical survey was to determine the volume of silt and water within the lakes to inform the volume of silt to be removed and the volume of the lake once remedial works had been undertaken.

Challenges:

Whilst the survey on the shore was routine work for us, surveying the bed of the lakes posed slightly more challenges for us. Normally we would use a small boat to navigate the lakes, but in parts, the lakes were very shallow due to the build-up of very soft silt which meant we could not walk on the silt without the risk of sinking. We used a combination of walking on the more firm areas and a small boat controlled by surveyors on the shore
for the softer silted areas.

Data:

• Data was collected on site through a combination of total station and survey grade GNSS
  receivers.
• This data was loaded in to our specialist survey software and three DTMs were created.
  One model showed the hard bed of the lakes, one model showed the soft bed (or top of
  silt) and the third model showed the water level.
• Using cut and fill calculations between the models within the software we were able to calculate the volume of silt to be removed and what the volume of water would be once remedial works had been completed.