Freeboard monitoringmeasured every minute, not every shift.
Freeboard is the number your facility is judged on, and it moves fastest exactly when nobody can safely go and read it. LevelSense measures it continuously, to within 5 mm, and tells you the moment it crosses a threshold you set.
The requirement
0.8 metres, above full supply level.
In South Africa, Government Notice R704 of the National Water Act requires any dam or tailings dam forming part of a dirty water system to be operated with a minimum dry freeboard of 0.8 metres above full supply level. GN R577 under the MPRDA sets a separate 0.5 metre requirement above the expected maximum water level for a 1:100 year, 24-hour event — usually the less onerous of the two, so freeboard is normally managed to GN 704.
Measured by hand
- One or two readings a day, in daylight
- Nothing overnight or during a storm
- A person out on the catwalk to take it
- Read off a staff gauge or marked pole
- Recorded in a logbook or spreadsheet
Measured by LevelSense
- As often as every minute, around the clock
- Continuous through storms and after hours
- Nobody on the catwalk to get the reading
- Accurate to within 5 mm, up to 8 m
- Two years of searchable history per device
Why it matters
Freeboard moves fastest when nobody is watching.
It falls as the facility fills
Deposition raises the pond continuously over the life of the facility. The margin you had last quarter is not the margin you have today.
Storms move it in hours
Heavy rainfall can take a compliant facility below its required freeboard between one inspection and the next — and that is precisely when getting onto the catwalk is least safe.
The record has to hold up
When a regulator or an auditor asks what freeboard was on a particular night, a twice-daily logbook is a weaker answer than a continuous series.
Freeboard questions
More detail in the tailings dam monitoring guide, or ask us directly.
What is freeboard on a tailings dam?
Freeboard is the vertical distance between the surface of the supernatant pond and the lowest point of the dam crest. It is the buffer that absorbs a storm inflow or a period when decant is not keeping up with deposition. On a tailings storage facility it is one of the primary indicators of how close the facility is to overtopping.
What freeboard is required in South Africa?
Government Notice R704 of the National Water Act (June 1999) requires that any dam or tailings dam forming part of a dirty water system be operated with a minimum dry freeboard of 0.8 metres above full supply level. Government Notice R577 under the MPRDA (April 2004) requires 0.5 metres above the expected maximum water level for a 1:100 year, 24-hour event. GN 704 is usually the more onerous of the two, so freeboard is normally managed to that figure. Confirm the requirement for your facility against its permit conditions.
How is freeboard usually measured?
Traditionally by a person walking the facility and reading a staff gauge or marked pole, typically once or twice a day, in daylight and in conditions safe enough to be out on the catwalk. That produces a handful of data points per day and no data at all during storms or overnight.
How accurately can freeboard be measured continuously?
LevelSense measures the distance down to the water surface and reports freeboard accurate to within 5 mm, up to 8 metres above the water, at an interval you set — as often as every minute.
What happens when freeboard approaches the required minimum?
You set two thresholds per device. Level 1 is an early warning while there is still time to plan a response; level 2 signals that a critical threshold has been crossed. Alerts are sent by email, SMS or WhatsApp to the people you nominate for each level.
Does continuous monitoring replace freeboard inspections?
No. It is not a substitute for your inspection regime. It tells you what freeboard is doing between inspections — overnight, during storms, and whenever getting a person onto the catwalk is not possible.
Know your freeboard, continuously.
Tell us how many tailings dams you need covered and we will send you a quote. Typically up and running within days of go-ahead.
Regulatory figures on this page are cited from SANCOLD, “Your Tailings Dam” (2020). This is general information, not engineering or regulatory advice — confirm the requirements that apply to your facility against its permit conditions and the current regulations.