RIVER MOUTHS ARE OPEN

After the rain: Swartvlei and Touws River (Wilderness)

Park Manager for the Garden Route National Park, Paddy Gordon has expressed relief that the breaching of Swartvlei and Touw estuaries, which took place on Wednesday 15 November, was so closely aligned to the estuary management plan. He affirmed the significance of keeping the mouth closed until the correct time and level of water measured above mean sea level. Swartvlei was ranked number 7 in South Africa by independent researchers for its biological diversity.

“Managing the system is complex, but the height of the water measured yesterday facilitated the decision made to breach/ open both the Swartvlei and Touws River mouths” he says.

The estuaries were breached subsequent to rainfall yesterday.  The Swartvlei Estuary system was monitored for 24 hours and rainfall was recorded as follows:

  • In Farleigh till 07:00 on the 15th of November 2017 – 48.0 mm
  • Sedgefield – 63.0 mm

Water height before the rain was at 1.74meters above mean sea level. However by 18:00 it was 1.79m rising to 1.8m by 06:30am

  • Touw River’s 24 hour rain measurement at Buffelskop  was 33.0mm at 07.00 and the water level at Ebb & Flow rest camp – 1.99 above mean sea level
  • Goudveld (forest)-54mm of rain measured.
  • Diepwalle (Knysna forest) – 50mm
  • Knysna (Thesen Island jetty)-35mm

Residents from Sedgefield came out in numbers to witness the breaching of the Swartvlei estuary. Channels were reportedly prepared days before and machinery on standby as reported by Jonathan Britton, marine ranger for Wilderness.

Scientist Dr. Ian Russel cautions against opening the mouth too soon as during the open and closed phase there is a unique ecological process that collectively works together to maintain a delicate food web. The estuary mouth will generally close naturally during the low rainfall periods as there is a reduction of the inflow of freshwater.

The closed phase is a time of ‘rest and recovery’ when some interesting and important ecological processes come into play.

(Picture by Mike Wood)