OUR COASTAL TREASURE
Our river, the Kromme, is more than just a feature in the landscape: it is a well-loved part of our lives in St Francis.
The river rises in the mountains of the Langkloof and flows into the sea some 95 kms later.
Early hominins in the greater St Francis area would have made use of the Kromme River estuary for hunting and fishing. But the estuary was not where it is nowadays. Lower sea levels during the ice age meant that the coast was about 45 km further south than it is today. The river had carved a valley down to the edge of the continental shelf and entered the sea at that point, some 120 m below today’s sea level.
As the sea level rose after the end of the last ice age, however, the shoreline moved slowly northwards and the river mouth came to occupy its present position.
Over the past five decades or so, the Kromme has come under pressure from several different processes, all man-made. These have remoulded the river to such an extent that the river’s meeting point with the coast can no longer be considered an estuary. Scientifically, it is now officially a “sea extension” according to the Dept. of Water Affairs’ nomenclature.
This is because there is so little fresh water flowing down to the mouth that it is too saline to be meet the criteria defining an estuary. This has affected all the plant, marine and animal life that populates the river.
Read on below to see how this came about and read how important it is for all of us to be aware of our role in the preservation of what we have and to remedy conditions where we can.
There is of course the Elephant Seal in the room – Climate change.
The Kromme - Click to read more...
How did the Kromme estuary become so saline that it can no longer be classified as an estuary?
This was mainly a result of the damming of the river, first by the Churchill Dam in 1943 and then by the Mpofu Dam (originally called the Elandsjagt) in 1983. These two barriers interrupted, and continue to interrupt, the natural flow of fresh water down the Kromme.
The Sand and Geelhoutboom rivers – both being sources of fresh water for the Kromme – have also been subjected to unnatural structural developments which have changed the amount and direction of their water flow.
In addition, the dams curtail the effect of periodic floods which happen naturally under normal circumstances. The result is intensified silting of the river bed and the mouth. Now only disasters such as a 100-year impact level flood would clean it out- but the collateral effects would be, as one could imagine, very high.
The salinity increases over the decades have had a knock-on effect on river life – both plant and creature – that has been profound.
Of the many habitats sustained by the river, there are four main and notable forms:
- Submerged Eel Grass Beds.
These have multiplied under the more saline environment. The weaker water flow, coupled with an absence of flood scouring, has allowed sediment build-up and the conditions for eel grass to flourish. This habitat is known to support Knysna Sea-horse but whether the species exists in the Kromme is yet to be seen.
- Intertidal Salt Marsh.
The Kromme is amongst the minority – only 18% – of South African rivers that are open to tidal action, a necessary condition for the existence of intertidal salt marsh. It follows that this river is important in the conservation efforts of this habitat. The largest area of salt marsh on the Kromme is on the north bank on the seaward side of the R330 bridge, but other pockets are evident for 4 kms upriver, on the west bank.
The main vegetation types are the Sarcocornia – salt- or glassworts – that are well represented in the Cape Floristic Region, but in addition we find the highly stress-tolerant Salicornia. This is a direct result of the increased salinity: bare sand patches appear from time to time and are then colonized by the Salicornia – also salt/glassworts. They become red when the salinity is very high and disappear when there is an increase in fresh water.
- Tidal Sand Flats
These do not support any vegetation in their own right but at low tide can be seen within exposed parts of Eel Grass beds and Salt Marshes.
- Reed and Sedge Beds
A prominent area is found on the south bank above the R330 road bridge.
As with the Eel Grass beds, the reed beds – the most abundant component species being Phragmites australis – have increased in coverage. This can only happen when their roots and rhizomes are located in brackish to fresh waters.
The Kromme attracts a wide variety of fauna but those most strongly associated with the river are the fishes, bivalves and crustaceans.
Some 24 species have been recorded in the lower reaches of the river, including bait fish such as four species of Mullet, and popular pan fish like Spotted Grunter, Blacktail, Zebra and the endangered White Steenbras. Leervis provide good sport and there are also two species of Pipefish in residence.
Only six of the recorded fish species actually breed in the river. The balance are marine breeders whose larvae and fry enter via the mouth.
The river is a dynamic system and from time to time it offers up interesting records such as sea turtles, Cape Sole, River Gurnard, Sharks and Rays.
- Crustaceans, Worms & Bivalves
The crustaceans, worms and bivalves living in the river are defined as “macrobenthic” which means that they are visible to the naked eye and live on or inside the deposits at the bottom of a water body such as an estuary where sand and mud(slate) flats provide shelter. Fisherman are very familiar with these as they form much of the contents of their bait buckets.
Some of the common bait species are:
- Pencil bait
Bait collection and harvesting requires a licence and is subject to bag limits on each species. There is concern in conservation circles that a lack of policing has sanctioned unacceptable abuse of the rules.
- The St Francis Bay Coastal Protection Scheme
Erosion of the beach at St Francis Bay has put at risk the sand dune separating the man-made canal system from the coastline and consequently the canal system and the adjacent homes, gardens, roads and infrastructure are under threat if the dune, known as the Spit, should breach.
A scheme to prevent this eventuality through a beach nourishment programme and the building of groynes has been put forward. Implementation was dependent on an environmental impact assessment, and this has now received a positive record of decision from the Department of Environmental Affairs.
A large portion of the nourishment of the beach involves dredging and dispersal of sand from the river. The issue is a complex one and if you would like to know more about it, the environmental assessment and the record of decision are available here.