Guest

St. Lucia Seal-off

Tuesday, September 23, 2008 at 08:00 am
Kian Barker
St. Lucia, South Africa
info@shakabarker.co.za
www.shakabarker.co.za

It was with great interest that I noticed that there is a positive shift in the management or the facilitation of the hydrodynamics of the St. Lucia Estuary system. This remarkable eco-system has been jerked back and forth through a series of management policies. However, there seems to be light at the end of the tunnel. Or I should write "Freshwater at the end of the tunnel!" Like any eco-system, when well managed there are untold benefits. We have to appreciate that in the 1950's this ecosystem and the factors affecting the Estuary have changed. Historical data needs to be carefully interpreted and certain of this info discarded to create a sustainable eco-system to maximize what potential remains within and around Lake St. Lucia.

However, some of the popular terminology needs to be evaluated. A drought should no longer be considered as a management option. But rather dry and wet cycles. Dry and wet cycles are natural Global features. If we refer to a drought - the general understanding is that this is an anomaly and it will eventually go away. Not in Africa. In fact in all ecosystems, the plants and animals that live within these eco-systems have a genetic ability to deal with these cycles. But when there is a change in a resident human population, agriculture and industry expands naturally certain challenges are created - there is less water for everyone. This is especially true during dry cycles. An aquatic ecosystems come under great pressure, especially St. Lucia as it is at the end of several river systems. Add climate change and the projected drying of this area, careful long-term management is required.

Climate change forecasts indicate progressively less rainfall for this area. However these dry periods will be punctuated by heavy rain in the form of Cyclones and intense low pressure systems dumping tons of rain. Therefore long term management practices taking this into consideration are the only way forward. There will be more dry periods, with less rain in summer, but generally an average year on year winter rainfall. If one splits the rainfall figure over the past few years into summer rain and winter it becomes apparent that there is less summer rain and average winter rainfall. Possible result of climate change, which create hotter summers. Higher air temperature means less of an ability for the atmosphere to carry moisture to create rain. This rainfall and temperature forecast pattern will remain in place for the foreseeable future. Trouble is that Lake St. Lucia looses most of it's water through evaporation in the hot summer months when there has been little or no rain. A rather bleak scenario.

What about the past history of Lake St. Lucia? When examining an area it is critical to look at how an eco-system formed. What factors and features resulted in the final product. Also how this "ecosystem" sustained itself, that we so affectionately refer to as Lake St. Lucia. Prior to the arrival of man and even subsequent to the arrival of man. The Umfolosi (Imfolosi) River delivered an estimated 60% of freshwater into Lake St. Lucia. However certain factors and decisions resulted in the canalization and diversion of the Umfolosi River. This precious load of freshwater was then dumped into the sea, along with it's load of silt and sediment. Taking this amount of freshwater out of any eco-system will have long and sustained effects. (The Aral Sea is a classic example, with the intervention of Global organizations the Aral Sea is back on a road to recovery). By looking at some basic agricultural figures to see the effects of removing the Imfolosi River it is possible to see why these recent changes are so important. The estimated evaporative index for this area is an estimated 2200mm per annum. Annual rainfall is approximately 1200mm. Therefore an estimated shortfall of water required to keep lake St. Lucia at sealevel is one meter of water over the whole lake system. Therefore as I mentioned we need to use history knowledge to understand how this eco-system operates to formulate an understanding as to what long-term management plans are required. The in-flow of the Imfolozi River assisted in this and kept lake St. Lucia "generally" balanced.

When this system is stressed by a dry cycle, then there is a net inflow of seawater (when the mouth is open). During this period sea sand is drawn into the estuary part of Lake St. Lucia. But when we enter a wet cycle there is a net-outflow of freshwater, that is diluted with the estuarine salt. During these net out-flows, sand is also carried out to sea. Unfortunately when the mouth was breach in March 2007 there was a net in-flow of seawater that brought in tons of sea sand. Because of the low lake level, fro the recent hot dry summer. It was a mere 120 days defore the mouth silted closed, shortly after opening the chanel linking to the sea was 2.3m deep. Closure was for two main reasons: a dry cycle so the lake was loosing millions of liters of water due to evaporation and the lack of the Imfolozi River, which would have counter-balanced the evaporative pressure placed on Lake St. Lucia due to the relatively large surface area to volume.

Therefore the current move to re-introduce the freshwater into lake St. Lucia is critical and should have been done years ago. As we all remember the devastating effects of the dry period of 2002/3. During this period the lake lost a huge biomass of fish and invertebrates. Had this simple policy been introduced this lake would not have suffered the permanent ecological scar of that ecologically disastrous period. Salinities were estimated to have reached five times that of seawater. Many of the fish species that died were considered protected or restricted in the sense of fishing regulations. Since very few organisms can survive in such high salinities, it is a great pity that current policies were not implemented then. Now we are heading in the right direction.

Monday, December 5, 2011 at 12:54 pm
Petrus Viviers
Richards Bay, South Africa
petrusviv@gmail.com
www.stlucia.org.za

Hi Kian

The important question is whether the authorities realize the importance of a functioning Estuary to the over all health of the Marine life. Kosi Bay and Richards Bay is not that great substitutes as marine nurseries while St Lucia Estuary remains closed.

Thursday, July 20, 2017 at 12:06 pm
Lena01
Yerevan, Armenia

thanks for the post

Thursday, July 20, 2017 at 12:06 pm
Lena01
Yerevan, Armenia

cool info

You must be a registered member and be logged in to reply to a topic.

Register here or sign in at the top of the page if you are already a member.