Infrastructure

Print

The Wetland

The Island Estate's wetland has since completion already proved to play a significant role in maintaining the excellent quality of the water in the Estate's canal. The wetland makes provision for islands and walkways adding to the tranquil atmosphere,

The constructed wetland on the site consists of a shallow, lined excavation containing a bed of porous soil gravel in which emergent aquatic vegetation has been planted. A coarse stone layer with a depth of 0.7m  was selected in this design aiming at polishing and reducing nutrient levels in the water.The water-loving plants, which will eventually cover between 60-70% of the wetland, are already flourishing.

wetland_01.jpg


The wetland further consists of a series of water connecting dams with varying volumes of water acting as cleaning filters for the canals. Water from the top canal is circulated through the artificial wetland, at a rate of 400 litres per second while water from the bottom canal is pumped at 780 litres per second to various outlet points in the top canals to prevent stagnation or dead spots in these areas. The water quality is further improved by continuously blending it with borehole water and stormwater .

The blue-green bacteria growing in the Hartbeespoort Dam cannot establish itself in the canals because of the growth environment created in them. The flow of water in the canals, preventing layer forming (stratification) of the water, and the lowering of the phosphorus and nitrogen content of the water contributes to a growth-restricted environment for the blue-green bacteria.

The management team is also monitoring the wetland closely and is especially happy about the number of birds which have fallen in love with their new habitat.

Irrigation System

The irrigation system was designed by Gert Le Roux of Controlled Irrigation and uses the latest equipment in Nelson's water conservation range. All the road verges are irrigated with the MP rotator and through a sophisticated variable speed pumping system, the pressure and flow operate optimally for water savings. The system was installed by Greenacres Landscapes in accordance with the LIA's recommended set of standards.

Due to the cooperation between the irrigation designers and contractors, the client has received a highly efficient, water saving irrigation system. The irrigation dams are situated in the service yard and are currently filled with borehole water. However once the estate is complete, they will be filled with water from sewerage works; the idea is to recycle water from sewerage to irrigation and minimise water use from the high yielding borehole. The pump installation consists of variable speed pumps with a filter system which is self-cleaning.

When the need for water in the system increases, a second pump engages to increase delivery.

Environmental considerations

In all aspects of the project, the developers were mindful of the environment. When the canals were mapped out on the site, it was found that certain trees were "in the way" of their intended positions and approximately 160 of these were saved and transplanted into the park areas. They comprised mainly Celtis and Olea species, as well as some Acacias which could not be transplanted due to their very long roots. Aloe species found on the site were also saved and replanted.From an ecological point of view, the developers have ensured that water in the canals functions independently from the adjacent Hartebeespoort Dam as the canals have been constructed above the dam's water level. The bi-directional lock system will be fully functional above the 80% level.

wetland_02.jpg

An artificial wetland has been created; this consists of a series of interconnecting dams with varying volumes of water acting as cleaning filters for the canals. Eventually, the wetland will be 60 - 70% covered with water-loving plants and reeds.

Tuesday the 23rd. © The Islands Home Owners Association, 2010 - all rights reserved