Zeekoevlei / Rondevlei Rehabilitation Study ... - Southern Waters

Southern Waters Ecological Research and Consulting
4. Issues, Options and Actions Required
4.1 Major Issues
Three major rehabilitation issues were identified, namely:
• the role played by groundwater, and particularly regarding the nutrient enrichment of
Zeekoevlei as a consequence of polluted seepages;
• phosphorus enrichment of the vleis, and the sources of said enrichment, including that
from the aforementioned seepage;
• the ecosystem processes that derive benefit from the drawdown process.
Several other issues, classified here as secondary in that they are components of greater
rehabilitation needs, were also identified and are dealt with later in this Action Plan (see
Section 5).
Together, all of the identified issues encompass and address those ecological aspects
identified by the Public Participation component of the Zeekoevlei / Rondevlei Rehabilitation
Study.
4.1.2 The Key Role of Groundwater
The geohydrological study conducted as part of this investigation revealed that groundwater
intrusion to both Zeekoevlei and Rondevlei forms a crucial component of the annual water
balance of these wetlands. This finding provided the last pieces of the puzzle of “ghost”
sources of phosphorus identified using mass balance modelling. The geohydrological
investigation encompassed the creation of a field of some 40 wellpoints around Zeekoevlei
and Rondevlei. This provides an established physical infrastructure for the continued
monitoring of groundwater patterns and quality in the groundwater control zone of these vleis.
The geohydrological investigation clearly illustrated the role of groundwater in the
functioning of the vleis, as well as inter-vlei sub-surface linkages across the Cape Flats. It
was determined that groundwater inflows contribute approximately 15% of the total annual
inflow into the two vleis, and play a critical role during summer when groundwater becomes
the sole source of supply. A key finding was that the inflow from groundwater approximates
between 4 and 5 mm per day, throughout the year. The study highlighted the importance of
Zeekoevlei / Rondevlei Rehabilitation Study: Action Plan
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