Page 24 - Thola Issue 17

22 Water and Sanitation
Umhlangane WQMS Results
Turbidity NTU
MAX of DO_mg
Flow Cumecs
STORM WATER
CONTROLS
The good
The city has extensive flood controls, canalisation (a dubious good), and storm water drains that prevent the City from flooding.
The bad
Storm water in many countries is treated together with waste water. Due to the nature of our rainfall, the sewerage system would have to be ridiculously large to treat storm water. The first flush from a rainfall event is highly polluted.
The peak in the graph (top) shows the increased flow from a storm
that creates an increased turbidity (cloudiness) due to soil erosion. You will notice the drop in dissolved oxygen at the same time due to severe, but temporary, pollution. The river before and after the event was experiencing
a major pollution problem that did not impact it quite as severely as the storm.
The worst news is that climate change may mean more intensive
ABOVE: Pollution chasing team in action.
rainfall events that will increase flooding and undermine existing water and waste water infrastructure.
Mitigation
First flush rainfall can mask serious pollution occurring within the city. A team of five ‘pollution chasers’ follow
up problems highlighted in the City’s river monitoring programme. The results of the river monitoring can be viewed on the city’s web site on http://www.durban.gov.za.
The City’s Coastal and Drainage Department has been contributing to a Water Research Commission project
thola: VOLUME 17. 2014/15