1.
Friends Of the Rivers of Hout Bay
Tim Biggs and Willie van Wyk
2015

2.
Site visit – 22 April 2015

3.
Proposed solutions…
Off-channel
gravel bed

4.
Implemented solution…
Heavily polluted low to
medium flows diverted
and pre-treated by
natural filtration
Important note:
None of the work performed to date has modified the river flow
or structure in any way but it is very important that licences be
obtained for any future work that might, well in advance.

5.
Downstream litter trap…
Just below outlet: Large
school of Galaxias
roaming here!

6.
Perfect location for a storm
water retention facility
(natural reed bed)
Draining naturally via existing
grassed ditch
Future projects

7.
Future projects

8.
GENERAL
Work done to date regarding
hydrodynamics of Hout Bay,
specifically looking at coastal
dispersion of river water and
sewage outfall
Numerical hydrodynamic
model of Hout Bay

9.
Typical dispersion of sewage
discharge during summer conditions
(surface layer)

10.
Typical summer current pattern
Location of
marine outfall
Improved
location

11.
RIVER WATER ABSTRACTION
What quantity of water is removed
from the Disa system?
Source: State of the Rivers report

12.
RIVER WATER ABSTRACTION
What quantity of water is removed
from the Disa system?
Disa River Original Disa Stream
Alexandra
128 Ml 126 Ml
Capacity of 18Ml/day Capacity of 3Ml/day
Kloofnek Treatment Plant Constantia Nek Treatment
DAMS
594 Ml 925 Ml 243 Ml
HOUT BAY CATCHMENT
33.8km²
DAMS
Woodhead Hely-Hutchinson De Villiers Victoria
Compiled from CCT info and State of the Rivers report

13.
Source: CCT website
RIVER WATER ABSTRACTION
What quantity of water is removed
from the Disa system?

14.
RIVER WATER ABSTRACTION
What quantity of water is removed
from the Disa system?
Source: State of the Rivers report
Total treatment capacity (Kloofnek and Constantianek) 21 000m³ /day 7 665 000m³/annum
Natural runoff, Disa and Original Disa 28 500m³/day 10 400 000m³/annum
Water supply system has the potential to remove 74% of natural runoff
The remaining 26% is subject to uncontrolled, mostly unlicensed abstraction by riparian property owners.
A hand count reveals approximately 110 properties. Let’s say 50% of those remove 1000l (1m³) per day for half the year,
the abstracted volume could be in the region of 10 000 m³/annum, or about 0.1% of the annual runoff.

15.
FURTHER WORK
Some of which is in progress:
• Estuarine morphodynamics
• River flood modelling
• Marine water quality modelling
• Sediment transport
Studies will compare the current scenario with historic
and optimised / rehabilitated scenarios

16.
A big THANK YOU to everyone who has contributed thus far !