In partnership with the City of Cape Town

TWO RIVERS URBAN PARK 18 February 2017 Co-design Workshop

Specialist Study: Modelling of Flood Mitigation Options on the Salt River

Melanie Attwell and Associates Specialist Study: Modelling Flood Mitigation Options on the Salt River

Since Task 2 Draft report November 2016: • Model changes, mainly correction of numerical leak at Liesbeek weir • Sensitivity analysis on changes to SRK 2012 model

2 1:20; 1:50 and 1:100 year flood current situation

Increase in flood level 1:100 year (m) Black River Downstream of N2 0.31 Downstream of Valkenburg Bridge 0.37 Downstream of M5 bridge 0.39 Liesbeek River Downstream of N2 0.05 Downstream of weir near Wild Fig 0.12 Downstream end of ponds near Wild 0.39 Fig Upstream of weir near Observatory 0.53 Road Downstream of Observatory Road 0.53 Junction with Black River 0.48 Salt River Downstream end of TRUP before rail 0.53 bridge Upstream of Section Road bridge 0.263 Mouth 0.00 1:100 year flood current situation, depth

4 Key findings

• The flood lines for the 1:100 now extend into the sport fields on the west of the Liesbeek and in the PRASA area; (and also for the 1:50 and partially for the 1:20)

• Maximum water depths in some footprints of scenario 7 areas are in the range of 0.8-2 m therefore can be life threatening.

• The impact of scenario 7 on increase in modelled water levels for the 1:20 and 1:50 flood, is maximum 5 cm. (1:100 not modelled).

• The mitigation measures which already did not impact the flood lines of the 1:100 year floods and even the smaller floods, are also not expected to have impact now (after corrections) on the 1:100 year flood lines;

5 1:50 flooding with Scenario 7

6 1:20 flooding with Scenario 7

7