1. FLOOD MANAGEMENT By: Joyce Mathole Directorate: Hydrological Service Department of Water Affairs and Forestry

2. FLOOD MANAGEMENT OPERATION IN THE VAAL / ORANGE RIVER SYSTEM Management of both minor and major floods in the Vaal / Orange River System is done by the Directorate Hydrological Service of the Department of Water Affairs and Forestry. The “Flood Room” in Pretoria serves as an information centre to collect, process and distribute rainfall, stage and flow data Normal operation of the individual dams in the system is the responsibility of the Departmental Regional Offices

3. The main objectives of flood management in order of priority are:- To ensure the safety of the structures. To minimise the damages. To ensure that the dams are 100% full at the end of each flood.

4. Vaal Dam Located in the Vaal River 65 km upstream of the town Vereeniging Equipped with 60 crest gates Discharge of one gate at FSL: ~ 105 m 3 /s Capacity of dam: 2 603 mil m 3 Catchment area of dam: 38 505 km 2

5. Vaal / Orange River System Vaal/ Orange System covers about 49% the size of the RSA, excluding Lesotho Vaal and Bloemhof Dams are the only dams equipped with spillway gates - some control possible

6. Data for the NWSRFS Rainfall Data (South African Weather Service) Real Time Flow stations (DWAF)

7. SAWS: Satellite Data

8. Radar Data

9. Rain Gauge Data

10. Spatial interpolation and mapping of rainfall

11. Real time data collection points in the Vaal / Orange River System 52 gauging stations collecting near real time flow and / or rainfall data - available on the Hydrology real time web site

12. Liebenbergsvlei River at Frederiksdal

14. Uses of Data Rainfall data: Input to Rainfall/Runoff models (Kovacs/Sacramento) Real Time Flow Data: Input to routing model (Muskingum) Weather forecast: Information for dam operation Above Info: Flood Management

15. Routing times in Vaal / Orange System (days) Flood warnings can provide time for people to take action to protect their property as well as allowing emergency services to prepare and plan for evacuations and other emergency actions

16. Overview of the 1988 major flood in the Vaal / Orange River System Spitskop Dam in the Harts River and Tierpoort Dam in the Riet River failed during the early stages of the rainfall event

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