African Environmental Development have developed software to speed up the determination of flood lines in the Republic of South Africa. The flood lines we produce are accepted by all authorities.
A Computer Generated Image of a stream, the 100-year return period flood line and the simulated view and location of two mine tailings dams in relation to the flood lines. In this particular case, the topography was exaggerated 5x, to provide the user with a "feel" of the elevation range.
Firstly, we model a "Design Storm" using the methods described in the University of the Witwatersrand Dept of Civil Engineering Hydrological Research Unit Report No. 1/72 “Design Flood Determination in South Africa”. Depending on various factors built into the simulation, the model provides us with a water discharge rate and a time frame over which the peak of the flood would occur.
The next step is to accurately survey the banks of the river or stream and to produce a number of cross sections through the stream or river valley. These will later be used to plot the elevation points of the flood line at that particular cross section.
A number of cross sections through the river valley is used to plot the flood line on either side of the river.
Once a profile of the stream or river valley has been made, the flood volume determined above, is routed through the cross sections using various factors such as slope, Mannings co-efficients for open channel flow, etc. and the actual flood elevation is derived using Report No 1/74 “A Simple Procedure for Synthesizing Direct Runoff Hydrographs” of the University of the Witwatersrand Dept of Civil Engineering Hydrological Research Unit.
The flood elevations are plotted on either side of the stream/river and the points are linked smartly to produce two continuous lines, one on either side of the stream.
In order to accurately determine flood lines, an engineer has to visit the site, as the Mannings co-efficients cannot be determined in any other manner.
The flood lines we produce are done in accordance with the official methods developed specifically for South African conditions and are accepted throughout South Africa by all Government Departments. We can produce flood lines with return periods from as short as 2 years up to 100 years. The flood lines are made available in DXF format (or any other CAD format) to the client using whichever co-ordinate system the client prefers.
