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The watercourse interpolation algorithm does not force flow paths to follow the imported watercourse alignments, rather it simply ensures that pixels along the watercourse alignments are linearly interpolated between intersected contour lines prior to interpolation of any surrounding pixels. In most cases, this will ensure the watercourse alignments are preserved in the drainage network. However, in some areas of low relief or complex stream paths, it may be found that calculated flow paths depart from imported watercourse alignments. If this presents a problem then stream burning (DEM Conditioning >> Burn Streams) can be implemented. This algorithm will artificially lower pixels that underlie watercourse alignments by a set increment (set in CatchmentSIM Drop Down >> Project Options >> General) to ensure they are represented as flow paths in the calculated stream network. However, it may slightly bias slope calculations that are generated later in the analysis.

Figure 12 illustrates the effect of application of the stream burning algorithm. It can be seen that the pre-stream burning flow path (green line) deviates slightly from the imported watercourse's path (blue line), whereas application of the stream burning algorithm has 'snapped' the flow path to the observed watercourse.

Figure 12 : Effect of 'Stream Burning' on Flow paths

Prior to using the stream burning algorithm it is important to determine if it is necessary, as its use can slightly bias calculated values for some of the topographic indices that are generated at a later stage, such as average vectored slope. Furthermore, in Figure 12 it could be argued that the pre-stream burning flow path is a better interpretation of the source contours (ie., steeper descent) compared to the imported watercourse alignment.