CatchmentSIM allows for the generation of stream networks which are used to define relationships between subcatchments and to determine hydrological measures such as drainage density, average flow length and stream / surface slopes. Stream networks also form the basis for the automatic catchment break-up algorithms incorporated within CatchmentSIM.
CatchmentSIM can calculate vector stream networks (Flow Mapping >> Generate Streams) with Horton / Strahler ordering based on channel head identification and the vector flow mappingalgorithm.
Development of Stream Network
The first phase of generating a stream network is identifying channel heads, the points at which accumulated runoff can be considered a stream. Channel heads can be identified in CatchmentSIM utilising a number of options. These include Stream Area Threshold (SAT) or a combination of SAT with Minimum Source Channel Length (MSCL). CatchmentSIM also allows for quantitative assessment of the minimum SAT value that can be adopted whilst preserving the geomorphologic properties of dendritic stream network.
For vector streams, flow is mapped from each channel head and intersections are recorded. Following this, Horton / Strahler ordering is calculated in accordance with the methodology outlined by Strahler (1957) and illustrated in Figure 25.
Figure 25 : Strahler's (1957) Revision of Horton Stream Ordering
Mapping of vector streams results in a set of connected vector polylines with Horton / Strahler orders calculated for each line segment. This can be displayed in CatchmentSIM with differing colours and line styles for each stream order and analysed with a variety of charts and derived hydrologic parameters using the View Attributes form.
Quantitative Assessment of SAT Value
CatchmentSIM has the capability to assess the geomorphologic properties of a stream network and check to ensure it is consistent with observed stream laws as defined by Broscoe (1959), Horton (1945) and Strahler (1957). If the stream network does not conform to these laws then the stream network may not have been generated at an appropriate SAT. CatchmentSIM provides analysis tools to determine the minimum SAT that can be utilised to generate a geomorphologically suitable stream network. This can be achieved using the SAT comparision chart. This is an important step because the stream network may be the basis for subcatchment break-up and hydrologic analysis.
