A decision support system is built in ArcGIS’s model builder using existing and customised toolboxes.

The tool uses rainfall event intensity data, a digital elevation model, roads vector layer and drain points layer to model drains likely to:

  1. directly connect runoff at road-stream crossings,
  2. cause gully erosion at drain outlet,
  3. connect with adjacent streams via concentrated flow,
  4. connect with adjacent streams via diffuse overland flow,
  5. volume of runoff likely to connect, and
  6. the quantity of suspended sediment potentially transported to the stream.

The tool uses genetic algorithms to find the optimal locations for additional drains to minimise stream pollution from road runoff.

A major output of the project is a DSS for simulating road to stream connectivity. The DSS is known as ROADCAT - Road Connectivity Assessment Tool.


ROADCAT is built with ArcObjects using the VBA language. Users of ROADCAT will require an ArcGIS licence and a licence for the Spatial Analyst extension to run the application.

Minimum data requirements are a digital elevation model (DEM; 1-20m grid cell size), a digital road network layer (roads shapefile), a digital layer of drain locations along the road (drain shapefile) and rainfall intensity information. Additional site-specific information is required for application of the model. Guidance on the collection of this information will be provided.