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:
- directly connect runoff at road-stream crossings,
- cause gully erosion at drain outlet,
- connect with adjacent streams via concentrated flow,
- connect with adjacent streams via diffuse overland flow,
- volume of runoff likely to connect, and
- 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.