Flows

Components for creating simple projections and analysis of surface water flows.

The associated model and definition that demonstrating the use of these components can be downloaded here. You will probably need to have installed the Groundhog plugin for the definition to work correctly.
Surface water flow paths across a littoral region

Surface water flow paths across a littoral region

Image via Philip Belesky for the “Processes and Processors” project (http://philipbelesky.com/projects/processes-and-processors/)

The “flows” components create naïve projections or simulations of surface water flows and provide further means to analyse the results of these calculations. The key component — the FlowPath — accepts a series of ‘drop points’ on a Surface or Mesh that become the starting locations of each hypothetical flow path. From there, each point samples the surface or mesh to determine its slope, which becomes a directing vector (i.e. one that points ‘downhill’). Each point is then moved along this vector a pre-specified distance, forming a line. The end of this line then becomes the starting point for the next sample; creating a recursive process where flow paths assemble themselves as Polylines that grow through this series of descending jumps.

This ‘gradient descent’ process repeats until a path crosses the edge of the form, a specified quantity of iterations are performed, or until the algorithm determines that the path has reached a point without a viable further downhill path. This halting calculation aims to identify a ‘basin’ where water might collect and pool rather than continue to flow downhill.

The component then produces as an output a series of Polylines, from which the beginnings, ends, and individual segments can be readily extracted. The process provides degrees of flexibility. By accepting any given set of Points (rather than enforcing a spatial grid or other formation) it offers the ability to work across a number of contexts, from situations where you may want to simulate a uniform distribution (say rain) or just a particular point-source of water.

The FlowPath component takes two forms a SurfaceFlowPath and a MeshFlowPath depending on the geometric type of the ‘landscape’ you want to test.

Flow Projection (Surface)
Component
Nickname
Srf Flows
Panel
Hydro
Icon
Icon for the Srf Flows component

Construct flow paths over a surface

Mode Name ID Description Optional Type
Surface S Base landscape form (as a surface) for the flow calculation SurfaceParameter
Points P Start points for the flow paths. These should be above the surface (they will be projected on to it) PointParameter
Fidelity F Amount to move for each flow iteration. Small numbers may take a long time to compute. If not specified or set to 0 a (hopefully) sensible step size will be calculated. NumberParameter
Steps L A limit to the number of flow iterations. Leave unset or to 0 for an unlimited set of iterations IntegerParameter
Thread T Whether to multithread the solution (this can speed up long calculations) BooleanParameter
Flow Points F The points of each simulated flow path ‘jump’ PointParameter
Flow Paths C A polyline linking each of the flow points into a path CurveParameter
Flow Projection (Mesh)
Component
Nickname
Mesh Flows
Panel
Hydro
Icon
Icon for the Mesh Flows component

Construct flow paths over a mesh

Mode Name ID Description Optional Type
Mesh M Base landscape form (as a mesh) for the flow calculation MeshParameter
Points P Start points for the flow paths. These should be above the mesh (they will be projected on to it) PointParameter
Fidelity F Amount to move for each flow iteration. Small numbers may take a long time to compute. If not specified or set to 0 a (hopefully) sensible step size will be calculated. NumberParameter
Steps L A limit to the number of flow iterations. Leave unset or to 0 for an unlimited set of iterations IntegerParameter
Thread T Whether to multithread the solution (this can speed up long calculations) BooleanParameter
Flow Points F The points of each simulated flow path ‘jump’ PointParameter
Flow Paths C A polyline linking each of the flow points into a path CurveParameter

Once calculated, these flow paths can then be used to support further analysis of the landscape’s hydrological features.

The first component for this is FlowCatchment. It uses the collection of pre-calculated flow paths to identify different catchment areas. To do so, it classifies each flow path into groups depending upon which paths finish or ‘drain’ into the same approximate location. This grouping is visually represented using a Voronoi diagram with each cell centred on the original Pts used as the ‘start’ of each flow path. Once formed, adjacent Voronoi cells whose origins drain to the same end location are joined together to form ‘catchment’ boundaries. Additionally, the different catchment groups are provided with a distinct color code and their cells/paths are output as distinct branches to aid further visualisation or analysis.

Flow Catchments
Component
Nickname
Catchments
Panel
Hydro
Icon
Icon for the Catchments component

Identify the catchments within a set of flow paths

Mode Name ID Description Optional Type
Flow Paths C The flow paths as generated by the flows component CurveParameter
Proximity Threshold T The distance between end points required to form a catchment NumberParameter
Catchments B The catchment boundaries identified CurveParameter
Flow Paths P The flow paths grouped by catchment CurveParameter
Color Codes C Colour codes the uniquely identify each path and boundary ColourParameter
Image of the flows component used across two hypothetical landforms
Grasshopper definition demonstrating how to use the flow and catchment analysis for Surface and Mesh form.

Grasshopper definition demonstrating how to use the flow and catchment analysis for Surface and Mesh form.

Philip Belesky, for https://groundhog.la