View Full Version : Representing Roads for 2d overland flow

April 17, 2015, 01:50 AM
Hi all,

I'm representing a road in using ICM 2d with 0.5m lidar data. I know that the accuracy of the airborne Lidar is +/- 150mm. Therefore the standard approach seems to be to create a mesh zone for the road and drop ground levels by 0.15m within it.

If I take this approach the above ground flooding is pretty much contained within the road surface. There is no property flooding from above ground flows.

However, if I take off the artificial 0.15m drop for the road the surface flow reaches and floods around certain properties which are known to be "at risk". I know that, in the past, the properties have on occassion flooded from surface flows. However, how much of the flooding is due to the above ground flow and how much is from private connections is unclear. There is also the issue of cars driving through the flood water, creating a bow wave which drives water above the road camber and pavement and towards the flooded properties.

So, based on the modelling, how much of the flooding problem is attributed to above ground flows is very sensitive to dropping the mesh.

Do I stick with the standard approach of -0.15m or fudge the mesh adjustment to something that feels right, maybe with some flooding from above ground flows on extreme events?

Kristian Ravnkilde
April 28, 2015, 03:12 AM
I'd try reducing the kerb height, locally at least - split up the roads polygon a bit, maybe. We can't really replicate all the finer details, so we have to fudge it a little.

Ann Pugh
May 6, 2015, 06:26 PM
Hi Neil - do you have any detailed survey from the location that you could use to provide more detail in the mesh at the critical point(s) ?