Using Hydrology Tools on Road Surfaces as Drainage Features

[MaxBeukers]

I need to calculate a sustainability index for the roading network in National Parks in South Eastern Australia.
So I want to Determing Sinks, Flow Accumulation and Slope Length on Roads
Key outputs I require are

1 Length road slopes (from crest to dip, gully, saddle where water falling own the road accumulates before the road rises again).

2 Sink point on a road (where water collects in saddles, dips or gullies before flowing off the road). NB SINK function in ARCGIS9.3 Hydrology tools appears to negate tis opportunity by enlarging the neighbourhood until a descent is found. I do not know the limit of this enlargement or how to disengage it).

3 Gradient of road slopes (fall over length of a segment of continually falling road)

I was hoping you might be able to help me

Thank you

[chriss_]

Hi
In general:If I had the task I would try to run the USLE (Universal Soil Loss Equation) on the whole DEM and intersect the result with my road layer. That seems to make more sense for me.

1) As far as I understand you assume that the water doesnt flow to the right and left from the road but flows all along the road until it reaches a sink. Also you dont consider water to flow onto the road from the surrounding. (I would doubt that ; ) )

Anyhow, you can intersect your roads with the DEM and create a new "Road DEM" that only covers your roads.
Build walls around your roads (ArcHydrotools/ build walls____e.g. 0.20m). In this way you will prevent the water flowing away from your road. Only if a sink is deeper then your wall is high the water will flow over your wall.
You should be able to calculate the flow direction, flow accumulation and sinks in arc hydrotools without any problems.

For the slope length this link might help you:http://skagit.meas.ncsu.edu/~helena/gmslab/erosion/usle.html

2  To your concern in point 2. I think with the approach above this should be no problem. I ve no DEM right here so i can't check it.

Please tell us your result on this.


Hope that helps
Good Luck