Error during the overlay process in ArcSWAT

[Aditya]

We are getting error during overlay, while working with large
watersheds. We are using SURGO soil layer and defining 3 to 4 slope
classification. After many trials we have found that it is related to
our selection of area threshold (i.e. no. of sub basins) and number of
slope classification. It fails when we use a low area threshold (i.e.
more no. of sub basins) and more slope classification. For example
when we overlay with area threshold of 15000ha to 40000 ha and 3 slope
classification, it fails but does not fail for 50000 ha and over area
threshold with 3 slope classification. On the other hand, it works
with area threshold of as low as 15000 ha with single slope
classification. We are using Arc GIS 9.1 with ArcSWAT 1.0.7. The
errors we get are "Object reference not set to an instance of an
object at ..." or some sort of unhandled exception.

I was wondering if anyone else encountered this error.

Thanks

[Naresh]

There might be other things, but have you checked whether the DEM
covers 100% of the watershed area ?

[JJ]

Hi, Aditya. I hesitate to answer because I am unsure, but you don't
seem to be getting a big response anyway. So, I'll try to answer:
You might simply be generating more hru's than your computer or the
ArcSWAT software can handle. That would explain why you can use a
lower threshold when you reduce the number of slope categories. - John
Joseph

On Sep 14, 9:04 am, Aditya <sooda...@gmail.com> wrote: