Irricad

Hi, can anyone tell me why I would get this result from a hydraulic gradline? It shows that the tape has a dramatic rise in elevation at the last contour line where the red marker is. In reality it is the same slope to the next contour line. These are 2' contours and the next 2' contour line is just outside of the zone area. I have had this problem on multiple designs. It is usually where the tape intersects with the last contour line within the zone area. I have been able to manually add a new contour line within the zone area to correct the problem, but I don't think it is very accurate.

Corby

Corby,

It is a bit hard to know what exactly is going on without seeing the design but here are a few things to check:-

1. If you are using the AEI Method did you receive a message that the maximum number of elevations was exceeded and therefore some were ignored? The ABOS Method does not have a limit and processes quicker (and is the preferred option). You can check the setting in Design|Design Parameters|Analysis Parameters - D.E.M. Options.

2. There may be a rogue elevation. Check if there are any elevation errors / anomolies using Design|Calculate Elevation Errors.

I had it set on ABOS method and I did not receive any max number of elevations error nor did I see any rogue elevations doing the check for elevation errors.

Does the DEM resolution or grid size have an effect on how often elevations are interpreted?

Also, when I originally loaded the contours and the georeferenced image, the image was slightly mis-aligned. I manually moved the image down into place and so that the contour outline and image size matched. The contours then looked like they were in the correct place. Could this have affected the contours by moving the georeferenced image that was originally placed by Irricad?

Yes, it may be that the grid is too coarse for this situation. Is there a levy to the right of the block? Because the contours are quite close together in this position a finer grid (increase the number) may solve the issue. You can also set the "D.E.M. Grid Size" to 0 so that IRRICAD will calculate the best grid size for this plan. Note this may result in a large number of grid points and consequently slow the generation and loading of the 3D DEM.