Georeferencing old Schematic Models

[Scott La Vanne]

I will frequently come across older non-georeferenced schematic models in HEC-RAS. These are typically perfectly fine models but don’t have the convenience of georeferencing. Fortunately these models usually come with a cross section map or, if I’m lucky, cross section shapefiles. Conceptually, there should be a way to take the old model and georeference it, without changing any of the hydraulic parameters, while making use of the horizontal geometry available. Has anyone developed an efficient approach to this? Preferably an approach that doesn’t involve a lot of manual data transfer?

[Westcotter]

Hi Scott,

This is what I am doing, and it seems a tough task because I also asked the similar questions here but no any answer yet.

Because I did some work, here are some tricks, which are open for discussion, might be helpful to you and others.

1. Collect all necessary information such as maps, field records, and documents about previous modeling work. For example, for some cross sections I have a topographic map to show their locations with good references such as farm yards, roads, and so on. Comparing with Google Map and such topographic maps, it is relatively easy to locate those cross sections.

2. Use HEC-GeoRas to define stream centerline. And I find that beginning and ending points of this stream line should be the same as in the previous model. I try to make stream distance right, though it is difficulty sometimes, because the total stream and downstream distance in previous model might come from paper-based topographic maps, so there are some differences in reach distance comparing with measured in DEM. I am still not sure which one should I use and trust.

3. If digitized stream distance is right (all done in HEC-GeoRAS), then XS cut lines should be in approximately right position when loaded in HEC-RAS. One can check this easily with Google map or DEM or LiDAR if using HECRAC 5.

4. Fine tune locations for each cross section. First adjust those XS cut lines with knowns locations, such as bridge, weir, and so on. Then remaining cross sections will be repositioned based on river length and cross reach lengths. This seems sure, but not sure yet.

5. With HEC RAS 5, one can compare elevation-station line with the line based on DEM or LiDAR. It is convenient, not sure which one should I trust and use. In my case, I have 70% of cross sections from the older non-georeferenced agree with DEM.

This is what I know, any more thoughts?

West

[Scott La Vanne]

Thanks for your feedback West. These sounds like good approaches. I’ll try this out and post back on here if I learn anything worth sharing.

Thanks again!

[Author]

Posts