Overlay Analysis in Map 3D 2010 for Floodplain Study

I’ve spent quite a bit of time over the past few months digging through the FEMA Guidelines and Specifications for Flood Hazard Mapping Partners. (And quite a few other sample documents and regulations.)

I’ve been learning about how different water resources projects come together- of course from a hydrology/hydraulic analysis perspective, but also from an exhibit and study perspective. I remember that the stormwater management and drainage reports that I did were largely an exercise in collecting data, creating maps, creating exhibits, documenting what we found… THEN taking it to the next level and crunching the numbers.

One exercise that often has to be done for flood studies is to identify parcels that are located within certain flood zones. This same idea also applies to a broad range of water resources, environmental, civil engineering, land planning, etc. projects. Thinking about finding certain land uses within a watershed, or parcels in a special zoning area, or green space within a municipal boundary.

You’ve been able to do an overlay between map topologies in Map 3D (and Civil 3D which is built on Map 3D) for a few years now, but I just learned how to do an overlay with data connected through the FDO.

You can find the command if you switch to one of the geospatial workspaces. This one is from the Task-based geospatial workspace.

I’ve recorded a short video showing the process.

Here is a summary of the tasks shown:

1. Drag and drop a .shp with county parcels into the drawing

2. Stylize the parcels to be a light gray, line-only style.

3. Drag and drop a .shp with floodplain information

4. Create a theme for the flood zones, then query only the zones I am most interested in.

5. Create a Feature Overlay to overlay parcel polygons with floodplain polygons.

6. Looking at the resulting overlay information noticing that the information about the parcels is now merged with the information about the flood zones.

Ways to take this further:

-Export the overlay table to .csv and taking the information into excel for further sorting and calculations, graphs, charts, summaries, trends, etc. (select all first)

-Create a layout tab, insert your appropriate sheet sized title block and build report exhibits

-Add aerial imagery, school locations, and any other information you need to study as part of due diligence, flood study, watershed study, etc.

-Export or convert critical polygons into AutoCAD objects either by exporting your map to dwg…

or using the Extract Feature from Geometry

Then use AECLINEWORKSHRINKWRAP to make a bounding polyline for things like… building a flood elevation surface to show on profiles and sections.

Thoughts on this? What types of exhibits to do you make that you don’t know how to get Civil 3D or Map 3D to do for you? What type of analysis do you still do by hand when it comes to preparing and overlaying data? What other types of reports do you create that could take advantage of this?

Comments

[Mark Spatz]

We do our stormwater curve number analysis with Map Topologies and Overlay Analysis. However we don't use the FDO do perform this task; only Topologies and Overlay Analysis on topologies.

Some have said to export our generated topologies for pre-cover, post-cover, drainage area, etc... to SDF files and perform as you have shown but it seems like more steps. What is KEY about topology overlay analyis is you can SAVE A TEMPLATE! So the next time you have to do an overlay analysis - and if you have a standard naming convention for your drainage, cover, and soils topologies and object data - you can simply load the saved overlay anaylsis template and you are off to the races!

It is working very well for us so far. On the back-side we also have an Excel spreadsheet that compresses the data with some VBA macros and pushes it directly into Hydraflow and HydroCAD.

[Earl Kubaskie]

I found a bit of a trick a couple weeks ago for generating floodplain boundaries.

We started with a ground surface from LIDAR, and generated cross-sections for our hydrologist to determine flood elevations.

Then I used a line/pline at each section, set at Mr Hydro's determined elevation, to create a "flood" surface. A volume surface comparing ground to the flood surface, using a contour-displaying style with a huge contour interval, then gives you a "zero" contour where the surfaces intersect - the floodplain boundary!