Modeling Hurricane Sandy’s storm surge in Autodesk Infraworks 360 – Part 2

In my previous blog, we saw how we could use Project Boulder for Infraworks 360 to simulate a storm surge similar to the one experienced during Hurricane Sandy and observe its effects on Lower Manhattan. What if we now wanted to start conceptualizing ideas for designing a system to protect the areas most affected by the storm surge? How would we approach that design process and how could we communicate it effectively?

In order to even begin considering those ideas, we need to establish our existing conditions, especially if our goal is to provide a proposal for a solution. We will want to create an environment that allows us to see exactly what we propose in context. This can seem like a daunting task, especially at the scale we are looking at which is downtown Manhattan. At the very minimum one would need the following:

• a digital elevation model (a.k.a. DEM) that represents the elevations of the area of interest
• orthographic aerial photograph(s) of the site
• roads
• buildings
• bodies of water

Fortunately Infraworks provides a tool called Model Builder that allows you bring in up to 200km worth of data from anywhere in the world into a model without having to do anything more than select your area of interest. The robustness of model you receive is dependent on what free data is available for the selected area, but with minimal effort you can start increasing the accuracy of your model.

Here is an image of what you would typically get from model builder. While it does provide a great deal of data in context with virtually no more effort than launching the software, it does leave a bit to be desired. The most obvious lack of detail is the fact that none of the buildings look as they do in real life.

The reason for that lies in the limitations of the underlying geospatial data. Because it is inherently 2 dimensional it lacks any definition of what happens in the Z-axis. What you would expect to get from a geospatial file for building footprints is a polygon representing that footprint and at best, some metadata that indicates the height of the building which can be extruded to the correct heights. Here’s an example of how that information would look in Civil 3D or Map 3D using a file obtained from NYC Open Data.

Aside from the buildings, there is often a lack of detail to be found in the orthoimagery and digital elevation models used by model builder, not through a defect in model builder, but instead due to the fact that the sources used by model builder, USGS 10 and 30 meter DEM for elevations, satellite images from Bing Maps for the aerial imagery and OpenStreetMap for roads and buildings may not be the best available.

Above are examples of what I got out of model builder vs. what I was able to research and download from the internet. The first comparison shows the terrain model from Model Builder and then Open NYC Data, and then the second shows a 30’ grid DEM in comparison to a 2’ grid DEM both obtained from the USGS National Map Viewer.

Here’s what the same model looks like with a bit of additional work of finding relevant SketchUp models on Trimble’s 3D Warehouse and processing them into Infraworks.

Those steps included converting the SKP files to DAE (Collada) files, Collada being an interchange file format for collaborative design activity which preserves both the geometry and textures of the original model and then manually placing them in their real-world coordinates. Incidentally the use of the Sketchup models in this context seems to fall under the legal conditions I reviewed on Trimble’s website that stated “Incorporating or including Models and Creations into a larger work or a deliverable for a third party (“Combined Work”), provided that the Combined Work includes substantial additional content to the original Model”.

The next step would be to design something that could prevent the storm surge from inflicting the kinds of damage it did to New York City so I started examining the winning proposals for the Rebuild by Design   design competition. One solution I loved in particular was the solution proposed by BIG  (Bjarke Ingels Group) in a collaborative effort with a number of planners, architects and engineers known as the “Big U” or “Dryline”. If you haven’t seen this proposal yet, be sure to watch the Vimeo video that explains the design concept.

I reviewed some of the documentation outlining what BIG had made available to the public regarding their proposal and selected something that could be approximated in a short amount of time.

I launched Civil 3D and roughly sketched out a shape that would be representative of the area I wanted to emulate based on BIG’s proposal

Once I had done that I wanted to produce that stepped effect but a simple offset wouldn’t do since there was a fair amount of variation among the tiers of the proposed berm. In order to make this step easier I exported my Civil 3D drawing as an EPS file that could be opened in Adobe Illustrator. Taking the original shape I drafted in Civil 3D, I created an interior boundary and used the Blend command to come up with a berm layout. Once I was happy with my results I re-imported the EPS file data back into Civil 3D and set the elevations for my proposed berm, and generated a Civil 3D surface.

From here, I went to 3ds Max and added some very basic textures and imported my model into Infraworks 360 and fleshed out the design with some of the built in modeling tools to add some realism i.e. lightpoles, trees, cars etc…

And now for the true test! I ran both the existing conditions and my new proposed berm and I was able to prevent a storm surge that would have otherwise completely flooded the selected area. Now of course instinct would have told you, yes building a 10 or 15 foot wall would prevent the surge from flooding the Battery, but using what I’ve shown you, you can specifically design something for yourself, test it out, and ultimately qualify what you’ve made!