Modeling Rivers, Channels, and Streams with AutoCAD® Civil 3D® 2010Dana Probert, Autodesk

CV118-4 Learn how to leverage AutoCAD Civil 3D to improve existing stream channels to reduce flooding and increase storage. We’ll examine three design scenarios: a simple channel, complex, naturalized channel, and an engineered concrete channel. The class will include discussion of different corridor subassemblies, the use of corridor targets, and other techniques to build a finished model of the stream, analyze capacity and create construction documents.

About the Speaker:Dana Probert is a civil engineering expert with over 10 years experience in the AEC Industry. Currently, Dana is Autodesk’s Technical Marketing Manager for Civil Engineering where her primary focus is environmental engineering. Prior to joining Autodesk, Dana worked for private consulting firms in the U.S. and Canada on a cross-section of land development and environmental engineering projects. Dana has a Bachelor of Science degree in Civil Engineering from Georgia Tech.

Dana can be reached at dana.probert@autodesk.com

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Modeling Rivers, Channels, and Streams with AutoCAD® Civil 3D® 2010

Corridors are typically thought of as a road design tool however, the versatility of the corridor model lends itself to many types of design including trenches, walls, berms, and in the case of our example project: streams.

If you are unfamiliar with the practice of stream restoration design, you may be surprised to find out that in many ways, the geometry of stream design can be much more complex than many road designs. The alignment of an improved stream is often very sinuous by design and the profile typically contains steep drops and rises to create an alternating riffle and pool effect. Also, stream designs are typically in constant transition with no cross section being the same as the one before or after it. Fortunately, the Civil 3D corridor handles this complex type of design very effectively and has already proven to be a powerful design tool for many stream restoration designs.

Class assumes you are very familiar with the concept of corridor building, including the use of targets. The class also assumes that you are familiar with label and style composition, surface building and other core skills.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

High Level Workflow for Streams and ChannelsWhile your individual workflow will surely vary, this class will encourage you to spend more time in the conceptual phase of the project and work through more alternatives. This process is certainly not linear- you may find yourself going back and forth as well as skipping steps in your own design process.

1. Build basemap GIS data such as parcels, FEMA polygons, land use Conceptual surface data such as Google Earth, DEM, public LIDAR

2. Preliminary design Build a first draft stream centerline alignment and profile; Build simple, first draft corridor

3. Preliminary analysis Check capacity, earthwork and other elements using dynamic tools to gain a feel for the

project constraints4. Refine basemap with more accurate data

Add aerial topo, ground survey Add stream cross section survey, soundings, etc. Add surveyed wetlands lines, surveyed parcel boundaries, etc.

5. Refine Design Iterate design with the more accurate basemap information.

6. Refine Analysis HEC-RAS, Mannings or other channel capacity calculations Revisit step 5 as necessary

7. Documentation Build necessary plan, profile and section sheets Annotate sheets with labels Create tables for linework and quantities Create simple visualizations for clients, public stakeholders, etc.

Embrace Conceptual DesignAs civil engineers, we seem to skip the process of conceptual design. While architects and urban planners will spend a significant amount of time sketching by hand or using conceptual design tools in Revit or SketchUp, civil engineers want to sit down with mouse in hand and “do it right the first time”.

I believe we have accepted this workflow because before now, we haven’t had a flexible tool for preliminary work. In order to test the feasibility of an alternative, we need a significant level of detail and understanding of how the design will come together. Personally, I know I could never truly understand a channel design until I saw it in plan, profile and section with a significant

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

amount of labeling and hydraulic analysis. I equate this workflow to creating a sculpture from a block of stone. I hesitate and make each chisel stroke with great thought because I know if I decide I don’t like it, I either have to start over or accept something less than optimal.

If we put that amount of effort into our sketches, we might as well have been doing a final design. Our project management, client expectations and billing structure have revolved around the idea that we settle on the first alternative that acceptably meets minimum requirements.

With Civil 3D, it is much easier to create robust alternatives that give the designer the information that they need to determine feasibility. I encourage you to take a step back from your current process and approach design as a clay sculpture. The artist is less afraid to take risks when using clay because they can try an alternative then reshape the clay if it turns out to not be exactly what they want.

Simple ChannelIn the first scenario, there is an existing agricultural ditch that is undersized. Currently, the ditch has a narrow “v” shaped cross section.

First, create an alignment that follows the path of the ditch.

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Existing Ground

Ditch Alignment

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Next, create a layout profile that follows the desired vertical design of the new ditch.

Next, build an assembly. Think of subassemblies as a toolkit. There are many combinations of tools you can use to customize your assembly. For this example, the assembly is built with Generic Links. The LinkWidthandSlope subassembly was used for the foreslopes and bench area, while LinkSlopetoSurface was used for the daylight slope.

Build a simple corridor that uses the Existing Ground as a target for the LinkSlopetoSurface subassembly.

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Ditch Profile

LinkSlopetoSurface

LinkWidthandSlope

Existing Ground

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Naturalized ChannelThe design process begins with the assessment of the current condition of the stream. If it is found to be in poor condition, another portion of the stream that is in good condition is studied and analyzed to determine its properties, including its geometry. One of the goals in improving the stream is to mimic these geometric properties in the improved section. Using this approach a designer or environmental scientist lays out a new alignment for the stream that matches the sinuosity of a healthy portion of stream.

Then, a new profile is designed to control the thalweg (path through the lowest elevation point of the stream) creating riffles and pools that match the healthy portion of the stream. Civil 3D’s alignment and profile tools are a perfect match to the needs of the stream designer, providing quick layout and easy editing of the stream geometry.

One challenge of stream design is that, unlike most road designs, the cross-sectional shape of the stream is constantly changing. Typical sections for riffles and pools occur at single points along the stream with transitioning taking place between them. Once again, Civil 3D meets this challenge with robust targeting capabilities. Any linear component of the stream geometry can be represented horizontally and vertically through the use of feature lines, profiles, or even 3D polylines. These features can then be targeted by one or more of the corridor subassemblies, creating the flowing design that is required for stream restoration.

Small Stream ExampleThe next project is a slightly more complicated design. The existing stream is not functioning properly. It is too narrow and highly eroded. In order to improve the stream, the designer wants to add meanders to the alignment and also a series of shallow pools and steep steps.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Once the alignments and profiles are created, an assembly similar to the previous example is constructed. The LinkWidthAndSlope subassembly is used for the foreslope and bench areas, while the LinkSlopetoSurface subassembly is used for the daylight area.

These subassemblies allow for the use of targets. In the previous example, the stream section stayed constant, so there was no need for targets. In this case, the top of bank point on the assembly will change to match a top of bank (bank full) polyline in the drawing.

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Meandering Alignment

Step and Pool Profile

LinkSlopetoSurface

LinkWidthandSlope

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Use these polylines as targets when building the corridor model.

Large Stream ExampleThe next project is a complicated design. This stream is larger, and while it doesn’t meander quite as much as the last example, it has a very intricate profile. The typical section for this stream is flat across the bottom, unlike our previous examples which were a “v” shape.

In addition to the intricate stream centerline profile, the designer has provided elevation information for the top of bank (bank full) condition. The corridor model for this stream will require both a width target and an elevation target.

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Polyline that follows proposed top of bank or “Bank Full”

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

While in our simple stream, we attached the assembly to the stream centerline, here we will take a different approach. In cases where you have lots of curves through your transitions, it is often better to experiment with different baselines to help eliminate crossing corridor sections. When the bottom of your stream is flat, consider leaving that part of the corridor out. The triangulation of the surface TIN will take care of bridging that gap.

In this case, it is best to construct two assemblies that will use the Top of Bank alignment and profile as their baselines, and target the Bottom of Bank alignments and profiles. This example uses the same LinkWidthandSlope subassemblies as before.

The corridor is built with two baselines- one for the right side of the stream and one for the left side of the stream. Here is a sample of the Corridor Properties dialog for this stream:

In the Set All Targets dialog, the Bottom of Bank alignments are targeted as width targets, and their corresponding profiles are targeted as elevation targets.

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Alignment that follows Top of Bank.

Alignment that follows Bottom of Bank.

Target to Bottom of Bank

Attachment Point to Top of Bank

Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

The final corridor will have a gap in the middle.

Once a surface is built from the corridor, however, it will become clear that the corridor points along the bottom of bank will create triangles in the surface, and the final surface model will show a complete picture for the stream.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Concrete ChannelChannels may be reinforced with concrete when higher slopes or velocities are encountered. While more and more jurisdictions would prefer vegetated swales, occasionally reinforced channels cannot be avoided. Civil 3D has several subassemblies that contain parameters for lining such as Channel, ChannelParabolicBottom, SideDitch, SideDitchUShape and SideDitchWithLid.

The process for building a corridor with a concrete channel assembly is the same as for the previous examples. You may be able to use one of the predefined channel subassemblies, or depending on the required section, it may be easier to build the assembly using generic links.

Several of the predefined channel subassemblies have built lining options which would make it easier to obtain concrete quantities. Note that the channel subassemblies have an attachment point at the depth location, as opposed to the channel invert. This may require you to build a separate profile at the depth location.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Construction DocumentsStream and channel projects are often challenging to document. There are many changes in vertical and horizontal geometry which lead to complicated contouring, intricate labeling requirements and lots of erosion control devices. Without Civil 3D, the designer may not provide enough detail to ensure the project is built exactly to their original design intent. Civil 3D makes documentation far easier to create, and much of it remains dynamic to the model to accommodate design changes and iterations.

Also note that you may create tables, labels, and analysis styles for yourself as the designer. Don’t hesitate to create a custom label that may never show up on the final plans, but gives you valuable feedback as you work through the design process.

ContoursWe all know that civil 3D surface styles will show the contours for any surface, but depending on the complexity of the stream, you may feel the need to do some small manual edits, or smooth the look of the contours. You may also be sharing the final linework for the project with a Landscape Architect or other professional that may not be using Civil 3D.

In these cases, you may wish to use the Extract Objects command and extract the contours from the surface as polylines.

Depending on how you’ve created your surface, the resulting polylines may have too many vertices for practical use.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Use the Map cleanup tools (type MAPCLEAN) and choose the polylines. Use the simplify objects option and check create arcs.

If the result still has too many vertices for your use, repeat cleanup and experiment with different to tolerance values.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Erosion ControlAll water management projects require construction erosion control plans, and many require long term or permanent erosion control measures. One typical requirement is erosion control matting.

Erosion control matting is required in areas of steeper slope. A surface analysis can help identify areas where matting will be required. Create a surface analysis for your stream surface that identifies a range of slopes.

One you have a feel for the slopes on the project, you may just want to identify the critical areas. You can change your slope analysis style to include one range that just flags the steepest pieces.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Not only will this identify where to place the matting, but it will also give you an area for quantities.

If you’d like to extract the slope areas as hatches, be sure to adjust the surface style so that the slopes are 2D Hatch. Use the Extract Objects command that we used to extract the contours as polylines and change the hatch to match your company standard.

Simple VisualizationAs with roads, corridor code set styles can be used with channels. You’ll have the most success with code set styles in channels that are straight or that have gentle bends. Also, unless your channel is entirely grassed, it will be difficult to differentiate between materials in a channel built from generic links. The concrete channel subassembly is a good one for applying render materials with a code set style. These materials will also go with the corridor to 3DS Max Design as long as the Civil 3D Object Enablers are installed.

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Modeling Rivers, Channels and Streams with AutoCAD Civil 3D 2010

Another option for exhibit creation is Autodesk Impression. Impression is available for free for subscription customers. With the Civil 3D 2010 Object Enablers installed, you can bring Civil 3D drawings into Impression and add color, shading and more. You may also find it useful to export your Civil 3D drawings to AutoCAD first, then open them in Impression.

Additional ResourcesNY Times: Science of Stream Restoration: A great article that simplifies stream restoration and includes a multimedia explanation.

Stream Restoration: A Natural Channel Design Handbook by NCSRI and NCSG: A guidebook on stream restoration design that includes lots of photographs and diagrams. The material is appealing for non technical readers, but lots of deep information for technical people as well. Required reading for understanding the process.

Timmons Group Stream Restoration Success Story and

McKim & Creed Stream Restoration Success Story: Using Civil 3D for stream restoration.

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