Optimize engineered waterway design

March 2009 » Feature Articles
While it has its roots in architecture and construction, building information modeling (BIM) is increasingly being adopted by the civil engineering community—and not just for land development projects that involve architects. The principles of BIM are also being applied to transportation projects and to environmental projects such as river restoration.
Adam Strafaci

Civil engineering firms streamline river restoration projects with building information modeling software.

Projects

Doctors Branch stream restoration, Wilmington, N.C

Magnolia Green mitigation, Chesterfield County, Va.

Civil engineers

McKim & Creed and

Timmons Group

Product application

BIM software allows civil engineers to increase productivity, achieve better accuracy, improve communication, and produce better designs in stream restoration projects.

While it has its roots in architecture and construction, building information modeling (BIM) is increasingly being adopted by the civil engineering community—and not just for land development projects that involve architects. The principles of BIM are also being applied to transportation projects and to environmental projects such as river restoration.

More than just a new approach to design, BIM is an integrated process that allows AEC professionals, including civil engineers, to explore a project’s key physical and functional characteristics digitally before it is built. Built on a foundation of coordinated and consistent project information, BIM enables civil engineers to develop more innovative designs; visualize, simulate, and analyze the appearance and performance of those designs; more accurately document them; and deliver them faster, more economically, and hopefully, with reduced environmental impact.

BIM is particularly well suited to the demands of river restoration projects, which possess highly complex geometries and include a host of challenging features such as riffle, run, pool, and glide sequences that designers must accurately model.

One such project is the Doctors Branch stream restoration in Wilmington, N.C. In the early 1960s, Doctors Branch was a healthy coastal stream that provided habitat for a wide variety of plant and animal species. Over time, however, increased erosion caused by nearby development carved out a canyon 12 feet deep and almost 20 feet wide, significantly degrading water quality and putting an adjacent sewer line at risk. More importantly, by 2008 this canyon had eroded sections of more than 30 backyards and, in two or three locations, was threatening nearby homes.

Existing conditions in Doctors Branch stream (courtesy of McKim & Creed, P.A.)

In reaction to citizen complaints, the city of Wilmington contracted civil engineering consulting firm McKim & Creed to design a new stream channel to stabilize the existing stream banks, improve the health of the riparian corridor, and protect adjacent properties and utilities.

"Our goal is to give the stream channel and banks a new, more stable geometry so they do not encroach any further," said Tim Schueler, P.E., senior project manager at the firm. In addition, McKim & Creed anticipates reducing downstream pollution caused by erosion by a factor of 100.

The first step in the process was to take field measurements to establish accurate width-to-depth ratios and other important baseline data. Then, using AutoCAD Civil 3D BIM software from Autodesk, McKim & Creed generated a 3D model of the existing stream.

Using that model as a foundation, the design team began work on a series of what-if scenarios for the city and local homeowners’ association—a process that would have taken too long, cost too much, and yielded less than optimal designs if conducted with traditional 2D drafting-based design software. By using a 3D modeling approach, the designers were able to significantly reduce the time needed to create five design options. "The entire process took around half the time it would have taken us with our previous 2D software," said Randall Mattingly, design applications manager at McKim & Creed.

A 3D model of Doctors Branch brings design to life for all project stakeholders. (courtesy of McKim & Creed, P.A.)

Another factor that contributed to increased productivity was the firm’s ability to use the BIM process to help keep the data in the model consistent and reliable. "Every time we needed to shift a stream alignment or make some other change, the software automatically updated the entire model in real time," said Mattingly. "There was no need to rebuild constantly."

This type of instant feedback helped the team make better, more-informed decisions. For example, during concept development, the team noticed that erosion was gradually exposing the adjacent sewer line. Working in a BIM environment enabled them to more easily see how their design concepts would impact the pipe and whether or not they would cause problems.

By presenting the design concepts in 3D, McKim & Creed demonstrated exactly how the proposed grade would restore land lost to erosion. "It really helped Wilmington understand that we are not going to do anything that will negatively impact the community," said Mattingly. Currently, the firm has finished the initial design process and plans to begin construction in 2009 after obtaining the necessary feedback and approvals from the city and local homeowners’ association.

Satisfy stringent permitting requirements
All of the benefits detailed above—increased productivity, better accuracy, and improved communication—combine to make BIM an excellent approach for handling the complexities of stream restoration projects. The Magnolia Green project in Chesterfield County, Va., serves as another example of how this process works. Zoned for as many as 4,886 residential units, this mixed-use development will significantly increase the load on the site’s existing stream channels.

Existing stream channel in the Magnolia Green project (courtesy of Timmons Group)

To complete the necessary environmental permitting process for the project, the consultant, Timmons Group, needed to use natural channel design techniques to mitigate the development’s impact on the channels. "Currently, the streams are actively degrading and eroding the existing channels," said Rebecca Draucker, P.E., environmental project manager with Timmons Group. By providing compensatory mitigation onsite, Timmons Group will enable the client to avoid purchasing costly mitigation banking credits.

The overall goal of the project is to increase flow capacity while stabilizing the eroding channels and mimicking natural channels with their complex riffle, run, pool, and glide sequences. The team must also stay under budget and on schedule.

Applying natural, or green, channel-design principles, Timmons Group used Civil 3D software to draw sections of the stream and create assemblies representing key features, such as riffles, pools, thalwegs, banks, and flood plains. From this preliminary work, the designers created a realistic, intelligent corridor model of the existing stream channels.

According to Ken Hoen, senior environmental designer at Timmons Group, "Streams represent a complex geometry that is extremely difficult to represent by hand or with 2D tools. Civil 3D freed us up to run with our ideas and make the streams appear exactly as we wanted."

Proposed corridor model in the Magnolia Green project (courtesy of Timmons Group)

Next, team members produced multiple what-if scenarios, analyzed the potential water flow, and changed the design accordingly, selecting options that minimized environmental impact, improved stream hydrology, and restored habitats for local flora and fauna. Because Civil 3D and its parametric change engine instantly reflected changes made in one place throughout the entire model, the team had confidence that the plans were solid. In fact, only six weeks after submission, county officials approved plans for the first 3,000 feet of the channel without a single comment. "That has never happened before," said Chris Dodson, environmental services manager at Timmons Group.

Leverage the model downstream
Probably the most significant advantage of BIM compared with traditional 2D design processes is the ability to extend the use of the information model beyond design, analysis, and simulation into construction and beyond. For example, when bidding begins, Timmons Group will leverage data from the 3D model to communicate important project information to the specialty stream restoration contractors, enabling them to provide more accurate bids. Once the contractor begins construction in the summer of 2009, the Timmons Group expects the 3D model will enable all parties to work together much more efficiently, helping to minimize unrealistic change orders.

During construction, the contractors will be able to load a variant of the 3D model onto GPS-controlled construction equipment, enabling machine operators to see the site model on their equipment. The Timmons Group expects this process will yield more accurate grading and minimize the need for field surveying.

Conclusion
BIM is a powerful way to streamline river restoration projects. On both the Doctors Branch and Magnolia Green projects, civil engineering consultants used BIM software to increase productivity, help achieve better accuracy, and improve communication—and also produce better designs. They also extracted data from the model for reuse in a variety of downstream processes. Because demand for these services is growing fast—and the number of skilled engineers is still so small—civil engineers who invest the time and effort to learn these new skills can gain a decisive competitive edge in today’s global design market.

Adam Strafaci is the senior industry marketing manager for Civil Engineering for Autodesk. Prior to joining Autodesk, Strafaci worked three years as a water resources engineer with a top 50 ENR design firm and seven years with a leading water resources modeling software company, as well as managing editor for a series of textbooks on water, wastewater, and stormwater hydraulic modeling. He can be contacted at adam.strafaci@autodesk.com.


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