Generations of agricultural production on the eastern end of Henrico County, Va., left 182 acres of land in undesirable conditions. Common agricultural practices such as livestock grazing and tiling impacted the waterways, riparian buffers and wetlands located on the site. These methods, along with the ongoing channelization and straightening of streams, severely impacted the quality of water and wildlife in areas of the county.
With pressure mounting from residential and commercial builders to develop a residential subdivision within the watershed, a stream mitigation bank was needed to offset the future impacts to these areas and provide a sustainable solution for what is to become an urban stream system.
Timmons Group was hired to design a $1.5 million sustainable development project to restore the streams within the James River watershed to their natural state--prior to agricultural disturbance--ultimately, to improve the quality of water and wildlife in the area. In addition, the project would provide Henrico County with compensatory mitigation options.
However, ensuring a sustainable outcome was no easy task. “Restoring a stream to its natural condition provides a set of unique challenges,” says Michael Elander, PE, a Timmons Group engineer and one of three project designers. “The biggest challenge with this project was its sheer size.”
The site required hydrologic and hydraulic analysis of more than 640 acres of drainage area and 10,000 linear feet of stream, consisting of 11 unique stream reaches and eight confluences. Furthermore, the natural streams provided their own set of hurdles. Unlike traditional stormwater design, which uses armored channels and oversized conveyances to avoid flooding, natural channel design seeks to match proposed channel parameters (such as width, depth, slope, cross-sectional area and floodplain--54 unique parameters in all) to a known stable reference condition to intentionally increase floodplain access. Frequent flooding is a desirable way to dissipate the power of the stream and reduce instability. However, each of the 11 stream reaches involved in Henrico County had unique design parameters--meaning the stream changes size and shape constantly as it cuts through the land--causing increased complexity for implementing a natural channel design. “This can prove to be a daunting task without the proper tools,” Elander says.
The complexity of this project required seamless collaboration and coordination among several stakeholders to achieve a design plan that was both feasible and economical. “As with any stream restoration project, the permitting process was challenging,” says Rebecca Napier, PE, the project manager for the Varina Stream Mitigation Bank. “Even though everyone agrees that these types of restoration projects are beneficial to our watersheds, much coordination is needed between federal, state and local agencies.”
In addition to collaborating with several government agencies, Timmons Group needed to demonstrate the benefits and expected impact of this project to adjacent landowners. In fact, Napier says that selling the project’s vision was pivotal to the project’s success.
Achieving seamless coordination and accurately representing the complexity of this project to all stakeholders--both internal project managers and external agencies reviewing the project--required dynamic software that could update on the fly, provide a clear and accurate workflow and visually bring to life the project’s goals. To achieve these objectives, Timmons Group leveraged the design, modeling and visualization capabilities within the Autodesk Design Suite.
Developing a conceptual design was one of the first stages in the project. Along with performing a standard topographic/existing conditions survey, a multidisciplinary team of environmental scientists, designers and surveyors specializing in natural stream channel design collected a series of geomorphology data using the Rosgen Stream Classification system.
While survey and data collection were being executed in the field, the design team started their conceptual design coordination. Traditionally, the survey file would be brought back to the office, processed and then handed off to the engineers for conceptual design plans. On this project, however, the design team was under a tight timeline to produce conceptual stream alignments, and they needed a quick and efficient way to convey the concept to others.
By using Autodesk Infrastructure Modeler, the team was able to quickly compile data from many different sources to generate a realistic 3D model of the existing conditions of the stream and surrounding areas. Through the use of custom styles, the portions of the stream channels that required improvement could be easily identified. The conceptual design could then be effectively conveyed internally for design coordination.
After the survey and geomorphology data had been compiled, the team used AutoCAD Civil3D as a building information modeling (BIM) tool to design the Varina Stream Mitigation Bank project. Using a combination of alignments, profiles, assemblies, cross-sections, corridors, feature lines and surfaces enabled the team to create a final 3D model that was not only functional but could also be easily handed off to contractors for accurate bidding and construction.
The complex design of these natural stream systems required the models to be accurate within inches. If the final design was not constructed within a tight tolerance of the proposed design, the project as a whole had the potential to fail.
The parametric change engine in AutoCAD Civil3D instantly reflects changes made in one place throughout the entire model, so the team had tremendous confidence that the plans represented the complicated models accurately. Elander says the transition between design, plan production and construction was virtually seamless using this software. “Civil 3D was a great tool for us to use with this project,” he explains. “It really allowed the design team to model the tight corridors necessary in these complicated streams without worrying if the software could keep up.”
One of the most difficult challenges to overcome during a design is when changes are required. In a 2D world, this hurdle can significantly increase the design timeline. Without 3D modeling capabilities, modifying an alignment of a stream reach or tweak elevations would require a new project from scratch.
Fortunately, model-based workflows have made complete redesigns a thing of the past. Design teams can react to changes much faster and manage several design iterations. This was crucial for the Varina project because small elevation changes were constantly taking place in the stream. “It was extremely reassuring, as a designer, to be able to put as much complexity into the 3D model as I needed,” Elander says.
Helping the client and reviewing agencies visualize the intended design was the next challenge. A set of construction plans, a 2D representation of the 3D model, can be cumbersome to understand. Believing that a 3D visualization would help illustrate their vision for the mitigated streams, the project team leveraged Autodesk 3ds Max to create a rendered picture of the intended design based on the 3D model created with AutoCAD Civil3D. “These rendered images open the communication doors between designer, client, landowners and reviewing agencies,” Napier said. “The team produced a video as well as several still images of the project to be utilized.”
By using effective software tools, the Timmons Group was able to work more efficiently and produce a superior project design. This translated into scrapping the residential subdivision and restoring the Varina Stream Mitigation Bank to its natural state.
“Ultimately, it was the ability to conceptualize, model and visualize the project before construction that resulted in happy clients and a distinct advantage to us in a very competitive marketplace,” Elander says.