Erosion Control June 2012 : Page 53
design the required storage with outlets to control the discharge to protect the downstream channel during construction. While I worked on the con-struction-phase grading and erosion control plan, another engineer using HydroCAD developed the post-construction stormwater management sys-tem consisting of retention and infiltration ponds.” One of the site’s challenges, explains Phillips, was its location adjacent to “the protective area of a municipal water supply. Downstream erosion was occurring due to the concentrated flows in-troduced by prior offsite construction, so we had to mitigate for that damage.” The versatility of the product proved beneficial in terms of erosion control. Phillips, who had used HydroCAD since before its official release in 1986, expected this on the project. “I have used it on projects in New Hampshire, Maine, Virginia, Delaware, and North Carolina,” he says. “I have used it to design projects and to review the work of others. HydroCAD is flexible and powerful; a skilled engineer can replicate a great variety of situations.” Steep Slopes and Large Storms Extreme weather events, steep slopes, and difficult soil can combine to become a formidable obstacle for any construction project. To face these chal-lenges, the Portsmouth, NH–based Maguire Group Inc. also turned to HydroCAD modeling software. “Recently, Maguire used HydroCAD to perform a hydrologic analysis of a commercial development on St. Thomas in the US Virgin Islands, which in-cluded two new commercial buildings and a build-ing expansion, parking, and other infrastructure on a 50-acre site,” says Marisa DiBiaso, a senior civil engineer at Maguire Group. “HydroCAD was used to model the complex pre-and post-development hydrol-ogy of the site because of its user-friendly interface that allowed the model to be easily organized while enabling us to analyze a wide variety of drainage conditions.” Site design for the ongoing project, which is currently in the permitting phrase, began in 2010. The site’s envi-ronment required extensive planning. “The biggest challenges for this project were the high runoff volume produced by the steep slopes, low permeability of natu-ral soils, and the 100-year design storm,” says DiBiaso. “The 100-year design storm is much larger in the Virgin Islands than most other areas of the US due to tropical climate in the Caribbean.” Having used HydroCAD modeling software for several years, Maguire de-cided to use the product in an erosion control capacity at the St. Thomas site. “The proposed drainage design re-“The biggest challenges for this project were the high runoff volume produced by the steep slopes, low permeability of natural soils, and the 100-year design storm.” quired capturing runoff from a large area of steep upland and conveying the stormwater through the site to a large deten-tion pond. To prevent erosion of the steep slopes, collection swales and a large closed drainage system were designed using HydroCAD. HydroCAD calculates stormwater flow depth and velocity, which are critical pieces of information when it comes to erosion control,” says DiBiaso. “The large detention pond also was designed using HydroCAD to detain the water-quality storm and attenuate stormwater discharge. In particular, the use of HydroCAD to model the outlet structures of the pond was critical to ensuring a safe design that allows for sedimentation to occur in the pond and prevents erosion at the discharge point.” Stormwater management capabilities coupled with previous performance were the primary reasons selecting HydroCAD as a tool made sense for this project. “I have been using HydroCAD for about seven years on over a dozen projects ranging from commercial/industrial sites to landfills to highways,” says DiBiaso. “I’ve been very happy with the results and have found HydroCAD’s online courses and webinars to be very beneficial.” Erosion control is closely tied in many ways to site design, from protecting a site from sediment runoff to shaping proper drainage as well as countless other measures of defense. In fall 2011, Strategic Land Services based in Suwanee, GA, estimated a 1,000-acre new state park in Gainsville, GA, which will feature boating areas, hiking sites, and RV camping locations. Strategic Land Services used Dallas, TX–based Vertigraph’s SiteWorx software program during the estimation stage of the Don Carter State Park project. The software can digitize existing and pro-posed contour lines, spot elevations, project boundaries, and other areas. Once a digitized blueprint is created, the program can calculate cut and fill volumes and other data. The program can demonstrate how proposed site elevations can be adjusted. Information in the printed or onscreen reports include a 3D graphic representation of both the site as it currently exists as well as the proposed site. At Don Carter State Park, John Plont, an estimator at SLS, used SiteWorx to calculate fill and “how much cut, fill, import, or export of dirt is needed to build the project,” he says. He has used SiteWorx OS on a half-acre site with 1,500 cubic yards of earthwork— the La O’wn Academy in Roswell, GA—as well as on the Don Carter State Park, a 1,000-acre site with more than 150,000 cubic yards of earthwork. “I’ve found SiteWorx OS to be very versatile and easy to use,” says Plont. The landscape at the Don Carter State Park provided a variety of chal-lenges. “The existing terrain is very hilly. There are a lot of cut-and-fill areas to calculate. It had multiple takeoff pag-es to run calculations on. The project was so large, I had to break it up into 14 different projects,” says Plont. “Most of the projects are one sheet; this one was on 14. I was in that program [SiteWorx] working on that project for two weeks.” For Plont, who says he uses the JUNE 2012 EROSION CONTROL 53
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