Montgomery County Region Goes LiDAR

By: Travis Elkins, GIS Coordinator, Town of Christiansburg Bob Pearsall, GIS Manager, Montgomery County Katherine Smith, GIS Coordinator, Town of Blacksburg

The towns of Christiansburg and Blacksburg, as well as Montgomery County, in Virginia are embarking upon a very significant project. The project includes creation of a new countywide topographic database and updating of existing orthophoto base maps in the towns and partial updating in county areas. The project became increasingly more important when existing data and orthophotos would no longer support various project specific applications. Another force driving the need for the project was storm water management. Along with new orthophotos and topography, the project will also provide a highly accurate digital terrain model (DTM) for the entire county.

Regional GIS participation is a hallmark for Montgomery County and the towns. In 2003, they worked together with Timmons Inc. to create an enterprise geodatabase foundation. For some time they had discussed a regional topographic and orthophoto update project and in early 2004 the town of Christiansburg began putting together a plan to issue a Request for Proposals (RFP) to professionally select a contractor. All agreed that going through a professional selection process gives a higher comfort level in the investment being made. Professional selection also helps assure the success of the project translates into useful and quantifiable benefits.

Each jurisdiction had many reasons for initiating the project, but for Christiansburg and Montgomery County, specific areas of concern were storm water management and floodplain mapping. As part of the Virginia Pollutant Discharge Elimination System, (VPDES) program all jurisdictions are responsible for storm water management. The town of Christiansburg was committed to the development of a storm water system map. Accurate base mapping and topographic data are essential in the delineation of drainage basins and determination of capacity of storm water channels and piping systems. Christiansburg intends to combine the new topographic data and orthophotography with field mapping efforts to create a map showing the location and size of all major storm water outfalls within the town limits.

Both the towns and Montgomery County have striven for many years to become “disaster resistant.” Local floodplain managers have championed this by initiating numerous actions to better protect the residents from the effects of natural disasters and substantially reduce disruption and loss. Efforts have focused on employing a doctrine of predisaster awareness, preparedness, and planning rather than postdisaster reactive actions that often occur. Early on it became apparent that too much land development and too few map changes or amendments to our 1978 Flood Insurance Rate Maps (FIRMs) meant that they were becoming less reliable to accurately predict flood-prone areas. The FIRM is an important part of a long-term countywide hazard mitigation strategy. As population and urban development have increased, so has the risk of severe damage and/or loss of life by flooding, storms, and other related events. Mapping floodplains helps to identify what areas are in danger under varying flood conditions. The FIRM maps provide an excellent source that is easily understood to help government planners and emergency management professionals identify areas of risk and prioritize their mitigation and response efforts. Floodplain maps provide not only detailed lists of threatened structures, but also form a cornerstone for a flood mitigation policy.

Many factors can influence flooding but probably none more than topography. Varying changes to topography through land development, road construction, utilities, and environmental factors can lead to significant problems and the potential of dangerous flooding. Accurate and up-to-date elevation data is essential for initial and revised flood forecast models in order to reasonably predict areas that are or will be affected by flooding.

Why choose LiDAR rather than traditional methods? With limited dollars to invest in the project, the jurisdictions looked for an approach that would not only produce a highly accurate and uniform product, but give the end users more flexibility when resampling of the source data was needed. Early on it became apparent that LiDAR (Light Detection and Ranging) fit everyone’s needs and would be the best approach. The jurisdictions also realized that LiDAR could be used for much more than storm water management and floodplain mapping. The source data would be useful for capital and facilities construction projects, economic revitalization, site plan reviews, public utility design and construction, and environmental modeling applications.

Acknowledgments: The Virginia Geospatial Newsletter. Volume 3, No. 2, Spring 2005