Infrastructure Management: Out of Sight, Out of Mind goes digital
Anne Arundel County, Maryland lies within the Chesapeake Bay watershed and is located mid-way between the Baltimore-Washington D.C. metropolitan areas. Rapid growth is changing the land use from a rural to an urban/suburban setting. The County’s Infrastructure Management Division (IMD) is making strides to manage their infrastructure to keep pace with this growth as well as recover their current structures. In the past the IMD relied on hand-drawn utility maps and hard-copy forms that were not entirely complete and were burdensome in providing comprehensive infrastructure management. Greenman-Pedersen Inc. (GPI) and IMD are working together to develop field procedures for recovering, inspecting, and mapping their infrastructure by developing database and GIS applications. The results enable the County to be more efficient and properly maintain the aging and expanding infrastructure.
With an ever expanding infrastructure Anne Arundel County’s Infrastructure Management Division (IMD) has the daunting task of maintaining the County’s infrastructure, such as pavement, guardrails, masonry, and drainage structures. Recently, the IMD has been emphasizing their drainage structure inventory, particularly their CSD networks. The IMD has been relying on hand drawn maps for location and inventory that are not up-to-date resulting in many CSD systems that have not been mapped, in addition, IMD must keep up with the growth occurring within the County. To assist the IMD in locating and managing their CSD infrastructure, GPI has developed a digital collection and management system that incorporates the power and flexibility of GIS.
IMD’s responsibilities range from routine maintenance to emergency repairs of CSD structures throughout the County. With the advent of EPA’s National Pollutant Discharge Elimination (NPDES) regulations, the County will also ultimately be responsible with the task of tracking stormwater discharge within those systems. To effectively manage their CSD infrastructure the County must first recover, inventory, and inspect their CSD systems in the field. The development of GIS, GPS, and field computer systems to digitally collect this information greatly enhances the accuracy and efficiency of locating and managing their CSD infrastructure. The goals of this project are:
A CSD system is made of several structural components, which are summarized below and are shown in Exhibit 1.
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Linear Structures |
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Exhibit 1 – Summary of CSD Structures
The Point Structures are each given a unique identification that is based on its grid location while the Linear Structures were uniquely identified through a combination of their upstream and downstream point structures. The ID’s are based in part on the Anne Arundel County grid system. The County is divided up into over 550 grids and each grid is comprised of 64 cells. These grids and cells, structure code, plus a sequential numbering system within each cell were used as the basis for labeling each structure. In addition, a single letter is used to identify the structure type. This allowed each structure to receive a unique label. For example, an outlet on Map G-10 and cell G-8 would be "G10G8O001". For a pipe on the same map and cell would be "G10G8P001-002" that started at the outlet G10G8I001 and ended at the next structure, say manhole G10G8M002 in the same map and cell.
The objective of the labeling scheme was to allow for future recovery of the system in the field based on the identification label that includes the grid map and cell. This also facilitated the hard-copy mapping by only having to post the sequential number since the maps would identify each grid and cell and a legend file would define the structure type.
GPI developed various tools to assist in the field recovery and inspections of CSDs. The two key utilities were the development of a Visual Basic interface (VBI) to the Microsoft Access database to log the field data and the integration of real-time differential GPS (DGPS). Each type of CSD structure had it’s own unique inventory and inspection parameters. The flexibility of VBI allowed for a separate digital form for each type of CSD structure. To make data collection easier and more efficient, standard inspection parameters were set to allow the use of pull down menus, numeric key pads, pre-defined comment check lists, etc. Exhibit 2 shows an example of a digital field form in the VBI.
Exhibit 2 - Example of Database Interface on a Field PC
The VBI was also used to read each structure location by reading the DGPS signal through the Communication port as a text string. These position strings are averaged then recorded when the user chooses to accept the Latitude/Longitude position. To ensure an accurate location, the program averages at least ten positions to obtain a final position. This results in sub-meter accuracy in locating structures, but does not require post-processing in the office following the field data collection.
Field crews consisted of two individuals. The chief inspector responsibilities included locating and inspecting structures, opening manhole covers, measuring pipes, and insuring that the proper number sequencing was being used. The second crewmember used the pen-based computer to record the inventory data and inspection results, GPS location, and assist the chief inspector. The field team utilized field phones to facilitate communication. This process streamlined the field process.
Data that was collected and entered in the field are written to a pre-defined Microsoft Access database file. This allows easy transfer of data from field equipment to the master database and was also used to develop the geo-referenced mapping. Following each field day, the first step in processing the data is the auto-generation of ArcView shapefiles for the CSD systems. A MapObjects application, known as CSD-Mapper, was developed that would read the CSD database and convert each structure type into to individual shapefiles, but also delineate the CSD system (see Exhibit 3). The CSD-Mapper application can quickly and accurately develop a comprehensive GIS model.
Exhibit 3 - Example of CSD ArcView Shapefiles and County Base mapping
To ensure the quality of the data in the CSD GIS model, several QA/QC steps were integrated in the field data collection and management procedures. In the VBI, data checks are provided by various techniques. For example the VBI was designed using defining pull-down menus with only acceptable data entries, pre-defined comments to maintain consistent inspections, formatted fields to ensure correct and complete data entry, and many other controls.
The CSD-Mapper is a powerful tool to automate the GIS data development, but also is an excellent utility to perform office QA/QC checks on the field data entry. The application creates a log file that shows errors that occurred when reading the pipe segments. This provides a check on both the point and linear structures (see Exhibit 4). Typically these errors occurred where a starting or end point could not be determined which aided in identifying errors within the CSD database.
Exhibit 4- Example of Errors highlighted in CSD-Mapper log file.
Another excellent tool for checking the CSD mapping was the use of ArcExplorer. The final shapefiles were then added to an ArcExplorer project to allow the inspector to quickly see spatially how the CSD structures and systems were laid out. The inspector could also see pipe errors that were not picked up by the log file from CSD-Mapper. These errors included pipes that were connected to the wrong structure, pipes that were not logged properly or any point feature errors. An error with points included wrong labels, and incorrect GPS points.
An ArcView GIS model was developed that included the CSD shapefiles, base mapping, and where necessary other GIS data. GIS file management of the ArcView project was crucial to prevent corruption of data or data loss, especially since data was collected and transferred on a daily basis. Since the GIS model was stored on a network, the ArcView project needed to be customized so that any user from any computer would be able to open and edit the project from their own desktop.
The first step was to setup proper directories on the network drive. These directories consisted of a base mapping directory, data/shapefiles directory, and a working directory. The base-mapping directory contained all vector base-mapping. The data/shapefiles directory contained the ArcView dbase files used to add as event themes. Also the shapefiles that were created from CSD-Mapper were copied over to this directory. The working directory contained all files that were created during geoprocessing.
The project file itself was set up to allow projecting of features and management of daily records. A view was created keeping the map units set to decimal degrees. This view was titled Lat, Long and this is where the event theme would be added and projected. The second view was titled according to the county grid that was being inspected; and the map units and distance units were set to feet.
The ArcView project consists of both raster and vector theme types. Base mapping consisted of vector files showing street maps and major hydrological features. These files were created using the ArcInfo translator. The files were converted from .E00 files to shapefiles. The raster images consisted of MrSid compressed aerial photography that was flown in the spring of 1998 (see Exhibit 5). The datum for the base data is Maryland State Plane Feet 1983.
The CSD data is created in the Latitude/Longitude coordinate system. In the ArcView project, this data is projected using the ArcView Projection utility extension. The new shapefiles are then overlaid on the County base mapping as well as the on the aerial photography. This provides the inspector a visual check on the accuracy of the GPS locations. The 1 US survey foot resolution of the photography allowed most CSD features to be visible. This allowed the user to improve the CSD structure locations in the ArcView project and also the CSD database.
Exhibit 5 - Example of CSD ArcView Shapefiles and County Aerial Photography
By developing database and GIS applications for use in the field and the office, CSD data can be efficiently collected and quickly integrated into a comprehensive GIS model. By utilizing digital field data collection, comprehensive data can be acquired that locates and identifies CSD systems. In addition, utilizing post-field mapping utilities, GIS data development can be automated. This provides a comprehensive approach to recovering all CSD infrastructure in the field to preparing complete CSD maps. This results in expediting the development of the GIS model. The GIS model then aids the IMD able to track their inventory and better target its maintenance/repair activities. The integrated applications are an investment in maintenance and repairs that will pay off with significant long-term cost savings, but also aid the County in providing fast and efficient service.
Peter Mattejat, PE, Sr. Project Manager, Greenman-Pedersen, Inc., Laurel, MD (301) 470-2772, p_mattejat@gpinet.com
Sean Triplett, Geographer, Greenman-Pedersen, Inc. Laurel, MD (301) 470-2772, s_ triplett @gpinet.com
Darryl Hockstra, Director, Anne Arundel County Infrastructure Management Division, Annapolis, Maryland