Zeki Taha, a technician with Transpotek, uses a Leica GS20 to locate the geographical position of an outfall. Photos: Transpotek
Outfall locations, attribute data, and related photos are accessed through ESRI's ArcGIS software.
The New Jersey Department of Environmental Protection released new regulations in 2004 for controlling the discharge of pollutants into the state's waterways from stormwater drainage systems. As part of this regulatory process, all municipalities, counties, state, federal, and private authorities—including highway authorities—are required to map the location and condition of all stormwater outfalls located on their property.
KS Engineers (KSE), headquartered in Newark, N.J., was awarded a contract by the New Jersey Turnpike Authority in late 2004 to visually inspect 2000 stormwater outfalls and collect related geographic information system (GIS) data. Work commenced in early February 2005 along the mainline of the Turnpike from Milepost 0.0 to 50.0, and along the Garden State Parkway from Milepost 0.0 to 60.0. Transpotek Engineers, based in Paramus, N.J., is working as a subconsultant to KSE.
KSE and Transpotek started by gathering the as-built plans for the Turnpike and Parkway from the Turnpike Authority's engineering office in Woodbridge. These plans were used to identify the existing outfall inventory on both highways. Initial locations were established from record plans, highway stationing, and milepost indications. After identifying the total number of outfalls, we decided to divide the study area into four segments—Turnpike northbound and southbound, and Parkway northbound and southbound. A field team consisting of one team leader and one technician was assigned to each segment for data collection and inspection.Collecting Data
The field teams are using a GS20 Professional Data Mapper handheld global positioning system (GPS)/GIS Collector with external antenna and Wireless Real-Time Corrections System (WoRCS) belt—a package from Leica Geosystem, headquartered in St. Gallen, Switzerland. This equipment provides wireless beacon correction data for the GPS observations. Office staff is using Leica GIS DataPro software to process GIS and attribute data. Tools within ArcGIS—a GIS-based software by ESRI—are used to link digital images of each outfall to the shape files. All post-processed data are exported to ESRI ArcGIS 9 software as shape files. Positional data for the outfalls are being collected in the New Jersey State Plane Coordinate System with submeter accuracy.
The field teams use the GS20 navigation function to locate each outfall. After locating the outfall, sometimes by clearing heavy brush or soil, the teams use the GS20 to record the X and Y coordinates of the structure. The outfall is then inspected and its attributes collected into the GS20. Finally, two digital photographs of the structure are taken. At the end of the fieldwork, the teams upload the data to a server for processing. In a typical day, each team can collect data for 10 to 15 outfall locations.
The location attributes include roadway (Parkway or Turnpike), direction (northbound or southbound), lane (mainline, ramp, service road, etc.), and milepoint. The team also enters the number of outfalls at the same milepoint—for instance, one headwall with two pipes. Other attributes include drain type, pipe shape and size, material, slope protection (grass or concrete), outfall condition, flow direction, and type of pipe end. A record is made of any evidence of “dry flow” (discharge when there has been no prior rain event) and whether the outfall flows into a United States Geological Survey quad sheet “blue stream.”
If an outfall is located in an area where the team cannot properly set up the equipment, attempts are made to record the position using an offset (distance-distance method). If the area is inaccessible and an offset cannot be performed, a note is made on the plan about the conditions preventing the team from recording the position. If possible, any attributes that can be seen are recorded.
When post-processing the data in the office, the team first uses ArcGIS to merge the week's shape files for either the Parkway or the Turnpike. Then, five fields are added to the database of the merged file: outfall identification number, photo A, photo B, and X, Y coordinates. The new fields are then populated using scripts within ArcGIS, while the images are linked manually using ArcGIS tools. This process is repeated for the second highway, and the two are merged.
In general, the teams have achieved consistent submeter accuracy using the GS20 PDM and WoRCS belt for real-time beacon corrections. At times the geometry of the satellites in relation to the team position produces less than favorable results in accuracy. In those cases, the team simply occupies the position long enough for the collector to indicate that positional accuracy has reached the required level.
Safety is always a concern when sending teams to work alongside a busy high-speed roadway. Each team working in the field is equipped with the proper safety equipment, including hard hat, reflective vest, vehicle strobe lights, and traffic cones. In order to increase visibility, vehicles with strobe lights are positioned behind the working teams. Whenever possible, the teams are instructed to walk behind the guardrail. Because the work started in February, the teams had to work under difficult conditions of rain, snow, sleet, ice, and cold. On some days, the teams simply could not work in the field due to the weather, and tried to make up the lost days by working over the weekends. As the weather has improved, so has productivity, and the field work should be completed this summer.
— Shahid is president of KS Engineers and Henriquez is GIS manager with Transpotek Engineers.