There's an economic and cultural renaissance of sorts happening in the City of Durham, North Carolina. With a renewed revitalization of its downtown district, the redevelopment and repurposing of former tobacco districts into tech hubs and chic, loft-style apartment complexes, the city is rapidly growing beyond its most-recently reported 250,000 population numbers. Durham is known for being one of the points in the high-tech research and development Research Triangle and home to Duke University.
The city's growth explosion prompted Edward Cherry, GIS administrator for the City of Durham Public Works Department, and his staff of 14 GIS professionals, to seek out ways to streamline data collection for the city's public works department. The department is tasked with managing all infrastructure data for the city, including mapping the impervious area for the city's $16 million a year Stormwater Utility Fee fund. "That is half a billion square feet of impervious area that we manage through digitization and review daily," Cherry said. "That fund was one of the main drivers for us purchasing satellite imagery."
After using several satellite imagery systems that were all fraught with the same problems - low resolution and infrequent captures - Cherry determined the city needed far superior quality in their mapping imagery. The demands of the growing city necessitated an imagery provider equipped to supply crystal-clear images that were up-to-date, captured multiple times of year in both leaf-off and leaf-on seasons, while also allowing accessibility through web-based services.
Nearmap's aerial imagery, captured every six months at a 2.8-inch GSD, proved to be the superior quality Durham's public works department needed. Dozens of projects - from road maintenance and pothole patching to water sampling and degradation - are all utilizing the improved imagery, which has proven to save the city money, reduce time spent out in the field, and allow crews to use real-time imagery when they are out working in the field.
Better Monitoring of Pavement Conditions – The City of Durham is responsible for maintaining a majority of their own road work, maintenance and repaving. As a result, the city pays for a road-condition survey which samples different sites, evaluating the level of degradation.
With Nearmap imagery, surveyors are better able to identify specific locations. "With over four to five different image captures at the high-resolution, they can see sections that have been paved most recently," Cherry said, mentioning how this new process has saved a significant amount of time. "We don't need to send crews out to an area where a stretch has already been paved."
With only once-a-year captures, the imagery was not as reliable due to any number of factors, including cloud cover that shaded the area or rain that, due to reflection, made the pavement appear newer than it was. "It really caused what we call static," Cherry said. "Access to frequent captures alone has made the service worthwhile."
Time Savings and Documentation of Road Repairs – Like any city, the patching of potholes is a constant, ongoing project. With imagery from Nearmap, however, the City of Durham has been able to eliminate several steps in the process.
Traditionally, the streets department has to send inspectors on location to spray paint and circle those areas that require pothole repairs indicating where the contractor’s work is needed. “Then we would produce maps and hard copies to direct those people ahead of time on a scheduled event,” Cherry said. Now the city uses an application integrated with Nearmap imagery where contractors can view the areas on their phone or tablet out in the field. The surveyors can edit and draw the areas that need patching instead of physically going out and spray painting them. “Then, in real time, the people doing the patching can see a very high-resolution image of where they need to do the work,” he said.
Those pothole image captures are also recorded for legacy work, so when questioned about how many potholes were patched and where they were located, the images are quickly accessible. “Then we can see where work has been done when we are billed for it,” Cherry said. “We can visualize the work, which is an added bonus.”
More Detailed Maps of City Riparian Zones– Previously, with only leaf-off imagery, surveys of riparian areas in Durham proved limiting. With imagery captured during both leaf-off and leaf-on seasons, riparian buffers around streams can now be monitored for growth and expansion. The buffers can be alerted if there are issues with a stream’s path, whether sediment is clogging up one part of the area or if there is repeated flooding or people intruding on a buffer.
Previously, with just leaf-off imagery, the public works department was only able to do extractions without any vegetation noise like shadows from trees. “Now with Nearmap captures collected at multiple times, we can see leaf-off and leaf-on and in between,” Cherry said. “That allows us to start pulling in land cover classifications that are more accurate, not solely time stamped for leaf-off.”
Accurate and Detailed Customer Billing– Serving some 78,000 customers throughout Durham, the public works office has found the high-resolution imagery has improved their billing processes by producing web service maps that capture individual storylines. Stormwater billing customers, for instance, can visualize their property with the impervious area mapped out and tied to their billing records.
“We’re able to show them what their annual billing costs are for their property,” Cherry said. In fact, the city is now able to do that over time, pointing out when a customer has added an extension to their house or added a driveway. “Now the customer can see that. And having this service web-based has not only streamlined the process but made it lightning fast.”
“Having access to imagery back to 2014, we’re able to go back in time during the thrust of development and monitor it forward,” Cherry said. “We’ve been able to update a lot of our development policies and review policies of the past and their success.”
The City of Durham Public Works Department provides a wide range of services, including street maintenance, engineering design, development review and stormwater quality and infrastructure maintenance. The department also ensures that the street infrastructure is safe and well maintained.