Researchers analyzed 14 years of flow records from U.S. Geological Survey stream gauges and similar data from the Flood Control District of Maricopa County to determine how hydrologic characteristics varied with urban development. The study looked at 19 watersheds that drained areas ranging in size from less than a square mile to 175 square miles.
Similar to wetter systems, researchers observed more high-flow events in the urban desert streams compared to nonurban desert streams, she explained. However, this was only at the lower flood threshold — there was no increase in larger floods with urban development.
“Overall, the urban stream syndrome manifests differently in this arid system — urbanization increases water retention and leads to less variable flows in stream ecosystems," said McPhillips.
McPhillips — who started the research as a postdoctoral scholar at Arizona State University before joining the Penn State faculty to focus explicitly on urban hydrology and green infrastructure — hopes to apply some of what she learned in the West to her new role. In the arid West, she noted, water quantity is more of an issue, and flash flooding is a really big concern, along with water availability in aquifers and water scarcity.
In the East — especially in the Chesapeake Bay drainage — stormwater management is equally linked to water-quality worries. Reducing pollution from urban runoff is one of the strategies for cleaning up the bay.
“Arizona was an interesting case study to try to understand more about urbanization and the role of intentional engineered stormwater management structures because urban areas there have developed a lot more recently, and they still are growing rapidly,” McPhillips said. “The Phoenix area has had pretty progressive stormwater management policies for a while, and we looked at some watersheds where there was an extremely high implementation of stormwater-control features. So we could start to detect whether or not they are influencing stream-flow patterns.”