Wet/dry mapping provides a low-cost, river-wide snapshot of hydrologic conditions for rivers with interrupted perennial surface flows.
Many people in the arid Southwest care about the fate of perennial streams and their associated riparian communities. The loss of flows in streams and rivers has social, economic, and ecological consequences, so managers and concerned citizens seek ways to track their status.
In 1999, the Nature Conservancy launched a volunteer program involving scientists, managers, and citizen volunteers in southern Arizona who participated in a low-cost, comprehensive, and enjoyable method for monitoring our rivers—wet/dry mapping.
Every year on the third Saturday in June, people walk or ride horses along desert streams to map where the streams have surface flow and where they are dry. With more than a decade’s worth of data, this work is helping scientists and managers better understand and manage our riparian and aquatic habitats. The data have been consistently collected at the end of the dry summer months, right before the monsoon rains typically begin.
Wet/dry mapping uses citizen scientists to map the extent of surface flow in a river where certain reaches dry up during the summer. It provides a snapshot of conditions along the entire river at the same date each year, allowing comparisons of year-to-year variability.
Wet/dry mapping has been used to:
We have conducted wet/dry mapping for more than a decade on the San Pedro River and its tributary streams. In 2010, the effort involved 125 people on foot, horseback, and kayak, covering more than 220 stream miles. Partners include the Bureau of Land Management, Community Watershed Alliance, Friends of the San Pedro River, Cascabel Volunteers, CONANP, BIDA, Reserva Forestal Nacional y Refugio de Fauna Silvestre Ajos-Bavispe, and Naturalia.
Data from the first twelve years of wet/dry mapping in the San Pedro Riparian National Conservation Area (SPRNCA) reveal that wetted length varies from year to year, but the river hasn’t significantly changed overall. That’s good news, and suggests that conservation efforts by public and private stakeholders have made a difference. Indeed, a five-mile section of the river shows a steady increase in its wetted length where irrigated farm fields were retired for water conservation.
Wet/dry data also have been critical to help inform other research and monitoring projects, including studies of riparian conditions within the SPRNCA.
The length of wetted channel through the SPRNCA correlates with the volume of flow at the USGS Charleston stream gauge on the day of each wet/dry survey, validating a strong relationship between these approaches. However, the two monitoring methods tell different, but complimentary stories. Stream gauges provide an understanding of hourly changes throughout the year at a fixed point on the stream, while wet/dry mapping helps us grasp landscape-scale changes throughout the entire river on a fixed date.
Additional information on how wet/dry data have been analyzed can be found in the recently published paper by TNC scientists Dale Turner and Holly Richter, Wet/Dry mapping: using citizen scientists to monitor the extent of perennial surface flow in dryland regions.
The wet/dry mapping approach has been applied in other stream systems around Arizona, including Agua Fria River (Arizona NEMO), and Cienega Creek (conducted by TNC, BLM, and Pima County), and tributaries of the San Pedro River such as the Babocomari River, Ramsey, Miller, Hot Springs, and Redfield Canyons, and Los Fresnos in Mexico.
Wet/dry mapping conducted since 2006 along Cienega Creek has revealed locations of previously-unmapped perennial flow. While locals knew better, official state maps did not recognize a major portion of Upper Cienega Creek, and two flowing reaches of its tributary, Empire Creek, as perennial. These locations were subsequently omitted from mapping efforts such as Arizona Game and Fish Department's statewide inventory of riparian vegetation in the mid-1990's. Further downstream where the creek has been tracked since 1984, once-reliable reaches now go dry in some years.
Wet/dry mapping turns a walk through the cottonwood forest into meaningful science. Participants in the past have included ranchers, realtors, regulatory agencies, environmentalists, City Councilmen, children, and reporters. It gives interested citizens a chance to learn more about their rivers and get their feet wet in the ecosystem. Along the way, mapping volunteers have encountered species such as coatimundi, mountain lion, leopard frogs, bear, Gila monsters, bobcats, gray hawks, and longfin dace.
Wet/dry mapping is simple. Using hand-held GPS units, people record the start- and end-points of every wet portion along a stream or river. Using GIS software, these points are translated to lines on a map for display and analysis. To learn more, download detailed instructions and sample data forms for conducting wet/dry mapping.
The streams and rivers covered by wet/dry mapping flow through a mix of public and private lands. To respect the concerns of property owners, we do not release the wet/dry field data or GIS files for private lands. We will share GIS files for public lands, upon request.
Click a map to view it larger. Visit our map gallery to download high-resolution maps.
Do you want to join one of the 125 other volunteers who help to map the San Pedro River? Learn more about volunteering opportunities with The Nature Conservancy.