It’s mid-August and temperatures are forecast for low 100s, so I need an early start. I’m going to bicycle a 20-mile stretch of the Chuck Huckelberry Loop path along the Santa Cruz River over the next two days to monitor surface flow in the streambed. In the height of the summer, it is best to get going before dawn to avoid the maximum heat of the day.
Long-time Tucson residents are likely aware that the Santa Cruz River was historically a perennial stream, flowing year-round. However, groundwater pumping over the last 100+ years has lowered water levels, and the Santa Cruz is mostly dry. The natural stream flow is now classified as ephemeral, flowing only in response to storms. Thankfully, the river now flows perennially in several stretches from discharges of highly treated wastewater into the streambed. This water helps replenish the groundwater while also supporting riparian vegetation (e.g., willows and cattails) and native fishes (such as Gila topminnow).
My assignment is to make monthly flow observations near the four locations where the treated water is released into the river: Irvington, Heritage, Agua Nueva, and Tres Ríos. I qualitatively note how much is discharged at each outfall and how far downstream the water flows, with photos to document my observations and coordinates recorded at each endpoint. My observations are mapped to help monitor the extent of flow variations in the river, which is tracked in the annual Living River reports. Natural flows from storm events (summer monsoons or gentle winter rains) contribute additional water to the river, occasionally resulting in continual flow that connects the monitored reaches.
I’ve run, walked, and bicycled along the Santa Cruz River path innumerable times since moving downtown in 2007, but up until now my observations of the river have been incidental at best. Now with a specific purpose in mind, I am much more attentive to the plants and animals that I see—especially where surface water is present. Birds are prevalent, in particular songbirds residing in the riparian vegetation, but I also see a fair number of roadrunners and raptors. Javelinas and coyotes ramble along the riverbed and up tributary washes searching, I’m sure, for food and water. Lots of lizards bask on the paved path, but I’ve only seen a few snakes. Sadly, the fish are tiny and shy, so typically aren’t seen from the path. Occasional signage along the path provides ecosystem and cultural information to curious path users.
My ride is enriched as I layer prehistoric, historic, and personal history on my awareness of the present ecosystem. The name “Tucson” derives from the Tohono O’odham word for “Black Hill,” referring to a prehistoric village at the base of what is now known as Sentinel Peak. In addition to the changed flow conditions of the river over the last 100 years, the streambed has been channelized and the banks armored, all to keep flow within a defined area and protect structures. I imagine that the natural streambed was a broad and braided set of channels that meandered through what is now Tucson.
As I ride along, I wonder what it must have been like when indigenous peoples lived here. Historical building foundations and other evidence of development over the past 100 years can now be seen along the path, and modern development—residential, commercial, and industrial—borders the linear park in many places. My personal history is also in mind: I’m riding my late father’s touring bike. My parents bicycled across the country in 1992, and I inherited his Trek 520. Although they did not pass through Tucson on their journey, I am channeling him as I ride along the path. There is a certain satisfaction in holistic awareness of the natural and anthropogenic, historical and modern, and cultural and personal influences and factors present along the Santa Cruz River.
On my first day of the August session, I visit the farthest upstream point: the Irvington outfall, about a quarter mile upstream (south) of the Ajo Way bridge. Flow from this discharge point comes from the Tucson Airport Remediation Project, is typically modest, and often extends only to just upstream of the bridge. The active channel where water flows meanders across the streambed, from the east side (where the outfall is) to the west. Riparian vegetation is relatively dense in this short reach, clearly reliant on the regular supply of water; downstream (north) from the bridge the vegetation quickly transitions back to xeroriparian all the way to Silverlake Road.
The Heritage outfall, about halfway between the Silverlake Road and Starr Pass Boulevard bridges, is also on the east side and part of my first day’s ride. This is where Tucson Water releases water as part of the Santa Cruz River Heritage Project. Again, flow from this discharge point is typically modest, and the active channel meanders across to the west side. Flows sometimes trickle past the Starr Pass bridge. The southeast toe of Sentinel Peak confines the streambed here, diverting the river slightly to the east. It appears that the bedrock from the mountain keeps the surface water from infiltrating into the subsurface; shallow groundwater probably supports the dense riparian vegetation along the west wide of the streambed whether or not surface water is present. Commonly, there’s a linear pool downstream from the bridge that doesn’t have a surface connection to the actively flowing segment. The extent of this pool, on the east side of the streambed, varies month-to-month, but it is always there. I suspect an underground hydrologic connection to the flow from the outfall.
On the second day I visit the much farther downstream Agua Nueva outfall, where treated water from the Agua Nueva Water Reclamation Facility is discharged about three quarters of a mile upstream from the El Camino del Cerro bridge. Flow from this outfall is sometimes quite significant, and surface water usually extends well downstream. I also make observations at the El Camino del Cerro and Sunset Links bridges—there is always flow at these locations—and from the path just past the confluence with the Cañada del Oro. Flow from the Agua Nueva outfall often reaches beyond the Cañada del Oro, but occasionally ends in this vicinity. Riparian vegetation is extensive from the outfall to the confluence with the Rillito River, but diminishes in density downstream of that point. Sometimes I cannot see the end of the surface flow reach from the path; I believe that under certain circumstances it may extend all the way to the Tres Ríos outfall.
The bridge at Ina Road is my last monitoring point. Discharge from Tres Ríos Water Reclamation Facility just upstream of the bridge is the largest of the four outfalls, resulting in multiple channels under the Ina Road bridge and a backwater pool that extends upstream for some distance. Although the active channels coalesce on the west side of the streambed, a small side channel apparently feeds a wetland along the east side, immediately south of the bridge. Cattails and songbirds are usually present here. Flow from this outfall extends miles downstream from here; I do not attempt to locate the downstream end of this flow segment.
The air temperature has reached into the 90s by the time I get home mid-morning on my second day of the August session, but monsoons are forecasted for the afternoon. It is hoped that we’ll get enough rainfall to result in significant runoff to supplement the artificial flows. Life in the streambed will be sustained by both natural and manmade influences. “The desert is beautiful, my friends” (to quote Petey Mesquitey) and desert rivers have a particular beauty that I enjoy every month for this assignment.
Photos and text by Chris Rife, volunteer
Maps by Madeline Friberg-Landon, volunteer