RCCZO -- Streamflow / Discharge, Surface Water Chemistry -- Estimating Surface Water Presence and Streamflow -- Southwest US -- (2010-2013)

Streamflow in arid and semi-arid regions is predominantly temporary but of significant importance for groundwater recharge and biogeochemical processes. However, temporary streamflow regimes remain poorly quantified. We use electrical resistance sensors and USGS stream gauge data to quantify streamflow intermittency as streamflow presence and water presence, which includes streamflow, ponding and soil moisture, in 13 southern Arizona streams spanning a climate gradient (mean annual precipitation from 160 to 750 mm). The monitoring washes were located in largely undisturbed military facilities, long term ecological research areas and a nature preserve. The most arid study washes, Black Gap (BG) and Sauceda Wash (SW), were located within the Barry M. Goldwater Air Force Base near Gila Bend, Arizona in the Lower Gila River Basin. Two semi-arid study washes were located on the Santa Rita Experimental Range near Sahuarita, Arizona in the Santa Cruz River Basin (SS and SR). Nine study sites were located on the Huachuca Mountains near Sierra Vista, Arizona and form part of the San Pedro River Basin. The study sites were located along 3 distinct elevations in 3 canyons: Huachuca Canyon and Garden Canyon which are located within the Fort Huachuca Army Post; and Ramsey Canyon, within the Nature Conservancy’s Ramsey Canyon Preserve. We established three cross-sectional transects 100 m apart at each reach, except Sauceda and Black Gap Washes where there were 5 transects, and installed electrical resistance sensors (TidbiT v2 UTBI-001 data logger, Onset Corporation, Bourne, MA) at the thalweg of each cross-sectional transect to identify surface water presence frequency and duration. The electrical resistance sensors were temperature sensors modified as outlined in Blasch et al. (2002), with 2 electrical leads exposed. We followed the method outlined by Jaeger and Olden (2012) to identify the onset and cessation of runoff. In brief, the onset of runoff is marked by the sudden and rapid increase in the relative electrical conductivity (EC) signal to a less negative or a positive number, while the termination of streamflow is also marked by a similarly sudden shift in the EC signal back to a more negative signal. In this study, EC = -94 indicates dry conditions. We were also able to quantify the duration of surface water presence as moist soil or ponded water because the EC signal for runoff is distinct from that of a moist soil and soil-drying conditions. Raw EC data and derived daily summaries of streamflow and water presence are reported.