Purgatory River above Trinidad Reservoir, Colorado, USA

Files

• README.md: this file
• USACE-RES_Purgatory-above-Trinidad_level0-raw_20200825-20240630.csv: raw data (level 0)
• USACE-RES_Purgatory-above-Trinidad_level1-qaqc_20200825-20240630.csv: processed data (level 1; refer to methods for further details)

Variables

• timestamp: ISO 8601 formatted date and time in Mountain Standard Time (UTC-07:00)
• DO_mgL: dissolved oxygen in milligrams per liter (mg/L)
• pH: pH, unitless
• spCond_uScm: specific conductance in microSiemens per centimeter (μS/cm)
• turb_FNU: turbidity in Formazin Nephelometric Units (FNU)
• temp_degC: water temperature in degrees Celsius (°C)
• discharge: stream discharge measured at U.S. Geological Survey (USGS) gage "Purgatoire River at Madrid, CO (07124200)"

Methods

Site Selection

Study sites were chosen to 1) maximize data quality and continuity, 2) provide instrument stability/safety from storm events and vandalism, and 3) allow for safe access for servicing over the full range of the hydrograph (Jones et al. 2017). Where possible, sites were located in geomorphically constrained stream reaches where flow is continuous and stream depth is stable and permits sampling over a wide range of stream discharge. Additionally, we preferentially selected sites with either natural (e.g., rock outcrops) or man-made (e.g., bridge pilings) permanent structures for affixing instrument housings. Where no permanent structures were available, we selected sites with stable riverbanks and profiles. Sites were chosen to be safely accessible at a wide range of river discharges and, when possible, to not require entering the water to access the instrument. Finally, permitting and access issues were considered when selecting sites, with preference given to sites on lands managed by the U.S. Army Corps of Engineers or other federal agencies. At each reservoir examined in this study, an upstream reference site and a downstream impacted site were selected for instrumentation. The upstream site was located as close to the inlet of the reservoir as possible, while avoiding sites that become inundated at high pool levels. The location of the downstream site was located as close to the outfall of the reservoirs as possible to assess the immediate downstream effects of the impoundment on water quality.

Instrument Installation

Instruments are housed in perforated aluminum or stainless-steel enclosures partially submerged in the river. Enclosures have a locking lid system that prevents vandalism and theft of the instruments, and where possible, the lid is notched to permit a cable to connect the instrument with a fiberglass enclosure that houses a battery, datalogger, and telemetry system. The cable provides power for the instrument and transmits data from the instrument to the datalogger. The datalogger contains an integrated cellular modem that transmits data to a server at the University of New Mexico. The battery in the datalogger enclosure is connected to a 20 watt solar panel via a charge controller, and powers the water quality instrument, datalogger, and telemetry system. Where permanent structures are available, enclosures are bolted or banded directly to a rock face, cement structure, or bridge piling. At sites without permanent structures, a piece of 4” angle iron is driven into the streambed at an angle to serve as the primary support for the instrument casing, with vertical and angled supports providing additional stability. The instrument casing is clamped to the primary support.

Data Acquisition

Foundational water quality parameters including dissolved oxygen (DO), temperature, specific conductance, pH, and turbidity data are collected at 15-minute intervals using Yellow Springs Instruments EXO multi-parameter sondes (YSI Inc./Xylem Inc., Yellow Springs, OH, U.S.A.). These instruments have been found to be robust and provide high quality data in highly turbid and dynamic river systems. Site visits are made at two to four week intervals to clean and calibrate the sondes following USGS standard operating procedures (Wagner et al. 2006). Briefly, equipment is cleaned and calibrated using laboratory-quality conductance, pH, and turbidity standards. Dissolved oxygen is calibrated in water-saturated air. Thermistors for temperature measurements are stable and do not require routine calibration. Batteries in the sondes are replaced when voltage falls below the manufacturer determined threshold. Readings before cleaning, after cleaning, and after calibration are taken alongside a laboratory calibrated comparison sonde to determine fouling drift and/or calibration drift.

Data Processing

All water quality data are quality controlled and quality assured (QA/QC'd) using Aquarius Workstation 3.3 (Aquatic Informatics, Vancouver, British Columbia, Canada) and graded according to USGS ratings for accuracy (Wagner et al. 2006). Suspect data are identified, and outliers and out of range data are be removed. Data are also corrected for fouling and calibration drift. This resource includes both raw (level 0) and QA/QC'd (level 1) data.

References

• Jones AS, Aanderud ZT, Horsburgh JS, Eiriksson DP, Dastrup D, Cox C, Jones SB, Bowling DR, Carlisle J, Carling GT, and Baker MA. 2017. Designing and implementing a network for sensing water quality and hydrology across mountain to urban transitions. Journal of the American Water Resources Association (JAWRA) 53:1095-1120. https://doi.org/10.1111/1752-1688.12557
• Wagner RJ, Boulger RW, Oblinger CJ, and Smith BA. 2006. Guidelines and standard procedures for continuous water-quality monitors: Site selection, field operation, calibration, record computation, and reporting. U.S. Geological Survey Techniques and Methods 1–D3. https://doi.org/10.3133/tm1D3