WaterQualityWatch -- Continuous Real-Time Water Quality of Surface Water in the United States

What is a surrogate?

A surrogate is a continuous in-stream sensor measurement used to compute or estimate the concentration of a water-quality constituent of greater interest. These computed estimates of water quality are available in real-time at a decreased cost compared to manual sample collection.

Near Real-Time Water Quality Information

Summary of surrogate approach:

  1. Install water-quality monitors at stations and transmit data in real time.
  2. Collect water samples over the range of hydrologic and chemical conditions.
  3. Develop site-specific regression models using collected samples and in-stream sensor values.
  4. Compute or estimate concentrations and loads.
  5. Publish the regression models.
  6. Display estimates of concentrations and loads from the continuous data and models, uncertainty, and probability on the web.
  7. Continued sampling to verify models and relations. (http://pubs.usgs.gov/fs/2014/3003/)
  8. Another approach using accoustics. (http://pubs.usgs.gov/fs/2014/3038/)

Continuously recorded data and data from periodic collection of water-quality samples are used to develop statistical relations between certain properties of water that can be measured continuously (the surrogate sensor measurements) and transmitted in near real-time and chemical constituents of concern that cannot be measured continuously. The approach is similar to the method used for many years to determine streamflow. Streamflow is determined on the basis of continuously measured water level or gage height that is used to develop a rating curve. A rating curve is the calibration of gage height measurements (the surrogate) used to compute streamflow. Continuous water-quality measurements such as turbidity and specific conductance are used as surrogates to determine concentrations of other water-quality constituents such as sediment, bacteria, nutrients, metals, and organic compounds. These computed or estimated values are being used by water-management agencies for a wide variety of purposes related to water regulation, total maximum daily loads (TMDLs), recreation, water treatment, and ecosystem health. Specific examples are provided under the links to state surrogates.

 

Continuous real-time estimates of concentrations and loads with a defined uncertainty gives hydrologists and management agencies an extremely powerful tool to increase our knowledge and understanding of the interaction between water quality and hydrology, geology, and land use. Many of these newly collected data can possibly lead to more effective management strategies to improve our water quality. The science and monitoring will provide the needed basis for addressing the multitude of decisions involving safe drinking water, irrigation, aquatic ecosystem health, wetland protection, native and endangered species preservation, and recreation.