A Momentous Anniversary for USGS Continuous Water-Quality Monitoring in Oregon

The water-quality monitor in the Tualatin River at Oswego Dam (station 14207200) was installed in May, 1991 as part of a cooperative study between the U.S. Geological Survey (USGS) and Clean Water Services — the primary wastewater and stormwater management utility in the Tualatin River basin. A large water-quality monitoring network in the basin has grown from that initial study to support a wide range of USGS studies that have provided foundational science for improved basin-wide management of water resources. Although the USGS has monitored streamflow and water temperature at many sites for much longer than 30 years, it is extremely rare to have a continuous dissolved-oxygen record for such a long period of time

Not only have the data obtained from the Oswego Dam monitor supported a rich history of USGS water-quality investigations and modeling, they have proven extremely valuable in supporting water-quality management and providing real-time feedback to wastewater treatment plant operators. For example, since 2001 Clean Water Services has been allowed some flexibility to discharge different ammonia loads depending on the capacity of the river to assimilate those loads. When the two redundant real-time dissolved-oxygen (DO) sensors at the monitoring site indicate that the river has no extra assimilative capacity for ammonia, then upstream treatment facilities are held to their most strict TMDL limits. However, when the river does have assimilative capacity, Clean Water Services has the flexibility to discharge ammonia loads that are higher than their strictest TMDL limits. In this way, the data from the continuous monitoring are not only used to show the water-quality conditions in the river but also to inform real-time management and regulatory decision making.

The deployment at Oswego Dam has also helped to inform water-quality monitoring across the USGS.

• The site has been used many times to test new instruments and sensors, and was used for the side-by-side sensor performance tests of products from different manufacturers. These tests benefit all instrument users in the USGS.  An example was one of the early side-by-side sensor tests for luminescent DO sensors.
• The two redundant DO sensors at the site have demonstrated how modern DO sensors are stable over time and, although such setups are rarely used by the USGS, we have shown that it is possible to use redundant sensors to heighten the accuracy and defensibility of our data.
• While the use of real-time water-quality data in management and regulatory decision making has not been widely employed across the nation, this approach represents a potential growth sector for USGS water-quality monitoring.
• The valuable insights gained from using the data at this site have not only been critical to understanding water-quality conditions in the Tualatin River, they have also been used in the assessment of other river systems.

You can explore these data in more detail with the USGS Data Grapher system.