Stormwater runoff pollution is a serious issue that faces almost every urban and suburban environment. In older city infrastructure, runoff from roofs, parking lots, and streets flows directly into the sewer system and must be handled by the municipal wastewater treatment facility, increasing the amount of work the system must undertake. For the past 30 years, the infrastructure for stormwater runoff has bypassed the sewer system and flows directly into streams, lakes, and other water bodies which risks the introduction of pollutants directly into the ecosystem.
In order to learn more about stormwater runoff and how to help mitigate it, Oregon State University in conjunction with Benton County, Oregon BEST, and other partners have launched a new facility for testing green stormwater treatment infrastructure, such as bioswales and rain gardens. Using data acquisition instrumentation and communication systems provided by Stevens Water Monitoring Systems, these sites are being continually monitored to help study the impact the green infrastructure on stormwater runoff.
Stormwater runoff from impervious surfaces causes localized flooding, combined sewer overflows, and waterway pollution. Bioretention is a type of green stormwater infrastructure that mitigates these issues by reducing runoff volume, peak flows, and pollutant loads through the use of green roofs, rain gardens, bioswales, and stormwater planters.
However, there is a lack of data for designing, modeling, maintaining, and quantifying the performance of these facilities over long term. In this field scale study, three newly constructed bioretention cells are being intensely monitored and compared side-by-side to improve the urban hydrological modeling and future implementation of these types of technologies in Benton County and beyond.
The tractors, equipment, and materials used to build roads in Benton County, Oregon are kept at the Benton County Public Works Department on the east side of Avery Park in Corvallis, Oregon. The first fall rains produce murky brown runoff, as can be seen in the Figure 1 below. The stormwater runoff from 2.3 acres (9,300 square meters) of the property area previously flowed, without treatment, into the local Mill Race that connects with the Mary’s River and Willamette River downstream.
The facility consists of an underground storage tank, a concrete sediment bay, and three stormwater treatment cells. The 1,500 gallon (5,700 liter) storage tank intercepts runoff from the site’s existing underground stormwater pipes. A small 1/3 horsepower effluent pump that sits at the bottom of the tank transfers the water into the sediment bay. Large particles are allowed to settle in the sediment bay before entering the three treatment cells. Water from the bay cascades over weirs into the cells, where it is slowed down, stored, and filtered by the soil and the plants.The runoff is now intercepted by a 3,300 square foot (307 square meters) stormwater treatment facility, known formally as The OSU-Benton County Green Stormwater Infrastructure Research (OGSIR) Facility, an Oregon Best Lab. The facility was designed and constructed in a collaborative effort between Oregon State University and the Benton County Public Works Department. Construction of the facility was completed in October 2014.
All of the instrumentation used in the facility was provided by Stevens Water Monitoring Systems, Inc. The measurements being made include continuous flow rate, evapotranspiration, soil water storage, and matric potential. The flow rate is measured with a combination of 45° stainless steel v-notch weirs and Stevens SDX pressure transducers.
Evapotranspiration is estimated using the data from a 5-parameter MetOne (MSO) all-in-one multiparameter sensor, a MetOne 370 precipitation gauge, and an Apogee SP-212 pyranometer. Volumetric soil moisture content is monitored with 20 Stevens HydraProbe soil probes, and allows for estimation of the soil water storage. Eight Tensiomark sensors are used to measure the matric potential of the soil, which allows for an estimation of the soil’s hydraulic conductivity. All of the facility’s data is logged with a Campbell Scientific CR1000 data logger, and it is transmitted to Oregon State University researchers using Stevens Cell-Net cellular telemetry which allows for remote monitoring of the facility.
The collected data enables monitoring and analysis of the inflows, outflows, water storage, and evapotranspiration calculation for the facility. The inflow and outflow data can be compared for individual storm events to quantify the reduction of the peak flows, which are responsible for overwhelming wastewater treatment plants – a critical benefit of bioretention facilities. In addition to the outflow data, the soil water storage and evapotranspiration data allow us to account for all of the water that is flowing into the facility.
The OSGIR facility using instruments provided by Stevens will enable monitor the full water balance over time. One of the research questions that is not well know is how the water balance changes during the first establishment period (first 1-2 years) of bioretention systems. The data collected at this site will enable researchers to quantify how the system performance changes over time.