Projects & Programs
Temperature Modeling of the Columbia River Using the RMA-10 Hydrodynamic and Temperature Model, Oregon/Washington
Columbia River temperatures exceed numeric temperature standards during certain periods of a calendar year. As a result, the Columbia River was placed on the list of "water quality limited" water bodies for temperature in 1996, per requirements of Section 303(d) of the Clean Water Act. This includes nearly the entire main stem of the Columbia River from the Canadian Border to the Pacific Ocean, including the Snake River from its confluence with the Salmon River to its confluence with the Columbia River. Washington, Idaho and Oregon have, in collaboration with the Environmental Protection Agency, initiated the Total Maximum Daily Loads (TMDL) development activity, as required by the Clean Water Act.
TMDLs for point sources are most commonly implemented through the National Pollutant Discharge Elimination System (NPDES) permits. The existing NPDES permits for various sources of heat to the Columbia River were reviewed and revised as dictated by the TMDL evaluation. Since one-dimensional (1-D) modeling shows little impact from typical point sources, two-dimensional (2-D) hydrodynamics and temperature modeling was done to better evaluate near- and far-field impacts from a pulp mill discharge. The model RMA-10 was used for this examination, because it can handle 1-D, 2-D, and 3-D simulations of hydrodynamics and temperature. PNNL staff were contracted by the Northwest Pulp & Paper Association to demonstrate that the temperature impacts from pulp and paper mill discharge are limited to the mixing zone region. The impact of the point source on Columbia River temperature decreases moving downstream from the discharge location due to far-field mixing and heat loss to the atmosphere. The difference in temperature with and without the point source is, at most, approximately 0.06ºC at 76 meters downstream from the discharge location. In comparison, the difference between the RMA-10 temperature results with and without the point source is less than 0.01ºC at four kilometers downstream of the discharge location. Columbia River temperatures have essentially recovered from the impact of the point source by four kilometers downstream of the discharge location.
Project Highlights:
- The study showed, conclusively, that most point-source discharges are unlikely to cause detectable increases in the large-scale Columbia River temperature regime
- The results showed that resolution of approximately less than 100 meters is required to detect near-field impacts of typical point sources
- The Columbia River recovers from point-source temperature impacts within a short distance (four kilometers) or period from the point of discharge.