Or. Admin. R. 340-056-0400 - Flow Determination Methodology
(1) The Department will determine the
instream flow need for pollution abatement based on stream specific analysis,
using the methodology described below for which there is adequate data, and
which, in the Department 's judgement, is most appropriate and
reliable.
(2) The flow
determination methodologies described below are based on existing users,
including facilities with discharge permits and existing land uses that
generate nonpoint runoff or otherwise impact the water quality of the
stream.
(3) Available and relevant
data on streamflow, water quality and pollution loading will be compiled to
determine the appropriate methodology and water quality parameters to be used
in making the instream flow need determination.
(4) The methodologies the Department will use
to determine the instream flow need for pollution abatement include, but are
not limited to, the following:
(a) Streamflow
-- Water Quality Correlation Analysis: Available data is analyzed to determine
whether a correlation exists between observed water quality and instream flows.
The streamflow condition at which water quality problems are minimized is
identified. This analysis accounts for point source, nonpoint source, and
background loads affecting the stream segment at the time the water quality
data were collected;
(b) Load
Assimilation Analysis: Information on pollution loads is used to estimate or
predict the flows needed to assimilate the loads in the stream. Dilution rule
requirements or simplified water quality models, based on available data, are
used to determine the flows needed to assimilate the permitted effluent
discharges (point sources) and estimated nonpoint source loads to the stream.
If the permitted discharges do not meet the minimum design criteria for
treatment and control of wastes specified in the basin rules (OAR 340-041) at
the time of the instream water right application, the Department may estimate
the instream flow need that will occur when the facility upgrades to the
minimum design criteria and base the water right application on that flow
level;
(c) Water Quality Modeling:
Special intensive stream investigations, such as those conducted in basins
receiving Total Maximum Daily Loads (TMDLs) provide detailed data on instream
water quality, point and nonpoint source loads, and streamflows. When this data
is available, it will be used to model the relationship between streamflow and
water quality, and estimate the instream flows needed to assimilate permitted
effluent discharges, estimated nonpoint source loads, or other factors
affecting water quality, such as temperature. In TMDL basins, dischargers
likely have to meet more stringent discharge limits than basin design criteria
require. These facilities may have permit limits for additional parameters than
are included in a typical permit ;
(d) Non-Degradation Flows Method: This
methodology applies only to Outstanding Resource Waters subject to the
non-degradation standard. For these waterbodies, the Department will strive to
maintain existing water quality and, therefore, existing streamflows. Any
reduction in streamflow could potentially contribute to a degradation of water
quality. A simple method to achieve this objective is to apply for an instream
water right for the median monthly streamflow or lake levels by
month.
Notes
Stat. Auth.:ORS 537.332 -ORS 537.360
Stats. Implemented:ORS 537.332 -ORS 537.360
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