From the variable grades, an overall grade is created for each reach. This grade reflects a composite score from each of the assessment variables using a weighted average as covered in the table below. If a reach lacked sufficient data for a given variable or metric, that variable or metric was excluded from the grading.
River flows over time are a primary driver of river system health, patterns, and dynamics. The flow regime assessment includes three metrics: peak flushing flows, summer base flows, and winter base flows. Minimum flow targets have been identified in selected stream reaches to establish goals for habitat function and health. Flow regime grades are only available for reaches where flow targets have been established.
Peak Flow | Summer Base Flow | Winter Base Flow |
|---|---|---|
17 | 66 | 17 |
Annual peak flows in the region are driven by snowmelt, typically peaking between June and July. These high flows play a critical role in stream health by flushing fine sediments and algae from the streambed, maintaining habitat for macroinvertebrates, fish spawning, and sculpin. Stream reaches are graded by tracking the highest 3-day average flow each year and comparing it to an established flushing flow target, with a goal of meeting that target at least once every two years.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 90-100 | Optimally functional | Reach experiences natural flows upstream of a diversion or 3-day peak flow achieves flushing flow target once every two years in at least 90% of years or the drainage areas is unaltered by dams or diversion structures |
B | 80-89 | Highly functional | 3-day peak flow achieves flushing flow target once every two years in at least 80% of years |
C | 70-79 | Mostly Functional | 3-day peak flow achieves flushing flow target once every two years in at least 70% of years |
D | 60-69 | Partly Functional | 3-day peak flow achieves flushing flow target once every two years in at least 60% of years |
F | 50-59 | Dysfunctional | 3-day peak flow does not achieve flushing flow target once every two years in at least 60% of years |
N/A | N/A | Not Graded | Not Graded |
After snowmelt recedes, streams rely on minimum base flows groundwater and rainfall to sustain aquatic life through the warmer months. Summer flows (April–September) are measured against established targets designed to maintain habitat quality and availability for native species. Stream reaches are graded on the percentage of summer days that daily mean flows meet or exceed the upper base flow target, which sets a conservative target to protect aquatic ecosystems.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 90-100 | Optimally functional | Reach experiences natural flows upstream of a diversion or upper minimum flow target is achieved at least 80% of the days April through September or the drainage areas is unaltered by dams or diversion structures |
B | 80-89 | Highly functional | Upper minimum flow target is achieved at least 60% of the days April through September |
C | 70-79 | Mostly Functional | Upper minimum flow target is achieved at least 40% of the days April through September |
D | 60-69 | Partly Functional | Upper minimum flow target is achieved at least 20% of the days April through September |
F | 50-59 | Dysfunctional | Upper minimum flow target is not achieved at least 20% of the days April through September |
N/A | N/A | Not Graded | Not Graded |
Maintaining adequate flow in winter is important for supporting trout egg incubation and spawning habitat. Winter flows (October–March) are tracked against minimum base flow targets and graded based on how often daily mean flows meet the upper target threshold. Monitoring winter flows presents unique challenges, and some stream reaches lack sufficient data for the full winter period due to difficult field conditions, leaving them ungraded.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 90-100 | Optimally functional | Reach experiences natural flows upstream of a diversion or upper minimum flow target is achieved at least 80% of the days October through March or the drainage areas is unaltered by dams or diversion structures |
B | 80-89 | Highly functional | Upper minimum flow target is achieved at least 60% of the days October through March |
C | 70-79 | Mostly Functional | Upper minimum flow target is achieved at least 40% of the days October through March |
D | 60-69 | Partly Functional | Upper minimum flow target is achieved at least 20% of the days October through March |
F | 50-59 | Dysfunctional | Upper minimum flow target is not achieved at least 20% of the days October through March |
N/A | N/A | Not Graded | Not Graded |