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.
Riparian zones are the areas between streams and uplands. Healthy riparian zones provide shade, filter runoff, stabilize streambanks, reduce erosion, provide wildlife habitat, and give floodwaters room to spread, slow, and soak into the floodplain. Roads, development, and sparse vegetation can fragment these areas resulting in reduced stream resilience. The riparian assessment includes three metrics: floodplain confinement, floodplain fragmentation, and riparian condition.
Riparian Habitat Condition | Floodplain Fragmentation | Floodplain Confinement |
|---|---|---|
50 | 25 | 25 |
Floodplain confinement measures how restricted the area alongside a stream channel is by topography or human development. When a floodplain is unconfined, high flows can spread beyond the banks, slowing water, promoting infiltration, and supporting healthy streamside vegetation. A confined floodplain accelerates flow and increases vulnerability to flood damage and erosion. Stream reaches are graded based on the ratio of confined channel length to total reach length, where lower confinement indicates a healthier, more functional floodplain.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 90-100 | Optimally functional | Unconfined. Confinement index of less than 0.1 |
B | 80-89 | Highly functional | Partly confined, planform controlled. Confinement index of 0.1-0.5 |
C | 70-79 | Mostly functional | Partly confined, margin controlled. Confinement index of 0.5-0.8 |
D | 60-69 | Partly functional | Confined. Confinement index greater than 0.8 |
F | 50-59 | Dysfunctional | Not used |
N/A | N/A | Not Graded |
Floodplain fragmentation measures how human development divides the floodplain into smaller, disconnected areas. A minimally fragmented floodplain allows water and sediment to move freely through the reach, supporting healthy hydraulics, sediment balance, and riparian habitat. High fragmentation disrupts these processes and degrades overall riparian health. Stream reaches are graded based on the density of fragmenting features (roads, buildings, other infrastructure) with lower fragmentation receiving higher scores.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 95 | Optimally functional | Floodplain intact (low fragmentation) |
B | 85 | Highly functional | Floodplain mostly intact (low to moderate fragmentation) |
C | 75 | Mostly functional | Floodplain moderately intact (moderate fragmentation) |
D | 65 | Partly functional | Floodplain significantly fragmented (moderate to high fragmentation) |
F | 55 | Dysfunctional | Floodplain severely fragmented (high fragmentation) |
N/A | N/A | Not Graded | Not Graded |
Riparian condition measures the ecological health of the vegetated area alongside the stream, including vegetation diversity, land cover, and land use. A healthy riparian area features diverse, self-sustaining vegetation that slows flood flows, reduces erosion, and provides habitat and movement corridors for wildlife. Stream reaches were assessed using GIS-based mapping across 163 stream miles and graded based on the degree of human alteration and overall vegetation health.
Grade | Scale | Description | Explanation |
|---|---|---|---|
A | 90-100 | Optimally functional | Native riparian conditions are natural and appropriate for a well-functioning river. Vegetation is self sustaining and species composition and diversity is characteristic of native riparian plant communities. Excellent channel connection and riparian supports characteristically patchy vegetation, with strong interspersion of patches and vertical structure. Habitats outside of the riparian zone are generally intact. |
B | 80-89 | Highly functional | Riparian habitat resembles native conditions but with detectable changes. Vegetation species composition, diversity and structural complexity are self-sustaining. Native species predominate, although minor presence of problematic species may occur. Scattered individuals of noxious species may be present, but do not threaten function. Habitat retains good connection to the channel maintaining moisture conditions and a high degree of patchiness and interspersion, with little homogenization or loss of vertical structure. Land use changes in areas adjacent to the riparian zone have minimal deleterious effects on system health. |
C | 70-79 | Mostly functional | Riparian habitat is notably different from native conditions. Decreased plant diversity, loss of characteristic species or structural complexity, and/or homogenization of vertical structure, patchiness, and interspersion are evident, but patches of woody vegetation exist. Although diminished, channel connection is still present, supporting soil moisture, intermittent disturbance, and mesic vegetation. Small populations of noxious species may occur, and a large proportion of the species are commonly exotic or invasive natives. Lands adjacent to the riparian zone are typically altered but do not substantially degrade riparian or instream habitat. |
D | 60-69 | Partly functional | Riparian habitat is highly altered from native conditions. Decreased plant diversity, loss of characteristic species and structural complexity widespread. Homogenization of vertical structure and patchiness is expected to be severe. The habitat may be isolated from the river, and noxious weeds, invasive species, or exotics may be prevalent or dominant. Clearing all or most woody vegetation is expected. Bare ground or impervious surfaces may make up a significant portion of land cover. Vegetation is commonly under cultivation or landscaped. Land use outside of the riparian zone may be intensive and exacerbating degradation. Riparian zone conditions contribute to river dysfunction. |
F | 50-59 | Dysfunctional | Riparian area is developed or wholly converted with predominantly bare ground, impervious surfaces or otherwise lacking vegetation owing to land use and management actions. Connection with the channel is expected to be severed. Riparian habitat function is essentially extinguished, and land use contributes substantially to river dysfunction. |
N/A | N/A | Not Graded | Not Graded |