Pfankuch-Rosgen Stability Exercise

Exercise Objective

Exercise Process

1. Either prepare the downloaded PDF or use the images on this page to follow the exercise.
2. Read the following river assessment for the C3 channel inventoried for your consideration:
   • Upper Banks Category conditions: landform slope is 50%, mass wasting is infrequent, debris jam potential is present but small items, vegetative bank protection is < 50% with lower vigor.
   • Lower Banks Category conditions: channel capacity is adequate, bank rock content is 40 to 65% with 6 to 12 inch cobbles, obstructions to flow is some present, cutting is little to none, and Deposition is some new bar increase.
   • Bottom Category conditions: rock angularity is corners and edges well rounded, brightness of bed material is mostly dull, consolidation of particles is moderately packed, bottom size distribution is moderate change in sizes, scouring and Deposition is 5 to 30%, and aquatic vegetation is present but spotty.

3. Determine the numeric value associated with the qualitative description of the Stream categories in the upper banks, lower banks, and bottom. This value is reported in the right hand column.
4. Record each numeric value and sum the values for each of the 15 Stream categories (landform slope through aquatic vegetation).
5. Use the modified Pfankuch-Rosgen rating sheet to determine the channel stability rating value as excellent, good, fair, or poor. Ranking based these qualitative terms depends on the river classification, the Pfankuch-Rosgen numeric score and use of the table, "Conversion of Stability Rating to Reach Condition by Stream Type" posted below.

Image modified courtesy of Rosgen