Type Aa+ streams are very steep (greater than 10% grade), well entrenched, have a low width-depth ratio, and are totally confined. The streambed is typically a step/pool morphology with chutes, debris flows, and waterfalls. The Aa+ stream types often occur in debris avalanche terrain, zones of deep depositions such as glacial tills and outwash terraces, or landforms that are structurally controlled or influenced by faults, joints, or other structural contact zones. Streamflow at the bankfull stage in the Aa+ stream type is generally observed as a torrent or waterfall. These stream types can be associated with bedrock and zones of deep deposition and/or be deeply incised in residual soils. The Aa+ can often be described as high-energy/high-sediment supply systems due to their inherently steep channel slopes and narrow/deep channel cross sections.
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