Hydraulic performance of a morphology-based stream channel design

The inconsistent performance of stream rehabilitation projects has generated debates over the use of morphological templates rather than detailed hydraulic information for channel designs. A rehabilitation project conducted in a reach of Deep Run, Maryland (United States), was monitored in order to assess commonly used approaches to channel design that rely on classification systems to describe the channel form, empirical relations to predict channel dimensions, and a single design discharge to evaluate the hydraulic conditions. Results from field measurements and observations indicated that the morphological conditions created in Deep Run were unstable. The morphology of the constructed channel was altered by storm flows smaller than the designed bank-full discharge and by floods that extended the flow width to the limits of the created meander belt. Hydraulic conditions associated with stabilization practices, vegetation, and gravel deposits influenced stability and unplanned adjustment patterns during flows contained within the active channel. Stability during flooding was diminished by reductions in floodplain roughness from vegetation removal and a decrease in flow path sinuosity. These findings illustrate the need for enhanced consideration of the relations between channel stability and hydraulic conditions at multiple scales and over a range of flow conditions in stream rehabilitation projects.