Design Reaches

A set of thirteen ‘Design Reaches’ has been developed to characterize reaches of the river that are geometrically and hydraulically similar.  This will enable designers and planners to consider and understand entire reaches of the River, rather than single-point-based characteristics.  The Design Reaches are labelled Reach A (near the mouth) through Reach M (near the confluence of Bell Creek and Arroyo Calabasas) as indicated below and range in length from approximately one to nine miles.

The Design Reaches were determined through a detailed analyses of the River channel geometry (width, depth, vegetation1, and slope) as extracted from the US Army Corps hydraulic 1-D HEC-RAS2 model as indicated in the figure below.   Additional hydraulic analyses of each Design Reach were also conducted to quantify the flow characteristics under a range of flow conditions.

US Army Corps hydraulic 1-D HEC-RAS model

1 Vegetation occurs in the soft-bottom reaches, and is represented in the HEC-RAS model by high roughness values (i.e., high Manning’s n).
2 1-D HEC-RAS model refers to the one-dimensional Hydraulic Engineering Center – River Analysis System model for the Los Angeles River based on HEC-RAS version 4.1.