# HY8:Contra Costa Basin

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The input variables required for this calculation is the following:

- Baffle Block Height Ratio — The ratio of the baffle block height to baffle block distance from the culvert.
- End Sill Height to Maximum Depth Ratio — ratio to determine the end sill height from the maximum depth.
- Basin Width — The channel width is recommended for the basin width.

The following figures show the design of a Contra Costa basin.

Variables from the figure

- D — Diameter of culvert
- y
_{0}— Outlet depth - y
_{2}— Approximate maximum water surface depth - y
_{3}— Basin exit velocity - V
_{0}— Outlet velocity - V
_{2}— Exit velocity - h
_{1}— Height of small baffle - h
_{2}— Height of large baffle - h
_{3}— Height of end sill - L
_{2}— Length from culvert exit to large baffle - L
_{3}— Length from large baffle to end sill - L
_{B}— Basin length