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Inlet and Gutter Spreads


You’ll notice on the results grid, plots and printed reports two categories of spreads.

  1. Gutter
  2. Inlet

For inlets located in sags, these two will be the same. For inlets on grade, the gutter spread refers to the spread just upstream of the inlet and is based on the gutter properties, flow, etc. Inlet spread refers to the spread at the center of the inlet face.

Cross-section of Inlet Spread

Cross-section of Gutter Spread

Gutter Spread

Studio Express uses the following form of Manning’s equation to compute the depth of flow in the gutter:

D = depth of flow in gutter in ft (m)
Q = flow in gutter in cfs (cms)
Z = reciprocal of the cross slope
S = longitudinal gutter slope
Kc = 0.56 (0.376)

For compound cross slopes, a trial and error procedure is used to compute D in the gutter, (Sw) and (Sx) sections separately. From this depth and cross-section geometry, the gutter spread is computed. This depth and spread is labeled “Gutter Depth” and “Gutter Spread” respectively in the reports.

Inlet Rating Curve
Gutter spreads are typically larger than Inlet spreads