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Inlet Spread - HEC-22 gutter spread and interception at every inlet

HEC-22 chapter 4 at every inlet of a pipe network: Q = C i A (or a direct Q), spread from the modified Manning gutter equation, curb-opening / grate / combination interception on grade or weir / orifice in a sag, the bypass carried to the next inlet, and SPREAD OVER ALLOWABLE flagged. One editable grid prefilled from the network; a center-justified table + CSV; the rows travel with the table.

Command VDCINLETSPREAD · VDC Utilities tab › Pipes panel
HEC-22 chapter 4 at every inlet of a pipe network: Q = C i A (or a direct Q), spread from the modified Manning gutter equation, curb-opening / grate / combination interception on grade or weir / orifice in a sag, the bypass carried to the next inlet, and SPREAD OVER ALLOWABLE flagged. One editable grid prefilled from the network; a center-justified table + CSV; the rows travel with the table.
Gutter section at an inlet: spread T and depth d (left) → Interception and bypass down the street (right) Q = (0.56 / n) Sx^(5/3) SL^(1/2) T^(8/3) spread T d Sx cross slope curb, opening h depressed gutter (a > 0): composite section Eq 4-4, Se for the curb opening On grade: Qi = E Q, bypass Q - Qi to the next inlet CB-1 E = 0.61 CB-2 E = 0.74 CB-3 sag: all in Q = 1.77 cfs -> Qi 1.08, bypass 0.69 CB-2: own 1.20 + 0.69 = 1.89 -> Qi 1.40, bypass 0.49 CB-3 (sag): 0.80 + 0.49 = 1.29, weir d = 0.21 ft, T = 10.5 ft SPREAD OVER ALLOWABLE (10 ft) curb opening: E = 1 - (1 - L / LT)^1.8; grate: E = Rf Eo + Rs (1 - Eo), splash-over from Chart 5 rows prefilled from the network; SL from the surface or the outflow pipe (marked)
Gutter / street   Inlet on grade (intercepts, bypasses)   Sag inlet / flag

What it does

  • Grid from the network: every inlet structure (by name / part tokens) is a row; SL from the surface up the gutter, else the outflow pipe, else assumed - marked.
  • Flow: Q = C i A or a direct Q, plus the bypass from the inlets that name this one.
  • Spread: Eq 4-2 (composite 4-4 with a depression), depth at the curb, velocity Q / A.
  • Interception: curb opening LT and E (Eq 4-22a / 4-23, Se with a depression); grate Eo, Rf (splash-over), Rs, E (Eq 4-16 to 4-21); combination = sweeper + grate; sag inlets as weir / orifice, the larger depth governing.
  • Table + CSV: inlet, type, Q own / bypass in / total, SL, Sx, T, T allow, d, E, Qi, Qb, flag; center-justified; the rows in its tag; Update rewrites it in place.

Notes

  • English units throughout (acres, in/hr, cfs, ft); names must be unique; bypass chains of any length, cycles stop.
  • Splash-over curves are Chart 5 fits in the settings file (eight grates) - edit them for your grate; the sag clear-opening ratio is a setting.
  • Draft work product: it computes from the values you enter. Settings under %APPDATA%\VDC\InletSpread\ (override VDC_INLETSPREAD_SETTINGS). Civil 3D only.

Dialog

Inlet Spread - HEC-22 gutter spread and interception at every inlet dialog
Inlet Spread - HEC-22 gutter spread and interception at every inlet - VDCINLETSPREAD

When to use it

  • A storm drainage report or plan needs inlet spread and capacity at every inlet.
  • A grading change moved a gutter slope and the spread table has to follow.

How to run it

  1. Run VDCINLETSPREAD. Pick the network (and a surface for the gutter slopes). The inlet structures fill the grid.
  2. Type each inlet's drainage area, C and i (or a direct Q), check SL / Sx / W / a / n, set the type, the curb or grate size and the allowable spread; name the inlet each one bypasses to.
  3. OK - Compute, then pick the table's upper-left corner. Read the flags and the ASSUMED-slope count in the summary.
  4. After a change: run again (the rows come back from the table), edit, and Update rewrites the table in place.

Options

  • Inlet types: curb opening, grate or combination, on grade (interception and bypass) or in a sag (weir / orifice depth, everything intercepted).
  • Depressed gutter: a local depression a > 0 switches to the composite section (Eq 4-4) and the equivalent slope Se for the curb opening.
  • Grate curves: eight splash-over curves (Chart 5 fits) in the settings file - edit them for your grate.
  • Bypass to: on-grade bypass is added to the named inlet; chains of any length.

Watch out for

  • The longitudinal slope is read from the surface up the gutter opposite to the outflow pipe, or from the pipe itself - a pipe slope is not a gutter slope; check the rows marked assumed / pipe.
  • English units only: acres, in/hr, cfs, ft; Q = C i A without the 1.008 factor, as HEC-22 does.
  • This is draft work product: the splash-over curves are chart fits, the clear-opening ratio is a default, and the agency's own method (or a different C / i) may govern.

Related: Pipe Table · Curve Numbers · Time of Concentration