Culvert Studio — Dyer Engineering

Culvert Studio Hydraulic design · HDS-5

Design identity

Culvert / crossing name

Notes (optional)

Barrel geometry

Shape

Material

Diameter (ft)

Barrels

Manning’s n

Suggested

Inlet configuration

Inlet edge / end treatment

Barrel profile

Length (ft, along barrel)

Slope (% = ft/ft ×100)

Upstream invert elevation (ft, optional)

Hydrology & tailwater

Design discharge Q (cfs, total)

Tailwater basis

Tailwater depth (ft above d/s invert)

Design checks

Max allowable headwater (ft above u/s invert)

Roadway / overtopping elevation (ft, optional)

Method: FHWA HDS-5 inlet- & outlet-control. US customary units.

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Live results update as you change inputs

Design aid — not a stamped analysis. Calculations follow the FHWA HDS-5 nomograph equations (full-flow outlet control assumption). Results should be reviewed and verified by a licensed professional engineer before use in design.

Basin identity

Basin / study point name

Notes (optional)

Drainage area

Land use / subareaArea acC

Pick a land use for a suggested C (Wise Co. Dev. Rules §6.08.B.4.a, or iSWM Table 1.6) or type your own. Multiple rows build a composite C.

Time of concentration

Tc basis

Time of concentration (min)

Minimum Tc (min)

Wise Co. §6.08.B.4.b minimums (proposed conditions): Park/Open 20 · SF residential 15 · Ind./Bus./Merc. 10 (county may direct 10). Existing/pre-development Tc uses raw TR-55 — set floor to 0. iSWM floor is 5 min. Local standard governs.

Rainfall & storms

County

Statistical series

i = b/(Tc+d)^e · TxDOT EBDLKUP 2019 (NOAA Atlas 14). AMS is the TxDOT standard; iSWM 2020 tables are AMS-based. Fitted 5–720 min.

Design storm (headline)

iSWM Cf factors

Off (default) per Wise County practice: Q = C·i·A. Apply adds iSWM Table 1.4 factors — Cf = 1.1 / 1.2 / 1.25 at 25 / 50 / 100-yr (500-yr assumed 1.25), Cf·C ≤ 1.0 — if a reviewer requires them.

Method: Rational Q = Cf·C·i·A per iSWM Hydrology (2020); Tc per NRCS TR-55; IDF per TxDOT/Atlas 14. US customary units.

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Live results update as you change inputs

Design aid — not a stamped analysis. Rational method per iSWM Hydrology (2020) with NRCS TR-55 travel times and TxDOT/NOAA Atlas 14 intensities. Results should be reviewed and verified by a licensed professional engineer before use in design.

Study identity

Basin set / study name

Round label (optional)

Notes (optional)

Save a set per review round — duplicate it before revising — so Round-1 numbers stay reproducible while revisions proceed.

Rainfall & storms

County

Statistical series

Design storm (headline)

iSWM Cf factors

Shared by every basin in the set: i = b/(Tc+d)^e, TxDOT EBDLKUP 2019 (NOAA Atlas 14). Cf off (default) per Wise County practice. Additional counties: see coefficient-pipeline.

Basins

Areas are hand-entered (measure in Civil 3D). Land-use rows are percentages of the basin area and build the composite C. Post-project computations must assume a fully developed watershed (min. land use single family) with upstream detention disregarded — Wise Co. §6.08.B.2/B.3: enter offsite areas twice, once as Existing (pre side) and once as Offsite FD (post side). Tc floors for proposed conditions (§6.08.B.4.b): Park/Open 20 · SF residential 15 · Ind./Bus./Merc. 10 min — set each basin’s floor to match its land use; existing basins use raw TR-55 (floor 0).

Study points

Basins sharing a study-point label aggregate there — many-to-one pairing is fine. Type per §6.08.I.7.d: detention outfalls must mimic the existing flow regime (sheet stays sheet). Optional 100-yr velocities run the §6.08.B.2 downstream checks: ≤5% increase, and no increase where existing V > 8 ft/s.

Detention estimate

Modified Rational (iSWM §1.5.2)

Pre/post peak comparison at study points: Rational Q = Cf·C·i·A per basin (iSWM 2020; Wise Co. §6.08); Tc per NRCS TR-55; detention volumes per iSWM §1.5.2 Modified Rational. US customary units.

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Live results update as you change inputs

Design aid — not a stamped analysis. Pre/post peaks by the Rational method (iSWM Hydrology 2020, Wise Co. Dev. Rules §6.08) with NRCS TR-55 travel times; detention volumes by the iSWM §1.5.2 Modified Rational approximation — not a routed analysis. Results should be reviewed and verified by a licensed professional engineer before use in design.

Culvert sizing guide

Inlet-control capacity, low tailwater · concrete RCP, groove-end headwall · slope ≈ 0.5%. A screening estimate — confirm the pick with a full design check.

Allowable HW / D 1.00

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Culvert sizing guide