Tools › Civil and Geotechnical › Hydraulics › Culvert and Storm Drain Hydraulics › Example
HDS-5 Design Guideline 1.3 circular culvert (200 ft³/s, 54 in concrete pipe) and the HEC-22 Example 7-3 storm drain energy grade line
| Tool | Culvert and Storm Drain Hydraulics |
| Source | Schall, J. D., Thompson, P. L., Zerges, S. M., Kilgore, R. T., and Morris, J. L. (2012). Hydraulic Design of Highway Culverts, 3rd ed. Hydraulic Design Series No. 5, FHWA-HIF-12-026, Design Guideline 1.3 (pp. DG1.1–DG1.4); Brown, S. A., Schall, J. D., Morris, J. L., Doherty, C. L., Stein, S. M., and Warner, J. C. (2009). Urban Drainage Design Manual, 3rd ed. Hydraulic Engineering Circular No. 22, FHWA-NHI-10-009, Example 7-3 (English units, pp. 7-69 to 7-92). |
| Level | Professional |
Problem
Culvert: a 25-year flood of 200 ft³/s crosses a new rural road through 200 ft of culvert on the 1 % stream slope, inlet invert at 100.0 ft, tailwater 3.5 ft, allowable headwater elevation 108 ft; find the inlet control and outlet control headwater of a 54 in concrete pipe with a groove end projecting (n 0.012, k_e 0.2), the controlling headwater and the outlet velocity, and the performance curve to 400 ft³/s. Storm drain: three inlets (0.64, 0.35 and 0.32 acres, C 0.73, inlet times 3, 2 and 2 min) and an access hole on four concrete pipes (n 0.013, 361, 328, 14.1 and 55.8 ft at slopes 0.03, 0.03, 0.001 and 0.01, 18 in minimum, 3 ft cover) to an outfall at invert 330.71 ft drowned by a pool at 333.5 ft, with the HEC-22 intensity table (7.1 in/h at 5 min); size the pipes, set the inverts with the crown-drop rule and carry the energy grade line up through the structures by the FHWA access-hole method.
Inputs to Enter
- Culvert: circular, D 4.5 ft, concrete pipe groove end projecting (HDS-5 Table A.1 Chart 1 scale 3: K 0.0045, M 2.0, c 0.0317, Y 0.69; k_e 0.2), n 0.012, L 200 ft, S 0.01, Q 200 ft³/s, EL_i 100 ft, EL_ha 108 ft, TW 3.5 ft, performance curve to 400 ft³/s in 8 steps, no road
- Storm drain (select the Storm drain tool): IDF i = 101.94/(t + 16.17)^0.8728 in/h, 5 min minimum, n 0.013, D_min 1.5 ft, cover 3 ft, outfall invert 330.71 ft, tailwater 333.5 ft; rows 40 (0.64 ac, 3 min, 361 ft, 0.03, ground 370.0), 41 (0.35 ac, 2 min, 328 ft, 0.03, 360.0, inlet straight), 42 (0.32 ac, 2 min, 14.1 ft, 0.001, 349.31, inlet 90°, inflow angle 90°), 43 (access hole, 55.8 ft, 0.01, 347.78); diameters sized
Answers
- Culvert inlet control: Q/(A D^0.5) = 5.93 (submerged), HW_i/D = 0.0317 · 5.93² + 0.69 − 0.5 · 0.01 = 1.799, HW_i = 8.10 ft, EL = 108.10 ft (nomograph 1.77 / 108.0 ft; HY-8 7.9 ft)
- Outlet control: V = 12.58 ft/s, H = (1 + 0.2 + 29 · 0.012² · 200/1.125^1.33) V²/2g = 4.70 ft (nomograph 4.7), d_c = 4.04 ft, h_o = (d_c + D)/2 = 4.27 ft, HW_o = 4.27 + 4.70 − 2.0 = 6.97 ft, EL 106.97 ft (nomograph 107.0)
- Inlet control governs: HW = 8.10 ft, 0.10 ft above the allowable; outlet velocity at normal depth 3.46 ft: V_o = 15.2 ft/s (nomograph 15.3, HY-8 14.9)
- Storm drain design: Q = 3.32, 5.13, 6.79, 6.79 ft³/s (book 3.3, 5.1, 6.75 with C A rounded), D_req 0.79, 0.94, 1.97, 1.28 ft → 18, 18, 24, 24 in; inverts 365.50/354.67, 354.06/344.22, 344.07/344.05, 331.27/330.71 ft (book 365.5/354.67, 354.07/344.23, 344.07/344.06, 331.27/330.71)
- Energy grade line: outfall pipe full, EGL_o 333.57, EGL_i 333.62, E_i 2.36, DI 0.269, E_ai 2.37, plunging C_P 5.21, EGL_a(43) 333.71 (book 333.68); 42: part full subcritical, E_i 1.66, C_θ 2.40 (90°), C_P 0.44, EGL_a 345.80 (book 345.81); 41 and 40: supercritical pipes, E_a = E_i, EGL_a 355.82 and 366.89 (book 355.85, 366.85); freeboard 3.1 ft at 40
Notes
The tool's default inputs are the culvert; choosing the Storm drain tool loads the Example 7-3 rows. HDS-5 prints nomograph readings (±10 % by its Appendix A.4) and HY-8 solutions; HEC-22 reads its hydraulic-elements and critical-depth charts and rounds to two decimals, which accounts for the last-digit differences; its Table 7-15 prints HGL_o = 335.50 ft at the outfall for 333.50 (misprint). Every number is reproduced by test_culvert_storm_drain.php (397 checks) with an independent scipy re-implementation in References/Culvert-Storm-Drain/checks/.