RipRap Calculator

December 28, 2025

This tool turns the GSWCC chart into an interactive workflow: enter the discharge and pipe parameters, and the calculator highlights the relevant curve and returns the apron sizing outputs (La, W, and D50), along with supporting hydraulics data.

Riprap Calculator

Riprap-Lined Outlet Protection

Input

Gravity capacity check: ON computes the design at min(Q, gravity capacity) and warns when Q exceeds it. OFF designs at the entered Q. Your input is never rewritten.
Tw ≥ 0.5·D0
Outlet depth (in)
24.00
Outlet velocity (ft/s)
15.92
F0 (nomograph)
1.98
Fr (outlet)
—
La (ft)
48.71
3·D0 (ft)
6.00
W (ft)
25.48
D50 (ft)
0.69

Storm model import (Hydraflow STM / SSA)

Hydraflow .stm, or SSA .sol (+ optional .map for real geometry): reads pipes, pre-checks outfalls

Schematic

W1 = 3·D0 = 6.00 ftTailwater: Tw ≥ 0.5·D0W = 3·D0 + 0.4·LaLa = 48.71 ftW2 = W = 25.48 ft

Full graph

Hover = tooltip · Click = set Q
05010015020000.511.522.533.541101001000Discharge, Q (cfs)Minimum Apron Length, La (ft)Median Riprap Diameter, D50 (ft)

Online summary

Current:Q (cfs): 50.00D0 (in): 24Length (ft): 50Slope (%): 1.00Outlet depth (in): 24.00Outlet vel. (ft/s): 15.92F0: 1.98Fr: —Material: RCPTailwater: Tw ≥ 0.5·D03D0 (ft): 6.00La (ft): 48.71W (ft): 25.48D50 (ft): 0.69dmax (ft): 1.04Thk (ft): 1.56Stone: Type 3
#Q (cfs)D0 (in)Length (ft)Slope (%)Outlet depth (in)Outlet vel. (ft/s)F0FrMaterialTailwater3D0 (ft)La (ft)W (ft)D50 (ft)dmax (ft)Thk (ft)Stone
Add rows to build a multi-pipe summary table.
• Q = 50.00 cfs exceeds the gravity capacity of 24.34 cfs. Pipe is pressurized; outlet assumed flowing full.
• High outlet energy (V = 15.9 ft/s, F0 = 1.98): consider a riprap basin or HEC-14 energy dissipator.
• F0 = V_full / √(g·D0): full-pipe Froude number, the parameter of the design curves.
• Fr = V / √(g·A/T): actual Froude number at the computed outlet depth.
• W1 (at the outlet) and W2 (end of apron) per GDOT Std. D-55B. Riprap blanket thickness = 1.5·dmax with dmax = 1.5·D50 (here dmax = 1.04 ft, thickness = 1.56 ft). Place riprap over geotextile filter fabric; verify stone gradation per GDOT Std Spec Section 805.
How to citeShow

Author ORCID: 0009-0000-1316-1362

DOI: 10.5281/zenodo.20974544

APA
Chernitsky, I. (2025). RipRap Calculator [Computer software]. Chernitsky.net. https://doi.org/10.5281/zenodo.20974544
IEEE
I. Chernitsky, "RipRap Calculator," Chernitsky.net, 2025. [Online]. Available: https://doi.org/10.5281/zenodo.20974544
BibTeX
@misc{chernitsky2025rip,
  author       = {Chernitsky, Ilia},
  title        = {RipRap Calculator},
  year         = {2025},
  doi          = {10.5281/zenodo.20974544},
  howpublished = {\url{https://doi.org/10.5281/zenodo.20974544}},
}