Dam Safety Calculators
Thirteen calculators covering the technical core of dam safety engineering — spillway capacity and routing, embankment seepage and filter design, riprap and wave runup, concrete gravity stability, breach peak discharge, and hazard classification. Each tool shows the governing equation, names every variable, cites a primary source (USACE EM, FEMA P-94, NRCS NEH, USBR, Froehlich 2008), and supports both Imperial and SI units. Designed for screening-level checks and sanity-checking HEC-RAS / SEEP/W / SLIDE / DSS-WISE outputs — not as a substitute for a finite-element seepage analysis or a 2-D hydraulic model where one is warranted.
Topical coverage parallels the ASDSO Dam Safety Toolbox wiki — hydrology, hydraulics, embankment, concrete, breach — but with the equations made executable. If you're looking for the qualitative reference text, the wiki is the better starting point. If you're looking for a number you can put on a calc sheet, start here.
Spillway Hydraulics & Routing
Spillway capacity has to handle the inflow design flood (see IDF lookup), routed through the reservoir's storage. Sizing a service or auxiliary spillway means picking a crest type, computing free-overflow discharge at design head, then routing the IDF hydrograph to confirm peak headwater stays below dam crest minus required freeboard.
Embankment, Seepage & Slope Protection
Earthfill and rockfill dams fail through internal erosion (piping), excessive seepage gradients, slope instability, or surface erosion of upstream slope from waves and downstream slope from spillway flow. Filter design and seepage control are the dominant defenses; riprap protects against wave action.
Loading & Concrete Stability
Concrete gravity dams are designed to resist water pressure, uplift, ice, silt, and seismic loads through self-weight. The screening checks are overturning about the toe, sliding on the foundation, and base contact pressure (no tension at the heel for normal load combinations).
Breach Analysis & Hazard Classification
Hazard classification drives the inflow design flood, which drives spillway sizing, which drives the rest of the analysis. For an existing or proposed dam, classification starts with the breach-flood inundation footprint downstream — meaning the breach peak discharge is the first number you need.
Standards and references used across these tools
- USACE EM 1110-2-1603 — Hydraulic Design of Spillways (ogee crest coefficients, chute hydraulics).
- USACE EM 1110-2-1601 — Hydraulic Design of Flood Control Channels (Maynord riprap, EM 1601 method).
- USACE EM 1110-2-1420 — Hydrologic Engineering Requirements for Reservoirs (wind setup, wave runup).
- USACE EM 1110-2-1901 — Seepage Analysis and Control for Dams.
- USACE EM 1110-2-2200 — Gravity Dam Design (overturning, sliding, base stress).
- USACE EC 1110-8-2(FR) — Inflow Design Floods for Dams and Reservoirs (hazard-based IDF).
- FEMA P-94 — Selecting and Accommodating Inflow Design Floods for Dams (hazard classification matrix).
- NRCS NEH-11 — Drop Spillways (NRCS straight-drop and chute-drop principal spillways).
- NRCS NEH-633 / TR-26 — Soil Mechanics — Filter Design (Sherard 1989 filter criteria, NRCS 2017 update).
- USBR Design of Small Dams (third edition, 1987) — ogee, stilling basins, embankment design.
- Froehlich, D.C. (2008) — Embankment Dam Breach Parameters and Their Uncertainties, ASCE J. Hydraulic Engineering 134(12).
- Xu, Y. & Zhang, L.M. (2009) — Breaching Parameters for Earth and Rockfill Dams, ASCE JHE 135(12).
- Chanson, H. (2002) — The Hydraulics of Stepped Chutes and Spillways, A.A. Balkema.
- Boes, R. & Hager, W. (2003) — Hydraulic Design of Stepped Spillways, ASCE JHE 129(9).
Companion: HydroComplete
These calculators are deliberately single-equation, screening-level tools — perfect for a calc-sheet sanity check or a back-of-envelope number. For full multi-step dam workflows (PMP downscaling, multi-storm sediment routing, stage-storage-discharge with custom hydrographs, inundation mapping), see the paid sister product HydroComplete.
Limitations. Every tool on this page is a screening-level check that assumes you've already confirmed the governing equation applies to your geometry, flow regime, and design assumptions. Dam safety analysis is a regulated practice in every U.S. state and most jurisdictions worldwide; these tools do not substitute for a sealed analysis by a qualified engineer with state dam-safety program approval, an FE seepage or stability model where required, or a 2-D hydraulic / breach inundation model for hazard classification. Use the cited sources to confirm applicability.