Floodline is a California flood-defense simulation built on real water-system physics — levees, weirs, pump stations, and reservoir releases. Six historical scenarios span the 1986 Yuba flood to the 2017 Oroville spillway crisis. $2 indie release on itch.io and Steam.
Each scenario starts with an inflow forecast and current system state. Choose levee inspections, pump activation, gate operations, and (in some scenarios) controlled-flooding releases. Score points for protected area, lose for inundation. Real CA water hydrology.
Yes — the six scenarios reproduce real events: 1986 Yuba, 1997 New Year's, 2006 Sacramento, 2017 Oroville spillway, plus two synthetic ARkStorm scenarios from the USGS multi-hazard project.
Water is routed with the local-inertial shallow-water scheme used by LISFLOOD-FP (Bates et al. 2010) on a 40 m grid with Manning roughness per land cover, so flood waves, backwater and levee overtopping behave like the real thing. Pump and gate response curves are simplified. Scenarios are calibrated against published post-event reports from USGS, DWR and USACE.
2017 Oroville. Three independent failure modes (auxiliary spillway erosion, main spillway erosion, downstream evacuation logistics) all in 72 hours of game time.
itch.io and Steam — search "Floodline". Single $2 purchase; free in-browser demo at boardgaminghub.com/Floodline.html.
Floodline routes water with the local-inertial shallow-water scheme of Bates, Horritt & Fewtrell (2010) — the solver inside LISFLOOD-FP and most modern 2D flood-inundation models — on a 40 m grid, in SI units, with Manning's roughness per land cover. It is not a full Saint-Venant / HEC-RAS 2D solver (the convective acceleration term is dropped, so it does not resolve supercritical shocks), but momentum, depth-dependent conveyance, backwater and wave propagation are all real. Everything below is exactly what the code does.
Each cell holds a water depth h above its bed z (terrain plus any structure). Between every pair of neighbouring cells the solver carries a unit discharge q (m²/s) that persists from step to step — this is the momentum. Each sub-step it is updated with
q⁺ = [ θ·q + ½(1−θ)(q₋ + q₊) − g·hf·Δt·∂η/∂x ] / [ 1 + g·Δt·n²·|q| / hf7/3 ]
Depths update from the face discharges: Δh = Δt/Δx · (Σ qin − Σ qout). Before that, a donor limiter scales every outgoing face of any cell whose scheduled export exceeds what it holds, so depths never go negative and total volume is conserved to floating-point precision — water enters only as rain, inflow or surge and leaves only through infiltration, pumps and the outlet. The time step obeys the CFL condition Δt ≤ 0.7·Δx / √(g·hmax) by sub-stepping whenever the deepest water demands it.
Levees do not fail on a simple height check — they accumulate stress while overtopped. When any neighbour's water surface exceeds the levee crest, stress builds as stress += dt · rate · (1 + 3·overtopping depth), where rate = 1.0 (0.5 if reinforced), so deeper overtopping fails a levee faster. A breach fires when stress crosses 5 (10 if reinforced); the crest drops 0.5 m and the solver's momentum equation produces the resulting breach wave. When not overtopped, stress relaxes at −0.5·dt. Sandbags erode under real flow velocity (> 1 m/s), not static head. Damage follows HAZUS-style depth–damage curves.
Scenarios are calibrated against published USGS, DWR and USACE post-event reports, but the model stays first-order: treat it as an intuition-builder for routing, storage and levee risk, not as a certified flood forecast.
Built by a practicing water-resources engineer. For the professional versions of this math, see the free open-channel & hydrology calculators at pe-calc.com, or HydroComplete for stormwater design software. To model a real drainage network, AquaSWMM runs SWMM free in the browser; to see a flood zone on site, FloodTruth overlays it in augmented reality.
Floodline is a flood-defense simulation built by a licensed water-resources engineer. You place levees, channels, pumps, and sandbags to keep town damage below a scenario threshold while storms raise river stages and saturate soils. The browser demo includes a training sandbox and Cedar Rapids 2008; the full release on itch.io adds the complete historical campaign described below.
Each scenario ships with a storm hydrograph, terrain derived from real valley geometry, budget constraints, and win conditions tied to damage percentage. Parameters are simplified for play but grounded in post-event reports from agencies such as California DWR, USACE, and USGS multi-hazard studies.
| Scenario | Event basis | What you manage |
|---|---|---|
| Training Ground | Synthetic tutorial basin | Learn levee stress, pumps, and channel routing without time pressure. |
| 1986 Yuba | Yuba County levee failures | Fast-rising Sacramento Valley flows; sandbag windows are short. |
| 1997 New Year's | California statewide flood | Multi-day rain on saturated soils; duration stress on levees. |
| 2006 Sacramento | Sacramento River high flows | Urban ring levees and pump capacity under prolonged stage. |
| 2017 Oroville | Oroville Dam spillway crisis | Spillway erosion, auxiliary spillway risk, evacuation timing — widely considered the hardest scenario. |
| ARkStorm West / East | USGS synthetic atmospheric river | Hypothetical megastorm footprints used in California resilience planning. |
| Cedar Rapids 2008 | Midwest slow crest | Gradual rise over days — a endurance scenario for pumps and pre-positioning. |
No. Floodline uses first-order hydrology appropriate for gameplay: routing, storage, and simplified gate curves. It is faithful in shape to real events, not a replacement for HEC-RAS or dam safety modeling. Treat it as an interactive way to understand why flood managers obsess over freeboard, spillway capacity, and forecast lead time.