Free Tool · D8 Flow Accumulation · HEC-18 Scour · 1-ft Contour · Civil & Surveying

Inundation Depth & Scour Analysis

Generate inundation depth and scour depth maps at 1-ft (0.3 m) contour detail from DEM + storm runoff. Auto-flag cells where inundation overlaps a constrained zone (Exhibit B-1 / Constraints Map). Satisfies contractor spec for onsite water inundation levels and scour analysis.

Runoff Source
From SCS-CN engine or manual entry
DEM / Topographic Surface (Optional)
Leave empty to use a synthetic slope model (area + slope only).
Soil Erodibility (Scour)
Constraint Zone (Optional)
Exhibit B-1 / Constraints Map bounding box — auto-flags inundated cells inside constrained zone.
Computing D8 flow accumulation…
Results
Screening model only · Not 2D HEC-RAS
Inundation
Scour
Constraints
Inundation Depth
Max inundation depth
26.05 ft
7.940 m
Inundated area
48.895 ac
197871 m²
🔒 Free preview: max depth, inundated area, scour summary. Sign in as Civil to unlock contour table, discrepancy table, and project save.
Scour Depth
Max scour depth
149.04 ft
45.428 m | τ_c = 20 Pa
Scour area (τ > τ_c)
0.895 ac
3622 m²
Erodibility: Medium (cohesive soft / sand) — τ_c = 20 Pa
🔒 Free preview: max depth, inundated area, scour summary. Sign in as Civil to unlock contour table, discrepancy table, and project save.
Constraints Map Discrepancies
No constraint zone entered. Enter Min/Max X/Y coordinates to flag inundated cells inside the constrained area.
Screening tool only. Not a substitute for 2D HEC-RAS or detailed HEC-18 scour analysis. Results must be reviewed by a licensed civil engineer.

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FrameAI Civil generates stamping-ready hydrology reports with inundation mapping, scour analysis, Constraints Map overlay, and owner notification letter.

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Frequently Asked Questions

What is the inundation model used? +
A simplified bathtub + D8 flow-accumulation hybrid (O'Callaghan & Mark 1984). Runoff volume from the SCS-CN engine is distributed across grid cells proportional to their upstream drainage area (flow accumulation). Depth = volume / cell area. This is a screening method — not 2D HEC-RAS. It does not route a hydrograph through channels.
What is the scour model? +
Bed shear stress τ = γ_w · d · S is compared to critical shear τ_c for the selected soil erodibility class (HEC-18 / Briaud 2008). Where τ > τ_c, scour depth d_s = k_s · (τ/τ_c − 1) · d. Critical shear values: Low (rock) 100 Pa, Medium (sand) 20 Pa, High (loose silt) 2 Pa. This is a preliminary screening result.
What does the Constraints Map overlay do? +
If you enter a constraint zone bounding box (matching your Constraints Map / Exhibit B-1 coordinate system), the tool flags every grid cell inside the constrained area that has inundation depth > 0. The discrepancy table can be pasted directly into the owner notification letter per the contractor specification.
How do I input DEM data? +
Paste XYZ points as CSV (x,y,z — one point per line). Units can be feet or meters — just be consistent with the constraint zone coordinates. No DEM? The tool builds a synthetic slope model from watershed area and average slope. For a real project, export XYZ points from your survey data or a 3DEP/LiDAR DEM.