Hydrologic Flow & Erosion Risk Assessment (Screening)

Objective

Provide parcel-scale insight into surface drainage behavior and terrain conditions to support early, decision-ready planning. Results are intended to help identify where surface water naturally concentrates and where terrain steepness may increase erosion risk during rainfall events.

• Identify coherent surface runoff pathways (primary drainage corridors).
• Differentiate localized issues from parcel-wide concern.
• Support targeted mitigation focused on specific flow paths.

Data used

• USGS 3DEP elevation data — hydrologic modeling inputs.
• Derived rasters — flow direction, flow accumulation, slope, and erosion-risk screening overlay.
• Base imagery for context (map visualization only).

Elevation data were hydrologically conditioned prior to flow modeling to improve realism of surface drainage pathways.

Approach

• Hydrologic conditioning of elevation data.
• Flow direction and flow accumulation modeling.
• Threshold-based identification of primary drainage corridors.
• Slope analysis to identify terrain steepness.
• Overlay screening: erosion risk where slope (≥6%) intersects concentrated runoff.

Key outputs

• Primary drainage path map (surface runoff concentration).
• Erosion-risk screening map (localized hotspots).
• Written interpretation with limitations and next-step guidance.

Summary of findings

• Distinct drainage corridors cross the parcel, indicating predictable runoff pathways during rain events.
• Erosion risk is concentrated where runoff corridors intersect steeper terrain—localized hotspots rather than parcel-wide concern.
• Results support mitigation strategies focused on specific flow paths instead of broad, non-specific interventions.

Limitations

• This is a GIS-based screening tool—useful for early decision support, not a replacement for engineering design.
• Subsurface drainage, soil infiltration variability, and constructed features may alter real runoff behavior.
• Follow-up field verification is recommended if planning significant earthwork or drainage changes.

Despite these limitations, the drainage and corridor patterns are consistent with parcel-scale terrain and provide a reliable basis for preliminary decisions.