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Technical overview

What HDAT does (engineering scope)

HDAT is designed to support highway drainage design end-to-end in one workflow:

  • Catchment hydrology: compute peak flows for multiple return periods using Rational and SCS methods.
  • Culvert hydraulics: evaluate inlet vs outlet control and size/select culvert combinations.
  • Channel hydraulics: size open channels using Manning equation; compute normal/critical depth and regime.
  • Road drainage: estimate spread, propose gully spacing, compute bypass progression, and sag inlet counts.
  • BOQ: convert designs into quantities for reporting (excavation, lining, protection, riprap, etc.).

What is documented here

This site documents the legacy behavior as a stable baseline, including:

  • Units and conventions.
  • Equations and decision logic.
  • Computation flow and intermediate values.
  • Verification targets (tolerances).

Primary inputs & outputs

Typical inputs:

  • Catchment properties (area, flowpath length, elevations/slope proxies).
  • IDF data (intensity/depth vs duration) for one or more return periods.
  • Method settings (Tc method, ARF enablement/threshold, CN/C values).
  • Culvert and channel geometry, slope, roughness coefficients.
  • Road drainage parameters (cross slope, longitudinal slope, roughness).

Typical outputs:

  • Peak discharge per return period (cumecs).
  • Hydrograph series (SCS path).
  • Culvert governing headwater ratio (H/D), control type, velocities, riprap sizing proxy.
  • Channel suggested dimensions, depths, regime classification.
  • Gully spacing, capture efficiency, bypass, sag inlet counts.
  • BOQ items and summaries.