Documentation - CIV Engineering

What This Platform Does

CIV Engineering is a web-based platform for culvert hydraulic analysis. It performs inlet control and outlet control calculations for circular concrete pipe culverts based on FHWA HDS-5 Third Edition standards.

The platform calculates controlling headwater depths, identifies flow control type (inlet vs. outlet), determines flow regime, and generates engineering outputs for design documentation and regulatory submissions.

Calculation Integrity

Core calculations use the FHWA dimensionless flow parameter Q/AD^0.5 with slope corrections per Appendix A. Inlet control coefficients (K, M, c, Y) are sourced directly from FHWA Table A.1. The engine is covered by 303 automated validation tests against FHWA HDS-5 published examples, and a structured audit of the physics engine is ongoing.

Who This Is For

For Professional Engineers (PEs), Engineers in Training (EITs), and engineering professionals involved in:

Drainage design for highways, roads, and infrastructure
Culvert sizing and performance verification
DOT submissions requiring FHWA-compliant hydraulic analysis
Hydraulic studies for environmental permits and regulatory compliance
Design optimization comparing multiple culvert configurations simultaneously

Users are expected to have working knowledge of hydraulic engineering principles, FHWA standards, and drainage design practice.

Why This Platform Exists

Correct FHWA HDS-5 implementation requires deep understanding of inlet and outlet control equations, proper coefficient selection, slope corrections, and flow regime determination. This platform fills the gap between complex desktop software (HY-8 requires Windows installation) and manual calculations (time-consuming and error-prone):

Web-based: No installation required, works on any device
Fast: Complete analysis in seconds vs. hours of manual calculation
Transparent: All equations, coefficients, and intermediate steps visible
Bulk scenarios: Compare dozens of design alternatives simultaneously
FHWA-compliant: Calculations validated against published examples
Professional outputs: Publication-ready charts and calculation reports

Analysis Paths

Four workflows to match how you work:

Design & Analyze

Complete culvert design from sizing through detailed performance analysis with professional reports

Multi-Scenario

Compare inlet types or analyze multiple design scenarios side-by-side

Calculation Explorer

Step-by-step breakdown of FHWA HDS-5 methodology with real-time interactive calculations

Compliance Validation

Check an existing culvert against jurisdictional criteria (WSDOT AOP, WDFW, MS4) and produce a defensible report

Key Capabilities

Inlet Control Analysis: FHWA Appendix A equations with K, M, c, Y coefficients
Outlet Control Analysis: Energy equation with friction, entrance, and exit losses
Flow Control Determination: Automatically identifies controlling condition
Design Matrix: Compare all pipe sizes across multiple materials simultaneously
Water Surface Profiles: Professional visualizations with pipe, water surface, critical depth
3D Section View: Longitudinal and cross-section render of the culvert assembly
2D Plan View: FHWA color-coded velocity heatmap with HEC-14 apron extents
Performance Curves: Velocity, energy loss, efficiency, and Froude number dashboards
Projects Dashboard: Save, load, and manage analysis projects with PDF download
Export: Excel spreadsheets and PDF calculation reports

Supported Inlet Types

Headwall, Square Edge: standard inlet with a perpendicular headwall
Headwall, Groove/Socket End: precast concrete pipe with groove end and headwall
Projecting, Square Edge: pipe projecting from the embankment
Mitered to Slope: inlet mitered to match the embankment slope
Beveled Ring, 45° Bevel: beveled entrance ring
Beveled Ring, 33.7° Bevel: beveled entrance ring

Programmatic Access (Public API)

The same HDS-5 compliance engine that drives the Compliance Validation tool is exposed as a public HTTPS API. Firms with existing ArcGIS Field Maps, Survey123, or Power Automate workflows can call the engine directly and receive a pass/fail result plus a defensible inspection PDF without leaving their platform.

Endpoints

POST /api/v1/compliance-check: run the engine against a jurisdictional criteria set, return JSON
POST /api/v1/compliance-check/report: same inputs, return the single-page inspection PDF
GET /api/v1/jurisdictions: machine-readable jurisdictions registry
GET /api/v1/health: unauthenticated uptime probe

Authentication and Reliability

Per-tenant API keys with optional endpoint and jurisdiction scoping
24-hour idempotency window via X-Request-Id for safe retries
Per-tenant tiered rate limits with standard X-RateLimit-* headers

Full API reference →

FHWA Standards & Validation

This platform implements calculations per:

FHWA HDS-5 Third Edition Appendix A: Inlet Control Energy Equation: Outlet Control

Inlet control, outlet control, and water surface profile calculations are covered by 303 automated validation tests against FHWA HDS-5 published examples. A structured audit of the physics engine is ongoing, with deeper edge-case coverage in progress: flow regime transitions, skewed inlets, and boundary condition extremes.

Example Validation: FHWA Design Guideline 1

54-inch diameter concrete pipe · 200 cfs · Groove end with headwall · 1% slope · 200 ft · n = 0.013
FHWA expected HW: 8.0 ft · Platform result: 7.925 ft · Error: 0.94% (within ±5% acceptance) · Control: Inlet (match)

Disclaimer

AS-IS: This software is provided without warranty of any kind. No representations are made regarding the accuracy, reliability, or suitability of any calculations or results.

PROFESSIONAL REVIEW REQUIRED: All hydraulic calculations and engineering designs must be reviewed, verified, and stamped by a licensed Professional Engineer in accordance with applicable state laws and regulations. This platform does not replace professional engineering judgment.

NO LIABILITY: The developers and operators shall not be held liable for any damages arising from use of this software, including errors in calculations, data loss, or professional liability claims.

Use of this platform constitutes acceptance of these terms.

How to Get Started

Step 1: Choose Your Path

From the landing page, select the workflow that matches your task: design a culvert to meet flow and headwater criteria, run a detailed performance study, or compare multiple inlet types side-by-side.

Step 2: Enter Parameters

Diameter (in)
Design discharge (cfs), or use the built-in Rational Method calculator
Inlet type
Length (ft), slope (ft/ft), Manning's n
Tailwater depth (ft)
Headwater and velocity thresholds for design checks

Step 3: Review Results

Controlling headwater depth and HW/D ratio
Flow control type (inlet vs. outlet) and flow regime
Outlet velocity, critical depth, normal depth
Design Matrix: pass/warn/fail across all sizes and materials

Step 4: Export Documentation

PDF Reports: Calculation report with full inputs, results, and design notes
Excel: Detailed calculation tables with all parameters
Projects: Save to your dashboard and return to any analysis later

Quick Tip

For typical highway drainage, use Manning's n = 0.013 for concrete pipe or n = 0.024 for corrugated metal pipe (CMP). Always verify tailwater from downstream channel analysis before finalizing design.