# TerrainLogic Grassed-Waterway Verification: Protocol and Findings

**Public engineering record | Preliminary planning**

## Validation question

Does TerrainLogic consistently carry site information into a preliminary vegetated-waterway design, produce internally coherent sizing and documentation, and clearly identify decisions requiring field survey, applicable state Field Office Technical Guide (FOTG) review, and professional approval?

## Product-scope decision

TerrainLogic is a preliminary planning and design-assistance system. It does not produce sealed plans, certify compliance, replace the responsible designer, or assume professional liability. Peak discharge, alignment, utilities, outlet stability, permits, constructability, vegetation establishment, and final dimensions require project-specific review.

## Governing references

Verification is grounded in applicable USDA-NRCS conservation-practice standards and engineering references, including CPS 412 Grassed Waterway, National Engineering Handbook guidance, approved hydrologic methods, and the governing state FOTG.

## Verification protocol

The public protocol separates:

1. dimensional, unit, boundary, and numerical checks;
2. independent worked-example comparison across the supported design range;
3. terrain and hydrology handoff checks;
4. professional review against applicable criteria; and
5. future field, as-built, and inspection evidence.

Reference cases cover low and high design grade, low and high discharge, supported vegetation/retardance selections, contrasting soil-erodibility classes, limiting capacity and stability conditions, and user-modified design inputs. Independent calculations must not call the production calculation helpers.

## Acceptance criteria

- Calculations remain dimensionally consistent and conserve reported geometry and earthwork quantities.
- Independent reference cases agree within declared numerical and reporting tolerances.
- Capacity, stability, freeboard, and geometry checks return the expected pass/review status at boundaries.
- Survey, profile, report, saved-design, as-built, and inspection workflows remain internally consistent.
- Missing or unverified hydrology, outlet, survey, vegetation, utility, or FOTG information is surfaced as a limitation rather than silently approved.

## Findings

- The combined preliminary-engineering verification matrix contains 50 checks; all 50 pass.
- The waterway matrix spans six representative combinations from 5 to 100 cfs and 0.3% to 2.0% design grade, with varied soil and vegetation conditions.
- Independent checks of section geometry, conveyance, and stability agree with the corresponding outputs within frozen numerical tolerances.
- An additional published worked example agrees within the precision available in its rounded source values.
- Focused automated engineering, report, survey, saved-design, lifecycle, and inspection tests pass.

## Validated claim at this stage

Within the tested numerical domain, TerrainLogic consistently evaluates its preliminary waterway sizing, geometry, conveyance, stability, freeboard, survey/profile, report, and lifecycle calculations. This is **software and calculation verification**.

It is not evidence that a user-supplied discharge, mapped corridor, vegetation choice, outlet, or proposed field design is correct for a particular site.

## Open validation requirements

Independent professional review, field-survey comparison, outlet-system evaluation, jurisdiction-specific criteria, constructed as-built comparison, and multiyear inspection evidence remain open. Until those are completed, all waterway outputs must retain preliminary-planning language.

Exact production equations as assembled, solver details, internal validators, source paths, tolerances used for development diagnostics, and correction history are maintained as confidential engineering records.