Inlet Library
Inlet libraries define the types of inlets available for your project — their geometry, hydraulic calculation method, and capacity characteristics. HydraStorm ships with several built-in libraries and supports creating custom libraries for municipality-specific inlet types.
Built-In Libraries
HydraStorm ships with eight built-in inlet libraries:
| Library | Description |
|---|---|
| Inlet Starter | Generic inlet types for getting started. Copy and customize for your needs. |
| HEC-22 Standard | Standard HEC-22 inlet types as defined in the FHWA manual. |
| iSWM / NCTCOG | Inlet types per the NCTCOG iSWM (Integrated Stormwater Management) manual. |
| McKinney, TX | Municipality-specific inlets for McKinney, Texas. |
| Plano, TX | Municipality-specific inlets for Plano, Texas. |
| Fort Worth, TX | Municipality-specific inlets for Fort Worth, Texas. |
| Frisco, TX (2025) | Municipality-specific inlets for Frisco, Texas. |
| Celina, TX (2024) | Municipality-specific inlets for Celina, Texas. |
Note: Built-in libraries are read-only. To customize one, use Copy to create an editable copy.
Inlet Type Categories
Each inlet type belongs to one of these categories, which determines the hydraulic method used to compute interception capacity:
- Grate — Captures flow through openings in a grate surface. Geometry defined by grate length, width, open area, and perimeter. Uses HEC-22 Chapter 4/7 grate interception equations.
- Curb Opening — Captures flow through an opening in the curb face. Geometry defined by opening length, height, and optional depression depth and width.
- Combination — A grate plus curb opening working together. The grate intercepts first; remaining flow is partially captured by the curb opening via a configurable credit fraction.
- Slotted Drain — A continuous slot along the gutter. Geometry defined by slot length and width.
- Wye/Drop Inlet — Area-based perimeter weir/orifice inlet. Geometry defined by perimeter, height, and area.
- Headwall — Pipe capacity method for headwall inlets. Capture equals the pipe full-flow capacity.
Hydraulic Methods
Each inlet category uses a specific HEC-22 hydraulic method to compute interception capacity. The method is determined automatically by the category — you do not select it manually.
| Category | Method | Reference |
|---|---|---|
| Grate | Hec22Grate | HEC-22 Chapter 4 (on-grade) / Chapter 7 (sag) |
| Curb Opening | Hec22CurbOpening | HEC-22 Chapter 4 (on-grade) / Chapter 7 (sag) |
| Combination | Hec22Combination | Grate + curb opening credit |
| Slotted Drain | Hec22SlottedDrain | HEC-22 slotted drain equations |
| Wye/Drop | PerimeterWeirOrifice | Weir/orifice calculation based on perimeter and area |
| Headwall | PipeCapacity | Capture = pipe full-flow capacity |
Note: On-grade inlets use the spread/velocity-based interception equations from HEC-22 Chapter 4. Sag inlets use the weir/orifice equations from HEC-22 Chapter 7. HydraStorm automatically selects the correct method based on the inlet's longitudinal slope.
Grate Types
For grate inlets, the grate type determines the splash-over velocity curve — the velocity at which water splashes over the grate instead of being captured. HEC-22 defines these standard grate types:
- P 1-7/8" — Parallel bar, 1-7/8 inch on-center spacing, no transverse rods (not bicycle-safe; highest hydraulic efficiency)
- P 1-7/8-4 — Parallel bar with 4 inch transverse rods (bicycle-safe)
- P 1-1/8" — Parallel bar, 1-1/8 inch on-center spacing, no transverse rods
- Curved Vane — 3-1/4 inch longitudinal, 4-1/4 inch transverse spacing; direction-sensitive (vanes must face oncoming flow)
- 30° Tilt Bar — 3-1/4 inch longitudinal, 4 inch transverse spacing; direction-sensitive
- 45° Tilt Bar (2-1/4" spacing) and 45° Tilt Bar (3-1/4" spacing) — two bar-spacing variants; HEC-22 does not publish an opening ratio for either and excludes both from sag service
- Reticuline — honeycomb grate; bicycle-safe but lowest debris handling and hydraulic efficiency of the set
Grate Selection Guidance
- Curved Vane grates have the highest capture efficiency for on-grade conditions and are the most commonly specified type in municipal standards.
- Reticuline grates have the lowest capture efficiency on-grade but are sometimes required for pedestrian safety in walkway areas.
- For sag conditions, the grate's open area and perimeter (not the grate type) determine capacity. All grate types with the same open area perform equally in sag.
Inlet Geometry Parameters
Each inlet type defines geometry parameters that feed into the hydraulic calculations. The required parameters depend on the inlet category:
| Parameter | Applies To | Description |
|---|---|---|
| Grate Length (ft) | Grate, Combination | Length of grate in direction of flow |
| Grate Width (ft) | Grate, Combination | Width of grate perpendicular to flow |
| Grate Open Area (sq ft) | Grate, Combination | Net open area of grate (used for sag weir/orifice calculations) |
| Grate Perimeter (ft) | Grate, Combination | Effective perimeter of grate (used for sag weir capacity) |
| Opening Length (ft) | Curb Opening, Combination | Length of curb opening along the curb face |
| Opening Height (ft) | Curb Opening, Combination | Height of curb opening |
| Depression Depth (ft) | Curb Opening | Local depression depth at curb opening |
| Depression Width (ft) | Curb Opening | Width of depression |
| Slot Length (ft) | Slotted Drain | Total length of slotted drain |
| Slot Width (ft) | Slotted Drain | Width of slot opening |
| Perimeter (ft) | Wye/Drop | Effective weir perimeter |
| Height (ft) | Wye/Drop | Inlet box height |
| Area (sq ft) | Wye/Drop | Effective orifice area |
Library Design Criteria
Each inlet library can optionally include design criteria that provide default limits for inlet analysis. When a library with criteria is applied to a project, these values are used unless overridden at the project level in Project Settings.
| Criterion | Description |
|---|---|
| Maximum spread on-grade (ft) | Allowable spread width for inlets on a continuous grade |
| Maximum spread at sag (ft) | Allowable spread width for inlets at sag (low) points |
| Maximum depth on-grade (ft) | Allowable ponding depth for on-grade inlets |
| Maximum depth at sag (ft) | Allowable ponding depth for sag inlets |
| Default clogging factors | Category-specific clogging reduction factors (e.g., 0.50 for grates, 0.10 for curb openings) |
| Combination credit fraction | Fraction of remaining flow credited to the curb opening in a combination inlet |
Note: Library design criteria are defaults only. You can override any of these values in Project Settings for the current project without modifying the library itself.
Creating Custom Libraries
To create a custom inlet library for your municipality or project requirements:
- Open the Inlet Library Manager from the Tables menu.
- Select a built-in library and click Copy to create an editable copy, or click New to start from scratch.
- Add inlet types with appropriate categories, geometry, and keywords.
- Configure geometry parameters to match the manufacturer specifications or municipal standard drawings for each inlet type.
- Optionally set library-level design criteria (spread limits, clogging factors).
- Save the library.
Custom libraries are saved to %LocalAppData%\HydraStorm\InletLibrary\. For firm-wide sharing across multiple workstations, set a custom library path in Program Settings.
Tips for Custom Libraries
- Start from the Inlet Starter library if you need simple, generic inlet types. Start from a municipality-specific library if one matches your jurisdiction.
- Include keywords in each inlet type's description that match your Civil 3D part descriptions. This enables the smart matching system to suggest inlet types automatically.
- Set library-level design criteria to match your municipality's drainage design manual. This saves time on each new project by pre-populating the correct spread and depth limits.
- When creating inlet types for manufacturer-specific products, use the geometry values from the manufacturer's published specifications or shop drawings.
Smart Matching
Like junction loss types, inlet type assignments use a learning system. When you assign an inlet type to a structure, HydraStorm remembers the association between the Civil 3D part description and the inlet type. On future projects using the same inlet library, matching descriptions are suggested automatically.
The matching system:
- Uses a sliding window of recent assignments per description
- Suggests with high confidence after 3 or more consistent assignments
- Falls back to keyword matching when no learned history exists
- Is scoped per inlet library — switching libraries resets suggestions
Note: Smart matching always suggests — it never auto-applies. You will see a confirmation prompt with the suggested inlet type, and you can accept or choose a different type. This ensures you always have control over inlet assignments.