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Some municipalities across New Zealand and other parts of the world require designers to use specified inlet grate types with defined inlet efficiency curves.
There are two ways in which the custom inlet grate type this can be incorporated into InfoDrainage:
1) Define custom grate inlet type based on the formula specified by K. MacKenzie and J.C. Y Guo, 2011 (technical paper attached) and allowing the user to enter the grate splash-over velocity coefficients.
2) Allow user to enter tabulated information to define the collection efficiency based on a given cross slope (with an ability to input a number of tables based on the number of cross slope ranges that may exist). 12d drainage software uses this approach.
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I did want to add that user inlets were added to xpswmm in 1997 and we it very useful for caltrans and Neensh inlets
This is a good summary of options for incorporating custom inlet grate types into InfoDrainage, especially given the context of specific municipal requirements in New Zealand and elsewhere. Here's a breakdown of my comments:
Strengths of the Analysis:
Relevance: It directly addresses a practical need for software to handle specific local regulations.
Clear Options: It clearly outlines two distinct approaches: a formula-based method and a table-based method.
Justification: It provides a source (MacKenzie and Guo, 2011) for the formula-based approach and mentions a competing software (12d) that uses the table-based approach, lending credibility.
Consideration of Practicality: It acknowledges the potential for varying cross slopes and the need to accommodate this in the table-based approach.
Comments and Further Considerations:
Option 1 (Formula-Based):
Advantages: This approach is more compact (requiring only coefficients) and potentially more flexible for extrapolation beyond tested conditions. It also aligns with established research.
Disadvantages: The accuracy depends heavily on the applicability of the MacKenzie and Guo formula to the specific grate types being used. The "splash-over velocity coefficients" need to be determined through testing or published data, which might not always be available.
Option 2 (Table-Based):
Advantages: This method is more adaptable to complex grate geometries where a simple formula might not suffice. It directly uses empirical data, which can be more accurate for specific conditions.
Disadvantages: Requires extensive testing to generate the tables for different cross slopes and flow rates. The tables themselves can become large and cumbersome to manage within the software. Interpolation between table values will be necessary and could introduce some error. The user must understand how to create and input these tables correctly.
Hybrid Approach? A possible third option could be a hybrid approach: using the formula-based method as a default or for preliminary design, and allowing users to override with tabulated data for specific cases where higher accuracy is required or where the formula is known to be inadequate.