SWMM5 Delphi GUI Dsubland.pas Summary

 Below is an overview of Dsubland.pas, a Delphi unit from SWMM 5.2 that implements a SubLandUsesForm dialog. This dialog is used to edit how land uses are distributed within a subcatchment. In SWMM, a subcatchment can be allocated among different land uses (e.g., residential, commercial, industrial) that have distinct buildup/washoff parameters for pollutants. The TSubLandUsesForm allows the user to specify what percentage of the subcatchment’s area each land use occupies.

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1. Purpose and Context

SWMM can model nonpoint source pollutant buildup/washoff using land use objects. Each Subcatchment can contain a mix of multiple land uses (for instance, 30% residential, 70% commercial). The TSubLandUsesForm helps the user assign these percentages:

• The user sees a list of land uses (one per row).
• For each land use, the user enters the percent of subcatchment area occupied by that land use.

These allocations can sum to 100%. During simulation, pollutant buildup/washoff rates are scaled by these percentages.

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2. Main Form: TSubLandUsesForm

2.1 Visual Components

1. PropEdit1 (TPropEdit):
   • A custom property editor placed on Panel1.
   • The editor has two columns:
     • Property (the land use name)
     • Value (the percent of subcatchment area).
2. PropList (TStringList):
   • Holds the values (the percentages) for each land use row.
3. OKBtn, CancelBtn, HelpBtn:
   • Standard form action buttons at the bottom.

2.2 Data Organization

• LanduseCount / PropCount: the number of land uses in the project.
• Each row in PropEdit1 corresponds to one land use.
• The name (land use) is shown in the first column, the user’s input (percentage) in the second column.
• The string list PropList holds these percentage values in the same order the land uses appear in Project.Lists[LANDUSE].

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3. Key Methods and Events

3.1 FormCreate

1. Sets up the PropEdit1 with column headings (“Land Use,” “% of Area”).
2. Allocates an array of TPropRecord (PropRecd) to match the number of land uses in the project.
3. For each land use name in Project.Lists[LANDUSE], it sets:
   • PropRecd[i].Name to the land use name,
   • PropRecd[i].Style := esEdit,
   • PropRecd[i].Mask := emPosNumber (ensuring only numeric input for the percent).

3.2 SetData(LandUses)

• Called externally to load an existing distribution of land use areas for a subcatchment.
• Each entry in the LandUses string list has the format: landuseName=percentValue.
• For each land use in the entire project, it checks if it appears in LandUses. If it does, the matching percentage is appended to PropList; if not, it appends an empty string (“”).

3.3 GetData(LandUses, Count)

• After the user presses OK, the form calls GetData to store the final distribution:
  1. Clears LandUses.
  2. Walks through each row in PropList.
  3. Converts the string to a float (P).
  4. If P > 0, it adds landuseName=P to the LandUses list, increments Count.
• This results in a list of land uses with nonzero percent allocations.

3.4 OKBtnClick

• The user’s final step.
• Calls:
  1. PropEdit1.IsValid (ensuring no invalid numeric inputs).
  2. ValidateInput:
     • Sums all percentages. If they exceed 101%, shows an error (“Percentages exceed 100%.“).
     • If OK, ModalResult := mrOK.

3.5 ValidateInput

• Gathers each line in PropList, parses it as a float, sums the values.
• If the sum > 101, returns an error. (The 101% threshold accounts for rounding error in user input.)

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4. Usage Example

1. A subcatchment has land uses: Residential, Commercial, Open Space.
2. The user calls SetData(LandUses) where LandUses might have lines like Residential=25 and Commercial=50 for the existing configuration.
3. The form displays three rows in PropEdit1: “Residential,” “Commercial,” “Open Space.” The first two have “25,” “50” and the third is blank.
4. The user changes values—maybe sets “Residential=30,” “Commercial=50,” “Open Space=20.” The sum is 100%.
5. On OK, GetData(LandUses, Count) returns these final lines, and Count=3.

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5. Summary

Dsubland.pas provides a simple TSubLandUsesForm dialog to let users specify or edit percentage allocations of land uses within a subcatchment:

• The form displays all land uses in the model (one row each),
• The user enters a percentage for each relevant land use,
• The form ensures the sum does not exceed 101%,
• The final data are stored in a string list for the subcatchment’s land uses.

This helps SWMM track which portion of the subcatchment belongs to which land use categories, crucial for pollutant buildup/washoff modeling.