SWMM - Snow Pack

Contains parameters characterizing Snow Pack, removal and melting in three types of subareas within a subcatchment:

1. Removable snow - consists of a user-defined fraction of the total impermeable area
   It is intended to represent areas such as streets and parking lots where plowing and snow removal can be done
2. Impermeable area - area of snow cover covering the remaining impermeable area of a subcatchment
3. Permeable area - area of Snow Pack that covers the entire permeable area of a sub-Catchment

Each of these three areas is characterized by the following parameters:

• Minimum and maximum snow melt coefficients
• Minimum air temperature for melting snow to occur
• Snow depth above which 100% area coverage occurs
• Initial snow depth
• Initial and maximum free water content

In addition, a set of snow removal parameters can be assigned to the washable area. These parameters consist of the depth at which snow removal begins and the fractions of snow moved to various other areas:

When editing a Snow Pack package, provide the following properties:

• Identification
  • Description (Description, String) - Use a friendly description when the item name is not enough
  • Name (Name, String) - name of the item
    Avoid names that are too long, or that contain the following characters: '*', '>', '<', '/', '\', '"', ':', ';', '|', '=', '`', '#', ',', '?'
  • Priority (Priority, Enum) - Information about the current state of the item. It might be:
    • Neutral: no problem
    • Critical: Some issue that prevents the item from being calculated or used
• Snow Removal Parameters
  • Converted to Immediate Snow Melt (ImmediateMelt, Double) - Fraction converted to immediate Snow Melt
  • Start Removal (RemovalBegin, Double) - Depth that must be reached before any snow removal begins
  • Other subcatchment (OtherCacthment, ObjectId) - Name of the subcatchment to which a fraction of the Snow Melt is transferred
  • Sum (SnowSum, Double) - Sum of fractions
    Informs the sum of the fractions below, which must be less than or equal to 1
  • Transferred to an impermeable area (RemovalImpervious, Double) - Fraction transferred to an impermeable area
  • Transferred to Permeable Area (RemovalPervious, Double) - Fraction transferred to permeable area
  • Transferred Outside (OutWatershed, Double) - Transferred Outside
  • Transferred to Another subcatchment (RemovalOther, Double) - Fraction transferred to another subcatchment
• SWMM
  • Parameters (Parameters, ListSwmmSnowPack) - Snow Pack parameters
    
    Each item (SwmmSnowPackData) in ListSwmmSnowPack has:
    • Item (Item, Enum) - accumulation type:
      1. Plowable snow - consists of a user-defined fraction of the total impervious area
         Intended to represent areas such as streets and parking lots where snow plowing and removal can be performed
      2. Impervious area - snowpack area covering the remaining impervious area of ??a subcatchment
      3. Pervious area - snowpack area covering the entire pervious area of ??a subcatchment
    • Minimum Melt Coefficient (DefrostMin, Double) - The snow melt coefficient (in degrees/day) occurring on December 21st
    • Maximum Melt Coefficient (DefrostMax, Double) - The snow melt coefficient (in degrees/day) occurring on June 21st
    • Base Temperature (BaseTemperature, Double) - Temperature at which snow begins to melt
    • Free Water Capacity (FreeWater, Double) - The volume of pore space in a snowpack that must be filled with melted snow before liquid runoff begins
    • Initial Snow Depth (StartSnowDepth, Double) - Snow depth at the start of the simulation
    • Initial Free Water (StartFreeWater, Double) - Depth of melted water held within the pack at the start of the simulation
    • Depth at 100% (DepthFull, Double) - The depth
    of the snow, beyond which the entire area remains completely covered and is not subject to any area depletion effect
• Removable Fraction (PlowableFraction, Double) - The fraction of impermeable area that is removable and therefore not subject to area depletion

Subcatchments are assigned a snowpack object via their Snow Pack property. A single snow object can be applied to any number of subcatchments. Assigning a snowpack to a subcatchment simply establishes the melt parameters and initial snow conditions for that subcatchment. Internally, SWMM creates a "physical" Snow Pack for each subcatchment, which tracks Snow Pack and melting for that particular subcatchment based on whether us parameters of Snow Pack, its amount of permeable and impermeable area and the precipitation history.