SWMM5 snow.c Summary

 The snow.c module in the SWMM 5 source code is responsible for modeling snow accumulation, snowmelt, and snow removal processes in the hydrological model. This module simulates the impact of snow on the runoff from subcatchments, including the accumulation of snow, the melting of snow due to precipitation and temperature, and the potential for snow removal from streets or other impervious surfaces.

Key Concepts and Functions in snow.c:

1. Snowmelt Parameters and Data Structures:

• Snow Keywords: These are identifiers used in the input data to refer to different types of snow surfaces (plowable, impervious, and pervious).
• TSnowpack: This structure represents the snowpack on a subcatchment, which includes the amount of snow (in depth) on different surfaces, the cold content (temperature-related energy storage), and the snow's free water content (meltwater).
• TSnowmelt: This structure holds parameters related to snowmelt, including melt coefficients, temperature base for melting, and other characteristics that affect snowmelt and snow accumulation.

2. Key Functions:

• snow_readMeltParams: This function reads snowmelt parameters from input data, including values like the melt coefficient, snow depth, and fraction of plowable impervious area.
• snow_createSnowpack: This function initializes a snowpack object for a subcatchment and assigns it a set of snowmelt parameters.
• snow_initSnowpack: This function initializes the state of the snowpack for a subcatchment, including assigning snow depth and free water content to different sub-areas (e.g., plowable, impervious, and pervious surfaces).
• snow_plowSnow: This function simulates snow plowing operations on the subcatchment, moving snow between sub-areas (e.g., from plowable to impervious or pervious surfaces).
• snow_getSnowMelt: This function computes the snowmelt rate based on precipitation (rainfall and snowfall), temperature, and other snow-related factors.
• snow_getSnowCover: This function computes the total volume of snow cover on the subcatchment.
• snow_setMeltCoeffs: This function sets the melt coefficients based on the current temperature or snow season of the year.

3. Snowmelt Calculation Process:

• Snow Accumulation: Snowfall is added to the snowpack. The snow depth on different surfaces (plowable, impervious, and pervious) is updated based on the snowfall.
• Snowmelt: Snowmelt is calculated based on precipitation and temperature. If it is raining, the melt rate is calculated using a rainfall-based melt model. If the temperature exceeds a certain threshold, the snowpack melts using a degree-day method. The meltwater is routed through the snowpack, and the cold content is updated accordingly.
• Snow Removal: Snow removal is simulated for plowable impervious areas. The snow removed is routed to other surfaces or subcatchments, and the snow depth is reduced.
• Cold Content and Temperature: The cold content (a measure of how much energy is required to melt the snow) is updated based on the temperature and the snow's previous state.

Summary of Key Concepts:

• Snowmelt: The process of snow turning into water as it melts due to temperature and precipitation. The rate of snowmelt is determined by the temperature and the snowmelt coefficients.
• Snowpack: The accumulation of snow and its characteristics, such as depth, free water content, and cold content.
• Subcatchment Snow Coverage: Different subcatchments may have snow on various surfaces, such as impervious or pervious areas, which influence the snowmelt process.
• Snow Removal: A process that removes snow from plowable impervious areas and transfers it to other areas or subcatchments.

Summary:

The snow.c module is an essential component of SWMM5 that simulates the interaction between snow, rainfall, and runoff. By modeling snow accumulation and melt, this module helps account for seasonal changes in runoff behavior due to snow cover. It includes a variety of parameters and functions to simulate snow accumulation, snowmelt, and snow removal, and it integrates this process into the overall hydrological modeling of subcatchments. The snowpack state (depth, cold content, and free water) is updated dynamically throughout the simulation based on precipitation and temperature conditions.