Snow Parameters (SWMM)
To view and edit Global Snow Parameters used for modelling snow fall and snow melt in the Property Sheet select Model parameters | Snow parameters from the Model menu.
For further information on the use of these parameters when simulating snow melt, see the Snow Melt Model topic.
The Object Properties Window for Snow Parameters contains the following information:
Database Table Name: sw_snow_parameters
|
Field Name |
Help Text |
Database Field |
Size |
Precision |
Default |
Error Lower Limit |
Error Upper Limit |
Warning Lower Limit |
Warning Upper Limit |
||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
Areal depletion curves |
This field contains a series of records defining the relationship between the area that remains snow covered and snow pack depth for both impervious and pervious surfaces. These are entered on the Areal Depletion Curves Editor which is displayed by clicking on the |
adc |
Array |
|
|
|
|
|
|
||
|
Antecedent temperature index weight |
Weight used to calculate antecedent temperature index. The degree to which heat transfer within a snow pack during non-melt periods is affected by previous air temperatures. Smaller values reflect a thicker surface layer of snow which results in reduced rates of heat transfer. |
antecedent_temp_idx |
Double |
|
|
3 |
0.5 |
0 |
1 |
|
|
|
Elevation above sea level |
Average elevation of the catchment above sea level. This value is used to provide a more accurate estimate of atmospheric pressure. The effect of wind on snow melt rates during rainfall periods is greater at higher pressures, which occur at lower elevations. |
elevation |
Double |
|
Z |
3 |
0 |
-9999 |
9999 |
|
6000 |
| Latitude | The latitude of the snow area in degrees North. This is used when computing the hours of sunrise and sunset, which in turn are used to extend minimum and maximum daily temperatures into continuous values. It is also used to compute daily evaporation rates from daily temperatures. | latitude | Double | 3 | 50 | -90 | 90 | ||||
| Longitude correction | This is a correction, in minutes of time, between true solar time and the standard clock time. It depends on a location's longitude (θ) and the standard meridian of its time zone (SM) through the expression 4(θ-SM). This correction is used to adjust the hours of sunrise and sunset when extending daily minimum and maximum temperatures into continuous values. | longitude_correction | Double | 3 | 0 | -60 | 60 | ||||
|
Negative melt ratio |
Ratio of an area's current snow depth to the depth at which there is 100% areal coverage. |
negative_melt_ratio |
Double |
|
|
3 |
0.6 |
0 |
1 |
|
|
|
Dividing temperature between snow rain |
The temperature above which precipitation (defined on the Rainfall tab of the Rainfall Event) will be treated as rain. At or below this temperature, precipitation will be treated as snow. |
snow_temperature |
Double |
|
CF |
3 |
1.1111 |
-273 |
100 |
|
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