SWMHYMO-TIMP & XIMP 1

[yanthi]

Could you please help me to figure out XIMP and TIMP in SWMHYMO model
My catchment area includes
Roof area ( run off coefficient n = 0.9) 0.5ha
grass area ( n= 0.25) 1.0ha
Asphalt area(n= 0.9) 0.8ha
Catch basins are located on asphalt area and roof drains connected to them.
Please some one help me to figure out TIMP and XIMP values for this catchment

If all the roof water, drains to grass
what would be TIMP & XIMP values?
Appreciate your help!

 

[Ryb01]

TIMP= total impervious area for your catchment(i.e 0.50 or 50%)
XIMP= total directly connected impervious area(i.e 0.30 or 30%). Directly meaning, runoof flows over a impervious surface(not pervious surfaces) and is then discharged to a storm sewer/outlet.

Both of these parameters need to be inputted as a fraction of the total catchment area in SWMHYMO.

TIMP for your site would be the roof area + asphalt area.
If the roof drains captured 100% of the runoff from the roof and the drains were conected to the storm sewer, XIMP=TIMP.

If your roof drains to a grassed area, your XIMP would only equal your asphalt area.

Something to consider.......is there driveways, sidewalk, SWM Pond??? These will also affect your XIMP and TIMP values.
Driveways, directly connected
SWM Ponds, directly connected
Sidewalk, not directly connected


Hope his helps

Ryb01