Slope Adjustments

The moisture condition II curve numbers provided in the tables are assumed to be appropriate for 5% slopes. Williams (1995) developed an equation to adjust the curve number to a different slope:

$CN_{2s}=\frac{(CN_3-CN_2)}{3}*[1-2*exp(-13.86*slp)]+CN_2$ 2:1.1.12

where $CN_{2s}$ is the moisture condition II curve number adjusted for slope, $CN_3$ is the moisture condition III curve number for the default 5% slope, $CN_2$ is the moisture condition II curve number for the default 5% slope, and $slp$ is the average fraction slope of the subbasin. SWAT+ does not adjust curve numbers for slope. If the user wishes to adjust the curve numbers for slope effects, the adjustment must be done prior to entering the curve numbers in the management input file.

Table 2:1-1: SWAT+ input variables that pertain to surface runoff calculated with the SCS curve number method.

Variable Name	Definition	Input File
IEVENT	Rainfall, runoff, routing option.	.bsn
ICN	Daily curve number calculation method: 0 calculate daily CN value as a function of soil moisture; 1 calculate daily CN value as a function of plant evapotranspiration	.bsn
CNCOEF	$cncoef$: Weighting coefficient used to calculate the retention coefficient for daily curve number calculations dependent on plant evapotranspiration	.bsn
PRECIPITATION	$R_{day}$: Daily precipitation (mm H$_2$O)	.pcp
CN2	$CN_2$: Moisture condition II curve number	.mgt
CNOP	$CN_2$: Moisture condition II curve number	.mgt