# 2:1.1.1 SCS Curve Number

The SCS curve number is a function of the soil’s permeability, land use and antecedent soil water conditions. Typical curve numbers for moisture condition II are listed in tables 2:1-1, 2:1-2 and 2:1-3 for various land covers and soil types (SCS Engineering Division, 1986). These values are appropriate for a 5% slope.

Table 2:1-1: Runoff curve numbers for cultivated agricultural lands (from SCS Engineering Division, 1986)

![\* Crop residue cover applies only if residue is on at least 5% of the surface throughout the year.](https://1348478613-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MTFpIHUB1K63DLhLJaf%2Fuploads%2FCraTKgWToLDGkMqpYsb7%2FTABLE1.jpg?alt=media\&token=3a52152f-6e97-41d9-861e-1a74dfd9d4f4)

![](https://1348478613-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MTFpIHUB1K63DLhLJaf%2Fuploads%2FUifPW5JBjmNeLqUeTrOC%2FTABLE2.jpg?alt=media\&token=9e0aca6a-7779-4573-9e4d-b5b040da86fd)

Table 2:1-2: Runoff curve numbers for other agricultural lands (from SCS Engineering Division, 1986)

![\[2\] Poor: < 50% ground cover or heavily grazed with no mulch;  Fair:  50 to 75% ground cover and not heavily grazed;  Good:  > 75% ground cover and lightly or only occasionally grazed.&#x20;
\[3\] Poor:  < 50% ground cover;  Fair:  50 to 75% ground cover;  Good:  > 75% ground cover. &#x20;
\[4\] Poor: Forest litter, small trees, and brush are destroyed by heavy grazing or regular burning;  Fair:  Woods are grazed but not burned, and some forest litter covers the soil;  Good:  Woods are protected from grazing, and litter and brush adequately cover the soil.](https://1348478613-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MTFpIHUB1K63DLhLJaf%2Fuploads%2FUyPi0qXXdTUAha3tmfPa%2FTABLE3.jpg?alt=media\&token=07db29c4-9dba-4428-87c1-a9f2d31b8906)

Table 2:1-3: Runoff curve numbers for urban areas (from SCS Engineering Division, 1986)

![\[5\] SWAT will automatically adjust curve numbers for impervious areas when IURBAN and URBLU are defined in the .hru file. Curve numbers from Table 6-3 should not be used in this instance.
\[6\] Poor:  < 50% grass cover;  Fair:  50 to 75% grass cover;  Good:  > 75% grass cover](https://1348478613-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MTFpIHUB1K63DLhLJaf%2Fuploads%2FcOYEUnXj5tXvhA30X9h0%2FTABLE4.jpg?alt=media\&token=5c432a05-07f5-4fb9-8345-eb9ae7c74fbe)