Listed below are the accepted coefficiency factors for roads, roofs and driveways.
| Type |
Coefficiency Factors |
| Roads |
|
| Asphalt Or Concrete With Curb-Gutters |
95 -100% |
| Asphalt Or Concrete With Roadside Ditches |
90 - 95% |
| Gravel Or Stone With Roadside Ditches |
80 - 90% |
| Undeveloped Land |
|
| Flat Pervious Soils With Vegetation |
5 - 10% |
| Rolling Pervious Soils With Vegetation |
10 - 15% |
| Flat Moderately Pervious Soil With Vegetation |
15 - 20% |
| Rolling Moderately Pervious Soil With Vegetation |
20 - 30% |
| Flat Impervious Soil with Vegetation |
30 - 40% |
| Rolling Impervious Soil With Vegetation |
40 - 50% |
| Any Lands Without Vegetation Add An Additional |
20% |
| Developed Land |
|
| Roofs, Driveways And Parking Lots That Are Asphalt Or Concrete |
90 - 95% |
| Yards, Roadside Woods, Outlots, Playground, Swamps, Parks & Etc. Refer To Undeveloped Land |
05 - 70% |
Group Soil Types
- Pervious Sand
- Moderately Pervious Sandy Loam
- Impervious Clay
Only with approval of the Water Resources Commissioner will a Group C (Impervious Soil) ever be used for retention basins.