FLOW DEPTH (D)

In the event the expected flowrate within the channel is unknown, the depth of the channel can be utilized as an estimate. In this case, the program assumes the channel is running completely full, thus assuming the maximum possible flow condition. This assumption is conservative, as many channels are not designed to flow completely full. Therefore, some products may be found to be unsuitable under the maximum conditions assumed, however, acceptable for typical, expected conditions. It is recommended to use the flowrate of the channel whenever possible.

FLOWRATE (Q)

The discharge (volumetric flow rate) of water within the channel. In order to compute the forces generated on the lining, the amount of water flowing through the channel must be known. This value is expressed as cubic feet per second (cfs) or cubic meters per second (cms).

FUNCTIONAL LONGEVITY

The estimated time period, based upon field observations, that a material can be anticipated to provide erosion control and agronomic benefits as influenced by composition, as well as site-specific conditions, including; but not limited to – temperature, moisture, light conditions, soils, biological activity, vegetative establishment and other environmental factors.

P-FACTOR

It is used to account for practices that reduce erosion separate from an erosion control product. An example of an application of the P-Factor would be using a bulldozer to track a slope. The default value for the P-Factor is assumed to be one.

R-FACTOR - RAINFALL FACTOR

The amount and intensity of rainfall is a critical input in predicting the volume of erosion on a project site. The R-Factor is the quantification of the rainfall amount and intensity for a given area, over a one year time period. R-Factor varies by location around the world. The USDA has mapped the United States and listed locations by city and state.

SOIL LOSS LIMIT (SLL)

The average depth of eroded material in inches that is acceptable for the site. A product will be determined acceptable for use if the predicted erosion in the protected condition is less than the soil loss limit. The factor of safety is computed as the ratio of the predicted, average soil loss in the protected condition to the soil loss limit. The default value for the soil loss limit is 0.01, which would allow 3340 lbs/acre to be eroded on the site over a year. The National Pollutant Discharge Elimination System (NPDES) governed by the EPA, has set a threshold of 4000 lbs/acre per year. Therefore, the default SLL in this program is set below the NPDES threshold to ensure that your site minimizes soil erosion. Lower SLL values would allow less soil erosion over a year and higher SLL values would yield more erosion over a year.