Hello!
I am using the SDR model for watersheds in the southeastern region of Brazil. In studies conducted in Brazil, there is no consensus on the value of the c factor for urban and water areas; some use 1, others use 0. Is there any recommendation from InVEST regarding this?
Thank you.
Welcome to the forum @isabelammartins -
We usually give a USLE C value of 0 to water areas. If the water bodies are lakes, then they are more likely to collect sediment than produce it. Also, SDR does not model erosion within the stream network itself, only over land, and the calculations stop once the sediment reaches a stream.
For urban areas, I calculate this value based on knowing what the urban area is like. Some are mostly pavement, in which case the value can be very low, close to 0. Some have a mixture of pavement and green space. For these, I will usually take a weighted average between the C value for pavement (0 or close to it) and the C value for forest, grassland, or whatever other land cover type best represents the green space. So if it looks like the area is around 75% developed, and 25% forest, you can take (.75 x C_urban) + (.25 x C_forest). If you know that there’s a lot of bare soil in the urban areas, then that can be included in the weighted average instead/as well.
~ Stacie