Dear Raviraj,

The topographic wetness index is defined as: ln(a/tanb)

where a is the local upslope area draining through a certain point per unit contour length and b is the local slope in radians.

Stream power index (SI) takes into account both a local slope geometry and site location in the landscape combining data on slope gradient and catchment area:

SI = ln (CA . tanG)

where CA and G are catchment area and slope gradient, respective

The sediment transport index is defined as :

STI = (As/22.13)^0.6 x (sinb/0.0896)^1.3

As is the upstream area and b is the slope at a given cell.

Regards

Bachir ACHOUR

Thank you sir @ Bachir ACHOUR for your answer. Is the a in TWI (Topographic wetness index) can be considered as Flow accumulation?

Dear Ravirej,

No, I don't think so. The index is a function of both the slope and the upstream contributing area per unit width orthogonal to the flow direction.

Regards

Bachir ACHOUR

what are the units of Topographic Wetness Index (TWI), Stream Power Index (SPI), and Sediment Transport Index (STI)