From the GMA Techline
Subject: Product specification We are proposing to stabilize a section of eroded riverbank with riprap. We would like to install a fabric beneath the riprap to hold the existing sandy soils in place.
Can you give us a recommendation?
The river is tidal and the area is exposed to full sun so UV is a factor to consider.
Reply: Your question is a common one that has had quite a bit of past research, to the point that AASHTO has a generic specification for this particular application.
The spec is embodied in AASHTO M288-05, and I will fax the appropriate info to you today.
Thanks for asking.