The fabric I plan to use is a non-woven polypropylene that is water and gas permeable but opaque. It is sold by Dupont under the brand name Typar and is commonly used for house-wrap in construction, riprap (shoreline structuring), sandbags and road construction to separate aggregate from soil. It is very durable and could be moved and re-used. There is much experience with Typar as a benthic barrier. The following is from the Lake Sutherland (Washington State) Association Newsletter regarding Typar.

“The new barriers have been the key to our success. Made of porous, non-woven fabric, not plastic, the material is rolled out underwater and secured with gravel-filled bags….The old barriers were made of burlap which degraded within a year, sometimes less, any stray milfoil readily established on top. The fabric barrier is much better. By preventing fragments from getting established, the new barriers have allowed us the breathing space to return and remove stray plants as they regrow or try to re-established.”

A 12 x 300 foot (3,600 sq feet) roll of Typar cost approx $350, or about 10 cents per square foot. Aquascreen, a product marketed for the purpose of benthic barrier applications, is sold for about 50 cents per square foot. Aquascreen has one advantage over Typar: A specific gravity of 2.5 as compared to .9 for Typar, which means that Typar is slightly bouyant. But the technique requires secure anchoring. The weeds want to stand up straight and must be held down, and while they decompose gases will accumulate and cause billowing to some extent even though the fabric is gas permeable, and this must be managed. This is the same challenge for any fabric. All else being about equal from what I have researched, price is the driving factor in the choice of Typar.