Current technical guidance on river scour and erosion control countermeasure design includes recommendations for either a granular or geotextile filter beneath countermeasures consisting of armoring materials. However, there has been little guidance on installation techniques for placing the filter underwater. The Transportation Research Board’s National Cooperative Highway Research Program Project 24-42 developed specific guidance for use by design, construction, and maintenance personnel on the function and installation of filters, particularly for underwater placement.
A survey of practitioners across the U.S. revealed that some underwater installation practices in other countries are still new and largely untried in the U.S, including the use of self-sinking geotextile composite fabrics and the use of a flexible tremie hose to deliver a slurry of coarse granular filter material to divers for placement underwater.
Practitioners in the U.S. indicated underwater inspection of a filter installation is not usually required before placing the armor layer on top. Our researchers recommended that this undesirable practice be rectified.
The research concluded the variety of available filter material types and placement techniques accommodates most underwater filter requirements, so in the vast majority of instances, a filter can be placed as an integral part of a properly designed and installed scour or erosion control countermeasure.