Coastal, Waterways & Floods

Coastal, Waterways & Floods

TYPAR Geosynthetics are imperative to the stability and performance of coastal and waterway applications. Our performance based products are designed to provide the strength, durability, and longevity necessary to protect shorelines, stream banks, levees, breakwaters,and dams from dynamic erosion forces and over-topping during rapid flood conditions.

Geotextile selection

Selection of a geotextile filter is key, as is the selection of stone size and layers for traditional approaches.

The geotextile should be sufficient to withstand initial installation as well as the intended use and loading of the area. Pore size should be sufficient to provide sustained permeability and filtration, allowing water to pass faster than the underlying soil. It must be flexible enough to conform intimately with the profile of the soil and rocks above it and withstand the points of the stone loading to avoid tears and punctures. 

Filter Properties
The amount of soil that can migrate through the geotextile filter depends on:

  • The relation of the geotextiles pore size, number and uniformity in relation to the particle size of the soil
  • Force magnitude (higher the force, greater potential for soil migration)
  • Inter-particle bonding and structure of the in-situ soil particle. Greater soil density yields greater inter-particle forces and less potential for the soil to migrate.

To function effectively as a filter, it is essential that the geotextile achieve a condition of equilibrium close to the geotextile/soil interface quickly once installed. Fine soil particles near the geotextile move due to the influence of seepage, establishing a natural filter. This process is complete one to four months following installation. The underlying foundation may become unstable if fine soil particles are able to pass through the geotextile, making the selection of the correct textile key to project success.

Geotextile performance is influenced by:

  • Particle structure, size distribution and pH of the soil
  • Geotextile pore size
  • Geotextile permeability in relation to the surrounding soil

As a general rule, when selecting a geotextile for filtration, the coefficient of the permeability of the geotextile should be 5 times greater than the underlying soil.

kg > 5 – 10ks

kg = coefficient of permeability for the geotextile
ks = coefficient of permeability for the soil


O90 < D85

O90 = apparent opening size for the geotextile (AOS)
D85 = particle size fraction for the soil

Similar to stone filters, the permeability of the geotextile is expected to be greater than the underlying soil. Site criteria will influence to what extent the geotextiles permeability will be greater than the surrounding soil. The relations between the AOL of the textile (095 or AOS) and the size of the underlying soil is key and depends on the characteristics of the soil – e.g. if it is cohesive.

See Table A for the effect that increasing a soils proportion of fines has on permeability. Table A shows typical values for the hydraulic conductivity of soil types.

Back to Coastal & Waterways Overview

Coastal defence showing traditional graduated stone silter system
Coastal defence showing traditional graduated stone silter system
Coastal defence showing traditional graduated stone silter system
TYPAR Permiability Coefficients for soil types


TYPAR Geotextiles
TYPAR Geotextiles