S25-107-Stormwater Report

Best Practice Erosion And Sediment Control                                       Erosion Hazard Assessment Form



                      Table 3 – Typical properties of various soil groups [1]
   Soil Groups                                           Typical properties [2]
     GW, GP               •    Low erodibility potential.
     GM, GC               •    Low to medium erodibility potential.
                          •    May create turbid runoff if disturbed as a result of the release of silt
                               and clay particles.
      SW, SP              •    Low to medium erodibility potential.
      SM, SC              •    Medium erodibility potential.
                          •    May create turbid runoff if disturbed as a result of the release of silt
                               and clay particles.
      MH, CH              •    Highly variable (low to high) erodibility potential.
                          •    Will generally create turbid runoff if disturbed.
      ML, CL              •    High erodibility potential.
                          •    Tendency to be dispersive.
                          •    May create some turbidity in runoff if disturbed.
Note: [1]       After Soil Services & NSW DLWC (1998).
      [2]       Any soil can represent a high erosion risk if the binding clays or silts are unstable.

Table 4 provides general guidelines on the suitability of various soil groups to various
engineering applications.

      Table 4 – Engineering suitability based on Unified Soil Classification [1]
                                            Embankments
                               USC                                        Fill         Slope        Untreated
Unified Soil Class                        Water           Non
                              Group                                                   stability      roads
                                        retaining        water
                                                       retaining
Well graded gravels            GW       Unsuitable      Excellent      Excellent      Excellent          Average
Poorly graded gravel           GP       Unsuitable      Average        Excellent       Average       Unsuitable
Silty gravels                  GM       Unsuitable      Average          Good          Average           Average
Clayey gravels                 GC        Suitable       Average          Good          Average       Excellent
Well graded sands              SW       Unsuitable      Excellent      Excellent      Excellent          Average
Poorly graded sands            SP       Unsuitable      Average          Good          Average       Unsuitable
Silty sands                    SM       Suitable [2]    Average        Average         Average            Poor
Clayey sands                   SC        Suitable       Average        Average         Average            Good
Inorganic silts                ML       Unsuitable        Poor         Average          Poor         Unsuitable
Inorganic clays                CL       Suitable [2]      Good         Average          Good              Poor
Organic silts                  OL       Unsuitable     Unsuitable        Poor         Unsuitable     Unsuitable
Inorganic silts                MH       Unsuitable        Poor           Poor           Poor         Unsuitable
Inorganic clays                CH       Suitable [2]    Average       Unsuitable       Average       Unsuitable
Organic clays                  OH       Unsuitable     Unsuitable     Unsuitable      Unsuitable     Unsuitable
Highly organic soils           Pt       Unsuitable     Unsuitable     Unsuitable      Unsuitable     Unsuitable
Notes:   [1]      Modified from Hazelton & Murphy (1992)
         [2]      Suitable only after modifications to soil such as compaction and/or erosion protection




IECA (Australasia)                                     November 2008                                         Page 4