Attachment C - Stormwater report

 6.            Erosion and Sediment Control (ESC)
6.1.         Erosion Risk Assessment
An erosion risk assessment has been conducted using the Revised Universal Soil Loss Equation (RUSLE). The
calculated soil loss is then used to determine the level of sediment control required, as well as stabilisation
and staging requirements. It must be noted that no soil sampling has been conducted on site, and as such,
a conservative erodibility (K) factor has been adopted based on soil mapping.

It has been assumed that no dispersive soils will be encountered on site. If at any time dispersive, or sodic
soils are encountered the client should contact the plan preparer for a review of the plans and procedures.

A = K x R x LS x P x C                                                                 Equation 1 (IECA 2008)

         Where:
                   A is the predicted soil loss per hectare per year
                   K is the soil erodibility factor
                   R is the rainfall erosivity factor
                   LS is the slope length/gradient factor
                   P is the erosion control practice factor
                   C is the ground cover and management factor

                K = 0.055
                R = 5923
                LS = varies
                C=1
                P = 1.3
As a conservative approach, a K factor of 0.055 has been applied, and represents silty loam soils.

Rainfall erosivity has been calculated using the following equation:

         R = 164.74 x 1.1177S x S0.6444

Where:

         S is the 39% AEP 6 hour rainfall event (mm) (IECA, 2008)

The erosion risk categories are summarised in Table 15.

Slope length/gradient has been varied to assess how the erosion risk varies as the slope of the site varies,
as summarised in Table 16.
Table 15 – Erosion Risk Categories

   Soil Loss (t/ha/yr)           Erosion Risk Category
         0 to 150                       Very Low
        150 to 225                          Low
        225 to 500                      Moderate
       500 to 1500                         High
          > 1500                         Extreme


Stormwater Management Plan – Lot 1 on SP108094, 305 Lake Macdonald Drive                                Page 26

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