24647 Seaview Tce Enviro Mgmt Plan

4.           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.

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

4.1.         K-factor – Soils
The geotechnical study carried out by Morrison Geotechnic (14 October 2014) reported soil profiles from
two boreholes (BH1 and BH2) and two test pits (TP1 and TP2). Soils were found to be wind blown dune
sand to depths of 5.2m (RL44.8m) in BH1 and 3.8m (RL46.3m) in BH2 over Teewah sands: brown medium
dense sand grading to very dense and yellow below RL37.8m in BH1 and RL42.0m in BH2. On the lower
slopes to the east of the site, surface dune sand overlaid Teewah sands and residual basement geology
(Tiaro Coal Measures sandstone) dominated.
The surface sand is loose, fine to medium grained with low plasticity silt fines, trace of coarse grained
gravel, mottled grey and pale brown. This is generally over silty sand, sandy clay/clayey sand and silty clay
above the sandstone bedrock.
A K-factor = 0.015 has been adopted for this analysis.

4.2.         R- factor – rainfall
A site specific annual rainfall erosivity factor of 5,659 has been calculated using Equation 2 below.

R = 164.74 (1.1177)S S0.6444                                                           Equation 2 (IECA 2008)

         Where:
                            R is the (annual) rainfall erosivity factor
                            S is the 2 year ARI, 6 hour rainfall event (15.8 mm/hr)

4.3.         LS - Slope-length
When considering sheet flow across the site’s exposed areas, the maximum slope lengths are quite small
during the initial piling and earthworks phases. It is not until works commence in the lower portions of the
site that slope lengths over the exposed surface reach a maximum of approximately 60m. Based on the
topographic information provided as part of the assessment, maximum slopes are expected to be
approximately 35%. A summary LS factors applied to each construction area (per Table E3 of IECA, 2008)
can be seen in Table 1.

4.4.         Cover (C) and Practice (P) Factors
Considering the works will expose the site area during construction a C factor of 1 has been adopted, to
reflect the level of cover offered. The C factor will reduce as construction is completed in areas.

71 Seaview Terrace, Sunshine Beach - Erosion and Sediment Control Plan                                   Page 3

Hutchinson Builders
17SUN-0024/1600102