24647 Seaview Tce Enviro Mgmt Plan

7.              Sediment Control
A Type 1 control (i.e. a sediment basin) is not triggered by IECA (2008) due to the fact that the disturbed
area is less than 2,500m². However, due to the potential soil loss and the proximity to conservation area, a
sediment basin is proposed. Item 33 of the Noosa Council Decision Notice requires that all discharges from
the site up to and including the 85th percentile 5 day rainfall event must not exceed 50mg/L of Total
Suspended Solids (TSS). To achieve this objective, calculations have been undertaken to determine the
sediment basin volume required to capture the 85th percentile 5 day rainfall event (i.e. 46mm).

A summary of sediment basin design specifications is provided in Table 6. A weighted average runoff
coefficient has been determined, assuming 90% of the site is compacted (Cv = 1.0), while the remaining
10% of the site is uncompacted, Class A material (Cv = 0.22). Therefore, the runoff coefficient applied to
the sediment basin calculation, Cv = 0.92.
Table 6 – Sediment Basin Design Summary


Catchment Area              Design Rainfall            Settling Zone   Sediment Storage Volume         Total Volume at Spillway
     (ha)                    Event (mm)                Volume (m3)          (RUSLE) (m3)*                        (m3)

        0.23                       46.0                    97.3                    40.6                         137.9

* Assumes a 3 month maintenance period

The required storage volume will be provided within the excavations to be undertaken for the proposed
pool. It is expected that due to the sandy nature of the site, settling of sediments will occur quite rapidly.
Testing of runoff captured in the basin must be undertaken prior to discharge from the site to ensure it
complies with the discharge criteria of 50mg/L of TSS. If required, flocculation will be undertaken to assist
in the settling of sediment particles.
*Note: a correlation may be established between site TSS and NTU by sampling and analysis of captured
surface water and the relative NTU limit may be adopted in place of TSS*

7.1.            Emergency Spillway
An Emergency Spillway has been included as part of the design for the proposed site sediment basin. The
spillway has been sized for a 1 in 50 year event. A summary of design parameters is included in Table 7.
Table 7 – Spillway Design Summary


   Time of                Rainfall         Peak Flow       Channel     Minimum       Horizontal Side        Proposed Lining
Concentration            Intensity           (m3/s)       Base Width   Depth (m)      Slope of Weir
    (min)                (mm/hr)                             (m)

        5                   292             0.19(1)           5.0       0.40(2)           1:2                  Geotextile

NOTE:       (1) 1 in 50 year ARI event
            (2) Depth includes freeboard




71 Seaview Terrace, Sunshine Beach - Erosion and Sediment Control Plan                                                      Page 8

Hutchinson Builders
17SUN-0024/1600102