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16-001014-01A (Swmp)
Attached to the e-mail Operational Works Application OPW16/0203 - 3 of 4.
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3 PEAK FLOW INVESTIGATION
Hydrological analysis using XP-RAFTS was undertaken to demonstrate that the development of the site with mitigation
measures would not result in adverse impact downstream. The methodology undertaken in this analysis is consistent with
the past approvals. The following scenarios were undertaken in this analysis.
Existing Scenario represents the hydrology for the catchment under existing conditions. Catchment parameters (i.e.
infiltration loss and lag parameter values) were adopted as per Water Technology’s Cooroy Flood Study (Report No.
J2835-01_R02v01 dated 26 July 2013) which is the adopted hydrological modelling for the area and was prepared
specifically for the Sunshine Coast Regional Council. The report and corresponding models were supplied by Noosa
Shire Council.
Peak flow results determined in this scenario were compared with developed peak flow results to assess the change
in peak flows at site discharge locations.
Developed Mitigated Scenario represents the hydrology for the catchment under proposed development conditions
with mitigation. This scenario was undertaken to determine the adequacy of the proposed mitigation measures to
reduce peak flows back to or below existing conditions, therefore demonstrate no adverse impact.
The Existing and Developed Mitigated Scenario were modelled using the computer package XP-RAFTS. XP-RAFTS
analysis enables the hydrological modelling of the site for numerous design storm events and land uses. The subsequent
sections indicates the various assumptions and procedures used in developing each XP-RAFTS model.
3.1 EXISTING SCENARIO
The Existing Scenario was undertaken to determine peak flows discharging from the site under existing conditions.
3.1.1 CATCHMENT CHARACTERISTICS
Existing Catchments were delineated based on existing survey and aerial information. Existing catchments provided are
in accordance with the Concept SWMP Report (No. B14158.W-03A dated November 2015), only the Fraction impervious
value for Catchment D1 (Trading Post Road) has been updated to reflect the latest survey information. Catchments were
also split into various sub-catchments for modelling purposes. Fraction impervious values have been determined using
detailed survey and aerial information. Vectored slope has also been measured from the survey.
A summary of the existing catchment details are provided in Table 3-1 below.
Table 3-1: Existing Scenario Catchment Details
Downstream Sub-
Overall Sub- Fraction
Sub- Catchment Vectored Slope (%)
Catchment catchment Impervious
Catchment Area (ha)
Northern A1 A2 0.78 0.12 0.7%
A2 A_OUTLET 1.62 0.10 2.9%
Central B1 B2 1.38 0.23 1.7%
B2 B3 3.66 0.01 2.5%
B3 B4 2.32 0.03 7.1%
B4 D2 0.55 0.25 4.0%
South C1 C2 0.93 0.32 0.8%
C2 C3 5.14 0.02 2.6%
C3 D 0.64 0.00 6.0%
Central & South D1 D2 0.35 0.44 4.4%
D2 D_OUTLET 1.20 0.09 4.0%
16-001014-01 | STORMWATER MANAGEMENT PLAN (SWMP) COOROY RETIREMENT COMMUNITY, TRADING POST
| PALM LAKE RESORTS ROAD, COOROY |7
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