Stormwater Management Report · MCU19/0008

           Manning’s roughness for of 0.06 was considered appropriate due to the land use of the site.
           A 2D head boundary line with a free outfall was used to define the 2D model extent to
            appropriately account for flow freely flowing east to Sunshine Beach.
Model Setup
Two models were developed for the site. These are summarised as follows:

Pre-developed model
           The existing site was modelled as a single catchment (Node A). The hydrograph of the
            catchment was linked to and evenly distributed across a rainfall/ flow area grid at the rear of
            the site. The peak flow rate discharging to Sunshine Beach was measured at a flow line at the
            rear of the site and the total runoff volume discharging to Sunshine Beach was measured as
            the total runoff inflow at Node A.
Post-Developed Model
           The developed site was modelled as two catchments. The rear portion of the site consisting of
            pervious areas (Node A) was modelled as per Node A for the pre developed model. The upper
            portion of the site consisting of impervious areas was linked to a storage node (Node B) linked
            to the 2D network. This node was used to model the detention/infiltration tank. The peak flow
            rate discharging to Sunshine Beach was measured at a flow line at the rear of the site and the
            total runoff volume discharging to Sunshine Beach was measured as the sum of the total runoff
            inflow at Node A and the total runoff outflow at Node B.
The catchment data for each model is summarised in Table 2 below:
Table 2 - Catchment Summary

 Model                   Node       Area (Ha)                Slope (%)           % Impervious

 Pre Developed           A          0.061                    25                  65

 Post Developed          A          0.021                    25                  10

                         B          0.040                    25                  83

3. 4       XP Sto rm Resu l ts

The results of the ensemble statistics utility are presented in Figures 2-4 below.




                             Figure 2 - Ensemble Statistics Utility Results; 0.5EY event



4 April 2019                                Stormwater Management Report                                  7
S18-030                                        22 Arakoon Crescent,