20230025_Gympie Tce Hotel SWMP

 STORMWATER QUANTITY
The existing site is developed and has a percentage impervious of around 95%. The estimated time of concentration
for the existing site is 5 mins due to the high percentage of roof areas and pipes connected directly to the existing
drainage network.

The proposed development will not result in an increase to the total impervious area of the site or reduction in the
time of concentration. Therefore, it is estimated that there will be no increase in stormwater runoff from the site due
to the development.

As there is no increase in stormwater runoff from the site, on site detention is not required for the development.
Furthermore, on site detention would provide limited benefit given the site is at the bottom of the catchment and
adjacent to Noosa River.

The site has been modelled using the DRAINS software to assess the peak flow hydrology of the site. The existing
condition has only been modelled to provide an indication of stormwater flow from the site.

An ILSAX model has been used to assess the proposed development against the ensemble of storm temporal
patterns for the East Coast North region. The models have been run using the ensemble of storm events for durations
from 5 minutes to 3 hours to determine the critical storm duration and the mean peak flowrate from the storms. The
temporal patterns have been imported from the ARR Datahub, and rainfall intensities have been imported from the
Bureau of Meteorology IFD rainfall data for the location.

A summary of estimated flows are provided in Table 6-1 below.

                                               Table 6-1 Existing Peak Discharge from Site

                                                                     Q (m³/s)
              AEP
                                            1/EX1                          1/EX2           2/EX2
              4EY                            0.036                         0.020            0.021
             0.5EY                           0.077                         0.042            0.046
              10%                            0.115                         0.062            0.068
               5%                            0.133                         0.071            0.079
               2%                            0.156                         0.083            0.092
               1%                            0.174                         0.092            0.103




Project number 20230025                                                                                         Page 14 of 22
File 20230025_Gympie Tce Hotel SWMP, 2023-05-31 Revision 0



P +61 7 5211 1003                 A 75 Noosa Drive, Noosa Heads Qld 4567           E [email protected]    recorconsulting.com