8. Volume 5 - Stormwater Management Plan

                                              LAMBERT & REHBEIN
                                                  ENGINEERS • MANAGERS • SCIENTISTS


3.5     DETENTION REQUIREMENTS
From the hydrological modelling it is evident that the development would cause an increase in the
peak stormwater flows. Therefore stormwater detention will be required to avoid adverse impacts
on downstream properties.

The stormwater detention system will attenuate all peak flows up to, and including, a Q100 storm.
Refer XPStorm outputs included in Appendix D for further details.

3.5.1   ABOVE GROUND DETENTION TANKS

The on-site detention will be provided by a detention tank located under the service station shop.
It is proposed to direct all flows from Catchment A, up to a Q100 event, to the proposed detention
tank.

Due to site levels, Catchment B bypasses the detention tank, however the tank has been
modelled to ensure the total flows leaving the site are less than pre-developed conditions.

The proposed lawful point of discharge for the stormwater is the existing gully pits located in
Project Avenue. The details for the proposed stormwater management and detention tank are
shown on the civil engineering plans enclosed in Appendix C.

The proposed details for the detention tank is shown in Table 7 below.
                           Table 7 Above Ground Detention Tanks Details


                     Q100 Max Depth (m)                                  1.65

                     Q100 Storage Volume (m3)                            34

                     Orifice 1 Diameter(mm)/Invert Level (m) *       130Ø / 0.0

                     Orifice 2 Diameter(mm)/Invert Level (m) *       150Ø / 0.65

                     Orifice 3 Diameter(mm)/Invert Level (m) *       200Ø / 0.8

                     High Level Weir Length (m) / Invert Level (m)    1.6 / 1.2

                    *Invert level from base of tank.

With the addition of the above detention parameters to the developed site, the attenuated peak
flows are less than the pre developed conditions. The attenuated peak outflows and percentage
increase/decrease to that of the pre development flows, for each storm event, are shown below in
Table 8.




 Ref: B16239CR002                                           - 8 -                     Stormwater Management Plan
                                                                                   Noosa Energy Centre - Noosaville