Storm Water management plan · MCU12/0133.03

Noosa Council documents


                  Bligh Tanner Consulting Engineers                                                                      Page 8
                  Noosa Flexi Learning Centre Stormwater Management Plan
                  August 2012




                  3 STRATEGY DESCRIPTION AND PLAN
                  The overall intent of the stormwater strategy is to mimic the natural hydrology of the site by
                  minimising the level of disturbance to the existing ground conditions.

                  Key features of the strategy include:
                     1. Maintaining ground-level permeability across 90% of the site:
                              a. Only 3% of the site (177 m²) will be slab-on-ground construction (for the Music
                                   building (due to soundproofing needs) and part of the Create building (due to
                                   the raised ground levels in that area). The majority of structures will be built on
                                   raised piers (consistent with a Noosa beach-house feel) to largely preserve
                                   ground level infiltration characteristics. The pier-construction technique will
                                   preserve large areas of shallow tree roots, which will assist in maintaining the
                                   natural infiltration rate of the soils and retaining natural biological nutrient
                                   removal capacity.
                              b. 7% of the site is carpark, and this will use permeable pavement to reduce
                                   runoff from small rainfall events.
                     2. 68% of the site free is free of structures (buildings/carparks) which will minimise
                         change to pollutant generation or infiltration properties. This area includes significant
                         retention of existing vegetation, as well as revegetation with existing species.
                     3. Roof runoff will be captured in rainwater tanks that are designed to suit the non-
                         potable water demands at the Flexi-Learning Centre. 25% of the site is covered in
                         roofs and about 60% of roof areas will drain to rainwater tanks, and about 60% of this
                         water is able to be reused. The overflow from these tanks will be diverted to
                         infiltration trenches. The balance of roof areas will drain directly infiltration trenches,
                         rather to via rainwater tanks, because the relatively low non-potable water demands
                         at the Centre do not justify harvesting water from every roof.
                     4. The mean annual volume of surface runoff leaving the site is expected to be about
                         20% less than existing levels (due to rainwater harvesting and infiltration).
                     5. Runoff from the site will enter the stormwater drainage system along Girraween Crt,
                         which drains through an existing bioretention/infiltration system at the end of the court
                         before reaching the Noosa National Park/Girraween Nature Reserve and Burgess
                         Creek. Whilst this existing bioretention system is not specifically needed to treat
                         runoff from the site (and probably isn’t designed to do so), it does provide an
                         additional layer of protection to the receiving environment (given the nature of the
                         intended use, there are unlikely to be any activities on the site that would generate
                         atypical pollutant loads).
                     6. The small increase in impervious areas means there is only a small increase in peak
                         flows under major storm conditions. The very small amount of flood detention
                         required (about 1 m3) will be easily accommodated within the site design at the
                         detailed design stage (as part of infiltration systems, additional landscape
                         depressions or additional airspace in rainwater tanks).
                     7. Overland flow paths will be similar to existing conditions, and under major storm
                         events water will sheet flow across the south-western boundary of the site on to
                         Girraween Crt and then flow west towards Burgess Creek.




                                                                                                     Print Date: 2 March 2020, 2:19 PM