Reference Document - MCU24 0155 (As Published).pdf

DCM BUILDING DESIGN

18 SHEARWATER STREET, PEREGIAN BEACH – STORMWATER MANAGEMENT PLAN
3         CATCHME NT ANALYSIS

The existing catchment for the site consists of a half road pavement and verge catchment as the
external component and the internal site as the internal component. Since the external component
area and catchment parameters would remain the same in both pre and post development scenarios,
the catchment analysis has been limited the internal catchment only.


3.1       Rati onal Method
As the site is small, a simple Rational method calculation is suitable to determine the pre and post
development flows.

The Rational method will be used as outlined in the Queensland Urban Drainage Manual (QUDM)
2016 edition, Chapter 4 – Catchment Hydrology.


3.1.1     C10 Values for Impervious and Per vio us Catchm ent Area s
The C10 values for each portion of the impervious and pervious catchment areas have been
calculated separately due to the highly permeable properties of the soil in the area. C10 values have
been calculated as from tables 4.5.1, 4.5.3, and 4.5.4 and will be taken as 0.35 for pervious areas
and 0.9 for impervious areas. These C10 values will be used for both Pre and Post Development
scenarios.


3.1.2     Time of Co ncentr ati on
From section 4.6.5 of QUDM a minimum time of concentration of 5 minutes has been adopted plus
another 1 minute for a total time of concentration of 6 minutes for the catchment.


3.2       Pre Developmen t
As shown in Figure 1 of this report, the total catchment area for the site is 546.5m 2 and the total
impervious area is 350.7m2.

Calculated C10 values and fraction impervious Fi are presented in Table 1 below.



Table 1: Pre Development Catchment Information

                                CATCHMENT INFORMATION
                                                           OVERALL
                                       PERVIOUS IMPERVIOUS
                        Area(m2)             195.8           364.5
                        tc                             6
                        Fraction
                        impervious, fi,
                        %                     35.8           64.2
                        1
                         I10                          74.8
                        C10                   0.35            0.9         0.70




                                                                                                Page 10 of 17