Appendix E - Stormwater Management Plan

Summary

Table A and B below indicate a comparison between existing and developed flood levels and
velocities within the existing channel on site.

Table A – Flood Level Comparison

 Cross Section      Ex WSL (m AHD)        Dev WSL (m AHD)         Difference (m)
       A                98.77                  98.67                   -0.09
       B                98.58                  98.57                   -0.01
       C                98.30                  98.30                    0.00
       D                97.97                  97.95                   -0.02


As indicated in Table A there are reductions in flood levels at each cross section location within the
existing swale due to the peak flow mitigation measures proposed. It is also noted that flood levels
will be significantly lower since they overtop the left channel embankment and sheet flows across
the site boundary (under both existing and developed conditions).

Table B –Velocity Comparison

 Cross Section      Ex Velocity (m/s)     Des Velocity (m/s)      Difference (m)
       A                  0.68                  0.95                    0.26
       B                  0.73                  0.87                    0.14
       C                  0.72                  0.94                    0.22
       D                  0.69                  0.68                   -0.01


While velocities within the existing swale have been slightly increased. The design velocity is less
than 1.0m/s which is not expected to cause scour.

Proposed Channel Capacity Immediately Downstream of Culvert Outlet

A check of the capacity of the proposed channel immediately downstream of the proposed culverts
was determined using Manning’s calculations (refer to the section below). Results indicate that flood
levels during the 1% AEP storm are well below the proposed level of the Caretakers building (by
more than 2m). Therefore, in the instance that Caretaker’s building floor levels are adjusted slightly
for detailed design, the building will not be impacting by flooding from the WQCP outflows.