1209 SWQMP Report_3 2013

                                                                                  Callaghan & Toth

Farm contour benches which form the existing catchment that drains all runoff to existing
dams at the base of each valley. The dams 1 & 2 shown on plan Plan 01 will have a 5m wide
broad crest weir spillway which will alternate flows to be equal to pre-development
concentrations.

The dam modifications have been modelled to act as a detention basin. The spillway size is
sufficient to reduce the increase in runoff from the roofs (Table 5.1) for a Q5, Q10 and Q100
storm back to predevelopment levels as shown in Table 5.2. Refer to attached Detail
detention basin calculations for Q10 Pre and Post development flow calculation for Dams
and Roofs in Appendix 5

         TABLE 5.1:        Pre-Development and Post Development Discharges

 Location                                            Q5              Q10                Q100
 Pre-Development Roof Area                       0.538 m3/s 0.638      m3/s 1.092           m3/s
                                                        3
 Post Development Roof Area                      0.769 m /s 0.851      m3/s 1.227           m3/s
                                                        3
 Roof Flow Increase                              0.231 m /s       0.221 m3/s          0.135 m3/s

         TABLE 5.2:        Pre Dam Spillway and Post Dam Spillway

 Location                                           Q5              Q10                  Q100
                                                       3
 Pre-Dam 1&2 Spillway                         2.200 m /s 2.58         m3/s 4.50             m3/s
 Post Dam 1&2 Spillway                       Spillway depth   Spillway depth        Spillway depth
                                                  0.24m            0.26m                 0.42m

                                                 1.81 m3/s        1.90 m3/s           3.49 m3/s
 Dam 1&2 Spillway flow                          -0.39 m3/s        -0.68 m3/s          -1.01 m3/s
 Decrease

The detention effects of Dam 1 & 2 spillways in all cases reduce the flows by more then the
increase in flow caused by the shed roofs.

As there are existing gravel roads already along the ridges the effect on runoff from the new
gravel roads is considered to be similar to the runoff from the existing roads.




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1209 Animal Husbandry – Top Forestry Rd, Ridgewood                             SWQMP_REV_3
September 2013