Response to Information Request - MCU12/0184

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                                                                               Callaghan & Toth

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 mJ/s    0.638 m3/s        1.092 m3/s
 Post Development Roof Area                      0.769 m3/s    0.851 m3/s        1.227 m3/s
 Roof Flow Increase                              0.231 m3/s     0.221 m3/s       0.135 m3/s


         TABLE 5.2:         Pre Dam Spillway and Post Dam Spillway


 Location                                             Q5          Q10               Q100
 Pre-Dam 1 &2 Spillway                         2.200 m3/s       2.58 mJ/s         4.50 mJ/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 mJ/s        -1.01 mJ/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 in considered to be similar to the
runoff from the existing roads.




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1209 Animal Husbandry   Top Forestry Rd. Ridgewood
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                                                                                  SWQMP
April 2013