EagFirRsp

- Overland flows through the Tait Street properties, around nodes N45 to N50.

- Water levels in Tait Street at Node 45, at the point of inflow for roofwater from the new lots 1 to 9.

- Water levels at Node N14B at the sag in Tait Street.

- Water levels at Node 11, midway along the creek between Tait Street and the caravan park.

- Water levels and flow rates in the creek at Node N2, at the point of discharge to the caravan park.


Water Levels At Node N36, At The Eagle Drive Sag

The pre-and post-development water levels in the Eagle Drive sag are summarised in Table 2, below.

In the pre-development scenario, the overflow level into No 14 Eagle Drive at EL 5.77 is just overtopped in
the AEP 20% (5 yr) storm and overtopped by 0.10 metre in the AEP 1% (100 year) storm which, because of
the almost flat overflow profile, generates substantial overflow rates into the property. The adjoining
properties, with ground levels of 5.82 and 5.84 at their Eagle Street frontages, are also at risk in the AEP 10%
and higher events.

In the absence of any mitigation, the post-development diversion of developed site runoff to Eagle Drive
would adversely affect water levels in the sag. However, with the proposed additional underground piping at
the sag and with an inlet chute cut into the verge, the water levels in the sag are significantly reduced and
overflows through the properties adjoining the sides of the basin are eliminated.

Nett Result: Complete impact mitigation; substantial benefit

Table 2: Water Levels At Node N36 In The Eagle Drive Sag
 Event                Pre-Development       Post Development
 AEP (ARI)             EL (m)                EL (m)
 AEP 1% (100 yr)       5.87                  5.80
 AEP 2% (50 yr)        5.87                  5.78
 AEP 5% (20 yr)        5.86                  5.77
 AEP 10% (10 yr)       5.85                  5.74
 AEP 20% (5 yr)        5.84                  5.72
 AEP 50% (2 yr)        5.75                  5.66
 AEP 67% (1yr)         5.71                  5.63


Overflow Rates Through The Park, Between Nodes N34 and N22

In the pre-development scenario, the relevant flows here are the overflows from the Eagle Drive sag. In the
post-development scenario, in the absence of the detention basin and its inlet and outlet, the diverted flows to
Eagle Street would cause an increase in overland flow rates at this location. However, with the basin in place,
the relevant flows are restricted to the overflows from the weir in the basin embankment, which will only occur
in events of AEP 20% or higher – lesser event flows will be piped underground through to the creek on the
downstream side of Tait Street.



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BSM Doc File EagFirResp.Doc