smiths lake planning study volume 1: text - Great Lakes Council

FLOODING AND DRAINAGE 32
60
50
Natural
Urbanised
40
30
20
10
0
0 0.2 0.4 0.6 0.8 Time 1 (hours) 1.2 1.4 1.6 1.8 2 2.2
Figure 3-4 Impacts of Development on Tarbuck Creek 1% AEP Flows
These higher flows and greater runoff volumes will also result in higher flood levels and
increased velocities. This usually causes scour of the creek bed and under-cutting of creek
banks. The subsequent bank slump into the creek can produce sedimentation of the creeks
further downstream where slopes are flatter and velocities are lower. This sedimentation is in
addition to the increased sediment load coming from the catchment through inappropriate
construction practices.
All of the impacts described above are able to be mitigated to varying degrees through the
implementation of a workable Stormwater Management Plan. A plan would need to be created
for each area of land to be developed taking into account the specifics of the site’s
characteristics (eg. soil types, slopes, type of development). These issues are discussed in more
detail in Section 4.
3.3.2 Impacts of Filling for Residential Development in SLVA
The primary impacts on the hydrological regime of filling for residential development include:
• loss of flood storage causing increased flood levels in some circumstances; and
• loss of floodway conveyance causing reduced flow capacity, increased velocities and flood
levels.
These two impacts are discussed below.
Loss of Flood Storage
In applying the first of these principles to the SLA, an important characteristic of the flood
behaviour requires consideration. As described in Section 3.2.1, the peak flood levels around
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