Middle Creek, Pearl Beach Floodplain Risk Management Study

Middle Creek is a small watercourse that drains through the village of Pearl Beach on the New South Wales Central Coast. The creek is an ephemeral stream that drains a 58.3 ha catchment that
is mostly undeveloped and which extends back from the coast to the escarpment (<strong>refer Figure 1</strong>).

Available anecdotal and recorded data indicates that flooding has occurred on many occasions,
most notably in January 1989, April 1989, February 1990 and January 1992. This flooding was
particularly severe in the vicinity of the Diamond Road crossing of the creek <strong>(refer Figure 1)</strong> and
led to significant damage to properties that adjoin the lower reaches of the creek. This and the ongoing risk has led to the development of a Floodplain management plan.

The <strong>“existing flood problem”</strong> relates to those areas of the existing floodplain where damages are
likely to arise as a consequence of flooding. It concerns existing dwellings and properties that
would be inundated during a flood, as well as all associated infrastructure within the floodplain,
including roads and utility services.

In this context, the “existing flood problem” is usually addressed by structural measures which
aim to modify flood behaviour and thereby reduce flood damages.

FLOOD DAMAGES

Data defining the floor levels of residential dwellings located along Middle Creek was provided
by Gosford City Council. This data was used with peak flood levels generated from flood
modelling to determine the depth of flooding in the vicinity of each building. This allowed the
depth of ‘over floor’ flooding to be determined (if any). The flood affected dwellings along
Middle Creek are identified in <strong>Figure 4</strong>.
Estimates of the flood damages associated with each of the 200, 100, 50, 20, and 5 year
recurrence floods and the Probable Maximum Flood (PMF) are listed in <strong>Table 3</strong>. The number of
properties predicted to be inundated during each flood are also listed. All damage costs are
expressed in 2007 dollars.

IMPLEMENTATION OF THE PLAN

The following floodplain management strategies are recommended for implementation under this
Floodplain Risk Management Plan. Further details of the actions associated with each strategy are
provided in <strong>Table 6</strong>
<ol>
<li>Construct two low level flood levees at the rear of properties between 10 and 16 Emerald
Avenue, Pearl Beach.</li>
<li>Encourage landowners to establish a Rivercare group and seek assistance from the Natural
Heritage Trust and Hunter-Central Rivers Catchment Management Authority to undertake
creek corridor management activities. These activities would include vegetation
management, bed and bank stabilisation works and small-scale works to increase channel
conveyance.</li>
<li>Install a piped stormwater system along Pearl Beach Drive to reduce the magnitude of
stormwater runoff carried by Middle Creek during large flood events.</li>
<li>Update Development Control Plan No.162 (Residential Development at Pearl Beach) to
include additional flood related development controls for the Middle Creek floodplain <strong>(refer
Section 3.4.1)</strong>, and incorporate changes into the new Citywide DCP. Strengthen all related
existing Council planning and development controls.</li>
<li>Monitor the extent of landscaping and bed or bank stabilisation works within the Middle
Creek floodplain in order to enforce the proposed requirements of the Gosford Citywide DCP.</li>
<li>Develop a formal Flood Emergency Response Plan for Middle Creek as a sub-plan to the
Gosford City Displan (2005), which is to include details of the recommended flood
evacuation route and flood refuge.</li>
</ol>

Tags: Middle Creek, Pearl Beach
Organization: Central Coast Council