Eastwood & Terrys Creek Floodplain Risk Management Study & Plan Flood Study Report

Brief description

The study area includes that portion of Terrys Creek within the City of Ryde from Terry
Road to the creek’s confluence with the Lane Cove River. In addition, as shown in
Figure 1, it includes all significant tributaries of Terrys Creek.

This report provides a description of the establishment and calibration of a computer
model of flood behaviour throughout the study area. This model will become the
primary tool for assessing both the existing flood behaviour and the changes which may
occur through the implementation of any flood mitigation options that may be proposed
during the course of the study.

#Catchment Areas
For the purposes of Council’s management of the stormwater systems within the City of
Ryde, the Terrys Creek catchment has been traditionally divided into the Eastwood and
Terrys Creek drainage subcatchments.

The Ryde component of the Eastwood subcatchment is about 169 hectares in area and
extends from the intersection of Marsden Road and Terry Road to Blaxland Rd,
Eastwood. The Terrys Creek subcatchment comprises an area of about 326 hectares
and extends from the intersection of Blaxland Road and Kings Road to the Lane Cove
River.

The upstream portion of Terrys Creek (within Parramatta City Council) has an
estimated area of 160 hectares, while the remaining portion of the catchment (within
Hornsby Shire Council) has an estimated area of 357 hectares. The estimated total
area of Terrys Creek is therefore approximately 1012 hectares.

The Eastwood town centre is located within the Eastwood subcatchment, and straddles
the Main Northern Railway Line (Figures 1 and 2). The railway embankment divides
the Eastwood town centre into eastern and western halves.

#Models
The DRAINS software has been used to model the hydrologic regime of the Terrys
Creek catchment to its confluence with the Lane Cove River (see Figure 2).
DRAINS is a comprehensive hydrologic modelling program for designing and analysing
various types of catchments and urban stormwater drainage systems. It also includes
some hydraulic modelling capabilities for pipes and overland flowpaths. It was first
released in January 1998 and is marketed by Watercom Pty Ltd. The software is widely
used in Australia and Council itself has used DRAINS for many years.

Following various discussions with Council officers, the widely used and Australian
developed TUFLOW model (Reference 9) was chosen as the principal hydraulic
modelling tool for use in the study.
There were seen to be numerous advantages of using a sophisticated two-dimensional
(2D) model such as TUFLOW for simulating flood conditions within Terrys Creek and its
tributaries. These advantages included not only the model’s ability to simulate flood
flows along a complicated network of overland flowpaths such as occurs in the study
area, but also the ability of the model to produce figures to aid community
understanding and acceptance of the flood study results.
The technical description of the TUFLOW model and its specific application to Terrys
Creek is provided in Appendix B.

Full description

Eastwood & Terrys Creek - Floodplain Risk Management Study & Plan - Flood Study Report October 2009