The flood study was undertaken in two stages. The aims of each stage of the flood study are:

Stage 1 - Hydrological Analysis

• Collate all the relevant data on Council's existing stormwater drainage system;
• Develop a hydrological model to investigate the drainage system performance for the 5, 10, 20, 100, 200 year ARI storms and the PMF;
• Identify the flooding problem areas for existing development conditions within the study area;
• Identify the flooding problem areas for ultimate development conditions (represented by all of the study area utilising OSD).

Stage 2 - Hydraulic Analysis

• Estimate the extent of flooding and flood levels for the PMF, 20 and 100 year ARI floods for existing development conditions, and
• Estimate the 20 and 100 year ARI flood levels and extent of flooding for ultimate development conditions.

Study Scope

The scope of the Stage 1 flood study was to use a hydrological model to estimate peak pipe and overland flows throughout the North Parramatta Precinct. The peak overland flows were used in the hydraulic modelling in Stage 2 to estimate peak flood levels and flood extents.

Design Rainfall Intensities used for the estimation of peak flows were obtained from Baulkham Hills Shire Council "Design Guidelines for Subdivisions / Developments." Storm durations from 5 minutes to 4.5 hours were used to produce rainfall patterns from which the D NS model estimates peak pipe and overland flows.

The results presented in this report are the worst case peak flow for each set of storm durations for a particular ARI storm. Where flood levels are noted, all levels refer to Australian Height Datum (m, AHD)