PURPOSE OF STUDY

The Spring Street Drainage Catchment covers an area of 224 hectares draining eastwards to an outlet at West Botany Street, within the suburbs of Rockdale, Banksia, Arncliffe and Bexley, as shown in Figure 1. Stormwater ultimately drains to Botany Bay via Muddy Creek.

Overland flows within the catchment have previously resulted in damage to property and inconvenience to residents. The aim of this study is to identify and assess the properties affected by overland flows using the DRAINS and HEC-RAS computer models.

Methods

This investigation followed a general methodology for analyses of established stormwater drainage systems:

• Compilation of data;
• Development and testing of a "base case" computer model, representing existing or ultimate conditions;
• Analysis for a range of design storms;
• Identification of key problem areas;
• Presentation of results in suitable paper and electronic formats; and
• Provision of the models and data to Council in forms suitable for future use.

Extracts from the DRAINS model produced in the study are shown in Figures 3 and 4. This included 829 pits, 34 nodes, 572 sub-catchments, 863 pipes and channels, and 623 overflow routes. Five detention basins were used for modelling complex parts of the network where ponding and flow splits occurred. The overall percentages of paved, supplementary (impervious areas not directly connected to the pipe system) and grassed areas were 64%, 4% and 32%, respectively.