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NSW Flood Data Portal

Flood study

Upper Muddy Creek Piped Drainage Analysis Stage 1

This study provides the piped drainage analyses of two Upper Muddy Creek sub-catchments:

  • Sub-catchment No. 1 (Main Line),
  • Sub-catchment No. 2 (Queen Street Branch).

These sub-catchments (Nos 1 and 2) have catchment areas of 85 hectares and 33 hectares respectively. The catchments incorporate the urban developed suburbs of Carlton and Bexley located within the Rockdale City Council area and drain to outlets in Muddy Creek. A small part of Sub-catchment No. 1 (30% of its total) falls within the Hurstville City Council area The drainage networks in the sub-catchments comprise mostly of concrete pipes and rectangular culverts, with some reaches occurring through private property.

Some overland flow paths within the sub-catchments occur through private property. Excess surface runoff has been known to cause inundation of the carpark of a block of units at Queen Victoria Street, Kogarah (Sub-catchment No. 1). There are few records of flood occurrences within either sub-catchment.

Hydrologic/hydraulic investigations have been undertaken to determine the response of the existing drainage system to the 1 in 2, 1 in 5, 1 in 10, 1 in 20, 1 in 100 ARI year events and the Probable Maximum Flood. The results of these investigations are quantified as peak pipe capacities and peak overland flows. A determination of the limiting drainage system constraints at various locations within the system is also provided. The investigation also estimated conduit sizes required to upgrade the drainage system so as to eliminate overland flows through private properties for the 1 in 5, 1 in 10 and 1 in 20 year design storms.

The DRAINS model approach was adopted for the hydrologic/hydraulic modelling of the study areas. The model is based on the hydrological component of the ILSAX model to determine runoff characteristics and applies the Hydraulic Grade Line method for hydraulic analysis of drainage system performance. The DRAINS model was set up to represent the contributing sub-areas and drainage network within the sub-catchments. The accuracy of the model(ed results at any location depends upon a number of factors, including the assumptions made in the DRAINS modelling, the quality of the pit and pipe data, assumptions made in determining the overland flow paths, and to a lesser extent, upon the accuracy of the design rainfall intensities.

The critical storm duration producing the majority of peak flows in the 1 in 100 year ARI event was determined to be the 25 minute duration storm for both sub-catchments. The 25 minute storm was subsequently adopted for all runs, however it should be noted that the 60 minute duration storm produces the peak flows at the bottom of the sub-catchments. Several areas within private property have been identified as prone to surface runoff affectation for the modelled design rainfall events.

It is recommended that following the next major storm Council should assess the deficiencies of the existing drainage system and gather information from residents situated near overland flow paths.

The investigations found that upgrading of the drainage system capacity would require installation of significantly large pipes, In many instances it would not be feasible in practice (difficult and expensive) to implement these upgrades through private property. As such, it is suggested that alternative overland flow management schemes be considered to address the specific problems of different areas.

The study has identified the following areas of further investigation:

  • to establish if the 1050 mm pipe exiting from Tindale Reserve, Short Street is operating at its full potential,
  • to undertake a post flood survey immediately (within 24 hours) following a large event (say greater than 1 in 10 year ARI) to review the appropriateness of the potential flood affectation for properties identified on Figure 15.

Additional Information

Field Value
Title Upper Muddy Creek Piped Drainage Analysis Stage 1
Publication Date 1 December 1999
Themes Land and Resource Management
Spatial Extent
Map data © OpenStreetMap contributors
Council/LGA Bayside Council
Author/ Prepared by Webb, McKeown and Associates Pty Ltd
Publish date 6 July 2017
Update date 26 July 2017
River Basin 213 - Sydney Coast and Georges River
Place Name Upper Muddy Creek
Approval State Approved
Submitted for approval 6 July 2017
Submitted by John Silk
Approved 26 July 2017
Approved by plattns
Data Comment

Report only; no other data. Legacy data; may have been superseded.

Identifier 5fe1da6d-56b6-4d0f-b779-f768369ced00