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•White Paper: Modelling Overland Flows And Drainage Augmentations In Dubbo

By J. Smith (Manager, Technical Support, Dubbo City Council)
Dr B.C. Phillips (Director, Cardno Willing (NSW) Pty. Ltd)
S. Yo (Senior Engineer, Cardno Willing (NSW) Pty. Ltd)

Dubbo has experienced a number of overland flooding problems at several locations within the city. Council had formulated possible augmentation works to address the problems and was keen to confirm that the proposed works would address the local flooding problems. The drainage system in Dubbo faces a number of challenges due to the relatively flat grades on stormwater drainage lines and the possibility that overland flows from a local drainage catchment may flow into an adjacent catchment via the road system. It has also been found that minor works like a roundabout can also initiate flooding of local properties.

Council had previously commenced the assembly of XP-SWMM model(s) of some of its drainage systems. Council also had available Aerial Laser Scanning (ALS) of the city.

In view of the sensitivity of overland flows to modest changes in intersection geometries and the problematic issue of the magnitude and direction of overland flows at many intersections in the city an XP-SWMM2D model of subcatchments 102, 103, 104, 105 and Boltje Street was assembled comprising the existing drainage piped system and 2D description of the roads based on available ALS data. The advantages of this modelling approach including the possibility of including roundabouts and other modifications of kerb-lines in the model and to assess the impacts on overland flows are discussed.

The modelling of the interaction of Council's piped drainage system and overland (road) flows is overviewed and the assessment of Council's proposed augmentation works is discussed.

It is concluded that the increasing consideration of extreme flooding in urban areas and the growing availability of aerial laser scanning of urban catchments is leading to the growing adoption of 2-D models as the new benchmark for urban flood studies in NSW and elsewhere. It was also concluded that:

• the combined 1-D/2-D modelling capabilities in the XP-SWMM2D package offers Dubbo City Council and others new opportunities to undertake more detailed investigations of urban drainage systems and of overland flows;
• the modelling completed to date has highlighted the interconnection of local drainage subcatchments and confirms observed overland flow problems in several areas in Dubbo;
• the assessments have highlighted the value of ALS data.

Click Here To Download:
•White Paper: Modelling Overland Flows And Drainage Augmentations In Dubbo