Hunter Water is a State Owned Corporation (SOC) providing drinking water, wastewater, recycled water and some stormwater services to a population approaching 600,000 people in homes and businesses across the Lower Hunter. Hunter Water has approximately 4950km of pressure water mains, varying in size from 20mm to 1350mm, with the oldest pipes dating from the original Walka Water Works scheme installed in the late nineteenth century.
The Challenge
The risks associated with the close proximity of pressure pipelines in the community have been demonstrated through several recent failures. There is increasing community expectation regarding management of infrastructure in ways that minimise such risk. These pressures are expected to grow over time as development encroaches on pipelines and infrastructure ages.
Pipe failures have caused significant property damage in the Hunter region, and in some instances were hazardous to the community. Hunter Water were able to estimate the likelihood of failure based on failure rate curves. However, the consequence of failure was unknown, so knowing which assets to prioritise for replacement was unclear.
The Solution
GHD have developed an innovative methodology for assessing the consequences of catastrophic water main failure. Over 250 km of trunk water mains (over 250 mm diameter) needed assessing. This was conducted by taking break flow rates from Hunter Water’s existing water supply network hydraulic models every five metres, which showed very large possible instantaneous flows (well in excess of 5,000 L/s) that could occur in some locations of the network.
GHD modelled the inundation areas and the nature of flooding at almost 60,000 individual locations. For roads, the flooding hazard area was estimated for each type of road (motorway, arterial and local road). Using unsupervised machine learning algorithms, together with supplied red blue green alpha (RGBA) imagery and classification of LiDAR strikes, GHD prepared a spatial model of surface roughness. Fences on the side and rear boundaries of residential properties were also included in the TUFLOW 2D flooding model. These models ran on multiple computers for weeks to process the significant number of simulations required. Open channel drainage was included in the model. Underground drainage might be included in future iterations, given the models potentially overestimate flooding impacts in some locations. Some of the initial sensitivity analysis at calibration sites did include underground drainage.
The Benefit
Hunter Water is now using this information to identify and prioritise locations for mitigation measures as well as cross checking against inundation information from recent break events, to allow further refinement of the model.