A catchment is an area of land, usually surrounded by mountains or hills, over which water flows and is collected. Water runs by gravity to the lowest point within a catchment. The water is called surface runoff if it stays on top of the land, or groundwater flow if it soaks into the ground. The surface runoff, along with any excess water from heavy rainfall is stormwater. When the water reaches the lowest point in a catchment, it eventually flows into a creek, river, lake, lagoon, wetland or the ocean.
There are many agencies responsible for managing the water that flows through the catchment, through urban and rural environments. This is why the Taskforce was brought together and includes a range of partner agencies and local government authorities.
Launceston has an extensive urban stormwater system and approximately 37 kilometres of natural waterways form and integral part of the stormwater network. In the central parts of Launceston there is a combined stormwater and sewage drainage system, which adds significant complexity to the system. TasWater manage the operation of the combined system on behalf of the City of Launceston.
Two working groups were formed to investigate mitigation options and potential investment strategies to improve water quality. The Catchment Action Working Group looks at catchment-wide diffuse loads and the Combined System Overflow Working Group assesses the impact of the combined sewerage and stormwater system on the Estuary.
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The following reports were developed for the Taskforce to aid in the development of the River Health Action Plan.
The original Launceston combined sewage and stormwater system was the second drainage system of its type installed in Australia.
The current system is designed to overflow during heavy rainfall events, which mostly consists of stormwater, but it does include highly diluted sewage.
The projects identified within the Tamar Estuary River Health Action Plan will help the infrastructure to better manage stormwater flows within the combined system and increase TasWater's storage capacity during rain events, further protecting the environment.
TasWater has fitted flow monitoring devices to the Launceston Combined System to measure flows during wet weather events as part of the River Health Action Plan. Check out this short video to find out more: The Flow Monitoring Survey TERHAP - YouTube
Action is underway to identify and mitigate sewerage intrusions in the separated stormwater systems of the Launceston area as part of the catchment works program.
Two local contractors were engaged to methodically investigate and locate sewage, which has been incorrectly plumbed into the stormwater system known as a cross connection. When a cross connection is identified the owner is informed and provided with assistance to rectify the problem. This generally involves digging up the sewer pipe and reconnecting it correctly to a sewerage main on the way to the treatment plant.
When sewage from a residence or business has been incorrectly connected to the stormwater system, untreated sewage travels through the stormwater system and ends up in the river or estuary, which degrades water quality and creates a public health issue for people recreating on the water.
Eleven stormwater catchments across the greater Launceston area have been investigated so far. There have been 40 cross connections identified, of which more than 75 per cent have been fixed. It is estimated that 13 megalitres of untreated sewage has been diverted from entering our waterways each year which is the equivalent of five Olympic size swimming pools.