What is Stormwater?

Stormwater can also be called rainwater run-off because it is the rainwater that runs off all the hard outdoor surfaces such as roofs, roads, concrete carparks and driveways.

These human made surfaces are impermeable (water can't soak through). This stops rainwater soaking through into the groundwater system (underground water system).

So when there is heavy rain, stormwater builds up unnaturally fast causing flooding. Flash flooding can be very dangerous and destructive, causing huge amounts of pollution to be dumped into the river.

The Natural Water Cycle

In a natural river catchment (one with no human made hard surfaces), rainwater is absorbed into the forest and soil, filling the groundwater system (underground water). This creates high groundwater flow.

Groundwater seeps into the creeks and wetlands and river, even during dry times and the ecosystem stays healthy.

Plants and trees also access this groundwater with their deep tap roots and so forests are continually cycling large amounts of water back up to the clouds. This is known as evapotranspiration.

The Urban Water Cycle

In an urban / city river catchment such as the Cooks River, most of the ground surfaces are hard and impermeable. This means that rainwater does not permeate (soak) into the groundwater system.

Like a big sponge, the catchment ecosystem becomes dry and unhealthy due to low groundwater flow.

There is also less plants and trees in an urban / city catchment and so there is less evapotranspiration.

Heat island effect also adds to this situation and so shade trees are very important.

The Cooks River Water Cycle

The two main sources of water flowing into the Cooks River Catchment are:

• rainfall (stormwater)

• and water imported from Warragamba Dam (tap water).

The Cooks River water map on left tells us that rainfall delivers more than twice as much water to the Cooks River catchment in comparison to water imported from Warragamba Dam.

This is a problem because 70% of this stormwater is being lost down the river.

So we are relying too much on our precious dam water which is of limited supply and should only really be used for our drinking water.

Water in the World

There is ~1.4 billion km3 of water on Earth covering approximately 70% of the Earth’s surface. This includes liquid water (in the ocean, lakes and rivers), frozen water (in snow, ice and glaciers), water that’s underground (in soils and rocks), and water that’s in the atmosphere (as clouds and vapour).

Although the Earth is covered mainly by water, only a small amount is available for consumption. The majority of the water on Earth (~97%) fills the ocean and is salt water. About 2% of the freshwater on the Earth is frozen (in ice sheets or in glaciers) and most of the remaining 1% is deep underground in rock layers, in shallow aquifers or as soil moisture. Of the remaining in lakes, wetlands and rivers (0.03%), it is approximated that 0.01% is available as accessible drinking water.

Stages of the water cycle

• Evaporation: water molecules are energised by the sun, breaking the bonds between them, allowing them to escape into the atmosphere as vapour gas. This process often leaves salt, minerals or metals from the liquid water behind.

• Transpiration: water returns to the air as it evaporates from plants, mainly through their leaves.

• Condensation: water vapour rises and cools, changing back into tiny water droplets that join to form clouds.

• Infiltration: water soaks into the soil or through cracks into the ground and seeps into groundwater or rivers, or is absorbed by plant roots. The amount of infiltration depends on the amount of rain, the type of soil and the amount of rock in the soil.

• Run-off: water is not absorbed into the soil (infiltration) but pools on the surface and flows across the land (surface water). Moving water tends to flow downhill and these flows come together to form creeks, streams and even rivers. Eventually these flows make their way to the oceans. The amount of surface runoff is determined by a number of factors such as heavier rainfalls, topography (slopes tend to have more water runoff than flat land as gravity pulls the water) and soil type (i.e. heavy soils like clay absorb water slowly so tend to have more runoff).

• Precipitation: water falls to earth when too much has condensed for the air in the atomosphere to hold. Precicipation can fall as either a liquid (rain) or a solid (snow, sleet or hail) depending on the air temperature. When precipitation falls on land, it can infiltrate, move across the surface as run-off or pool on the surface (water storage) before evaporating

Stormwater and Pollution

Freddy explains how stormwater and sewage are both part of the 'urban water cycle' but are different systems of water. Sewage is the waste water that drains from toilets, sinks and laundry and drains inside buildings. Whereas Stormwater is rainwater that falls on all the outside surfaces such as roofs, roads, driveways, carparks etc. Stormwater flows too quickly over these hard surfaces and pollution is washed into waterways and into the river.

Ways we can help keep our waterways clean

Ballina Shire Council has developed a fantastic video that highlights the impacts of behaviour on our waterways.

Our gutters and drains are all part of a large stormwater system. When it rains, stormwater runoff from our streets and homes can wash dirt, litter and other pollutants into our waterways.

Down the Drain

A short film about storm water drains, where they go, naturalised vs unaturalised ones, and what you can do to help, as they all end up in our rivers and harbours.

Check out how this PLC student has told the story of drains with the intent of increasing awareness and showcasing better ways of caring for our waterways.