Creekcare

Acacia Sapplings - Whites Creek - photograph Aurora Sice

New Native Bush, Whites Creek Valley
Photograph Aurora Sice

Urban water cycle in natural landscapes

Improving natural landscapes and planting trees improves stormwater management, acts as a carbon sink, reduces temperatures, increases biodiversity and adds to the general amenity of suburban areas.

Water sensitive urban design enables catchments to store more water and reduce the severity of flash floods.

Improving the biodiversity of drainage systems can help to reduce pollution and floods. In new suburban areas of outer Sydney many drains are lined with natural rocks. Flood plains along creek valleys should be preserved.

Creek corridors should be improved by planting trees in valleys. Water harvesting from drains can be used to irrigate trees. Stormwater management is improved when infiltration basins are constructed and trees can improve the efficiency of infiltration basins by removing water from soils and allowing water to freely infiltrate into dry soils.

Pollution in water is reduced when it filters through natural ecosystems. Soils are very efficient pollution filters. Many pollutants stick to the sides of clay particles and bacteria and other microorganisms eat and break down organic pollutants in soils.

Water should be encouraged to infiltrate into soils. Mulches and vigorously growing plants encourages surface soils to absorb more water and improves the stability of soil structure.

Wetlands cleanses polluted water, improves biodiversity and acts as a carbon sink. Wetlands can store up to 300 tonnes C/ha and bushland can store 100 - 200 tonnes C/ha. A typical home emits 2 tonnes Carbon in a year and 300 tonnes stored in a wetland is equivalent to Carbon emitted by 150 homes in one year.

Artificial water cycle

Water Cycle in a Suburban Home
Illustration by Ted Floyd

The urban water cycle in towns and cities differs from the natural water cycle in bushland.

In cities additional water is supplied to houses and industry by the town water system. Waste water is disposed of in the sewage system. The water catchment is altered and many creeks are converted to concrete lined drains.

Town Water Supply

Potable water is high quality water treated to remove harmful microorganisms and is distributed to houses where people can drink the healthy water.

In Sydney water is harvested and stored in large dams on rivers surrounding the city and is treated and piped to houses and industry.

Warragamba dam, south of Sydney is the largest storage dam and Prospect reservoir is the largest water treatment works. Throughout the suburbs many concrete reservoirs are found in high spots where water is stored to even out water supply over 24 hours of a day. Pumping stations are needed to distribute the water.

Droughts are common in Australia and storage resevoirs need to be larger than many overseas cities. Sydney's reservoirs need to store more water than the total amount of water needed in several years.

Water use in Sydney is about 600 billion litres a year. Major dams store 2,400 litres.

Potable water supplied to town water systems is very valuable and should be used wisely. Large storage dams need to be built and valuable land is drowned under water. Town water supplies are treated and this costs money and uses energy.

Water harvesting

Town water should only be used when clean, healthy water is needed. A large proportion of water does not need treatment to health standards high enough for safe drinking.

Potable water is not needed for watering gardens or flushing toilets. Many industries do not need potable water.

The use of potable water directly from taps needs to be reduced and alternate water supplies should be utilized. Suburban water harvesting should be used when high quality potable water is not necessary for health reasons. Falling rain can be harvested directly in the suburbs and gardeners are now encouraged to install rainwater tanks.

Industry and Councils can save water by harvesting rainwater runoff for industrial purposes and irrigating parklands. Whites Creek wetlands provides a continuous supply of partly treated water, even during droughts and this water supply should not be wasted.

Trees can be irrigated by water harvested from council stormwater drains. Well watered, fast growing trees will reduce floods and store carbon in a greenhouse sink.

Sewage systems

Whites Creek Sewage Aqueduct
Photograph Irene Revel

Sewage is collected in pipes and treated before disposing to natural water systems.

In Sydney most sewage is partially treated and disposed by long tunnels at ocean outfalls. In the western suburbs sewage works dispose of treated water into local rivers.

Sewage leaks

A major environmental problem is leaking sewage pipes. Stormwater often enters sewage pipes and the sewage system becomes overloaded and over flows into the stormwater drains. Sewage systems are designed with special stormwater overflow outlets.

Old sewage pipes begin to crack and sometimes leak into stormwater systems. Occasionally pipes are broken during construction works.

Grey water: is the portion of sewage that does not contain toilet wastes.

Black water: is sewage containing toilet wastes.

Black water is a more serious health problem than grey water and it needs to be treated in large, central sewage works.

Grey water generally has a low health risk. If sensible procedures are followed grey water can be used to water gardens or flush toilets.

Waste water from the bathroom, laundry and kitchen are the main sources of grey water. Some detergents can effect plant growth if irrigating with grey water it is best to not use detergents containing boron or a high sodium content.

Often grey water especially waste water from the kitchen sink will clog the fine nozzles in underground trickle irrigation systems. It is best not to use irrigation systems with small nozzles.

Irrigating gardens with grey water will help to maintain flourishing plants even during severe droughts. When greywater is used in gardens this reduces the sewage load and this reduces problems caused by sewage leaks. The utilization of grey water will reduce the use of valuable tap water.

Illegal connections: sometimes stormwater is disposed directly into the sewage system. This is called an illegal connection in Sydney and in early Sydney this was acceptable and this practice still occurs in some old buildings. The disposal of stormwater into the sewer is acceptable practice in some overseas cities.

Urban catchments

Catchments differ in natural and urban areas. The volume of water runofff during rainfall is greater in urban areas increasing flooding. Runoff can be more than six times in the suburbs compared to natural bushland.

A high proportion of surface soils are impermeable. Roads, concrete and buildings seal the surface preventing rainfall entering soils. Impermeable soils increase water runoff and downstream flooding.

When streets and houses are constructed land is leveled, drainage lines filled in and runoff collected in surface gutters running alongside streets. Gutters on the surface collect little seepage from soils. Urban drainage is efficient in removing surface runoff and not very affective in draining waterlogged soils. Water collected in roadside gutters flows down gully pits into buried pipes.

Stormwater is discharged into creeks and rivers. Many small creeks are converted into stormwater drains. The natural features of creeks are destroyed by the concrete, water holes are filled in, the bed of the drain has an even slope, waterfalls and rapids are leveled, plants, animals and fish find it difficult to live in this hostile environment.

Pollution is concentrated in drains and becomes a problem when discharged into natural waterways. Flood plains, billabongs, anabranches, swamps are all destroyed. Biodiversity in the creek and along the creek corridor is reduced.

Stormwater drains are designed to rapidly remove floodwater while it is raining.

Whites Creek concreted as a Storm Water Drain- photograph Tom Worthington

Whites Creek Storm Water Drain
Photograph Tom Worthington

In the late 1800s many outbreaks of disease occurred because of polluted water. Sewage directly entered creeks and swamps. To improve health, sewage systems and stormwater drains were built in Sydney.

In 1897 the sewage aqueduct over Whites Creek was completed carrying sewage from Balmain to an ocean outlet at Bondi. In 1898 to 1938 Whites Creek was canalized and converted from a natural creek into a concrete stormwater drain. These engineering works improved health and reduced diseases.

It is now 100 years after the first creeks were canalized and converted into concrete stormwater drains. Conditions have changed and it is doubtful if there is a need for completely concrete stormwater drains similar to Whites Creek.

Water borne diseases are now rare. Only a small amount of sewage leaks into drains.

Groundwater

Leakage of excess water can occur down a soil profile beyond the root zone and into the groundwater. In urban areas impermeable surfaces reduce water reaching the groundwater. Cutting down trees decreases the removal of soil water by transpiration and the groundwater may rise. The groundwater can either rise or fall after urbanization.

Salting occurs when salts in the subsoil are brought to the surface by a rising water table. Surface salting often kills plants and damage brick buildings. Salty subsoils are common in some parts of Western Sydney.