Flood peaks are higher in urban areas because there are more impermeable surfaces and water flows faster down concrete drains.
Water flowing in a concrete gutter flows about three times faster than in a grass waterway. Eco-designed waterways which meander increases the length of the waterway and reduce the slope. Waterways incorporating natural features will increase the time of concentration and reduced flood peaks.
Many years ago stormwater was an unhealthy curse. Typhoid, dysentery, bubonic plague and measle germs lurked in smelly creeks and swamps. Council engineers built concrete drains and filled in swamps to make parks with cricket ovals and football fields.
The diseases are now rare and also natural creeks with clean water and fish are rare. People living in crowded cities miss the peace and beauty of bushcreeks.
To convert polluted drains into clean healthy creeks the total catchment needs to be treated. It is impossible to bring back the bush to all parts of the suburbs. We should aim to mimick nature when possible especially in drainage lines and along creek valleys.
Modern society has invented new poisons, killing fish and turtles. Pollution from factories and roads have replaced the typhoid germs and when there is heavy rain, sewage leaks into stormwater drains flowing into the harbour.
It would be very nice if smelly, concrete drains were converted into clean urban bushcreeks with tasty fish and gentle turtles. Bushcreeks should mimick nature with rocky banks, native grases and shady trees forming green corridors for native animals on the move. Creeks should have a few bends and numerous small rockpools.
Water catchments is the land above creeks where water flows over the soil surface down into the creek. A catchment divide is a ridge between two catchments seperating water flow between creeks. The Great Dividing Range in NSW is the catchment divide between coastal rivers flowing into the Pacific Ocean and the Murry River flowing into the Southern Ocean in SA.
Opportunities exist for the construction of sunken gardens in street scapes where water is diverted from roadside gutters into landscaped areas. Many trees planted alongside streets would benefit from receiving extra water from roadside gutters. Water from gutters culd also be diverted into landscaped areas constructed in traffice management schemes.
In urban catchments trees should be planted alongside streets. It would be ideal if water flowing down gutters was used to irrigate street trees.
Impermeable surfaces should be removed to allow water to infiltrate into soils. Excess concrete and tar should be dug up, planted with grass and water encouraged to soak into soils.
Concrete gutters collect and carry toxic chemicals downstream into creeks and harbours. Toxic chemicals are seldom broken down in concrete drains and collect on the bottom of the harbour where they remain for many years.
Grass waterways trap pollution and stormwater soaks into soils where many toxic chemicals are broken down by soil micro-organisms and become harmless.
Bringing back nature helps to filter out pollution. Flash floods are reduced when water soaks into soils covered by grasses and protected by trees. Concrete in creeks and gutters increase flooding and pollution poblems are multiplied. Replacing concrete with trees and grasses improves environmental qualities of creek systems.
Creekcare including catchment care and soilcare all work together to ensure our waterways are healthy with clean water, croaking frogs and tasty fish.
A big effort should be made to mimick nature. We cannot create perfect nature, but we should have a go to make a good imitation.