Raindrops are a heavenly gift from the gods landing on earth with a powerful thud. The energy in a little raindrop smashes unprotected soils into small particles forming a seal on the soil surface. Planting trees and ground cover mimics nature and protects the soil surface from the beating action of raindrops.
The soil is the frontier of the water cycle on land and soils should be nurtured and protected to ensure the success of creekcare projects.
When raindrops come to earth they are absorbed by the soil or if there are lots of them they will flow downhill over the land surface. The more rain absorbed by soils the more water available for plant growth. Large volumes of runoff can cause flooding in creeks and rivers further down the catchment.
Natural eco-systems absorb more water than suburban soils. Large expanses of land in the suburbs are covered by buildings, roads and paving. These impermeable surfaces are sealed, preventing water entry. It is best to reduce the area of impermeable soils when possible so as to encourage soils to absorb water.
In natural eco-systems surrounding Sydney up to 70% of rainfall is absorbed by soils compared to 10% in the suburbs. In the suburbs a very high proportion of the rain immediately becomes runoff causing flash flooding.
Rainfall absorbed by soils is pumped back into the atmosphere by plants. Transpiration is the movement of water from soils up the roots and stems of plants and then out into the atmosphere through small holes in the surface of leaves. Water movement up the roots and stems is essential to carry plant nutrients from soils to the growing points of the plant.
In natural eco-systems transpiration by growing plants is a very important segment of the water cycle. About one half of rainfall in natural areas surrounding Sydney is pumped back to the atmosphere during transpiration by growing plants.
"Water is life" (Three leaflets by Ted Floyd, First published by Friends of the Earth 1996)
These three leaflets highlight how soils in the Whites Creek catchment should be managed to help reduce flooding and pollution. Creekcare programs also need to follow a soilcare program. These leaflets emphasize the importance of replacing paving and other impermeable surfaces with healthy soils. A stable soil structure increases the amount water absorbed by soils and reduces flooding. Water is purified and pollution removed when water flows through wetlands and eco-engineered drainage lines.