Carbon sinks in soils and Water Sensitive Urban Design, enhancing life in the suburbs.
By Ted Floyd
In parks and gardens, multi purpose projects are needed to obtain the highest value from scarce land resources. Rejuvenation and tender loving care of water features in creek corridors add special value to city living.
Pockets of bushland and water features help to reduce urban floods and create carbon sinks. Transpiration cools the atmosphere and wetlands purifies water. Biodiversity is increased and native animals return to the suburbs. Well designed little pieces of nature add many values to urban landscapes and are truly multipurpose.
Plants encourage rainwater to infiltrate into soils and transpire water back into the atmosphere. Growing plants reduce floods and soil erosion.
Water harvesting and reuse by irrigation reduces floods and increases plant growth. Backyard water tanks or larger storage ponds in council parklands are excellent ways to store water. Stormwater runoff is a very valuable asset and it should not be allowed to flow down hill causing floods and general environmental havoc.
Good soil husbandry especially by maintaining a high level of organic matter, increases water infiltration and improves water holding capacity.
Greenhouse gases are reduced when growing plants absorb carbon dioxide from the atmosphere and manufacture organic materials by photosynthesis. A considerable mass of carbon can be stored in vegetation and soils.
Soils, plants and water act together in the suburbs enhancing Water Sensitive Urban Design and creating carbon sinks in soils.
The water cycle begins when water is evaporated by the sun mainly from the sea, which becomes water vapor and forms into clouds. Some of the cloudy vapor blows inland where it falls as rain before eventually flowing back into the sea.
In suburban areas water cycle is changed in many ways. Town water is suplied for drinking and household uses. Waste water is removed as sewage. Large expanses of urban soils are impermeable increasing flood flows and creeks are converted into concrete canals.
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 downstream.
Many soils in urban areas are impermeable because they are covered by buildings, roads, swimming pools and paving. Nearly all rain falling on impermeable surfaces flows downhill and often causes flooding.
Water is absorbd by plant roots from soils and flows up stems to the leaves. Transpiration occurs when water vapor flows from leaves into the atmosphere.
Common problems in urban catchments are flash floods and water pollution. To successfully control these problems the total area of the catchment should be treated with appropriate measures.
Control of stormwater runoff should begin at the soil surface were rain comes down to earth. Often pollution and flooding go together. Sediment in flood water is a major pollution problem.
Water Sensitive Urban Design should nurture opportunities to restore the natural water cycle.
Infiltration of rainwater into soils and growth of vegetation is the front line of action in restoring the natural water cycle.
Water, plant growth and climate change go hand in hand.
In urban landscapes creeks have often disappeared, buried in pipes or converted into ugly, concrete drains.
The rehabilitation of urban creeks is truly multipurpose.
Wetlands are a special little piece of nature.
Every home owner with a back yard can create their own little piece of nature. Home gardens can reduce flooding by storing rain fall in soils and in water tanks. Small carbon sinks can be created in backyards.
The build up of organic matter in soils increases plant growth because the movement of water and air is facilitated, water holding capacity is increased and microbial activity is improved. The destruction of soil organic matter is an early symptom of soil degradation.
Organic matter in soils is a carbon sink.
Healthy soils have an adequate amount of organic matter, stable structure, and are teaming with lively microorganisms. The combination of vigorous pant growth and many active microorganisms helps to build up a healthy soil.
Plant materials in soils are eaten by soil microorganisms converting essential nutrients into soluble forms available for absorption by plant roots. Healthy microbes make a healthy soil.
In urban landscapes soils and water interact in many ways.
Raindrops fall onto soils and water is absorbed by soils becoming available for plant growth. Excess water flows over the soil surface and adds to downstream flooding. Stormwater runoff on bare soil causes erosion and soil particles add to water pollution.
Vigorous plant growth requires fertile, soils and adequate water.
Impermeable soils reduce water infiltration and plant growth. Many streets are wide and excess tar should be ripped up and revegetated. Rain gardens can be established in urban streetscapes. Water infiltration is increased when back yard paving is reduced.
Planet earth is a closed system where only a small amount of material enters or leaves our planet. Often cycles occur where materials go round and round, changing from one form into another and shifting from place to place. Nothing is created or destroyed, materials may look different and visit different places and return to where they started from.
Water follows a well known cycle and there is a growing interest in the carbon cycle. The carbon and energy cycles in living ecosystems are closely related. Soils are important in the nutrient cycle of living ecosystems. Nitrogen follows a complicated cycle in soils and legume plants are able to absorb nitrogen gas from the atmosphere for plant growth.
Sunlight is the primary source of energy on planet earth.
The natural forces on earth are eratic and unpredictable. In Australia we need to live with floods and droughts. City living and impermeable soils exacerbates the destructive forces of flash floods. Should bigger and better concrete drains be constructed or should the total catchment be treated by Water Sensitive Urban Design? Is restoration of the natural water cycle more appropriate than buried pipes?
The skillful use of natural water resources in cities can be the basis for the most exciting little pieces of nature. Wetlands and rehabilitated creeks are very valuable multi purpose natural resources. Creeks are too precious to be destroyed by drainage engineers.