Water sensitive development involves simple design and management practices that take advantage of natural site features and minimise negative impacts on the water cycle. It is part of the movement towards more sustainable solutions that protect the environment and maximise use of natural resources.
Urbanisation has resulted in a significant increase in paved and impervious surfaces. Paved surfaces have significant adverse impacts on the water cycle. They contribute to increased stormwater discharge and the need for expensive drainage infrastructure. They also reduce infiltration to the subsoil preventing water from re-entering the system to recharge subterranean aquifers or from being re-used on site by vegetation.
These impacts can be reduced by:
- Limiting the area of paved surfaces
- Directing stormwater off from paved surfaces to landscaped areas, garden and lawns
- rather than the street drainage system
- Using porous paving / alternative surface systems
- Employing swales and berms
Porous paving/alternative surfaces
Porous pavement is an alternative to conventional impermeable pavements with many stormwater management benefits. These surfaces allow stormwater to be filtered by a coarse sub-base and allow infiltration to the underlying soil.
A number of products are available including:
- Pavements made from special asphalts or stabilised gravels/ aggregates
- Concrete grid pavements
- Concrete, ceramic or plastic modular pavements
These products can be used in conjunction with underground stormwater tanks which allow for stormwater infiltration or re-use. Modules can be interlocked to produce maximum stability under high weight bearing load situations.
Filtering
Studies show that oils and greases are subject to microbial decontamination in porous paving. The addition of sand filters and retention trenches with geotextile fabric lining further aids in decontaminating stormwater.
Infiltration capacity of porous paving in heavier soils can be improved by:
- Providing a retention trench below the sub-base
- Providing an overflow to the street drainage system or other stormwater management
measure. - Limiting the run off area contributing stormwater to the porous paving surface
Unsuitable soils
Porous paving must be carefully designed in areas with:
- High water table levels
- Soil salinity
- Clay soils that collapse in contact with water
- Rock with little or no permeability
Swales and berms
Swales are shallow, low depressions in the ground designed to encourage the accumulation of rain and let it infiltrate into the soil. Swales ideally are tree lined or vegetated and store water for the immediate landscape as well as help cleanse the water as it percolates down. Swales can be installed separately or as part of a larger water rain catchment system.
Berms are raised beds or mounds that can be used to direct water to swales. Ideally berms and swales should be designed into the landscape where there is any noticeable slope to slow and capture run off.
Swales can be grassed, gravel or rocked and designed to slow and retain the flow of run off. Soil in the swale should not be compacted or sealed but should be loose to encourage absorption.
Swales lined with native plants are an extremely cost-effective, and often overlooked low-tech water conservation technique.
