Looking after all our water needs Looking after all our water needs Water sensitive urban design Infiltration basins and trenches Summary Main benefits Design factors Target pollutants Infiltration basins are depressions • They are very effective in sandy • Consider the soil type (not in loose aeolian sands) and • litter and organic matter infiltration capacity of the soil. designed to capture and store soils. • coarse sediment stormwater prior to infiltration into the • The pollutant removal effectiveness depends on the vegetation • They are simple to construct • suspended solids soil profile. Infiltration trenches are and have low maintenance type and cover and phosphorus retention index of the soil. below ground linear devices that store requirements. • Base should be at least 300mm above the maximum or • nitrogen stormwater prior to infiltration. • They maintain site water balance controlled groundwater level. • phosphorus • heavy metals This brochure is part of a series that and can replenish local ground- • Installation will be more difficult if rock or other hard material is water. present. explain various aspects of water sensitive urban design. Please see • Infiltration basins can be • Prevent mosquito breeding by adequate design – no water Water sensitive urban design in integrated in public open space. ponding after 96 hours between November and May in the south-west of Western Australia and throughout the year in the Western Australia for background • Trenches can be used in north. information on water sensitive urban confined areas. • Ensure they are integrated with the landscape design of public design. open space. Where they can be used in the water sensitive urban design process Treatment train Safe Land use Source control Runoff control conveyance and planning and discharge Capture, use Retention, and inltrate detention and Flood rainfall conveyance management Total water cycle outcomes Appropriate Prevent and Reduce through reduce discharge and location and transmission of reuse pollutants at pollutants good design their source Protect people and buildings Minimise runoff Minimise erosion from ooding Up to the 1 in 1 Up to the 1 in 5 Up to the 1 in 100 year ARI event year ARI event year ARI event Design scale College Grove, Bunbury, before Infiltration trench backfilling, Infiltration basin, flush kerb swales, Infiltration basin, flush kerb swales, Precinct District Street Lot (subdivision) and after a storm Meadow Springs, City of Mandurah retained trees, Seascapes, City of retained trees, Seascapes, City of Mandurah, before a storm Mandurah, after a storm Looking after all our water needs Looking after all our water needs Water sensitive urban design Infiltration basins and trenches Subsoil crate Crate style infiltration trench Pipes connected Free draining Required reading sand backfill storage units Geotextile surround into crate units to separate crates Australian runoff quality: a guide to from soil media water sensitive urban design, 2006, Pre-treatment and Engineers Australia, available at sediment removal <www.arq.org.au>. Excavation line Stormwater management manual for Western Australia, 2004–07, Overflow outlet Department of Water, available at Stormwater <www.water.wa.gov.au>. See Section inflow 3.1 of Chapter 9 – Structural controls. Direct infiltration into Water sensitive urban design: basic Filtration surrounding soils procedures for ‘source control’ unit Inlet into Note: This design can of stormwater – a handbook for storage Infiltration and be adapted to a basin, Australian practice, 2004, Argue, JR Infiltration from base units percolation zone particularly for retrofitted (Editor), University of South Australia. and piped catchments Infiltration basin Turf or plantings aids re- Ponding in basin pro- moval of coarse sediment vides detention storage prior to infiltration Stormwater inflow Basin to be shaped Sandy loam or insitu soil and landscaped to integrate with public Gravel or filter zone if re- open space Department of Water quired to enhance infiltration 168 St Georges Terrace Perth Western Australia Insitu soil Grade base at 1% from toe of batters to central PO Box K822 Perth low point Western Australia 6842 Infiltration into soil Ph: 08 6364 7600 • Fax: 08 6364 7601 (Source: Thompson McRobert Edgeloe Group 2008) www.water.wa.gov.au The department acknowledges the past project contributions of the Leschenault Catchment Council. June 2011 21592_100_06/11.