Why is sediment control important?

How should sediment be controlled on site?

In WA, all land developers, builders and other tradespeople working on construction sites (and their subcontractors) must comply with legislative requirements to prevent soil erosion (by water and wind) and sediment run-off from construction sites reaching roads, gutters and drains, to prevent water pollution. This includes during subdivision, home building, home renovations, landscaping, installing swimming pools and during roadworks and other public infrastructure works.

Inadequate management of soil and sediment-laden runoff on construction sites is commonly caused by:

Lack of stabilised entry/exit points.
Unnecessary site disturbance (such as parking or driving on exposed soil).
Not diverting upslope water (from offsite).
Lack of sediment controls such as sediment fences, sediment traps or turf strips.
Incorrect placement and protection (covering) of soil and builders sand stockpiles.
Delays in connecting downpipes to stormwater drains.
Insufficient site checks and regular maintenance of sediment controls.
No emergency plan being in place for unexpected weather events.

Did you know?
All soil erosion (including dust), sediment runoff and sediment stormwater pollution incidents can be reported to your Local Council.

Image courtesy of Healthy Land and Water’s Water by Design Program.

Did you know?
Sediment controls can be up to 90% effective at reducing sediment runoff during normal flow. The effectiveness of sediment controls however reduces dramatically during storm events so everyone has a responsibility to make sure erosion and sediment controls are installed on site, regularly inspected and maintained.

How can this environmental risk be minimised?

All those involved in subdivision, building and other works where soil is disturbed can minimise sediment pollution and environmental risks by:

Identifying highly erodible soils that may require additional erosion and sediment control measures.
Minimising their ‘footprint’ of soil disturbance by protecting their site from erosion by stabilising and covering the soil as soon as possible to stop both fine and coarse particles from leaving site.
Maintaining as much vegetation, grass, mulch, and other soil coverage on their site as practical.
Stabilising steep areas to control erosion caused by water run-off and diverting water around the site.
Cleaning up any soil or mud that is deposited on the roadway from vehicles delivering materials or that runs off site at the end of the working day. Use a broom or shovel and deposit it back on site – never use a hose or sweep sediment onto the road, into gutters or down the drain.

Did you know?
Uncontrolled sediment on construction sites has lasting and far-reaching effects on the ecosystems and societal values of streams and receiving waters (Chin, 2006; Leopold et al., 2005).

Why is controlling soil, sand, silt and mud on subdivision, building, roadworks and other development sites so important?

Pollutants such as soil, sand and cement can be blown or washed away from subdivision, building and other construction sites. Appropriate erosion controls should be used on roadwork and other public infrastructure work sites, residential, commercial and industrial developments. When appropriate erosion controls are not used, soil, sand and cement travels through the stormwater drainage system and can pollute local parks and sensitive environments such as rivers, wetlands, estuaries and oceans.

Preventing sediment loss is far less expensive than ‘cleaning-up’ and remediation
During and after urban development activities, it is often necessary to sweep roads, repair and maintain stormwater and Water Sensitive Design (WSD) infrastructure, to restore natural environments. It is costly to enforce compliance with sediment control conditions.

Costs are also incurred to retrofit poorly installed and/or maintained erosion and sediment control measures that have failed to prevent sediment loss (e.g. raingardens damaged by soil and silt and mud) or for revegetating where plants have been damaged or washed away.

Soil and sand leaving land development sites and reaching drains and waterways can:

Impact water temperature, channel shape and speed of flow
Change structure of the riverbed
Erode creek and riverbanks
Interrupt the free movement of water
Reduce how much water a wetland can hold
Increase weed growth
Increase mosquito and midge breeding habitat and populations by creating shallow depressions and reducing natural mosquito predators (SERCUL, 2016)
Reduce macroinvertebrates and fish populations by covering the macroinvertebrate egg bank, the plant seedbank and beneficial algae (SERCUL, 2016)
Contain high levels of introduced nutrients, promoting toxic algal blooms
Negatively impact recreational, cultural and heritage values, aesthetics and tourism

Did you know?
In WA, the costs of managing sediment loss from construction sites are primarily borne by local government. The cost to one Local Government in Perth is predicted to be as high as $2+ Million this financial year (Sediment Task Force, 2024).

Did you know?
Sediment washed off from hard surfaces in urban and industrial areas make up a large proportion of the sediment in the stormwater drainage network. Contaminants in stormwater can adsorb to sediment. This especially happens when soils previously contaminated by pesticides, herbicides and fungicides are re-mobilised during subdivision and building. Suspended sediment and the contaminants associated with it can also be transported with groundwater.

Just how much sediment is leaving land development sites?

Frequent ‘minor non-compliance’ with legislative requirements to ‘keep soil on site’ results in a large cumulative sediment pollution impact. Recent research confirms sediment loss during land development is a big deal:

During storm events at the Heron Park Estate subdivision site in Perth, sediment was discharged at a rate of 0.005 kg/day/m² sand. When baseflow intersected with seasonally high groundwater this rose to 0.014 kg/day/m² sand. The measured rates of sediment discharge amounted to approximately 17,000 kg/ha of exposed sand/year (University of Western Australia/CRC-WSC 2020).
8,000 mg/L of Total Suspended Solids (mostly sediment) is delivered
to the Derwent Estuary in Tasmania via stormwater runoff every year, with a large percentage of this sediment load being attributed to erosion from building and construction sites (Derwent Estuary Program, 2009).
Recent research conducted by Healthy Land and Water (HLW) in South East Queensland estimated that annual sediment contribution from construction activities can be up to 202,000 tonnes of mobilised sediment per annum (up to 40% of the total sediment load entering waterways per year).
The USA’s Environmental Protection Agency (EPA) lists sediment as the most common pollutant in rivers, streams, lakes and reservoirs. It has determined that while natural erosion produces nearly 30% of the total sediment in the USA, accelerated erosion from human use of land accounts for the remaining 70%, and that the concentrated sediment releases come from construction activities, including relatively minor home-building projects such as room additions and swimming pools (USA EPA, 2012).

Did you know?
Sediment entering waterways is the number one issue affecting water quality in South East Queensland. Effective erosion and sediment controls on building sites can prevent the loss of around 1 tonne of soil on a 500m2 lot. That’s 10 tonnes (one dump truck load) less soil lost for every 10 houses built! (Healthy Land and Water, 2019).

Did you know?
If you stop a layer of soil one centimetre deep from leaving your building site this is the same as stopping five trailer loads of soil being deposited in waterways (Ipswich City Council, 2020).

What are the Benefits of Controlling Sediment on Construction Sites to the Community and the Environment?

Sediment Task Force is working to control sediment

Together with builders, residents, Local Government and environmental managers, the Sediment Task Force is working to control sediment to:

Protect hydrological functions of rivers, wetlands and other water ways
Reduce the risk of flooding houses and roads as a result of blocked stormwater drains
Prevent sediment from smothering the reeds, plants and seagrasses that keep our rivers, wetlands and oceans healthy
Protect aquatic invertebrates and benthic algae populations, whose presence is necessary for waterways to remain healthy ecosystems
Prevent fish, prawns, crabs and other aquatic wildlife being killed due to the detrimental effects of sediments entering ecosystems
Prevent sediment from covering grass in the parks that receive stormwater runoff
Reduce nutrient enrichment of waterways and associated algal blooms
Prevent the creation of breeding grounds for pest and potential disease causing mosquitoes and midges and protect public health from mosquito-borne diseases and pathogens
Help to maintain stormwater management systems such as biofilters, pervious paving, infiltration cells and tree pits that are critical to protecting our rivers, wetlands, marshlands and oceans
Reduce the risks of accidents on roads and paths.

Success in sediment control will

Reduce the costs to governments and the community for stormwater and river and wetland management
Protect wetland hydrological and biological functions and water quality values
Protect our local parks (where storm water is often discharged)
Protect the aesthetic value of rivers, wetlands, marshlands and oceans that are icons of the natural beauty of Perth and regional WA
Reduce sand and sediment build up on roads
Reduce the costs of supplying sand for building sites and fill for urban development.

Sediment control reduces mosquito risk

Land clearing for the subdivision and construction of buildings and infrastructure in Western Australia often results in soil and building sand making its way into nearby gutters and drains.

From here, it is transported through the storm water system and deposited into wetlands, rivers, creeks and streams.

This increased sedimentation can lead to the establishment of isolated surface water pools; increased deposition of sediment in existing pools, making them shallower; and the formation of “alluvial fans” along waterways. This increases the availability of breeding habitat for pest mosquitoes and can lead to an increase in the number and diversity of flood plain mosquito species (SERCUL, 2017).

Sedimentation can fundamentally modify waterway habitats. Issues such as declining water quality (caused by increased water temperatures), decreased oxygen levels, increased incidence of pathogens, and, as a result, a decrease in the number of mosquito predators, are all considered “triggers” for increased mosquito populations (SERCUL, 2017).

The drying climate predicted for South-West Australia will further challenge efforts to maintain water quality and availability in the landscape, and effective erosion and sediment control management will become more important. The increased frequency of intense weather events will increase erosion and may result in greater amounts of sediment being blown or washed off site.

To manage and prevent the increased occurrence of mosquito-borne diseases and mosquito nuisance, it is therefore essential that the management of soil erosion, sediment runoff and sand drift, during the construction of subdivisions, buildings, and public infrastructure, is improved.

The Department of Health encourages and supports local governments in Western Australia to develop a Mosquito Management Plan (MMP). MMPs should consider that all urban development must include preventative measures to mitigate sediment loss – not just in the case of constructed wetlands but also for developments in close proximity to natural wetlands and waterways.

Implementation of MMPs is often the role of Environmental Health Officers (EHOs). EHOs can assist by immediately reporting incidences of sediment loss and/or sedimentation to their Compliance or Environmental Officer. To highlight the impact of sediments, officers should look for: the presence of mosquitoes or mosquito larvae; stagnant water (including water in roadside culverts); flooding; a change in flow and depth of rivers, pools and/or streams over time; sediment deposition, and/or the infilling of lakes and estuaries.

Did you know? Erosion control is the cheapest control measure and achieves the best outcomes.

Erosion and sediment controls must:

Be put in place before any excavation or earthmoving takes place.
Be maintained until the end of construction and/or when the site is stabilised.
Not divert stormwater onto neighbouring properties.
Not cause erosion.

Photos above: Daily and weekly site checks and sediment ‘clean-up’ maintenance regimes need to be undertaken on all subdivision and industrial, commercial and residential construction sites, with extra checks made before and after rain. Photo credits (L-R): DBCA, R Janes and Sediment Task Force.

*Top header photo: Sedimentation of Wooroloo Brook, caused by sediment runoff from a roadworks site. Photo Credit: Sediment Task Force

Sediment Task Force

Sediment Solutions