The Queensland Division of the Institution of Engineers Australia has issued guidelines for engineers on appropriate practices to manage and control soil erosion and sediment movement. Although developed as guidelines for Queensland construction sites, the majority of the manual is applicable across state borders. The guidelines advise engineers on the effects of soil erosion and sediment runoff and recommend possible erosion minimization and sediment control strategies. This paper draws on information in the guidelines.
Background and Need
Extent of urban and infrastructure-related erosion
While past attention has focused on agricultural erosion, the extent of urban and infrastructure related types has been largely ignored. The 1990 report, `Towards an evaluation of the off-site costs of soil erosion in Queensland', prepared by the
Institution of Engineers, Australia (Qld), found that public expenditure on remedial works in that state was more than $31M per year, and it can, for the most part, be avoided.
Urban and infrastructure development has two vital characteristics in respect of erosion: the area affected at any one time is relatively small; and the developers have control over what occurs on their sites. The opportunity to control erosion and sedimentation therefore exists, as do the means, since most development sites have access to appropriate equipment.
Effects of soil erosion and sediment runoff
The consequences of soil erosion and sedimentation are more serious than is readily apparent. Even a casual consideration of the various on-site and off-site effects can identify items with immediate cash-flow significance such as increased downtime on construction sites after storm events.
Long-term effects, such as ecological impacts on urban creek systems, also reduce the quality of a development's appeal. Without high quality and active ecosystems, riparian bushland becomes just a stand of trees, and creeks become just a means of stormwater drainage.
Strategies for overcoming erosion
Strategies presented within the guidelines are aimed at increasing the awareness of limitations imposed on developments by the given site conditions, and improving the management of developments and their impact on the environment. Ultimately the solutions are deeply entrenched within the ideals of ecologically sustainable development and are encompassed by the ideals of the Mission Statement for an effective Erosion and Sediment Control Program, namely: To prevent controllable erosion and to minimise the adverse effects of sediment transport.
Soil erosion and sediment controls are already widely used within the development industries of NSW and the ACT. Within the ACT, it is reported that: `The subdivision development phase of urban land development has consistently achieved a

high level of control, with substantial retention of sediment (90%) and suspended solids (60%)'.
Costs associated with erosion and sediment control
Although it is not possible to establish a true benefit:cost ratio for on-site erosion and sediment control, this should not be used as an excuse to dismiss the need for reasonable controls.
Costs incurred by introducing erosion and sediment controls will not be borne solely by the development industry but will ultimately be passed onto the community.
Consequently, justification for such costs should not be solely industry-based, but should be a decision made by an appropriately informed community.
How can the guidelines help?
The guidelines are intended to assist competent and experienced engineers to make environmentally sensitive judgments for implementation of erosion and sediment control measures on construction sites. They are no substitute for professional experience, training and local knowledge.
The techniques referred to do not represent a required standard, but should be considered as a guide only. Compliance with these guidelines does not relieve the engineer of the responsibility to apply sound professional judgement to protect the health, safety and welfare of the public. Additionally, the existence of special site conditions or environmental constraints may require greater levels of protection than indicated within the guidelines.
Investigative Procedure
Erosion and sediment control investigations should follow a well documented stepwise process, and with all assumptions and goals clearly stated. The recommended procedure for investigating requirements of a development includes the following steps.
Step 1 - Identify issues and concerns
Step 2 - Develop goals and objectives
Step 3 - Erosion potential study
Step 4 - Investigate and evaluate alternatives
Step 5 - Select Best Management Practice (BMP)
Step 6 - Develop an Erosion and Sediment Control Program
Step 7 - Implement and maintain the Program
Step 8 - Monitor Program and review BMP guidelines
Step 1 - Identify issues and concerns
Local issues and concerns should be determined by clearly defining the nature of the development project, local environmental values and expected environmental risks during and after the development phase. In addition, seek advice from adjoining landholders, local interest groups and regulatory authorities.
Without clear identification of both the local and regional issues and concerns, significant investment into erosion and sediment control design and implementation can be wasted. Possibly the most important issue to be investigated is what form or

degree of sediment runoff will adversely affect downstream environmental values.
As an example, downstream concerns may be related to one of the following forms of pollutant: coarse sediment runoff, fine-sediment runoff (turbidity), or nutrient runoff, often associated with the finer sediments.
Such concerns are usually related to the type of receiving water downstream of the development. The receiving waters usually consist of a watercourse, lake, estuary, bay, open sea or combination thereof. These concerns must be assessed on a site-by-site basis, and advice will probably be required from a specialist in the field of in-stream ecology.
As a general guide, the table below may be used as an initial indicator of local concerns with regard to coarse sediment and runoff turbidity.
In the table below, the terms `regular storm events', `most storm events' and `extreme events' may be defined by the local authority or initially assumed to be less than Q1, less than Q2 and greater than Q2 respectively.
When determining the dominant downstream receiving water, consideration should be given to both the environmental values of the waterways and the potential travel distance of the sediment.
Possible site constraints should be identified during the planning stage of a development, for example: soil limitations, topographic limitations, and water limitations.
Step 2 Develop goals and objectives
The determination of goals and objectives is usually influenced by the nature of the development proposal and the legal requirements associated with the development.
The more immediate construction goals need to be placed in a broader long-term framework. The importance of identifying realistic goals and objectives cannot be overstated.
Receiving water
Pipe network
Creek (naturally clear flow)
Creek (naturally turbid flood flow with clear base flow)
Creek (naturally turbid)
River (naturally clear)
River (naturally turbid)
Lake
Estuary
Bay
Sea
Typical sediment runoff concerns
Concern priorities
Sediment control
Sediment and turbidity control during all but extreme events
Sediment control
Low-flow turbidity control - the smaller the storm event, the greater the required degree of on-site control or treatment
Sediment control
Sediment and turbidity control during most storm events
Sediment control during regular storm events
Sediment and turbidity control during most storm events
Sediment and turbidity control during regular storm events
Sediment and turbidity control during regular storm events
Sediment and turbidity control during regular storm events

Step 3 - Erosion potential study
Various forms of erosion potential mapping exist, including Urban Capability
Mapping and Erosion Risk Mapping.
Urban Capability Mapping can be used by local authorities during the revision of the local Town Plan, or for the rezoning of large areas of land. Erosion Risk Mapping can be used by developers during the planning stage of large developments or developments upstream of critical environmental areas.
The need for an erosion potential study should be discussed with the relevant approving authority. In the absence of any local guidelines or legal requirements, it is recommended that an erosion potential study be carried out on any development where the total disturbed area is expected to exceed five hectares, or if the development is upstream of an environmentally significant waterway.
In any case, it will be necessary to identify the cause of existing and potential future on-site erosion problems, and to consider the off-site impacts of any proposed drainage, erosion and sediment controls.
Step 4 - Investigate and evaluate alternatives.
Investigations into the erosion and sediment control benefits of alternative development designs and construction techniques should first include a review of the proposed site layout, staging of works, and construction sequence, then investigation of alternative drainage, erosion and sediment control measures.
The various alternatives should be evaluated by incorporating the goals and objectives developed in Step 2 with the principles of erosion and sediment control in the guidelines.
Questions relevant to investigation of alternative site layouts
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Can the proposal be altered to minimise land clearing and land shaping?
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Can the proposal be altered to allow permanent stabilization of disturbed areas as soon as land shaping is complete?
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Can undisturbed areas be used as sediment buffer zones during construction?
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Can site entry points be located so as to minimise soil contamination of vehicles, and is it possible to allow the early establishment of all-weather parking areas?
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Is it possible to locate imported material and soil stockpiles in areas that minimise onsite traffic movement?
Questions relevant to investigation of proposed staging of works
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Can the works be staged to make best use of existing buffer zones and stabilized areas?
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Can the development be staged so that most of the ground disturbance occurs outside periods when rainfall is highly erosive?
Question relevant to investigation of proposed construction sequence

Will it be possible to obtain early access to the site for the purpose of preparing stable drainage paths prior to formal site establishment (eg. grassed channels, level spreaders and drop chutes)?

Control measures
The guidelines include recommended drainage, erosion and sediment control measures as well as detailed information on erosion and sediment control in special situations.
Step 5 - Select Best Management Practice (BMP)
The wide variety of site and soil conditions demands an equally wide variety of solutions to adequately address on-site erosion and sediment control. Selection of best management practice for the given site conditions should be based on the following criteria:

Cost-Effectiveness: Performance histories, both in the field and laboratory, should be evaluated for a number of materials or control measures, and then judged in relation to their purchase, installation and maintenance costs.

Availability: The materials must be readily available from a local supplier, or be available for shipment within a suitable time frame.
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Feasibility: Realistically, the materials must be capable of relatively quick and easy application with minimal on-site training requirements. Each material or method should be assessed in relation to its flexibility or applicability to the full range of expected field conditions.
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Durability: It is usually necessary that materials maintain their structural integrity during the construction phase and until vegetation (or other final surface condition) establishes effective erosion control.
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Compatibility: Materials should be selected with due regard to community acceptance and environmental sensitivity.
Step 6 - Erosion and Sediment Control Program
An Erosion and Sediment Control Program may be developed by implementing the principles of erosion and sediment control which are set out in the guidelines. The adopted Program should include the following features:
 use of available resources
 maximum utilisation of existing terrain
 realistic, practical, and easily understood control measures
 cost-effective solutions
 flexibility with performance-based objectives and allowance for future program amendments
 provision for open communication between developer, consultant, contractors and regulating authority
Step 7 - Implement and maintain the Program An Erosion and Sediment Control
Program should be implemented and maintained in accordance with the
`Supporting Documentation' and the `Specifications and Construction Details' supplied with the Program Documentation.
Step 8 - Monitoring and guideline review Monitoring the effectiveness of an
Erosion and Sediment Control Program is an essential part of responsible site management. Monitoring needs to be periodic and regular, not only before, but also after development.
Monitoring requirements may vary from weekly inspections on small sites (say, less

than 0.5 hectare) supported by simple diary notes discussing the required maintenance needs of the various control measures implemented, to extensive downstream water quality sampling and detailed log book entries on larger construction sites or when working near environmentally sensitive areas. Monitoring should assess all likely offsite impacts.
Erosion and Sediment Control Programs should be living documents that can and should be modified as designers increase site knowledge and experience in soil and water management.
Information about the Guidelines Document
Initial funding for the preparation of the guidelines was provided through the
National Soil Conservation Program. The principal work on the document was done by Mr Grant Witheridge for the Queensland Division of the Institution of Engineers,
Australia.