GUIDELINESVersion 3 / 2004

Erosion Treatments for UrbanCreek Guidelines

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CONTENTS

1 Introduction 2

1.1 Objectives of guidelines 3

1.2 Introduction to Brisbane’s creeks 3

1.3 Effects of urbanisation 3

1.4 Why treat creek erosion 5

2 Use of guidelines 7

2.1 Intended use of guidelines 8

2.2 How to use the guidelines

3 Bibliography

Part A - Problem identification and selection of remedial works

Section A1 Procedure for problem identification and selection of remedial works

Section A2 Site Assessment Form

Section A3 Erosion type fact sheets

Section A4 Erosion treatment techniques

Section A5 Product and construction unit rates

Section A6 Products

Part B - Supplementary information

Section B1 Mechanics of urban creek erosion

Section B2 Detailed appraisal of erosion treatment techniques

Section B3 Erosion treatment techniques for hydraulic structures

Section B4 Rock chute design guidelines

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CONTENTS

1 Introduction 2

1.1 Objectives of guidelines 3

1.2 Introduction to Brisbane’s creeks 3

1.3 Effects of urbanisation 3

1.4 Why treat creek erosion 5

2 Use of guidelines 7

2.1 Intended use of guidelines

2.2 How to use the guidelines 8

3 Bibliography 9

Part A - Problem identification and selection of remedial works

Section A1 Procedure for problem identification and selection of remedial works 10

Section A2 Site Assessment Form 25

Section A3 Erosion type fact sheets 31

Section A4 Erosion treatment techniques 39

Section A5 Product and construction unit rates 79

Section A6 Products 84

Part B - Supplementary information

Section B1 Mechanics of urban creek erosion 89

Section B2 Detailed appraisal of erosion treatment techniques 98

Section B3 Erosion treatment techniques for hydraulic structures 147

Section B4 Rock chute design guidelines 170

4 Creek Erodibility Guide

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1 Introduction

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1.1 OBJECTIVES OF GUIDELINES

These urban creek erosion guidelines provide information for Council staff and the community on erosion treatment techniques. They were developed because of the unique characteristics of urban creeks compared with most rivers and rural watercourses which already have a number of useful guidelines.

The guidelines discuss the treatment of urban creek erosion, not the prevention of creek erosion. Urban creek erosion can be significantly reduced, but not necessarily prevented, by appropriate catchment management techniques such as the use of Water Sensitive Urban Design (ie. grass swales, bio-retention, natural channel design, rainwater tanks, porous paving, etc).

1.2 INTRODUCTION TO BRISBANE’S CREEKS

The city of Brisbane surrounds the mouth of the Brisbane River, with a catchment area of some 5,000 km2

which discharges into Moreton Bay. Brisbane’s main urban creeks have catchment areas ranging from less than 30 km2 and up to 300 km2.

Creeks to the south of the Brisbane River are usually south-to-north oriented, with headwaters on the flat and a barely distinguishable divide between the Brisbane River and the adjacent river-basin to the south. Creeks to the north of the Brisbane River usually have a west-to-east orientation, draining from headwaters near the southern end of the D’Aguilar Range with its steep upper catchments.

A number of the urban creeks north of the Brisbane River discharge directly to Moreton Bay. These include Cabbage Tree Creek, Nundah Creek and Kedron Brook. All creeks south of the Brisbane River (except Tingalpa and Wynnum Creeks), discharge to the Brisbane River.

In the 175 years since European settlement, land use characteristics of the creek catchments around Brisbane have changed significantly. Early clearing of vegetation for agricultural purposes altered the hydrology and sedimentology of the catchments. Continued urban expansion plus urban infilling will continue to change the character of the catchments of Brisbane’s urban creeks and the morphology of the creeks themselves.

1.3 EFFECTS OF URBANISATION

The effects of urbanisation on a catchment can be listed in the following categories:

Hydrology:

decreased runoff travel time

changes in rainfall intensity and frequency of thunder storms (Mein and Goyen, 1988)

possible reverse of the dominant weather season, particularly in temperate climates where summer thunder storms can dominate stream morphology in urban catchments, compared with winter storms that may have dominated the undeveloped catchment

approximately a ten-fold increase in the one-year ARI discharge with a relatively minor increase in the 100-year ARI peak discharge (Mein and Goyen, 1988)

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U.S. studies show it is typical for the pre-development 10-year peak flow rate to occur in the post-development every 1.5 years, and a pre-development 25 year peak flow may have a post-development frequency of 5 years (Roesner, 1992)

approximately a two-fold increase in the total runoff volume (Mein and Goyen, 1988)

urbanisation will probably have a greater impact on sandy catchments compared to clay catchments because of a greater potential for reductions in infiltration capacity.

Catchment surface storage features:

loss of flood plain storage area and the resulting adverse effects on peak flood discharge

urbanisation may initially increase or decrease the catchment storage or depression storage. However, with time local flooding problems are solved by 'better' catchment drainage resulting in a decrease in this surface storage and an increase in peak runoff discharge.

Groundwater

possible changes to groundwater levels

base flow or dry weather flow can change through variations in catchment infiltration, groundwater levels and the effects of urban garden and lawn watering.

Creek erosion:

in-bank erosion of natural watercourses

wider and shallower stream channels with fewer pools to support a diverse range of aquatic life.

Stormwater quality:

pollution of stormwater runoff

increased sedimentation of waterways.

Riparian vegetation and ecology:

changes in the dominant riparian vegetation

greater extremes in water temperature in the remaining pools caused by a loss of the tree line canopy

permanent change to the watercourse ecology

introduction of watercourse structures such as culverts, pipe crossings, dams, weirs and drop structures that can restrict migration of aquatic life and riparian fauna

changes to the location of the salt-water/fresh-water interface.

Urbanisation also changes the discharge in receiving creeks by:

1. increasing storm runoff volumes (because of cleared vegetation and increased impervious area)

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2. reducing the travel time needed for storm runoff to reach creeks (due to a more efficient drainage network within the catchment)

3. increasing peak discharge levels, especially in low and middle sized floods (i.e. up to bankfull), increasing the frequency of bankfull discharges and creek erosion.

The magnitude of increase in peak discharge and the increased frequency of flooding as a result of urbanisation depends on:

climatic conditions density of development previous land uses location and extent of development within the catchment characteristics of the stormwater catchment catchment topography the nature of soils.

Urbanisation of a catchment usually affects sediment transport with:

1. a marked increase in sediment delivered to the creeks during the development of the catchment

2. a decline in sediment delivery to the creeks following development and stabilisation of the catchment and

3. an alteration of textures and mineralogies of sediments delivered to the creeks which impact on the creek’s morphology and ecology.

1.4 WHY TREAT CREEK EROSION

Urban creeks are a valuable asset to any urban landscape. They deserve to be preserved. Morrison and Williams (1995) say that urban creeks and all streams, have:

ecological values economic values recreational values aesthetic and cultural values scientific and educational values.

Regarding these values, Urbonas and Benik (1990) put forward the following reasons for stabilising degraded urban creeks.

(i) The primary need to stabilise creeks in an urban area is to protect the massive investment in infrastructure and property. The cost of damage to public utilities such as electrical lines, telephone lines, gas lines, roadway culverts, bridges and roads is often a cost for the public sector. As the area urbanises and more land is subdivided, property lines become very important. It is not practical or financially feasible to allow degrading creeks to encroach onto valuable land.

(ii) Riparian habitat corridors are being recognised as valuable assets in urban areas. Riparian habitats can be, and often are, destroyed as a creek destabilises because of urbanisation. It will often take years for a degrading creek to stabilise itself to a point where vegetation will re-

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establish without assistance. The gullied nature of the degraded creek will provide poor access and will be less attractive to wildlife.

(iii) Damage to aquatic habitat is another reason for stabilising degrading creeks. As creeks degrade bed, forms are altered and existing stream beds are destroyed. The bed will eventually re-establish itself, as it will after a catastrophic event, but the healing process may take a long time.

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2 Use of guidelines

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2.1 INTENDED USE OF GUIDELINES

These guidelines have been prepared for use on urban creeks within Brisbane, Queensland. Urban creeks outside Brisbane could have different forms of erosion and these guidelines might not be appropriate.

These guidelines have generally been developed for non-alluvial streams. For erosion control in sandy or gravel/rock based watercourses, seek experienced professional advice.

2.2 HOW TO USE THE GUIDELINES

The guidelines are in several sections. The purpose of each section is described below. To use the guidelines successfully it will be necessary to become familiar with the contents of each section.

To identify the cause of erosion and select the most appropriate remedial technique, follow the procedure in Section A1.

Part A:

Section A1 provides details on the recommended investigation procedure. Section A2 has a standard Site Assessment Form; Section A3 contains erosion identification fact sheets and Section A4 provides information on various erosion treatment techniques. Sections A5 and A6 give details on unit rate construction costs and local products and product distributors.

Part B:

Part B contains supplementary information on the mechanics of creek erosion (Section B1), detailed appraisal of the various erosion treatment techniques (Section B2) and information on the treatment of creek erosion associated with major creek structures such as drop structures, culverts and energy dissipators (Section B3). Recommended guidelines for the design of loose rock chutes are in Section B4.

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6. Maccaferri Group (-) Maccaferri Gabions and Reno Mattress – Technical Specifications. Maccaferri Pty Ltd.

7. Mein, R.G. and Goyen, A.G. (1988) Urban Runoff. Civil Engineering Transactions, Institution of Engineers, Australia.

8. Morrison, A.J. and Williams, W.D. (1995) Urban Drainage and Aquatic Ecology. Paper 8 in ‘Environmental Aspects of Urban Drainage’, seminar proceedings, Stormwater Industry Association, Sydney.

9. Roesner, L.A. (1992) Current Water Quality Issues in Stormwater Management in the United States. Proceedings of International Symposium on Urban Stormwater Management, The University of Technology, Sydney, Australia 4-7 February 1992. Institution of Engineers Australia, National Conference Publication 92/1.

10. Standing Committee on Rivers and Catchments, Victoria (1991) Guidelines for Stabilising Waterways. prepared by The Working Group on Waterway Management, Armadale, Victoria.

11. Urbonas, B. and Benik, B. (1990) Stream Stability Under a Changing Environment. Chapter 6 in ‘Stormwater Runoff and Receiving Systems – Impact, Monitoring and Assessment’ edited by E.E. Herricks.

12. U.S. Corps of Engineers (1970) Hydraulic Design of Flood Control Channels. Department of the Army.

3 BIBLIOGRAPHY

1. Department of Land and Water Conservation, NSW (1995) Waterwise Brochures. (various)Advisory notes for rural landholders from the NSW Department of Land and Water Conservation,NSW, Australia. ISSN 1038-2283.

2. McLaughlin Water Engineers Ltd. (1986) Evaluation of and Design Recommendations for Drop Structures in the Denver Metropolitan Area. Prepared for the Urban Drainage and Flood ControlDistrict, Denver Colorado, USA.

3. McLaughlin Water Engineers Ltd. (1989) Evaluation of and Design Recommendations for Drop Structures in the Denver Metropolitan Area – Addendum and Errata. Prepared for the UrbanDrainage and Flood Control District, Denver Colorado, USA.

4. Maccaferri (1981) Flexible Gabion Structures in River and Stream Training Works Section One.Officine Maccaferri S.p.A. Bologna.

5. Maccaferri (1981) Flexible Gabion Structures in River and Stream Training Works Section Two –Longitudinal structures. Officine Maccaferri S.p.A. Bologna.

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K2004-01387© Brisbane City Council 2004