Publication (Technical report): Sand slugs and stream degradation: the case of the granite creeks, North-east Victoria

Publication Type:	Technical report / Consultancy
Publication Name:	Sand slugs and stream degradation: the case of the granite creeks, North-east Victoria

Reference Information

Davis, J. and Finlayson, B. (2000) Sand slugs and stream degradation: the case of the granite creeks, North-east Victoria. Technical Report 7/2000, CRCFE, Canberra.

Optional Information

Attached document(s):

Entire Document (2.1MB)

- Granite Creeks .pdf

Chapters 1-3 (500KB)

- Ch 1-3.pdf

Chapter4 (870KB)

- Ch 4.pdf

Chapters 5-7 (840KB)

- Ch 5 - 7.pdf

ISBN:
1876810483

Other information:

Full report attached below
(PDF 2.1MB)

Sand Slugs and Stream Degradation: the Case of the Granite Creeks, North-east Victoria

Jennifer Davis & Brian Finlayson

TABLE OF CONTENTS
1. Introduction	1
1.1. Background and content	1
1.2. Objectives and approach	2
1.3. Report outline	3
2. Catchment descriptions	5
2.1. Introduction	5
2.2. A general description	5
2.2.1. Climate and hydrology	6
2.2.2. Geology, geomorphology, pedology and stream condition	6
2.2.3. Land use and vegetative cover	8
2.3. Other physical characteristics	8
3. Methods	11
3.1. Introduction	11
3.2. Historical analysis	11
3.2.1. Documentary evidence	11
3.2.2. Anecdotal evidence	12
3.2.3. Historic cross-section data	12
3.3. Assessing present condition	13
3.3.1. Field inspections	13
3.3.2. Sediment budget	13
3.3.3. Sediment tracing using particle size distributions	14
3.3.4. Scour chains	19
3.3.5. Suspended load sampling	22
3.3.6. Bedload sampling	24
4. Analysis of historical evidence: establishing baseline conditions and potential erosion triggers	27
4.1. Introduction	27
4.2. Explorers and the Overlanders	27
4.3. Pastoral runs	28
4.4. The Granite Creeks area in the second half of the nineteenth century	29
4.4.1. Creek morphology	30
4.5. The Creightons Creek area in the 20th century	34
4.5.1. Creightons Creek: the hill country	34
4.5.2. Creightons Creek: the flats	38
4.6. Evidence of erosion and sedimentation along Castle Creek and Pranjip–Nine Mile Creek	41
4.6.1. Castle Creek	41
4.6.2. Pranjip–Nine Mile Creek	45
4.7. Potential sources of disturbance	47
4.8. Patterns of aggradation	54
4.9. Pre-settlement erosion and aggradation	56
4.10. Conclusions	57
5. Assessing present condition	59
5.1. Field observations	59
5.1.1. Erosion	59
5.1.2. Aggradation	63
5.2. Sediment budget	65
5.3. Sediment tracing using particle size distributions	66
5.3.1. Fine fraction method	66
5.3.2. Histogram comparison	68
5.3.3. Coarse fraction method	70
5.3.4. McLaren technique	71
5.4. Scour chains	79
5.5. Bedload sampling	82
5.5.1. Bedload transport rates	83
5.5.2. Particle size distributions	84
5.5.3. Dune movement	85
5.6. Synthesis	85
6. Discussion of results	87
6.1. Introduction	87
6.2. Objective and hypotheses	87
6.3. Implications for rehabilitation	88
6.3.1. Introduction	88
6.3.2. Minimising further sediment input	88
6.3.3.Sand slug movement	89
6.3.4. Improving the in-stream environment on the sand slug	92
7. Conclusion	93
7.1. The Granite Creeks	93
7.2. Beyond the Granite Creeks	94
7.2.1. Methodological outcomes	94
7.2.2. Final outcomes	94
References	97
Appendix A	102
Appendix B	104
Appendix C	106
Other publications by the CRC for Freshwater Ecology	107
Acronyms and explanation of some terms	vii

Abstract:

1. INTRODUCTION
1.1. Background and context

Stream and land degradation have occurred throughout south-eastern Australia since European settlement, resulting in gullying, channel incision and channel widening, and the release of large volumes of sediment (Rutherfurd 2000).

The fate of the sediment depends to a certain extent on its particle size distribution. Fine sediments (clays and fine silts) remain entrained in flow for sufficient time to be transported significant distances downstream from the site of erosion or out onto floodplain units where they are stored for long periods of time (Meade 1988). To transport the sand and gravel fraction, on the other hand, requires much more energy. As a result, this fraction remains in the stream channel and is transported slowly downstream in an episodic manner by large flood events. If the material eroded from a catchment is predominantly fine the major form of degradation is a deepening and widening of the channel, as well as sedimentation downstream on the floodplain. If the eroded material is predominantly coarse, degradation takes the form of changes in channel dimensions and stream sedimentation, or sand slug development.

A sand slug is a discrete body of sand deposited in a stream channel. Sand slugs were first described by Gilbert (1917) in relation to hydraulic mining debris deposited in the Sierra Nevada, in California. Since then, sand slugs have been reported in a variety of locations, both in Australia (e.g. Knighton 1989; Erskine 1994; Rutherfurd & Budahazy 1996) and throughout the world (e.g. Pickup, Higgins & Grant 1983; Lewin & Macklin 1987; Madej & Ozaki 1996).

Nicholas et al. have described slugs as ‘bodies of clastic material associated with disequilibrium in fluvial systems over time periods above the event scale’ (Nicholas et al. 1995 p. 502). In other words, a slug is a discrete volume of sand and/or gravel material that is released into a stream channel and only very slowly transported out of the stream network by the stream flow. The slug can fill the width of the channel to depths of the order of metres, and extend over distances of hundreds to thousands of metres. The front of the slug is referred to as its ‘snout’, and this can be a well-defined face or front, downstream of which negligible deposition is apparent.

The physical impact of a sand slug is to drown the stream’s natural bed form (e.g. submerge pool and riffle sequences)and alter the channel form (Nicholas et al. 1995). In many instances a sand slug will transform a stream channel, producing a shallow flat bed. This alters the channel roughness and reduces the channel capacity, altering the stream hydrology and hydraulics. The stream will break out of the channel more frequently, low flows may occur beneath the sand and pools will no longer persist during dry spells. Large woody debris is submerged by the sand and the channel boundary material is often altered. Such changes have an impact on in-stream habitat and thus the stream ecology. Alexander & Hansen (1986) found that the introduction of sand into a stream in the upper midwest of the USA resulted in the channel becoming shallower and wider. As a consequence the static water volume decreased, channel diversity was reduced, fish cover was reduced and velocities increased, all of which contributed to a more stressful environment for fish. Stream temperatures also increased slightly and benthic invertebrates were reduced to half. All these factors were found to contribute to a significant reduction in brook trout (Salvelinus fontinalus).

In south-eastern Australia sand slugs derived predominantly from stream erosion have tended to be associated mostly with granite catchments (Rutherfurd 1996). Granite catchments produce sediment that is dominated by sand-sized particles and so it is no surprise that when stream erosion and gullying occur in these catchments, sand slugs usually result. Large areas of south-eastern Australia are dominated by granitic geologies (Russell & Coupe 1984; Douglas & Ferguson 1988), and the influence of European settlement has been felt throughout the region, so stream degradation in the form of sand slug development is probably more widespread than is currently recognised. While sand movement in granite catchments has been studied at several sites in south-eastern Australia (e.g. Erskine 1994; Rutherfurd & Budahazy 1996; Brooks & Brierley 1997, 2000), those studies have been confined to large catchments (of the order of 1000 km 2 in area) and have been concerned primarily with the physical impact of sediment slugs on the streams. Similarly, the international literature detailing sand slugs is still limited and concentrates on gravel slugs or slugs resulting from mining waste (see review by Nicholas et al. 1995). Madej & Ozaki (1996) describe a sand slug derived from catchment erosion, but the Redwood Creek catchment in USA is very steep compared with the low gradient catchments common in Australia.

The work presented in this report is concerned with the development and movement of sand slugs in several small anabranching streams in central Victoria (the Granite Creeks, tributaries to the Goulburn River), with an emphasis on the effects on stream ecology and rehabilitation. We believe that similar conditions apply in small catchments elsewhere in Australia so that the lessons from this project should be useful to landholders, Landcare groups and river managers.

This report not only provides an insight into the triggers for sand slug development in small granite catchments, but also looks at the influence of anabranching on sand slug migration. The results from the investigation are also considered in relation to the probable effects on stream ecology and the implications for ecological restoration. The methods associated with the investigation are clearly described and so provide a template on which investigations of a similar nature might be modelled.
Such a template could be of particular use to community groups contemplating stream rehabilitation activities.

1.2. Objectives and approach

This report presents some outcomes from the project called ‘Restoration of Degraded Rural Streams: the Granite Creeks Landcare Project, North-East Victoria’ (the Granite Creeks Project). The Granite Creeks Project has been developed to investigate the potential for ecological restoration of rural streams degraded by sand slugs. The Granite Creeks area has been chosen as the main field site for a variety of reasons, including the involvement of the local Landcare groups, the fact that preliminary ecological work has been carried out previously (O’Connor 1991) and because the site is readily accessible to researchers, being just two hours drive from Melbourne. The other advantage offered by the Granite Creeks site is that there are a number of streams with sand slugs which provide replicates and facilitate experimental investigations.

The project is multidisciplinary in nature and requires both ecological and geomorphological input. As a result the project has two components: an ecological component and a geomorphological component. This report gives the results of the geomorphological investigation. Before restoration works can be planned, it is necessary to determine where the sand comes from and how it moves. Consequently the objective of the geomorphological component of the project
was:

to determine the levels of sediment input into selected streams from the catchments of the Strathbogie Ranges, and the movements of such sediments within the streams.

Two key hypotheses were developed to investigate this objective:

1. that increased inputs of sediment (sand) to Strathbogie Range streams have resulted from post-settlement catchment land use;

2. that downstream sedimentation associated with accelerated erosion in the catchments, post-settlement, is mitigated through sediment storage in the catchment slopes and tributary valleys.

There are more than ten creeks that could be considered part of the ‘Granite Creeks’ because they flow off the Strathbogie Ranges and across the Riverine Plain into the Goulburn River, but only three were selected for study in this project. Castle Creek, Creightons Creek and Pranjip–Nine Mile Creek are being studied during the ecological component of the project, and thus these three creeks have also been the subject of the geomorphological investigation.

The tasks required to address the two key hypotheses can generally be categorised as those associated with identifying historical stream condition and those associated with assessing present stream and catchment condition. In essence, the historical analysis was concerned with identifying the forms of the creeks at the time of European settlement, how those forms have adjusted since European settlement and the factors driving that change. The main objectives of the analysis of present condition were to find out if the processes driving change in the past are still active and whether or not the creeks are starting to stabilise. It was necessary to understand why the creeks are in the state they are in today before the fieldwork associated with current assessment was finalised and this led to the project being split into two parts. The first part, which consisted of the historical analysis, was carried out in the first half of 1998; and the assessment of present condition was conducted in the second half of 1998 and the first half of 1999.

1.3. Report outline

Chapter 2 of this report describes the physical attributes of the three selected catchments, and Chapter 3 details the methods associated with the historical analysis and the assessment of present condition. Chapter 4 presents the results of the historical analysis, and Chapter 5 gives the results of the assessment of present condition. The outcomes are discussed in relation to the overall project in Chapter 6 and final conclusions are presented in Chapter 7.

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