ENVIRONMENTAL GUIDELINES FOR RIVER MANAGEMENT WORKS
FOR THE STANDING COMMITTEE ON RIVERS AND CATCHMENTS
8571(F1) Published for the Standing Committee on Rivers and Catchments by the Department of Conservation & Environment Edited by Georgina Katsantoni Designed and Typeset by Dead Set, Fitzroy Printed by Victorian Government Printing Office ISBN 07306 2062 X © 1990 GUIDELINES
Gu IDELINES
FOREWORD
INTRODUCTION TO RIVER MORPHOLOGY AND ECOLOGY 1
RIVER MORPHOLOGY 1
RIVER ECOLOGY 6
GENERAL ENVIRONMENTAL GUIDELINES 11 STREAM MORPHOLOGY 11 PROTECTING THE STREAM ENVIRONMENT 12 RECREATION 14 GUIDELINES
Guidelines
Foreword The Department of Conservation and Environment is involved in river management activities throughout Victoria. Most river management works are undertaken by statutory river management authorities which receive funding through the Office of Water Resources. The Department recognizes its responsibility to ensure that stream works take adequate steps to protect or enhance the aquatic and streamside environment.
This report is one in a series prepared for the Standing Committee on Rivers and Catchments to assist government agencies and other authorities involved in river management. It provides a basic introduction to river morphology and ecology and describes the environmental effects of river management works. It also brings together a number of case studies and suggests ways in which major types of river management works should be carried out to protect stream environments.
Horrie Poussard Convenor Standing Committee on Rivers and Catchments GUIDELINES
Introduction to River Morphology and Ecology
When Europeans settled in Victoria less than River morphology two centuries ago, these natural instabilities were This introduction to river morphology briefly regarded as incompatible with the way the land was describes and explains the processes which have to be used. European land uses altered the 'graded' shaped the way in which Victorian stream systems equilibrium and introduced new instabilities into the have evolved through time and the way in which system. The magnitude of these new instabilities these stream systems have responded to external varies throughout the State and even within river influences such as land use changes and stream basins but, as a generalisation, the effect of European management activities. settlement on the stability of Victorian streams has been severe.
Drainage basin morphology Tune scale perspectives Stream stability Viewed on a human time scale, many stream The majority of streams in Victoria are dynamic instabilities are regarded the cause of severe alluvial streams characterised by a capacity to alter environmental degradation. Viewed from the their own boundaries. Variations in the balance perspective of a time scale in the order of hundreds between sediment supply and sediment transporting to thousands of years these changes may be perceived capacity, both along the length of a stream and as fluctuations within a more or less steady state. within a cross section, cause the channel to alter its Fig. 1 (see page 2) schematically illustrates four slope, depth, width, shape or location. For most of time scales. The vertical axis in each case is a their lengths these alluvial streams flow through bed notional elevation at a point in the drainage system, and bank material which was initially carried there or it could represent other variables such as sediment and deposited by that stream or its ancestors. Given transport or size composition of bed material. the right conditions, the stream will be able to move Fig. 1(a) represents a time scale in the order of that material once more. days. Generally speaking, within this time scale, the Over thousands of years, these processes drainage basin will appear to be in a state of static produced 'graded' stream systems. Most streams had equilibrium. Static equilibrium over time periods of adopted a grade, shape and plan-form which 1 day is generally observed in all but the most balanced the variable inputs of water and sediment. unstable of Victorian streams. Only during major The concept of stream stability does not imply erosion events (corresponding to the episodic events static stability in either the long or the short term. in Fig. 1(c)) will it be possible to observe changes Short-term instabilities (such as scouring a bank or occurring 'before your very eyes'. filling or creating a deep hole) reflect short-term Fig. 1(b) represents a time scale in the order of variations in water and sediment inputs. 100 — 1000 years. Within this time scale fluctuations Natural processes may be manifest as gradual of drainage basin variables become apparent. Never- changes to the stream system occurring, sometimes theless fluctuations are observed to be on either side imperceptibly, over a period of years. Sudden and of a more or less steady state, and the drainage basin dramatic channel changes may occur as the result of appears to be in steady state equilibrium. Steady a rare or catastrophic natural event such as flood, state equilibrium is apparent in many Victorian bushfire or landslip, or as the culmination of a streams and is typified by a meandering system. In gradual progressive change, eventually reaching a such a system, fluctuations of bed level will occur as threshold condition (channel avulsion, for example). the result of major and moderate flood events, or the Such natural instabilities are present in alluvial progression of meanders and associated riffles and streams regardless of human interference. Over time, pools through the system, with a period in the order these mechanisms have created the floodplain and of centuries. channel characteristics evident in the present day Fig. 1(c) represents time scales in the order of stream system. 1 000 000 years. Within this time scale progressive (a) Static Equilibrium (c) Dynamic Metastable Equilibrium
1
co e5P6\5°
1 00 - 1 000 years
(6) Steady State Equilibrium (d) Progressive Change
Figure 1. Perspectives on timescales changes or trends become apparent. Superimposed When sediment supply is less than sediment on the trends are episodic events where major transport capacity (Fig. 2(a)) all available sediment changes occur over relatively small time periods. is flushed out of the system and remaining bed This has been termed dynamic metastable material and bank material is generally erosion equilibrium. Episodic erosion is typified by major resistant. deepening episodes moving through the stream When net sediment supply is approximately systems. An excellent example would be Bruthen equivalent to net sediment transport capacity (Fig. Creek in the Yarram area where a major incision has 2(b)) in a stable and natural flood plain system, occurred and is progressing upstream. It is likely that sediment will be moved without net scour or there has been an increase in episodic erosion events deposition. Of course, storage and scour will occur in in the last two centuries as a result of human some places and temporary storage also occurs as the influence. (Note that one of the causes of result of variations in flow and sediment inputs, but fluctuations in the 100— 1000 year time scale is an there is no net accumulation or depletion. In ongoing complex response to such an episodic meandering reaches of many Victorian streams, event.) where sediment supply is locally out of balance with Fig. 1(d) is the traditional geomorphic view the sediment transporting capacity, then deposition originally proposed by Davis and represents time or erosion will occur (Fig. 2(c)). scales in the order of tens of millions of years. At this When sediment supply from upstream is greater scale the fluctuations and episodic events disappear than the ability of the stream to transport sediment into the general trend of progressive change within deposition occurs. The result is frequently a braided the erosion cycle. stream or the formation of alluvial fans or deltas. Continuing deposition makes these inherently Fluvial system concepts unstable morphologic forms. The sediment Fluvial systems can generally be divided into three deposition zone is represented in Victoria by the geomorphic zones. Fig. 2 is a simplified and idealised lower reaches of main stem tributaries and also by representation of the fluvial system. the lower reaches of those streams which drain The basic characteristics of each of the three directly or via lakes to the sea. Examples include the zones in Fig. 2 can be explained by comparing the lower Avon, Tambo and Snowy Rivers in Gippsland amount of sediment available to the stream with the and numerous alluvial fans flanking the north amount of sediment that the stream has the capacity western slopes of the Strathbogie Ranges or the to transport. Beechworth hills in north-east Victoria.
2 Sediment production zone Sediment transfer zone. i Sediment deposition zone.
(al Sediment supply less than sediment transport capacity. (b) Sediment supply approx. equivalent to sediment transport capacity. (c) Sediment supply greater than sediment transport capacity.
Stream Profile
Figure 2. Idealised fluvial system
The upper zone, termed the sediment production zone is typical in mountain regions. Within this zone the stream flows on bed rock or through very large bed material (pebbles and gravels) and the presence of smaller alluvial material is rare. In Victoria, where rates of denudation are very Low by world standards, the term sediment production zone is somewhat misleading. Large lengths of Victorian rivers belong to the sediment transfer zone. Within this zone, the stream typically flows through flood plains and terraces of alluvium. It would generally have a meandering character and point bars in the stream channel. In the sediment deposition zone net deposition occurs, and the stream is likely to be braided. Examples include alluvial fans and deltas.
Complex response in stream systems alluvium. Rejuvenation of this stream is initiated, causing the stream to incise (Fig. 3(b)). Rejuvena- A complex series of reactions may be triggered by a tion could be caused by, for example, a downstream single event within the drainage basin. A single lowering of base level from climate change or major event such as uplift, subsidence, flood, erosion in the main stem; or it could be triggered by bushfire or gullying episode may produce a chain of local changes to channel conditions such as de- reactions which goes on for decades. snagging. Fig. 3 represents the complex response to Once the event is triggered, the deepening will channel rejuvenation observed in an experimental move upstream, cutting through the deposited drainage basin. Fig. 3(a) shows a graded stream (in alluvium and even into the parent material. As the sediment transfer zone) flowing through its own erosion moves upstream, increased sediment loads
(a) (c) Rejuvenation Upstream erosion stoPs
Groded stream Braided stream
(b) (d) Erosion moves upstream Li Incised stream Renewed stream incision
Figure 3. Example of complex response to channel rejuvenation 3 GUIDELINES
are induced at downstream sections, and the stream is forced into a depositional phase. A wide shallow braided stream is formed on the newly deposited material as illustrated in Fig. 3(c). As the upstream erosion reaches its limit, sediment supply to the downstream areas decreases, and the stream goes through a cycle of renewed incision as illustrated in Fig. 3(d). Thus initial channel incision and terrace formation is followed by deposition of an alluvial fill, channel braiding, and lateral erosion, and then, as sediment yield from upstream decreases, renewed incision forms a low alluvial terrace or floodplain. The whole cycle may then begin again. Ongoing complex response is occurring in streams in north-eastern Victoria as a result of major changes induced by the mining era. Yackandandah and Hodgsons Creeks were both subject to enormous increases in silt loads during mining. Their floodplains became swamped with silt and the 2 3 4 5 6 channel adopted a straight and braided course. As 10 10 10 10 1 0 sediment supplies from mining decreased, the Mean Discharge cis straight course incised into the newly deposited Figure 4. Meandering and braided streams alluvium and in the case of Hodgsons Creek into the parent material as well. So in these cases an influx of sediment from upstream has ultimately led to meandering stream to a braided stream. It is possible deepening in the channel. The incision episode that development in catchments can increase flow produced large quantities of sediment which is now regimes sufficiently to force a stream from causing siltation problems downstream. meandering to braided.
Geomorphic threshold Energy Thresholds may occur within or outside the fluvial Concepts based on availability of energy help to system. Crossing a threshold induces a major response explain many stream related processes. from an otherwise slow and progressive change. Rain reaching the ground has a potential energy by virtue of its elevation and thus an ability to do External variables such as climate or tectonics work. As the rainfall becomes runoff and accumu- change progressively until an episodic response is lates in streams and rivers this potential energy is initiated within the drainage basin. A good example is expended by: isostatic adjustment whereby progressive removal of • transfer to kinetic energy of flow; material from a drainage basin ultimately leads to • doing work overcoming resistance to flow; and uplift as a result of decreased load on the earth's crust. • doing work by picking up and transporting Such movement induces major response in the sediment. drainage basin. A delicate balance exists between the available Thresholds within the fluvial system occur when energy and the energy being dissipated by flow and progressive internal change within the drainage basin sediment transport. Too much energy leads to flow reaches some limit which induces a response. For ex- acceleration and erosion; too little energy leads to ample, in the m ulling of a channel, sediment is stored deceleration of flow and deposition of suspended in the channel bed until a critical slope is reached at material. the downstream end of the storage; then incision will A natural stream chooses its course of flow in such commence for no apparent reason. In a meandering a manner that the rate of potential energy stream, meanders develop and sinuosity will increase expenditure is a minimum. The stream will seek an until a limit is reached and a meander cut off occurs. equilibrium state between flow conditions (channel Fig. 4 illustrates the threshold between meander- shape, slope, planform, etc.), and the amount of ing and braided streams. Increasing slope or sediment transported, such that the energy expended increasing discharge can trigger a change from a is a minimum.
4 • GUIDELINES
The energy balance varies with time and in decreased flood levels in main streams during space. Time dependent variations result from the filling of major water storages; and variability of water flows, sediment supply and • other human-induced changes to inputs of water temperature. The energy balance will also vary from and sediment from the catchment. reach to reach, between cross sections and also from Channel deepening, once triggered, causes point to point within a cross section. The result is severe local increases in grade and substantial the diversity of stream processes which occur in increases in channel capacity and stream power. The nature such as aggrading or degrading reaches, channel adjusts by widening and further deepening meander growth and progression, point bar growth and the increased capacities compound instabilities. and movement, pools, gullying, shoals and channel Deepening moves upstream, either by upstream avulsion. advance of a reach of locally high gradient, or the On the Ovens River upstream of Wangaratta, in upstream advance of a major erosion head. the Whorouly area, massive increases in sediment loads were initiated by upstream alluvial mining in Bank erosion the late 1800s through to the early 1900s. The Erosion of stream banks is frequently associated with balance between flow, sediment and energy was bed instability as described in the previous section. It disrupted. Insufficient energy was available to carry occurs as either scour or slumping. Scour is the direct the flow in the existing river course and deposition, removal of bank material by the flowing water. widening and straightening of the river channel Slumping describes the various mechanisms whereby resulted. When cessation of mining in the early 1900s sections of bank material cave into the stream. led to reduced sediment loads, the new river form had Scour is caused by the tractive force of the flowing too much energy. As a result excess energy has been water against the bank material. Slumping often expended on bed and bank erosion as the river seeks results from bank scour or from deepening of the to re-establish its narrower meandering course. stream channel. Both scouring and slumping are natural processes Channel deepening which contribute to the movement of streams and Many streams in Victoria are either actively the creation of floodpla ins. The processes may be deepening or show signs of recent past incision. The aggravated by a number of natural and human- causes of such widespread changes are complex and induced factors such as: many factors have contributed, not all of which are • instabilities in the bed as described in the in response to human intervention. Frequently, a previous section; small change in stream or catchment conditions can • removal of binding and protective vegetation trigger a major change in stream characteristics by from bed or banks; crossing a geomorphic threshold. Possible triggers • natural or human-induced short-term or long- include: term changes in hydrologic or sediment regime • natural response to natural variations in water (see 'Stream Stability'); and sediment inputs (flood, wildfire, landslips, • fluctuations in channel water level; etc.); • bank saturation from off-stream sources; natural long-term cyclic processes within the river • the presence of seams of readily erodible material system as part of its dynamic balance (cycles of in the bank profile; cutting and m ulling moving repeatedly through • acceleration of flow around debris and stream the system); blockages; draining of on-creek swamps by channelisation; • trees falling from banks; and removal of streamside vegetation which had • surcharging effect on the bank of trees, buildings acted to bind bed and banks and retard stream or pump sites. flows; removal of snags and obstructions from stream River morphology and river bed and banks; • extraction of bed material: management • concentration of flows through bridges by road An understanding of stream morphology is essential and railway embankments; to ensure that stream management strategies stream response to wholesale catchment clearing recognise the fundamental processes which are at the either as a direct response to increased runoff or as root of a stream instability problem and to allow the a complex response to increased sediment loads; full effects of a stream management prescription to • lowered base level for tributaries resulting from be recognised and allowed for.
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The underlying causes of stream management important to the ecology of the river. The problems must be recognised if effective and floodplain, with its more or less ephemeral water economical management is to be achieved. If the bodies, is an extension of the riverine habitat, and processes are not understood there can be no basis provides a source of nutrient, and a refuge from for selecting appropriate strategies. Bank erosion for which the biota of the river can be continually example, is frequently initiated by channel replenished. This is particularly important for plants, deepening. There is no point in treating the banks and those animals which cannot move upstream unless the bed is stabilised first. Major channel against the current, as these are at risk of being instability may often be the result of high upstream gradually swept downstream. Flooding provides the sediment loads. If this is recognised and understood, route by which they can be replaced from economical solutions may sometimes be achieved. populations in the billabongs. Floods also provide a Stream management activities may initiate channel greatly extended area of highly nutritious waters changes upstream and downstream. Stabilising an which is very important for the spawning and early active erosion head may interrupt a cycle of erosion survival of many species of fish, such as Golden and deposition moving through the system and Perch. Flood waters are usually the means by which trigger a renewed cycle of incision downstream. De- floodplain water bodies such as billabongs are filled, snagging may be carried out to induce thannel and help recharge the water table which maintains rejuvenation but it is difficult to predict how far such floodplain vegetation such as River Redgums. changes will extend. Stabilising eroding banks may alter the sediment balance of the system and induce Water chemistry new instabilities. The quality of the water in a river depends primarily on the geology of the catchment, but can be altered by land use. These can cause chemical River ecology pollution and turbidity from rural run-off and urban Rivers provide a complex habitat for a wide range of effluents. The amount of turbidity is most likely to plants and animals. This habitat is made up in part be affected by river management practices. by the physical characteristics of the river (flow, Increased turbidity can reduce the photosynthetic water chemistry and temperature, substrate and activity of algae and aquatic plants. Water temperatures can be affected by the amount of bank and bed morphology) and in part by shading of the river, or by the velocity and depth. interaction between the plants and animals living in All fish and invertebrate species, being cold- and adjacent to it. There is a dynamic relationship blooded, are very sensitive to the temperature of between a river's aquatic and riparian zones and their surroundings, and are adapted to particular many animals utilise both. In addition, the riparian temperature regimes. In temperatures outside these corridor has considerable importance for the regimes, the growth and development of aquatic adjacent terrestrial environment. insects may be so slow that they fail to complete their life cycles. High water temperatures are Physical characteristics accompanied by low oxygen levels which can kill fish and have an adverse effect on macro- Flow regime invertebrates. The velocity of the flow has a considerable impact on the habitat of plants and animals in the river. Substrate High velocities limit the growth of aquatic plants, and force animals to spend most of their time in The substrate through which the river flows will have sheltered areas within the river. In a fast flowing a strong influence on the habitat it provides. Coarse river the populations of animals will be limited by substrates (rocks, gravel) provide a lot of sheltered the amount of shelter available. These may be small water for animals to take refuge from the current, and cavities between particles of sand or gravel, deep a large surface area which can be colonised by algae holes, areas of quiet water behind and under weed and small sessile animals. Larger aquatic plants will beds, rocks or snags, and backwaters along banks. only be able to grow well in areas of deposition of The amount of shelter will also determine the finer sediments, behind large rocks or snags or in species present, as some plants and animals can cope deep holes. Coarse gravel can be important as a with the problems of living in high velocities, while spawning site for fish. others can only survive in slow water. When rivers flow through finer sediments (sand The frequency and extent of flooding is very and clay), the growth of aquatic plants will generally
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be better, but the fine, mobile sediments are less The most important energy source is the suitable for small aquatic animals and sessile algae. introduction of organic material which falls or is In these rivers, submerged wood (snags) becomes washed in from the surrounding land. This is mainly very important as it provides the main surface area plant material (leaves, branches and logs) but also for growth of algae, and crevices and sheltered holes includes the bodies of animals. The food chain is for small animals and fish. Many fish spawn in and based on the animals which eat this material around snags in rivers that have fine sediment as directly, or which feed on the bacteria and fungi their eggs would be smothered on the bed of the which are the agents of decay. river. Insects that feed directly on the fallen leaves are known as shredders, and include species of stoneflies, Morphology mayflies, caddisflies and midges. Other species feed A natural river develops a wide diversity of form along by scraping algae, fungi and bacteria from the leaves, its length, with a sequence of pools and riffles, vari- wood or rocks and gravel, on which they grow. A ation in depth and width, and a meandering course. third group, the collectors, feed by collecting the Banks vary from steep and undercut on outside bends, very small particles of organic matter which are in to shallow and sloping on inside bends. This is a suspension in the water, or in the sediments. They filter the water, spin nets to catch the detritus or dynamic system which changes gradually or suddenly gather small particles from the substrate. They as a result of floods. The variety in form provides a include species of mayflies, caddisflies and midges much wider range of habitats than a channel of and also crustaceans such as shrimps and yabbies. uniform width and depth would do. Large rocks and These smaller macroinvertebrates provide food snags in the river can change the channel morphology for larger predatory macroinvertebrates such as by creating scour holes or undercut banks, and dragonflies and damselflies, and for fish, tortoises, become part of the bed morphology themselves, platypus and many birds. greatly increasing the surface area available for the growth of algae and associated species. Habitat requirements River biota Aquatic plants The biota (living organisms) in the river form a complex interacting network of primary and Plants are one of the primary sources of energy in the secondary producers, herbivores and carnivores, aquatic system. They capture nutrients from the predators and scavengers. There is also a strong sediments and the water, and make them available to interaction between the aquatic biota and that of aquatic animals. They also provide intricate the riparian and floodplain habitats. The most variations to the physical structure of the aquatic visible and best known members of these habitat by increasing the area of substrate on which communities are the fish, platypus and large birds algae and microscopic animals can grow and by such as herons and cormorants. These are generally modifying flow, water chemistry, light availability near the end of the food chain, and their existence and temperature in their immediate vicinity. in the river depends very strongly on the presence of The growth of aquatic plants in a stream is the smaller, less conspicuous animals and plants adversely affected by unstable substrate, high which provide their food. turbidity and highly concentrated flows. The presence of physical diversity such as fallen wood, Food chain backwaters, bars or riffles and pools can increase plant growth by creating areas of slower flow and The basis of the food chain (see Fig. 5, page 8) is an sedimentation. Even in a stable system, the growth input of energy from outside the system. This may be of weed beds is variable as the plants modify their from sunlight, by means of photosynthesis by algae own environment. There may be a constantly and aquatic plants. The contribution from this changing pattern of plant distribution over the bed source depends on the amount of suitable substrate of the stream or any one site as the processes of for algal growth, the suitability of the sediments for sedimentation and erosion succeed each other. the development of aquatic weed beds, the water Weed beds provide food and shelter for small fish velocity, and the turbidity of the water and the and macroinvertebrates by accumulating silt and nutrient content of the water and substrate. The rate organic debris, and by creating protection from the of photosynthesis will depend on the depth to which current and from predators. This is particularly light can penetrate into the water. important in rivers without riparian vegetation
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(------>- Amphibians
Terrestrial Invertebrates Aquatic Invertebrates
Terrestrial Plants /Aquatic Plants
Figure 5. The food chain
which could provide a constant input of small throughout the length of the stream, microhabitats branches and leaves to supply shelter, and food. within the stream are most important, particularly for the small animals. Aquatic animals Invertebrates The distribution and numbers of invertebrates, fish, The microinvertebrates are microscopic animals and aquatic reptiles and mammals can generally be which live either amongst the algae growing on related to the availability of suitable habitat. wood or rocks and gravel in the stream, or free in the Although broad habitat zones can be defined water. The free forms particularly depend on
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sheltered water to avoid being swept downstream too Other vertebrates quickly. They are replenished from floodplain water Tadpoles and frogs generally use still waters on the bodies during floods. These tiny animals are very floodplain, which often depend on flooding from the important food sources for larval fish and larger river for their existence. If the river has quiet back- invertebrates. They feed on algae or on the bacteria water with abundant vegetation, tadpoles can also and fungi which colonise the decaying leaves and survive there, but cannot live in flowing water. As wood in the stream, or float freely in the water. flooding is reduced and the wetlands of the floodplains The macroinvertebrates, which include small disappear, or are grazed bare, the riparian habitat crustaceans, and many aquatic insects, are often the becomes more important for the survival of frogs. most numerous animals in the stream. They are the Some snake and lizard species use the river scrapers, shredders and collectors of the food chain. margin, but generally' need shelter and slow water They also require shelter, to a greater or lesser conditions. Platypus have similar habitat degree, and the greater the physical diversity of the requirements to fish, as their main food supply is the steam bed, the more species can inhabit the stream. macroinvertebrates which feed on accumulations of They provide the major food source for fish and organic matter. They also need access to earth banks, platypus. Many of the insects spend the adult part of protected from stock trampling, for burrows. Water their life as terrestrial forms (e.g. dragonflies, rats feed on yabbies, mussels and frogs and need mayflies) and require riparian vegetation for shelter shelter and suitable banks for burrows. so that they can successfully complete their life Snags which protrude from the water are useful as cycle. The flying insects are valuable food for roosting and preening sites for many of the birds riparian bird species as well as fish. which feed along the river, such as darters and cormorants. Kingfishers need a vantage point from Fish which they dive into the water while fishing. They The most important aspects of fish habitat are most often use overhanging branches along the bank. shelter and food supply: some species also have special requirements for spawning sites, such as clear Riparian habitat gravel for Trout and hollow logs for Blackfish and Murray Cod. Many species also need to be able to Vegetation migrate up and down the stream. About 70% of the Riparian plants provide the major energy input to fish species that occur in coastal drainages need to most Victorian river systems, in the form of leaf and migrate between freshwater and the sea at some stem material falling into the water. Much of the stage of their life cycle. In inland waters, species material falling into the stream moves down the bed such as Golden Perch and Trout also make spawning in the current until it is trapped in an area of quieter migrations. Structures in streams which create water, so riparian vegetation can be a source of barriers to fish movement may prevent migrations energy for a considerable length of river below the necessary for spawning or, in species which have eggs site of growth. or larvae which are swept downstream, Riparian plants provide habitat for the terrestrial recolonisation of the upper reaches may not be part of the life cycle of many aquatic species. Species possible and the species will disappear from the such as mayflies do not live long or feed in their catchments above the barrier. flying stage, but need sheltered sites to rest in until Fish require instream habitat such as snags for they lay eggs. Dragonflies and damselflies rest in tre many purposes other than substrate for food supply or rushes when not hawking for food. Frogs need and shelter from the current. Stream features help protection from predators while feeding on the fish to establish territories, and provide markers to sheltered margins of rivers. enable them to hold their position in the current. They also use the pattern of shadow cast by snags to Temperature provide camouflage and to shelter from sunlight. The full range of wood debris from twigs and The trees and shrubs growing on the banks shade the leaves, to large logs, is important in providing the water and can significantly reduce the water full range of useful habitats. Small fish, both small temperature. Temperature is a very important species and the juveniles of larger species, shelter in controlling factor in the life cycle of aquatic insects the tangles of small branches and twigs, while larger and some fish and species adapted to a particular fish maintain territories around big logs and root temperature regime in a river may not survive in the masses, and the scour holes they create. same river with cleared banks.
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Significance of native species A change from native to introduced herbaceous vegetation will result not only in loss of the native Deciduous willows and poplars have a very different plant species to the area, but an unknown diverse pattern of leaf fall to the evergreen eucalypts. The invertebrate fauna. Lizards, birds, and frogs which use deciduous species have soft leaves, which all fall these invertebrates as food supply can also be during a brief period in the autumn or winter, and affected. Even native vegetation which is not break down in a relatively short time in the water. indigenous to the area will not support all the animal By contrast, eucalypt leaves are shed throughout the species previously present in the vegetation originally year, but predominantly in the summer, and break occurring on that site. down much more slowly, so providing a more continuous supply of food for decomposing and shredding organisms in the river, which are at the The surrounding terrestrial environment base of the food chain. Riparian vegetation can have great importance to Eucalypts also supply fallen branches which the ecology of the surrounding terrestrial develop hollows for fish to inhabit. Willows do not. environment as well as to the river. Many animal These hollows are particularly important as species can use the terrestrial habitats only if they spawning sites for species such as Murray Cod and can also have access to the richness and diversity of Blackfish. the riparian habitat. This is particularly the case now The riparian vegetation, both herbaceous and that most land adjacent to rivers and streams has woody, provides an important habitat for many bird been cleared and sown to alien pasture species. and animal species, which depend to a greater or In many areas the riparian vegetation along the lesser extent on the water for their needs, or stream is the only remnant of semi-natural alternatively, depend on the plants which require vegetation left in an area, and the survival of many the riparian habitat. The extent to which the native species depends on this even if they can use vegetation is indigenous to the locality is as the farmland for some of their requirements. important as the actual density of vegetation The continuous nature of the riparian zone may present. Most animals are, to a large degree, also function as a very important corridor between specialists adapted to use particular species as food, remnants of natural vegetation which are separated or shelter. Introduced plant species do not provide by cleared land. Such corridors will be extremely suitable habitat for the majority of indigenous important in the future in maintaining populations animals. For example, few native insects will eat of native animals in such natural remnants, allowing willows, so a willow will support a very impoverished recolonisation after catastrophes such as fire. Main- fauna compared with a River Redgum. This in turn tenance of a corridor along the river is important in provides less food for birds, spiders or fish in the itself, simply to allow movement of species along the adjacent river. river, and to maintain the supply of leaf and woody Similarly, introduced grasses and herbs will not materials to the stream along its length. provide food for the many animals such as butterflies which are restricted to one or a few native herbaceous species for their food supply. Little is Sedimentation known about the habitat requirements of most The vegetation of the riparian corridor can act as an Australian invertebrate animals or the specific important buffer zone, filtering run-off from cultiva- relationships between plant and animal species. ted, grazed or eroding land, protecting streams from However, most species are specialists and will not excessive sediment which particularly affects the readily adapt to different food supplies. habitat of invertebrates and fish spawning.
10 GUIDELINES
General Environmental Guidelines
Stream morphology 1. Food supply. 2. Cover (shade and protection from predators). Erosion or sedimentation can severely degrade the 3. Shelter (from fast flowing water). stream environment. Works designed to arrest those 4. A general diversity of habitat. processes or reduce their impact are likely to benefit All four are easily influenced (sometimes the environment. Although these processes are positively) by works undertaken to modify or stabilise essentially 'natural', many of Victoria's streams are the river. undergoing rapid change as a result of European settlement which can devastate stream Food supply environmental values in at least the short term, i.e. An adequate food supply requires a regular supply of several generations. plant detritus on which the microinvertebrates can The direct effects of stream modifications on the feed and form the basis to the food chain. This is most morphology of the stream are usually quite obvious, as easily achieved where the river is overhung by mature works are usually undertaken with the specific intent trees and receives a regular supply of falling leaves and of modifying erosion or deposition which would otherwise occur in the normal course of events. branches. Management strategies which have the greatest Less obvious, but well understood by river effect on food supply are those that disrupt these managers, are the potential secondary effects of elements. Removing the base for fungal and algal works such as changes in velocity or sediment load. growth and the detritus trap offered by snags and Works which reduce the sediment load of a stream by stabilizing an eroding bank or bed or by removing trees close to the bank probably have the most serious effect. Even lopping overhanging trees trapping sediment at some point, may increase the potential for erosion downstream. This is because will reduce food supply. The replacement of local native vegetation by the more sediment that is carried by a stream, the exotic species is also significant. Leaves and branches less is its power to erode. from exotic species are much less suited to native All measures which increase flow velocity or animals, and the use of deciduous species will lead to channel capacity such as de-snagging, channelisation, an absence of supply of detritus during the winter meander-cutting and levee banking have the months. They also tend to decompose much more potential to cause channel deepening upstream. rapidly than native species and fallen trunks and branches are less likely to have hollows that are General guidelines useful for cover and shelter. Good river management requires the consideration of The use of native plants from outside the region the effects of works on morphology and an evaluation can effect the presence and or abundance of of the environmental costs and benefits of any strategy associated animal species in a given stretch of river. before it is undertaken. In some cases, it may be better Revegetation with local native species will to allow morphological change to occur and direct restock the food supply at a site which might have management towards achieving rapid rehabilitation been damaged by clearing, grazing or engineering after a new equilibrium has been reached. works. The use of local timber in management works It is important to consider the morphological such as brushing and log weirs will also contribute to effects both direct and secondary. The question must food supply by providing both suitable habitat for always be asked: 'what would be the result, over invertebrates and a base for fungal and algal growth. time, if the proposed works did not take place'. Cover and shade Protecting the stream environment Cover is provided by overhanging (undercut) banks, snags, boulders, rock crevices and instream vegetation, The vitality of the stream environment depends while shade is provided by riparian and instream primarily on four factors: vegetation.
11 Rock beaching, bank battering, snag removal separate fish ladders are required. This is of particular and sand and gravel removal all reduce cover for fish importance in coastal areas where many species rely and lopping or removal of trees removes shade. on upstream migration to complete the breeding cycle. Some management works can provide or maintain cover. Brushing and the anchoring of snags into the Guidelines bank provide cover along a stabilised bank. Alignment training and installation of groynes can 1. Snags should be left within the stream as they provide cover and allow the establishment of some provide shelter for aquatic animals. instream vegetation. Fencing and planting of bare 2. If snags must be moved, where possible, they banks will provide shade. should be drawn to the bank of the stream and anchored there, where they cam still provide cover shelter and an energy source as the Shelter material decays. Works directed at increasing channel capacity often 3. Maintain and replace native vegetation along increase water velocity and reduce shelter. This is river banks wherever possible. If overhanging likely to occur with snag removal and meander cut- branches are lopped these should be retained in offs. Sand and gravel removal can also affect shelter the river. if the bed is left uniform. Rest areas and increased 4. Revegetate with species present locally, ideally opportunities for shelter to develop can occur with using seedlings grown from seed collected locally. strategies designed to curtail bed erosion such as Plant trees close to bank to maximise instream chutes, weirs and drop structures. These can create inputs. pools of still water immediately downstream or 5. Willows and other exotic species should be upstream of the works. avoided. 6. Avoid disturbing the stream bed and banks. Where disturbance is inevitable the riverbed Diversity of habitat should be left uneven with a suitable supply of Healthy rivers have contrasts in light and shade, cover. Logs and branches may be returned to the exposure and cover, fast flowing and still shallow and river bed to supply shelter, and cover, and to deep water. This creates a variety of habitats for provide spawning sites. different species of micro and macroinvertebrates, a 7. Instream structures should provide crevices and variety of other food sources for fish and the condi- overhangs. tions for basking, feeding, hiding and spawning. 8. Timber should generally be used in preference to Strategies which have the greatest impact on concrete, steel or rock. Brushing for example, diversity of the instream environment are snag provides better instream habitat than beaching removal, sand and gravel extraction, vegetation with rock. removal, lopping of trees or their replacement by 9. Always design to allow for fish passage. Give exotic species, and meander cut-offs or other forms special attention to this in coastal streams where of channelisation. migration is a vital part of the life cycle for many Some management strategies, such as chutes, species. weirs and drop structures, create areas of fast and slow moving water (like pools and riffles). Alignment Protecting the streamside environment training and groynes create scour holes, and The greatest risk to the streamside environment introduce obstructions that give rise to a wide range from river management works arises from four of bed conditions. effects: 1. Discontinuities introduced in the riparian Fish passage corridor or in the interface between instream, Works undertaken to control erosion such as chutes marginal and riparian environments. and weirs can present a complete barrier to fish 2. Disturbance to vegetation cover at the time the passage. These structures can be designed to works are constructed, creating the opportunity incorporate rest areas for fish passage. A series of low for weeds to be introduced. rock or timber weirs for example will generally be 3. The planting of willows or poplars on the banks. preferable to a single high wall. 4. The exposure of bare soil surfaces to wind and Where the required change in elevation is too water erosion. great to incorporate fish passage in the design, The fencing of the river bank and planting of
12 GUIDELINES
Many birds nesting and feeding
Many insects on leaves and bark
Very few birds nesting or feeding
Few insects on leaves and bark
• Hollows in branches •`1 , Insects and leaves fall into Leaves all fall in autumn water all year
Light shade Shelter in undergrowth for birds, reptiles and Man small animals frogs Fooc for fis and plahjpus Few small animals
Figure 6. Native and exotic riparian vegetation native vegetation which is now often done in degrade riparian habitat values. Planting of exotic association with river works helps to protect the trees to maintain bank and verge stability should be streamside environment. kept to a minimum. Discontinuities Breaches of the natural vegetation along the Guidelines riverbank can seriously disturb the movement of and 1. Avoid discontinuities in river bank vegetation. exchange between the insects and animals that Where this does occur with rock beaching or inhabit that environment bank battering for example, revegetate as quickly Bank battering and rock beaching will severely as possible. affect bank vegetation, and the construction of rock 2. Avoid using filter cloths for bank protection, chutes or weirs can also seriously damage bank vege- etc., in areas where the regeneration of tation, possibly permanently, if filter cloth is used. vegetation is desired. The cutting of floodways is also likely to cause a 3. Minimise the amount of earthwork required. permanent break in continuity, as trees and shrubs Avoid exposing bare earth for any length of time are usually removed or slashed in order to maintain and revegetate as quickly as possible. the hydraulic capacity of the floodway. 4. Avoid the use of exotic plants wherever possible. Where works such as groynes may depend upon Disturbance the quick growth offered by willows, plant The risk of weed invasion as a result of bare willows in a regular pattern and return to the site disturbed soil is present almost everywhere and any to poison the willows once native vegetation has time work is undertaken, but, as might be expected, established. the more extensive the earthworks, the greater the 5. Ensure that areas on the river bank which are risk. Bank battering represents the greatest risk, but fenced off for revegetation are of sufficient width earthworks associated with construction of chutes or to create a suitably diverse and stable weirs, with rock beaching or bank brushing, environment. A width of 30 metres would be construction of levees or floodways, also give rise to required on a large stream or river. considerable risk. 6. Use indigenous species, ideally from seed grown locally for revegetation. (In some areas natural Exotic vegetation regeneration may occur quite readily after The introduction of exotic vegetation can seriously fencing.)
13 GUIDELINES
7. Special attention should be given to re- River management works may affect scenic establishing any disturbed marginal vegetation. values, access, fish movement and habitat values. Replanting of seeds arid sedges at the margin Generally speaking, if habitat and visual landscape should be an integral part of a revegetation values are maintained, recreational values are also program. Local grasses and small shrubs should likely to be maintained. also be included. 8. Provide strong permanent fences to protect regeneration areas from stock. Access to the river Guidelines for both stock and people must be controlled. 1. Consider every part of the river environment as a potential recreational reserve. Recreation 2. Where boating is, or could become an important activity, take account of requirements for access Rights of access exist over the reserves which border to, and passage along the river. many Victorian rivers for walking or fishing. 3. Maintain and enhance ecological and aesthetic The popularity of a given reach of river depends values for their direct contribution to the quality on the ease of access and proximity to population of recreational experience. centres. Every part of the river reserve, however, has a potential recreation value.
14 GUIDELINES & CASE STUDIES
GUIDELINES AND CASE STUDIES
INTRODUCTION 15 ROCK BEACHING 16 BRUSHING 19
GROYNES 21 ALIGNMENT TRAINING 24 SNAG MANAGEMENT 27 REVEGETATION (NATIVE SPECIES) 31 REVEGETATION (EXOTIC SPECIES) 33 SAND AND GRAVEL EXTRACTION 35 ROCK CHUTES 37 DROP STRUCTURES 41 CHANNEL MODIFICATION 44 BANK BATTERING 47 MEANDER CUTOFFS AND FLOODWAYS 49 LOPPING 51 LEVEE BANKS 52 URBAN CHANNELISATION - HARD LINING 54 URBAN CHANNELISATION - FLOODWAY 57 RETARDING BASIN 58 GUIDELINES & CASE STUDIES
Guidelines and Case Studies
Introduction The most common river management strategies or works which are widely practised in Victoria are described in the following sections. The environ- mental effects of these 16 works are examined and recommendations are made on the factors to be considered in carryout out the work. Specific measures that should be incorporated to minimise environmental impact or enhance the result are described. Case studies are presented to illustrate each type of management works.
15 GUIDELINES & CASE STUDIES
ROCK BEACHING Strategy being placed adjacent to the soil and the largest at the water face. Rock is placed on stream banks to protect against If small stone is not available, filter cloth or erosion by providing: appropriately sized filter layers are sometimes provided • a layer of physical protection between bank between the rock and the bank material. material and the flowing water; and It is not always necessary to protect the whole bank; • support to the bank against mass failure of bank rock may be used to stabilise only the toe of the bank. material. Environmental effects Alternatives When eroding banks are stabilised by rock beaching, Brushing can be used as an alternative to rock scouring may occur downstream as a result of beaching, if material is available. It is more reduced sediment loads. Crowding of meanders and attractive but less secure than rock beaching. development of unstable alignments may also occur. Groynes may also be used to protect banks. Aquatic habitat Description Rock beaching can create a uniform bank lacking Rock from a quarry or from surrounding land or any habitat diversity. If the bank is battered and similar material such as broken concrete is placed on straightened, shelter associated with undercut banks the face of the bank. and pools and accumulated debris will be lost and The bank may be battered to a design slope. there may be local sedimentation. Rock used for beaching varies in size, colour, and To provide a diverse habitat, banks should be as hardness. Basalts and granites are common. Typical irregular as possible in shape. A wide range of rock rock is graded in size up to 600 mm, the smallest stone sizes should be used to provide a variety of crevice
16 GUIDELINES & CASE STUDIES
sizes. Ceramic pipes can also be included. Snags should be kept to a minimum. should be incorporated into the rock where possible Endeavour to maintain debris, pools and stream and frequent breaks in the rockwork where the habitat diversity. stream can contact the original earth bank will Use coarse, uneven sized rock to provide large greatly reduce the adverse impact of the works. The interstices and greater habitat opportunity. rock placed at the base of the bank should also be Fence and plant with indigenous species. uneven, to create some diversity in bed form, and Attempt to establish native vegetation close to the some sheltered water. water's edge. Avoid using filter cloth wherever possible to Riparian habitat allow roots of indigenous plants to establish easily. Battering of the bank causes destruction of any Do not plant willows and poplars in the rock. Rock existing riparian habitat, loss of the natural shape of should be enough to protect the bank on its own. the bank, and the soil disturbance will enable the invasion of introduced weeds. Earth movement on banks should be kept to a minimum and diversity Rock beaching: Case study 1 and unevenness of bank form should be maintained as much as possible. Existing native vegetation and Mitchell River at Henderson's Property, Wyung litter should be preserved as much as possible. If the Mitchell River Basin — Number 224 bank must be battered, it should be as irregular as Works by Mitchell River Improvement Trust possible and the use of berms should be considered to assist in revegetation. The bank should be fenced and replanted as quickly as possible to reduce weed invasion. The use of a rock mixture with a range of stone sizes will avoid the need to use a filter cloth. A component of soil in the mixture helps binding but also assists vegetation to establish. Planting should include reeds and rushes in soil pockets in the rock as well as indigenous shrubs and trees. The success of plant growth in the rock will depend on the depth of the rock, whether filter cloth has been used and how quickly silt accumulates in the crevices. Filter cloth will reduce root development and make plants Site summary susceptible to summer drought. It may be necessary to insert soil pockets for plant establishment. This is a flat, meandering section of the river just Rock beaching will create a break in the riparian upstream of tidal and salt water influence. Severe corridor, and ground burrowing species such as willow congestion was relieved by willow removal in platypus, water rat and bird species will lose nesting 1950s and 1960s. sites. The significance of this will depend on the The channel is 45 m wide and 5 m deep. scale of the works. On a large scale, rock beaching Adjacent land use is pastoral with urban significantly reduces diversity of bank habitat on the development (Baimsdale) on high terraces. stream. On a small scale, the rock may increase High steep eroding bank was unevenly scalloped, marginal deposition and trap organic matter, which as a result of willow removal. Bank material is non- may have a positive effect in an otherwise bare cohesive free-running sand. stream, particularly if rock size is uneven, and the water margin is irregular. Works summary Recreation Rock protection was provided to the lower half of Rock beaching will inhibit access to water for the bank. boating, swimming or angling, particularly if Before rock was placed the bank was battered to successfully colonised by dense vegetation. remove unevenness and to provide a bench half way down the bank. Rock was placed below the berm. Grass and shrubs were planted on the upper bank Guidelines and berm. Bank straightening or battering and channel Rock is well graded granite up to 500 mm in size. remodelling should be avoided and earthworks No filter was provided.
17 GUIDELINES & CASE STUDIES
Effects Rock beaching: Case Study 2 Continued erosion at this site threatened a bend House Creek at Wodonga South immediately cutoff. Resultant shortening would have led to downstream of Pearce Street Bridge upstream deepening and possible downstream Kiewa River Basin — Number 402 instabilities. Consequences from an individual case Works by Rural City of Wodonga such as this were not considered likely to be severe, but it was considered the cumulative effects of such Site summary incidences would become major if not treated. The works have reduced downstream siltation. Small creek in parkland setting within urban area. The earthworks straightened and 'smoothed' Subject to severe and sudden floods from a seriously alignment and battered the original bank. This has gullied rural and developed urban catchment. reduced some natural diversity in habitat types. All debris appears to have been removed. The berm Works summary constructed lends itself to planting of trees which Broken concrete was placed on the creek bank as will overhang the water. Large rocks provide habitat protection against erosion. for small fish and invertebrates in interstices. Restricting facing to below the berm reduces the Effects visual impact of an alien material introduced to the lower flood plain. Although the broken concrete is probably adequate The planting and regeneration associated with to stabilise the eroding bank, this treatment these works is likely to improve the riparian habitat. destroyed the original riparian habitat. No new The planting is a mixture of indigenous, native non- vegetation can establish. indigenous and introduced species, and some As the beaching is on a high bank, generally regeneration of indigenous species is also occurring. above water level, its effect on aquatic habitat is As it matures, it will provide valuable habitat. minimal. As siltation increases amongst the rocks, some The broken concrete is an eyesore especially in marginal vegetation will develop. This will be an urban parkland setting. limited but better than that occurring under willows. Comment Comments Given the setting of the works in public parkland, The technique chosen for bank protection seems on a rather bare stream lacking in habitat diversity, appropriate for the site. the opportunity should have been taken to provide Less earthworks would reduce impact both during some useful habitat, as well as landscape construction and subsequently but with the penalty improvement. This could have been achieved with of less security and lower economy of rock usage. careful rockwork and planting. The use of rock for stabilising only the lower bank and of treating the upper bank with vegetation is an environmentally appropriate technique. The works could have provided more habitat diversity. The bank should have been made less even, with variation at the water line and toe of the bank giving diversity of water velocity and depth. The use of cottonwoods in the planting should not have been necessary for security of the works and all indigenous plantings would have provided better riparian habitat. Some soil pockets would have enabled more rapid development of vegetation on the lower bank and/or at the water margin.
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GUIDELINES & CASE STUDIES
BRUSHING Strategy loads. Crowding of meanders and development of unstable alignments may occur. Logs, trees or other brush are anchored against the stream bank. Brushing forms a temporary barrier that Aquatic habitat traps sediment and material falling from the bank until vegetation can establish. Brushing, if it extends well down into the water, 4 provides shelter for young fish, woody material as a Alternatives substrate for many invertebrate animals, still water to trap sediment and organic matter, spawning sites for Rock beaching or groynes may be considered, • fish and resting places for birds and aquatic animals. particularly if brushing material is unavailable. Rock If the bank is not battered too much before brushing, beaching would generally be more secure than access to the earth bank may still be possible for brushing, but has a greater environmental impact at burrowing species like platypus and crayfish. the site. Riparian habitat Description If the bank is battered prior to brushing, the existing Brushing can consist of any wood material, ranging vegetation will be destroyed. Even if battering is not from large redgum logs and trees through to tea tree carried out, the riparian vegetation will probably be brush mattresses. damaged during the construction of the brushing. Bank preparation can range from nil through to The associated soil disturbance will allow the extensive battering. invasion of weeds, which may need to be controlled. Brush is usually anchored by piles or by Considerable damage may be done to the site from `deadmen' in the bank. Light brushing is held down which the brushing is obtained. Care should be by weights and cables. taken not to deplete remnant stands of floodplain Freshly cut trees are more effective than dry logs trees. Both the works site and the site from which because of weight and abundance of leaves and fine the brushing is cut should be fenced to allow branches. regeneration or replanted. Willows should not be used for planting in brushed sites, as they will Environmental effects prevent the growth of any indigenous species, and will provide a greatly inferior riparian habitat. When eroding banks are stabilised, scouring may Willows and poplars should not be used for brushing occur downstream as a result of reduced sediment material unless dead prior to use (e.g. by poisoning).
711.
4141,, 443?
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GUIDELINES & CASE STUDIES
The site should be fenced and planted with A deep scour hole exists adjacent to the river indigenous trees and shrubs, as soon as possible, to bank. Up to 10 m of lateral bank movement during reduce weed growth. 1986 winter threatened property, established bank-line The brushing will provide useful roosting and downstream, and breakthrough into old river course. resting sites for birds and reptiles, increase habitat diversity along the bank and provide sheltered areas Works summary for growth of marginal vegetation. Emergency brushing was placed during 1986 winter Landscape and supplemented by additional brushing during 1986-87 summer. The use of materials indigenous to the area makes Brush is mainly green Redgum trees cut from brushing a more visually appropriate technique than various locations in the vicinity. rock beaching. Some piles were driven to anchor brush and willow stakes were planted throughout the brush. Recreation Access to the river for recreation may be reduced Effects but, as in the case of rock beaching, the technique is The brushing extending well below water level not likely to be used at favoured access points. provides a considerable amount of instream cover. This is particularly important as the river in this area Guidelines is likely to contain Blackfish and Murray Cod — species which are known to rely heavily on wood Use a minimum of earthworks and battering in order debris for cover and spawning sites. to retain as much of the original habitat and The locality is reasonably well timbered so trees vegetation as possible. were available for use as brushing. Nevertheless, Soil disturbance, should be kept to a minimum brushing of this type severely reduces remnant to reduce weed invasion and all disturbed areas floodplain Redgum stands. should be fenced and replanted if necessary. Some regeneration may occur on bank as seed will Brushing should extend well into the stream at be shed from lopped branches used in brushing. As low water levels to provide habitat and should be left the leaves and smaller branches breakdown, and silt is uneven. trapped in the brushing, vegetation will regenerate Material for brushing should, wherever possible between the logs, increasing the value of the habitat. be obtained At the time of inspection, soon after completion of • from floodplain or forest areas specially managed the works, the site had not been fenced. for the purpose; • by thinning areas of dense vegetation; Comments • by taking one or two trees from each clump of trees without destroying the whole clump; or The site should be fenced and some planting of • by supplementing brushing material with dry indigenous species carried out. Plantings should logs, exotic species, or other locally abundant include ground cover species which will help material. consolidate the bank and provide habitat diversity. Do not use river bank vegetation for brushing material.
Brushing: Case study Ovens River at Bin's Property, Whorouly Ovens River Basin — Number 403
Site summary This is a relatively steep and straight section of the Ovens River within a wide floodplain. The channel is 50 m wide, typically 5 m deep and there is a history of bank erosion in the vicinity.
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GUIDELINES & CASE STUDIES
GROYNES Strategy Aquatic habitat Groynes are permeable or impermeable fences or The construction of groynes can disturb the bed of barriers, projecting from the stream bank into the the stream and cause temporary damage, both at the stream to provide protection to vulnerable stream works site and downstream. The shelter provided by banks by obstructing the current adjacent to the bank. the groyne will generally compensate for this and improve the stream habitat. The scour holes which sometimes develop, particularly behind impermeable Description groynes, create pools sheltered from fast flows. Permeable groynes are most often built using steel or Groynes can also trap debris, provide instream timber piles faced with open horizontal or vertical markers and greatly increase stream bed diversity. timbers. Generally less than 50% of the flow area is The stabilisation of eroded banks and the obstructed by the structure. trapping of sediment will reduce sedimentation on Impermeable groynes can be constructed from the stream bed further downstream, and provides a randomly placed or stacked concrete blocks, riprap, more diverse stream margin. gabions, reinforced concrete walls, etc. The scale of the structure depends upon site Riparian habitat conditions, but a distinguishing characteristic of Permeable groynes create areas of slack water and groynes compared to retards is that the height of a deposition and greatly increase the diversity of the groyne closely approaches bank height at least at its stream margins. As deposition progresses, marginal landward end. vegetation will develop, increasing the interaction Groynes on Victorian streams would typically be between the water and land habitats. There is no 2-5 m high and 5-15 m long. break in the riparian corridor, and the natural bank Heavy planting, usually of exotic species is morphology is not significantly altered. required to provide long-term stability of groyne Disturbance of the bank during construction structures. may encourage weed invasion and should be kept to a minimum. The site should be fenced, and planted Environmental effects with indigenous species to stabilise the bank and the new deposition areas. Reeds, bulrushes and rushes When eroding banks are stabilised, scouring may should be planted to speed up the deposition process. occur downstream as a result of reduced sediment If willows are used, they should be poisoned or loads. Crowding of meanders and development of lopped to allow growth of native species after the unstable alignments may also occur. bank has stabilised.
21 _ GUIDELINES & CASE STUDIES
Groynes provide useful resting and roosting sites Guidelines for birds and reptiles. Impermeable groynes interrupt the riparian Use of natural materials (timber) to be preferred over corridor to some extent for small species. They are concrete or steel. Wherever possible, allow debris to not extensive enough to significantly reduce the collect against groynes without clearing. water-land interface, and may provide shelter for Minimise work on banks and within the stream species such as lizards. This is particularly valuable bed. Don't move stream bed material just to make on bare banks with no mature trees or well- the job look tidy or to make an even width channel. developed litter layer. Always fence and revegetate. Restrict use of Impermeable groynes create scour areas and exotics to essential areas only and group exotics to slack water, and increase the diversity of the stream allow later eradication. Extend fencing upstream and margin. The deposition areas, in association with downstream beyond actual works sites. fencing, increase marginal vegetation. Impermeable groynes interrupt the riparian corridor for small Concrete block groynes: Case study species, but are not extensive enough to significantly Avon River Downstream of Weirs Crossing reduce the water-land interface, and may provide Thompson River Basin — Number 225 shelter for some species such as lizards, replacing Constructed by Avon River Improvement Trust snags which are generally scarce in river reaches where groynes are needed. Site summary Landscape See case study for permeable timber groynes.
Until vegetation grows, groynes can appear starkly Works summary unnatural, particularly impermeable structures such as concrete blocks. Where willows are used, groyne Randomly stacked concrete block groynes built out structures are disguised by vegetation within a few from river bank. Vegetation (mainly willows) years and the typically steep bank is then replaced by established in embayments. dense vegetative cover. This however introduces an Effects unnatural element and willows should eventually be replaced by native species. The scalloped stream Groynes have effectively stabilised the bank. bank line remains as an unnatural feature. Scour holes around concrete blocks create fish
22 GUIDELINES NOW habitat diversity. Vegetation provides some shade, bank end. Groynes built from large timber piles with although lack of native vegetation reduces food horizontal rails supporting vertical facings. values. The diversity of habitat along this previously Effects bare and eroding bank has been greatly increased. The mix of willows, and naturally regenerating Works have arrested erosion of high bank. wattles, is not as useful as all native vegetation Vegetation (chiefly exotics) is establishing at the toe would be but the willows are probably necessary for of the bank and contributing to stability. stabilizing the banks in the early stages at least. The Willows have been planted thickly behind concrete blocks provide some shelter and basking groynes and are the dominant vegetation. Some sites for reptiles, and resting and fishing points for regeneration of bullrushes, nettles and other native birds. The dense willows may reduce access to the species is occurring. The development of some ripa- bank for burrowing species. rian vegetation on this previously bare and eroding Planting on top of the bank, in a narrow fenced bank is of great value, even though the willows domi- plantation, has not been very successful. nate. Sheltered areas behind groynes add diversity to Until masked by vegetation, the groynes are a stream margins which is particularly important on this starkly unnatural addition to the landscape. The reach of the Avon which is otherwise dominated by willows are also incongruous in this setting. bare banks and generally raw gravel beds. Planting in a narrow fenced plantation has been Comments generally unsuccessful in the exposed site on top of the The density of willows could be reduced in favour of bank. native species as the bank stabilises, and reeds should be introduced. A wide plantation on top of Comments the bank should be planted of carefully selected A wide plantation on top of the bank would allow indigenous species to increase the width of the for gradual natural battering. Careful selection of riparian corridor. This would have great value for the species is necessary for the exposed conditions. surrounding cleared rural land, as well as for the river environment. Successful establishment of vegetation on top of the bank would be of advantage for the generally treeless rural environment as well as for riparian habitat. Permeable timber groynes: Case study Establishment of wattles and other riparian Avon River Upstream of Weirs Crossing shrub species would be of advantage behind the Thompson River Basin — Number 225 groynes, to increase the habitat diversity, although Constructed by Avon River Improvement Trust on such a difficult site willows may be the most effective species for stabilisation. Site summary Major change in channel form has occurred throughout this reach of the Avon River since European settlement. The channel is now up to 200 m wide and incised up to 10 m below the level of the floodplain. Severe erosion occurring on 8 m high steep bank on outside of large meander bend.
Works summary Large stayed needle groyne structures built in 1982. Groynes are 25 m long and over 3 m high at the
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ALIGNMENT TRAINING
Strategy in response to their more favourable and predictable behaviour. `Training fences' or 'retards' are built on the stream bed Fence design must allow for bed scour along to train the stream channel into a chosen alignment. training fences and at the end of retards. Alignment training is used to move the stream channel away from vulnerable or eroding banks and to remedy unstable alignments. Environmental effects The term 'training fence' implies a low fence When eroding banks are stabilised scouring may type structure running more or less parallel with the occur downstream as a result of reduced sediment flow (usually enclosing an erosion pocket) the term loads. Crowding of meanders and development of 'retard' implies a low fence type structure running unstable alignments may also occur. out from the bank across the flow. Alignment training works will frequently cause a Retards and training fences are characterised by localised shortening of the stream course. Alignment their low height above the bed relative to bank height. design should recognise the curvature of naturally Materials used vary widely depending on occurring stable bends in the vicinity and avoid availability and other factors. Steel or wooden piles excessive straightening. In an extreme example, are the most common anchoring mechanism, com- course shortening associated with alignment training mon materials for facing the fence include chain could lead to deepening of the bed at the works site wire mesh, logs and brush, or horizontal timbers and upstream and bed control measures will fixed to piles. sometimes be a necessary component of alignment Gravel or cobbles may be bulldozed from else- training works. where in the water course and piked behind retards. Stockproof fencing and vegetation are important Aquatic habitat components of all alignment training works. In the 1970s longitudinal training fences were favoured and When eroding streams lose channel definition, the several major works were carried out in Victoria resultant wide, shallow, uniform reaches provide using chain wire mesh fences, around the circumfer- little aquatic habitat diversity. There will be little ence of the design alignment, in 15 m square embay- cover for fish or other stream fauna, and often fish ments. More recently the use of retards has increased numbers are very low.
24 GUIDELINES & CASE STUDIES
If, in association with the construction of align- Alignment training: Case study 1 ment training works, there is some relocation of bed material to help redefine the channel, this uniformity King River at Cheshunt will be exacerbated in the short term. However, with Ovens River Basin — Number 403 containment of the stream into a stable channel, some Constructed by Ovens and King River Trust habitat diversity can gradually redevelop. If the structures extend into the water, they may provide physical instream cover, and also encourage the development of scour holes, and a more varied bed form. The collection of debris on fences, and accumulation of sediment and associated vegetation on the stream margins will also gradually provide increased habitat diversity.
Riparian habitat The works may damage existing riparian vegetation during construction. Fencing will encourage regener- ation although the disturbance may allow weeds to invade. The deposition around the training fences will usually be initially of coarse material, with a Site summary slower build up of silt. There will therefore be a slow Steep, fast flowing river with gravel to cobble bed. progression to a mature vegetation, as the silt and Irregular meanders with channel width of organic content of the new banks increase. The approximately 40 m and depth of 2 m. Irregular riparian habitat immediately adjacent to the stream floodplain generally several hundred metres wide. will therefore be impoverished for some time, lacking Rapid erosion during 1986 winter led to unstable both species diversity and physical diversity (litter alignment. Alignment training works were and logs). The original banks will be remote from the completed during the summer of 1987. stream, which may have adverse effects on burrowing species, and a reduction in organic input to the Works summary stream until the new bank margin is vegetated. If willows are used in association with the Pile and brush retards approximately 1 m high were alignment fences the progression to a mature native constructed on the stream bed. Old railway lines vegetation will be prevented. were used as piles with brush tied to cobbles. Brush Where brush and logs are used on the training was obtained locally by felling Redgum trees and fences, material must be cut locally. Damage to willows. riparian vegetation is inevitable. Gravel and cobbles were bulldozed from adjacent point bar deposits and placed between retards. Willow stakes were planted along retards and Guidelines along the old bankline; the site was fenced from stock. Banks were planted with indigenous native species. Minimise earthworks in the bed of the stream. Do not leave the channel bed regular and flat bottomed Effects — introduce irregularities in depth and shape. Leave untouched areas of stream between It is too soon to judge the effectiveness of these works, adjacent works sites. but experience with similar sites suggests that they Use timber and logs in preference to steel or wire should successfully stabilise the reach, provided scour mesh, etc. at the ends of the retards does not undermine the Minimise use of willows in training works. structures. Introduce native reeds and rushes along water's edge. Successful alignment training works in this If willows are needed, plant in such a way as to vicinity will prevent premature loss of the natural allow future removal. For instance, restrict plantings levee and delay diversion of the King River into the to lines aldng training fences. adjacent Stoney Creek. Take care with alignment design to minimise Rapid improvement in habitat values is expected straightening and monitor any deepening tendencies during the first few seasons after construction. upstream. The works at this site had just been completed at
25 GUIDELINES & CASE STUDIES
the time of inspection. The site had been fenced and Site summary willows laid between alignment logs. Further Major change in channel form has occurred planting of native shrubs is planned. when throughout this reach of the Avon River since deposition begins, regenerating will occur along the European settlement. Channel now up to 200 m margin, but growth of the willows will reduce the wide and incised up to 10 m below the level of the development of good riparian habitat. Some floodplain. regeneration of eucalypts and wattles can be Large point bars associated with new meander expected before the willows get too thick, and as pattern have become susceptible to formation of deposition builds up soil on the raw gravel. point bar cutoff chutes. These destabilise the stream The log fences will add diversity to the stream alignment and cause unpredictable bank erosion margin, providing shelter and roosting sites for riparian downstream. animals. They will, to some extent, act as snags. • Despite the sympathetic use of natural materials Works summary the overall effect is rather unsightly. If native vegetation eventually predominates on both the new Low retards have been constructed from wire mesh and old banks, the effect will be a substantial on cables supported by timber posts to control and improvement. reverse development of point bar cutoff chutes. Earthworks conducted in conjunction with this work decreased stream bed diversity. The loss of part Effects of a pool area, the 'smoothing' of the river bed and the removal of larger substrate particles have all The retards have been very effective in causing contributed to a reduction in instream habitat. Such deposition on the point bar and in the cutoff chutes. habitats are particularly important for both Trout In the long term, build up of point bars will and Blackfish found in this area. Instream habitat confine the stream, and channel capacity problems will be provided by one of the retards which extends may result. into the water. Stabilising of point bars will provide a defined channel and this will be beneficial to instream Comments habitat diversity. Diversity of instream habitat has already been improved by the development of Willow growth should be restricted by lopping, or poisoning, as the native species become established vegetation. and the new bank is stabilised. The mesh retards are stabilising wide shifting The major impact at this site results from beds of gravel which were previously too unstable to bulldozing of bed material. Less earthworks or a more maintain any vegetation. The new deposits of gravel uneven finish would have prevented loss of habitat are very raw and a long period of silt and organic diversity. matter deposition will be necessary before mature vegetation will develop. The pioneer wattles and Alignment training: Case study 2 herbs will gradually build up organic debris and nutrient levels so that the succession to stable Avon River Downstream of Weirs Crossing floodplain vegetation can proceed. The river in a Thompson River Basin — Number 225 more stable course will enable marginal vegetation to develop and gradually increase the diversity of the habitat. Growth of shrubs along this margin will contribute organic debris to the stream and provide shelter and shade on the margins.
Comments It is most important to exclude grazing animals from the river bed. The pioneer wattles could be lopped as they mature so they will not be swept out by floods, and will continue to build up the soil. To date, willows have not been used. Native species establish readily and will provide a much better habitat.
26 GUIDELINES & CASE STUDIES 114 SNAG MANAGEMENT
Strategy and streams is of major importance to fish and other aquatic organisms. Fallen trees or blockages of debris are removed from or moved within the stream channel. Shelter and orientation Reasons for snag management include: • to prevent acceleration of flow around the ends Snags provide shelter areas and spawning sites for of the blockage leading to bank erosion; fish. Fish need shelter from fast water, predators, • to rejuvenate a reach of stream by triggering bed competitors and sunlight. Most fish species prefer deepening; or not to bt in direct water currents, but position • to increase the hydraulic capacity of a reach. themselves in sheltered areas behind obstacles such as logs. Such features are also used as 'stream markers' to provide orientation and territorial areas Description for many species. Logs are used by larger fish whilst Snag management can range from isolated instances associated wood debris (smaller branches, twigs, leaf of pulling snags against banks to intensive snag litter, etc.) may be used by smaller species and removal over long reaches of river. juvenile fish. In all cases heavy equipment is used to move the snag, usually by winching. The snag may be cut into Spawning pieces before it is moved, or moved in one piece. Species such as Murray Cod and River Blackfish are Where the snag is removed from the channel known to use hollow logs as spawning sites. Many completely, it is usually hauled clear and burnt. In other species which have adhesive eggs are also likely other cases, the snag may be pulled against the to use log surfaces for spawning. Juvenile fish may use channel bank and secured, or it may be re-aligned the aggregations of wood debris and leaf litter built up within the channel. Sometimes, protruding limbs are around snags as shelter and feeding areas. removed and the remainder of the fallen tree left in the channel. Importance to the food chain The build up of wood debris, leaf litter and other Environmental effects organic matter around snags is important in the The management of snags is one of the most crucial cycling of nutrients within the stream. Trapping of issues for river managers as their presence in rivers such matter allows time for its decomposition and
viArotorrlituarillu - .7. etiallkI P
27 GUIDELINES & CASE STUDIES 114 the establishment of invertebrate communities to Bird roosting and preening complete this task. It is difficult for such commu- Exposed snags provide roosting and preening sites for nities to establish if the organic matter is continually birds and are very important for species such as moving. This decomposition process forms the basis cormorants, darters, herons and kingfishers. Water for the stream food chain. The invertebrates rats, lizards, frogs and tortoises will also use them for involved provide a food source for fish and other resting and feeding. If a fallen tree spans the stream, organisms. The smaller, planktonic and food inverte- it can provide a passage across the stream for small, brates are a particularly important food source for terrestrial animals. newly hatched fish which must have a constant food supply. The wood surfaces of snags themselves Boating and swimming provide valuable attachment sites for many other invertebrate species. This is particularly important in Snags may obstruct kayaking, canoeing and power lower stream reaches where sand or silt substrates boating. They have the severest effect on fast boat- provide poor habitat for most invertebrates. Snags ing and water-skiing, particularly where the effects of and accumulated debris provide large surface areas changes in water level are not easily perceived. for invertebrate colonization and thus are significant On the other hand they can provide interest and in providing a base for the food chain. variety for the canoeist, an integral part of the natural environment which the canoeist seeks to Diversity explore. The extent of modification required to provide reasonably clear passage for canoeists is Snags ensure an increased diversity of water types. likely to be very modest and can be achieved with Their presence may provide pools, scour holes, minimal impact on the stream environment. In areas gutters and general undulations in the substrate. which are popular for fast boating however, removal Such diversity offers many shelter areas for stream of all but the most clearly obvious obstructions may occupants. Substrate diversity may also occur with be required. the production of sediment deposits around snags Submerged snags may pose a danger for thought- which may be used by burrowing invertebrates and less swimmers, and discourage others from taking to fish species such as larval lampreys. the water. They can also provide features of interest, diving platforms, refuges and backwaters for swimmers. Abundance The abundance of fish has been found to correlate Guidelines closely to the extent of logs and wood debris in a In recognition of the high value of snags to the stream. The addition of wooded shelter areas in aquatic environment: streams increases fish numbers in several species • opt for management rather than removal of (including Trout); declines in both fish numbers and snags; pull the butt of a fallen tree onto the species diversity have been recorded in streams bank, but leave the rest of the tree across the following snag removal. stream, lop protruding branches to limit debris Riparian habitat build—up or to allow boat access, but leave the rest of the tree, The removal of snags from the stream causes physical damage to the riparian vegetation adjacent - move the snag within the channel to to the site. The accompanying soil disturbance may minimise adverse effects without completely provide invasion opportunities for weed species. removing the tree, If the snags are moved onto the bank, rather • do not cut down trees on banks just in case they than pulled out of the stream, the slack water behind may fall in; the snag will encourage deposition and increase • snags should not be removed for aesthetic or marginal vegetation growth. recreational reasons except in rare cases where If deposition behind the snag is considerable, an very restricted areas might be modified or cleared island may form. This will provide greater riparian for specific purposes; diversity, with the additional protection from River banks damaged by snag removal work may predators provided by an island. require repair or replanting. The hole in the bank left by the tree as it falls If bank erosion is likely to be a serious problem, creates greater diversity in bank profile and allow the snag to remain and control the erosion associated habitat. using an appropriate erosion control technique.
28 GUIDELINES & CASE STUDIES
Snag management: Case study 1 and an old timber bridge to the north. Unsightly industrial buildings on the west bank are screened by Ovens River, Wangaratta, Upstream of Stockbridge willows in summer. Ovens River Basin — Drainage Division IV, Basin 3 The maintenance of clear still water can be Works by Ovens and King River Trust justified from an aesthetic point of view in such an urban setting. Snag removal is therefore beneficial to Site summary the visual landscape. This site is on the Ovens River within the urban area of Wangaratta. There is a highly developed Comments terrace on one bank and floodplain opposite. The If the snag remained it could pose a threat to the channel is approximately 40 m wide and 4 m deep. bridge if struck by log or debris dam. The site is within the plains section of the Ovens End branches could have been lopped (and River, downstream of its confluence with the King dropped into stream) to allow boat passage. The log River, and lies at the southern edge of a large flood- could therefore have been realigned in the channel plain which extends over one kilometre to the north. rather than removed. Bed material is sand and silt; riparian vegetation is mixed exotic and native species. Land use is urban commercial and urban parkland. Snag management: Case study 2 A large River Redgum (approx. 1 m in diameter) Thompson River at Sale had fallen from the river bank across the Ovens river Thompson River Basin — Number 225 immediately upstream of an old wooden bridge (The Works by Mid-Gippsland Rivers Management Board Stockbridge').
Works summary Most of the reclgum log was removed from the river channel, and disposed of. Roots and part of the trunk were left in the stream adjacent to the bank.
Effects The cumulative effect of such works is to cause the Ovens River to persist in this location. The removal of snags prevents a debris dam effect and therefore retards the tendency for this channel to be superseded by other waterways within Site summary the floodplain. The loss of shelter for fish however is The site is on the lower section of the Thompson particularly important in this case as availability is River which is flat and highly sinuous. There is already limited due to continual snag removal in this significant remnant vegetation in flood areas but the part of the river. majority is grazed. The channel is 20 m wide and 3 A consequent decrease in the diversity of stream m deep. bed, also reduces available instream cover. The loss of a food source through removal of Works summary trapped organic matter and invertebrate attachment sites will result in a lower productivity of the food chain. A large River Redgum had fallen into the stream. It Loss of potential spawning sites, particularly for was winched around within the channel to lay along Murray Cod and River Blackfish, which are the toe of the bank. important angling species. Such species support a sport fishery for the local urban population. Effects The works had only a minor impact on riparian vegetation; minor damage was caused to the bank In this situation, relocation of the fallen tree within resulting from physical removal of the tree. Impact the channel gives some protection to a vulnerable was low because of the highly modified nature of the bank, and removes the threat of erosion caused by vegetation. the blockage and diversion. This provides an This is a picturesque stretch of river alongside a example of maintaining instream habitat, whilst park bounded by the main road bridge to the south preventing any likely problems.
29 GUIDELINES & CASE STUDIES Iliii4
The alignment of the snag with the bank has morphologic response is complex, complicated by created an area of slack water which has enabled the combined effects of de-snagging and other long- better growth of marginal vegetation where the bank term trends induced by upstream impoundments and is out of reach of grazing stock. Unfortunately some profound changes to natural flow regimes. willows have been planted. The snag provides Rejuvenation of the main channel may be a roosting and feeding perches for birds, and resting desirable effect in the long term, if ana-branch and sunning sites and shelter for reptiles. Access to development and abandonment of the main channel the bank for burrowing species is unimpeded. is to be avoided. However, these effects must be better investigated if they are to be used as Comments arguments in favour of de-snagging. The regular widespread removal of snags auto- If the site was fenced, regeneration of local species matically removes a large percentage of potential would be rapid and willows would be unnecessary. spawning sites for species such as Murray Cod. The Murray Cod is by far the most popular angling Snag management: Case study 3 species in this area. Localised damage to banks during snag removal Murray River — Albury to Howlong was considerable in some cases. Removal of Works by River Murray Commission overhanging trees by lopping has reduced shade and Site summary input of debris at some sites. Removal of willows has probably resulted in new The site is in a sinuous but relatively steep section of growth of willows further downstream as broken the Murray River. There is a very wide floodplain branches can move down the river and take root. (several kilometres) with numerous floodplain There has probably been loss of slack water areas features (meander scrolls, oxbow lakes, natural along the margins, with removal of some snags, but levees, ana-branches, etc.). There is scattered the effects have not been documented. vegetation throughout the floodplain with patches of exotic vegetation along the river banks. There are Comments gravel and sand bars within the channel. De-snagging in this reach of the Murray River has Works summary potential for major morphologic and environmental effects. Appropriate habitat and hydraulic criteria Snags were removed to increase channel capacity for should have been developed with a view to irrigation flows. Material removed includes River determining a more appropriate strategy or a more Redgum logs of various sizes and large amounts of selective level of snag removal. More appropriate overhanging willow growth. strategies could include: Effects • adjustment of snags within the channel instead of removal; Bank erosion is likely to increase as a result of • leaving snags in, and suffering any consequences; channel rejuvenation. In this case study, • removing willows only.
30 --, _ _ "-----',,,„ .,....,--- - ...... „„-,--- __ _ ------,..------_--- _2--- :->-,..: _-/- 2--- _7,- 1-- GUIDELINES & CASE STUDIES ----,____,.------— —,------T. -----
REVEGETATION WITH NATIVE SPECIES Strategy The presence of vegetation on banks and verges will not prevent major bank erosion due to deepening Improvement in aesthetic and habitat values is of the stream or changes of course. It will stabilise the sought by protecting stream verge from stock, to bank, help to maintain the stream in a stable align- encourage natural regeneration or allow planting of ment and reduce fretting erosion and sediment loss to trees and shrubs. Contribution to stream stability is the stream. also expected, particularly in smaller streams. A narrow band of vegetation can inhibit stream stability by: Description • increasing the rate of formation of a narrow Works sites or other selected streamside areas are 'natural' levee; protected by stockproof fencing. In small streams • causing concentrations of flow and opportunities and also for many larger streams, both sides must be for scour at high volume overflow points; fenced if stock access across the watercourse is to be • obstruction and erosion risk associated with prevented in times of low flow. fallen trees and debris in channel. Fences need to be permanent as they are under In the short term, these effects are relatively rare considerable pressure from stock when feed in the and minor, but the long-term morphologic impli- adjacent land is scarce. cations of a dense verge of streamside vegetation in an Security against stock ingress is particularly otherwise largely cleared, unobstructed and heavily difficult wheraences must cross or abut waterways, utilised valley floor must be carefully considered. and at stock watering points. These pose real prob- lems in practical re-vegetation programmes. Aquatic habitat Re-vegetation with nursery stock is necessary wherever remnant vegetation is scarce. Plantings Riparian vegetation provides an important source of may require a large investment of labour, not only organic matter for the food chain in most streams. in the initial stages but also for follow-up watering, As most native plant species are evergreen, this rabbit control, weed control, and clearing of grass input occurs year round rather than seasonally. Such from the young plants. This can be minimised by material from native species generally takes longer to using individual rabbit guards and mulching for process and hence provides a nutrient source over a weed control. longer term than that of exotic species. The Experience has shown that streamside plantings, processing of this material is conducted by almost always on highly permeable alluvial material, invertebrates (shredders), which are all adapted to in an area of water table drawdown, will invariably native vegetation. These invertebrates, mostly require watering during at least the first summer, if aquatic insect larvae, with terrestrial invertebrates success is to be assured. which fall into the stream form much of the food Width of streamside revegetation areas varies but source for fish. is most commonly 5-10 m. For maximum benefit, the Riparian vegetation also provides inputs in the fenced area should be at least 20-30 m wide. Narrow form of snags and organic debris. Such inputs are plantings of a few metres are much less successful for important in providing shelter and spawning areas bank stability or for habitat development. for fish and attachment sites for invertebrates. In some areas emphasis is put on planting of Hollow logs are particularly important as spawning indigenous species, preferably grown from locally sites for species such as Murray Cod and Blackfish. collected seed. In other places introduced native As such hollows mainly occur in native trees rather varieties are more common. Effort is typically con- than introduced species, planting with natives centrated on shrub and tree species with only rare should be encouraged. Woody debris is particularly instances of work with native grasses, sedges and important in rivers with fine sediments, to provide reeds. Practical applications of direct seeding techn- firm substrates for algae and animal attachment. iques in the riparian zone are rare. Riparian vegetation also produces stream shading which itself provides a form of instream Environmental effects cover and reduces water temperatures. Riparian zones of adequate width (at least 30 m) also provide The principal effect of vegetation is generally a long- buffer strips for the stream. Such zones can filter term contribution to stability. sediments, fertilizers and other pollutants which may
31 GUIDELINES & CASE STUDIES T be washed into the stream. Siltation is an increasing unknown effect on populations of the smaller more problem in streams and reduced riparian zones have sedentary species. contributed to this. Smaller native plant species During revegetation particularly by planting, soil together with leaf litter can form effective buffer strips. disturbance should be kept to a minimum, particularly where some native herbaceous species Riparian habitat persist, so that weed introduction will be minimised. Indigenous riparian vegetation will increase Fencing allows the growth of the understorey input of organic material into the stream, which will species, particularly sedges and reeds on the water increase the food supply for aquatic organisms for margin. These will often establish naturally if there some distance downstream of the revegetated site. is a source of seed upstream. On a very bare stream, Revegetation with dense planting can inhibit planting may be necessary, particularly of the access to the river. Trails should be created through common reed (Phragmites austxalis), which is a very plantations where access is appropriate and desirable. useful bank stabiliser. Trees and shrubs should ideally be grown from locally collected seed, and reflect the vegetation Guidelines native to the area. Trees are an important component Use indigenous species grown from locally collected of the riparian habitat but are often less valuable than seed as far as possible to maximise environmental shrubs and herbaceous species as bank stabilizers. benefits. The indigenous vegetation provides habitat for Revegetate as close as possible to the water's a large variety of species of animals, from insects edge to increase benefits to aquatic habitat. and spiders, to reptiles, birds and mammals. Some Plantings should reflect the variety and layout of of these will be intimately associated with the the natural vegetation. Use a range of plant types. river, while others use the riparian corridor as a Place emphasis on grasses, sedges and reeds, and on base for visits to the adjacent cleared rural land, or smaller shrubs. Plant in close clumps or randomly as a corridor allowing movements across the rather than in rows, to increase chances of country from one area to another (e.g. from coast subsequent regeneration. to hills). Implement public education and involvement in Many aquatic species have to spend part of their planting and maintenance and encourage life cycle on land and suitable riparian vegetation landowners to care for fences and plantations. may be an essential part of this. The vegetation will Stream verge revegetation areas should be as wide build up soil and litter which may, also interrelate as possible, at least 30 m on a large stream or river. with the aquatic environment. Be prepared for major establishment costs over The extent of continuous riparian vegetation several years including control of weeds and vermin along a stream has bearing on its value as habitat. as well as tending of plants. It may also be necessary The greater its uninterrupted length, the greater the to implement fuel reduction burning programmes to population of riparian species that can be supported minimise the risk of wild fire. (both plant and animal) and the more resilient these Always build strong permanent fences. Provide populations will be. Breaks in the corridor have an access points for stock and recreation.
32 GUIDELINES & CASE STUDIES
REVEGETATION WITH EXOTIC SPECIES
Strategy Aquatic habitat Stream banks are planted with exotic species such as In most rivers the riparian vegetation makes a major willow or poplar varieties, to enhance stream contribution to the food supply of the aquatic fauna. stability. Plantings of exotics are often used as a Both quantity and quality of this input are very stand-alone strategy or in conjunction with other important. Exotic vegetation is usually deciduous so works. the major leaf fall will occur over a short period in autumn. This is in marked contrast to native Description evergreen vegetation, which tends to shed leaves over a long period of the year, with a peak in Willow varieties in common usage include basket wil- summer. The soft leaves of exotics decompose more low, black willow and golden willow. Weeping willows rapidly than eucalypt leaves creating a feast and are generally not favoured. Various varieties of dwarf famine food supply in streams lined with willows or willow have been trialled with mixed success. poplars. The invertebrates which depend on leaf A fast growing species which will sucker from its material have evolved in an environment of more roots is the cottonwood. This and various other regular food supply, and their life cycles are unlikely to poplar varieties have been used in different parts of be able to make full use of autumn leaf falls. the State. The woody debris which is such an important Willows and cottonwoods can be grown from part of the environment of most streams is supplied stakes cut from branches. Stakes can be planted by from the riparian vegetation. Willows and poplars pushing into soft material, using a crowbar, by water have soft wood which is not as persistent in the jetting in sand, or by hand or power auger where water as eucalypt wood and they are far less likely to appropriate. drop twigs and branches into the stream. They The Most common use of exotics is at the toe of a generally do not develop hollows which can be of bank or out into the stream in support of structural great importance as spawning sites in snags for fish measures such as groynes or alignment training works. species such as Murray Cod and Blackfish. The large Proper long-term management is required to quantities of bark shed by River Redgums in counter the adverse effects of willows including: particular are also a very valuable part of the aquatic • branches and twigs broken from trees may take habitat which is absent from streams lined with root downstream; willows or poplars. • willows can grow into and across the stream, Effective filtering of runoff into the stream is creating blockages and forcing the stream in rarely provided by exotic plantings. Little behind the root mass; undergrowth can survive under heavy willow shade, • large trees can become unstable on high banks and the deep litter deposits which can form effective and fall into the stream. filters will not develop. Black willow and golden willow have an upright single trunk habit which minimises these problems Riparian habitat although the black willow has been observed to seed thousands of young trees under certain Exotic tree and shrub species provide a better circumstances. Basket willows have a multi-trunk riparian habitat than bare heavily grazed banks. bushy habit and are used to restrict water flows (in a They provide shade and some organic input into the developing ana-branch, for instance). stream. However, a very limited variety of animal species will use such vegetation, as few native insects Environmental effects will live on willows. The heavy summer shade of exotic deciduous species greatly reduces or prevents Willows have a dense root system, quite unlike that herbaceous growth and little marginal vegetation of native species. They tend to create a bank form will develop. The water-land interface therefore is quite different to that in naturally vegetated streams. poor habitat for aquatic species emerging for the ter- By encroaching on the stream bed, they may form restrial part of their lifecycle, or for reptiles or frogs. islands and change the course of the stream or block Birds which feed on insects and nectar, or seed, and it, causing a breakout further upstream. Overgrowth need hollow branches for nesting, will also be absent. by willows can have serious adverse effects on Establishment of exotic herbaceous species, for boating, swimming and angling. example, sowing down battered banks with pasture
33 GUIDELINES & CASE STUDIES .2_ plants, can prevent establishment of native woody or restricted to those situations where their stabilising herbaceous species and provide inferior riparian habi- characteristics are essential. tat, although it may be effective in stabilizing the bank. It should be possible to plant willows in conjunc- tion with native plantings, in such a way that willows could be progressively culled as stability Guidelines develops. Willows, cottonwoods or other exotics should not be Take care with the black willow in case of seeding. planted as a matter of course. Their use should be Be prepared for ongoing willow maintenance.
34 GUIDELINES & CASE STUDIES o SAND AND GRAVEL EXTRACTION
Strategy Extraction of sand or gravel adversely affects the aquatic habitat. Colonisation by invertebrates is Accumulations of bed material (usually sand or interrupted and bed vegetation and accumulations of gravel) within the stream channel, are excavated woody and leafy material are destroyed. Habitat and removed. diversity is decreased by removal of snags and other bed perturbations. Disturbance of bed material will Description cause fine fractions to enter suspension. Re- deposition can propagate environmental impact Excavation is usually undertaken by dragline, downstream. excavator or loader, working within the channel or Direct damage to bed and bank vegetation by from the bank. machinery and stockpiles is inevitable during Excavation can be at a single site, a series of extraction works. Swamps or wetlands on the sites, or continuous, sometimes over several floodplain are likely to be destroyed by channel kilometres of stream. It may involve the full width of deepening as a result of extraction of sand or gravel. the bed or just bars of accumulated material. Extraction works benefit all types of boating by Material is typically stockpiled on the stream maintaining a clearer channel. The destruction of verge pending removal. the riverbed will reduce fish numbers in the area.
Environmental effects The impact on the passive enjoyment of the riverbank by walkers and picnickers will also be severe. Many Victorian stream systems are subject to the pas- sage of a 'slug' of sediment slowly moving through the channels, originally initiated by land clearing, mining, Guidelines gullying, wildfire, or other episodic erosion event. Extraction works need to be properly planned and This 'slug' of sand or gravel may swamp existing areas of activity identified with the view of channels with sediment and initiate profound protecting adjacent environmentaly valuable areas changes in the fluvial morphology. Extraction may or stream zones. The period of operation each day or lead to rejuvenation of the stream channel. Without during each week needs to be governed by the need proper care, investigation and monitoring, to minimise the effect of turbidly on downstream rejuvenation can be excessive, causing deepening conditions, especially during low flow conditions. and bank collapse upstream, and an unpredictable Commercial operations should establish a Trust response downstream. Fund of regular payments for the purpost of
35 GUIDELINES & CASE STUDIES o rehabilitation after cessation of operations. Such Works summary rehabilitation should aim to create natural stream Sand is extracted annually by dragline and stock- conditions providing a comparable habitat to piled on the bank for later removal and use. undisturbed streams in the area. Extraction is limited to the previously existing Minimise the length of stream which is affected channel cross-section. by the extraction. Deep or repeated excavation at one restricted site is preferable to minor extractions Effects over a long section of stream. Minimise damage to riparian habitat by working Extraction temporarily replaces the wide flat bed and and stockpiling on one bank only. shallow flow with a narrower deeper channel. Introduce irregularities to the excavated channel The works have been effective in preventing the bed or banks by leaving some areas of shallow flow downstream advance of the silt front into areas not amongst the deeper areas. yet affected by siltation. they have prevented Reinstate snags after excavation is complete, or abandonment of the existing channel and, in the create artificial obstructions. long term, will rejuvenate the channel in its existing location. The uniformity of the excavated channel Sand extraction: Case study provides little habitat opportunity. All debris has been removed. Fifteen Mile Creek at Wangaratta South Riparian vegetation has been destroyed at the Ovens River Basin — Number 403 sites of stockpiling and removal operations. Development of wetlands within the floodplain Site summary has been curtailed.
This section of creek is subject to severe deposition of Comments sand. The channel annually fills to within a metre of the top of bank with medium-grained granitic sand. A more intense sand extraction operation within a The adjacent land is subject to regular siltation confined area would minimise impacts whilst still and waterlogging, the creek being 'perched' above achieving the benefits. the level of the adjacent land. Diversion of the To reduce the need for future extraction opera- stream into another course at the side of the tions, it is important to minimise the input of floodplain is a possibility. sediment upstream. The channel is approximately 10 m wide, and is excavated regularly to a depth of approximately 3 m along a 2 km section of creek.
36
GUIDELINES & CASE STUDIES ••-
ROCK CHUTES
Strategy which mobilises the sediment and by acting as a sediment trap. This reduces downstream siltation and Rock weirs or chutes are constructed in the stream may even trigger a new cycle of deepening below the bed to prevent the upstream advance of bed structure. Where they are used to stabilise an effluent deepening and to cause deposition of material channel, rock chutes may delay the formation of a upstream. breakaway course.
Description Aquatic habitat Sized and graded rock is placed on the excavated bed The most adverse effect of rock chutes is on fish of the stream and on adjacent banks. The structure passage along the stream. The extent of these effects usually includes a filter layer (either of graded is dependent on the height, slope, size and design of crushed rock or filter cloth) and a cutoff wall of the structure. The ability of fish to negotiate concrete, sheet piling, or piles and timbers, which structures varies between species but sudden rises/ also provides a fixed crest. drops and steep gradients without resting areas Chutes may be geometric in design, with usually cause problems. The expansion of a stream excavated trapezoidal cross section, or constructed to bed over a wide area may reduce water flow to follow the existing channel cross section. impassable trickles, whilst a major concentration of Rock may be graded or single sized. Rock up to flow through a narrow channel may provide an 600 mm in dimension is commonly used. impenetrable area of high velocity flow. Spaces and Typical chutes range from 1 m to 5 m high and small pools among rocks provide valuable resting from 10 m to 50 m wide. Bed grade within the chute areas for fish migrating upstream. is usually between 6:1 and 10:1 but flatter grades Fish passage is particularly important in coastal may be necessary when only small rock is available. areas where almost all species need to move between freshwater and estuary at some stage of their life Environmental effects cycle. Spawning migrations also occur however with species such as Golden Perch and Trout in inland Cycles of deepening and m ulling moving through waters. stream systems are natural processes, although Formation of pools and riffles in stabilised creek frequently aggravated by human activities. Successful sections may provide additional diversity of aquatic rock chutes halt the upstream advance of the habitat. The addition of rock and trapped sediment deepening process. may also increase substrate diversity. Rock chutes may reduce the amount of sediment Interstices between the rocks will provide passed downstream both by reducing the erosion habitat areas for smaller fish and aquatic organisms.
37 GUIDELINES es? CASE STUDIES
Riparian habitat Guidelines In the short term, the rock facing destroys any Use less formal structures where possible (see Case existing riparian and stream bed vegetation, and study 1) as they provide greater habitat diversity creates a significant break in the streamside corridor. than more formally engineered structures. With time, sediment may build-up amongst the Incorporate a pool above the chute to increase rocks, and vegetation may establish. The use of filter habitat diversity. cloth may provide a significant barrier to root A variety of rock sizes and logs incorporated in development, and restrict the establishment of the chute will provide a diverse habitat. Filter cloth perennial species. may impede the establishment of vegetation. Both the general disturbance caused by the Fence the site and banks up and downstream, to works and the importation of material associated allow revegetation and maintain the area and the with them are liable to be accompanied by the structure regularly. introduction of weed species which may not have Avoid long steep chutes by using several small been present formerly or which are now able to chutes if possible. become better established on the disturbed ground. Provide for fish passage on steep chutes by Introduction of weed species will have impact incorporating a low flow diversion or channel within downstream as well as on the works site. the chute, a meandering channel down the side, or Where a pool is formed upstream of the chute, face, or a series of steps. riparian vegetation may become more extensive and diverse, providing potentially improved habitat for
riparian animals and greater interaction between Rock chute: Case study 1 riparian and aquatic environments. lithe works area is fenced to exclude stock from King River Ana-Branch at Oxley previously grazed stream banks, the riparian habitat Ovens Rivers Basin — Drainage Division IV, Basin 3 will be greatly improved. Both the diversity and Constructed by Ovens and King River Trust abundance of vegetation will increase. The stabilisation of a previously eroding stream Site summary bed and bank, and the resultant deposition of The site is at a developing ana-branch of the King sediment, provides substrate for improved growth of River adjacent to a highly sinuous reach of the main riparian vegetation. stream. The ana-branch is relatively straight and
38 GUIDELINES & CASE STUDIES
incised through cohesive alluvial material. The King River will continue to phase out in favour of channel is approximately 20 m wide and 3 m deep. the newer straighter channel. Deepening in ana-brach progressed upstream Transforming the narrow gutter of the ana- during 1974 and 1981 floods to within several branch into a pool and riffle bedform has increased hundred metres of the King River. instream diversity. Areas of slow velocity in the pool, The river was accumulating sand and silt and and velocity shelters behind rocks, with the had lower capacity than the ana-branch. associated development of more variety of substrate, The adjacent land use is cattle grazing with a have provided new habitats. Developing riparian major road bridge 50 m downstream of the main vegetation has increased shading, and inputs to the structure. stream. The low structure does not impede fish Works summary passage. Rock up to 600 mm in diameter was placed more Fencing has allowed natural regeneration of than 1 m thick on the bed and banks. There was wattles and eucalypts, and sedges along the water little prior excavation and no cutoff wall or fixed margin which is improving the habitat of the bank crest were incorporated. and verge. The planting of willows and poplars was The site was fenced and planted with willows, not necessary. They hinder the native vegetation by poplars and indigenous and non-indigenous shading out the indigenous species, particularly the eucalypts. The chute was constructed summer marginal herbs. 1982-83. Comment Effects The chute is an environmentally sensitive solution The chute will delay the diversion of the King River to the problem which existed at this site, and to date into the ana-branch. It will encourage siltation in the works have been effective. Because of the the ana-branch and reduce the siltation of the main relatively informal nature of the structure, some branch of the river. However in the long term, the movement of rock is likely to occur in severe events diversion is inevitable as the existing course of the and partial or complete failure is a possibility.
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Rock chute: Case study 2 Existing downstream siltation problems will be Brudien Creek at Woodside reduced. Reduced sediment loads downstream may South Gippsland River Basin — Drainage Division II initiate new bed adjustments and trigger new cycles Basin 27 of erosion and deposition. Constructed by Shire of Alberton River Trust Although fish habitat in reaches of Bruthen Creek downstream of the rock chute has been Site summary severely degraded by erosion, the stabilisation of such areas will allow substantial rehabilitation of Major bed instabilities, active for several years aquatic habitats. culminated in a 5 m erosion head moving upstream Prior to works, it is likely that the erosion head over 1 km during floods in 1978. As the head would have posed a barrier to fish passage. progressed upstream a channel typically 4.5-5 m Unfortunately this rock chute maintains such a deep with 4 m bed width and 20 m top width was barrier. Fish passage is particularly important as the created. majority of fish species found in such coastal streams For 20 km or more downstream of this site the require to migrate between the freshwater and creek is subject to dramatic cycles of severe siltation estuarine reaches at some stage of their life cycle. and secondary head cuts. The absence of species such as Grayling, Tupong and The adjacent land use is grazing. Upstream, the Galaxiids in the upper reaches may be attributed to creek is shallow and ill defined with limited remnant such barriers. Improvements to fish habitat made by riparian vegetation. A road bridge exists several the reduction of erosion and sedimentation and hundred metres upstream of the structure. consequent stabilisation of the stream may be offset by a lack of access. Works summary The rock chute, constructed in 1981 to arrest Comments upstream advance of the erosion head, is a major A series of smaller chutes with low gradients, a structure of its type and the largest in Victoria. The formal fish ladder or an alternative low flow channel chute incorporates concrete cut-off walls upstream around the works would have allowed fish to pass. and downstream with large rock (nominally 600 The works have arrested severe environmental mm) overlaying filter cloth. Major excavation work degradation associated with upstream progression of preceded construction. The works area was fenced. a major erosion head and improvements to environmental values will now be possible Effects throughout the stream system. The chute has arrested upstream movement of the major erosion head.
40 GUIDELINES & CASE STUDIES
DROP STRUCTURES
Strategy Drop structures may reduce the amount of sediment passed downstream both by reducing the A fixed step built in the stream bed to prevent erosion which mobilises the sediment and by acting as upward advance of deepening. The step is usually a sediment trap. This reduces downstream siltation constructed of, for example, steel sheet pile, and may even trigger a new cycle of deepening below reinforced concrete or gabions. Rock chutes are a the structure. Where they are used to stabilise an special case which have been treated separately for effluent channel, drop structures may delay the the purposes of this document. formation of a breakaway course. Structures create a fixed step in stream bed level and can impound a pool of water to encourage Aquatic habitat deposition of material upstream of the structure. A further pool of water at the downstream toe of Drop structures and weirs usually cause serious the structure is an essential feature for the impediments to fish passage. The extent of the dissipation of the energy of falling water. effects is dependent on the design of the structure, but most incorporate a drop or extremely steep Description gradient which is impassable for fish moving upstream. Few incorporate any form of fish ladder or Reinforced concrete drop structures can vary from bypass channel. small structures dropping minor tributaries over heights of less than a metre to major engineering Riparian habitat structures of five metres or more in height, able to carry flood flows from large catchments. The construction of the works causes considerable damage to the riparian zone, depending on the scale Common to all structures are cutoff walls, wing of the structure. lithe site is fenced, the vegetation walls and an energy dissipating arrangement. Vertical should soon recover, but weed invasion may occur drop structures and sloping chute type structures are common. on the disturbed ground. Sheet piling wiers consist of a row of interlocking When a pool is formed upstream of the drop structure, riparian vegetation may become more steel sheeting driven across the stream. Special abutment and energy dissipating treatment is extensive and diverse, providing improved habitat required to prevent erosion damage. Rock is most for riparian animals, and greater interaction between commonly used. riparian and aquatic environments. The stabilisation of the previously eroding stream bed and bank downstream of the wotks may Environmental effects improve growth of riparian vegetation, if the stream Cycles of deepening and m ulling moving through is fenced and stock excluded. stream systems are natural processes, although The structure may create a significant break in frequently aggravated by human activities. the riparian corridor, particularly for small animals. Successful drop structures halt the upstream advance This may be lessened if the associated fenced and of the deepening process. vegetated area extends far enough from the stream margins to extend round the ends of the structure.
Guidelines Attempt to use several small structures rather than one large structure, in order to reduce impact on the continuity of the riparian corridor. Ensure that fencing and revegetation extend around the ends of the structure. Low level by-pass channels should include a vegetated verge to maintain the continuity of the riverine corridor. Allow for fish passage by incorporating a fish ladder or bypass channel into each structure.
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Drop structure: Case study 1 Drop structure: Case study 2 Reinforced Concrete Chute Sheet pile drop Cardinia Creek at Beaconsfield Main Drain Bunyip River Basin — Number 228 Bunyip River Basin — Number 228 Works by Dandenong Valley Authority Site summary Site summary The stream is a man-made channel constructed to Cardinia Creek drains a mixed urban and rural drain swamp areas. Adjacent land use is pasture and catchment to the south-east of Melbourne. A major intensive agriculture. The channel is straight and channel incision progressing upstream through flanked by levees. pastural land has been arrested by the drop structure.
Works summary Works summary The structure is a major reinforced concrete chute A sheet pile wall was driven across the channel to with a low flow diversion channel and fish ladder. create a low drop of approximately 600 mm. Rock was placed to control downstream scouring. Effects Effects The structure has stabilised a major erosion head which was progressing upstream and threatening The structure has prevented upstream deepening. farmland and major assets. Downstream siltation The sheet pile weir caused a direct drop of about from the erosion head has been controlled. 600 mm which would prove impassable to most fish This drop structure incorporates a channel to species. This weir forms one of a series along Main enable fish to pass upstream. Common Galaxias are Drain, and may be seen as responsible for the found upstream and downstream of the structure. absence of migratory fish species such as the Spotted Galaxias, Australian Grayling and Tupong Common and Spotted Galaxias, Tupong and have not been found in Cardinia Creek above this Australian Grayling from reaches of the Bunyip drop structure although they are present almost River system. Although the weir did provide an immediately downstream. These species are upstream pool with respite from the constant fast apparently unable to negotiate the bypass channel. velocities, it was inaccessible to most fish. The pool created above the drop structure The riparian zone of this channelised stream provided a large deep floodplain type habitat for a contains very little native vegetation. The majority variety of aquatic organisms. of species are introduced. The works do not create a The works destroyed riparian habitat at the site. major break in the riparian corridor and disturbance Fencing since construction has resulted in good during works would not have had a significant effect vegetation growth around the weir above the on the existing vegetation. structure, but the area around the works has been sown down to grass and is mowed, creating a break in the riparian corridor. The fish ladder diversion flow is also very formal, and there is no natural vegetation along it, so it does not provide any riparian habitat.
Comment The fish passage channel should have had a lower gradient and incorporated a pool and riffle sequence as resting areas. This would have allowed all migrating species to move upstream. The size of the structure precludes any continuous riparian habitat development. The provision of a fish ladder could have provided an important corridor for many other species as well as fish if it had been less formal, and was vegetated.
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Comment Effects The use of a structure which impedes water flow but A log weir is a cheap solution if logs are available but allows fish passage would have been preferable. Low offers very low level of security. level rock chutes could have been used or a double The natural appearance of this structure was sheet pile wall with staggered gaps between adjacent particularly pleasing. piles. This low level weir provided a series of cascades It would be possible to encourage native species and small steps in water levels rather than a sudden such as wattles and reeds to improve the riparian drop. This allows a greater chance of fish migration habitat. The channelised stream is in a very upstream although passage may remain difficult until impoverished condition. flows are high. Only slight modifications would be required to the design of a weir of this nature to Drop structure: Case study 3 provide specifically for fish passage. The constructon of the weir requires cutting of Log Weir local timber which might have had some impact on Thompson River at Cowarr nearby vegetation. Thompson River Basin — Number 225 The logs do not break the riparian corridor to Works by Rural Water Commission any great degree, as the weir is fairly low. Planting of exotics on the banks has pre- Site Summary vented the development of a diverse marginal At the site of the main Rainbow Creek control vegetation, so the riparian habitat is impoverished structure, this low level weir controls water levels in in species. the Thompson River during low flows. Comment Works Summary The log weir has some of the value of snags. Planting Logs were anchored in a heap across the stream to of indigenous species instead of exotics would have create a weir approximately 1 m high. greatly enhanced the riparian habitat.
43 GUIDELINES & CASE STUDIES
CHANNEL MODIFICATION
Strategy deepening, widening and straightening followed by complex morphologic responses. Deepening may A range of strategies involving the use of earth- proceed for tens of kilometres upstream of the works moving equipment within the stream channel are site. Major deposition sites downstream usually used to deepen, widen, straighten or otherwise follows. modify the stream cross-section. Usually, the aim is to reduce the impact of bed material deposits on flow Aquatic habitat alignment, to protect adjacent land, or to increase channel capacity. Channel modifications devastate the aquatic environment by changing stream length/ width/ depth, water velocity and substrate. Description Complete channelisation involves the removal Earthmoving equipment such as bulldozer, excavator of all riparian vegetation/ aquatic vegetation, or dragline is operated either within the channel or instream snags, debris and cover and a reduction of from the bank to rearrange bed material within the stream bed diversity to form a uniform channel with stream channel. few of the attributes of a natural stream. This frequently involves removal of bars or The removal of snags, organic debris, stream bed islands from the channel bed with excess material diversity and alterations to substrate reduces species being pushed up against an eroding bank. The net habitat, spawning sites and inputs to the food chain. effect is usually a straightening of the channel, or at Resultant uniform velocities provide little shelter for least a smoothing out of bends. many species and over long distances may be Channel modification also includes stream detrimental to fish passage. straightening and channelisation for drainage or The loss of habitat and formation of adverse flood control. stream conditions result in a decrease in species Channel modification is at least temporarily diversity, richness and biomass. Shifts in faunal effective in increasing channel capacity, and thereby composition are likely to occur in conditions which reducing flooding and improving drainage. will favour a few tolerant organisms. Fish species It is sometimes effective in producing a new such as eels, goldfish and carp often dominate alignment but rarely provides any lasting bank channelised stream reaches. protection. Riparian habitat Environmental effects Major channel modification earthworks will normally also modify the banks and verge. Vegeta- Channel modification will rejuvenate the stream tion is destroyed and riparian diversity is lost. Stream channel. Channel rejuvenation involves initial rejuvenation may drain adjacent wetland areas.
44 GUIDELINES & CASE STUDIES
Guidelines channel forcing a breakout of floodwater across grazing land approximately 200 m to Queens Creek. Channel modification is a stream management The natural levee on the main channel was eroded technique with high environmental costs. It should and concentrated overflows occurred. Headward only be employed after all the consequences have erosion initiated a channel scour working back from been thoroughly assessed and other options have Queens Creek toward the river. been considered. It should not be employed as a bank protection or alignment training technique. Works summary • Identify the potential upstream and downstream Blockages of snags and bed material were removed by impact as part of the basic investigations of bulldozer working in the bed of the river. Large optimal solutions. quantities of bed material have been bulldozed from • Retain channel diversity by maintaining the the stream bed to reform the stream channel. Excess natural stream channel as much as possible. gravel was placed against the stream bank at the • Replace debris, logs, boulders, etc. after overflow location. earthworks to enhance stream habitat. • Minimise damage by working from one bank Effects only. The works have reformed the stream channel at this • Leave remnants of natural stream and native location preventing concentrated overflows and vegetation. imminent river diversion. • Establish and maintain vegetation. Reductions in stream bed diversity and the removal of debris and larger substrate particles have Channel modification: Case study 1 effectively reduced the amount of cover for fish species present (Trout and Blackfish). The works have King River at Cheshunt (Betton Property) widened the stream channel and produced a shallow, Ovens River Basin — Number 403 flat bed which provides essentially no fish cover. Works by Ovens and King River Trust The battered bank of coarse gravel will take a long time to accumulate sufficient silt and organic matter to Site summary support mature vegetation. Fencing and planting will This site is on the upper reaches of the King River contribute to restoration, but this will be slow. floodplain tract. It is a steep channel with bed material up to 300 mm. The channel is typically Comment 30 m wide, 2 m deep and the floodplain is I km wide. This is an example of work with a high environ- The floodplain is cleared for grazing and intensive mental impact over a localised area. agriculture. Less uniformity of the battered bank and some During winter of 1986, an accumulation of snags left along the margin would have helped to snags, debris and bed material blocked the main restore habitat diversity.
45 GUIDELINES & CASE STUDIES 451
A narrower low flow channel would have tion increased downstream and in Westemport Bay. prevented some of the adverse effects of a wide Main Drain is an example of the type of shallow cross-section. destruction of aquatic habitats that can be caused by Bank protection works (such as rock beaching) channelisation. would have allowed greater flexibility in cross Carried out over a large expanse of river, this section size and shape, and reduced the scope of waterway now consists of a straight channel with channel modification works. uniform, fast water velocities, little instream habitat and no riparian trees or shrubs. The diversity, Channel modification: Case study 2 richness and biomass of fish species have been found to be lower in this section than in sections of the Main Drain Bunyip River immediately upstream. Such Bunyip River Basin — Number 228 reductions can be attributed to a loss of fish habitat Works by Rural Water Commission and spawning sites in the form of snags, velocity shelters, organic debris and shade. Site summary Erosion heads in the upper catchment which Extensive swamp and wetland areas were drained by have been triggered by the channelisation of Main progressive major channelisation works throughout Drain also cause destruction of the aquatic this century. environment in these areas. This is a highly modified channel with no remnants of natural morphology or soil profiles. The Works summary banks are mostly vegetated with exotic herbaceous Main Drain, constructed by excavation and levee species and the riparian habitat is very impoverished. banking, is a straight channel with basically This condition is probably maintained by continuing trapezoidal cross section. works along the drain and grazing.
Effects Comment Works have been effective in creating large areas of Any diversity, either physical or in the vegetation, highly productive agricultural land. would improve the habitat. Planting of trees and Channelisation has triggered major incision epi- shrubs would also contribute useful habitat to the sodes in upstream waterways and major sedimenta- over-cleared surrounding rural areas.
46 GUIDELINES & CASE STUDIES H.
BANK BATTERING
Strategy Environmental effects The natural slope of a stream bank is reduced by earthworks to improve stability. Battering is usually Aquatic habitat supplemented by vegetative or structural protection Undercut banks can form an important source of measures. The success of bank battering as a stand instream cover to fish species. Bank battering usually alone erosion prevention measure depends on the removes habitat and associated snags and wood type of erosion, the type of bank material, and the debris. Similarly, riparian vegetation which over- stability of the stream bed. Battered banks may hangs the stream (and provides shade and inputs of continue to erode at the toe either by direct removal terrestrial invertebrates, organic matter, debris and of material or by undermining and collapse. snags) is also removed. These functions are all of Where a stream bed or bank toe has been great importance to aquatic species. This becomes stabilised, battering is often employed to pre-empt more critical as riparian zones in general are reduced. the natural battering process. This has a largely Bank battering works will cause downstream cosmetic function but can also prevent bank material washing into the stream during the natural sedimentation. battering process and contributing to downstream sedimentation. Riparian habitat Except for slip circle type failures, battering as a Bank battering is very destructive to any natural stabilisation measure against stream bank erosion is vegetation surviving on the river bank. The works likely to fail in the long term unless structural or vege- remove any existing vegetation, destroy the natural tative stabilisation is successful. This is because the soil profile, and encourage the invasion of weed fundamental components of the erosion process species onto the disturbed soil. Resowing of the remain essentially unchanged by the battering process. battered banks generally uses exotic pasture species. Even if indigenous shrubs are planted, the herbaceous Description layer cannot easily be replaced, and will become dominated by exotic species. If willows or poplars are Earthmoving equipment is used to excavate the planted, the chance of re-establishment of indigenous streambank. Excess material is usually removed from the site. species is reduced further.
47 GUIDELINES & CASE STUDIES 16
Battering creates uniformity, and removes any Site summary diversity of the bank. This reduces habitat diversity This small creek has suffered a past incision episode. for many species, particularly for bank burrowing The bed now appears stable but the banks are steep species, and greatly reduces shelter and tending to slump in places. Impact on the natural form of the river and on continuity of streamside vegetation will usually be Works summary highly adverse. lithe bank is not too high, an alternative to The upper two-thirds of bank has been battered back bank battering is fencing and planting without soil on a 2:1 slope. The area has been fenced and disturbance. Establishment of vegetation at the toe planted with indigenous vegetation. will stabilise natural battering. Effects Guidelines The works have reduced bank collapse thereby reduc- Battering is a technique which has serious ing downstream sedimentation. Exclusion of grazing environmental impacts and should not be used and re-vegetation have contributed to bank stability. simply to tidy the banks. The need for and benefits The battering works removed the small amount of a battering project should be clearly identified of remnant vegetation although most trees were before its use is contemplated. retained. The vegetation removed, mostly melaleu- Don't batter long lengths of bank. The works, if cas, has regrown quickly and, within a period of two considered necessary, should be carried out only in years, the streamzone has considerably more plant short stretches, with natural banks left wherever cover than it had prior to the works. The original possible. Wherever possible, allow natural battering vegetation and bankform lacked diversity due to to occur, protected by fencing and revegetation. erosion and siltation. Diversity of bank form was Use the steepest batter possible, except where retained by varying the degree and slope of safety considerations are important. battering (often to retain larger trees) and leaving Avoid temptation to make banks tidy. the lower part of the bank it its original state.
Comments Bank battering: Case study 1 Fencing alone would not have been sufficient to Deep Creek at Princes Highway stabilise the creek in the long term. Introduction of Bunyip River Basin — Number 228 some indigenous shrub species which have been lost Works by Dandenong Valley Authority through clearing and grazing would have improved the habitat further.
48 GUIDELINES & CASE STUDIES
MEANDER CUTOFFS AND FLOOD WAYS
Strategy A series of meander cutoffs can drastically shorten a reach of stream, leading to major deepening which can Floodways allow high water to cut across a meander progress upstream. Such channel rejuvenation may or bend without low flows being affected. Meander cut- may not be desirable depending on management offs divert the entire channel through the short cut. objectives. Floodways and cutoffs are usually employed: Meander cutoffs can result in the loss of large • to reduce erosion threat at the meander bend; lengths of stream which are replaced by short reaches • to reduce flood levels by increasing flood of channel usually consisting of uniform fast water capacity; or velocities and devoid of instream habitat. Such • to re-juvenate the stream channel. reaches provide little habitat for aquatic organisms compared to the areas lost. Description Some benefit may accrue to the aquatic environment if the old meander remains as a Floodways and cutoffs involve excavation of a billabong or wetland. channel across the narrow neck of a meander bend. Floodways have little impact on aquatic organ- For a floodway, the floor of the excavation is isms provided they are not allowed to develop into stabilised at a level higher than the stream bed. For a meander cutoffs. They do have permanent effect on cutoff, either the excavation is deep enough to riparian vegetation which is usually removed to divert the stream, or else no stabilisation measures maintain the hydraulic capacity of the floodway. . are employed, and the excavation is allowed to erode Cutoffs reduce the length of the riparian zone, until the stream diverts through the cut. but if the cutoff meander continues to hold water BOth techniques are effective at reducing flood and its banks and verges are not grazed, a valuable level and erosion risk on the meander bend. habitat will be provided, changing from river to billabong to swamp as it silts up. Environmental effects Meander cutoffs and floodways have potential for Guidelines major impact on stream morphology. Meander cutoffs can have severe morphologic consequences which should be investigated before the technique is employed. The dramatic changes to the environment brought about by a cutoff should be carefully managed. The abandoned river course and its verges and banks should be regarded as a valuable resource and grazing should be prevented in that area. Floodways must be adequately protected and maintained if they are not to develop into cutoffs.
Meander cutoff: Case study Latrobe River at Farmer's Flood Cut Latrobe River Basin — Number 228 Works by Mid-Gippsland River Management Board
Site summary The site is at the lower reaches of Latrobe River which is highly sinuous and perched significantly above surrounding floodplain. Adjacent land use is
49 GUIDELINES & CASE STUDIES grazing with some remnant floodplain vegetation. Floodway: Case study Bank materials are stiff, cohesive clays. Ovens River at Pioneer Bridges, Everton Works summary Ovens River Basin — Number 403 Works by Ovens and King River Trust A floodway constructed in the 1950s has now eroded and become the main river channel cutting off Site summary nearly 1 km of river and replacing it with a narrow 50 m short-cut. This is a meandering section of the Ovens River The old river course is rapidly filling with sand. under threat of abandonment in favour of an alternative channel straight down valley grade. Effects Repeated erosion has reduced the natural level on the outside of the bend despite protection measures. Morphologic response to cutoffs in this vicinity is delayed by the resistant nature of the material. Works summary Nevertheless, repeated cutoff development will lead to a straighter stream course which will ultimately A floodway 20 m wide, 1.5 m deep and approxi- enter a new phase of adjustment. mately 50 m wide was excavated and stabilised in the Rejuvenation of the stream in this location will 1960s. The area was incorporated into a demonstra- delay diversion of the Latrobe River to a lower part tion trial of cottonwood plantation as an alternative of the floodplain. frontage land use to intensive cultivation. This cutoff has resulted in the loss of nearly 1 Effects km of riverine habitat which has been replaced by a 50 m channel consisting of uniform, fast water The floodway has reduced the erosion threat on the velocities and no instream cover. This loss of habitat outside of the meander bend, improved the for aquatic organisms must result in a reduction in hydraulics of the bridge approach and reduced the species numbers. threat of a breakaway by improving channel capacity. The land adjacent to the abandoned meander is As this floodway only comes into effect at high grazed, but well vegetated with gums and wattles. It is flows it has little effect on the aquatic environment. providing very useful riparian habitat for the environs The floodway is planted with cottonwoods, and is of the river and the newly created billabong. Removal heavily shaded in summer. There is very little herba- of grazing would further improve the vegetation. ceous growth. Operation of the floodway protects the opposite bank and enables the riparian vegetation there to remain stable. The site is used as a picnic area.
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LOPPING
Strategy when lopping, some branches should be dropped into the water to improve instream cover. Root Streamside trees are lopped to prevent collapse of masses are an extremely valuable habitat which will trees and bank into the stream or to prevent be lost to the stream, as will the hole left in the bank obstruction of the channel. should the tree be allowed to fall. Lopping of willows may improve the riparian habitat, as it reduces the heavy shading and may allow more diverse marginal vegetation. However, dense mature willows would have such a compact root system that few other species could compete even in the absence of shading. Lopping of eucalypts would reduce habitat for tree dwelling animals, and the addition of leaf litter, and fallen timber to the stream bed and verge. The removal of overhanging trees and branches will remove important roosting and resting sites for birds. Kingfishers in particular use vantage points above the water for perching between feeding dives. This is particularly important when riparian trees are sparse. The prevention of trees falling into the stream maintains bank uniformity. Much of the useful habitat diversity in bank morphology is due to trees The strategy is effective in preventing collapse of falling and breaking the line of the bank. However, trees into the stream and in preventing obstruction. when trees are sparse, their loss to the riparian Bank damage is prevented. habitat may be a serious loss. Lopping should be kept to the minimum required to maintain stability. Description When riparian vegetation is sparse, fencing and planting should be carried out to guard against future Willows, eucalypts, wattles or other trees have loss of trees. Planting of reeds and shrubs along overhanging branches removed. In most cases trees margin will help to stabilise bank and protect trees. continue to grow. Guidelines Environmental effects Keep lopping of eucalypts to a minimum, and where Streamside vegetation provides shade and important possible, cut only part of the tree, leaving some inputs of snags and organic debris as forms of branches overhanging the water. instream cover. Terrestrial invertebrates and organic Allow some branches to fall into the stream to matter (leaves, etc.) from such vegetation are satisfy instream woody debris requirements. important inputs into the food chain. Therefore, Fence and plant where appropriate.
51 GUIDELINES & CASE STUDIES
LEVEE BANKS
Strategy The prevention of overbank flooding causes the loss of floodplain aquatic habitats. These habitats Earthem banks are constructed to control the spread generally provide conditions quite different from the of floodwaters by confining water to a limited area to main stream. Habitats such as swamps and billabongs reduce the frequency of flooding or to control have unique aquatic faunas and can provide essential erosion associated with flood overflows. spawning and rearing areas for many fish species. Warmer water temperatures and constant high density Description food supplies in these areas have been suggested as Alignment is stripped of topsoil, and compacted clay ideal conditions for many species including Murray fill is placed to form an impermeable bank. Finished Cod and Golden Perch (yellow belly). The reduction bank is usually covered with topsoil and grassed. of floodplain waters has meant a severe reduction in the preferred habitats of species such as the Dwarf Galaxias and Pygmy Perches. Environmental effects The retention of waters within the main channel Levee banks have potential for major impact on can also severely increase water velocities. fluvial and floodplain morphology. Confinement of flood flows to the channel sec- Riparian habitat tion of the floodplain will cause the channel to alter The building of levee banks requires considerable characteristics such as planform and cross-section soil disturbance and generally resowing with exotic geometry. These changes will result in erosion. pasture. This will destroy any existing natural The gradual process of floodplain siltation will vegetation at the works site, and encourage the be interrupted in areas now excluded from flooding, invasion of weed species. and accelerated in areas still flooded. Depending on The prevention of flooding on the flood plain stream characteristics, the leveed area may rapidly outside the levee will drastically change the water become perched. relations of this area with considerable impact on When levees breach during floods major scours both wetland and dryland environments. The water occur as the result of concentration of flow. table will probably fall, and the drought resistance Long levees or shorter levees at critical locations of many perennial plant species will be affected. offer major obstructions to natural flow regimes, and Many riparian species depend on regular or can significantly alter the flow characteristics which intermittent floods for parts of their life cycle. The created the stream and floodplain morphology. reduced water supply to wetlands will increase the Levees will affect flood patterns upstream of the frequency with which they dry out. This, among works area. other changes, will increase the incidence of grazing damage and resulting habitat destruction. Aquatic habitat The area inside the levee will be subject to Interaction between floodplain and mainstream increased frequency of flooding and increase water habitat is probably very important to both environ- velocities. If it is fenced, the habitat on the face of ments in ways which are as yet poorly understood. the bank may improve in the absence of grazing.
52 Guidelines preventing premature overflows and reducing risk of scour that would lead to a breakaway course. The levee should be as far from the river as possible, to maintain maximum floodplain habitat. Effects Consideration should be given to the regular overtopping of levees, say on g 1 in 5 year return The levee bank prevents concentrated and period, to provide a better balanced answer. premature overflows but is out-flanked by floodwater The site should be fenced to improve the habitat during major events. value of the remaining floodplain, which should The floodplain of the river has been highly include some swamps or lagoons inside the levee. modified and sown down to pasture. There is no In rural areas cellular zones of protected land floodplain habitat inside the levee at the section interspersed with flood channels that include inspected. The riparian habitat is therefore very poor swamps and wetlands may be a better alternative to except on the steep face of the bank which is out of confinement along the stream. reach of stock. The levee prevents all but major floods from Levee bank: Case study 1 reaching naturally swampy areas further from the river which may have provided useful temporary Latrobe River at Marshall's Property feeding areas for waterfowl, but the intensively Latrobe River Basin — Number 228. grazed floodplain no longer has any useful permanent Works by Mid-Gippsland River Management Board wetlands.
Site summary Comments The site is at the lower reaches of the Latrobe River. A series of silt trap fences within the overflow could, The river is highly sinuous and perched significantly with time, have a similar effect as the levee as above the surrounding floodplain. Adjacent land use trapped silt builds up ground levels. is grazing. If the levee had been set further back from the river and the area fenced, the riparian habitat would Works summary have been enhanced. The highly modified floodplain A 2 m high levee was constructed to block a at the works site has left little natural environment. concentrated overflow point from the Latrobe River An impact on upstream areas is likely but unknown.
53 GUIDELINES & CASE STUDIES
URBAN CHANNELISATION - HARD LINING
Strategy Riparian habitat Channel capacity is maximised by channel The riparian habitat is destroyed by concrete or enlargement, straightening and lining. masonry lining, and modified severely by rock lining. Where trees and shrubs are planted along the Description channel, they may provide useful bird habitat, but there is no effective land/water interface and the The channel is excavated to a design cross-section aquatic part of the habitat is virtually unusable. and grade, and lined with concrete, masonry, rock or Where rocking is used, there may be some silt grass. A low flow channel is usually provided. build up, and some plants and animals may be able to use the available niches, but the modification of Environmental effects bank and bed of the stream will have been so great that there is little chance of a complex riparian Natural stream morphology is lost. Channelisation community developing. can trigger deepening further upstream. Siltation can Some large concrete channels are popular reduce the capacity of channelised section. venues for trail bike and minibike riding. This use
Aquatic habitat can be dangerous and a cause of disturbance to surrounding residential areas. Concrete or masonry channelisation removes all There may be an opportunity to use the verges of instream habitat and substrate and converts a urban channels for recreational activities but safety is meandering stream with a range of widths, depths an important consideration. and velocities into a uniform channel. All cover Water bodies are highly valued in the urban areas and spawning sites are removed. There is a lack environment, and retention of a natural stream of debris and suitable attachment sites for most course is to be preferred whenever possible. invertebrates. In most cases riparian vegetation is also removed and so inputs of terrestrial invertebrates and organic matter are not available. Guidelines Shallow flows over concrete or masonry Hard lining of urban streams is an extreme measure channels can result in raised water temperatures. and should be avoided wherever possible. This often results in algal growth which further The lengths of concrete or rock lining should be reduces water oxygen levels. Such habitats are kept to a minimum. The channel should be shallow unsuitable for aquatic organisms and areas of such during low flows and side battering should not be so channel usually contain no fish. steep that they are dangerous.
54 GUIDELINES & CASE STUDIES
Maximise the environmental values of the low substrate, shade and riparian inputs have all been flow channel by creating meanders, pools and riffles, removed. Long reaches of shallow water with fringes of natural vegetation, etc., whilst maintaining uniform flow velocities with no shelter areas may overall waterway capacity of high flow channel. also impede fish passage. Fish numbers in Re-assess existing scheme with a view to Dandenong Creek are low and areas of channel such rehabilitation when major maintenance becomes as this have been found to contain few or no fish. necessary. There is no riparian habitat in this section of the Urban development should be planned to creek. The planting along the margins may have minimise adverse effects on the hydrology of the some terrestrial habitat value in an urban context, catchment, and to incorporate flood mitigation but it has no riparian component. measures such as retarding basins. Development in floodplain areas should be minimised. Urban channelisation: Case study 2 Urban channelisation: Case study 1 mulium Mullum Creek, Ringwood Yarra River Basin — Number 228 Dandenong Creek, Dandenong Works by Melbourne and Metropolitan Bunyip River Basin — Number 228 Board of Works Works by Dandenong Valley Authority Site summary Site summary This creek flows from highly urbanised catchment This channel runs through a highly developed urban through a narrow creek reserve. area. It was built in the late 1960s to replace a Prior to European settlement the creek at this heavily eroded gully in which a number of lives had location was not a perennial stream. The existing been lost by drowning. creek upstream of the urban area which appears to be the original stream is the result of clearing during a Works summary fairly long period of orchard and general farming A multi-stage concrete and grass lined channel was activity. This left the stream moderately incised and constructed to increase the capacity of the channel. probably with relatively minor erosion. The indigenous riparian habitat was destroyed by Effects the farming activities and, prior to the creek works, the banks were overgrown with blackberries. The large expanses of Dandenong Creek which have Urbanisation and extensive removal of the been channelised in this manner provide almost no blackberries led to rapid deepening of the creek bed habitat for most aquatic organisms. Instream cover, and undercutting of the banks.
55 GUIDELINES & CASE STUDIES 1111
Works summary stream meander, rock substrate and depth variations, diversity of habitat and instream cover cannot be Very extensive creek modification works over a compared with a natural stream. Cover areas for fish 1.5 km reach. in the form of undercut banks, snags and organic Major earthworks within the creek reserve, debris are not present. Although the new substrate culminating in a channel lined with individually will provide some attachment sites for invertebrates, placed large rock. Past failures of vegetation to small particles are absent. become established on the highly dispersive soils has The previous riparian vegetation, being largely led to the extensive use of filter cloth underneath blackberries and other exotic species, was largely the rock to prevent soil from leaching between the removed by the works. Some planting of riparian rock interstices. Channel incorporates bends, minor species is proposed, but the extensive use of filter width variations and rock chute drop structures with cloth may make this difficult. The verge will be regu- sheet piling cutoff walls. larly mowed to maintain the urban parkland setting. The work incorporates many of the features of a Effects natural stream including variation of verge treatment The works were intended to pass an appropriate and contrast between running and still water. The design flow and avoid previous flooding and erosion effect is a major improvement on the more problems. conventional treatment of urban channel isation. Although this channelisation has incorporated a
56 -\— GUIDELINES & CASE STUDIES ky-r-
URBAN CHANNELISATION - FLOODWAY Strategy This treatment is preferable to concrete channelisation as the open grass swale of the Channel capacity is maximised by construction of a channel can be useful open space. In circumstances floodway; with low flows accommodated on a low where the alternative is highly polluted, very low flow conduit beneath the floodway. flows the low flow pipe and grassed channel may offer visual and practical advantages. However, it is Description not a satisfactory substitute for open flowing, reason- ably clean water whenever that can be achieved. Roodway is usually trapezoidal in cross-section, grassed and regularly mown. Pits in the channel floor drain water into the low flow pipe. The floodway Guidelines provides for high channel capacity while the low flow Avoid such extreme measures wherever possible. pipe allows easy access for maintenance and mowing Compromise with environmental values as necessary. of the channel bed. Low flows with high concentra- Avoid low flow conduits as they completely tions of pollutants are conveyed within the conduit. remove any environmental values of the stream. Re-assess existing schemes as major maintenance Environmental effects becomes necessary. Urban development should be planned to Channelisation may trigger upstream deepening. minimise adverse effects on the hydrology of the Siltation may occur on channelised section. catchment, and to incorporate flood mitigation The piping of water in this way no longer leaves measures such as retarding basins. Development in the waterway as a stream. All natural aspects have floodplain areas should be minimised. been removed, the removal of all natural habitat, light, substrate, etc. means that few species of aquatic Urban floodway: Case study organisms will persist in such an environment. Mile Creek Extended piping which provides long uninterrupted Bunyip River Basin — Number 228 reaches of uniform fast water velocities may cause Works by Dandenong Valley Authority passage problems for many fish species. The piping of the low flow removes the land- Site summary water interface except in short periods of high flow. There is therefore no rijiarian habitat. Any The creek flows from an urbanised catchment vegetation along the floodway has only terrestrial through a narrow creek reserve in an urban area. habitat value. Works summary A low flow pipe was placed beneath a grassed flood- way channel.
Effects The floodway has no aquatic environment suitable for naturally occurring waterway organisms and no riparian habitat. A pleasant suburban open space has however been created which also has some value as a sediment trap protecting downstream natural waterway conditions. Regular maintenance of such an area achieves attractive townscape compatible with abutting residential zones. A major question of a more natural looking open waterway in such a situation is its incompatibility with residential living and the more difficult task of continuous removal of urban rubbish.
57 GUIDELINES & CASE STUDIES
RETARDING BASIN
Strategy riparian habitat. The building of the basin may destroy an existing wetland by reducing its water Flood peaks are reduced by temporary storage of holding capacity, and therefore reduce the available floodwaters and controlled release. They should be riparian habitat along the stream. seen as an augmentation of the natural floodplain If designed with imagination, flood basins can storage characteristics within the catchment and a provide an attractive element in the landscape. means of offsetting the effects of urbanisation in Excavation may be used to provide for some reducing infiltration of rainfall into the ground. permanent water while maintaining capacity. This will meet environmental as well as aesthetic Description objectives. Retarding basins are impoundments with weir or pipe outlets. The storage area may be used for a Guidelines variety of purposes such as parkland, car park, farm land, etc. when not inundated. Retarding basins maintained with some water, and ungrazed, will improve the riparian habitat. Some attention should be given to the likelihood of Environmental effects creating mosquito-breeding sites, particularly in Impoundments may restrict upstream advance of urban areas. The water should be kept deep enough deepening and act as sediment traps. to maintain fish, rather than as a very shallow Retarding basins, like drop structures and weirs swamp. are likely to pose problems to fish passage unless they A low flow channel or fish ladder should be incorporate a facility to avoid this. Retarding basins provided for fish passage on larger waterways. can be designed to replace floodplain habitats which Banks should be shaped to blend with natural have been previously lost. contours and trees used to diversify the landscape. lithe storage is maintained wet, and is not The use of retarding basins to confine the effects grazed or mown, it may provide useful riparian of flood flows derived from urban catchments and so habitat, depending on the growth of the vegetation provide an impact similar to flows derived from the around it, and the rate of changes of water level. original rural state is of importance to the mainten- If the storage is maintained dry, and only fills ance of aquatic environmental values in downstream occasionally, it will not contribute any additional natural water courses.
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