The flow of water through the landscape, down gullies, depressions, creeks, streams and down into the main rivers helps define catchments. The ridges, hills and mountains that act as catchment boundaries are also the sources of headwaters for a catchment’s river system. Catchments occur at different scales in the landscape. For instance, the Calder River is a sub-catchment of the Inglis River, and Hook Creek is a subcatchment of the Detention River
Management of small waterways in the larger catchment is important because they often make up the bulk of the stream network in a river catchment What we do in riparian areas which are at the boundary between land and water, has implications for the entire catchment.
Waterways can take many forms, rivers, streams, creeks, wetlands, lakes and billabongs.
What is a riparian area?
The riparian area is land alongside your waterways and can be quite narrow or extensive, particularly where it includes large floodplains or river terraces. Riparian land can be connected to the waterway by proximity (a riverbank) or by waterflow (a floodplain, wetland or lake foreshore)
Riparian areas are an important interface between what happens on the land and what happens in the water. A well-managed vegetated riparian zone alongside the waterway provides an important buffer between agricultural or industrial activities and the waterway and goes a long way towards retaining good water quality. Riparian areas are also often moister and more fertile than adjoining areas
It is important to recognise that riparian areas need to be managed in an ongoing manner and that they cannot be fenced and forgotten.
Functions of a well-managed riparian area
Riparian areas that are in good condition and well vegetated can provide a number of valuable roles that maintain good water quality and stable river systems:
Trap and store sediment
Sediment and nutrients from the adjacent land area are prevented from entering the water.
Sediment builds soil and banks in the riparian area
Stabilise banks
Stable banks resist erosion and prevent widening and movement of the channel.
Store water and energy
Flood waters are slowed down by vegetated and stable banks, reducing erosion and flood damage.
Well vegetated banks trap flood debris and so reduce damage and energy in high flows.
High flows over the floodplains are trapped to recharge underground aquifers and build up soil and nutrients
Filter and buffer water
Riparian plants absorb and trap nutrients and contaminants, preventing them from polluting the water.
Overhanging vegetation shades the water, protecting in-stream animals and preventing unwanted algae from growing.
Provide food and habitat for in-stream animals and plants
Create a micro-climate for stock and wildlife by reducing air and water temperatures in hot weather and act as a buffer when wet and cold.
In-stream animals such as the Giant Freshwater Crayfish rely on inputs of organic matter (dead leaves and wood) for their food.
Many in-stream animals require dead wood and litter to hide from predators or shelter from fast-flowing water
Many plants and animals can only live in riparian areas where there is abundant water, rich soils and cool, moist conditions
Other animals which may not be dependent on the riparian zone yearround, may use them during certain times of the year or in certain parts of their life cycle
Provide corridors for movement of animals and seeds across the catchment
Seeds of plants and animals move about the landscape along corridors between patches of native vegetation.
and “messiness”
Complexity and “messiness” of a good riparian area.
Tea tree covered wetland forms part of the riparian zone with the river along the timbered zone in the background and floodplain cleared for pasture production
Benefits of well-managed riparian areas
Clean water
Safer water for domestic use.
Healthier and more productive livestock
More wildlife – fish, platypus, crayfish.
Healthy floodplain soils
Better retention of water, nutrients and sediments. Retention of water on the floodplain, particularly upstream, reduces velocity and damage downstream
Improved agricultural production with topsoil retained on site.
Healthier soil organisms.
Stable banks
Less erosion of land and productivity. Retention of fences, infrastructure and stock
Safer access for recreation purposes.
Flood control
Slow down and reduce “flashiness” of floods.
Erosion problems reduced. Fewer losses of stock and infrastructure
Healthy plant communities
Good shade and shelter for stock. Shading effect of vegetation stabilises the water temperature and reduces potential for algal growth.
Good stock fodder during less productive times (remain green for longer during drought, might allow very short-term grazing)
Good habitat for birds and other animals, which keep insect pest numbers down and hence reduce use of insecticides
Control of weeds.
Perennial plants help stabilise banks
Woody debris and leaf litter provide habitat for fish and other in-stream wildlife, and woody debris provides erosion control by protecting the toe of the bank.
Moderate stream temperatures
Trap carbon and can be used towards carbon neutrality
Create wildlife corridors across the landscape and connect remnant patches of habitat that may have been fragmented by urban and agricultural development.
Healthy animal communities
Birds including raptors and owls provide chemical-free rodent and rabbit control.
Bats help control insect crop pests. Insects provide pollination and help control pests and diseases
Better stock management with fenced riparian areas
Losses of stock either into river or into neighbours are minimised through fencing out of waterways
Reduced mixing with neighbour’s stock minimises disease transmission across properties.
Stock health improves because contaminated water during low flows is not consumed
Mustering stock and grazing management is easier
Reduce effects of climate change
Riparian soils and leaf litter store large amounts of carbon and are better at reducing nitrates than terrestrial soils.
Well managed riparian areas protect against erosion and can lead to better stock management
Erosion processes in the riparian area
Streambankerosion
Even healthy rivers erode their streambanks; it is a normal process that shapes rivers. However, problems occur when changes along the river affect the rate at which streambank erosion occurs.
Changes can include removal of native riparian vegetation or allowing stock to access the river Removal of vegetation reduces bank stability and removes the armouring effect of the root systems, often increasing the speed of the water flow
Some plants create a protective mat on the surface which also slows flow down and traps nutrients and sediments. Stock access on the banks leads to bare ground, pugging, soil compaction and loss of soil structure leading to parts of the
The loss of riparian vegetation also means that pollutants such as nutrients, pathogens and pesticides that can attach to sediment particles will run off the land into the waterway.
Above: Erosion on outside bends and stock access to the river lead to sedimentation and turbidity
A narrow riparian zone and scattered vegetation and tree roots along an outside bend do little to hold the bank together
Stock access to waterways can lead to bare tracks (loose and unprotected soil), sedimentation, turbidity and contamination from effluent
Fencing can be used to exclude stock from waterways, allowing banks to stabilise and reducing sedimentation
Logs can be aligned along the toe of the bank to protect from erosion
Streambed
erosion
Streambed erosion occurs when the bed of the river starts to erode away and the channel deepens. Streambed erosion is a sign that the channel gradient has become steeper for some reason and the river is adjusting itself to a more stable gradient
There are four main processes that lead to bed erosion:
An obvious sign of bed erosion is a headcut, which appears as a sharp change in gradient, like a small waterfall in the bed of the river. The headcut will keep working its way upstream and will often lead to undermining and collapse of the river banks as the river deepens
1. Increased channel slope as a result of channel straightening, gravel extraction and/or de-snagging activities
3.
Sediment starvation when weirs, dams and blockages obstruct the downstream movement of sediment.
2. Channel constrictions that narrow the channel and increase the flow of water sufficiently to erode the stream bed
4.
Increasing flow or energy due to an increase in water entering the drainage system. This may be due to vegetation clearing upstream, releases from dams and de-snagging.
Repairing streambed erosion is not easy and often much more expensive than repairing streambank erosion. Some examples of bed erosion are obvious whilst others require some sort of technical expertise to identify.
Removing sand and gravel, straightening channels and removing vegetation from the top of the high bank can lead to bed lowering in the channel As the bed lowers nick points or head cuts show up in the channel and work their way upstream River banks get eroded at the base and continually collapse leaving vertical banks as the bed lowers
(Photo: Alice Wade)
River and stream behaviour
All rivers and streams erode Erosion is a natural and essential process in rivers and streams. However, erosion within streams has been accelerated by human impacts such as vegetation removal, water extraction, gravel removal, infrastructure construction and stock access Streams and rivers constantly change under natural conditions, but these changes can be accelerated as a result of things such as erosion or climate change Flow, sediment transport and bank properties play a role in both streambank and stream bed erosion.
It is important to realise that erosion may be impacted by processes occurring in one part of the river or stream, either upstream or downstream of the erosion. For example, gravel extraction or crossing construction downstream may cause bed and bank erosion upstream When trying to mitigate erosion or improve water quality in your section of stream, it is important to realise that this may only be achieved through working with neighbours or on a catchment wide scale
It is therefore recommended to start any rehabilitation measures in the upper catchment as the benefits of rehabilitation accumulate in the downstream direction.
When planning any mitigation or improvement works, it is important to remember that water flow is fastest on outside bends which can often be undercut, with vertical batters and actively eroding banks. Water flow is slower on inside bends and sediment and transported material will often get reworked and moved on inside bends.
The severity of the erosion and the cost of rehabilitation are also factors to consider
It is certainly advisable to get technical advice from extension staff when trying to interpret your local river or stream behaviour and work out the most effective rehabilitation strategy
Water flows fastest on the outside bend and sediment accumulates on the inside of the bend
Rivers are naturally dynamic, but human impacts can accelerate that change.
River rehabilitation measures
When working in riparian zones, any rehabilitation measures are likely to be more successful when landholders across a sub catchment work together. In other words, landholders on both sides of the waterway and adjoining landholders agree to fence to exclude stock or reestablish vegetation to provide a corridor and buffer zone. It is also important to address the causes of the problem, not just the symptoms, for example bed or bank erosion visible on one site may be linked to activities happening within the waterway above or below the erosion site.
It is also important to consider your whole farm plan when locating crossings or fences that need to cross gullies, streams and rivers on your property. See the section below on crossings for more detailed information It is best to avoid constructing crossings or fences within or adjacent to bends in the river. Stock will track and concentrate along fencelines and crossings should not obstruct or alter the natural size and flow of your waterway.
Before embarking on detailed rehabilitation works, it is useful to prioritise and stage rehabilitation works It gives you a chance to identify what works well and to undertake most cost-effective works first.
In general, works are usually done in this priority:
First, conserve and improve “near pristine” river sections or reaches first “Near pristine” reaches act as reference reaches and guide rehabilitation strategies for reaches in poorer condition. These may be well vegetated areas with minimal bed or bank erosion visible
Then, protect good condition reaches from destabilising processes. For example, an eroding gully or drain may have potential to destabilise this section of river
Next, look to enhance channel recovery processes. This may mean, for example aligning a fallen tree along the toe of the bank to allow protection from erosion, sediment build up behind the log and natural regeneration of native vegetation.
Rehabilitating highly degraded reaches is likely to involve a higher level of financial investment, time and resources.
Revegetation on top of the riverbank will provide adequate riparian width and better bank stability Fences are installed to exclude stock from the waterway
Erosion treatment options are often divided into “soft” and “hard” engineering solutions
Soft engineering attempts to re-establish the stream’s natural geomorphology and may include revegetation or installation of large woody debris.
Hard engineering may use materials such as rock to construct permanent structures and this is often used when protecting major built assets. However, it requires design and engineering advice and is a lot more expensive to install and may have consequences on river behaviour, such as migration of erosion areas downstream or impact fish movements
In many cases the establishment of riparian vegetation will be the most effective measure long term provided plantings can get established before being impacted by high or flood flows.
Effective rock jobs on outside bends need to be placed around the whole meander bend and revegetated as part of the “hard” engineering solution.
Inadequately designed rock jobs can lead to bank erosion problems occurring downstream of the engineered works.
Fencing
Fencing to control stock access to your riparian area can have multiple environmental and productivity outcomes if planned appropriately. As well as excluding stock from the riparian area, fencing may enable new paddock subdivision, improved farm management, form part of a laneway for stock movement or allow later paddock layout to take advantage of future shade and shelter
Fencing may not mean stock are totally excluded but rather the timing and stocking rate are carefully managed. For example, small numbers for a day or two to reduce height of groundcover without damaging shrubs or banks and ensuring sediment and nutrients can still be trapped. If you are planning to graze riparian areas for short periods consider:
Avoid grazing when soils and banks are saturated and vulnerable to damage from trampling.
Avoid drought periods when feed is likely to be minimal and stock may graze trees and shrubs
Avoid grazing when grasses are flowering and setting seed, otherwise species will be lost from the site. Avoid periods after fires and floods when rehabilitation needs to occur Allow good long rest periods between grazing of any riparian zones. If you have undertaken riparian planting, you probably won’t be able to graze for several years until plants are established
Ideally, riparian areas should be fenced above the limits of the highest flood to minimise damage to fencing infrastructure and reduce maintenance requirements. It is important to identify the top of the high bank and ensure river terraces and sediment bars are included in the fenced off area Buffer widths between the waterway and fence need to be adequate to ensure sediment and nutrients can be filtered. The buffer width required will depend on a number of factors such as:
Steepness of surrounding slopes. Soil type.
Bank erosion.
Slope of the batters (vertical batters will continue to erode until they find a more stable slope)
Ease of fence construction when trying to keep fences relatively straight.
As a general rule, allow a buffer of at least 10 m from the edge of the high bank on a small waterway and 20 m from the edge of the high bank on a larger waterway. For an effective and diverse wildlife habitat, allow at least 30 m Stock tend to track along fencelines so it is important to ensure the constructed fence is not right on top of or immediately adjacent to an eroding bank, as this will lead to further bank erosion
Wallaby wire fences can be installed when wide and well vegetated buffers are in place and located above flood level
When waterways are fenced to exclude stock, it is also important to consider your whole farm plan and the presence of shade and shelter. Sometimes riparian areas may be the only remaining vegetated areas on the farm that provide shade and shelter during summer or calving and lambing cycles. Windbreaks and shade and shelter areas need to be appropriately sited on the farm
The type of fencing used will depend on the stock type, location of a power source, difficulty of the site, flood regime, and cost Fencing is easier when it is parallel to water flow, but this isn’t always possible and fences across waterways require ongoing maintenance to ensure stock exclusion.
Electric plain wire fencing is cheaper and easier to maintain on floodplains, less likely to catch trash and debris in high flow events, unlike mesh or ringlock.
However, three wire electric is probably required to control cattle and sheep. Drop and lay down fences can also be used in frequently flooded areas, such as inside bends or floodplains, but are more expensive to construct and require ongoing maintenance.
Fences will always be impacted in high flow events, particularly when situated on part of the floodplain, but if the fence is of simple design and relatively easy to construct, then it is also cheaper to maintain.
Electric fences are dependent on a power source and need regular inspection to ensure no damage or short circuits. The creation of wildlife habitat or a wildlife corridor is likely to require mesh or wallaby fencing, which is more expensive to repair and likely to trap and collapse under the weight of flood debris.
Above: Dung beetle on barbed wire, Photo by "Granny Wendy", posted in Facebook by ABC Hobart in February 2021
Right: Wallaby fences trap flood debris and can collapse under the weight, requiring ongoing maintenance
Things to consider when designing and constructing your fence:
Build as far above the flood line as possible.
Build parallel to the water flow
Do not build the fence across the waterway, or if you must, seek an appropriate technical design and be prepared to check and repair this section frequently
Avoid too many curves or corners where debris can build up.
Use plain wire in preference to barb or mesh, to avoid debris build up, and importantly, to reduce harm to birds, bats and dung beetles that can be killed by barbed wire
Avoid using droppers that collect debris.
Drive in posts rather than backfill or infill
Reduce space between fence posts.
Maintain wire tension which will help minimise debris loads
Reinforce end assemblies.
Ensure gateways are on high and stable ground and as far away from the watercourse as possible.
Consider drop down fence options in high flood risk zones such as low floodplains with flood runners across them.
Measure the buffer width to the fence from the edge of the high bank.
Riparian revegetation
A well-managed riparian area will have vegetation with a diverse mix of native plant species, including grasses and herbs, reeds and sedges, a mix of shrubs of different heights and a tree layer of one or more species, with seedlings of shrubs and trees visible Riparian plant communities are often denser and faster growing, largely due to access to moisture.
Revegetation of riparian areas may be required where there is little or no native vegetation and the chances for natural regeneration are limited. Infill vegetation may be required if there are limited species present, for example the shrub layer or canopy layer is completely absent, or the riverbank is vegetated but the top of the bank is not.
Revegetation needs to be carefully considered as it requires investment in
Local provenance seed or plants need to be used, which means collection of local seed and growing out of tubestock, which usually requires a six-to-twelve-month lead time, at least. Most sites require at least one season of weed control before planting. Revegetation is usually done to stabilise streambanks, improve water quality, provide habitat and shade, assist with weed control or improve farm management.
Many landholders report that native plants regenerate naturally after stock are excluded from riparian areas. If natural regeneration does not happen in the first 18 months, or is patchy and sparse, replanting should be undertaken
However, if you want quicker results or need to address a particular problem
Same area several weeks after fence erection to exclude stock. Regrowth but infill planting required to establish shrub and understorey layer
Left: Riparian vegetation – missing a shrub layer and understorey and native regeneration heavily impacted by grazing
Right:
Revegetation tips
Planting is usually more effective than direct seeding. You can use tubestock or advanced plants
For improved water quality for example, planting along smaller feedin drainage lines or planting out along the tops of banks may be a better option.
Planting to stabilise banks will be most effective at the toe of the bank and on outside bends. Revegetating a site after undertaking weed control will reduce the risk of reinvasion
A mix of grasses, shrubs and trees makes it harder for weeds to reestablish.
Direct seeding is quick, cheap, and effective but requires excellent site preparation to reduce competition and needs follow up watering. You also require a local supplier of locally collected native seed.
Locally based species or local “provenance” should be used for revegetation as they are adapted to local temperatures and conditions and have a better survival rate
Deciding which species belong where on the riverbank, is also very important A good guide is to check elsewhere in the catchment where there might be remnants of native vegetation. For example, sedges and reeds are important for protecting the toes of riverbanks. In many Tasmanian rivers, woolly tea tree occurs right on the edge of the stream while blackwood and dogwood occur further back where it is not as wet.
Larger trees with deep root systems, such as the eucalypts are best on the top of the bank where the roots penetrate deeper into the soil profile to hold the banks together. Excluding grazing is essential until plants are above browsing height and if using tubestock, it will also be necessary for the first couple of years to protect plants from wildlife browsing using tree guards or appropriate fencing materials
Cradle Coast NRM has a planting guide for each local government area that suggests the best species for riparian areas
Adapted from Lovett, S. & Price P. (eds), 2007, Pronciples for riparian lands management, Land and Water Australia, Canberra Redrawn from Malanson (1993) Illustration Paul Lennon
Revegetation using corflute guards
Revegetation using cardboard guards, better anchored with two or more stakes.
Weed control
Rivers are naturally prone to soil disturbance and erosion, making them perfect environments for weed invasion. Waterways are also very effective at dispersing seeds, especially after regular high flow or flood events Weeds will out compete native species for light and nutrients and often grow faster than natives.
Weeds such as willows like moist environments and some species will grow from a single cutting or branch washed downstream. Weeds will often invade riparian zones after stock are excluded, if the area has been highly eroded or pugged up by stock and rich in nutrients, prior to fencing
It is therefore important to revegetate bare sites as soon as possible after stock exclusion Weed control requires careful planning and may need a staged approach so that large areas of bare ground are not left behind. It is also important when removing weeds such as willows that the stumps are left in the riverbank and poisoned in situ to allow long term bank stability, particularly on outside bends, while native vegetation gets fully established.
Weeds such as blackberry, for instance, might provide the only bank stability if no other vegetation is present or they can provide protection to seedlings In this scenario, it is important to only treat small areas at a time and revegetate areas as they are cleared. On the other hand, weeds such as foxglove can be treated over large areas at the rosette stage, given that their seed remains in the ground for extensive periods of time.
Same
Top right: Blackberry infestation of cleared floodplain from roadside infestation despite good riparian buffer zone
Bottom right:
area 12 months after spraying
Monoculture of willows in cleared areas along river bank.
Foxgloves on lower river terrace They are best controlled at the rosette stage before they flower.
Any weed control in riparian zones must only use herbicides registered as suitable for use near watercourses. Further information can be found at nre.tas.gov.au/invasive-species/weeds/weed-publications-and-resources
Large woody debris in streams
Sticks, branches and whole trees that enter the waterway from the riparian zone or the floodplain are often referred to as large woody debris (LWD).
Fallen logs are often blamed for problems such as erosion and flooding and hence removed. Local erosion can occur around fallen logs in rivers but this is actually beneficial as it leads to formation of pools and riffles along the waterway Removing the log takes away this habitat value and may also lead to the problem moving downstream.
Large woody debris is important in waterways for many reasons:
It provides essential habitat and shelter for aquatic and terrestrial organisms – rotting timber is a food source for animals such as the Giant Freshwater Crayfish It also provides a surface for algae to grow. It helps protect the banks from erosion by slowing down the flow. It provides numerous different environments from slow moving deep pools to fast flowing chutes. It looks more natural than rock in a riverine setting when used as erosion control
It impacts stream morphology, stability and sediment transport – wood removed from stream can increase sediment transport capacity which in turn impacts channel stability. Fallen logs can act as bed control structures and allow pools and riffles to form.
It is more cost effective to use for erosion control than rock and also often requires smaller machines and lighter equipment if it needs realigning.
Large log jams that lie perpendicular to the flow and cover more than 10 per cent of the channel’s cross section may increase the risk of the waterway breaking its banks in flood flows However smaller blockages or those at bed level are unlikely to have major impact on water levels. There is little evidence that logs and branches have a dramatic effect on flooding Rivers will flood irrespective of the presence of wood Log jams have been constructed and used to deflect flows from eroding banks and reinstate pool and riffle sequences in waterways around Australia
Woody debris provides good habitat value and leads to the formation of pools and riffles along the waterway
Over the last few decades, the focus of river management has moved from actively removing snags or woody debris, to retaining or reinstating them as part of river rehabilitation efforts If wood is causing problems such as erosion or flooding it can be repositioned within the waterway, usually so that it is aligned with the flow. Retaining logs, particularly those with the root mat attached, means they can be used for erosion control However, re-positioning or removing the LWD may initiate bank erosion by diverting flows or it could increase stream velocity in the middle of the channel
This can mobilise bed sediment and lead to channel deepening, significant disturbance or sedimentation, particularly if it has been in place for a long time.
Therefore, it is recommended that you seek technical advice from your local NRM organisation or a geomorphologist before undertaking any timber removal or realignment within waterways Any in stream works may also require approvals from state or local government bodies nre.tas.gov.au/Documents/6-woodydebris-in-waterways.pdf
Logs can be laid along the toe of banks to stabilise and prevent erosion.
Logs properly located on outside bends can armour against erosion and trap debris and sediment, provided they are well keyed in to the bank.
Waterways and Farm Management
It is important to recognise that waterways flow through a catchment and any in stream activities upstream or downstream may affect your section of waterway through your property or your neighbours up or down stream.
Stock watering systems
If riparian areas are fenced off to exclude stock from the waterway, then it will be necessary to provide stock with alternative watering points. Off stream watering points may be added to an existing farm water supply system or may have to be a completely new system, if nothing currently exists
Capturing, storing and supplying water across your farm will depend on a number of factors:
The source of your water – waterway, groundwater bore, dam or mains supply.
Your daily and seasonal water needs. Power supply – diesel, electric, solar, wind powered
Security of system – if you are an absentee landholder then a reliable system is very important.
Topography of the property – for example is there a high spot for water tank storage to enable gravity feeding?
Type of watering points – Troughs or dams It is easier to maintain better water quality in troughs Dams need an appropriate site and stable spillways and are more difficult to maintain good water quality if stock have direct access to the dam Dams have higher evaporation
Location of watering points – for example on floodplains concrete troughs are less likely to move in flood events than poly troughs, although they are more expensive initially to purchase
Generally, the cheapest systems use gravity to move water around the property, which involves pumping water to a tank or dam on higher ground which then gravity feeds to watering points below. Watering points may also require gravel underneath them due to concentration of stock, pugging and erosion potential which could lead to the destruction of the trough.
It is recommended that you seek professional advice when designing a water supply system and in trying to establish pump and pipe sizes. Landholders do have the right to extract water for stock and domestic purposes from a waterway on or adjoining the property Bores can be expensive to construct and equip and water quality needs to be tested to ensure it is adequate for stock use. If you decide to construct a bore or dam as part of your water supply, you may also require local or state government approval and licensing.
Visit: nre.tas.gov.au/water/water-licences or nre tas gov au/water/dams/building-afarm-dam
Concrete troughs are more likely than poly troughs to survive high flows on floodplains. Gravel under and around the trough will limit erosion and pugging from stock access in wetter periods.
If you currently have no option but to allow stock to drink from the waterway, then ensure there is limited time they can spend in the waterway by creating a fenced and gated watering point that is properly constructed and where access can be controlled.
Fences will have to extend into the water to ensure stock cannot travel upstream or downstream or along the stream banks This option will require regular fence maintenance and it may be more economical to fence out the waterway completely
Also ensure the watering point is on an inside bend or straight section of river, where water flow is slower and often material is coarser, rather than on the faster flowing outside bend where banks are more prone to erosion and steepening
Crossings in streams
Crossings are an important part of farm operations and good siting of crossings is essential to minimise environmental damage and reduce long term maintenance.
There are a number of factors to consider when deciding on what type of crossing you need:
The shape and size of your waterway –wider waterways require more extensive structures Steep sided riparian areas are likely to impact the design of your crossing
Water volume – high velocity streams will require stronger foundations
Frequency of use of crossing – is it used frequently and in all weathers?
Volume and type of traffic. Soil types.
When building your crossing make sure you:
Select a straight section of waterway, not a bend, because the force of the water is directed down the middle of the waterway rather than towards a bank
Select a site after a bend and not before a bend as water tends to accelerate around the outside of the bend, making banks unstable for construction.
Build the crossing straight across the waterway because if it is built at an angle, water flow will be concentrated in one small area, or the crossing may direct water towards the bank and cause erosion.
Choose a naturally higher site in the bed of the waterway This reduces height to which you need to build crossing and reduces the crossing’s exposure to flow of water.
Make sure site has a firm footing and avoid eroding or boggy areas
Avoid steep slopes
Choose a narrow part of waterway as it will be cheaper and easier to build. Discourage stock from lingering at the crossing – ensure lack of shade and angled fencing using electric wire to move them on and off the crossing
In deciding on what type of crossing to install consider the cost of the structure versus the cost of ongoing and regular maintenance, as well as the likely frequency of use.
With all in stream structures there will be ongoing maintenance involved –maintenance to ensure the structure is still performing and can allow fish passage and secondly to remove debris build up.
In general, to minimise environmental damage and in descending order of preference, use bridges, culverts, and bed level crossings such as causeways, fords and stock crossings.
Bridges
Bridges span the entire width of the waterway and are unlikely to impede flow. They are used when a crossing is likely to be frequently used or a waterway is deep or prone to flooding.
Although more expensive to construct and install, they will usually require minimum ongoing maintenance.
They are the most appropriate crossings where banks are steep or actively eroding
The bridge needs to be strong enough to support the maximum load. The banks need to be well supported and protected without reducing the width of the channel
Footings may need to be armoured with rock if located in an actively eroding waterway Retain as much vegetation as possible alongside your bridge crossing to stabilise the banks and prevent erosion
Timber and steel tray bridge across the river. The bank under the bridge needs to be reinforced with rock or timber.
Culverts
Culverts are raised crossings that use round or square pipes to allow water to flow underneath Culverts can be arched, boxed or piped conduits, usually made of concrete or galvanised steel. They allow water to pass under the road or crossing.
Culverts are relatively simple to construct and are suitable for permanent waterways that flood infrequently.
The bottom of the culvert should not be more than 50 mm above the bed of the waterway to avoid water stagnation at the inlet and scouring and erosion at the outlet. Use a compactible backfill that will not wash away, for example gravel or cobbles are coarse enough to withstand the water velocity but can packed down by machine. Maintain protective vegetation on the banks and you may have to protect the full height of the banks with rock
The size of the pipe needs to be large enough that flood flows can pass over and around the crossing and maintain an even depth across the width of the waterway. Culverts are not suitable for waterways that carry heavy sediment or debris loads, as they get blocked up. Round culverts, that are the most commonly used, are one of the worst designs in allowing fish and crayfish passage. They can create high water velocities and turbulence within the culvert pipe, the water flowing through may be too shallow for some species and the culvert can become blocked by debris The downstream end may become “perched” above the natural streambed meaning species cannot enter it and scouring or a plunge pool is created at the outlet.
A scour pool forms at the downstream end, particularly when the outlet is “perched” above bed level.
Debris build up against the upstream end of the pipe.
A pipe installed at bed level is less likely to have erosion and scouring. However this inlet needs rock protection or a collar around the upstream end to protect against scouring and soil collapse around the pipe.
Square pipes or box culverts are better than round pipes for fast-flowing waterways because they disperse water, reduce its velocity and reduce the risk of erosion at the outlet. A box culvert is a culvert with an open bottom that has the natural waterway running through it It can be rounded, square or rectangular in shape Sometimes they are set on a concrete base Water velocity and turbulence in box culverts normally reflects the natural flows and they are less likely to get blocked by debris. Like bridges, some large box and arch culverts do not significantly alter the bed or width of the waterway.
Poorly designed and poorly located crossings and culverts can cause downstream erosion and undermining and collapse of the crossing. Although more expensive initially, bridges are easier to maintain long term and provide less blockage in stream. Pipes, culverts and crossings need to be installed at bed level and the downstream outlet needs armouring with rock to prevent scouring and deepening.
Bed-level crossings
Bed-level crossings are the cheapest and easiest types of crossings to build and maintain, but they are really most suited to waterways that flow infrequently or only experience low flows. These structures should be located in areas where the waterway is straight and well defined with minimal gradient. Bends, riffles and pools need to be avoided. They are usually built in a shallow section and provide a firm surface for crossing
Causeways are structures that raise the bed of the stream level. They allow water to go through a pipe underneath in low flow, but they go under water in high or flood flows They are suitable for wide shallow streams with gravel and soft substrate, and where regular and intensive use is not planned.
However, pipes can get easily blocked, especially if they confine flow, and smaller pipes do not favour fish or crayfish movement
Fords are crossings that are usually level with the bed of the stream with low flows passing over the structure rather than through a culvert below They are wet crossings so really can only be used in low or intermittent flows. They are suitable for waterways with low or intermittent flows with limited or no defined drainage channel and little or no vegetation Use angular rounded rock as it will resist movement better in high flows and if it can be located on bedrock this will minimise disturbance to fish passage
Bed-level crossings, such as fords, are more suited to rivers with low or intermittent flow and need to be situated on straight sections of river
Stock crossings are natural stream crossings that have little or no modification, only suitable for low or no flow situations Given the damage stock can cause to the waterway (water quality, pugging, and structural damage) the use of these crossings should be controlled and minimised.
When building a bed-level crossing, stabilise the bed using a coarse, compactible material and keep the crossing as low as possible (ideally less than 300 mm high). It is also a good idea to protect the bed and banks with rocks to prevent scouring and erosion and establish good native vegetation.
The approaches of any of these types of crossings also need to be designed and have suitable gradients to ensure that sediment-laden runoff doesn’t enter the waterway
When considering construction works in waterways it is important to seek technical advice and permits may be required from local and or state government agencies Visit: nre.tas.gov.au/conservation/flora-oftasmania/tasmanias-wetlands/wetlandswaterways-works-manual
Stock crossings need to be kept away from river bends and need to be used infrequently in streams with regular flow to avoid erosion and sedimentation of the waterway
Ongoing management of your riparian area
Excluding stock from the riparian areas is a good first step in improving farm management, but riparian areas, like other areas of the farm, need ongoing management and maintenance
Probably the biggest issue when stock are first excluded is the growth of exotic weeds that prevent native vegetation from becoming established The first two to three years after stock exclusion are the most critical time for weed management and maintenance. Identify your weeds and establish what is the most effective time to control them. Herbicides need to be registered for use near waterways and are generally best applied when the weed is actively growing, whereas manual or mechanical removal is often easier when the plant is dormant.
Coordinating weed control work with neighbours is also important when trying to tackle large weed infestations and when trying to prevent re-infestation upstream and downstream
Revegetation will help out-compete the weed problem, but plants and guards will require regular checking and may need hand weed control or slashing in the first couple of years to reduce competition while they get established
Improvement in your riparian habitat can be assessed in several ways:
Is the vegetation growing in three distinct layers? – Groundcover of reeds and grasses, a mid-storey shrub layer and a canopy tall tree layer.
2.
1 Is the vegetation indigenous to the area or at least native vegetation? – A good mixture of different native species that are common in the local area.
3.
Is the habitat continuous or fragmented? – Native vegetation is extensive and runs in a corridor either side of the waterway rather than weeds or sparse vegetation or isolated and scattered trees.
4
Is there a lot of plant debris on the ground and in the water? - Branches remain where they fall, ground has a lot of leaf litter, and the waterway contains woody debris.
5
Are native plants spreading and selfseeding naturally? – Both the midstorey shrub layer and tree canopy are showing signs of natural regrowth.
Weed competition for plantings can come from pasture grasses as well as weeds such as blackberry, willows thistles and foxgloves.
Climate change
Climate change will continue to impact waterways and on-farm managed riparian areas. More extreme climatic events, such as frequent and larger floods or extended dry periods, changes and increases in seasonality, will impact both riparian areas and ongoing farm management.
Riparian vegetation and adequate buffer widths in riparian areas will become critical in maintaining bank stability Connectivity in riparian areas and adequate vegetation cover will be essential to provide refuge for species and ensure adequate shading and maintenance of water temperatures
Long term species change of both flora and fauna may occur and it will be important to monitor your riparian corridors for species changes or weed invasion.
Climate change will also likely impact the hydrology of the waterway and the extraction patterns for both irrigation and domestic use. Sea level rise will also impact the hydrology and estuarine areas
Erosion and sediment loads will change and have impacts downstream in the catchments
Decision-making about farm planning, size and design of crossings, water supply sources and watering point locations etc. will need to adapt to changes in species composition, water supply and waterway erosion and sedimentation
Riparian areas in good condition will likely become important in providing landscape connectivity and refuge
Climate change and sea level rise will impact rivers and their estuaries, as well as any floodplain or foreshore development.
