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The Chapter 12 Land management on floodplains
Version 2, 31 March 2014
Notes for people reviewing this chapter
This is the second draft of a chapter on floodplain management prepared by Bruce Carey, retired
soil conservationist as a voluntary project for the Queensland government. It is for the
publication Soil Conservation Guidelines for Queensland. This will replace the 2004 publication
Soil conservation measures – a design manual for Queensland which is no longer available on
the Queensland government website, but can be downloaded chapter by chapter from the
Department of Environment and Heritage Protection library catalogue.
The current chapter on floodplain management in the soil conservation manual only refers to the
use of strip cropping on the Darling Downs floodplain. This chapter has a much wider focus
with the intention of capturing some of the experiences from the widespread floods over the last
few years.
With around 50 pages, this chapter is not intended for extension purposes. However it is hoped
that it has been written in a style that will be relatively easy for people with an interest in this
topic to understand. That could include landholders , students , academics, scientists, community
groups , deskbound people working in policy, regulation and funding programs in government
and NRM agencies.
Some of the diagrams have been copied from other texts. If they are used in the final publication
they will require a redraw (with appropriate recognition) for consistency.
I would be appreciative of any comments on this chapter by May 16, 2014.
Bruce Carey
[email protected]
12 Cringle Place
Mt Ommaney Q 4074
Phone 07-3376 1183
This information been produced to assist public knowledge and discussion, and to help improve
the management of floodplains and streams in Queensland. It has been prepared from the
publications listed under Further information with further input from people with experience in
the subject field.
The author accepts no responsibility or liability for any loss or damage caused by
reliance on the information, management strategies or recommendations in the guidelines.
Users of the guidelines must form their own judgement about the appropriateness to local
conditions of a management strategy or recommendation in the guidelines.
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Table of contents
List of figures ......................................................................................................................... 3
12.1 Introduction ................................................................................................................... 4
12.2 Floodplain evolution ..................................................................................................... 4
12.3 Soils and land use on floodplains ................................................................................... 7
12.4 Impacts of flooding in rural areas .................................................................................. 8
12.5 Erosion on floodplains ................................................................................................... 9
12.5.1 Gully formation on floodplains ......................................................................................... 11
12.6 Erosion control strategies for floodplains ..................................................................... 13
12.6.1 Surface drainage on floodplains......................................................................................... 13
12.6.1.1 Residual flow drains ............................................................................................................................. 15
12.6.1.2 Managing concentrated runoff flowing onto floodplains ................................................................... 17
12.6.2 Managing grazing lands on floodplains .............................................................................. 18
12.6.2.1 Watering points ................................................................................................................................... 19
12.6.2.2 Fence location ...................................................................................................................................... 20
12.6.2.3 Types of fencing for floodplains .......................................................................................................... 20
12.6.3 Managing extensive cropping on floodplains ..................................................................... 22
12.6.3.1 Cropping systems on floodplains......................................................................................................... 22
12.6.3.2 Direction of crop rows .......................................................................................................................... 22
12.6.3.3 Strip cropping........................................................................................................................................ 23
12.6.3.4 Land levelling ....................................................................................................................................... 29
12.6.4 Managing intensive cropping on floodplains ...................................................................... 29
12.6.5 Infrastructure on floodplains ............................................................................................ 29
12.6.5.1 Roads.................................................................................................................................................... 30
12.6.5.2 Farm roads and access tracks .............................................................................................................. 31
12.6.5.3 Railway lines ......................................................................................................................................... 32
12.6.5.4 Levee banks.......................................................................................................................................... 32
12.6.5.5 Irrigation structures ............................................................................................................................. 35
12.6.5.6 Weirs .................................................................................................................................................... 35
12.7 Riparian filter strips ..................................................................................................... 37
12.8 Wetlands ..................................................................................................................... 42
12.9 Legislation .................................................................................................................. 43
12.10 Further information .................................................................................................. 43
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List of figures
No table of figures entries found.
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12.1 Introduction
Queensland is a large state with many different floodplain landscapes with climates ranging
from wet tropical areas (average annual rainfall 2000 to 4000 mm) to dry inland deserts (average
annual rainfall 150 to 250 mm). Catchments east of the Great Dividing Range include small
coastal catchments as well as much larger catchments such as the Burdekin and Fitzroy. Coastal
catchments tend to have mor is e active streams with relatively narrow floodplains. Inland
streams flowing to the Gulf, Lake Eyre and the Murray Darling catchment are slower moving
and often have vast areas of floodplains.
An important function of a floodplain is to dissipate energy by reducing flow velocities Flooding
is a natural occurrence and is responsible for shaping our landscapes. Floodplains act like flood
mitigation dams by temporarily storing water on the floodplain to reduce flood peaks and the
downstream impacts of flooding.
Rural landholders are generally more aware of floods than are urban people. While floods in
urban areas are usually associated with disaster, floods in rural areas can provide benefits such
as a natural irrigation of agricultural lands. However, significant flooding events may cause
extensive damage. These floods can be decades apart and past lessons on management are easily
forgotten.
Floodplain management needs to consider a broad range of aspects including erosion potential,
downstream impacts, maintenance of biodiversity, flood dynamics, river geomorphology,
existing land uses and infrastructure requirements. This chapter provides guidance on the
management of floodplains in order to minimise the effects of soil erosion, to help stabilise
floodplains and to allow continued use of these highly productive lands. Related information is
provided in Chapter 13 Stream stability.
(#####Comment: the 120 page 2000 publication ‘Standing Committee on Agriculture and
Resource Management, ‘Floodplain management in Australia - Best practice principles and
guidelines’ (CSIRO Publishing) covers floodplain management in urban areas and makes
virtually no reference to rural floodplains).
12.2 Floodplain evolution
When we observe a stream and its floodplain, it is easy to think that they are static. But all
floodplains are evolving. They have undergone major changes to reach their current state and
they will continue to evolve in the future. Figure 12. 1 (based on an animation from the Victoria
Resources Online website) shows how a floodplain can evolve as a result of landscape uplift and
past changes in climate and sea level.
Over thousands of years a stream changes its location as it deposits alluvial sediment over its
floodplain. Erosion of the floodplain occurs if land uplift or falls in sea level increases the
erosive power of the stream. Alluvial (sometimes called fluvial) terraces can be formed by
down-cutting and bed erosion in a stream which can lead to increased velocity of a tributary,
causing that tributary to erode toward its headwaters. Such terraces are underlain by alluvial
sediments of variable thickness and may be well above flood levels even from extreme events.
Kapitzke, et al, 1998 pointed out that the conspicuous stream terraces at the back of some coastal
plains in North Queensland can generally be attributed to lower base levels associated with
lower sea levels during the last ice age.
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Figure 12. 1 Terrace development on floodplains
(Based on an animation from the Victoria Resources Online website)
http://vro.dpi.vic.gov.au/dpi/vro/wgregn.nsf/pages/wg_soil_maffra_geology_geomorphology_di
agram
The neighbouring Fitzroy and Burdekin Rivers in central Queensland have by far the largest
catchments of any rivers along the eastern seaboard. Jones, 2006, pointed out that these two
catchments were once small coastal catchments with their headwaters in the coastal mountain
range which is still present today. These coastal streams were short and steep in comparison
with those in the interior, allowing a more active erosional environment along the coast. As the
coastal streams expanded, the drainage divide moved rapidly westwards through gaps in the
coastal range. Stream capture began a phase of regional erosion, where rills and gullies
transported large quantities of sediments to the coast. Large volumes of sediment were
transported beyond the present coast during periods of low sea-level and contributed to a major
eastward bulge on the central Queensland continental shelf. (######Comment – contact
[email protected] if you would like a copy of Mal Jones’s power point ‘A tale of two rivers’)
Some other coastal streams have gone through a similar process. The lungfish and a turtle
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species in the Mary River were once only found in inland streams, but this changed when the
inland streams were captured by the Mary River (Peter McAdam personal communication).
The higher parts of catchments are usually steep areas where streams have a rocky base and
velocities can be high. Sediment is produced and moved to downstream parts of the catchment.
Sections of streams in higher areas can develop floodplains but they are usually narrow and may
have slopes of around 0.5%. Further down the catchment, sediment is deposited, the width of the
floodplain increases and land slopes may be around 0.1% or less.
As the slope in the stream gets less, streams start to meander on alluvial floodplains where the
sediment supply exceeds the capacity of the stream to transport it further downstream. Figure
12. 2 (Kapitzke, et al, 1998) shows several features associated with a stream on the floodplain
including meanders, billabongs (oxbow lakes) and point bars.
Figure 12. 2 The principal components of
meander geometry
Source Kapitzke, et al, 1998 - plate 2.6
Source : Rutherfurd, et al, 2000 pg 118
- ###########new diagram to be prepared incorporating both of the above diagrams
Geomorphological processes involved in the development of streams in north east Queensland
are described in Kapitzke, et al, 1998. He pointed out that meander wavelength is typically
around 10 times the channel width and about 5 times the mean radius of curvature. Such
regularity indicates meanders are not the result of purely random processes such as local
differences in bed and bank cohesion, but rather a function of an internal property of the stream,
such as excess free energy. By developing meanders a stream is able to increase its length and
reduce its gradient to minimise and uniformly spread energy expenditure along its course.
Rutherfurd, et al, 2000 described how coarser sediment (sand or gravel) can travel down a
stream network in pulses depending on the steepness in the channel and how fine the sediment
is. Sources of sand are gully erosion (especially in granite catchments) or widening of the
stream. The slugs can fill pools in a stream and destroy habitat. Slugs typically move slowly
downstream as a sediment wave. There can be rapid bed aggradation as the slug arrives,
followed by a gradual fall in the bed as the wave passes. Evidence of the movement of bed
material can be observed where there is infrastructure such as bridges, piers and pipes. As the
fine sediment moves through an armoured gravel bed can remain. Some sediment will be left
behind on point bars, as benches, and on the floodplains. If these deposits get colonised by
vegetation, then the channel will gradually narrow and a new sinuous channel will form.
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Brooks, et al, 2006 provided the following indications that a stream has been impacted by a
sediment slug:
 bed form homogenisation
 reduced channel capacity
 overbank sedimentation in the form of sand sheets or crevasse splays deposited on fine
grained floodplain material
 channel avulsion and/or excessive lateral channel migration
 braiding (i.e. multiple low flow pathways with in-channel bars dividing flow threads).
Sediment deposition in large streams leads to the development of braided alluvial channels
divided by islands or bars. Streams usually develop braided channels when sediment load is high
and coarse, banks are erodible, and discharge is high relative to slope. Similar processes lead to
the development of deltas such as that found at the mouth of the Burdekin River and some of the
rivers flowing into the Gulf of Carpentaria such as the Mitchell and the Gilbert.
Extreme floods can result in stream avulsion which is an abrupt change in stream course and
consequent abandonment of the pre-existing channel. It is usually the result of aggradation
which is the progressive raising of the stream bed due to sediment deposition. Vegetation
growing in a stream may have been there for 100 years but could be removed by an extreme
flood which makes drastic changes to the stream.
More information on sediment movement in streams is provided in Section 13.3 of Chapter 13
Stream stability.
12.3 Soils and land use on floodplains
Flood deposits can vary from clays to loams, sand and gravel. Coarser material is the first
material to be deposited when a stream breaks its banks. Finer material such as silt and clay are
deposited in back plains further away from the stream.
Some of the best agricultural lands are located on floodplains where deep, fertile soils have been
deposited by floods over thousands of years. The availability of irrigation, either from surface or
groundwater sources, greatly increases the value of floodplain soils.
The terraces shown in Figure 12. 1 will have different soil types depending on the age of the
terrace and its parent material. For example, some tributaries of the Lockyer have high terraces
of grey and brown clays (vertosols), lower terraces of black clays with silver leaf ironbark and
Moreton Bay Ash (vertosols) and more recent terraces with black and brown clays (dermosols)
(Bernie Powell Pers. Com)
The largest expanse of floodplain soils used for cropping in Queensland is on the Darling
Downs where the clay soils of the Condamine River floodplain stretches for a length of 220 km
(Warwick to Chinchilla) with a width of up to 40km (Figure 12. 3). This area is mostly used
forgrain growing and cotton.
Figure 12. 3 The Darling Downs floodplain
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In coastal areas, floodplains are used for growing sugar cane and horticultural crops. In the south
east corner, the floodplains of creeks like the Lockyer and Warrill are valuable areas for
horticultural production. In western Queensland and the Gulf, vast areas of floodplain are used
for grazing, and the St George–Dirranbandi area for irrigated cotton and summer grains.
12.4 Impacts of flooding in rural areas
Floods on floodplains used for grazing can damage infrastructure such as fences and roads.
Associated erosion can ‘consume’ riparian vegetation, productive pasture land in ‘frontage’
country, damage infrastructure such as roads, yards, and buildings, and degrade cultural sites.
However, flooding can also be very beneficial. For example, pastures in the Channel Country in
the Lake Eyre catchment of the arid south-west, sometimes receive a natural irrigation from
floods occurring as a result of heavy rainfall in upper catchments that could be 500 km away.
High velocity flows can have the following impacts on floodplains used for cropping:
 loss of top soil and associated nutrients, organic matter and biological activity
 loss or damage to crops from high velocity flows and waterlogging
 loss and damage to farm infrastructure including , roads, irrigation equipment, fences and
farm machinery
 sand and silt deposition affects land productivity and impairs the use of machinery
 debris deposition in cropping lands affects crop production and possible contamination
 prevention of access to land
 streambank erosion and the loss of adjacent land.
Silt deposits can usually be incorporated with existing soils relatively quickly and can help
rejuvenate soils to improve soil fertility. However, sand deposits on floodplain soils can
significantly reduce their quality and cause them to become ‘droughty’ because of reduced
moisture holding capacity (Wilson, 2013).
Downstream effects of flooding include:
 reduced water quality, and loss and damage to terrestrial and riparian ecosystems
 sediment and nutrient deposition in water courses, lakes and coastal areas
 loss of riverine, estuary and marine habitat and biodiversity
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
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damage to infrastructure
the spread of weeds.
Sediment in streams can emanate from hill slopes, floodplains or from the bed and banks of
streams. A high proportion of this sediment can be sourced from gully erosion and the erosion of
stream beds and banks during major floods.
In rural areas, hill slopes are mostly used for grazing. Such land is susceptible to erosion when
heavy rain occurs at times when there is minimal pasture cover caused by high grazing pressure.
Where grazed landscapes are susceptible to gully erosion this becomes a significant source of
sediment for streams.
In Queensland only 2.5% of the total land area is used for growing crops. The dramatic soil
losses that occurred on cultivated hill slopes prior to the 1980s are now generally a thing of the
past. This is due to the widespread adoption of soil conservation practices including the use of
stubble to protect soil in fallow periods (e.g. zero tillage in cereal crops and trash blanketing in
sugarcane), contour banks and farmers retreating from very steep slopes as a result of low
economic returns (Carey 2012). However continued vigilance is required. There is currently a
scarcity of people with the appropriate skills to plan, design and implement soil conservation
measures. As a result, some areas are showing signs of significant erosion which is readily
apparent from satellite imagery.
In considering the impact of soil erosion on the water quality of streams, the episodic nature of
soil erosion needs to be understood. There may be minimal soil loss in a catchment for several
years until a significant rainfall event occurs. The longest soil loss experiment ever conducted in
Queensland (1976 to 1990), was on a hill slope on cropped land on the eastern Darling Downs.
The most erodible soil treatment (stubble burnt) had soil losses that varied from an average of 78
t/ ha/yr from 1980 to 1983 to 14 t/ha/yr from 1984 to 1987 (Wockner and Freebairn 1991.
The rate of sediment movement through the stream network also needs to be considered. Particle
size is an important consideration and suspended sediment such as that produced from
dispersive soils will travel the greatest distance. Sediment does not have a direct pathway from
its source to its outlet and there are many locations where sediment can be stored. A lot of hill
slope erosion occurs as a result of localised storms and the runoff produced may not reach a
significant stream. It may be many years, decades or even centuries before the soil loss on a hill
slope reaches the catchment outlet (Finlayson and Silburn 1996).
12.5 Erosion on floodplains
Erosion on floodplains is associated with both streams and their floodplains. Streambank and
stream bed erosion is covered in Chapter 13, Stream stability. Flooding in Queensland is most
common in the summer months. However winter floods also occur, especially in southern areas
of the state.
The risk of erosion on floodplains depends on the land management practices that are used, the
velocity of the flows and the amount of incision in stream channels. In steeper landscapes,
channels have narrower floodplains where flood velocities can be high. In flatter landscapes,
floodplains are much wider allowing floods to minimise their velocity by spreading out.
The erosion risk varies considerably over different parts of a floodplain. Flow velocities can be
higher in channels on floodplains, where infrastructure concentrates flows and where local
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runoff might discharge onto a floodplain.
Fast flowing creeks flowing into rivers will have a high erosion potential. But if the flood in the
river rises, the inflow from the creek will be retarded because of the backwater effect and the
flow in the creek will become stationary.
No two floods are the same. Factors affecting the nature of a flood event include:
 the duration, intensity and extent of the rainfall
 the catchments where most rainfall occurred
 the direction of the rain producing system in relation to the catchment (e.g. whether it was
stationary, moving upstream or downstream)
 the ability of the soils and other catchment surfaces to accept rainfall (depends on soil type
and depth, vegetation, and the amount of soil moisture when the rainfall occurs).
When considering a large area like the state of Queensland, extreme flood events are more likely
to occur than we might expect. For every thousand streams in the state, there is a probability
that a one-in-1000 year flood event will occur, on average, once in each year. The event could
occur at the mouth of a river or on a small tributary in an upper catchment following an
exceptionally high local rainfall event. The concept of a ‘return period’ for floods is not well
understood by the general public. A cloudburst confined to the catchment of a small creek might
produce a one-in-100 flood event in that creek. However it would have minimal effect on a river
into which it flows.
A natural assumption would be that most flooding occurs when a stream breaks its banks.
However, on many floodplains the stream banks form elevated, natural levees that will be
among the last areas on the floodplain to become submerged. As a stream rises, the most
common source of initial flooding are low points where a stream can escape onto its floodplain.
This usually occurs where local runoff would normally flow into the stream. These points are
sometimes referred to as ‘breakout’ areas. As a flood gets higher, high risk erosion situations can
develop where streams follow preferential paths and take ‘short cuts’ (e.g. by bypassing a
meander).
Floodplains formed in past geological eras may have soils and topography that are characteristic
of a floodplain but are rarely, if ever, flooded. Some parts of a floodplain can be in a backwater
where velocities and the erosion risk are very low. On the vast floodplains of inland Queensland,
floods are usually slow-moving as they spread out over flat floodplains. Because of the low
velocities, they create minimal erosion risk even if there is very little pasture cover on the
floodplain. However significant erosion can occur in any areas of a floodplain where deeper
flows and higher velocities occur.
High risk erosion areas can be where creeks from upland areas discharge onto floodplains. This
situation occurs on the eastern slopes of the Darling Downs where creeks such as Linthorpe and
Ashall spread out onto ill-defined flow paths on the Condamine River floodplain (Figure 12. 3).
As these flows get closer to the Condamine River their velocities and erosion potential are
reduced because slopes are lower and the floods have had an opportunity to spread over a vast
area.
The risk of erosive flooding in the Brigalow floodplains between Dalby, Jandowae and
Chinchilla is lower than that for the creek outlets on the eastern Darling Downs. However, the
levelling of melonholes (gilgai) to make the land more suitable for cropping has reduced the
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amount of rainfall that is retained on the surface and increased the rates and volumes of flood
flows (McLatchey and Watts 1985).
12.5.1 Gully formation on floodplains
As discussed in Section 12.2 Floodplain evolution, stream incision is often a natural occurrence
which can be driven by processes occurring downstream rather than upstream. Where streams
are incised, there is a much higher risk of gully erosion on a floodplain and in the adjacent
catchment. Runoff from floodplains occurs as a result of local rainfall or when floodwaters are
draining off a floodplain as flood levels fall. Concentrated flows can be delivered to steep stream
banks by cattle pads, roads and tracks or levee banks. The ‘knick point’ where runoff enters the
incised stream becomes a cascading waterfall where gully formation will occur. Headward
growth of these gullies can cause them to retreat into adjacent river terraces and elevated
floodplains (Figure 12. 5).
In Figure 12. 4, the channel AB is initially flooded from a downstream direction when flood
flows from the creek escape at point A where there is less creek incision. As the depth of flow in
Swan Creek increases, flood waters enter the channel AB from upstream. Flows in the channel
will be deeper and faster than the flow on the land surrounding it and gullying can occur. As the
flood recedes, these channels drain the floodplain. Their saturated condition makes them
susceptible to further gullying especially if there is a head cut where it flows into the gully (point
A in Figure 12. 4). It is possible that the channel AB was once the main channel for the creek or
that it could become the main channel at some time in the future.
Figure 12. 4 Gully formation can occur in channels on floodplains
A system of advancing gullies (Figure 12. 5 and Figure 12. 6) on a floodplain can coalesce to
form a continuous front (Shellberg and Brooks, 2013). Examples of this process are found in
the rivers flowing into the Gulf of Carpentaria. Alluvial gullies are often associated with
dispersive soils. Runoff may be generated from local rainfall, river backwater, overbank
flooding and groundwater seepage. Growth of such a gully system would normally occur as a
flood recedes with floodwaters from the floodplain draining into the stream channel. Some
alluvial gullies drain away from main rivers and deposit sediment into local creeks and lagoons.
Figure 12. 5 Cross-section of an alluvial gully eroding into a terrace from a riverbank
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(Source: Shellberg and Brooks, 2013)
Figure 12. 6 Growth of an alluvial gully system on the Mitchell River floodplain
(Source: Shellberg and Brooks, 2013)
More detailed information on gullies can be found in Chapter 15 Gully control (Comment :Yet
to be written but will be based on a series of 20 factsheets that I was working on until my
retirement in November 2012. )
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12.6 Erosion control strategies for floodplains
Erosion control strategies on floodplains need to consider the erosion that occurs in channels as
well as the general removal of soil from the floodplain. Where floodplains are subject to erosive
flooding, the main objectives are to avoid practices that concentrate flood flows and to keep the
whole of the floodplain covered in suitable vegetation. Cultivation creates a layer of loose
topsoil above a layer of soil that has been compacted by the regular trafficking of tractors,
equipment and harvesters. Floods can easily strip away this valuable layer of topsoil exposing
the compacted soil which has some resistance to erosion. Zero tillage provides a more erosion
resistant layer of topsoil protected by standing stubble or crops planted into the stubble.
However young crops planted into a stubble-free paddock will be vulnerable to erosion.
Many floodplains are natural grasslands used for grazing. These close growing species provide
protection by reducing flow velocities and holding soil together. They also play a role in filtering
out sediment, nutrients and pesticides. When floodplains are cropped, the aim should be to
mimic this system by selecting appropriate crops and management practices.
While dense vegetation provided by grasses and crops protects soil from erosion on floodplains,
trees and shrubs play a different role in protecting against erosion on streambanks. Tree roots act
like reinforcing rods that interlock and hold the soil together. This is especially important when
stream banks have additional weight under saturated conditions. Trees and shrubs also reduce
flow velocities against the bank. The role of trees in stream stabilisation is discussed in
Chapter 13.
The following sections provide more information on erosion control strategies for floodplains:
 12.6.1 Surface drainage on floodplains
 12.6.2 Managing grazing lands on floodplains
 12.6.3 Managing extensive cropping on floodplains
 12.6.4 Managing intensive cropping on floodplains
 12.6.5 Infrastructure on floodplains
12.6.1 Surface drainage on floodplains
Most floodplains are traversed by channels which have an important hydrological and ecological
role. The flow in these channels is episodic and they are usually lined with a variety of close
growing species including grasses and weeds which provide erosion protection for channels
subject to erosive velocities. There are often trees and shrubs on the banks and sometimes in the
channel itself.
In local storm events, floodplain channels convey runoff from the local catchment. In this
situation, a densely vegetated channel provides erosion control and it functions as an effective
sediment trap. Like any filter, it can become overloaded. Sediment deposited in a channel can
lead to prolific grass and weed growth which will cause increased resistance to flow. This
improves the filtration affect but the next runoff event may attempt to find a new route. This
process is more likely to occur on very low sloping floodplains and where the channel has
minimal capacity. It explains how deltas evolve at the outlets of some rivers.
When a stream is in flood, floodplain channels can accommodate the initial overflow when the
flood commences to spread onto a floodplain. When the flood inundates the entire floodplain,
channels will carry a greater depth of flow and higher velocities than the adjacent parts of the
floodplain unless it is in a backwater. As a flood recedes, channels carry the residual flows back
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towards the stream. Channels also connect wetlands to streams.
Flows over floodplains follow preferential pathways influenced by channels, roads, railway
lines, levee banks and the varying amounts of resistance provided by vegetation. A diversion of
flood flows on higher parts of the floodplain may have a dramatic impact on the direction the
flood takes.
Waterways can be constructed on floodplains to facilitate surface drainage. Chapter 11
describes different cross-sections used for waterways in cropping lands. In upland areas, the
flow in waterways is normally contained by retaining banks as shown in Figure 12. 7. Such
waterways have gaps at intervals to allow the entry of runoff from adjacent contour banks.
Figure 12. 7 Waterways with retaining banks are not suitable for floodplains
Waterways with retaining banks are not suitable for floodplains because they interfere with the
spreading of floods during a major event. When a flood is receding they do not allow the entry
of residual flows to assist in draining the floodplain.
A grassed strip along a channel in land used for cropping is not likely to accommodate runoff as
the resistance to flow will divert runoff onto bare cultivation on one or both sides of the strip. If
the flow velocity is great enough, erosion will occur as shown in Figure 12. 8.
Figure 12. 8 Flows on floodplains seek out bare soil in preference to grassed areas
For channels to successfully accommodate runoff on floodplains they need to be subsurface with
no retaining banks (Figure 12. 9). If conditions permit, grass-lined channels should be slashed
regularly so that grass growth does not provide too much resistance to flood flows creating a
similar situation to that shown in Figure 12. 8. Sediment deposited in waterways should be
removed before it creates problems . Such work is best done in autumn after the greatest period
of flood risk and when there is sufficient warmth and moisture for new grass growth to occur. If
the grass cover is removed as part of the maintenance work, oversowing with a temporary crop
(e.g. oats in winter or millet in summer), may be necessary to provide protection until the grass
cover is re-established.
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Figure 12. 9 A parabolic shaped subsurface waterway
original ground level
Where a tree- lined channel on a floodplain has insufficient hydraulic capacity, a subsurface
channel could be constructed on one or both sides of it to augment the capacity of the channel.
Some texts (e.g. Lovett S and Price P (2001),) and Lovett S et al 2003) recommend that drains in
paddocks are shaded to reduce the temperature of water draining into adjacent waterways, and
also reduce the growth of in-stream nuisance plants and algae, which may also be flushed into
adjacent waterways during higher flows. However, flows in channels draining paddocks are
usually episodic. Dense grass growth maintained in a relatively short condition is best for
erosion control and filtration in waterways and channels draining paddocks. Shade provided by
trees will normally reduce grass growth. Trees would also inhibit access from earthmoving
equipment if it became necessary to desilt the channel.
Wetlands can be incorporated in surface drainage systems to improve the quality of runoff
before it leaves a property.
12.6.1.1 Residual flow drains
In some parts of a floodplain, residual flows may persist for several weeks after a major flooding
event or prolonged wet period. They can interrupt farming operations and cause waterlogging.
Residual flow drains (Figure 12. 10) have been used on the Darling Downs floodplain (any other
areas ???) to remove residual flows from cultivation allowing for more timely access after floods
and to even out moisture conditions over the cultivated area (Begbie 1977, Cummins and Bass
1978). If the trickle flows are saline, a residual flow drain will protect agricultural land from
contamination.
Figure 12. 10 Residual flow drain
crop
Residual flow drains on the Darling Downs have been stabilised using species such as kikuyu
and African star grass. In wetter areas, water couch and salt tolerant couch grasses could be
considered. The outfalls for the drains into streams may need to be stabilised by rock or other
stabilisation measures.
12.6.1.1.1 Planning residual flow drains
Residual flow drains should be co-ordinated from property to property and should be subsurface
so that they do not interfere with flood flows. On the Darling Downs,they have been located
along the length of the main flowpaths of some of the floodplain catchments. Their location and
effectiveness has been reliant on the goodwill and co-operation between the floodplain
stakeholders across whose land the residual flow drains have been constructed.
In general, residual flow drains should be located so as to run parallel to the natural flow path as
Draft - Soil Conservation Guidelines for Queensland
16
closely as possible. This minimises earthworks and decreases the potential for diversion of
flows. Changes of direction should be accomplished with gentle curves rather than sharp bends
to avoid erosion-inducing turbulence. The risk of erosion in a residual flow drain can be
minimised if the drain is not located in the deepest section of the flood flow where high
velocities may occur during floods. With approval and co-operation from Local Government,
residual flow drains may be constructed along roadsides. However, they should remain separate
from road table-drains to avoid destabilising the road as a result of long-term saturation of
foundations associated with residual flows.
Residual flow drains may be subject to Local Authority by-laws pertaining to levee banks. In
catchments where Water Resource Plans have been approved under the provisions of the Water
Resources Act 2000, there may be controls on new works requiring approval as assessable
development if such works are likely to increase the ‘take’ of overland flow water.
12.6.1.1.2 Design of residual flow drains
Residual flow drains should be subsurface without any banks above normal ground level that
would divert flood flows. They are at risk of erosion during flood events especially when they
flow between well-advanced crops which have a high retardance to flood flows.
There are no hard and fast rules for determining the capacity of a residual flow drain. If possible,
observations of the trickle flow should be made to determine the required capacity. Bass and
Cummins (1978) quoted a ‘rule of thumb’ method for drain design for the Pittsworth Plains as
0.21 m3/s per 1000ha for upland catchments plus 0.07 m3/s per 1000 ha for plains catchments.
Residual flow drains can be stabilised using species such as kikuyu and African star grass. In
wetter areas, water couch and salt tolerant couch grasses could be considered (Bass 1985).
Where spring flows persist, it may not be possible to maintain a permanent vegetation cover and
designing the drain for bare soil conditions may be the only option.
Residual flow drains with a bare channel are vulnerable to erosion especially considering the
saturated soil conditions that would exist during flooding. Because they are located on
floodplains where slopes would normally be less than 0.3%, it is possible to ensure that
shallower flows can be kept below a velocity of 0.3 to 0.4 m/s. Additional protection could be
provided with drop structures or sod chutes with energy dissipaters.
Outfalls are one of the most important sections of a drain. They allow water to free-flow from
the drain into a disposal area. Outfall into deeper drains, pump sumps, etc, need to be rock
protected to prevent erosion or other suitable stabilisation measures.
12.6.1.1.3 Construction of residual flow drains
Drains should be constructed during dry periods with very broad-sided batters that can be
cropped part way down the channel sides to avoid scours developing from the channel sides
back into the cultivation.
Drains generally produce significant amounts of spoil because they are constructed below
normal ground level. This spoil should be placed so as not to interfere with overland flow paths.
It should be spread as shallow fill on adjacent cultivation, placed as spoil banks aligned with the
direction of flow, or removed totally from the area. It is inadvisable to construct a raised road
parallel to the drain as this can interrupt or divert flow, or induce erosive flow velocities as a
consequence of increased depth of flow.
Draft - Soil Conservation Guidelines for Queensland
17
Crossings over residual drains should be constructed so as not to affect flows in the drain.
Ideally, crossings should be constructed as gravel inverts either at or slightly above (max. 100
mm) bed level of the drain. The thickness of gravel required will depend on the weight and
frequency of traffic; a minimum of 200 mm depth of gravel is necessary, but for heavy traffic
loading, a thickness of up to 300 mm over a suitable geofabric would be required. Culverts
require sufficient cross-sectional area to pass flow with minimal surcharge level upstream of the
structure. Box-shaped culverts are preferable. Professional design will often be necessary.
12.6.1.1.4 Maintenance of residual flow drains
Drains need to be well maintained to retain their function. Vegetation should be managed by
slashing, spraying, or occasional grazing. Silt deposits should be removed. In many cases, it will
be necessary to virtually reform the drain at regular intervals. Ancillary structures such as inlet
works, outfalls and drop structures also require ongoing maintenance. When the channel is wet,
vehicles should only cross drains at a constructed crossing. Access for maintenance is not
possible until the drain has dried out.
12.6.1.2 Managing concentrated runoff flowing onto floodplains
There are a number of options for dealing with the situation where concentrated flows spill onto
floodplains. A grass spreader outlet (Figure 12. 11) may be used at the point where a waterway
meets a strip cropping area. Another option is to design and build a dam with provision for
bywashes on either side discharging into a subsurface channel or sill. Maintenance of these
outlet areas is critical. They are subject to high rates of sedimentation, which may direct flows
away from the grassed area and onto adjacent areas that will be vulnerable to erosion.
Relatively narrow strip widths are required immediately below any spreading devices to
accommodate the high velocity flows. The waterway delivering the runoff to the grass spreader
requires regular maintenance including slashing, strategic grazing and desilting.
Figure 12. 11 Grass spreader at a waterway outlet onto a floodplain
Draft - Soil Conservation Guidelines for Queensland
18
Strip cropping
(Narrow strips with erosion resistant crops and high levels of anchored stubble)
Monto Vetiver Strip
Monto Vetiver Strip
Grass
spreader
outlet
Grassed
waterway
from
upland
catchment
12.6.2 Managing grazing lands on floodplains
This section should be read in conjunction with Section 12.5 Erosion on floodplains.
On floodplains used for grazing, the most erosion susceptible areas are usually riparian land
often referred to as ‘frontage country’. Streambanks and frontage country often have steep
slopes which greatly increases the erosion potential.
Riparian areas need careful management. Livestock are attracted to them because of the
availability of water, shade and favourable pastures. Heavy grazing pressure can make these
areas subject to severe erosion. Streams with high or wooded banks have fewer points of access
and cattle can incise paths when scrambling up or down banks, leading to stream bank and gully
erosion.
The erosion in riparian areas is often associated with local rainfall rather than from flooding.
High grazing pressure results in bare soil which is vulnerable to erosion from raindrop impact
and readily produces runoff which soon concentrates to cause erosion. Areas with dispersive
soils are especially vulnerable.
The relative roles of trees and grasses in the control of erosion on riparian areas needs to be
understood. As discussed in Chapter 13, tree roots help to strengthen steep streambanks.
However bare soil under trees is very susceptible to erosion. Groundcover species such as
grasses provide protection by absorbing raindrop impact and reducing the erosion potential of
overland flows. Gully formation is common in land adjacent to incised streams. Dry gullies
flowing into streams can best be managed by encouraging grass growth rather than tree growth.
Draft - Soil Conservation Guidelines for Queensland
19
Persistent, heavy grazing pressure can lead to woodland thickening in both frontage land and the
catchment in general (Department of Environment and Resource Management 2011). A
resultant lack of fire and reduced competition from the herbaceous layer allows woody plants to
proliferate. This can lead to:
 reduced grazing value
 reduced soil surface cover
 increased risk of erosion
 colonisation by pest plants
 limited access for management purposes (e.g. mustering and weed control).
Any clearing of regrowth to manage woodland thickening needs to be carried out in accordance
with the Vegetation Management Act 1999.
(#######Comment: the following information is extracted from the DERM 2011 publication,
Managing grazing lands in Queensland)
Fencing riparian zones and providing off stream water points can have a number of benefits
associated with restricting stock access to the area, including:
 preventing the disturbance and bogging of the stream bed
 preventing the formation of cattle pads that can cause gullies
 assisting the rehabilitation of gullies
 improving water quality
 reducing the spread of weeds
 making stock mustering easier.
Fencing of riparian areas allows grazing pressure to be more closely controlled. Restricting the
grazing of riparian areas to early in the dry season can have the following benefits:
 It directs grazing onto the green leaf of pasture grasses (reducing the amount of browsing
on trees and shrubs).
 High levels of ground cover are maintained (pastures have had a chance to be spelled
over the wet season).
 It takes advantage of high feed quality compared to surrounding areas.
 Reduces the risks of erosion damage and sedimentation of the stream which can result
from stock accessing saturated streambanks.
More information on this topic can be found in Chapter 9 Impacts of land management practices
on riparian land in Principles for riparian lands management (Lovett S, and Price P. (eds)
2007).
12.6.2.1 Watering points
The high costs associated with fencing limit the amount of riparian land that can be protected.
This is especially so on large outback properties where there can be significant areas of
floodplain or riparian land. Off stream watering points (troughs) at permanent water holes, can
be used as an alternative to fencing, as they reduce the time cattle spend in creeks and water
holes. In many cases, stock prefer to drink from well-placed troughs, particularly if access to the
watercourse is difficult, water quality is low, or there is danger (e.g. crocodile habitats).
Where streambanks are susceptible to erosion, damage can be minimised if stock are provided
with access at a carefully selected section of the stream . Boggy areas and bends in stream
Draft - Soil Conservation Guidelines for Queensland
20
should be avoided. A formed access point requires a graded slope into the stream. The surface of
the waterway access point is then protected by using concrete, compacted gravel, logs or similar
materials to form a walkway. Cross-stream fencing may be required to prevent animals
wandering along the streambank.
12.6.2.2 Fence location
Strategies for fencing riparian areas include:
 establishing a frontage paddock by fencing out the upland areas adjacent to the
floodplain
 fencing out high priority water bodies such as natural springs
 fencing out areas that are especially vulnerable to gully and streambank erosion
 fencing the immediate riparian area (refer to Section 13.5.4 Riparian zone widths for
streambank stabilisation in Chapter 13 Stream stability).
During a flood, fences can collect debris, such as dead grass, and the resultant increase in force
can cause a fence to be flattened or swept away. If a fence is not a boundary fence, consideration
should be given as to how the fence is aligned to the direction of the flood flow. Fences at right
angles to the direction of moving floodwaters are most susceptible. When planning or realigning
fences, it may be possible to reduce the length of fences exposed to flood flows. Fences parallel
to the flow and fences in a flood backwater will suffer minimal damage.
Sections of fences that are regularly damaged by floods can be constructed so that they lay flat
during a flood. In accessible areas where a significant flood is expected, it may be an option to
remove the wire from some sections of the fence before flood levels rise.
When fencing off riparian areas, fences should not be too close to the stream . Section 13.5.4
Riparian zone widths for streambank stabilisation in Chapter 13 Stream stability provides
guidance on a suitable widths for riparian areas. A well fenced riparian area can be used for
strategic grazing. It also means the bends and curves of the stream can be cut out and this
reduces the construction and maintenance costs for the fence.
Where it is necessary to fence down a streambank, the amount of disturbance necessary can be
reduced by using existing live trees as fenceposts (tree to tree) to avoid the need for tree clearing
and soil disturbance.
12.6.2.3 Types of fencing for floodplains
Lovett, et al, 2003 described a number of fencing options for use on floodplains and riparian
areas.
Hanging fences can be built across narrow streams so that animals cannot walk along the stream
to bypass fence lines Hanging fences are usually suspended from steel cable or multi-stranded,
high-tensile fencing wire strung across the stream. In order to prevent them being damaged or
destroyed during floods, they have hanging panels which are designed to ride up with heavy
flows and return to their normal position once the peak flow has passed. The hanging panels are
usually galvanised iron or ringlock hinged across the cable. They may be damaged by debris
coming down in a big flood, but the damage is usually not severe and the panels can be cheaply
and easily repaired or replaced.
Electric fences can be used along and across streams. An electric fence is not only much cheaper
to construct, but it is much cheaper to repair following an unexpectedly large flood. Steel
Draft - Soil Conservation Guidelines for Queensland
21
droppers will usually survive a flood unless hit by large debris, so it is often only the cost of a
length of electric fencing wire that has to be covered. When placed across the stream a steel
cable is used as a horizontal support, from which steel chains or hinged panels are hung. The
chains and/or panels are separated electrically from the grounded cable, and all are electrified
and able to move independently, allowing floodwater and debris to pass underneath. Portable
electric fences are another option that allow landholders to control stock movement along
streamsides, and have the added advantage that they can be quickly moved if there is advance
notice of a likely flood peak.
Drop fences are designed to be either manually operated (dropped) before a flood, or to drop
from their anchor points under the pressure of floodwater and debris (Figure 12. 12). Once the
floodwaters have receded, these fences are quick and simple to pull back up and reattach to their
anchor points. They can also be dropped to allow stock or vehicle movement from one paddock
to another to minimise the need for gates.
Figure 12. 12 Drop/lay down fence
Source: Lovett S, Price P and Lovett J 2003), Managing Riparian Lands in the Cotton Industry,
Cotton Research and Development Corporation
Electronic fencing has been developed overseas as an alternative to fixed fencing, particularly
for cattle. The stock wear a receiver initially developed in the form of an ear-tag, and transmitter
boxes are located to form a boundary between the riparian area and the rest of the paddock. The
transmitters emit a continuous signal which defines the boundary. The ear-tags respond by
producing firstly an audio signal, followed by an electric stimulus to the animal’s ear if it
attempts to enter the exclusion land. Tests have shown that cattle quickly get used to this form of
fencing, which is cheaper than conventional fixed fences and can be moved quickly in the event
of a flood peak. This type of fencing is under active development in Australia, with the aim of
Draft - Soil Conservation Guidelines for Queensland
22
bringing the price down to a level at which it can be adopted widely. (Comment - this paragraph
was written in 2003(Lovett et al) - has this technology advanced???????)
12.6.3 Managing extensive cropping on floodplains
This section should be read in conjunction with Section 12.5 Erosion on floodplains and Section
12.6.1 on Surface drainage.
A key strategy for controlling erosion on floodplains is to reduce flow velocities by encouraging
flood flows to spread out over the floodplain. Cropping practices play a major role in achieving
this but roads, railway lines, fence lines, levee banks and irrigation infrastructure must also be
considered. Such structures can contribute to erosion by diverting and concentrating flood flows.
The effective control of erosion on floodplains requires the co-operation of landholders,
agencies and companies responsible for infrastructure, and all levels of government. Soil
conservation measures on floodplains need to be planned and implemented in a co-ordinated
manner. Affected landholders and agencies need to work together to ensure that floodwater is
spread over the entire floodplain. A piecemeal approach is seldom effective in managing
widespread flooding.
12.6.3.1 Cropping systems on floodplains
Where broadacre crops are grown, practices such as zero tillage and strip cropping are used for
erosion control. In the areas of highest risk, the best strategy may be to change the land use to
the permanent cover provided by a native or sown pasture.
In broadacre situations, crops with multiple stems and leaf material that remain intact after
harvest provide the most resistance to flood flows and the best erosion protection Such crops
include the summer crops of sorghum and maize and the winter crops, wheat and barley. Crops
like sunflower, cotton, mung beans and chick peas provide less protection because they have
single stalks and their mature leaves readily disintegrate. A cover crop such as wheat can be
planted into cotton stubble to provide rapid protection after harvest.
Zero tillage is recommended because it allows stubble to remain anchored into the soil. Loose
stubble can be a hazard on a floodplain when it floats downstream in a flood and gets deposited
against a standing crop, a fence line or where it blocks a road cross-drainage structure. This
leads to obstruction of flows and their diversion.
Zero tillage should also be combined with opportunity cropping—planting a crop whenever soil
moisture reserves are considered sufficient. This leads to an increase in cropping frequency (e.g.
three crops in two years).
Heavy farming equipment such as tractors and harvestors can cause depressed wheel tracks
especially under moist conditions. These tracks can lead to diversion and concentration of flows.
Their impact can be minimised if they are at right angles to the flood flow or by levelling them
with specialised renovating machinery.
12.6.3.2 Direction of crop rows
Flowing water will always take the easiest pathway. Floods seek out paddocks or parts of
paddocks that offer the least resistance to flow such as bare fallows or crops that provide
minimal cover. Floods can be diverted by crops depending on how they are orientated to the
contour. Figure 12. 13 compares three different directions for crops in relation to flood flow.
Draft - Soil Conservation Guidelines for Queensland
23
Figure 12. 13 How crop direction affects flood flows
The layouts shown in diagrams (a) and (b) accept flood flows without diversion, whereas the
layout in diagram (c) can lead to a diversion of flood waters.
Diagram (a) shows floods flowing through alternating summer and winter crops that are grown
in a rotation on the contour. Strip cropping (Figure 12. 14) has been used since the late 1950s to
control erosion on parts of the floodplain subject to erosive flooding. It can be readily seen on
satellite imagery around the localities of Dalby, Jimbour, Norwin and Bongeen. More
information about strip cropping is provided in the next section.
Diagram (b) shows crop rows in the same direction as flood flows. This practice has been
adopted by a number of farmers in recent years in conjunction with controlled traffic farming
(CTF), zero tillage and opportunity cropping. ‘Up and down’ directions can improve drainage in
wetter years on lower sloping parts of the floodplain. A potential concern where the floodplain is
susceptible to erosive flooding is that floods could cause erosion by flowing down wheel tracks.
Such paddocks would also be vulnerable if a crop was not planted because of drought. In a strip
cropping system half of the strips could still provide cover in this situation.
Diagram (c) shows how floods can be diverted by crops grown in rows at a diagonal to the
contour. This is likely to lead to a concentration of flows with the potential for serious erosion. It
can also lead to the diversion of flows out of their natural catchments and create problems for
downstream landholders. Satellite imagery often shows strip cropping following quite different
directions in the same locality. In many cases these strips will have been implemented without
the use of topographic data and without taking into account the need to manage flows across the
whole of the floodplain.
12.6.3.3 Strip cropping
Strip cropping is the growing of alternating strips of crop on the contour at right angles to the
flood direction. The aim is to reduce flow velocities by encouraging floods to spread rather than
concentrate. It is used to control erosive flooding in broadacre crops on Darling Downs
floodplains. For it to work effectively, crops need to have good resistance to flood flows such as
that provided by some winter and summer cereal crops.
Strip cropping ensures that there is always a crop or standing stubble in every strip to help
spread water and reduce flow velocity. Strip cropping can provide protection in a drought when
Draft - Soil Conservation Guidelines for Queensland
24
alternate strips cannot be planted, or when an erosion-inducing crop is planted. It can also
improve water quality by filtering out sediment, nutrients and pesticides. Since strip cropping is
carried out in parallel strips, it is compatible with controlled traffic farming (CTF).
Local flooding can sometimes occur when there is heavy rainfall in an upland catchment but
little rain on the floodplain. In this situation, strip cropping can spread floods and provide a free
natural irrigation of crops. Strips with a mature or harvested crop may often have significant
cracks which can accept runoff from adjacent strips that are in fallow and more likely to produce
runoff.
Minor drainage lines passing through strip cropping can become waterlogged in wet years. This
can lead to some crop loss and restrict machinery access until the soil dries out. However, these
low spots may have higher yields in drier years. They can be eliminated by land levelling and
may tend to heal naturally when sedimentation occurs when flows meet strips of crop.
Strip cropping requires a high level of management. Care needs to be taken to ensure spray drift
does not occur from one strip to another. Shields, droplet size and attention to wind speed and
direction are part of the management options.
Strip cropping should be combined with conservation cropping and crop rotation techniques to
ensure that there is always a crop or standing stubble in every strip to help spread water and
reduce flow velocity. Stubble needs to be anchored to avoid it floating and subsequent
deposition where it may cause problems such as the blocking of road cross-drainage structures.
Incorporating opportunity cropping into a strip cropping system provides greater protection from
erosive flooding. Opportunity cropping is the practice of planting a crop whenever soil moisture
reserves are considered sufficient, rather than according to a rigid rotational pattern. This leads
to an increase in cropping frequency (eg. two crops in three years) and greater levels of surface
cover.
Figure 12. 14 Strip cropping on the Darling Downs floodplain
As well as controlling soil erosion, strip cropping improves water quality by assisting in filtering
out sediment, nutrients and pesticides.
For more detailed information about strip cropping, the following publication is recommended:
Better Management Practices – Floodplain Management on the Darling Downs, published in
1999 by the Queensland Department of Natural Resources.
Draft - Soil Conservation Guidelines for Queensland
25
Strip cropping layouts need to be designed and implemented in a co-ordinated manner. The
adoption of strip cropping practices on a single property will have limited overall benefit. All
affected landholders, including farmers, local and state governments must work together to
ensure that floodwater is spread over the entire floodplain. Co-ordinated planning and
implementation of strip cropping of the whole floodplain is required to minimise the effects of
structures such as roads, railway lines, irrigation infrastructure and levee banks that may divert
and concentrate flood flows.
12.6.3.3.1 Strip cropping widths
Some attempts have been made to develop formulae to determine recommended strip widths
based on criteria such as land slope, flow rates, soil erodibility, crop rotations and management
(Ruffini et al 1988). Many of these formulae were developed when bare fallows were normal
practice. The widespread adoption of zero tillage has meant that entire properties may be
protected by crop or standing stubble at the one time. If such a cropping system could be
guaranteed, irrespective of seasonal conditions, then strip cropping would not be necessary,
provided the crop rows were at right angles to flood flows. However strip cropping provides the
following benefits:
 Strips under erosion-inducing crops, such as sunflower and cotton, may have crops that
provide protection in the adjacent strips.
 Strips remaining in fallow because of drought may be protected by crop stubble in adjacent
strips.
Table 12.1 is a guide to strip cropping widths based on the topographic situation and the level of
protective cover provided by the crop rotation and management system. The determination of
the level of protective cover is somewhat subjective but some guidance can be obtained from
Tables 12.2 and 12.3.
It is necessary to refine the width of the strip to achieve compatibility with the various widths of
the commonly used machinery on the property.
Table 12.1 Recommended strip cropping widths for floodplains subject to erosive flooding
Level of protective Recommended strip cropping width
(metres)
cover provided by
the crop
Slopes of 0.4% to 0.5%
Slopes of 0.2% to 0.3%
Slopes of 0.1% and less
management
Plains in lower areas
Creek outlets and narrow
system —refer to
Plains – upland flow
subject to widespread
valley floors
tables 12.2 & 12.3
inundation
High
50
80
100
Moderate
25
40
50
Low
Not recommended
Not recommended
30
Table 12.2 Guide to determining the level of protective cover provided by a crop management system
Level of protective cover
Stubble
provided by the crop
Cropping system
management
management system
High proportion of crops providing high cover levels.
High
Zero tillage
Opportunity cropping whenever possible.
Moderate
Reduced tillage
A moderate proportion of crops providing high cover
Draft - Soil Conservation Guidelines for Queensland
Low
Bare fallow
26
levels. Low levels of opportunity cropping.
One crop per year with a high proportion of crops
providing low levels of cover.
Table 12.3 Level of protective cover provided by crop type.
Level of protective cover Crops
Comment
wheat, barley, sorghum,
Crops grown in wide rows provide less
High
maize
protection
Legume crops leave little or no stubble after
sunflowers, chick peas,
harvest. Cotton is an effective crop at slowing
Low
cotton, mung beans
floodwaters during active growth but the stubble
provides little protection after harvest.
12.6.3.3.2 Strip cropping direction
Detailed topographic and flood flow-path information is necessary in order to determine the
most appropriate direction for strips on floodplains. Ideally, topographic information should
have an interval of 0.25 m or less for slopes of less than 0.5%.
If it is necessary to locate strips in different directions due to a change in the direction of
flow/slope, then a pivot line is required at the change in direction (Figure 12. 15) For the width
of strips on either side of the pivot line to be equal, the angles at which the strips deviate from
the pivot line must also be equal. The minimum angle for a pivot is dependant on machinery
width, but is generally about 70° as sharper angles will leave unplanted headlands especially
when multiple-hitch machinery is used.
If the pivot angles are unequal it will be necessary to manage the strips on either side of the pivot
line as separate blocks. These systems are more difficult to manage as it is necessary for the
pivot line to become a headland where tractors and machinery can turn around. With no crop
growing on the pivot line, it could easily become a route for floods to follow and cause erosion.
Figure 12. 15 Strip cropping layout with a pivot to provide for change in strip direction.
Draft - Soil Conservation Guidelines for Queensland
27
36
0.
2
5
36
0.
0
359
key
.75
line
359
.5
80¡
80¡
359
.0
35
9.
ot
lin
e
25
piv
358
.75
Source: Eacott 1979
In order to improve workability and ensure that strips are located on the contour, it may be
necessary to insert a correction strip as shown in Figure 12. 16. Correction areas would normally
be used for growing grass. Cropping them could be an option if they are of sufficient size.
Figure 12. 16 Correction area in a strip cropping layout
n
co
ur
to
lin
e
correction
area
(Source: Macnish 1980)
In Queensland, it is generally not practical to use strip cropping directions that would provide
Draft - Soil Conservation Guidelines for Queensland
28
protection from erosive winds. The heavy texture of most cropping soils in Queensland means
that they are not susceptible to wind erosion. Such layouts would need to be at right angles to
erosive winds (generally from the south-west) and would not be compatible with any strips or
runoff control measures that may be required for control of erosion by water. The adoption of
conservation cropping measures should be sufficient to provide protection against wind erosion
in the Queensland environment where wind erosion is not considered to be a serious problem in
cropping lands
12.6.3.3.3 ‘Give-and-take’
‘Give-and-take’ refers to an exchange of land between neighbours to help the spread of
floodwaters. Problems often arise where two strip cropping layouts meet at a boundary line.
There is usually an access track on both sides of the boundary where water tends to concentrate,
causing washouts. This can be overcome by neighbours interlocking their strip cropping layouts
and each landholder farming an equivalent area of their neighbour’s land as shown in Figure 12.
17. Alternative means of access in strip cropping layouts is described in a later section.
Figure 12. 17 ‘Give and take’ to overcome concentrated flows along fencelines
In some strip cropping layouts, the strip will meet the fence line at very sharp angles creating
corners that are difficult to work. These corners are often left to grass up, creating potential weed
problems. By the use of ‘give-and-take’ with a neighbour, these problems are overcome (Figure
12. 18).
Figure 12. 18 ‘Give and take’ to avoid difficult corners
Before
Areas
difficult
to work
or allowed
to grass up
After
Boundary line
Difficult corners removed
by give and take
Draft - Soil Conservation Guidelines for Queensland
29
12.6.3.4 Land levelling
The presence of rills and gullies in a paddock can make it difficult to achieve an effective spread
of flood flows and make crop management more difficult. They are also susceptible to further
erosion during a flooding event. Runoff flowing in such depressions may result in poor crop
establishment or even the need to replant a crop. Old headlands and fencelines can also lead to
ponding, waterlogging and flood diversion.
Land levelling combined with strip cropping can assist in achieving a more effective spread of
floodwaters. It may be carried out with the use of a land plane drawn behind a tractor, scraper or
tractor drawn bucket. The use of laser equipment assists the process.
To have minimal impact on natural flow paths, all land levelling should be carried out in such a
way that the down-field and cross-field slopes align with the natural slope of the land. Land
levelling should be designed to blend with natural surface profiles both within and surrounding
the block. This will avoid significant differences in finished heights on the block boundaries,
which can promote concentration of flows and erosion.
In many parts of the Darling Downs floodplain where there are no stock on farms and no stock
routes, fences have been removed. Removal of fences must be accompanied by levelling of soil
build-up and erosion scours along them. Where fences have been removed, corner posts should
be retained along portion boundaries to prevent the need for a re-survey on the sale of the
property and avoid encroachment of cultivation onto road reserves
12.6.4 Managing intensive cropping on floodplains
This section should be read in conjunction with Section 12.5 Erosion on floodplains and Section
12.61 on Surface drainage and Chapter 14 Horticultural production and soil conservation.
Alluvial soils on valley floors and floodplains are ideal locations for horticultural crops because
of the fertile soils and availability of irrigation. Because of the low slopes, the risk of erosion is
minimal, provided the land is not subject to erosive flooding.
Where the risk of erosive flooding is high, an alternative land use such as a permanent pasture
should be considered. Levee banks can be used to protect some paddocks, but they may increase
the risk of erosion in adjacent areas as discussed in Section 12.6.5.4 Levee banks. Drainage lines
between blocks of crops also need to be managed to minimise erosion. A suitable buffer width
should be maintained on all drainage lines and riparian areas (refer to Section 13.5.4 Riparian
zone widths for streambank stabilisation)
Horticultural crops are generally more susceptible to erosion then close growing cereal crops
such as wheat barley and sorghum. Strip cropping is used to spread flood flows in cereal
growing areas on the Darling Downs floodplain but it has not been adapted for use in
horticulture on floodplains. The use of beds or mounds to improve drainage for horticultural
crops may also lead to concentration of flood flows and erosion and would limit the
effectiveness of strip cropping.
12.6.5 Infrastructure on floodplains
Roads, railway lines, fences, levee banks and irrigation structures can significantly interfere with
the natural spread of floodwaters. This can lead to concentration of floodwaters and increase the
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risk of erosive flooding and damage to other lands and properties. This topic is also covered in
Chapter 16 Property infrastructure.
12.6.5.1 Roads
Roads can modify flood flows depending on their height above ground level, which is normally
300 mm to 600 mm, and their orientation towards the direction of the flood flow. Figure 12.19
shows how the direction of a road might be orientated within a floodplain landscape. The section
of the road A—B is running directly up and down slope and would cause no diversion of floods
no matter how elevated it was. The section B—C is running diagonal to the slope and may cause
significant diversion. The section C—D is on the contour and at right angles to the direction of
flood flow, and should not cause diversion of flow providing there is adequate cross-drainage.
Figure 12.19 The orientation of a road to the contour affects its impact on flood flows
D
C
contour lines
B
A
direction of flood flow
(Source: Marshall 1988)
On the wide Darling downs floodplain, where there are numerous properties, roads cross the
floodplain in a variety of directions in relation to the topography. But in most floodplain
situations, roads take the shortest route across the floodplain which is at right angles to the
direction of flow (C to D in Figure 12.19). Such roads are provided with culverts or inverts, to
accommodate lower flows. In major floods, the road can act like a weir with floodwaters
flowing over the road surface. A road in this situation needs to be designed to minimise the
erosion risk created by flow through the culverts or the flow passing over the road. A series of
box culverts (rectangular shape) are preferred to pipe culverts because they allow for a lower
road profile and they allow for a better spread of flows to reduce their erosion potential
downstream. Where a road is causing major erosion or pondage problems, it may be possible to
relocate the road.
While road cross-drainage structures can lead to erosion downstream, they can also halt the
advance of a gully head advancing up a stream by performing the role of a drop structure. Their
success in doing this depends on the structure not being undermined by the advancing gully.
Low floodways may be unacceptable for major highways if they flood too frequently and create
road safety issues. On sections of the Darling Downs floodplain where erosive flooding is a
problem in cropping areas, a number of roads have been lowered to 100—200 mm above natural
ground level (Figure 12.20). Such a road acts as a long floodway and creates much less backup
of water than a raised road. Floodwaters flow over its full length in a shallow controlled flow.
As the overfall below such a road is small, turbulence is minimal and less damage will be
experienced on the cultivated land below. Low roads require adequate signage and should have
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a cross-fall to prevent water lying on the road after the flood has passed. Where it may be
necessary to include an invert in such roads, the invert level should be no more than 100mm
above natural ground level.
Figure 12.20 Floodwaters spreading across a low level road on the Darling Downs
12.6.5.2 Farm roads and access tracks
The same issues that apply to public roads can also apply to farm roads and access tracks. Roads
connecting a farmhouse and buildings on a floodplain to a public road are sometimes built to the
same height as the public road to maintain access during a flood. However such access can cause
significant divergence of flood flows depending on how it is orientated to the contour. Where
flow diversion is likely, formed property roads on floodplains should be constructed no more
than 100 mm above natural ground level.
Unformed roads and access tracks are often below normal ground level after a period of use and
maintenance by a grader. Roads in this condition concentrate runoff and flood flows and can
soon become an eroding gully. Low banks, or ‘whoa-boys’, placed at intervals across such roads
and extending into adjoining cultivation will minimise this problem. ‘Whoa-boys’ on
floodplains should be no more than 200 m apart so that runoff is released in small quantities
onto adjoining land. Where spoil windrows are created by grading, they should be levelled with
the soil being moved back onto the road.
Access tracks through cultivated paddocks should be relocated regularly, where practical, to
avoid them becoming subsurface. Crops can be planted across tracks and right up to paddock
boundaries so that the whole paddock is protected from erosion by a growing crop. Tracks
through a strip cropped area can be zigzagged to reduce the possibility of flow concentrating
along the track and causing erosion (Figure 12.21)
Figure 12.21 Zigzagged track through a strip cropping layout
ip
fallow str
crop strip
a
access tr
ck
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Where serious erosion causes a road to be abandoned, land levelling the area should be
considered. If this is not practical, close growing vegetation should be planted and whoa- boys
should be considered.
Where formed roads cross drainage lines or creeks, an invert, floodway, causeway, culvert or
bridge is required. Inverts are constructed by removing the soil in the crossing and replacing it
with a heavy gravel or concrete. A sheet of geofabric below the gravel ensures that the soil and
gravel remain as separate layers, which increases the effective life of the invert. Culverts (pipes)
need to be sized according to the area drained. They are susceptible to blockage from siltation as
well as the growth of grass and weeds.
The following Queensland government fact sheets provide more information on this topic
L239 Erosion control on property roads and tracks - cross-sections and locations
L240 Erosion control on property roads and tracks - managing runoff.
12.6.5.3 Railway lines
Railway embankments on floodplains are typically raised at least 500 mm above normal ground
level and hence have potential to cause considerable impediment and diversion of flood flows.
The loose stone ballast supporting railway sleepers is easily removed by floods leaving the rails
and sleepers unsupported. For this reason, railway lines are always constructed on embankments
to raise the railway above expected flood levels.
Railway lines on the Darling Downs were constructed in the late 1800s or early 1900s when
there was little cultivation on the floodplain. Since then there has been considerable change in
the patterns of overland flow resulting in inadequate railway cross-drainage at many locations.
Subject to budget restraints, Queensland Rail is willing to consider suggestions for improving
rail cross-drainage.
12.6.5.4 Levee banks
Artificial levee banks are usually constructed on floodplains with the intention of protecting land
from flooding. When parallel to a watercourse, they can attempt to contain the flood within the
watercourse. When built across the floodplain at right angles or diagonal to the flow direction,
they can attempt to divert the flood around the protected area.
Any above-ground structure on a floodplain can influence flood flows and may have some of the
attributes of a levee bank. This includes structures built to harvest or to distribute water as part of
an irrigation scheme, roads and railway lines. Depending on their orientation to the direction of
flood flow, even debris-laden fences can act like levee banks and cause some diversion of
floods. For more information on these topics, refer to Sections12.6.5 Infrastructure on
floodplains, 12.6.2 Managing grazing lands on floodplains and 12.6.5.5 Irrigation structures.
The consequences of an artificial levee bank and any legislative requirements should be
carefully considered before construction. Levee banks and other above-ground structures can
have the following impacts on floodplains:
 They can concentrate flows leading to higher velocities, erosion of land, loss of crops,
damaged irrigation infrastructure and damaged public infrastructure such as roads.
 They may cause floods to take new directions and increase the flood risk in other areas.
 Levees and other structures, along a watercourse may result in deeper flows and higher
velocities in streams, which increases the risk of bed and streambank erosion and can
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increase flooding problems for downstream properties.
 If levee banks fail, or overtop, damage may result to the area that they were intended to
protect
 They can act like a dam and prevent local flows from the ‘protected area’ from entering the
stream.
(See also Section 12.4 Impacts of flooding in rural areas, Section 12.6.3 Managing extensive
cropping on floodplains, and 12.6.4 Managing intensive cropping on floodplains.
Figure 12.22 to Figure 12.25 show different situations in which constructed levee banks might
function on a floodplain.
 Figure 12.22 shows a flood spreading over its floodplain.
 In Figure 12.23, a levee bank prevents flooding on one side of the stream, by diverting flood
flows to the other side of the stream.
 In Figure 12.24, levee banks on both sides of the stream prevent floods from spreading onto
the floodplain.
 In Figure 12.25, levee banks are protecting a house and buildings (A) on one side of the
floodplain and a paddock (B) on the other side.
Figure 12.22 A floodplain during a flood
Figure 12.24 Levee banks preventing floods
from escaping onto the floodplain
Figure 12.23 A levee bank confining the
flood to one side of the stream
Figure 12.25 Levee banks to control
flooding around buildings and a paddock
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The impact of levee banks depends on the velocities of flow normally experienced on a
floodplain. Some sections of a floodplain can have very low velocities even during a major
flood. On extensive floodplains with very low slopes, floods can spread out over wide areas and
velocities remain low. Low velocities are also experienced where land is flooded by a backwater
effect. In general, flood velocities increase as the depth of flow increases. Levee banks may have
minimal adverse impact in a small flood event, but their impact may be considerable during a
major flood.
A high erosion risk is created in situations where levee banks on a floodplain intercept and divert
runoff to an incised stream. The virtual waterfall at the outlet of such a bank will cause serious
gullying.
The design of a levee bank can include the provision of a spillway to allow a levee to be
overtopped during a major flood at a point where the resulting damage is minimised. Another
consideration in the design is to consider some way of dealing with the runoff that is generated
from the area protected by the levee bank e.g. if a levee bank parallel to a river obstructed flows
from a local creek or drainage line it would act like a dam for any runoff flowing towards the
river.
Levee Bank Legislation (preliminary text only – requires comment/ amendment by DNRM
policy people)
Some Local Authorities with floodplains have established Local Laws under the Local
Government Act 2009 to give them control over levee bank constructions and minimising the
risks associated with poorly designed, or inappropriately located, levee structures, e.g. the
Waggamba Planning Scheme. The Operational Works provisions of a Planning Scheme may
require Development Approval for construction of levee banks and other structures that equate
to levees.
Construction of levee banks may also be controlled under the provisions of a Water Resource
Plan approved under the Water Act 2000, relating to control of overland flows that may result in
a change in the take of water.
Liability with private or public property damage should also be considered.
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12.6.5.5 Irrigation structures
Any above–ground structures associated with irrigation such as ring tanks, diversion banks,
supply channels and head ditches may interfere with flood flows. Such structures should be
designed and constructed in a manner that allows floodwaters to pass through without causing a
concentration or diversion of flows onto other lands. Most infrastructure for irrigation on the
Darling Downs floodplain has been constructed on sections of the floodplain that are less
vulnerable to erosive flooding. However in recent years there has been an expansion of the
irrigated area in areas subject to erosive flooding.
Irrigation infrastructure may also be subject to development controls by Local Government
Levee Bank Local Laws, or Water Resource Plans.
12.6.5.6 Weirs
A note from the author
In 2004, the concept of Natural Sequence Farming (NSF) was launched by Peter Andrews on
ABC's Australia story. It was voted the most popular story of the year and has since been
repeated, along with a couple of follow-up stories. Peter Andrews work was acknowledged when
he received the Order of Australia medal in 2011.He has been invited to Queensland by NRM
agencies on many occasions to speak at field days and Landcare conferences. NSF has been
promoted in two books written by Peter Andrews ‘Back from the Brink’ and ‘Beyond the Brink’.
An example of the numerous press articles promoting NSF is this August 2013 article in the
Sydney Morning Herald : http://www.smh.com.au/comment/why-i-love-a-desiccated-juicelesscountry-20130731-2qzjl.html#ixzz2cNvDrIAX
One of the cornerstones of NSF is the construction of ‘leaky weirs’ in streams to encourage
stream flows to spread out and to ‘hydrate’ the adjacent floodplain. It is my view that it is
generally impractical to construct a leaky weir with sufficient height to cause it to flood the
adjacent floodplain. I acknowledge that there are many people who say that it has been
successful, but I have never seen any documentation of this for Queensland, in spite of numerous
visits to the State by Peter Andrews..
The media has often stated that the rusted on views and legal requirements of bureaucrats have
been holding back the widespread adoption of NSF. I think it is time that relevant government
departments and NRM agencies formed a view on the issue. The following is an attempt to get
the discussion started. In view of the continuing interest in NSF, I think that this chapter which is
about land management on floodplains needs to say something about this concept. Otherwise
governments can be accused of keeping their heads in the sand.
Weirs are constructed in creeks and rivers by various agencies primarily to store water for use by
the community and to increase groundwater recharge. The major difference between a weir and
a dam is that dams usually have relatively narrow spillways, whereas floods pass over the entire
length of the wall of a weir.
Weirs are very effective at trapping bedload sediment and this can significantly reduce their
storage capacity. Brooks, et al, 2006 pointed out the trapping of sediment by weirs and dams can
lead to sediment starvation downstream of the structure. This can cause channel incision as the
stream attempts to supply the missing sediment.
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A major advance in the design of weirs was the development of the Minimum Energy Loss
(MEL) structures by Professor Gordon McKay in the late 1950s (Chanson 2002). The design
allows for the streamlining of flows above and below the weir structure and provides significant
cost savings. A MEL weir is typically curved with converging chute sidewalls and the overflow
spillway chute is relatively flat. The downstream energy dissipator is concentrated near the
channel centreline away from the banks. The amount of energy dissipation required is small
compared to a traditional weir. A number of weirs in Queensland incorporate this design
including the Chinchilla Weir on the Condamine River.
Since 2004, there has been considerable interest in the concept of ‘Natural Sequence Farming’
(NSF). One of the cornerstones of NSF is the construction of ‘leaky weirs’ in order to encourage
streams to spread out over their adjacent floodplains in order to ‘rehydrate’ the floodplain.
Leaky weirs are constructed from materials such as rocks or logs which detain flows but allow
some water to pass through them. However leaky weirs (like any filter) will gradually become
clogged by sediment and lose most of their permeability.
In rural areas, it is desirable to encourage floods to spread out over their floodplain using various
management techniques as discussed in Section 12.6 Erosion control strategies for floodplains.
However, the construction of a leaky weir has a limited capacity to achieve this. In order to
make floods spread out over their floodplain, the wall of a leaky weir would need to be higher
than its floodplain (Figure 12. 26). However, floodwaters rising above the creek bank would
soon bypass the weir and return to the creek creating an erosion hazard at the overfall as shown
in Figure 12. 26.
Figure 12. 26 A weir with a height above the level of a floodplain is prone to failure
The construction of a weir would be a major undertaking for a landholder, especially in incised
streams, and they would be prone to failure. It would also be necessary to obtain a permit before
their construction.
Leaky weirs have a role in the stabilisation of gullies as discussed in Chapter 15, Gully Control
(still in draft form). The purpose of these structures is to deposit sediment behind them to
encourage the growth of vegetation, which in turn encourages more sedimentation. However for
this purpose, it is recommended that weirs have a height of less than 50 cm especially in
dispersive soils which are the most vulnerable to gullying. A common cause of failure of
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structures built in dispersive soils is the bypassing of the structure from erosion of the side walls.
The higher the structure, the more likely this is to occur. Another problem with high weirs is the
cost and technical difficulties associated with the need to deal with the energy of the water that
flows over the structure.
Leaky weirs encourage sedimentation and the growth of vegetation to stabilise the floor of the
gully. However, it would generally be impossible to completely fill a gully using this technique.
Most gullies carve out far more capacity than they require and even in a major run off event,
they carry a relatively small amount of run-off. Many gullies in upland areas have retreated
almost to the head of their catchment which explains why they carry very little run-off.
#######Author comment: I have two draft fact sheets promoting the use of leaky weirs for gully
control and I can send them to anyone interested in the topic. The use of these weirs has been
promoted by soil conservationists for over 30 years, but there has been limited uptake of this
practice. I can also provide reviewers with a copy of my photostory on ‘Gullies with small (or
no) catchments’.
12.7 Riparian filter strips
A note from the author
In 2008 I was asked by DERM colleagues who were modelling sediment movement in
catchments to give a soil conservationist’s perspective on the role of riparian filter strips in
trapping sediment emanating from agricultural land. My views have always been that riparian
filter strips have a very limited capacity to do this. I prepared a PowerPoint presentation on the
topic which mostly features photos, animations and diagrams. I subsequently gave the talk on
about 10 occasions in 2008 including to the Queensland Landcare conference. I never found
anyone who disagreed with what I had to say. I can send reviewers a copy of the latest version
of this presentation - just send an e-mail to [email protected]
This is the first time I have expressed my views on this issue in a written publication. My views
are based on my observations and discussions with many people. I have done no formal
research work on this topic and I don't believe any such research is likely to tell us anything that
we don't already know.
There are numerous publications extolling the virtues of riparian filter strips but the following
is a quote that implies that riparian filter strips do not filter as much runoff as many people
expect them to (Source: Improving Water Quality - the third fact sheet in a series dealing with
the management of riparian land produced by Land and Water Australia (2002))
“To be effective, a filter strip needs to be established or maintained at points where overland
waters enter small river channels. In most catchments, this does not mean a strip of set width
along both sides of a stream.
There may be large parts of the landscape where little or no overland flow enters the stream
channel. You may decide to maintain healthy riparian vegetation in these areas to improve bank
stability or provide wildlife habitat, but they are less important if your primary objective is to
reduce sediment and nutrient movement”.
I have had an e-mail exchange with two overseas authors on riparian filter strips (Marc Stutter,
UK and Mike Dosskey USDA) and we reached common agreement. Marc Stutter did a review of
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the research work on riparian filters and he told me that ‘almost exclusively, the studies are
short term covering single or a few events and often in artificial plot situations where natural
erosion processes, such as convergent flow, do not occur’.
It is my experience that scientific papers referring to riparian filter strips fail to mention one
essential word and that is ‘contour’. If a filter strip is not on the contour it will divert rather than
accept runoff. It seems to me that most authors on riparian filter strips are not aware of this.
Often quoted publications are McKergrow et al 1999 and 2004 (Performance of grass and
rainforest riparian buffers in the wet tropics, Far North Queensland) which refer to an
experiment in North Queensland which showed that filter strips below an eroding banana
plantation trapped up to 80% of the exported sediment. This may well have been the case, but
the study refers to a level one stream and it is hardly a riparian buffer. Banana plantations
require effective soil conservation practices to minimise soil loss in the first place. Any
concentrated runoff in and from the plantation needs to be via well grassed channels until it
reaches a stream as described in this recent YouTube video on erosion control in bananas
produced by soil conservationist Daryl Evans at Innisfail
https://www.youtube.com/watch?v=bbl9-dIr-NY - he has also written a DAFF fact sheet on the
topic which I believe has been held up in the publication process.
The above diagram (Lovett S and Price P (Eds) (1999). Volume 1, Riparian Land Management
Technical Guidelines: Principles of Sound Management) illustrates a situation similar to that
described by McKergrow et al 1999 and 2004. It would only apply for level one streams. In
these situations it is essential that sound soil conservation practices (year-round cover and
runoff management where necessary) are applied on the whole of the steep hill slope so that
there is minimal movement of sediment and nutrients to the ‘stream’.
.
I believe that landholders are aware that riparian filter strips have limited value and scientists
can lose their credibility by continuing to advocate their use. Runoff only occurs two to three
times a year on most rural properties. It creates a lot of interest and excitement and landholders
know exactly where it goes as it flows from paddocks to streams. They know that runoff soon
concentrates and that it doesn't get into streams as a spread flow over streambanks.
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Riparian vegetation has many essential functions. Chapter 13, Stream stability describes its vital
role in stabilising stream banks and provides guidelines for suitable widths to achieve this
function. The roots of trees and shrubs stabilise streambanks and their foliage assists in reducing
flow velocities against the bank. Ground cover on stream banks protect them from erosion by
raindrop impact and the overland flows from the bank into the stream. Riparian vegetation also
plays a key role in promoting biodiversity by providing habitat (including shade) that benefits
both terrestrial and aquatic forms of life and provides an important corridor of travel for a
variety of wildlife.
Riparian vegetation also provides a useful buffer between the stream and paddocks used for
cropping. This provides protection to streambanks from erosion and minimizes air drift of
agricultural chemicals towards the stream. A 5 metre buffer that is 2 km long only takes up 1 ha
of land.
However the role of riparian strips in filtering out sediment and nutrients from runoff from
adjacent catchments is overplayed. This is contrary to the view commonly expressed in
literature throughout the world. Examples of references for their recommended use in
Queensland include Boulter SL, et al, (2000), Karssies LE and Prosser IP (1999), Lovett S and
Price P (eds) (1999), Lovett S and Price P (2001), Lovett S, Price P and Lovett J (2003) and
McKergrow, et al (1999 and 2004).
Runoff from catchments does not enter streams by flowing over stream banks. Examination of
any topographic map or satellite image will show that runoff must concentrate as it moves
towards a stream and its eventual outlet into the ocean or an inland lake. The normal pathway is
for it to enter a stream at well-defined points or it might discharge onto a floodplain sometimes
via wetlands.
Figure 12. 27 Flows concentrate as they move down a catchment.
Figure 12. 27 shows how flows concentrate as they move downstream. Level one and two
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‘streams’ would be better defined as drainage lines rather than streams. They often occur within
a paddock which may only produce runoff on two or three occasions in a year. Runoff exits
most paddocks at only one or two locations and sometimes as a level three ‘stream’. A very high
proportion of catchment runoff is produced in low order stream levels. Very little ‘new’ runoff
gets into a stream by flowing over the banks of high order streams. Maps illustrating the
proportion of various stream orders for south-east Queensland catchments can be found on the
Healthy Waterways website http://www.healthywaterways.org/Home.aspx .
Runoff from eroding soils adjacent to drainage lines on floodplains is not likely to filter through
a vegetation strip. For filter strips to be effective, they need dense vegetation such as grass.
However grass provides considerable resistance to overland flows especially on the very low
slopes on floodplains. Should sediment deposition occur at the interface between bare ground
and dense grass, the vigorous grass growth and additional height caused by the deposition will
increase the potential for the strip to divert flows.
Runoff will always take the easiest pathway and if a grassed strip (or a sediment fence in urban
areas) is to accept runoff from bare ground, it must be on the contour, otherwise flow diversion
will occur. Dense strips of grass parallel to a stream will not be on the contour as shown in
Figure 12.28.
Figure 12.28 Grass strips parallel to streams on floodplains are unlikely to accept runoff
Figure 12. 29 (a) is a typical situation but would occur in level I and level II stream where the
contours would be convergent. Any run-off flowing towards the stream would be readily
diverted by a dense grass strip. Figure 12. 29 (b) covers a situation of a stream on a floodplain
where the flood flows are parallel to the stream. Figure 12.28 (c) and Figure 12. 29 show a
stream with a natural levee which directs local runoff away from the stream rather than towards
it. Most streams on floodplains have natural levees caused by the deposition of coarse sediments
when the flood escapes from the stream channel. Stream banks with natural levees can be the
highest land on some floodplains and are only submerged in a major flood event. When streams
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have natural levees, their floodplains are first flooded from breakout areas where drainage lines
on the floodplain join the main stream. The safest place to build a home on a floodplain is often
the natural levee on the streambank.
Sediment fences are widely used on construction sites with the intention of preventing sediment
from moving off-site. Because runoff follows the least line of resistance, a sediment fence can
only function correctly if it is on the contour. Most sediment fences are on a diagonal to the
contour and only serve to divert and concentrate runoff.
Figure 12. 29 Cross-section of a floodplain showing a natural levee on the stream bank
(Based on Figure 2.3 Managing for water quality within grazing lands of the Burdekin
catchment - guidelines for land managers, Coughlin, et al, 2008)
Sediment in streams can come from streambank erosion or erosion of the land in the catchment.
Where land is used for agriculture, there should be minimal movement of soil from paddocks in
the first place. This can be achieved by soil conservation measures including the use of land
according to its suitability, maintenance of adequate levels of ground cover and managing runoff
so that it enters streams via well grassed waterways.
Where land is cropped, runoff is less likely to enter grassed channels traversing floodplains as
discussed in Section 12.6.1 Surface drainage on floodplains. Figure 12. 8 shows how grassed
channels at normal ground level will divert flows onto the bare ground on either side of them.
The use of subsurface channels (Figure 12. 9) will overcome this problem.
The whole of a floodplain can effectively function as a filter strip if it is protected by good
cover. This is achieved by strip cropping and zero tillage in broadacre agriculture. It is more
difficult to protect horticultural land from erosive flooding on floodplains (refer to chapter 14
Horticultural production and soil conservation). In grazing lands, grazing pressure needs to be
managed to maintain a permanent cover. Sustainable grazing practices are described in the
publication Managing grazing lands in Queensland (Department of Environment and Resource
Management 2011.
Upland cropping areas need to be protected by minimal or zero tillage and measures such as
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contour banks. Contour banks can trap 80% of the sediment they receive from the contour bay
above it (refer to Chapter 9 Contour banks). Stubble covered contour bank channels and grassed
waterways reduce the velocity of flows and filter runoff as it flows towards a stream.
Phosphorus and nitrogen attached to clay particles can be deposited where sediment is trapped.
In urban areas, erosion control measures need to be adopted on new land developments and
construction sites. Water sensitive urban design (WSUD) practices reduce the rate at which
runoff flows from catchments with a high component of impervious areas. Drainage lines that
connect urban areas to streams can act like a filter and trap sediment if they are lined with dense
vegetation.
When grass acts as a filter it is most likely to trap coarser sediments such as sands and loams
rather than very small clay particles. However, non-dispersive clay particles can maintain some
cohesiveness when carried in runoff and a significant amount of it can be deposited when flow
velocities are reduced. In contrast, dispersive clay particles can remain in suspension even in still
water such as dam storages.
Riparian vegetation can improve the quality of ground water by the process of denitrification
(Rassam, et al, 2006). Denitrification enzymes can function in anaerobic conditions where there
is a carbon rich root zone to fuel bacterial processes. This process can occur where there is a
flow of shallow, slow-moving groundwater through the riparian zone and bringing nitrate
towards the stream. However this process only occurs when the water table is higher than the
stream or where there is seepage from the stream into the streambank. Water tables above
stream level occur in more humid climatic zones but rarely in drier environments.
Heavy rainfall in a catchment can contribute runoff to vegetation on floodplains that may have
received minimal rainfall. Under these circumstances the vegetation can absorb runoff as well as
providing a filtering function. This situation sometimes occurs when runoff from upland areas
on the Eastern Darling Downs meets the floodplain. Strip cropping at the creek outlets can
spread this runoff providing natural irrigation. In outback river systems, dry floodplains in the
‘channel’ country can absorb runoff that may take a week or more to flow from higher parts of
the catchment that have received good rainfall.
Uniform, dense grasses that are stoloniferous with rhizomes are best suited for filter strips.
Tussocky grasses and forest floors are not very effective for filtration. The Queensland
government fact sheet L271 Soil conservation waterways - Plants for stabilisation lists species
suitable for use in grassed waterways and which could be considered for use in filter strips. The
publication Managing riparian lands for the sugar industry provides a list of grass species
suitable for riparian buffer strips (Lovett and Price, 2001).
12.8 Wetlands
Queensland has a diverse array of wetlands with a wide range of biological and hydrological
values. Wetlands cover many habitat types including flowing waterways (rivers and creeks),
shallow coastal waters (e.g. mangroves, saltmarshes and tidal flats), permanent and seasonally
ponded waterbodies lakes, swamps, marshes, peatlands, mangroves, and constructed dams and
reservoirs. The variable nature of Queensland’s climate means that many wetlands are
ephemeral and can remain dry for lengthy periods. Artificial wetlands can be constructed in
drainage lines to improve water quality and ecological functions.
Wetlands can be lost or degraded by clearing, draining, or exotic weed invasion. To maintain
Draft - Soil Conservation Guidelines for Queensland
43
wetlands in good condition, it is necessary to limit the amount of sediment and nutrients they
receive by the adoption of sound soil conservation practices in their catchments. Runoff flows
directly into wetlands from the land around them and they need to be protected by surrounding
buffers, as well as good management throughout their catchments.
Grazing animals are attracted to wetlands and they can have a significant impact on them. Such
areas need to be managed to ensure that the land surrounding wetlands are protected by adequate
levels of vegetation (refer to Section 12.6.2 Managing grazing lands on floodplains.
The Queensland government website WetlandInfo http://wetlandinfo.ehp.qld.gov.au/wetlands
contains a wide range of information about wetlands and their management . This includes the
publication Queensland Wetland Buffer Guidelines (Department of Environment and Resource
Management 2011), which provides information for designing a wetland buffer and identifies its
benefits and future management needs.
12.9 Legislation
Author comment – input is required from Queensland government policy people on what to
include in this section. Relevant legislation could be as listed below (based on 2001 and needs
updating . The publication Lovett S and Price P (2001), ‘Managing Riparian Lands in the Sugar
Industry: A Guide to Principles and Practices’ provided concise summaries of this legislation

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
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
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

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Water Resources Act 2000 (see chapter 13 Stream stability for updated information on
this act)
Vegetation Management Act 1999(see Chapter 13 Stream stability for updated
information on this act)
Land Act 1994
River Improvement Trust Act 1940
Rural Lands Protection Act 1985
Fisheries Act 1994
Nature Conservation Act 1992
Environmental Protection Act 1994
Sustainable Planning Act 2009
Chemical Usage (Agriculture and Veterinary) Control Act 1988.
12.10 Further information
Land and Water Australia fact sheets available on line (http://lwa.gov.au/products/list/3069 )
1 Managing riparian land
2 Streambank stability
3 Improving water quality
4 Maintaining in-stream life
5 Riparian habitat for wildlife
6 Managing stock
7 Managing woody debris in rivers
8 Inland rivers and floodplains
9 Planning for river restoration
10 River flows and blue-green algae
11 Managing phosphorus in catchments
12 Riparian ecosystem services
13 Managing riparian widths
Draft - Soil Conservation Guidelines for Queensland
44
Australian Landcare magazine, December 2003, Special issue on riparian fencing.
Bass GA (1985). Residual flow drains on the Darling Downs. In Proceedings of the Fourth
Australian Soil Conservation Conference, Maroochydore, Queensland.
Begbie DK (1977). Report on the study of the Linthorpe and Aubigny Catchments, Darling
Downs, Qld. A report prepared for Linthorpe No. 5 Soil Conservation Group and the Central
Darling Downs Advisory Group Committee, Queensland Department of Primary Industries,
Brisbane.
Boulter SL et al (2000). Native vegetation management in Queensland. Queensland
Department of Natural Resources.
Brooks, A. et al. (2006), Design guideline for the reintroduction of wood into Australian
streams, Land & Water Australia, Canberra.
Carey B (2012) Achieving soil conservation in Queensland – a pictorial history. Queensland
Landcare web site:
https://dl.dropboxusercontent.com/u/40874340/2013%20Qlinks/1302/Achieving-soilconservation-in-Queensland.pdf
Chanson Hubert (2002). History of minimum energy loss, weirs and culverts, 1960-2002,
Special Seminar SS1, Department of Civil Engineering, the University of Queensland.
Coughlin T, O’Reagain P, Nelson B, Butler B, Burrows D (2008). Managing for water quality
within grazing lands of the Burdekin Catchment – Guidelines for Land Managers. Burdekin Dry
Tropics NRM Solutions Ltd, Townsville.
Cummins VG and Bass GA (1978). Report on a study of the Pittsworth Plains and associated
upland catchments, Darling Downs, Queensland. Queensland Department of Primary Industries,
Brisbane.
Department of Environment and Resource Management (2011), Queensland Wetland Buffer
Planning Guideline, 54 pp, Queensland Wetlands Program, Brisbane, Queensland.
Department of Natural Resources (1999). Better Management Practices – Floodplain
Management on the Darling Downs. Department of Natural Resources, Queensland.
Department of Sustainability and Environment 2007, Technical Guidelines for Waterway
Management, Department of Sustainability and Environment, Victoria.
Department of Environment and Resource Management (2010). Soil conservation waterways Plants for stabilisation DERM Fact sheet series L271, Department of Environment and
Resource Management, Queensland.
Department of Environment and Resource Management (2011). Managing grazing lands in
Queensland. Queensland Department of Environment and Resource Management.
Department of Natural Resources (1999). Land Use Practices for Wet Tropical Floodplains,
Queensland Department of Natural Resources. Department of Natural Resources and Water
(2007). Queensland Urban Drainage Manual
Draft - Soil Conservation Guidelines for Queensland
45
Eacott LS (1979). Practical aspects of planning and implementing strip cropping systems on
very low gradient land. Division of Land Utilisation Report 79/4, Queensland Department of
Primary Industries.
Finlayson B and Silburn M (1996) Soil, nutrient and pesticide movement from different land use
practices and subsequent transport by rivers and streams. In proceedings of a national conference
on Downstream effects of land use, Rockhampton, Qld, 1996 (Edited by HH Hunter, AG Eyles
and GE Rayment).
Jones MR (2006) Cenozoic landscape evolution in central Queensland, Australian Journal of
Earth Sciences 53, (433 – 444)
Kapitzke IR, Pearson RG, Smithers SG, Crees MR, Sands LB, Skull SD and Johnston AJ
(1998). Stream Stabilisation for Rehabilitation in North-East Queensland. Land and Water
Resources Research and Development Corporation, Occasional Paper 05/98, Canberra.
Karssies LE and Prosser IP (1999) Guidelines for riparian filter strips for Queensland
irrigators, CSIRO Land and Water, Canberra, Technical Report 32/9.
Layden I (2011), Wetland Management Handbook: Farm Management Systems (FMS)
guidelines for managing wetlands in intensive agriculture Department of Employment,
Economic Development and Innovation, , Queensland Wetlands Program, Brisbane QLD.
Lovett S and Price P (Eds) (1999). Volume 1, Riparian Land Management Technical
Guidelines: Principles of Sound Management, Volume Two: On-ground Management Tools
and Techniques, Land and Water Resources Research and Development Corporation, Canberra.
Lovett S and Price P (2001), Managing Riparian Lands in the Sugar Industry: A Guide to
Principles and Practices, Sugar Research & Development Corporation/Land & Water,
Australia, Brisbane.
Lovett S, Price P and Lovett J (2003), Managing Riparian Lands in the Cotton Industry, Cotton
Research and Development Corporation.
Lovett S, and Price P. (eds) (2007), Principles for riparian lands management, Land & Water
Australia, Canberra.
Macnish S (1980). A review of strip cropping practices on the eastern Darling Downs.
Division of Land Utilisation 80/1, Queensland Department of Primary Industries.
Marshall JP (1988). Floodplain Management for Erosion Control and High Productivity on the
Darling Downs. Division of Land Utilisation, Queensland Department of Primary Industries.
McKergrow L, Prosser I and Heiner D (1999). Preliminary results on the effectiveness of
riparian buffers in Far North Queensland, Proceedings, Second Australian Stream Management
Conference, 8-11 February, Adelaide, South Australia, pp. 439-444
McKergow LA, Prosser IP, Grayson RB and Heiner D (2004) Performance of grass and
rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water quality, Australian
Draft - Soil Conservation Guidelines for Queensland
46
Journal of Soil Research 42(4), pp 485 – 498.
McLatchey JF and Watts TR (1985). The implications of levelling gilgais in southern inland
Queensland. Proceedings Australian Soil Conservation Conference, October 1985,
Maroochydore, Queensland.
Peck G (2006a). Property planning: fencing to land type-riparian lands. Fitzroy Basin
Association fact sheet.
Peck G (2006b). Property planning: Sustainable grazing on riparian lands - Why and how to do
it . Fitzroy Basin Association fact sheet.
Peck G (2006c). Property planning: Using off-stream watering points. Fitzroy Basin
Association fact sheet.
Price P and Lovett S (eds) (1999). Riparian Land Management Technical Guidelines, Volume
Two: On-ground Management Tools and Techniques, LWRRDC, Canberra.
Prosser I and Karssies L (2001), Designing filter strips to trap sediment and attached nutrients,
River and Riparian Land Management Technical Guideline No. 1, Land & Water Australia,
Canberra.
Rassam D W, Fellows C S, De Hayr R, Hunter H, and Bloesch P (2006). The hydrology of
riparian buffer zones; two case studies in an ephemeral and a perennial stream. Journal of
Hydrology 325, 308–324.
Ruffini J, Smith R, Hancock N and Glasby T (1988). Flood Strip Cropping, Guidelines for
Selection of Strip Widths. Darling Downs Institute of Advanced Education, School of
Engineering, Centre for Engineering in Agriculture. Technical Report No 11/88.
Rutherfurd I, Anderson B, and Ladson, A (2007). Managing the effect of riparian vegetation on
flooding. In Principles for riparian lands management. Edited by S. Lovett and P. Price. Land
and Water Australia, Canberra, pp. 63-84.
Shellberg J and Brooks A (2007). A Fluvial Audit of the Brisbane River: A Basis for Assessing
Catchment Disturbance, Sediment Protection, and Rehabilitation Potential, Australian Rivers
Institute, Griffith University, Queensland.
Shellberg JG, and Brooks AP (2013). Alluvial Gully Prevention and Rehabilitation Options for
Reducing Sediment Loads in the Normanby Catchment and Northern Australia. Griffith
University, Australian Rivers Institute, Final Report for the Australian Government’s Caring for
our Country - Reef Rescue Initiative, 312pp. http://www.capeyorkwaterquality.info
Standing Committee on Agriculture and Resource Management, (2000) Floodplain
management in Australia - Best practice principles and guidelines. CSIRO Publishing.
Staton J and O’Sullivan J (2006) Stock and waterways: a manager’s guide. Land & Water
Australia, Canberra.
Victorian Resources on Line (2013) Diagrammatic representations of Terrace development
(animation)
Draft - Soil Conservation Guidelines for Queensland
47
http://vro.dpi.vic.gov.au/dpi/vro/wgregn.nsf/pages/wg_soil_maffra_geology_geomorphology_di
agram
Water and Rivers Commission (2000). Flood proofing fencing for waterways. Advisory note for
land managers on river and wetland restoration. Water and Rivers commission, Western
Australia.
Wilson PR (2013). Floodplain management in the Burnett Catchment, Burnett Mary Regional
Group http://www.bmrg.org.au/files/9713/7827/4601/Flood_plain_managementa.pdf
Witheridge GW (2010). Watercourse Erosion Part 1, Fact Sheet, Catchments and Creeks Pty
Ltd, Brisbane.
Wockner GH and Freebairn DM (1991). Water balance and erosion study on the eastern Darling
Downs—an Update, Australian Journal of Soil and Water Conservation, Vol 4, No 1, pp 41-47.