The benefits of riparian vegetation in the Pimpama Catchment

Riparian vegetation on your farm

What is riparian vegetation?Riparian land is the land alongside waterways such as rivers, creeks, streams, gullies, drains, wetlands or lakes. Riparian vegetation is the plants, trees, shrubs and grasses growing in this area.

Riparian vegetation plays a critical role in minimising the impact of landuse on local and downstream waterways as well as providing a variety of benefits to the adjacent land.

Historical clearing has left us exposedUnfortunately, clearing and degradation of riparian vegetation has occurred across the Pimpama Catchment, an issue common throughout Australia. Concerns around floods led to the perception that riparian vegetation worsened flooding, leading to its widespread removal.

However, extensive scientific studies and computer modelling have helped inform us that healthy and diverse riparian vegetation has only a very minor impact on flood heights and duration. The benefits of riparian vegetation, however, both environmental and economic, are widespread and significant, and many councils, governments, and community groups are now working to repair this important ecosystem.

Overstorey

Understorey

Groundcover

Aquatic plants Instream wood

Find out how healthy riparian ve�etation benefits both your farm and beyond

Local benefits of riparian vegetationHealthy and diverse riparian vegetation provides many benefits for your farm and local waterway.

Improving Stewart’s farm for over 15 yearsThe Stewart family’s 116 hectare cane and cattle farm borders the Pimpama River. Over the past 50 years Ken Stewart has watched how the fast moving and erosive flood waters of the river were impacting on his farm. Ken decided over 15 years ago to plant a small section of riparian vegetation to prevent erosion in one corner of his property. He now boasts of the benefits of the healthy and diverse riparian vegetation North East Albert Landcare helped plant along the entire 2 kilometres of Pimpama River bordering his property.

Taking up a total of just 1/4 hectares of his productive land, Ken, North East Albert Landcare and local school children have transformed his riparian strip from a bare, eroding bank to a wildlife sanctuary with a diverse array of native trees, shrubs and grasses. The productivity of his land has improved due to reduced water velocity and erosion, and the valuable soil stays on the farm and not down the river.

Ken has also found that the riparian vegetation has greatly reduced his fencing costs and maintenance as it traps a lot of debris in the flood waters which used to destroy his fences. The money and effort put in has more than paid for itself through savings in fencing and repair works and the protection of the farm from floodwaters.

The riparian area requires minimal maintenance following the inital weed removal and planting effort. Routine weed removal is carried out for 6–12 months, after which the native trees and shrubs help keep weeds in check and the system is mostly self-maintaining. The benefits of the riparian vegetation were seen within 3–5 years and continues to improve with time.

Reduces erosionTree roots help stabilise the stream bank and reinforce bank structure. The main water flow is kept in the stream. Bank moisture is maintained and won’t crack and break during the dry and won’t slump in the wet.

Maintains productive landThe velocity of floodwaters is reduced and valuable soil is kept in place. Established trees serve as a wind break. Planting trees opens up carbon offset opportunities.

Traps and filtersDebris and soil flowing down the river is trapped by the roots and leaves of the vegetation. Less debris means less damage to fences during floods. The filtering effect prevents sediment, nutrients and attached contaminants from entering the water improving water quality for irrigation.

Reduces pest invasionsThe movement of rats onto properties is reduced with riparian vegetation. Habitat is improved for natural predators which help control insect and other pests.

Provides food and habitatTree roots and large instream wood provide important habitat and food for in-stream and terrestrial wildlife. Beneficial insects and animals thrive and prey on pest species, and pollinate important agricultural plants. Fish populations find protection at all life stages from eggs to adults.

Prevents weeds and algaeTrees create shade over the stream which helps control riparian weeds and nuisance in-stream plants and algal growth.

Cools the waterShading by trees and shrubs cools the water and minimises temperature extremes. This is important for the survival of in-stream plants and animals and helps build a diverse and productive ecosystem.

Visually pleasingWith trees comes improved amenity and aesthetics which can lead to increased land values. There are more opportunities for recreational activities such as kayaking and fishing.

Providin� benefits for landowners

And it looks beautiful too

Productive land protected from erosion

Habitat for beneficial insects and animals

Sediment and debris is trapped by vegetation

Water flow kept within streamTree roots stablise

streambank

Food and habitat for productive and diverse ecosystem

Trees serve as wind break

Sediment and nutrients are filtered and prevented from entering waterways

Moisture in streambank prevents cracking and slumping

Fencing costs reduced as vegetation slows down floodwaters

How will riparian vegetation affect flooding on my property?Comprehensive modelling in the Woongoolba floodplain has shown that riparian vegetation has only a very minor impact on flood duration and height.

Modelling compared flood impacts on areas with cleared riparian vegetation to areas with a riparian width of 6–10 metres. Under worst case rainfall and flood conditions, areas with riparian vegetation experienced only 20 minute increase in inundation time with a negligible impact on flood height. The figures below detail the modelling results for two different points in the catchment.

Flat landscapes and backwater effects were shown to have a much �reater impact on inundation duration than riparian ve�etation.

Riparian vegetation benefits extend across the catchmentIn a study investigating the hydrology of a Pimpama cane field, Rassam et al. (2002) demonstrated that oxidation products from acid sulphate soils such as metals are mainly leached from soils located close to cane drains where a steep water table draw down was observed.

In addition, nutrient levels in the water (total nitrogen, organic nitrogen and total phosphorus and dissolved nitrate+nitrite) were elevated. The high nutrient levels are likely reflecting the intensive agriculture in the Pimpama catchment.

Riparian vegetation plays a very important role in trapping and filtering sediment, nutrients and contaminants which greatly improves water quality for stock, irrigation and human consumption. Less erosion also means less sediment entering the waterways.

Improved water quality in the streams and rivers has a flow on effect downstream and helps build a healthy and more resilient Moreton Bay and Broadwater.

Riparian vegetation provides important habitat and corridors for wildlife, connecting fragmented habitats.

Recreation and aesthetics are improved across the landscape with more opportunities for people to enjoy the rivers and appreciate their natural beauty.

Let’s work together to improve riparian vegetation for you, the Pimpama community and beyondLocal landcare groups are a great place to get guidance on how to start improving your riparian strip. Contact North East Albert Landcare via the Gold Coast Catchment Association webpage for how you can get involved goldcoastcatchments.org

The City is committed to work together with landowners to improve riparian vegetation. You can find out more about the modelling project, what we have achieved so far and our plans for the future on our website. A full report is available.

InformationP 1300 GOLDCOAST E pimpama@goldcoast.qld.gov.au W cityofgoldcoast.com.au

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10 metre riparian widthcleared riparian bank

Middle reaches

10 metre riparian widthcleared riparian bank

Lower reaches

Will riparian vegetation decrease groundwater?Evaporative transpiration of cane plants and other agricultural plants has a greater impact on groundwater table levels than riparian vegetation. In fact, the removal of vegetation throughout a landscape can lead to raised water tables and salinisation of land.

Riparian vegetation can help improve land salinisation conditions.

Will riparian vegetation take up arable land?The width of riparian vegetation planted depends mostly on benefits sought. Less width is needed if the main aim is sediment trapping, greater width is beneficial for wildlife and conservation efforts.

Generally, the minimum amount recommended is the entire bank from low water level to high bankfull level plus the top of the bank. This land is generally considered to be the least productive on the farm and can be difficult to access, but can provide so many benefits if vegetated.

There may be a small profit loss in not harvesting crop from this part of the land, but benefits far outweigh the costs.

Optimal width to promote wildlife movement and ensure conservation is 100 metres or more. Restricting stock and vehicle access to the riparian zone will minimise the threat from weeds and ensure it is sustainable in the long term.

Although five or more metres width of riparian vegetation is recommended, any planting will be beneficial to the ecosystem.

Runoff from the land carries sediments and nutrients ( ) into the waterways

Riparian vegetation helps to improve water quality in local streams and rivers, and out to the Broadwater and Moreton Bay

Riparian vegetation plays an important role in filtering and trapping sediments and nutrients, with a bigger area providing bigger benefits

Sediments and nutrients are trapped in tree roots

Rassam DW, Cook FJ and Gardner EA (2002). Field and laboratory studies of drained acid sulphate soils Irrigation and Drainage Engineering, ASCE, 128:107-115.

Alluvium (2013). Pimpama River geomorphology and riparian vegetation study. Report P412019_RO3 by Alluvium Consulting Australia for Gold Coast City Council.

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For informationP 1300 GOLDCOAST (1300 465 326) W cityofgoldcoast.com.au

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