Sediment Demonstration Grant Case Studies

Introduction

Since European settlement, landscapes have been cleared of native vegetation, exotic plants have been introduced, and grazing of stock has occurred down to the stream banks.  These activities have significantly increased naturally occurring erosion to levels that are contributing to the degradation of our waterways.  Results of erosion can range from the loss of valuable land, damage to infrastructure, decline in aquatic health and changes to flow regimes, potentially increasing damage during floods.

TEER Sediment Demonstration Grants 2011/12

NRM North’s Tamar Estuary and Esk Rivers (TEER) program is helping landholders mitigate sediment input to waterways through innovative methods, not commonly applied in Tasmania.  The TEER has offered funding to successful applicants through the Sediment Demonstration Grants 2011/12. Priority was given to innovative projects developed by landholders that effectively reduce sediment loads within the South Esk, North Esk and Meander Valley catchments. These priority catchments generate the highest loads of sediments within the Tamar catchment and contribute towards the excessive siltation of the Tamar River estuary.  The grants also aim to bring landholders together, involving people in waterway management.  Technical advice is provided to build capacity, supporting a strong knowledge base and the ability to act.

Demonstration Projects

The successful applicants incorporated innovation into their works in varied ways. 

  • Trialling the use of in-stream rock gabions, experimenting with different orientations to prevent the build up of debris dams which release sediment when they collapse
  • Two neighbouring landholders are working together to remediate a scoured flood channel running parallel to the Tyne River.  Onsite tours with surrounding landholders will generate further social investment in waterway management
  • Three private landholders are using timber structures in varied designs to stabilise stream banks, such as engineered log jams (ELJs) and timber field piles. 

Timber In Streams

The reintroduction of wood to streams, conducted by five landholders, provide many benefits including bank protection, flow diversion, improvement of breeding habitat for native fish, substrates for biofilm to establish which is the foundation of freshwater food webs, supports the sequestration of nutrients and thereby improving water quality.  Some examples are engineered log jams (ELJs) or the installation of timber field piles.  The largest drawback of these designs is finding enough wood of appropriate size, type and located on site or near enough.  In many cases, timber is preferable to rock as traditional rock revetments act to harden the bank, maintain the flow path and, at times, increase flows creating bigger problems downstream.  These examples were taken from the Design guideline for the reintroduction of wood into Australian streams(Brooks 2006).

Case Study 1: Using in-stream gabions as sediment traps

Landholder:  Timberlands PacificA large debris dam forming in a stream with no streamside reserves.

Grant:            $5,000 (placement of cages)

In-kind:          $5,030 (wire, rock and materials)

 

The sediment problem

Timberlands Pacific is a forestry management company managing coups in the upper South Esk catchment.  Some of these plantations were planted before the Forestry Practices Code governed operations, where the land was completely cleared of native vegetation with no streamside reserves.  If heavy east coast rainfall follows harvesting, debris dams harbouring sediment can form in stream channels.  When these debris dams collapse under the weight of water impounded behind, large amounts of sediment can be carried downstream, scouring stream banks, damaging bridges and culverts and increasing sediment supply to the South Esk River and beyond.

What are the aims of the project?Excavator placing rock gabions in the stream channel to catch large debris.

The in-stream works are intended as a short-term measure to help contribute to stream stability and reduce debris-induced erosion.  The long-term aim is for all streams to have streamside reserves that will help to prevent large amounts of debris entering the streams compromising bank stability.

How does the project demonstrate innovation?

Gabions are commonly used as revetment structures to improve bank instability directly; however this project is trialling the use of gabions in the stream channel.  The rock filled cages are spaced in a line, perpendicular to the flow, to trap debris before they accumulate in large amounts as debris dams.  The gabions are installed at accessible points where it can be readily removed from stream channels. 

How are the works beneficial?

By allowing debris to be cleared and gabions maintained on a regular basis, collapsing debris dams, storing large amounts of sediment are no longer a threat to the downstream water quality and stream banks.  The gabions also help to break up strong flows and encourage sediment to drop out of suspension. 

 

Case Study 3: Log deflector jams to stabilise river banks

Landholder:  Deloraine Landcare

Grant:            $13,763 (earthworks, rock excavation and plants)

In-kind:          $17,670 (logs with root balls attached, rock, soil and labour)

The sediment problem

Like many catchments, the Meander has historically been intensely cleared for various land practices, removing native riparian vegetation in the process.  This creates unstable stream banks and allows flows to actively scour and transport sediment downstream.  Deloraine Landcare has helped to stabilise and restore the riparian zone on the Meander River, upstream of the township of Deloraine.

What are the aims of the project?

The aim of the project is to help stabilise the bank, prevent further erosion, reduce the sediment loading to the Meander River and beyond, and encourage native riparian vegetation to establish creating connectivity through the landscape supporting biodiversity.

How does the project demonstrate innovation?

Bank-attached, log deflector jams are not yet a common method used in Tasmania, however is widely adopted on mainland Australia.  A series of jams were installed to deflect the flow from the bank, and to break up the stream energy and high velocities which aid erosion.  Materials were sourced from the farm, such as the hardwood trees with the root balls attached used for the structure.   A minimum of six logs for each structure are placed in a grid pattern with root balls facing into the flow allowing the structure to be pinned back into the bank. 

How are the works beneficial?

This innovative design reintroduces timber to the stream providing for; bank protection, flow diversion, the creation of deep pools for improved fish habitat, complex cover and breeding habitat for native freshwater fish, substrates for biofilm to establish, and can aid in the sequestration of nutrients. These works all help to improve water quality.

 

Case Study 4: Working together to rehabilitate an ephemeral flood channel

Landholders:  Tyne Valley Fam and Creek Peeks

Grant:            $40,000 ($20,000 each, earthworks, rock excavation, fencing and plants)

In-kind:          $40,000 ($20,000 each logs with root balls attached, rock, soil and labour)

The sediment problem

An ephemeral flood channel has broken away from the Tyne River in the South Esk catchment and is running parallel to the river whenever heavy rainfall causes flooding.  Flood waters are actively scouring large holes and creating head cuts, sending sediment downstream affecting water quality and impacting on aquatic ecosystem health.  The flood channel runs through adjoining properties where treatment will only be successful if a combined solution is found and supported through landholder partnerships.

What are the aims of the project?

The aim of the project is to prevent further scouring by lining the holes with geofabric, filling the holes with rock and large woody debris, and establishing native plants along the banks and in the channel. This will act to roughen, add texture and structure to the channel bed.  Once the plants take hold and stock has been fenced off from the project site, the vegetation will prevent further scouring and become more resilient during and after major flood events.

How does the project demonstrate innovation?

The flood channel runs through two adjoining properties, where the landholders have come together to formulate and implement a solution, putting aside boundaries.  The Sediment Demonstration Grants are actively encouraging, supporting and facilitating landholder partnerships to ensure the best outcome for landholders, land managers and the environment.

How are the works beneficial?

Reducing the sediment loads to the Tyne River will help improve the water quality and aquatic ecosystem health downstream.  Revegetating ephemeral streams and preventing stock access increases native habitat and works to enhance biodiversity and connectivity through the landscape.  Landholders working together on a common problem to find a shared solution builds upon existing relationships and allows knowledge to be shared within the community and encourages social investment in waterway management.

 

Case Study 5: Timber field piles helping to restore streams after willow removal

Landowner:             Kingston

Grant:                         $10,150 (excavation works and matting)

In-kind:                       $13,000 (Labour, plants and rock)

The sediment problem

The project site is located on the Ben Lomond Rivulet, a tributary of the South Esk River.  Years of willow infestation has created in-stream diversions and a series of head cuts.  Five years ago willows were removed, significantly increasing erosion and releasing sediment to the waterways.  The area is subject to severe seasonal flooding making it evident an erosion solution and remediation was needed.

What are the aims of the project?

The aim of the project is to stabilise the bank, prevent further erosion and reduce the sediment loads to waterways.   The re-establishment of native riparian vegetation will have multiple benefits for the aquatic ecosystems, water quality, biodiversity and floodplain resilience.  The remediation works will assist in safeguarding the considerable natural values of the area.

How does the project demonstrate innovation?

Timber pile fields were installed to reduce the energy of high flows, creating eddies which encourage the deposition of sediment around the base of the piles.  Unlike large wood structures, the field piles do not cause significant scouring during high flows.  The method is not commonly used in Tasmania, however many successful examples can be seen on mainland Australia.  Promoting the use of sustainable, natural materials in river works is important to maintain the stream’s integrity.

How are the works beneficial?

This innovative design reintroduces timber to the stream, providing bank protection, flow diversion, sediment deposition and works to improve the resiliency of streams during severe flooding events.  Multiple benefits are achieved through bank stabilisation, stream and riparian rehabilitation, and encouraging the important role timber plays in providing habitat and aquatic ecosystem processes.

 

Case Study 6: Engineered log jam to prevent bank erosion

Land owner:         Armidale Stud

Grant:                     $20,000 (earthworks, soil and plants)

In-kind:                  $29,540 (logs with root balls attached, rock, some fencing and labour)

The sediment problem

The project site is subjected to seasonal flooding where the banks have been cleared of riparian vegetation and woody debris is no longer evident in-stream.  With approximately 5 m of eroded bank, the flows regularly breach the banks, cutting a path into the floodplain.  This scenario is common in the lower reaches of the Meander River.

What are the aims of the project?

The aim of the project is to help stabilise the bank, prevent further degradation, and reduce the sediment loading to the Meander River, by installing a series of bank-attached, log deflector jams.  Fencing off the riparian zone will exclude stock, preventing further damage to the bank and protect the revegetation of the streamside zone, providing a buffer zone and important riparian habitat.

How does the project demonstrate innovation?Amidale Stud project showing completed bank stabilisation works on the Meander River

Bank-attached, log deflector jams as yet, are not a common method used in Tasmania.  A series of three jams were installed to deflect the flow from the bank, and to break up the stream energy and high velocities which aid erosion.  Materials were sourced from the farm, such as the hardwood trees with the root balls attached used for the structure.   A minimum of six logs for each structure are placed in a grid pattern with attached root balls facing into the flow allowing the structure to be pinned back into the bank.

How are the works beneficial?

This innovative design reintroduces timber to the stream providing for; bank protection, flow diversion, the creation of deep pools for improved fish habitat, complex cover and breeding habitat for native freshwater fish, substrates for biofilm to establish, and can aid in the sequestration of nutrients. These works all help to improve water quality.

 

 

Supported by
Tasmania - Explore the possibilitiesLaunceston City CouncilWest Tamar CouncilGeorge Town CouncilNorthern Midlands CouncilMeander Valley CouncilHydro Tasmania

0.1098 s - Server Process Time

cache - Request Source

711 - Page ID