Suburban River Low-cost Riverbank erosion

 

DESCRIPTION
Measures

 

 Live palisades consist of a row or series of rows of live cuttings, placed in a bank to resist or stabilize erosion. The live cuttings are driven into holes made in the soil of the bank up to two-thirds of their length side by side to form a palisade. The cuttings will develop a dense root network that will resist the erosion of the bank. Different types of cuttings can be included in the live palisade to improve biodiversity.
Location

 

 Live palisades are a suitable streambank protection measure where surface erosion has started on a bank but has not advanced to more serious gulley erosion and an inexpensive control method is needed. Construction is easy and can be done rapidly.
Design options and performance Palisades are a low-cost and easy method to stabilize a bank and once installed are immediately effective. Their effectiveness will improve with time and as the root systems develop the soil will be stabilized and evapotranspiration will dry out the soil.
Feasibility criteria

 

 ●    Technical design: The size of the cuttings depends on the purpose for which they will be used. Where palisades are planted in lines to protect slopes against erosion, cuttings are from 2 to 4 cm in diameter and about 0.5 m long, but if used to stabilize gully erosion larger stakes up to 1 m in length are used. A horizontal pole is joined across the top to strengthen the structure. Cuttings are taken from a locally available shrub or small tree that grows well in similar sites and can grow well from cuttings by producing many shoots. Donor trees should be 6 to 18 months of age. Cutting shall be made with sharp tools with no damage to the bark. The tops shall be cut perpendicular and the bottoms trimmed to 45⁰. Once cut the cuttings are wrapped in jute sacks and kept in the shade while being transported to the site or may be stored in water for up to two days. They are placed in pre-formed holes up to two-thirds of their length.

●    Soil media: n/a

●    Soil slope: Suitable for steep banks

●    Surface cover: n/a

●    Materials: Live cuttings
Operation      and maintenance Replacement of some cuttings which fail to grow may be needed but otherwise, no maintenance is required unless the vegetation impacts other activities in the stream or river bank.
Cost and benefits Low-cost measure which can effectively stabilize banks and reduce erosion. As the root systems and foliage grow the palisade becomes more effective at stabilizing the bank while at the same time, it adds to the biodiversity of the site and creates new habitat.
 Design solutions

 

 This is a low-cost design solution that can be applied by planting lines of palisades to prevent slope erosion or to check gully erosion.  Cuttings should be taken from a locally available shrub or small tree that grows well in similar sites and can grow well from cuttings by producing many shoots. Cuttings from the common Golden Dewdrop or Thanh Quan (Duranta erecta) have been successfully used for constructing palisades in Northern Vietnam.
Environmental performance The posts are expected to root along the entire below-ground length of the palisade and thus produce a dense cylinder of roots that will protect the bank from erosion as the steam encroaches on the palisade. When the live palisade matures into trees they will provide significant ecological benefit. Various species of cuttings can be added to increase the vegetation cover and enhance the diversity.
Sources ●    ICEM, 2017. Promoting Climate Resilient Rural Infrastructure in Northern Viet Nam, Technical Report 17: Technical Guidelines for Slope Protection. Prepared for the Ministry of Agriculture and Rural Development and Asian Development Bank. Hanoi.

●    ICEM 2017. Slope Protection Designs and Specifications, TA-8102 VIE: Promoting Climate Resilient Rural Infrastructure in Northern Vietnam, Technical Report No. 18. Prepared for Ministry of Agriculture and Rural Development and Asian Development Bank. Hanoi.

●    Lammeranner, P., Rauch, H. P., and L. Gregor. 2007. Implementation and Monitoring of Soil Bioengineering measures at a Landslide in the Middle Mountains of Nepal. Plant and Soil, 278.

●    Pathak, S. 2015. Bio-engineering measures for soil erosion control.

●    Polster, D. F. 2003. Soil Bioengineering for Slope Stabilization and Site Restoration. Mining and the Environment.

 

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Originally developed under the ADB ‘TA-9417 VIE: Secondary Green Cities Development Project – Output 2: Demonstrated sustainable and resilient development in Hue, Ha Giang and Vinh Yen’. Adapted for the UN-CTCN project ‘Climate risk assessment for subnational adaptation and establishment of a local climate information system for climate change adaptation (LISA) in Cambodia’.