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Deliverable D.T1.2.1

The proposal for the most effective technological solutions to protect from bank erosion and to reduce the pollution load

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Content

1. Introduction 3

2. River Mustoja catchment area 3

3. Most effective technological solutions to protect from bank erosion and to reduce the pollution load 5 4. References 9

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1. Introduction The main objective of WP T1 is to review existing methods and technologies for improvement of water quality (WQ) and ecological status of small urban water bodies. Based on the review, appropriate solutions will be selected. In Tallinn, the best technical solution against bank erosion will be selected for River Mustjõgi, to reduce peak discharges and transport of different pollutants in Tallinn’s most affected residential area will be evaluated. The desktop study is about technological solutions to protect from bank erosion, environmentally friendly solution using natural materials as wood, stone etc. will be reviewed. Bank erosion is often caused by human activity, leading to remarkable changes in waterbodies. The result is increased flow patterns, high flow velocity and sediment rate and finally bank erosion. Human activities have significantly changed the riverbed and flow patterns of River Mustoja. River alteration started in 17th century, land use was changed and channels, network constructed for drainage of Kristiine meadows. In the 19th century, industrial activity picked up in the area, accompanied by brisk industrial and residential construction, the construction of both private and rental homes, as well as extensive standard housing construction during the Soviet era. During the 1960s and 1970s, the stream bed was gradually closed to the stormwater pipeline. In the 1970s, rainwater collected through the intersection of the Marja Street rainwater collector and the Laki Street rainwater pipe at the intersection of Mustjõe and Marja Streets was channeled into the Mustjõe Stream through two 1500 mm diameter pipes.

2. River Mustoja catchment area and status It is estimated that around 60 000 people live in the catchment area. In residential areas, the population density is higher in the Mustoja middle and upstream catchment areas. Industrial, production areas are concentrated in the lower reaches of the Mustoja catchment area and strormwater is discharged to the stormwater system just before River Mustoja open part starts. According to the Estonian Land Board Estonian Topographic Database ETAK, approximately 50% of the total Mustoja catchment area is under the impervious surfaces. Production areas share from the total impervious area is about 10%, production buildings 5%, roads form 23% and residential and public buildings 10%. In such urbanisation situation, runoff coefficient can reach 0.8 thus 80% of precipitation form runoff. All rain and melting water collected in the catchment area is directed through pipes and drainage ditches to the River Mustoja. Stormwater outfalls with high discharge velocities and rapidly fluctuating discharge causes flooding and bank erosion resulting in land loss and endanger built property. There are properties and buildings that are very close to the shore (figure 1 and 2)

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Figure 1. River Mustoja and properties borders

Figure 2. River Mustoja propertises near the stormwater outlet (left) and Saarma street (right) River Mustoja banks are steep (figure 3) in places and hanging banks have formed, crumbling of banks is going on. Largely, he streambed is narrow (ca 3 m in the bottom and ca 5 m on the top) to restore slopes (figure 3), avoiding damage to plants and trees by widening the bed. The stream is permanently filled with water. During dry periods, flow is quite stable, long-term average is estimated between 80 l/s and 130 l/s that can increase up

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to 3 – 5 m3/s during extraordinary heavy rain. Due to erosion, deposition of eroded material further downstream and sedimentation of the eroded material will occur.

Figure 3. River Mustoja Saarma Street profile (upper left and bottom left), middle part of the river (upper right and bottom right) According to monitoring results, organic matter, total organic carbon, nitrogen and phosphorus content of sediments is rather high, especially in the middle course of the river. Higher levels of metals in water and sediments were detected. The overall River Mustoja water quality is poor. (Deliverable D.T1.1.1. Report on local water quality monitoring and assessments of ecological problems in the pilot water bodies in Tallinn, Turku and Söderhamn) [1]

3. Most effective technological solutions to protect from bank erosion and to reduce the pollution load

In order to identify the best solution to erosion in the project output O.T.1.1. Review of tested and verified technology solutions preventing of nutrients and hazardous substances, including litter inflow from small urban waterbodies’[2] list of suitable methods and technologies for avoiding bank erosion prepared. Different restoration options, traditional engineering treatment, biotechnical and soil engineering solutions were studied. Based on the initial desktop studies and River Mustoja today’s situation, three possible approaches for solving the bank erosion problem to

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investigate in more detail were selected: large wood, timber-retaining walls, stone (riprap), stone walls (gabions) and stone mattresses. Use of large stones to protect waterbodies banks from erosion is old and traditional approach. Small-sized stones are available almost everywhere at affordable price and can be quickly placed. Individual rocks can adjust to flow patterns that is an advantage over concrete walls or large panels. However, there is limit for slope, slopes steeper than 2:1 can cause riprap loss due to erosion and sliding. [3] Stone baskets or gabions use for bank protection started in 1950s in cases where flow velocity was too high to riprap because of small sized stones and/or steep slope. Baskets are made from galvanized wire (Figure 4). Between the rock-filled baskets can set plants. For consistency and durability of the stones special mattresses made of galvanized or PVC coated multi-stranded steel wire is designed. The hexagonal mesh structure of the stone mattress can withstand high pressure without breaking or cracking. Galvanized steel mesh, especially if covered with PVC, has a long life. Stone mattresses are economical, especially when the filler stones are located near the workplace. Over time, the stones in the mattress sink into each other, the gaps between the stones settle down and plants start to grow. In this way, a stream similar to the natural will form.

River Bank 2*1*0.5m Reno Mattress Retaining Wall With Rock Basket Gabion

Cages http://www.wiremeshsteel.com/sale-9925637-river-bank-gabion-reno-mattress-with-rock-

bucket-gabion-cages-fit-bridge-protection.html

Swan River. Best Management practices for foreshore stabilisation. Approaches and

decision-support framework. Direct shore stabilisation approaches. Swan River Trust.

December 2009 [4]

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River Jägala, stone bakets https://www.hydroseal.ee/kivikorvid/

Engineered revetments, gabions [5]

Gabions filled with rocks https://www.maccaferri.com/ca/products/gabions/jumbo-gabion/

River Leevi reservoirs stone mattresses https://www.hydroseal.ee/kivikorvid/

Figure 4. Gabions and stone mattresses examples In urban areas, human activities have significant impact to waterbodies morphology and hydrology, as well as biodiversity, thus effective, simple and cost-effective protection measures are required. Use of wood can be appropriate choice in forest rich regions and can be easily used for waterbodies bank protection. According to the survey done by scientists from Austria and Germany about the use of large wood in stream restoration, experiences from 50 projects in Germany and Austria were analysed. Most of the structures, 72%, were fixed dominantly with wooden piles in stream or boulders or buried in the bank, other not at all. The low failure rate observed as fastening of the structures was sufficient. However, researches stress that to assess final stability, high flows occurring during the life span of wood structures should be considered. Implementation costs (placement and fixation of 1 m3 of wood volume), maintenance costs excluded, differed between 28 projects, median cost was low, 396 euros m-3. [6] By the overview in Manual on the use of timber in coastal and river engineering by Matt Crossman Jonathan Simm, timber is renewable and is an environmental friendly material,

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especially if recycled or come from sustainably managed forests. Relatively low energy required for its production and (except transport and processing) being virtually ‘carbon neutral’. Minimal expected life is according the manual is 7 – 25 years. [7] According to another guidance Waterways. Wetlands and Drainage Guide- Part B. (Christchurch City Council) the average life for most timber used in Christchurch's waterways is 35-45 years. Despite this, there is also stated that timber is not a sustainable option due to the need for future replacement. [8] Examples of use of wood in bank protection is on Figure 5.

https://www.landscapeinn.com/wood-walls/ Pärnu River in Pärnu City - bank

fortification with Impregnated wooden poles (05.11.2013, Maaleht )

https://www.grdesignandconstruct.com.au/gallery/portfolio/frankston-city-council-kananook-creek-retaining-walls-boardwalk-renewal/

Pärnu River in Pärnu City - bank fortification with Impregnated wooden

poles (05.11.2013, Maaleht)

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https://maps.calgary.ca/HealthyRivers/

https://g-continent.ru/en/vidy-rabot/beregoukreplenie-2/

Figure 5. Examples of use of wood in bank protection One of the old timber structures is a system of interconnected poles and planks. The weakness of such solution is that timber that is out of the water is under the serious risk of degradation. There is a need to use durable species and to employ preservative treatment that increase the life span. [9] Periodic maintenance is also required to ensure the durability of the impregnated timber structure, but the timber must be dry for this purpose. Based on analysis of observed different studies, nevertheless, there is no sufficient certainty that wood material will survive in a water-variable environment for a long time. For flows with quick and high fluctuation in time and extreme flows, as well as narrow streambed that is specific for River Mustoja, the structures with small-sized stone are more appropriate than from large wood, timber. Rock gabions can occupy area of narrow horizontal extent. Rock-mattress, likewise rock gabions are durable and porous, thus preventing build-up of hydrostatic pressure, also tolerate differential placing. References

1. Deliverable D.T1.1.1. Report on local water quality monitoring and assessments of ecological problems in the pilot water bodies in Tallinn, Turku and Söderham

2. HeaWater project output O.T.1.1. Review of tested and verified technology solutions preventing of nutrients and hazardous substances, including litter inflow from small urban waterbodies (Tallinn, Turku, Söderhamn)

3. Bank Stabilization Design Guidelines, 2015. U.S. Department of the Interior Bureau

of Reclamation Technical Service Center Denver, Colorado

4. Best Management practices for foreshore stabilisation. Approaches and decision-support framework. Direct shore stabilisation approaches. Swan River Trust. December 2009.

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https://www.dpaw.wa.gov.au/images/documents/conservation-management/riverpark/Management/Best%20management%20practices%20for%20foreshore%20stabilisation%20-%20Direct%20shore%20stabilisation%20approaches.pdf

5. Amrapalli Garanaik, Joel Sholtes. River Bank Protection., CIVE 717 - April 11, 2013 https://www.engr.colostate.edu/~pierre/ce_old/classes/ce717/PPT%202013/River%20Bank%20Protection.pdf

6. Jochem Kail, Daniel Hering, Susanne Muhar, Marc Gerhard and Sabine Preis, The use of large wood in stream restoration: experiences from 50 projects in Germany and Austria. Journal of Applied Ecology 2007. 44 , 1145–1155

7. Matt Crossman, Jonathan Simm, Manual on the use of timber in coastal and river engineering; published by Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD.URL: http://www.thomastelford.com

8. Waterways. Wetlands and Drainage Guide-Ko Te Anga Whakaora mõ Nga Arawai Rēpõ • Part B: Design Christchurch City Council • February 2003 https://www.ccc.govt.nz/assets/Documents/Environment/Water/waterways-guide/12.-Waterway-Erosion-Protection.pdf

9. Timber for marine and fresh water construction by A. C. Oliver, M.Sc., A.l.W.Sc. Edited and metricated by W. H. Brown, F.I.W.Sc. Published by Timber Research and Development Association Hughenden Valley, High Wycombe, HP14 4ND. Buckinghamshire, England Lic