| Country | Finland | ||||
| Site Name | Ritobäcken | ||||
| Summary | Conventional dredging of ditches and streams to ensure agricultural drainage and flood mitigation has severe environmental impacts. We assessed the main benefits of an alternative, nature-based two-stage channel design with floodplains excavated along the main channel. We conducted investigations at Finnish field sites (primary field site: Ritobäcken, Finland) and performed a literature survey focusing on Boreal and Continental climatic conditions. The 820 m long two-stage channel was constructed in 2010. The study results show that two-stage ditches provide efficient flood control and drainage, and likely improve stream water quality and biodiversity. The obtained knowledge can be used to estimate environmental effects from the similar type of drainage solutions in rural areas. | ||||
| NUTS Code | Helsinki-Uusimaa | ||||
| RBD code | FIVHA2 | ||||
| Transboundary | 0 | ||||
| Data provider | Kaisa Västilä, SYKE | ||||
| Source(s) | |||||
| NWRM(s) implemented in the case study |
Floodplain restoration and management Wetland restoration and management Buffer strips and hedges |
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| Application Site Coordinates | Latitude | Longitude | |||
| 60.3336 N (two-stage channel outlet) | 25.2199 E (two-stage channel outlet) | ||||
| Climate zone | Cool temperate moist | ||||
| Mean Rainfall | 630 mm/year | ||||
| Average temperature | 6 °C | ||||
| Average runoff coefficient | 0.200 | ||||
| Water quality inflow | |||||
| Mean annual runoff range | 150–300 mm | ||||
| Average slope range | nearly level (0–1%) | ||||
| Vegetation class | Site surrounded by agricultural and forested areas; the banks and floodplains of the channel are covered by grasses and shrubs. | ||||
| Monitoring impacts effects | |||||
| Performance impact estimation method | Retention of suspended sediment (SS) and particulate phosphorus (P) based on repeated cross-sectional monitoring, continuous monitoring of water level, discharge and SS loads, and water sampling during baseflow and rainfall/snowmelt events; plant and pollinator diversity through field investigations; improvement in drainage and flood mitigation based on cross-sectional surveys and measured and modelled water levels | ||||
| Performance impact estimation information | The case study compiles together results from earlier published research and new analyses | ||||
| Runoff reduction | Rather small as volume of floodplain low in comparison to catchment area | ||||
| Peak flow rate reduction | Rather small as volume of floodplain low in comparison to catchment area | ||||
| Water quality overall improvements | Positive impact through increased retention of suspended sediment and phosphorus on the floodplain | ||||
| Water quality Improvements Phosphorus (P) | The retention efficiency per 1 km of two-stage channel length was 16.3% for the floodplain in relation to the total load and 3.5% considering the entire cross-sectional channel area. The significant re-suspension of earlier deposits from the low-flow channel in the first 2 years after construction decreased the total retention efficiency. | ||||
| Water quality Improvements (P) unit | % retention of total load per 1 km of two-stage channel length | ||||
| Water quality Improvements Nitrogen (N) | Not determined; two-stage channel sites from USA show increased nitrogen removal through denitrification | ||||
| Water quality Improvements Nitrogen (N) unit | |||||
| Water quality Improvements Total Suspended Solid (TSS) | The retention efficiency per 1 km of two-stage channel length was 13.6% for the floodplain in relation to the total load and 2.1% considering the entire cross-sectional channel area. The significant re-suspension of earlier deposits from the low-flow channel in the first 2 years after construction decreased the total retention efficiency. | ||||
| Water quality Improvements (TSS) unit | % retention of total load per 1 km of two-stage channel length | ||||
| Soil quality overall soil improvements | The solution may have positive impacts on soil quality by likely ensuring the long-term functioning of drainage and flood control, which likely maintains good soil structure and composition | ||||
| Key lessons | The Ritobäcken case study represents a research work which aimed to assess whether and how a two-stage channel improves and regulates stream water quality and flow. | ||||
| Financing mechanism | Investment costs of two-stage channels can be publicly subsidized through the Centres for Economic Development, Transport and the Environment (ELY centres) and partly by landowners. | ||||
| Success factor(s) | Type | Role | Comments | ||
| Existing case studies | main factor | Contributed real-life cost and performance data | |||
| Careful design of the channel | main factor | Benefits through frequent floodplain inundation | |||
| Supporting landowners | main factor | ||||
| Collaboration with stakeholders | main factor | Research-development-practice link | |||
| Financing | Type | Comments | |||
| Other | Investment costs can be subsidised | ||||
| Barrier | Type | Role | Comments | ||
| Lacking long term water quality data | main barrier | Long term effects have to be estimated | |||
| Lacking data on monetized benefits | main barrier | Need to use estimations which are as close as possible | |||
| Driver | Type | Role | Comments | ||
| Dredging need | main driver | Growing need for re-dredging has been recognized which could offer an opportunity to increase the number of two-stage channels | |||
| Financing share | Land surveying & planning costs were covered by an R&D project and construction costs by local state authority (ELY-centre) | ||||
| Direct benefits information | Two-stage channels can enhance biodiversity and water quality in agricultural channels in comparison conventional dredging. This could also partly serve the implementation of The Water Framework Directive (2000/60/EC). | ||||
| Costs investment information | |||||
| Costs (operation, maintenance) | No operation costs, maintenance costs low with less need for maintenance compared to conventional dredging. | ||||
| Costs total information | Initial construction cost of two-stage channels is higher than conventional maintenance dredging, but the life-cycle maintenance costs are estimated to be notably lower. The costs related to lost field area can be largely mitigated by integrating two-stage channels into CAP-AES as eligible vegetated buffer. | ||||
| Ecosystem improved biodiversity | Yes | ||||
| Information on Ecosystem improved biodiversity | The two-stage channel design provides a more natural-like habitat with increased plant and fish biodiversity. | ||||
| Ecosystem provisioning services | |||||
| Ecosystem water supply | Low-flow channel of the two-stage channel enables more constant water flow and supply in the stream, and ensures higher water levels during low-flow periods compared to conventionally dredged channels. | ||||
| Ecosystem impact climate regulation | Good and sustainable drainage of the fields and flood mitigation. | ||||
| Information on Ecosystem flood control volume | Maintains good drainage of the fields with less need for maintenance compared to conventionally dredged ditches, thus decreasing the need for ecologically harmful re-dredging. | ||||
| Policy description | The study deals with Ritobäcken two-stage channel, in Sipoo municipality. The channel was carefully designed to improve drainage and water quality and to prevent harm to stream biodiversity. The aim was to evaluate the total costs and monetary environmental benefits of the two-stage channel approach in comparison to the conventional dredging. The pilot-scale results can be up-scaled to larger agricultural catchments. We also investigated the bottlenecks in the financing and governance hindering the mainstreaming of two-stage channels. | ||||
| Part of wider plan | No | ||||
| Policy pressure | No | ||||
| Policy requirement directive | No | ||||
| Policy impact | Not yet | ||||
| Policy wider plan | Based on this study, our target was to provide recommendations on how to tackle the bottlenecks, and propose how to finance two-stage channels, including their integration into the CAP-AES based on their optimal spatial targeting with respect to other types of vegetated riparian buffers. | ||||
| Policy area | |||||
| Policy target | |||||
| Target purpose |
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| Application scale | Reach-scale (820 m long two-stage channel) | ||||
| Area (ha) | 0.33 (Area of the two-stage channel) | ||||
| Area subject to Land use change or Management/Practice change (ha) | 0.33 | ||||
| Size | 0.33 ha | ||||
| Constraints | Sipoonkorpi natural park right downstream | ||||
| Inflow volume | 0.12 m3/sec | ||||
| Outflow volume | 0.12 m3/sec | ||||
| Annual peak flow rate | ~1.4 m3/sec | ||||
| Public consultation | |||||
| Contractual arrangements | Design contractual arrangement | ||||
| Design consultation activity | |||||
| Design land use change | |||||
| Design authority | |||||
| Authority type | Role | Name | Comments | ||
| Regional environmental authority | Initiation; Implementation | Uusimaa Centre for Economic Development, Transport and the Environment (ELY) | |||
| University | Monitoring | Aalto University | Water Protection Association of the River Vantaa and Helsinki Region, and Uusimaa ELY Centre participated in monitoring in 2010-2011 | ||
| Designing consultant | Design | Ympäristötekniikan inisnööritoimisto Jami Aho Oy | Design of the two-stage channel | ||
| Construction company | Construction | ||||
| Private landowners | Knowledge sharing with others interested in the solution | ||||
Ritobäcken case study - Factsheet
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Ritobäcken case study
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