Case study:Gadebridge park river restoration: Difference between revisions

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{{Project background
|Reach length directly affected=415
|Project started=2015-10-07
|Works started=2024-09-04
|Works completed=2025-07-01
|Project completed=2026-07-22
|Total cost category=more than 10000 k€
|Funding sources=Environment Agency, AffinityWater, Dacorum Borough Council
|Investigation and design cost category=more than 10000 k€
|Investigation and design Lead organisation=JBA Consulting
|Investigation and design Other contact forename=Oliver
|Investigation and design Other contact surname=Francis
|Stakeholder engagement Lead organisation=Environment Agency
|Stakeholder engagement Other contact forename=Kelly
|Stakeholder engagement Other contact surname=Standbrook
|Works1 and supervision cost category=more than 10000 k€
|Works and supervision Lead organisation=BAM Nuttall Limited
|Works and supervision Other contact forename=David
|Works and supervision Other contact surname=Bugden
|Post-project management and maintenance Lead organisation=Dacorum Borough Council
|Post-project management and maintenance Other contact forename=Robert
|Post-project management and maintenance Other contact surname=Cassidy
|Monitoring Lead organisation=Environment Agency
|Monitoring Other contact forename=Kelly
|Monitoring Other contact surname=Standbrook
|Supplementary funding information=Total project cost: £4.148 million. EA FCERM £2.268 million, EA Water Resources £1.510 million. Affinity Water £250k. Dacorum Borough Council £120k.
Fiver Rivers were subcontracted by BAM to undertake the ecological elements of the works- placement of gravels, planting etc.
}}
{{Project overview
{{Project overview
|Status=Complete
|Status=Complete
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The project was designed by JBA Consulting Limited and delivered by BAM Nuttall Limited.
The project was designed by JBA Consulting Limited and delivered by BAM Nuttall Limited.
|Monitoring surveys and results=Macrophyte survey- August 2025:
|Monitoring surveys and results=Baseline surveys were undertaken for the project site pre-works. There were a limited number of Macrophytes species and a very homogenous community in the mill channel. In terms of fish, in the 2021 survey we were suffering low flows. The highly modified old channel had no resilience in such conditions and offered very little habitat for fish during those flows. We confirmed this, as we recorded trout on a survey in 2022 further upstream, where restoration work had been carried out previously.
 
Post construction surveys:
 
Macrophyte survey- August 2025:
New species:
New species:
*Persicaria maculosa (Redshank)  
*Persicaria maculosa (Redshank)  
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In a fisheries survey in September 2025, we recorded high numbers of minnow, and similar counts for stickleback and bullhead. Most significantly we recorded 14 trout in the ~100m section, with a few different age classes represented. We also undertook a detailed habitat survey to help assess how the habitat will change in the coming years.  
In a fisheries survey in September 2025, we recorded high numbers of minnow, and similar counts for stickleback and bullhead. Most significantly we recorded 14 trout in the ~100m section, with a few different age classes represented. We also undertook a detailed habitat survey to help assess how the habitat will change in the coming years.  


Summary of improvement- In the 2021 survey we were suffering low flows. The highly modified old channel had no resilience in such conditions and offered very little habitat for fish during those flows. We confirmed this, as we recorded trout on a survey in 2022 further upstream, where restoration work had been carried out previously. Our work within the park restored a more varied range of habitats that could be used across more flows.
Summary of improvement- Our work within the park restored a more varied range of habitats that could be used across more flows.


Our 2025 post works survey showed a significant increase in numbers of "minor" species, all of which are prey items for trout. Their increased abundance is a great sign of river health and will support trout numbers in the park. Habitat requirements change as trout are in different life stages. The trout we recorded were from a few different age classes, from juveniles to adults. This shows that even in a 100m section there is enough variety in habitat to support a population of trout.
Our 2025 post works survey showed a significant increase in numbers of "minor" species, all of which are prey items for trout. Their increased abundance is a great sign of river health and will support trout numbers in the park. Habitat requirements change as trout are in different life stages. The trout we recorded were from a few different age classes, from juveniles to adults. This shows that even in a 100m section there is enough variety in habitat to support a population of trout.
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A Kingfisher and 3 Grey Wagtail have also been spotted on site since the restoration was completed.
A Kingfisher and 3 Grey Wagtail have also been spotted on site since the restoration was completed.
Surveys are ongoing, including water vole, riverfly, hyporheic, flow, temperature, macrophytes, invertebrates and fish.
|Lessons learn=*Factor in a good contingency for the project, thinking about the contractors available on the framework, increases in material costs, inflation, FTE charges, compensation events. Have a good understanding of any changes to the design, working with the designer to estimate cost increases.
|Lessons learn=*Factor in a good contingency for the project, thinking about the contractors available on the framework, increases in material costs, inflation, FTE charges, compensation events. Have a good understanding of any changes to the design, working with the designer to estimate cost increases.
*The project group should contain members of the required level of authority. Set accountabilities early to avoid delays and misunderstanding plus each team's minimum requirements. Technical team leads should have ownership of their elements of the project to ensure all discussion items are logged and addressed.
*The project group should contain members of the required level of authority. Set accountabilities early to avoid delays and misunderstanding plus each team's minimum requirements. Technical team leads should have ownership of their elements of the project to ensure all discussion items are logged and addressed.
Line 75: Line 53:
*Engage with the local community in a variety of ways eg. project web page, mailing list updates, project mailbox, Facebook, Twitter, council newsletters, onsite signage, community events.
*Engage with the local community in a variety of ways eg. project web page, mailing list updates, project mailbox, Facebook, Twitter, council newsletters, onsite signage, community events.
}}
}}
{{Project background
|Reach length directly affected=415
|Project started=2015-10-07
|Works started=2024-09-04
|Works completed=2025-07-01
|Project completed=2026-07-22
|Total cost category=more than 10000 k€
|Funding sources=Environment Agency, AffinityWater, Dacorum Borough Council
|Investigation and design cost category=more than 10000 k€
|Investigation and design Lead organisation=JBA Consulting
|Investigation and design Other contact forename=Oliver
|Investigation and design Other contact surname=Francis
|Stakeholder engagement Lead organisation=Environment Agency
|Stakeholder engagement Other contact forename=Kelly
|Stakeholder engagement Other contact surname=Standbrook
|Works1 and supervision cost category=more than 10000 k€
|Works and supervision Lead organisation=BAM Nuttall Limited
|Works and supervision Other contact forename=David
|Works and supervision Other contact surname=Bugden
|Post-project management and maintenance Lead organisation=Dacorum Borough Council
|Post-project management and maintenance Other contact forename=Robert
|Post-project management and maintenance Other contact surname=Cassidy
|Monitoring Lead organisation=Environment Agency
|Monitoring Other contact forename=Kelly
|Monitoring Other contact surname=Standbrook
|Supplementary funding information=Total project cost: £4.148 million. EA FCERM £2.268 million, EA Water Resources £1.510 million. Affinity Water £250k. Dacorum Borough Council £120k.
Fiver Rivers were subcontracted by BAM to undertake the ecological elements of the works- placement of gravels, planting etc.
}}
{{Case study status
{{Case study status
|Approval status=Approved
|Approval status=Approved

Revision as of 09:33, 22 January 2026


Project overview

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Status Complete
Project web site http://https://www.colnecan.org.uk/index.php/the-action-plans/rivers-gade-and-bulbourne/rivers-gade-and-bulbourne-projects/302-channel-restoration-gadebridge-park
Themes Environmental flows and water resources, Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits, Urban
Country England
Main contact forename Kelly
Main contact surname Standbrook
Main contact user ID
Contact organisation Environment Agency
Contact organisation web site http://https://www.gov.uk/government/organisations/environment-agency
Partner organisations Affinity Water, Dacorum Borough Council
Parent multi-site project
This is a parent project
encompassing the following
projects 		No
Drone footage of new channel and central footbridge.

Project summary

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The River Gade, a globally rare chalk stream with poor ecological status within Gadebridge park, used to flow down a ‘perched’ channel created to supply water to Bury Mill. It was disconnected from its floodplain and over widened, leading to sluggish flows and a build-up of silt and vegetation. The EA Gauging Station Bury Mill and other in-channel structures acted as barriers to fish movement. Being disconnected from groundwater and spring flow had a significant impact on low flow resilience and to wildlife. Partnered with Dacorum Borough Council and Affinity Water Limited, this Environment Agency lead project diverted 415 metres of river channel to the valley bottom through the park. The Bury Mill gauging station was replaced with an ultrasonic one to allow fish passage. Work progressed from 2018 with construction complete in June 2025.

With the inclusion of spring water flow, which was previously piped beneath the park and discharged at Kings Langley 5 Kilometres downstream, 6.5 kilometres of river has been improved. 0.85 hectares of habitat was created, 3.9 hectares habitat enhanced, 0.9 hectares buffer strip created and 1.1km water body opened to fish passage. The river corridor now provides better resilience to low and high flows and the impacts of climate change. Two new bridges and a large gravel access point to the channel were provided for the local community.

The project was designed by JBA Consulting Limited and delivered by BAM Nuttall Limited.

Monitoring surveys and results

Edit project overview to modify the Monitoring survey and results.


Baseline surveys were undertaken for the project site pre-works. There were a limited number of Macrophytes species and a very homogenous community in the mill channel. In terms of fish, in the 2021 survey we were suffering low flows. The highly modified old channel had no resilience in such conditions and offered very little habitat for fish during those flows. We confirmed this, as we recorded trout on a survey in 2022 further upstream, where restoration work had been carried out previously.

Post construction surveys:

Macrophyte survey- August 2025: New species:

  • Persicaria maculosa (Redshank)
  • Callitriche obtusangula (Blunt fruited water starwort)
  • Sparganium erectum (Branched bur-reed)
  • Lemna minor (Duckweed)
  • The total number of species has increased from 18 to 24 new ones

Increase in cover:

  • Ranunculus penicillatus subsp. Pseudofluitans (Brook watercrowfoot)
  • Veronica anagallis-aquatica (Water speedwell)

Fisheries: In a fisheries survey in September 2025, we recorded high numbers of minnow, and similar counts for stickleback and bullhead. Most significantly we recorded 14 trout in the ~100m section, with a few different age classes represented. We also undertook a detailed habitat survey to help assess how the habitat will change in the coming years.

Summary of improvement- Our work within the park restored a more varied range of habitats that could be used across more flows.

Our 2025 post works survey showed a significant increase in numbers of "minor" species, all of which are prey items for trout. Their increased abundance is a great sign of river health and will support trout numbers in the park. Habitat requirements change as trout are in different life stages. The trout we recorded were from a few different age classes, from juveniles to adults. This shows that even in a 100m section there is enough variety in habitat to support a population of trout.

BNG has increased by 10% from 26.8 units to 29.53 units

A Kingfisher and 3 Grey Wagtail have also been spotted on site since the restoration was completed.

Surveys are ongoing, including water vole, riverfly, hyporheic, flow, temperature, macrophytes, invertebrates and fish.

Lessons learnt

Edit project overview to modify the lessons learnt.


  • Factor in a good contingency for the project, thinking about the contractors available on the framework, increases in material costs, inflation, FTE charges, compensation events. Have a good understanding of any changes to the design, working with the designer to estimate cost increases.
  • The project group should contain members of the required level of authority. Set accountabilities early to avoid delays and misunderstanding plus each team's minimum requirements. Technical team leads should have ownership of their elements of the project to ensure all discussion items are logged and addressed.
  • Make sure all staff have the training and capabilities to conduct their role within the project team and they have available resource.
  • Develop a robust benefits realisation strategy early on to enable a better understanding of the benefits to all parties and a greater financial contribution.
  • Walk the line of works with the Topography Plan and Tree Survey before commencing works at site, to check for mapping discrepancies.
  • Ensure a close working relationship with the designer and the technical teams to avoid delays.
  • Engage with the local community in a variety of ways eg. project web page, mailing list updates, project mailbox, Facebook, Twitter, council newsletters, onsite signage, community events.

Project background

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Reach length directly affected (m) 415415 m <br />0.415 km <br />41,500 cm <br />
Project started 2015-10-07
Works started 2024-09-04
Works completed 2025-07-01
Project completed 2026-07-22
Total cost category more than 10000 k€
Total cost (k€)
Benefit to cost ratio
Funding sources Environment Agency, AffinityWater, Dacorum Borough Council

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design more than 10000 k€ JBA Consulting Oliver Francis
Stakeholder engagement and communication Environment Agency Kelly Standbrook
Works and works supervision more than 10000 k€ BAM Nuttall Limited David Bugden
Post-project management and maintenance Dacorum Borough Council Robert Cassidy
Monitoring Environment Agency Kelly Standbrook

Supplementary funding information

Total project cost: £4.148 million. EA FCERM £2.268 million, EA Water Resources £1.510 million. Affinity Water £250k. Dacorum Borough Council £120k. Fiver Rivers were subcontracted by BAM to undertake the ecological elements of the works- placement of gravels, planting etc.



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Location: 51° 46' 43.64" N, 0° 29' 26.48" W
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Catchment and subcatchment

Catchment

River basin district Thames
River basin Colne

Subcatchment

River name Gade (Upper stretch Great Gaddesden to confluence with Bulbourne / GUC)
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m) 253253 m <br />0.253 km <br />25,300 cm <br />
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Grassland
Waterbody ID GB106039029900



Site

Name Gadebridge Park
WFD water body codes GB106039029900
WFD (national) typology freshwater, Chalk stream
WFD water body name Gade (Upper stretch Great Gaddesden to confluence with Bulbourne / GUC)
Pre-project morphology Impounded, Over deepened, Over-widened, Single channel, Straightened
Reference morphology
Desired post project morphology Actively meandering, Pool-riffle
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present Yes
Species of interest Orange Balsam, American signal crayfish (Pacifastacus leniusculus), Water Vole
Dominant hydrology Groundwater
Dominant substrate Silt
River corridor land use Urban, parkland, farmland
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Reasons for river restoration

Mitigation of a pressure Barriers to fish migration
Hydromorphology Freshwater flow regime, Width & depth variation, Substrate conditions, Flow velocities, Connection to groundwaters
Biology Fish, Fish: Abundance, Macrophytes and/or phytobenthos: Average abundance, Fish: Species composition
Physico-chemical Oxygen balance, Temperature
Other reasons for the project Moving the river to valley bottom and connecting it with its flood plain will make it more resilient to high and low flows and the park more usable for more of the time.


Measures

Structural measures
Bank/bed modifications 1:3 and 1:6 banks, Introduction of spawning gravels, Creation of pools and riffles, creation of buffer zones, Creation of low flow channel, gravel river access point, preservation of historic mill leat
Floodplain / River corridor Creation of multi stage channel, Improving fish migration, Lowland meadow, Maintenance of riparian vegetation, Introduction of spring flow, New ultrasonic gauging station
Planform / Channel pattern Creation of meanders, Improvement of channel morphology, Improving fish migration
Other Introduction of 2 foot bridges
Non-structural measures
Management interventions
Social measures (incl. engagement) Engagement with a wide range of stakeholders, 2 events in the park, Junior river wardens programme, school visits, tours and presentations for local interest groups, social media video, Information boards, mailing list, project website, project mailbox, community satisfaction survey
Other Ecological survey, Monitoring via Fixed Point Photography, Climate change adaptation, Definition of environmental objectives and indicators and monitoring program., Removal of Stevenson Stones for display


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Connection to groundwaters Yes Yes No No Yes Awaiting results
Freshwater flow regime Yes Yes No No Yes Awaiting results

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Fish Yes Yes No No Yes Improvement
Invertebrates Yes Yes No No Yes Awaiting results
Macrophytes Yes Yes No No Yes Improvement

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Oxygen balance Yes Yes No No No Awaiting results
PH Yes Yes No No No Awaiting results
Temperature Yes Yes No No No Awaiting results

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
River Habitat Survey Yes Yes No No Yes Awaiting results
Mammel survey Yes Yes No No No Awaiting results
Public opinion Yes Yes No No No Awaiting results
river bank vegetation Yes Yes No No Yes Awaiting results


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://https://www.dacorum.gov.uk/home/all-news/2025/08/06/river-gade-restoration-in-gadebridge-park-nears-final-phase Dacorum borough council
http://https://consult.environment-agency.gov.uk/engagement/gadebridge-park-information-page/supporting documents/gadebridge-park-faqs-aug-2025pdf Environment Agency FAQ
http://https://www.gov.uk/government/news/river-gade-returns-to-its-natural-course-through-gadebridge-park news article
http://https://www.bbc.co.uk/news/articles/c1mg3mn98kdo news article
http://https://www.affinitywater.co.uk/sustainability/restoration/river-gade affinity water

Supplementary Information

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