River Restoration Summary
FLOW CIC worked with Herts and Middlesex Wildlife Trust to deliver detailed river restoration designs for the River Hiz, a priority chalk stream within the Ivel catchment. The project aimed to improve habitat diversity, resilience to low flows, and floodplain connectivity across 6 km of river. Through a combination of detailed walkovers, drone surveys, optioneering, and flood modelling, FLOW developed buildable, fully consented designs that restore natural processes and enhance conditions for species such as brown trout, macrophytes, and water vole. Interventions include large wood installations, beaver dam analogues, bank re-grading, and natural flood management features.
Requirements
As part of a partnership project to improve 6km of priority chalk river in the Ivel catchment, Herts and Middlesex Wildlife Trust commissioned FLOW CIC to carry out river restoration optioneering / feasibility through to detailed design of preferred options. The restoration designs should:
- Improve the resilience of the rivers to low flow conditions;
- Address the impacts limiting their recovery (i.e. dredging, realignment, unwanted access etc.)
- Improve the diversity of in-channel habitats to support populations of fish (notably brown trout), macrophytes and water vole (for future reintroduction);
- Increase connectivity of the river to floodplain habitats (existing and new) and improve quality of existing wetland features, such as reedbeds and wet grassland;
- Ensure designs are compliant with local EA flood risk and permitting conditions.
Approach
- Desk-based assessment: We collated a geodatabase of all open access information, including additional information provided by the client. This included: LiDAR, Flood Risk Mapping, Tree Preservation Orders, Conservation Areas, Designated and non-designated nature conservation sites, Heritage Sites, Geology, Hydrology, and Site Management Plans.
- Client meetings and stakeholder walkovers: Each site was visited with key stakeholders better to understand management regimes, opportunities, and constraints.
- River Restoration feasibility walkovers: All sites were walked, with opportunities and constraints mapped using ESRI Field Maps, allowing all data to feed directly into the project geodatabase.
- Drone Survey: A variety of drone imagery was taken, including stills, 360-degree panoramic images, video, and gridded flights, to produce orthomosaic base mapping.
- Optioneering: The results of the desk-based assessment and walkovers were reviewed in an optioneering report, which included a range of options for each site, all of which scored against the project objectives:
- River Restoration Outline and Detailed Design: We developed preferred options into buildable designs compliant with CDM 2015. A bespoke topographic survey was also undertaken to inform the designs.
- Flood Modelling: Flood modelling was carried out to ensure the proposed works do not increase flood risk.
- Consenting: Separate Flood Risk Activity Permits and Land Drainage Consents were submitted on behalf of the client to ensure all works are fully permitted.
Outcome
Detailed design and consent packages were delivered for multiple sites through working in partnership with the client, landowners and other stakeholders. Planned interventions include:
- Large wood installation: installation of deflectors, where possible, through the hinging of existing limbs
- Beaver dam analogue: mimicking the floodplain reconnection benefits of natural beaver dams, beaver dam analogues provide multiple benefits
- Bank re-grading: Restoring a more naturalised bank gradient
- Natural Flood Management (NFM): Removing material from the floodplain to increase water storage
- Bed Level Raising: Importing gravel to raise bed levels where historic dredging has removed material.
Testimonial
“I employed FLOW CIC to develop detailed designs for 6km of chalk stream in the North of Hertfordshire. The project was across 3 distinct rivers, various sites and involved multiple landowners, stakeholders and interested parties. Adam and Maddie at Flow were really open and responsive to working with everybody, they went above and beyond to make sure everyone’s comments and views were reflected back in a sensitive design that was environmentally beneficial. They were accommodating when design review required multiple meetings and changes, in response to unconnected flooding incidents and Local Authority responses. Would highly recommend.”
Sarah Perry – River Catchment Coordinator at Herts and Middlesex Wildlife Trust.
Please find out more about our River Restoration Design Services here.
