Sam updates us on his research findings, which STF is proud to have helped to fund through the Penny Eastwood Bursary programme. If you are involved in academic research, or citizen science that explores NFM and SuDS, we’d love to hear from you, and help you to share your findings! Please get in touch at secretary@slowtheflow.net.
Hi, my name is Sam Townsend. I have been volunteering for Slow The Flow since 2018, and have been the charity’s Secretary for over a year. I am now also proud to say that I have passed my Master’s By Research on the influence of natural flood management wood structures on water quality and particulate organic matter retention in headwater streams. My case study site was Hardcastle Crags, where Slow The Flow volunteers have installed 1000 ‘leaky dams’ over 10 years. I was fortunate to be a recipient of the Penny Eastwood Bursary.
I have shared my academic journey across several blogs, and I’m proud to have contributed meaningfully to advancing a key part of Slow The Flow’s strategy: to provide evidence of the benefits of natural flood management (NFM) and sustainable drainage systems (SuDS) at identified sites, including ‘slowing the flow’, improvements to habitat and water quality.
If you haven’t read my previous posts, I became involved with Slow The Flow by chance. My A-Level Geography teacher mentioned the charity during a lesson about the Boxing Day Floods in the Calder Valley, which inspired me to volunteer and strengthen my UCAS statement. Now, more than eight years later, I’m still very much involved, and supporting Slow The Flow as we move into the next chapter of our charity’s transformation.
Over the past decade, NFM has become a main component of catchment-scale strategies to mitigate flood risk while delivering wider ecological benefits. In upland environments such as Hardcastle Crags in West Yorkshire, the installation of Natural Flood Management Wood Structures (NFMWSs) has come about from a community-led partnership between Slow The Flow and the National Trust.
My research, at the University of Huddersfield, set out to address this gap by evaluating how NFMWSs influence seasonal water quality and particulate organic matter (POM) retention in headwater streams. While the hydrological and geomorphological impacts of NFMWSs are well documented, very few studies have tried to quantify their effects on nutrients, metals, suspended solids, and organic matter dynamics. Understanding these processes is essential if NFM is to become more mainstream, but there is a need for more evidence-based river catchment management to help drive future policy development and funding.
Study Design and Approach
Fieldwork was undertaken across eight headwater streams in Crimsworth Dean during Winter 2022 (water quality) and Spring 2023 (water quality and POM). Sampling locations included:
- Upstream of NFMWSs
- Downstream of NFMWSs
- A control stream with no NFMWSs
- Agricultural streams
- The main channel (Crimsworth Dean Beck)
In order to investigate the impact the NFMWSs have on water quality, laboratory analysis at the University was undertaken on nutrients (nitrates, phosphates), metals, total suspended solids (TSS), and POM (organic matter content, depth, particle size) characteristics . Statistical analysis included Kruskal–Wallis tests and a linear mixed-effects model to explore the drivers of POM accumulation.
Key Findings
1. Seasonal variation in water quality was pronounced
The study identified some seasonal differences:
- Nitrate concentrations were significantly higher in Winter 2022
- In Spring 2023, phosphate levels and phosphorus in sediment were significantly higher, likely due to increased biological activity and more interactions between the bed-sediment and the stream.
This could suggest that seasonal changes cause NFMWSs to influence nutrient behaviour differently at various times of the year.
2. NFMWSs enhanced particulate organic matter retention (reduced erosion and siltation downstream)
The influence of NFMWSs on POM was one of the strongest outcomes of this study:
- Sites with NFMWSs exhibited higher POM content than the control stream.
- A greater proportion of fine particles (<0.212 mm) was retained at NFMWS sites, supporting the hypothesis that these structures trap fine organic material.
- There was no significant difference in POM depth between NFMWS and control sites; however, the mixed-effects model indicated that greater POM depth is a strong predictor of higher POM content, regardless of the site type.
These results suggest that NFMWSs generate hydraulic environments that facilitate the trapping of organic matter.
3. Nutrient and metal responses were variable
While some parameters aligned with the hypotheses, others did not:
- Several metals varied between sites and seasons, but not always in statically significant ways.
- Some results contradicted initial expectations or lacked statistical significance.
This variability highlights the complexity of biogeochemical processes in upland headwaters and the need for longer-term, catchment-scale monitoring.
Implications for NFM
The research demonstrates that NFMWSs influence more than hydrology. They can influence sediment and water interactions, enhance nutrient dynamics and fine organic matter retention; plus, potentially support ecological functioning through increased organic matter availability.
These findings strengthen the evidence base to show that NFM has multiple benefits, contributing to both flood mitigation and water quality enhancement, and hence biodiversity. It also supports the importance of structure design and placement. The gap between the log and streambed, the number of logs, and the hydraulic setting all influence biogeochemical activity.
Future Directions
To build on this work, future research should:
- Examine the effect of NFMWSs at catchment scale rather than an individual site.
- Examine long-term nutrient and sediment trends, and address the general lack of monitoring for NFM.
- Explore how different NFMWSs designs influence ecological processes.
As NFM continues to expand across the UK, evidence-based insights such as these are essential for guiding best practice and informing national policy frameworks.
