SpongeScapes Comic - Long-term Impact of River Restoration

With Imogen edwards Rivers are vital, but human activities have disrupted their natural flow, harming ecosystems and worsening floods. Restoration seeks to reverse these impacts to help rivers recover. Immy’s PhD studies how restored rivers evolve over time. She studies the Cole and Lymington Rivers in the UK, using long-term ecological and hydrological data to assess the effectiveness of restoration so we can understand how to better protect rivers in a changing environment. Credits : SpongeScapes has received funding from the European Union’s Horizon Europe research and innovation programme under Grant Agreement n°101112738 and from the UK Research and Innovation/HM Government. Views and opinions expressed in this publication are those of the author(s) only and do not necessarily reflect those of the European Union or the UK Research and Innovation / HM Government. © 2025 - International Office for Water for the SpongeScapes project. Script, drawing and colouring of the comics: Élisa Bézier and Jean Combette (OiEau) Imogen Edwards PhD thesis supervised by: Prof. Dr. David Sear (University of Southampton), Prof. Dr. Peter Shaw (University of Southampton), Dr. Alejandro Dussaillant (UKCEH) Proofreading : Imogen Edwards, Dr. Alejandro Dussaillant, Dr. David Sear Text before script : Chloé Déchelette (OiEau) long-term impact of : The Lymington River was affected by forestry and straightening of streams in the 19th century, drying out the landscape, disrupting seasonal flooding and degrading woodlands. The Cole River was shaped by human activity for nearly 900 years, mainly for milling and agriculture. Rivers are vital, but human activities have disrupted their natural flow, harming ecosystems and worsening floods. These rivers have been heavily modified over centuries. West of Oxford, in the Thames River Basin District. Cole river Near Southampton, in the New Forest National Park, a protected area in the South-East River Basin District. Lymington river While each restoration was tailored to their location, they shared common goals : improving flood storage, enhancing habitat diversity, and creating a more aesthetically pleasing river environment.” Both rivers were restored starting in the 1990s. My research looks at how well these efforts worked. But how do I study that? Through ecology and hydrology! One thing I study is river roughness - how much resistance the riverbed, banks, vegetation or artificial obstacles oppose to flowing water. For example, a smooth, straight, obstacle-free river flows fast. If there are small stones in the riverbed, they will exert a counterforce, and the river will then be slower And if the riverbed is full or rocks, plants and fallen branches, then the water encounters a lot of resistance, its speed is ‘broken’ by all these obstacles. Time plays a crucial role here, although we as humans are caught up in our daily routines, we don’t often notice the slow natural processes. While woody debris and rocks may slow water for now, over decades or centuries, the constant flow of water will wear them down, allowing the river to flow faster. For the Lymington River, I focus on hydrology and hydraulics. What’s the difference? For this site, we have over 40 years of hydrological and hydraulic data, which is rare. This will certainly allow us to answer the question: has restoration changed the river’s natural hydrology? Hydraulics is all about the physics of moving water, how water flow in specific places, whether natural or artificial: in streams, lakes, irrigation channels, land, urban pavement, soils or aquifers. It looks at things like water levels and flow speed, which are closely linked to fluid mechanics. 0,34 m/s Hydrology is about the natural water cycle, how water moves from one ‘compartment’ to another on Earth: the oceans, the surface or underground on the continents. It covers rainfall, runoff, infiltration into the soil, evaporation, and so on. Now, follow me at the New Forest! Here, fieldwork focuses on hydrological aspects of river restoration. I map and analyze key hydraulic features to evaluate changes in riverbed roughness over time. Desk work will also involve synthesizing findings from the long-term monitoring studies, reviewing existing literature on restoration impacts, and compiling the results into a coherent analysis of the restoration's effectiveness. And now, Desk work ! I organize and analyze the macroinvertebrate data collected during fieldwork. But this is not the only case study I work on… I spend a lot of time in the lab sorting the samples to identify the macroinvertebrate species, I quantify their abundance and diversity at each site. Then, I compare species richness, abundance, and community composition as well as velocities, and sediment samples between the restored and unrestored sites. For the Cole River, I focus on ecology and biology. Ecology is a branch of biology. Biology is a very very broad field. For example, woodlice are decomposers that are very sensitive to dehydration, so if you find them in soil, it is very likely that this soil is moist, cool and rich in organic matter. My work involves: Fieldwork - collecting samples (a fun part of my job, with lots of fresh air!) Lab analysis - examining samples to determine species richness and their relative abundance. In this sample, I found 5 different species. That’s the species richness. By analyzing these bio-indicators, I can assess the health of the Cole River’s ecosystem and the impact of restoration efforts. What is it, you may ask ? let’s take an example with the mayflies! Altogether, there are 20 individuals - and 10 of them are mayflies. So mayflies make up 50% of the sample. That’s their relative abundance. I study macroinvertebrates - invertebrates large enough to see without a microscope (think insects and tiny aquatic creatures). Why them? Because they’re abundant in all types of running water, easy to sample, and provide great insights into ecosystem health. My research uses bio-indicators, organisms - plant or animal - that tell us about environmental conditions. Restoration success isn’t just about ecology or hydrology - it’s about both. We need both physical and biological data to evaluate a river’s health. Hydrology / Hydraulics ecology And here's the tricky part: how do we measure success of restoration? Of course, It’s not just about counting species, but understanding what they tell us and knowing which ones indicate good ecological health for these kinds of streams. Should we compare a restored river to its pre-restoration state? to a healthy river in similar conditions (reference ecosystem)? Or to how it might change in the future under climate change? The answer is not simple. Nature always surprises us! For example, I found more macroinvertebrates in unrestored sections of the Cole than in restored ones. Why ? The restored areas are dense with vegetation and quite dark, while the unrestored sections have grazed banks, which creates a mix of light and shade - and this is exactly what macroinvertebrates love ! That’s what makes my research exciting! It highlights the need for long-term monitoring and well-documented methods so that future scientists can build on past work. River restoration doesn’t always go exactly as planned. We try to reduce flooding, improve water quality, and restore habitats, but nature has its own way of responding, sometimes in unexpected ways. That’s a humbling lesson! That doesn’t mean we should give up on river restoration. We just need to study rivers over a long period of time to understandthese complexities better.