Monthly macrophyte surveys of the CEH River Lambourn Observatory at Boxford

This study has resulted in the collection of a unique dataset of seasonal macrophyte growth over a six year period, encompassing extreme levels of flow both high and low. Although not analysed the results of the surveys are presented in this report. The data collected would enable subsequent investigation of the impact of weed cuts on the composition, density, cover and recovery time of these species and the relationship between macrophyte growth, hydraulic roughness, flow regimes and sediment transport/deposition

An assessment of the potential for natural flood management to offset climate change impacts

Natural Flood Management (NFM) aims to work with natural processes to reduce flood risk, and can potentially contribute to integrated flood risk management (alongside engineering solutions) by providing landscape-based resilience to climate change impacts. Here, two approaches are used to assess the extent to which NFM could offset the impacts of climate change on floods in Great Britain. The first looks at specific catchments where there is quantitative evidence for the effect of NFM measures on peak flows. The second takes a broad-brush national view, assuming two potential levels of NFM reductions in peak flows. Both approaches use flood impacts derived from climate change projections for a range of future time-slices and emissions scenarios. The results show that NFM measures are much less likely to be able to offset the impacts of climate change for later time-slices and for higher emissions scenarios, but also that the chance of offsetting the impacts of climate change in any individual catchment will depend on its type (how sensitive it is to climatic changes) and its location (due to spatial variation in climatic changes). Confounding factors in the analysis include any time lag associated with the NFM reduction in peak flows, and different effects of NFM on peak flows of different return periods. It is also unclear whether there is any relationship between a catchment's type and its practical potential for implementing NFM, or the level of peak flow reduction that NFM could achieve; any such relationship could be critical in determining the overall potential for NFM to offset climate change impacts in different catchments. Although the focus here is Great Britain, a similar approach could be applied internationally

Instream and riparian implications of weed cutting in a chalk river

Macrophyte growth is extensive in the iconic chalk streams that are concentrated in southern and eastern England. Widespread and frequent weed cutting is undertaken to maintain their key functions (e.g. flood water conveyance and maintenance of viable fisheries). In this study, a multidisciplinary approach was adopted to quantify coincident physico-chemical responses (instream and riparian) that result from weed cutting and to discuss their potential implications. Three weed cuts were monitored at a site on the River Lambourn (The CEH River Lambourn Observatory) and major instream and riparian impacts were observed. Measurements clearly demonstrated how weed cutting enhanced flood flow conveyance, reduced water levels (river and wetland), increased river velocities, and mobilised suspended sediment (with associated chemicals) and reduced the capacity for its retention within the river channel. Potential implications in relation to flood risk, water resources, downstream water quality, instream and riparian ecology, amenity value of the river, and wetland greenhouse gas emissions were considered. Provided the major influence of macrophytes on instream and riparian environments is fully understood then the manipulation of macrophytes represents an effective management tool that demonstrates the great potential of working with nature

Quality Assurance of the modelling process

The present paper briefly describes a new modelling support tool (MoST) aimed at facilitating better quality assurance of the modelling process. MoST comprises a Knowledge Base with guidelines on good modelling practise for seven scientific domains. It supports multi-domain modelling and working in teams of different user types (water managers, modellers, auditors/reviewers, stakeholders and members of the public). The key functionality of MoST is to: (a) Guide to ensure that a model has been properly applied; (b) Monitor to record decisions, methods and data used in the modelling work and in this way enable transparency and reproducibility of the modelling process; (c) Report to provide suitable reports on what has been done by the various actors. MoST has been developed under the HarmoniQuA project (www.HarmoniQuA.org

Understanding the controls on deposited fine sediment in the streams of agricultural catchments

Excessive sediment pressure on aquatic habitats is of global concern. A unique dataset, comprising instantaneous measurements of deposited fine sediment in 230 agricultural streams across England and Wales, was analysed in relation to 20 potential explanatory catchment and channel variables. The most effective explanatory variable for the amount of deposited sediment was found to be stream power, calculated for bankfull flow and used to index the capacity of the stream to transport sediment. Both stream power and velocity category were highly significant (p<<0.001), explaining some 57% variation in total fine sediment mass. Modelled sediment pressure, predominantly from agriculture, was marginally significant (p<0.05) and explained a further 1% variation. The relationship was slightly stronger for erosional zones, providing 62% explanation overall. In the case of the deposited surface drape, stream power was again found to be the most effective explanatory variable (p<0.001) but velocity category, baseflow index and modelled sediment pressure were all significant (p<0.01); each provided an additional 2% explanation to an overall 50%. It is suggested that, in general, the study sites were transport-limited and the majority of stream beds were saturated by fine sediment. For sites below saturation, the upper envelope of measured fine sediment mass increased with modelled sediment pressure. The practical implications of these findings are that (i) targets for fine sediment loads need to take into account the ability of streams to transport/retain fine sediment, and (ii) where agricultural mitigation measures are implemented to reduce delivery of sediment, river management to mobilise/remove fines may also be needed in order to effect an improvement in ecological status in cases where streams are already saturated with fines and unlikely to self-cleanse