The removal of dams, weirs or barriers to river flow, is frequently a contentious issue. This is because of the competing demands of flood protection and the ecological, social, economic and cultural health of the river. Many of the barriers are old or obsolete and there is an international drive to create ‘free-flowing rivers’ with no or fewer barriers, thereby increasing longitudinal connectivity. This has been most noticeable in North America and continental Europe, and less apparent in the UK. We explore the issues around weir removal with a case study of a lowland southern English river, the River Rother, West Sussex, in a predominantly agricultural catchment where weirs have been constructed for a variety of purposes over the last ~1000 years. The river is dominated by inputs of sand-sized sediment with very low organic matter content that is frequently stored upstream of structures. The multiplicity of stakeholders and the strong interests of the fishing and farming communities render decision-making about structure removal or modification to improve fish passage difficult. There is also the demand for potable water abstraction by the local water company which would be affected by dam removal and the potential release of the fine (mostly < 2mm dia.) sediments stored immediately upstream of the weirs. This paper subsequently explores selected issues around weir removal under the requirement of the European Water Framework Directive to achieve Good Ecological Status and explores guidance on best practice; including the decision which weirs to remove and in which order.

Channel banks can contribute a significant proportion of fine-grained (<63 µm) sediment to rivers, thereby also contributing to riverine total particulate phosphorus loads. Improving water quality through better agricultural practices alone can be difficult since the contributions from non-agricultural sources, including channel banks, can generate a ‘spatial mismatch’ between the efficacy of best management applied on farms and the likelihood of meeting environmental objectives. Our study undertook a reconnaissance survey (n=76 sites each with 3 profiles sampled) to determine the total phosphorus (TP) concentrations of channel banks across England and to determine if TP content can be predicted using readily accessible secondary data. TP concentrations adjacent field topsoils and local soil soil type/texture and geological parent material were examined as potential predictors of bank TP. Carbon and nitrogen content were also analysed to explore the impacts of organic matter content on measured TP concentrations. The results suggest that channel bank TP concentrations are primarily controlled by parent material rather than adjacent topsoils, but significant local variability in concentrations prevents the prediction of bank TP content using mapped soil type or geology. A median TP concentration of 873 mg kg -1 was calculated for the middle section of the sampled channel bank profiles, with a 25 th percentile of 675 mg kg -1, and 75 th percentile of 1159 mg kg -1. Using these concentrations and, in comparison with previously published estimates, the estimated number of inland WFD waterbodies in England for which channel bank erosion contributes >20% of the riverine total PP load increased from 15 to 25 (corresponding range of 17 to 35 using the 25 th and 75 th percentiles of measured TP concentrations). Collectively, these 25 waterbodies account for 0.2% of the total inland WFD waterbody area comprising England.

In many parts of South Africa, soil erosion rates are high, and likely to be exacerbated by the longer droughts and more intense rainfall that are predicted in long-term regional climate change scenarios. Suspended sediment loads (SSL) and yields (SSY) are accepted means of expressing and comparing sediment transport and soil erosion rates. Land care and water security initiatives in South Africa require these data to provide benchmarking, and trajectories of change. International researchers began in the 1970s to investigate SSL estimation approaches. These investigations typically used near-continuous turbidity data from installed probes as a surrogate for sampled SS, and auto-samplers to monitor SS concentration and develop sediment rating curves. Biophysical and socio-economic conditions in South Africa differ markedly from the northern hemisphere environments where foundational studies were conducted. SSL estimations in South Africa are associated with extreme hydrological regimes, remote study areas and lack the resources required to collect and analyse representative SS data. There is a dearth of measured SS data, and of observed SSL and SSY for South African catchments. Using measured SS data from the Tsitsa River catchment (Eastern Cape, South Africa) we found that a discharge-weighted interpolation estimator was more appropriate than regression estimators, and that SSY responses to biophysical factors were in some ways more similar to northern hemisphere norms than expected. Lack of technical, infrastructural, human and financial resources were our main constraints to monitoring and estimating SSY. Our findings highlight the challenges of, and provide some guidance for, estimating directly measured SSL in the southern Africa region and inform future research in resource scarce areas.