Impacts of flow regulation and Artificial Floods in an upland stream ecosystem

Mitigation of ecological impacts associated with stream regulation is now a legislative priority and Artificial Floods have been suggested as a potential tool to achieve this aim. However, understanding of the impacts of stream regulation and Artificial Floods on downstream ecology is currently limited. This thesis provides detailed reviews of both of these topics and identifies key contemporary research priorities. These priorities were subsequently addressed through assessment of the impact of stream regulation and Artificial Floods on downstream hydrology, physical chemistry, coarse sediment transport and benthic macroinvertebrates in an upland subcatchment of the River Humber, UK. Evidence that regulation was associated with significant impacts on hydrology (e.g. flood frequency, rate of change), physical chemistry (particularly flood pH and diurnal stream temperature range) and macroinvertebrates was identified, but impacts were found to vary spatially and temporally, indicating the importance of site specific and temporal factors. Control of hydrological characteristics was demonstrated during Artificial Floods which generally resulted in reductions of electrical conductivity, dissolved oxygen and pH and no change in stream temperature. Evidence for coarse sediment transport in line with overspill events prior to Artificial Floods was identified, but little evidence for change in macroinvertebrate assemblage was found. Evidence for the use of Artificial Floods as a management tool was greatest for coarse sediment transport and pH but overall, limited potential was demonstrated, bringing into question their validity as management techniques in some regulated streams and provoking requirement for further research. The findings of this thesis, methodological developments, conceptual advances and recommendations are therefore considered to have advanced the science and understanding of regulated stream management. Such progress is vital in this rapidly developing research field.