Hydroecological restoration of the River Cray at Hales Meadow – determining “Replenish” metrics. Final report

• UK Chalk rivers have suffered significantly from anthropogenic realignment and channel alteration as a result of the industrial pressures of modern society. This has had a detrimental effect on the natural balance of these valuable ecosystems. Recognised internationally as highly sensitive (River Cray has its own Biodiversity Action Plan) with increasingly threatened habitats, the collective response to their ecological decline has paved the way for the development of river restoration practices. Private industry involvement in funding collaborative restoration projects is increasingly seen as a positive approach to reducing the impact their commercial activities have on the freshwater environment, as well providing much needed support to community conservation initiatives. • This report outlines the methodical and scientific approach taken to quantifying measureable physical metrics of success following the undertaking of a programme of restoration enhancements on an urban stretch of the River Cray in Kent. A well established methodology was used with real field data that was simulated using model projections to predict a probable habitat suitability scenario post restoration. • The physical habitat suitability scoring approach determined that the overall suitability of the river channel for juvenile brown trout was poor in terms of velocity and depth diversity. Pre-restoration the channel form presented an adequate range of velocity but little variation in depth. Depth was thus deemed the hydraulic parameter that required significantly improving. • The study concluded that the restoration measures implemented to the channel have not significantly improved the immediate availability of suitable physical habitat for juvenile brown trout at low flows. However it is envisaged that in the longer term some improvements will have been made as the morphology of the channel adapts to the change in hydraulics. • Unfortunately unprecedented rainfall over much of the UK during 2013 and the resultant sustained high flows over 2013/14 meant it was impractical to obtain the low flow field data required to validate the hydraulic model projection. • Targeting an alternative suitable fish species at the same juvenile life stage may yield more realistic results and provide a greater value of the metric indicator. In addition, a more suitable and economically viable alternative could be the use of a more rapid assessment technique that relies less on the capture of high resolution field data from low flows