Durham E-Theses Evaluation of land management impacts on low ows in northern England SMITH, KATIE,ANNE How to cite: SMITH, KATIE,ANNE (2012) Evaluation of land management impacts on low ows in northern England, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/3501/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk Evaluation of land management impacts on low flows in northern England Msc by Research Thesis Katie Anne Smith Bsc (Hons) Dunelm St Cuthbert’s Society Durham University Department of Geography Declaration of Copyright I confirm that no part of the material presented in this thesis has been previously submitted by me or any other person for a degree in this or any other university. In all cases, where it is relevant, material from the work of others has been acknowledged. The copyright of this thesis rests with the author. No quotation from it should be published without prior consent and information derived from it should be acknowledged. i Abstract Low flows are becoming an increasing issue in the UK. The effect of an increasing population on water supply demand is bringing awareness of the issue of extreme low flows risk to the attention of water and environmental managers across the country. Summer droughts in the Lake District in 2010 which followed winter flooding have raised the question of whether land management can be applied to reduce low flows risk in the area. This is the issue considered in this project. This master’s thesis, funded by the Adaptive Land-use for Flood Alleviation (ALFA) project of the EU set out to discover whether land management, vegetation change or changes in farming practices, could help reduce the risk of extreme low flows in Cumbria, England. The hydrological model CRUM3 was applied to simulate the river discharge of the Dacre Beck under different land management change scenarios. Sensitivity analysis and a rigorous Generalised Likelihood Uncertainty Estimation experiment proved the model’s efficiency at predicting low flows discharges as well as flood peaks. Results of vegetation change scenarios demonstrated that a cover of natural grassland provided the best water supply to the river during low flows. Increases in cover of the land by each 1% of the catchment area in natural grassland resulted in a 1% increase in stream discharge during extreme low flows periods. The location of the land assigned to vegetation change was shown to be insignificant. Scenarios of improved agricultural practice were modelled to simulate the reduction of compaction in the catchment by soil aeration. This revealed more impressive increases in river discharge during extreme low flows than the vegetation change. Though the compaction scenarios were theoretical, feasible increases in low flows discharge could reach 100%. Since flooding has also been a proven issue in this region, the scenarios were also assessed for their impacts on high flows. The most beneficial vegetation type at reducing high flows was deciduous woodland, though this had been seen to have a negative effect on low flows. Natural grassland had negligible effect on catchment high flows. Compaction reduction was however discovered ii to be a potential simultaneous management solution to both high and low flows, as whilst potentially increasing low flows by up to 100%, it could also decrease high flows by up to 8%. Further research would be required to make accurate estimates of the potential improvements to high and low flows, but this project has demonstrated that reducing compaction is definitely beneficial to the catchment hydrology. iii Acknowledgements I would like to firstly thank my supervisors, Dr Sim Reaney, Dr Richard Hardy and Professor Stuart Lane who have helped me hugely in the first research project of my academic life. They have been incredibly patient and encouraging while I tackled the steep learning curve of hydrological modelling. A huge thank you to Dr Nick Odoni who gave his clever and enthusiastic help in devising an efficient sampling strategy; and to Dr Dave Milledge who helped me track down all the data I required. Thanks to the Environment Agency for that data. Dr Ian Pattison whose previous work was the basis of this research was a huge help, and Calum Baugh’s advice on the model was invaluable. Everyone at the Eden Rivers Trust and all those involved in the ALFA project gave enormous support, and particular thanks go to Lucy Dugdale and Tom Dawson. All those who helped with the fieldwork; Ed, Lizzie, Steph, Ian, Ben, Alex and all the other research Master’s students who kept me laughing. Finally thanks to my moral supporters; Alex, Bobbi and Duncan, to my parents Sue and Mike and the rest of the family who have endured my geographical ravings! iv Chapter One: Introduction....................................................................................................1 1.1 Introduction.........................................................................................2 1.2 The Importance of Low Flows.............................................................6 1.3 Land Use Change and Catchment Hydrology ..................................13 1.3.1 Vegetation Change ....................................................................13 1.3.2 Compaction................................................................................15 1.3.3 Previous Land Use Change Research Methods........................16 1.4 Hydrological Models and Low Flows ................................................17 1.5 Aim and Research Questions...........................................................19 1.5.1 Research Questions ..................................................................19 1.6 Thesis Structure ...............................................................................21 Chapter Two: Study Catchment Characteristics ..............................................................22 2.1 The Dacre Beck Catchment.............................................................23 2.2 Location............................................................................................23 2.3 Catchment Characteristics................................................................23 2.3.1 Topography................................................................................23 2.3.2 Channel Network ......................................................................24 2.3.3 Rainfall.......................................................................................26 2.4 Geomorphology................................................................................26 2.4.1 Bedrock Geology .......................................................................29 2.4.2 Superficial Deposits ...................................................................30 2.4.3 Soils ..........................................................................................30 2.5 Land-Use..........................................................................................33 2.5.1 Agriculture..................................................................................33 2.5.2 Land Cover ................................................................................34 2.6 Ecology.............................................................................................34 v 2.7 Potential for Research and Current Projects ....................................36 2.8 Summary ..........................................................................................36 Chapter Three: Methods........................................................................................................38 3.1 Introduction.......................................................................................39 3.2 Hydrological Modelling of Low Flows................................................39 3.3 The Connectivity of Runoff Model.....................................................39 3.3.1 CRUM3 Structure.......................................................................40 3.3.1.1 Weather ..................................................................................40 3.3.1.2 Hydrological Processes ..........................................................42 3.3.1.3 Landscape ..............................................................................47 3.3.1.4 River Channel.........................................................................49 3.3.2 Data Requirements....................................................................50 3.3.3 Sensitivity Analysis ....................................................................51 3.3.4 Generalised Likelihood Uncertainty Estimation (GLUE).............51 3.4 Studying Land Use Change..............................................................52 3.4.1 Vegetation Change in CRUM3...................................................53 3.4.2