Provenance and Transfer of Fine Sediment in the Lugg Catchment, Herefordshire, UK Jason Paul Stopps A thesis submitted to the University of Gloucestershire in accordance with the requirements of the degree of Doctor of Philosophy in the School of Natural and Social Sciences July 2018 Word Count 85,999 ABSTRACT An extensive fine sediment research monitoring programme, funded through the SITA Trust’s ‘Enriching Nature’ programme, has been undertaken to evaluate the value of a catchment-wide, monitoring approach to establish spatial and temporal patterns and sources of fine sediment in the Herefordshire Lugg catchment. The aim of the project was to investigate the sources and patterns of fine sediment movement to help target management resources to reduce the impact of excessive siltation. Continuous (15 minute) flow and suspended sediment concentrations were monitored at five sink sites between April 2009 and November 2012 to assess the spatio-temporal variations in suspended sediment. Episodic high suspended sediment concentrations in the Lugg catchment persistently exceeded 25 mg L-1 over the period of study. Delivery of suspended sediments to the sites was also monitored using time-integrated samplers. A sediment fingerprinting and mixture modelling procedure based on geochemical properties was utilised to identify key sub-catchments that persistently delivered fine sediment over the period of study. Sources of fine sediment were also identified and evaluated based on differing land use types in four of the main sub-catchments recognised as important contributors of sediment at the catchment scale. The sediment fingerprinting technique was refined to incorporate appropriate weighting and correction factors to improve the ability of the composite fingerprint to discriminate between source types. The monitoring programme established the spatial and temporal characteristics of fine in-channel sediment and its sources within the wider catchment. Priority sub-catchment areas that posed the greatest risk of being fine sediment pollution sources were identified as the Cheaton Brook, Curl Brook, Ridgemoor Brook and Moor Brook. The sub-catchment scale sourcing results indicate that if siltation problems in the Lugg catchment are to be tackled effectively, catchment managers should target the reduction of fine sediment from farm track surfaces in the Cheaton, Curl and Moor Brook sub-catchments, while targeting the reduction of sediment mobilised from arable and pasture surfaces in the Ridgemoor Brook sub-catchment. This study has therefore assisted in ii strengthening the evidence of the sediment problem in the Herefordshire Lugg catchment and has provided an evidence base to aid catchment management to enable the implementation of mitigation measures in an effective targeted approach. iii DECLARATION I declare that the work in this thesis was carried out in accordance with the regulations of the University of Gloucestershire and is original except where indicated by specific reference in the text. No part of the thesis has been submitted as part of any other academic award. The thesis has not been presented to any other education institution in the United Kingdom or overseas. Any views expressed in the thesis are those of the author and in no way represent those of the University. Signed ……………………………………………Date ……………………… iv TABLE OF CONTENTS ABSTRACT ......................................................................................................... ii DECLARATION ................................................................................................. iv TABLE OF CONTENTS ...................................................................................... v LIST OF FIGURES ............................................................................................. x LIST OF TABLES .............................................................................................. xx ACKNOWLEDGEMENTS ............................................................................... xxv CHAPTER 1 INTRODUCTION ................................................................................................ 1 1.1 The Sediment Problem .............................................................................. 1 1.2 Land Use and Sources of Fine Sediment .................................................. 4 1.2.1 Sediment Sources from Agricultural Topsoils ...................................... 4 1.2.2 Sediment Sources from Channel Bank Erosion .................................. 6 1.2.3 Sediment Sources from Road and Farm Track Surfaces .................... 6 1.3 Policy and Management ............................................................................ 8 1.4 Approaches to Catchment Sediment Source Identification ...................... 10 1.4.1 Traditional Methods ........................................................................... 11 1.4.2 Sediment Fingerprinting Technique ................................................... 13 1.4.3 Classifying Potential Sources ............................................................ 16 1.5 Significance of Study Area ....................................................................... 21 1.6 Rationale ................................................................................................. 23 1.7 Aims and Objectives ................................................................................ 25 1.8 Thesis Structure....................................................................................... 27 CHAPTER 2 STUDY CATCHMENT ...................................................................................... 28 2.1 Introduction .............................................................................................. 28 2.2 Catchment Setting ................................................................................... 28 2.3 Geology ................................................................................................... 29 2.4 Soils ......................................................................................................... 31 2.5 Land Use ................................................................................................. 33 2.6 Hydrological Regime ................................................................................ 35 2.7 Summary ................................................................................................. 40 v CHAPTER 3 METHODOLOGY ............................................................................................. 41 3.1 Introduction .............................................................................................. 41 3.2 Catchment Scale Analysis ....................................................................... 44 3.2.1 Study Sites Selection ......................................................................... 44 3.2.2 Field Monitoring Strategy ................................................................... 48 3.2.3 Field Sampling Approach .................................................................. 55 3.3 Sub-Catchment Scale Analysis ............................................................... 67 3.3.1 Sub-Catchment Selection .................................................................. 67 3.3.2 Suspended Sediment and Source Material Sampling ....................... 68 3.4 Laboratory Preparation and Analytical Procedures.................................. 77 3.4.1 Grain Size Analysis ........................................................................... 77 3.4.2 Geochemical Property Analysis ......................................................... 81 3.5 Summary ................................................................................................. 86 CHAPTER 4 SPATIO-TEMPORAL VARIATIONS IN SUSPENDED SEDIMENT ................. 87 4.1 Introduction .............................................................................................. 87 4.2 Rainfall and Flow Characteristics............................................................. 87 4.3 Fine Sediment Characteristics ................................................................. 91 4.3.1 Site-based grain-size characteristics ................................................. 91 4.3.2 Particle Size Composition of Suspended Sediment .......................... 94 4.3.3 Summary ......................................................................................... 100 4.4 Suspended Sediment Flux Monitoring ................................................... 101 4.4.1 Rating Relationships ........................................................................ 102 4.4.2 Suspended Sediment Summary Statistics ....................................... 104 4.4.3 Suspended Sediment Yields ........................................................... 114 4.4.4 Summary ......................................................................................... 117 4.5 Suspended Sediment Dynamics ............................................................ 117 4.6 Discussion ............................................................................................. 123 4.7 Conclusion ............................................................................................. 132 CHAPTER 5 STATISTICAL PROCEDURES AND FINGERPRINTING TECHNIQUE ........ 136 5.1 Introduction ............................................................................................ 136 5.2 The Fingerprinting Approach ................................................................