Hydrology of the Chalk Aquifer in East Yorkshire from Spring Recession Analysis
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Hydrology of the Chalk Aquifer in East Yorkshire from Spring Recession Analysis Nozad Hasan Azeez Submitted in accordance with the requirements for the degree of Doctor of Philosophy University Of Leeds School Of Earth and Environment 2017 The work in Chapter 6 and 8 of the thesis has appeared in publication as follows: Azeez, N., West, LJ and Bottrell, SH (2015) Numerical simulation of spring hydrograph recession curves for evaluating behavior of the East Yorkshire chalk aquifer. In: Doctor DH; Land L; Stephenson JB (Ed) Proceedings of the 14th Sinkhole Conference pp.521-530. October, 7th. 2015 I was responsible for analyzing information, constructing numerical models, interpretation the results and writing the paper. The contribution of the other authors was reviewing the results and writing. ii Acknowledgements I would like to thank Dr Jared West and Prof Simon Bottrell for their time, support, guidance and supervisor through the duration of this project. I also wish to thank and appreciate Dr Noelle Odling for her supervision during the first and second year of this study. My special thanks to Dr Raul Perulero Serrano for his help with using Groundwater Vistas 4 modelling software. Many thanks to Rolf Farrell from Environment Agency for provision of the flow rate data. My thanks to Kirk Handley for his assistance in the field. I would also like to say thanks to Chartell Bateman and Dominic Emery of the Field and lab facilities, School of Geography/ University of Leeds for providing the stream flow meter. I would like to extend my thanks to my family for their encouragement, my wife for her supports throughout my study and for my lovely son Nali. The Human Capacity Development Programme (HCDP) Ministry of Planning /Kurdistan Region-Iraq are gratefully acknowledged for funding this project. iii Abstract: This thesis presents a study of the flow system in the unconfined Chalk aquifer in East Yorkshire, based on the behaviour of spring discharge during the recession period. Groundwater is an important natural water resource in the UK, nearly one-third of England’s water supplies are provided by groundwater (almost 60% of the total by the Cretaceous Chalk aquifer). Springs drain water from large areas of the Chalk aquifer in East Yorkshire, so the discharge is governed by cumulative effects from flow systems and recharge. This study investigates whether the recession curve of spring hydrographs can be used to identify the characteristics of aquifer flow system, e.g. the extent of fracture and conduit flows. For this purpose analytical, hydrochemical and numerical modelling approaches been used. Due to the complexity of the hydrogeological system in the study area, various data sets have been used to conceptualize two gauged catchments within the Chalk aquifer outcrop area. Therefore climatic, hydrological, geological information has been collated and field monitoring of groundwater level, groundwater temperature, stream water temperature, stream water electrical conductivity, spring water CFCs concentration and stream water discharge undertaken. Annual recharge and water balances were calculated and interpreted for the two catchments (Kirby Grindalythe and Driffield). Geological information has been used to construct geological models of the two gauged catchments; hydrological conceptual models have been developed through combining hydrogeological information with the geological models. Actual evapotranspiration and rainfall data have been used for calculating annual recharge and estimating the timing of the start of the spring recession period for each hydrological year (i.e. the cessation of groundwater recharge). A tabulation method technique was used for constructing a Master Recession Curve (MRC) for selected gauged springs over 15 hydrological year recession periods. The MRC approach averages out the variation in between recession curves from different hydrological iv years, thus removing the effects of recharge variations between years, to produce a recession curve reflecting mainly topographical and hydrogeological factors. The MRC were analysed using the Maillet method; the Kirby Grindalythe MRC can be represented by a single recession coefficient, whereas that for the Driffield catchment was better represented by a two-segment curve (i.e. two recession co- efficients). This result showed that the springs in the Kirby Grindalythe catchment drain from an aquifer consisting of a single reservoir, whereas that in the larger Driffield catchment may indicate a dual-reservoir aquifer (probably a network of smaller fractures in the interfluves, with a network of larger fractures or conduits in the valley). In order to investigate whether the topographic divide represents the groundwater divide, and also to investigate whether the gauged springs were responsible for draining all recharge water from the catchments, water balance has been calculated for each catchment. The result revealed that in both study catchments the net rainfall recharge is always greater than outflow (spring discharge plus abstraction). This result showed that either there is uncertainty in the catchment size (ie the topographic divides are not the groundwater divides) or there is groundwater discharge from the study catchments. The ratio of net rainfall recharge/spring outflow from water balance was compared to the maximum flow rate during the recession for water years 2010-2014. The ratio was fairly constant for Driffield catchment with average value 3.5, but in Kirby Grindalythe catchment the ratio was about 5.6. The most probable reason for this difference is that a considerable portion of the groundwater is flowing out from both catchments in the form of subsurface flow. The concentration of CFC11 and CFC12 in the water samples during the recession period of the springs were monitored in order to estimate the residence time of the groundwater in the aquifer. The result showed that the groundwater is contaminated with CFCs; therefore, the concentration of CFCs in the water samples was not able to be used in the Groundwater age estimation. It was noticed that the concentration v of the contaminated CFCs has a pattern; therefore its pattern was compared with the pattern of the stream flow rate. A correlation has been noticed between CFCs concentration and flow rate. Through the analysis of this correlation it has been found that this correlation can be used for estimating flow system in the aquifer. In addition, the mixing CFC-11 and CFC-12 model has been used for estimating the flow system in the studied catchments. The results showed that Driffield catchment includes two flow systems. It is also showed that Kirby Grindalythe catchment consists of two sub-catchments; one of the sub-catchments feeds Duggleby-1 spring and the second one feeds Duggleby-2 spring. The sub-catchment which feeds the Duggleby-1 contain two flow systems and the sub-catchment which feeds Duggleby- 2 contain single flow system. Transient three-dimensional numerical models were developed to simulate both Kirby Grindalythe and Driffield catchments. The aquifers in each catchment were simulated with the finite difference block centred groundwater model MODFLOW2000 using Groundwater Vistas version 6 (GV 6). The recession curves from the models were calibrated to the observed MRC in each case. The outcome confirmed that in Kirby Grindalythe catchment the chalk aquifer consists of a single reservoir flow system, whereas in the Driffield catchment the aquifer consists of a double reservoir flow system. vi Contents CHAPTER 1. INTRODUCTION ............................................................................. 1 1.1. GENERAL BACKGROUND: .................................................................................... 1 1.2. LITHOLOGY OF THE UK CHALK: ......................................................................... 1 1.2.1. The Chalk distribution and stratigraphy in the UK .................................... 3 1.3. HYDROLOGY OF THE CHALK............................................................................... 4 1.3.1. Chalk Porosity: ........................................................................................... 5 1.3.2. Chalk hydraulic conductivity and transmissivity: ...................................... 6 1.3.3. Chalk hydraulic storage coefficient: .......................................................... 7 1.3.4. Vertical variation of the permeability in the Chalk: ................................... 7 1.4. THE KARSTIC BEHAVIOUR OF THE CHALK: .......................................................... 8 1.5. GROUNDWATER REGIME AND SURFACE WATER COURSES IN EAST YORKSHIRE: . 9 1.6.1. Type of springs .......................................................................................... 12 1.6.2. The importance of springs as a hydrologic tool: ...................................... 13 1.7. STUDY AREA: .................................................................................................... 14 1.7.1. Description of the catchments used in this study ...................................... 16 1.8. AIMS: ................................................................................................................ 20 1.9. SPECIFIC OBJECTIVES: ...................................................................................... 20 1.10. THESIS LAYOUT: ............................................................................................. 22 CHAPTER 2. GEOLOGY OF THE EAST YORKSHIRE WOLDS: DEVELOPMENT OF GEOLOGICAL MODELS FOR THE