Hydrological Modelling for the Rivers Lavant and Ems
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Hydrological Modelling for the Rivers Lavant and Ems S.J. Cole, P.J. Howard and R.J. Moore Version 1.1 September 2009 Acknowledgements The following Environment Agency representatives are thanked for their involvement in the project: Paul Carter, John Hall, Colin Spiller, Tony Byrne, Mike Vaughan and Chris Manning. At CEH, Vicky Bell and Alice Robson are thanked for their contributions. Revision History Version Originator Comments Date 1.0 Cole, Draft of Final Report submitted to the 14 August 2009 Howard, Environment Agency for comment. Moore 1.1 Cole, Revision incorporating feedback 30 September 2009 Howard, from the Environment Agency. Moore Centre for Ecology and Hydrology Maclean Building Crowmarsh Gifford Wallingford Oxfordshire OX10 8BB UK Telephone +44 (0) 1491 838800 Main Fax +44 (0) 1491 6924241 ii Acknowledgements CONTENTS Acknowledgements ......................................................................................................... ii List of Tables ................................................................................................................... v List of Figures................................................................................................................ vii Executive Summary....................................................................................................... xi 1 Introduction......................................................................................................... 1 1.1 Overview............................................................................................................... 1 1.2 Forecast requirements for the Lavant and Ems catchments ................................. 2 1.3 Specific objectives of the project.......................................................................... 3 2 The extended PDM model for groundwater catchments ................................ 4 2.1 Introduction........................................................................................................... 4 2.2 The standard PDM ................................................................................................ 4 2.3 The extended PDM ............................................................................................... 5 3 Data requirements and availability for modelling......................................... 13 3.1 Introduction......................................................................................................... 13 3.2 Rainfall................................................................................................................ 13 3.3 River levels/flows ............................................................................................... 21 3.4 Potential evaporation .......................................................................................... 25 3.5 Well levels .......................................................................................................... 31 3.6 Groundwater abstractions and flow augmentation ............................................. 33 4 Data quality control.......................................................................................... 37 4.1 Raingauge data.................................................................................................... 37 4.2 Well level data .................................................................................................... 43 4.3 River level/flow data........................................................................................... 44 5 Strategy for modelling...................................................................................... 49 5.1 Introduction......................................................................................................... 49 5.2 Strategy for model assessment............................................................................ 49 5.3 Strategy for model conceptualisation ................................................................. 51 5.4 Hydrogeological support to model conceptualisation ........................................ 54 6 Model application to the Lavant and Ems...................................................... 57 Contents iii 6.1 Model calibration and assessment.......................................................................57 6.2 Model sensitivity analyses ..................................................................................68 6.3 Model recalibration .............................................................................................77 6.4 Forecasting performance.....................................................................................83 6.5 Model performance summary .............................................................................90 7 Summary and recommendations .....................................................................92 7.1 Summary .............................................................................................................92 7.2 Recommendations ...............................................................................................93 7.3 Conclusions and the way forward .......................................................................98 References ......................................................................................................................99 Appendix A Monthly MORECS and MOSES data ............................................102 Appendix B Raingauge data analysis supplementary information ...................103 iv Contents List of Tables Table 1.1 Alarm trigger levels for the Ems at Westbourne .............................................. 2 Table 2.1 Parameters of the standard PDM model ........................................................... 6 Table 2.2 Additional parameters of the extended PDM model ...................................... 12 Table 3.1 Tipping-bucket raingauges in the vicinity of the Lavant and Ems catchments. Height and SAAR (Standard Average Annual Rainfall) are taken from CEH datasets.................................................................................................................... 15 Table 3.2 Met Office daily raingauge records (available at CEH). ................................ 16 Table 3.3 Details of the best radar data available over the catchments. ......................... 18 Table 3.4 Long-term ratio biases using Nimrod composite radar data over the period 21 November 2003 to 30 September 2008. ................................................................. 19 Table 3.5 River level/flow stations in the Lavant and Ems catchments ......................... 21 Table 3.6 Long-term monthly average MORECS PE amounts for square 183 over the 1971-2007 water years (using MORECS records held at CEH). ........................... 26 Table 3.7 Differences between the annual MORECS PE/AE totals derived from data held by the Environment Agency and CEH for MORECS square 183 and the period 1971-2007.................................................................................................... 26 Table 3.8 Differences between the monthly MORECS PE, AE, rainfall and SMD data held by the Environment Agency and CEH for MORECS square 183 and the period 1961-2007. Shading indicates values which are different........................... 27 Table 3.9 Groundwater well level stations in the Lavant and Ems catchments ............. 32 Table 3.10 Well level data supplied by the Environment Agency. ................................ 33 Table 3.11 Groundwater abstraction sites in the Lavant and Ems catchments............... 34 Table 3.12 Details of the daily abstraction and flow augmentation data provided by the Environment Agency. ............................................................................................. 35 Table 3.13 Water year abstractions and flow augmentation for the Ems. ...................... 35 Table 4.1 Tipping-bucket raingauges in the vicinity of the Lavant and Ems catchments: start dates of data provided. .................................................................................... 41 Table 4.2 Sets of linear raingauge weights for the Lavant and Ems catchments derived using the integrated multiquadric method. ............................................................. 42 Table 4.3 Periods when the flow of the Ems at Westbourne is above the upper limit of the rating curve. ...................................................................................................... 47 Table 6.1 Summary of main differences in the approach and datasets used to calibrate the extended PDM for the Lavant between the Moore-Bell calibration (2002) and the project calibration. ............................................................................................ 57 Table 6.2 Extended PDM model parameters for the Lavant and Ems catchments. ....... 59 Table 6.3 R2 and rmse statistics for flow in the Lavant and well levels at West Dean Nursery.................................................................................................................... 60 Table 6.4 PDM model water balances (mm total) for the Lavant over the calibration and evaluation periods. In brackets is the output component as a fraction of the rainfall input. ....................................................................................................................... 63 Table 6.5 R2 and rmse statistics for flow in the Ems and well level at Pitlands Farm ... 65 Table 6.6 PDM model water balances (mm total) for the Ems over the calibration