Hydrology of Soil Types: a Hydrologically Based Classification of the Soils of the United Kingdom
Total Page:16
File Type:pdf, Size:1020Kb
1'Institute of 1 HydrologyI Report No. 126 Hydrology of soil types: a hydrologically based classification of the soils of the United Kingdom Natural Environaent Research Council Report No. 126 Hydrology of soil types: a hydrologically-based classification of the soils of the United Kingdom D.B. Boorman, J.M. Hollist & A. Lilly* November 1995 Institute of Hydrology !Soil Survey & Land 'Macaulay Land Use Crowmarsh Gifford Research Centre Research Institute Wallingford Silsoe Craigiebuckler Oxfordshire Bedfordshire Aberdeen OX10 8BB MK45 4DT AB9 2QJ UK UK UK Tel: 01491 838800 Tel: 01525 863000 Tel: 01224 318611 Fax: 01491 832256 Fax: 01525 62247 Fax: 01224 311556 Telex: 849365 Hydrol G Telex: 826838 © Copyright Institute of Hydrology 1995 ISBN 0 948540 69 9 IE Report No. 126 published by the Institute of Hydrology November 1995 Cover picture: The cover picture shows one of the ephemeral streams in Glen Nevis. The soils in the background have a predominantly peaty surface layer which either overlies coarse textured moranic drift (HOST class 15) or has developed directly on hard coherent rock (HOST class 27). The foreground shows a large expanse of bare rock with some thin mineral soils (all HOST class 22). The catchment responds rapidly to rainfall but the waterfall dries to a trickle only hours after the rain ceases. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Abstract A hydrologically-based classification of the soils Applications of the classification have been of the United Kingdom was developed based on developed that improve estimates of existing data sets that describe both the soils parameters required in low flow and flood and their distribution, and the hydrological estimation procedures. The report contains response of catchments. The classification was sufficient detail of the methodologies so that based on conceptual models of the processes they may be used in combination with soils that occur in the soil and, where appropriate, information obtained from previously published the substrate. The resulting scheme has 29 maps. Since the classification is based on soil classes, based on eleven response models, senes it is independent of scale and may be Soils are assigned to classes on the basis of used with many different soil data sets. Access their physical properties, and with reference to on a national basis to the classification is the hydrogeology of the substrate. provided by the 1:250,000 reconnaissance maps produced during the 1980s. The classification is known by the acronym HOST, standing for Hydrology Of Soil Types. The map on the following page shows the distribution of HOST classes on a 1 lan grid. For each square only the most extensive class is shown. Contents Page Executive Summary i Abbreviations Ui 1 Introduction 1 2 From WRAP to HOST 2 2.1 The Winter Rainfall Acceptance Potential classification 2 2.2 Catchment-scale hydrological variables 4 2.3 Soil data and maps 14 2.4 Linking the catchment and soil data 25 3 The HOST classification system 26 3.1 The basis of the HOST classification system 26 3.2 HOST response model descriptions 28 3.3 Sub-divisions within the framework of models 30 3.4 Validation of the HOST classification 32 3.5 HOST class distributions 37 4 Applications of the HOST classification 38 4.1 Low flow estimation (Q95, MAM(n)) 38 4.2 The estimation of standard percentage runoff 51 5 Access to the HOST System 63 5.1 Manual overlay 63 5.2 The 1:250,000 soil data set 64 5.3 The 1 km HOST data set 65 6 Conclusions 67 Acknowledgements 67 References 68 Appendices A A brief history of the development of the HOST classification system 69 B Assignment of HOST classes to map units 73 C Catchment data used in the development and calibration of HOST 86 D Maps showing the distribution of the 29 HOST classes 108 Executive summary It is difficult to overstate the importance of soils percentage runoff. The distribution of the soils in influencing hydrological phenomena at both was taken from the national reconnaissance the site and catchment scale. Although much mapping at a scale of 1:250,000 completed for information is available to describe soils and England, Wales and Scotland in the 1980s. In their distribution, most of this needs Northern Ireland a special HOST map was considerable interpretation before it can be prepared prior to the completion of a 1:250,000 readily used by hydrologists. The Hydrology Of soil map of the province. Soil Types (HOST) Project has produced a classification of the soils of the United Kingdom The HOST classification is based on the soil that can be applied via existing national maps to series so it can be used with many different soil aid hydrological studies and analyses. data sets. At the 1:250,000 scale, groups of soil series are combined into map units, which may The HOST classification is based on conceptual contain more than one HOST class. Other soil models of the processes taking place within the maps are available that show the distribution of soil and, where appropriate, substrate. These individual series and it will be possible to use models have three physical settings: these with the HOST classification to refine hydrological parameter estimates. i) a soil on a permeable substrate in which there is a deep aquifer or groundwater The report contains complete methodologies for (i.e. at >2 m depth), the estimation of low flow variables (mean annual minimum and the 95 percentile flow) and ii) a soil on permeable substrate in which the Flood Studies Report standard percentage there is normally a shallow water table runoff. Existing users of these methods can use (i.e. at <2 m depth), and, the information contained in this report with previously published maps to obtain HOST- iii) a soil (or soil and substrate) which based estimates of model parameters. contains an impermeable or semi- permeable layer within 1 m of the surface. A product of the HOST project is a computer data set based on a 1 lan grid that covers the Within these situations are variations that allow whole of the UK, although data for Northem for different soil properties (e.g. a peaty top Ireland are currently less reliable than for the layer), and wetness regimes (e.g. as indicated rest of the UK. Using the data set will greatly by the presence of gleying), that give rise to a speed up the process of abstracting HOST total of 11 models. The 11 models are further classes for catchments or sites of interest. These sub-divided into 29 HOST classes, based on data may be leased from any of the other properties or the geology of the substrate. collaborating organisations. The classification was developed using The HOST Project has been a collaborative databases of physical soil properties with venture between the Institute of Hydrology, Soil feedback from catchment scale hydrological Survey and Land Research Centre, Macaulay variables, mainly base flow index and standard Land Use Research Institute and Department of Agriculture Northem Ireland. Abbreviations a. a regression coefficient AMP(D) annual D-day minimum flow having probability of exceedance P BFI Base flow index CWI Catchment wetness index D Duration in days DANI Department of Agriculture Northem Ireland DPRcvl Dynamnic contribution to PR from CWI DPRRAN Dynamic contribution to PR from RAIN fse factorial standard error FSR Flood Studies Report FSSR Flood Studies Supplementary Report GRADMAM Gradient of duration relationship in low flow frequency HOST Hydrology Of Soil Types HOSTI Fraction of HOST class n IAC Integrated air capacity IH Institute of Hydrology LFHG Low flow HOST group MAF Mean annual flood ME Mean flow MAM(D) Mean annual mirnimum of duration D days MLURI Macaulay Land Use Research nstitute MO Meteorological Office NRA National Rivers Authority NWA National Water Archive P Exceedance probability PR Percentage runoff ox Flow exceeded by x% of all flows. Qx(D) Flow exceeded during x% of all periods of duration D days *l Coefficient of detemination R(Q 1 ) QxJQss R(Q99 0 99/ 095 RAIN Event rainfall in mm RPB River Purification Board SAAR Standard perod annual average rainfall (mm) s.e.e. standard error of estimate SPR Standard percentage runoff SSLRC Soil Survey and Land Research Centre SWA Surface Water Archive WRAP Winter rainfall acceptance potential WRAP= Fraction of WRAP class n 1 Introduction Soils have a major influence on hydrological Since the HOST classification is based on the processes. Their physical properties govern the physical properties of the soils and their effects storage and transmission of water within the on the storage and transmission of soil water, it soil, and these properties combine with other is largely independent of scale and will have a characteristics of the soil to provide chemical number of applications outwith the prediction of buffers and biological filters. While these effects river flows at ungauged sites e.g. the evaluation occur and may be observed at the very small of sewage sludge acceptance potential, the scale, the influence of the soil properties may estimation of pesticide residues, and improving also be seen in the integrated response of whole predictions of the effects of soil acidification. catchment systems. Although these effects are recognised, they remain largely unquantified and many hydrologists struggle to interpret the 1.1 Guide to the report wealth of soils information, in the form of maps, monographs and surveys, that is available to It is anticipated that readers of this report will them. come from a wide variety of backgrounds. Many hydrologists may not have delved more One attempt to classify soils according to their deeply into the hydrological aspects of soils than hydrological response was the Winter Rainfall that presented to them in the WRAP Acceptance Potential (WRAP) scheme classification.