MIGUELA. MARINO ANDJAMES N. LUTHIN Department of Civil Engineering and Department of Land, Air and Water Resources, University of California, Davis, California, U.S.A. ELSEVIER SCIENTIFIC PUBLISHING COMPANY Amsterdam-Oxford-New York 1982 ELSEVIER SCIENTIFIC PUBLISHING COMPANY Molenwerf 1, P.O. Box 21 1,1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER/NORTH-HOLLAND INC. 52, Vanderbilt Avenue New York, N.Y. 10017 Library of Congress Cataloging in Publication Data Marino, Miguel A. Seepage and groundwater. (Developments in water sciences ; 13) Bibliography: p. Includes index. 1. Seepage. 2. Groundwater flow. I. Luthin, James N. 11. Title. 111. Series: Developments in water science ; 13* TC176.M35 627' .oh2 81-3214 ISBN 0-444-41975-6 (U.S.) MCR2 ISBN 0-44441975-6 (Val. 13) ISBN 044441669-2 (Series) 0 Elsevier Scientific Publishing Company, 1982 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or other- wise, without the prior written permission of the publisher, Elsevier Scientific Publishing Company, P.O. Box 330,1000 AH Amsterdam, The Netherlands Printed in The Netherlands V PREFACE This book covers a broad range of seepage and groundwater problems. It describes the physics of water flow through porous media and soil physical problems associated with that flow. In addition, the book discusses important practical problems of groundwater and illustrates different methods for solving those problems. Among the problems covered are: control of shallow water tables, seepage under dams and other hydraulic structures, flow to wells, evaluation of aquifer tests, construction and maintenance of wells, and exploration for groundwater. During the past few years, several books have been published in the broad field of groundwater hydrology. These books are concerned to a large extent with water-quality problems associated with groundwater and do not treat the wide variety of problems that we have dealt with in our book. They do not emphasize methods of obtaining solutions to groundwater problems to the same extent that we do, nor do they emphasize the engineering design of groundwater management devices. The writing of a book with such an emphasis was motivated by the authors' teaching of seepage, drainage, and groundwater courses at the University of California at Davis to undergraduate and graduate students that have widely varying backgrounds and interests. Chapters 1 through 6 were written by J. N. Luthin, and Chapters 7 through 12 were written by M. A. Marifio. This book is designed for use an as undergraduate text in groundwater and seepage courses in civil engineering, agricultural engineering, hydrology, and soil and water science curricula, but it can also be used as a text in introductory seepage-and-drainage and groundwater courses at the graduate level. This book should be useful also to practicing engineers, hydrologists, and agriculturalists in the area of groundwater and seepage problems. VI We are indebted to the Department of Civil Engineering at the University of California, Davis, for the assistance provided in the typing of the manuscript. Both the Department of Civil Engineering and the Department of Land, Air and Water Resources at U.C. Davis have assisted us, directly or indirectly, in the preparation of this book. To these and to Irma, Raquel, and Ad we are indebted. Miguel A. Marifio James N. Luthin Davis, California November, 1980 VII UNITS AND CONVERSIONS Length 1 inch (in) = 0.08333 feet (ft) = 0.02540 meters (m) = 2.540 centimeters (em) = 254 millimeters (mm) 1 foot (ft) = 12 in = 0.3048 m = 0.3333 yards (yd) 1 mile (mi) = 5280 ft = 1609 m = 1.609 kilometers (km) Area 2 1 inch2 = 6.452 em2 = 64516 mm 2 2 1 foot2 = 0.0929 m = 929 ern 2 1 acre = 43560 ft2 = 4047 m2 = 0.4047 hectare (ha) = 0.004047 km 2 1 mile2 = 640 acres = 2.590 km Volume 1 inch3 = 16.387 cm3 = 1.639 x liter (1) = 4.326 x U.S. gallons (gal) 1 foot3 = 2.832 x m3 = 7.477 U.S. gal = 28.320 1 = 2.295 x lou5 acre-feet 3 6 1 mile3 = 4.167 km = 4.167 x lo9 m3 = 3.378 x 10 acre-feet MaSS 1 pound (lb) = 453.59 grams (g) = 4.536 x 10-1 kilograms (kg) Pressure 2 2 3 2 2 1 pound/in (lb/in or psi) = 6.895 x 10 newton/m (N/m ) 2 2 = 0.0703 kg(force)/cm (kgf/cm ) = 0.0680 atmosphere (atm) 5 1 atm = 1.013 bar = 1.013 x 10 N/m2 = 1.033 kgf/crn2 = 14.70 psi Velocity and hydraulic conductivity 3 1 foot/second (ft/s) = 0.3048 m/s = 26.3347 x 10 m/day 3 = 43.1902 x 10 inches/hour (in/hr) = 645.7627 x lo3 U.S. gal/day/ft2 (gpd/sq ft) -7 1 U.S. gal/day/ft2 = 4.078 x m/day = 4.720 x 10 m/s VIII "ransmissivity 2 2 -1 2 1 ft /s = 9.290 x lo-' m /s = 802.656 x 10 rn /day = 86400 ft2/day = 6461.3808 US. gal/day/ft (gpd/ft) 2 -7 2 1 U.S. gal/day/ft = 1.242 x lo-' m /day = 1.438 x 10 m /s Discharge 3 3 3 1 ft /s (cfs) = 0.02832 m /s = 28.32 l/s = 2446.848 m /day = 448.874 U.S. gal/min (gpm) = 6.464 x lo5 U.S. gal/day (gpd) 1 CHAPTER 1 POROUS MEDIA - SOIL The porous media that contains groundwater is a three-phase system. It consists of a solid phase (soils), a gaseous phase (air) and a liquid phase (water). The solid phase may consist of consolidated rocks such as limestone, granite, lava and schists. It may be semiconsolidated materials such as sandstones and shales or it may be unconsolidated alluvial deposits and soils formed in place by weathering processes. 1J THE SOLID PHASE The pores in consolidated rocks such as granite are due to fissures and cracks in the rock. In limestone, water often moves through solution channels. In lava, there are gas channels, cracks and unconsolidated sediments that transmit the water. Because of the irregular nature of the pores in these rocks, a successful method of analysis has not been developed. The pores, cracks and interstices occur in a complex fashion and are not always interconnnected. Experience with local conditions forms the best basis for judgement in evaluating seepage through this material. On the other hand, the pores in sandstones, schists, unconsolidated sediments and soils are more or less interconnected. The physical basis for the flow of water through these materials is well understood. These materials form the bulk of the groundwater areas. l.l.A Soils and Unconsolidated Sediments The solid phase of soils and unconsolidated sediments consist of individual particles of various sizes. These particles are classified according to their sizes as cobbles, gravel, sand, silt and clay. Cobbles have an average diameter greater than 76 mm. Gravel sizes range from 4.75 mm to 76 mm. Sands are 0.074 mm to 4.75 mm in diameter. Silt is 5 to 50 microns and clay is less than 5 microns (5 x meters). 2 Groundwater aquifers usually consist of sands and gravels. Agricultural soils which require drainage contain silts and clays. In engineerin, terminology, silts and clays are grouped together as "fines" having Soil Classification Corps of Engineers Sieve or Screen Sieve Opening, mm 2 in 50.8 1-112 in 38.1 1 in 25.4 314 in 19.1 1.4 in 6.35 No 4 4.75 No 10 2.00 No 40 0.42 No 60 0.25 No 100 0.149 No 200 0.074 Cobbles greater than 3 in; -76 mm Coarse gravel 314 to 3"; 19.05 - 76 mm Fine gravel 4 mesh to 314 in; 4.75 - 19.05 mm Coarse sand 10 mesh to 4 mesh; 2.00 - 4.75 mm !Medium sand 40 mesh to 10 mesh; 0.42 - 2.00 mm Fine sand 200 mesh to 40 mesh; 0.074 - 0.42 mm 3 an average diameter less than 50 microns. The properties of silts differ from clays. Silt particles vary in size from 0.005 to 0.05 mm (in the unified engineering classification). The individual silt grains are plate like and can easily slip over each other. The presence of silt gives a slipperiness to the soil when it is worked in the hand. Silt is generally nonreactive. It does not swell or shrink when exposed to water and the individual silt particles do not adhere to each other. Because of its slipperiness and lack of cohesion, silt is undesirable for construction purposes. Ditches dug in silty materials are often difficult to maintain because of the unstable ditch banks. 1.13 Clay Fraction The clay fraction of the soil plays an important role in the fertility of the soil, its shear strength, its permeability and many other aspects of soils from both an engineering as well as an agricultural viewpoint. Clay particles are considered to be less than 5 microns in diameter. A micron is equal to meters and is usually given the symbol p (Greek mu). Individual clay particles cannot be seen in an optical microscope. An interesting and important feature of clay particles is the tremendous surface area they possess. For example, if a cube 1 cm on the edge is subdivided to the size of clay, we have the surface areas given by the following table. Length of edge Number of cubes Total surface 2 1 em 1 6 cm 2 0.1 cm 10 60 cm 2 0.01 cm 10 600 cm 2 0.001 cm 10 6000 em 2 10l2 6 m 2 60 m 2 10l8 600 m 1O2l 6000 m2 = about 1-1/2 acres. 4 l.l.B.l Clays as Crystals The clay minerals have a chemical composition that includes primarily SO2, A1203, Fe203 and H20 along with varying amounts of MgO, CaO, K20, Na20, and P205. It has been shown that the clay minerals are built up of units of alumina and silica. The alumina unit consists of two sheets of closely packed oxygen atoms or hydroxyl groups which are held together by aluminum atoms in such a way that one aluminum is surrounded by six oxygen atoms, or hydroxyl groups, one from each sheet. Two general types of clay crystals have been identified; kaolinite and montmorillonite. The kaolin group of clays is characterized by having one silica and one alumina layer. The sheets are very compact and there is no room for ions or small molecules to be inserted between the sheets. The colloidal properties of kaolin are determined by the external surfaces alone. The ionic reactions are a result of the unsatisfied valences on the edges of the particles. Kaolin does not swell or shrink with water. Montmorillonite differs from the kaolin group in that it has expanding lattices. The crystal lattice of montmorillonite expands and contracts as the amount of water that is present in the lattice changes. It is apparent that montmorillonite has a large internal surface due to this expanding lattice. The expanding lattices of montmorillonite result in very high hydration and large amounts of ion exchange. Not only are the cations and water absorbed on the outer surfaces, but also on the internal surfaces within the crystal. In fact, most of the exchangeable ions are found between the sheets of the crystal. It has been shown that the individual clay particles have a crystalline structure. This structure is different than the structure of the parent minerals from which the soil has been formed. As a result of the crystalline structure, the clay particles possess a net negative charge. This negative charge arises from several possible mechanisms. 1. Broken bonds around the edges of the silica-alumina units give rise to unsatisfied charges which are balanced by absorbed cations.