Seepage and Groundwater

491 Pages·1982·5.949 MB·English

by  Miguel A. Mariño and James N. Luthin (Eds.)

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.