, • GWSC 5 1 Outline

GROUND-WATER GEOLOGY AND HYDROLOGY

•• By Arthur M. Piper

Introduction What is ground-water geology? Geology and its division.a Mineralogy and crystallography

Petrology and pet~ography Historical geology Stratigraphy Paleontology Structural geology • Geodesy Geomorphology Economic geology Ground-water geology Ground water a d~c mineral deposit Hydr,,ology and the hydrologic cycle Potamology Limnology Ground-water hydrQlogy Cryology Sciences closely related to hydrology Meteorology • Oceanology (oceanography) GWSC 2 Outline-Con.

Geologic phases of ground-water investigations include or involve- - ' . • "Rocks" of all types Rocks of all ages Geologic structures ~fall types Geologic mapping, to express determinations of-­ Stratigraphy Paleontology Structure Sedimentation Geologic history Geomoll)hology Petrogr~phy • Test drilli~ and other specialized procedures of sampling Geophysical studies

Elect~ic logg~ng· '"'\ Gamma-ray logging nectr~cal resistivity surveys Seismic surveys Geochemical studies Gro'llll:d-w~ter hydraulics All or most phases of hydrologic cycle Horse se~se In summa.ry--what are the attributes of a ground-water geologist? • GWSC 5 3 Outline-Con •

Geologic controls _on occurrence and movement of ground water • Type of rock Porosity and types of interstices

Primary Secondary Sizes of interstices in relatioQ to capillary effect Conditions cont!olljJlg porosity Arrangement Qf grai~s Size of grains Shape of grains Degree of assortment • Range in porosity Reduction in porosity owing to­ Compaction Deflo~ulation of clay Cementa ti on Metamorphism Weathering

Increase in porpsity owing to sQlution Evaporites

Limestone and dolomite

Source of CO2 Types of openings subject to solution Origin of solution openings with ~espect to water table Features of limestone terranes • Wells in limestone GWSC S 4 Outline-Con.

• Mechan;i.cal analys_es Stratigraphy related to deposition Regional st~atification Local stratification

Lateral gradations in texture and grai~ si~e Facies changes Modes of origin Marine Continental Volcanic Glacial • Unconfonnities Dikes and sills · Structure related to defonnation Folds Homocline Monocline Anticline Syncline Metho_ds of po_rtr~~ng ·folds Geologic maps Profile sections

Isometric block (fence) diagrams • ·stru_cture contour maps GWSC 5 Outline-Con •

Structure related to defonnation-Con. • Faults Normal or gravity Reverse Qr thrust

Overthrust and underthrust Joints

Geologic ma~ping on aerial photos Use of matched stereo pairs Field stereoscopes How to record data Need to walk out contacts and structures • Transferr.ing data to base map Measurement of geologic sections Methods Texture of sediments Color of rocks Acid tests Structural features Fossils

Use of soil maps in geologic mapping

Use of vegetation _changes in geologic mapping • GWSC 5 6 Outline-Con •

Test drilling • Consolidated rocks Unconsolidated rocks Cable tool Hydraulic rotary Drilling m:ud Drilling speed "Feel". of drill

Mud circulation Catching samples Description of samples • Field Office Preparation of samples Compressed-air rotary Jetting Power auger Electric or gamma-ray logging

• GWSC 5 7 Outline-Con •

Zones of subsurface water • Capillarity Influence ~r grain size Hygroscopic water and "hygroscop~c coefficient" Water yielding and r~taining capacity of rocks Specific yield and specific ~etention Limitations of definitions Time factor Size of sample Methods of determining Laboratory • Field MQisture equivalent Field capacity Wilting co~fficient Movenent of grqund water Turbulent flow Laminar flow Critical velocity Darcy's law

Permeability and coefficient of permeability Transmissivity and coefficient or transniissibility • GWSC 5 8 Out.line-Coµ.

• Movement of ground water-Con. Relations Permeability to porositr Porosity to velocity Permeability to texture and grain size Specific yield to porosity Specific yield to grain size

Geologic structure and stratigraphy-their control of occurrence and movement of ground water Confined versus unconfined gro~ water Artesian water and the artesian system Old concept • Meinzer 1 s work Theory of compressibility and elasticity of artesian aquifers Elastic compression Plastic deformation

'Iheis I c,oncept of coefficient of storage Quantity r_eleased from storage by compression of aqll:1-fer and exp_ansion of water ·

Jacobs' work Expansion of water alone Subsidence from withdrawal of nuids Water fields Oil fields Determination of subsidence • Leakage of confining beds (Aquicludes) GWSC 5 9 Outline-Co~•

Geologic structure and stratigraphy-their control of occurrence • and movement of ground water~Con. Effects or faults As conduits Aquifers produced by erosion along fault scB:rps As barriers Fmphasized by cementation Effects of' dikes and sills . Relation or ground-water reservoirs to the flow of streams--a function of' the geol_ogy Northern Indiana Sand Hills of' Nebraska • Semi-arid central Oregon Limestone terranes Relation of' geology to quality of' water Relation to rock types Mixing of waters of different quality Surface and ground waters Ground waters Leakage of' aquiclu:ies Wells tapping more than one aquifer Wells having leaky casings • GWSC 5 10 Outline-Con •

Relation of geology to quality of water-Con. • Soft~ning and hardening of ground waters by natural base exchange Salt-water intrusion

Along seacoasts and islands

~ Ghyben-Herz?erg ~rinciple Artesian aquifers Other conditions Connate water Industrial wastes Oil-field brines St~atification of fresh and salt waters • The source of water derived from wells Essential factors controlling action of an aquifer Condition of equilibrium in aquifers A few chosen examples Southern High Plains of Texas Large valley Qf perennial stream Big Sandy Creek Valley, Colorado Closed desert valley

Grand Junction, Colo., artesian basin "Safe" Qr economic yield • GWSC 5 11 Outline-Con •

Hints on maps, field procedures,_ and expression of results • Preparation for field season Previous geologic and hydrol~gic work Base maps Federal USGS USGS&GS

Forest Service scs Corps of Engineers State • Highway Dept. or Planning Comm . Geol. Surveys

Engineer's off~ce Board of Agriculture County arrl city engineers Mounting maps Aer~al photQs, sources USGS, Map Information Office USDA SCS, AAA, Forest Service USC&GS

Anny Air Corp_s

TVA Fairchild Aviation Corp . • Other private agencies GWSC 5 12 Outline-Co~-

Hints ,.on maps, field procedures., and expression-of results.Col\• I • Records of wells and springs When to contact drillers Questioning drillers Filling ,out schedules Sketch maps Measuring depth to water Water-table contour maps Spacing of contours

By proportion

By graphic methods • Transfer method Direct method

By special dev~ces Interpretation Direction of mavement Gradient Recharge Discharge Relation tp geology and transmissibility Ground-water divides Relation to streams Maps showing changes in grown-water storage .Lines of equal chSllJe in water levei Construction of polygons • Determination of storage changes GWSC 5 Outline-Con • 13

Hints on maps, field procedures., and expression of results-Con. • Depth-to-water maps Maps of bedrock topography Isopach maps Isolith or lii;.hofacies maps Maps showing availability of ground _water

•

• GWSC 5 Geol. 1

Hydrologic cycle

® • WATER PRf:CIPITATEO FROM ATMOSPHERIC VAPOR ~ I

TeffiPOrary storaq• ...... ir,e Infiltration Over-land runoff ______Wastaqe bLl1,bltmatinn ______J MelT waterl

Capillary Sublftar1ne repl11nish111ent spr,nqs

Soil-water • exces5

_ _ Consum~e waste __ -----; I t Wi1hdrawal e Consu~ptive (@@ waste by water - lov,,,q plants ♦ Discharqa

Solid flow lines indicate movement of water as liquid; broken lines, movElllent as vapor. Heavy flow lines (lower central part of diagram) indicate man's principal changes in the natural cycle. M, components of the cycle for which records of measurements are common and fairly extensive, though not everywhere comprehensive; m, components which are not measured readily, and for which more extensive records and improved techniques of measurement are needed; s, components of natural water consumption that can be, or ultimately must be salvaged in substantial • part. GWSC 5 Gaol. 2

• Porosity and void ratio The pQrpsit7 of a rock or earth is its property of containing interstices or void spaces. It can b~ expres·sed quanti_tatively as the ratio, usually a percentage ratio, of the aggregate volume of all interstices to the gross volume of the rock or earth (including interstic.es) •

P = 100 (Tvi) = 100 (V-vm)--r- (1)

where P • porosity, in percent V • gross volume vm = aggregate volume of mineral p~ticles vi= aggrega~e volume of interstices • (2)

where 'Yd= specific gravity of dry sample (gross dens:j.ty, interstice~ included) 'Yt'\1 = mean specific gravity of mineral particles 'Ys • specific gravity of water-saturat¢ sample

The void ratio of a rock or earth is the ratio of the aggregate volume of its interstices to the aggregate volume of its mineral particles.

Void ratio (3) • GWSC 5 Geol. 3 • General range in porosity of natural sediments and sedimentary rocks Percent Samstone • • • • • • • • • • • • • • • • • • • • • • 4-30 Sand, clean and unifonn • • • • • • • • • • • • • • • 25-45+ Gravel, clean and uniform •••••••••••••• 25-45+ Sand and gravel, ~ed • • • • • • • • • • • • • • • 15± Silt and clay As deposited • • • • • • • • • • • • • • • • • • • 40-90 Compacted and dewatered ••••••••••••• 20-40 Shale • • • • • • • • • • • • • • • • • • • • • • • • 3-20 Limestone • • • • • • • • • • • • • • • • • • • • • • <1-15+ • £2mpaction of fine-grained material According to Athy, L. F., Density, porosity, and compaction of sedimentary rocks: .Am. Assoc. Petroleum Geologists Bull., vol. 14, PP• 1-24, January 1930

(4)

where Pz • porosity of clay at depth z

P0 • porosity of clay at land surface b • a constant e d the base for Napierian l~garithms (2.718 •••• ) • GWSC 5 Geol . 4

Processes in compaction of clay and shale

(A.f'ter Hedberg, H. D. , Gravitational compaction • of clays and shales: Amo Jour. Science, vol. 31, pp . 241-287 , 1936. )

EXPULSION ,- OF - FREE WATER "C EXPULSION 0 OF ADSORBED ,, WATER :I: LOSS or WATER > THROUGH en CHEMICAL COMB "' I NATION MECHANICAL REARRANGEMENT en OF 0 • PARTICLES ,- MECHANICAL 0 DEFORMATION OF PARTICLES ,, :I: ► SOLUTION CJ) AND RECRYS- ,,, TALLIZATION

ELASTICITY IN THE PRESENCE OF WATER

0-10 10-35 PER CENT 35- 75 75-90 POROSITY REC RYS TAL- MECHANICAL OCWATERING MECHANICAL STAGES LIZATION DEFORMATION REA~~~~E- • GWSC 5 Geolci 5

Grade sizes for granular materials /yo S. Dept .. Agriculture, modifie§ • Tyler standard mm in screens, mesh* Gravel >2 > 0.079 < 9 Very coarse sand 2-1 0.019-00039 9-16 Coarse sand 1-0.5 Oo039-0o02Q 16-32 Medium sand 0.5-0.25 0.020-0.010 32-60 Fine sand 0.25-0.125 0.010-00005 60-115 Very fine sand 0.125-0.062 0.005-0.0025 115-250 Silt 00062-0.005 0.0025-0.0002 Clay < 0.005 < 0.0002 . . . . *Approximate.

Relatio_n of grain size to porosity and penneability /J.fter Foley, Sedim.enta~ion and ground watei/

• Grade size, percent by weight 'E ctS Pennea- f/l 'E 'E . § P~ros- ctS ctS 'E rn bility r-f Q) l'I] rn ctS ity Q) rn rn Q) +> (Meinzer M Q) d r-f ~ {percent) ~ (\j 17.l s Q) •r-1 •r-1 units) M 0 •r-1 ~ Cl) 8 e, 0 ~ "O 0 Q) ~ (.) ~ ~ ~ ~ ~ 4 • • o.6 1.0 3. 0 5.7 24.7 44.o 21.0 58 . 2 2x10- • • . . • • 2.~ .9 LO h~.1 h2.J 55.5 2x10-l 19.6 24._2 17 .4 25.9 8.8 1,.3 1.5 37 . 0 3xl0 15.4 ]5 .2 20 . 2 l9o5 16.4 7. 0 4.5 1., 26. 3 1.5x102 29.7 16.9 18.9 17.1 15.4 1.3 -4 .2 27 .1 4. futlo2 17.9 31.4 32.2 14.o 2.0 .8 .4 31.4 1.2x103 4o.4 15.5 22.8 16.5 3.9 .4 • .2 .1 21 . 2 2.6xlo3 75 . 2 B.6 9._4 5.2 .7 -2 o2 23.4 4. 2x103 68.2 14.8 11.8 4.2 .4 ol .2 25 . 6 l .Jtl~ 90.0 7.9 1.0 1. 0 ._l ol .1 38.0 9xl

Notes.- Heavy "stair-step" line shovs approximate mean gr~e size • • Among the 10 samples, co~ficient of permeability ranges 4.5x108 to 1. GWSC S Geol. 6 Thiclmess and facies maps

--, ----~--~ l · f ~- r I • • ~ ••• T" 1 I ·----1 I I I • ·· -~

., I

• .....

'I . .. 1 i • · I 'lfl'Tr · -;.• -•-"-w---- THICKNESS MAP OF HARTVILLE FORMATION , ·,., ..... r .• ,,.,' ·• ..... ,,., .•

(after Love., J. D• ., Henbest., L. o., and Denson, N. M., Stratigraphy and paleontology of Paleozoic rocks., Hartville area, eastern w,omiJJg.J A thickness (isopachous) ~ap such as above may be combined w1 th_ pattern · or color SJ'IIU)ols to discrim11 .:J ce various L. thologic f':.cies or other lithologio characteristics. A series of such maps can clarify stratigrap!:ic relations between several members in a canplex tonnation. See: Craig., L. c,, and others, Preliminary report on the stratigraphy of the Mornaon formation and • Colorado Plat~au regions . Geol. Surve7 1'E related formations ot the u. s report 1180, Nov. l9Sl. GWSC S Geol. 7 Types ot unconformities (a-a) in relation to well prospects (After Meinzer, o. E.: U. s. Geol. Survey Water-Supply • Paper 489, fig. 55)

V • •I I I B z I

t. UY W M )' J z

D • Y W X )' S "'

E w ,c I I

A., Region undetonned; lower (water-bearing) series of rocks eroded into a hilly terrane before upper series deposited; aquifer (stippled) may be extremely discontinuous. B., Region undeformed; lower series eroded nearly to a plain; aquifer more continuous than in A. c., Lower series of rocks warped ge~tly before upper (water-bearing) series deposited; aquifer may be fairly continuous. Locally., as at either end ot ~action, the beds of the two series may be strictly parallel. D., Lower series stronglf tilted and eroded into a hilly terrane before , upper (water-bearing) series deposited; aquifer may be most discontinuous. E., Lower (water-bearing) series strongly tilted and then beveled bef~re upper series deposited. Recharge opportunity variable, as aquifer may -not crop o~. . ., F., Lower series strongly tilted clockwise and beveled, upper (water-bearing) series deposited, region then tilted counter-clockwise and eroded to moderate relief. GWSC S Geol. 8

Geologic map and section of a structural dome

(mack Hills, s. Dak.; after N. H. Darton, from U. s. Geol. • Survey Water-Supply Paper 489, pl. 23)

Tertiary~ and uppemlOltc..taceout [2j P.,..lhaleand Colondo poup [ill] Dakota sandstone to Lakota sandstone inclusive § Moniaon formation to Permian inclusive

Pennsylvanian,~ Misaiaslp­ pian. and Ordovician . Cambriani(Lt~ndwoud formation)

·-;-.;_.,. ·,;;:-::J·\I \I\•· - r\ '} ,),,,, Pre-Cambrian jCl'lllit.e, St:hist, etc., and la&t!r mtru1dw rt.X·k~

The P.rincipul •·ater-liear• • lnr formation is the l)a. kota sandstone, which ii a v~ important soun.~ of arte1ian water. Other l'.l'C()lniled water-bearing formations are the Lakotu aandatone (Lower Creta­ ceous), which lies not far below the Dakota and is mapped with It; the Min• nelusa sandstone (Penn• sylvanian); and the Deud­ wood fonnation. The tee· tion show• how the dbltri­ bution and depth of thetie water beann are affected by the Black Hill» uplift

Feet epoo .B

SECTION ALONG LINE A-B zo'lll'-'=--==o_____ zo=====~,... ___60MtU:5

The layered rocks of the dome crop out in concentric bands, with the • youngest along the periphery and the oldest at the apex of the dome. GWSC 5 Gaol. 9

Geologic map-and section of a structural basin

(Southern peninsula of Michigan; after A. C. Lane, from • U. s. Geol. Survey Water-Supply Paper 489, fig. 53)

EXPlANATION

Sa,inaw -formation

•

Again the layered rocks crop out in concentric bands, but here the • youngest ·is at the center and the oldest along the periphery. GWSC 5 Geol. 10

• Isometric ("fence") diagram ! i ' :, : ! t__ i \. i " j,. : :' I f \ I , , : i ' \ /!

r,, rJL J -~ '·" .., . '

. ··- -~~--- ..-"<"~:~ :.-_·::·.::. ·=:.:•-·: .. ~--- .\.... ········- • ~ '• .. . ~ . . '·t · "·'· ,,._, ...... I ·..... ·.·.. ·.·.

Diagram showing sandstone beds in the McAlester shale or Oklahoma (af'ter T. A. Hendricks: U. s. Geol. Survey Bull. 874-D).

Such diagrams may effectively bring out interfingering of members or facies changes within a fonnation, stratigraphic relationship of one formation to another, features 9f geologic structure, etc. If drawn on sea-level datum, actual dimensions and positions are represented. On the other hand, a stratigraphic horizon marker may be taken as the base in order to emphasize some stratigraphic relAtionship • • GWSC 5 Oeol. 11

Measurement of dip by method of cotangents Where exposures are scattered and generally linear, and especially if dips are gentle, the method of cotangents is a simple and effective • means of determining amount and direction of dip. First, measure apparent dips and their directions on three or more linear exposures. Choose exposures whose directions "fan" at least 60°, as in a branching arroyo or on the no~e and either flank of a spur_. Typical observed data might be as follows: Apparent Exposure Direction Cotangent of diE aE,Earent diE 1 s.15°w. 310 16. 35 2 S.55°E. 53 11.43 3 s. 3°w. · 410 12~.71 4 S.67°E. 41° 12.71 5 S. 2°E. 40 14.30 Second, plot the cotangents as vectors from a common point. Then, the straight 11;.ne through {or averaging) the vector tips is the line of true strike CAB) and the vector to that line (OT = 10.65) measures the cotangent of true dip. 'lhus:

• 0 N '\

\ B \ \

II o/ M II //\

LI> / ~True dip 5°20' S.35°E. /

Carry a condensed table of cotangents in notebook {also of sines, • cosines, and tangents). GWSC 5 Geol. 12

Measurement of di b lane-table traverse or from records of wells

Where gentle and variable, as in an area of slight warping, dip • can be measured effectively by plane-table traverse. Use larger scale as dips flatten, In the sketch below, let A, B, and C be three points located on sOD').e convenient horizon marker, with plane-table altitudes and scaled distances as shQWn.

N

7 I "' I •• . '--- ~ , A= 153 (altitude) Dip 4° N. 36"E. J(~e below)

On line which connects highest and lowest of the three points (AC) interpolate point S whose altitude equals that of the third point (B). Draw and project BS, the line of strike. 'lhrough C (or A) drQp a perpendicular to BS projected-that is, s•c.

Then S1 C = 118 ft (scaled)

Vertical component of S 1 C • 8 ft '(a1t.' B - alt. C) Tangent of.dip angle = ~ = 0.068 1 8 = 360 ft/mi Dip = 3o54, say 4° • GWSC 5 Geol. 13

Measurement 9f thickness of inclined strata, ,. reconnaissance methods Where t~rrane permits t+averse at right angles to strike of inclined beds, set Abney level or Brunton compass to angle of dip and measure in multiples of "eye height," as below. Traverse uphill ordinarily. This is the simplest case, but it affords only reconnaissance accuracy.

•-::--_-____§_ -- _.,.---- __.-- -­8 h h

Stratigraphic thiclmess = T • h-cosd" (5) where h = eye-height multiple 6 • angle of dip

'lhe general case is covered by Mertie, J.B., Graphic and mechanical • computation of thickness of strata and distance to a stratum: u. s. ~ol. Survey Prof. Paper 129-C, pp. 39-52, 1922. Here, the traverse is r\Ul along whatever course is practicalo If moderate accuracy suffices, use a Brunton compass to measure angles and pacing or a sµrveyor's tape to measure distances.

Then T = s (sin({ .cos c1 .sin 6 + sind oCOS 6) (6)

where s = slope distance along traverse ct. = azimuth angle of the traverse, measured from or to the strike of the strata d = slope angle of the traverse S = dip of the strata

Here, the second tenn is { + when dip and slope are opposite in direction - when dip and slope are alike in direction When the traverse is horizontal, d is zero, and

T = s (sin Ci{ •sin S ) (7)

Equations (5) and (6) can be solved readily on a slide rule (most of which have an "S" scale for sines but no scale for cosines) • Merely remember that cos 8 - sin(900-0 )o Mertie (op. cito) gives a nomograph for solving equation (6) graphically, but this is neither • simpler nor faster than a slide-rule computationo GWSC 5 Geol. 1.3-Con. In practice~ data generally are tabulated in the notebook at the time of traverse and computed later (in evening). For exainple: Slope distance = 80 ft = s Azimuth 0£ traverse = N. 25°E.1 (X. = 55° • Strike of strata = N.3ooW. Slope -of traverse = 15° • d Dip of strata = 50° N.60°E. = 6 (in direc.tio.n op~site that of land surface)

ih~ (using "A" and "S" scales on the slide rule):

0 0 T = 80(sin 55° •cos 1.,0 .sin 5o ) + 80(sin 15° .cos 5o ) = + 13.3 = 61.8 rt

•

• GWSC S G~l. 14

Measurement of thiGlmess ot inclined strata b lane-table traverse or from records of well~ Wherever a ~recise measurement is d~sired~ especially if terr~ • is rough and the section is thick and complex, a traverse by plane tabl~ and s_tadia C(IIU'10nly is the moat practical, Stations are identified in terms of horizon~l and vertical dist~ce~£ rather than ¥1 tez:ms of sloPe distance and slope angle, as in equation 6. Plane-tab'l~ scale is adapted to the particular situation. On such a traverse let A, B, c, D, Ebe traverse points on successive partings between beds, with altitudes ani lpce.l dip as shown below (dip meas~ed as on Geol .. 12).

E =-200 (altitude)

N

' • ' '-(s=4° )

C=l40

I C ' ' ' ' ' '

' "' ' ' ' • ' ' GWSC 5 Geol. 14-Con.

The determination 9f thiclmess can be wholly by graphic methods or partly by graphics and by computation. First, through the several traverse points draw strike lines such as A-A" projected; then, draw •• A'B 1C1D1E1 i~ the direction of dip. To complete by graphics, construct section as though r.otated downward to the right about A1 E1 as the axis. Lay off A1A11 equal to the detennined altitude of A (plus or minus any convenient amount), and so on. Draw A"a", B"b", etc., according to measured dip, then scale thicknesses as shown. Using _natural vertical scale as on the sketch,. this method requires precise drafting if dips are less than about 10° or more than about 4o0 • However, the dip can be expressed as a tangent (0.068 on Geol. 12) and drawn at either an exaggerated or reduced vertical scale. Thicknesses then can be measured at whatever vertical scale is used.

To complete by computation, scale A1 B1, B1C1 , etc.; these are ·horizontal components of the traverse segments. Corresponding vertical components are computed from the detennined altitudes. In the sketches below: •

let h = horizontal component v ~ vertical component then

= h•sin 6 + v•cos 6 (8)

The plane-table traverse, as here described, is analogous to an array of well records that define horizontal positions and altitudes on successive stratigraphic horizons •

• cwsc 5 Gaol. 15

Rubber stamp used by Holbrook, Arizo, office to systematize description of geologic sections

'Ihe following stamp is imprinted in the notebook for each bed • described. TYPE: COLOR: F w TEXT: vc - c - m - f - vf - s - c ROUNDING: wr - r - sr - sa - a SORT: good fair poor CEMENT; hard finn weak TYPE: COMP: ACC: qtz feld mica femag Caco3 arg INCL: rare cam abund TYPE: BED: n mas gnrl irr fs vt t tk vtk ( ) I-BED: TAN sim comp . wedg H L FEST nor plung asy 0 - 1 1 - 20 ' to aeol Fluv Other: SURFACE MK: BA.SE: grad sharp flat irr TOPO: CL ver rnd irr IDG SL reg irr roll cov WEA: sm rnd blky pit knob Etch FOSSILS: AQUIF: good fair poor RECHARGE: poor • THICKNF.SS: Field: Truf?: Ex:p:ianation

TYPE: Insert "sandst_one," 11 ailts tone,, " "limestone, " _etc. COLOR: F - color of fresh fr~cture W - color Qf weathered surface

TEXT (Texture): In the Wentworth scale (see also Geol. 5) vc - very coarse : 2 mm - 1 rmn c - coarse 1 mm - Oe5 mm m - medium 0.5 mm - Oo25 mm f - fine 0.25 mm~ 0.12 mm vf - very fine 0.12 mm. - 0. 06 rmn s - silt si~e 0.06 mm - Oo004 mm c - clay size less than 0.004 mm ROUNDING: wr - well-rounded SORT (Sorting): r - rounded sr - sub-rounded sa - sub-angular a - angular

t' CEMENT (degree of cementation): TYPE: List cementing minerals'- etc. COMP (composition): Show dominant minerals, etc • ACC (accessory • minerals) : qtz - quartz femag - ferromagnesians feld - feldspar CaC03 - calcium carbonate mica - mica arg - argillaceous material GWSC 5 Qeol.- lS-Con.

lNCL {µ10;lusicms): rare - rare TYPE: DesQribe or identifr com - cOllJlD.On abu.n - abundant BED (bedding): fl~ .f'lat rs - £1s-sj_le • mas - 1'a.assive vt. - very- thin (1/2-2 in) gilrl - gnarl7 t - thin (2 i1r.2 ft) irr - irregular tk - thick (2-4 ft) vtk - ver,-thiok (h rt and urQ) X-BED ( cross-bedding or cross-laminations) a TAN - tangential H - high-angle FEST - festoon sim - suiple L - low~l~ nor~ normal comp - C

1 0 - 1 - 20 1 to Aeol - aeolian O - 1 1 - small s-ca.. i~e- Fluv - fiuviatile 11-201 - medim scale oth~r - desoribe 201 over - large scale SURFACE MK (s"Qr:face markings): Describe BASEi grad - gradational flat - fiat sharp - sharp ir:r - irregular • TOPO (tOPQgraphic exp~asion): CL - cliff L1'G - led~ reg .. regular ver - vertical SL - slope irr - iri-egular . rnd - rounded roll - rolling irr - irregular COV - covered WEA (weathering characteristics): · sm - am.ooth pit - pitted rnd - rollll.ded knob - knobby . ···. blky - bloolcy" Etch (etched characteristics) - crosa-Jaminations.,. etc. FOSSILS: Describe type, occurrenc~, ~d ,reservation

-AQUIF- {.Aquifer)'.} good, fair, or ;poor_ expectation rrm RF£HARGE: field ~bservationa

THIC~: Field - field unit~ or intervals True - true value., corr,eted for dip •• GWSC 5 Hydrol. 1

Zones of subsurface wateri after-- ' y • MeinzerJ/ Terza~hi Versl~ " f..i LAND SURFACE ...,Q) Soil water ~= Discontinuous m-Q) capillary water Water of ~ (Mainly separate pendular H ...... ,.I> rings and stage ...,Cl) Intermediate envelo~es) fl i vadose water al i •ri ...,.,... .p trn rn f..i ~ Semi-continuous Q) 0 capillary water Water of ~.,... (Larger openings .funicular ~ unsaturated, stage_ ~ A 0 p < atm) •1"'1- Fringe water ~ (capillary fri~e, 1 f..i p C atm -- Q) p < atm) • rd ...,~ Continuous Water of 0 'S ~ capillary water capillary H. ft-t 8 (p < atm) stage 0 ~ N (,) 0 pa atm WATER TABLE f..i

~ 0 A 0 ~ ...,o,i 0 ~ ~- Ground water ..., (phreatic water, rd rn pleurotic water; , Ground water ~ 0 p > atm) 2i 0 N

Q) bO J Internal water 1/ Meinzer k O.E .: U. s. Geol. Survey f+-4 (juvenile water, water-Supply per 494, p. 23 ,. 1923. magmatic water; Terzaghi, Karl: Hydrology, ~ y 0 may be whqlly chapt. 9, 1942. H in chemical Versluys, J.: Internat. Mitt • ft-t 1/ 0 ~on) Bodenkunde, vol. 7, PP• 117-140, . 1917 . Q) s::1 • 0 N .- ..... -----·------GWSC 5 Hydrol. 2

Surface tension and capillary rise

At an interface between two fluids, molecular fo~ces c~eate a tensile stress in the surface of separation-this stress is known as surface tension. • For water against air, this ·stress is fairly large (0o073 g/cm at 20°c}; thus, water can resist hydrostatic tensile stresses of many atmospheres without losing its continuity.

If the lower end of a vertical tube of very small (capillary) diameter is dipped into a liquid, the liquid comes to rest within the tube with its surface either above or below the free liquid surface outside the tube, depending on the composition of the liquid, the material of the tube; and impurities in the liquid or on the tube. If the liquid is clean water a:rxi the "tube" is glass or one of the common earth materials, the water will rise in the tube, as in the sketch below. - rx; I

2r 2r = diameter of tube

h0 = ,capillary rise

Here, pressure is atmospheric at the level of the free water surface both outside and inside the tube; pressure al.so is atmospheric on tp.e water meniscus within the tube. Thus, weight of the water within the tube is sustained by surface tension in the meniscus, and the raised water column is under tension-that is, pressures ar~ less than atmo.spheric. 2 At equilibrium 1'(r o/hc = T 21f'r-cos CX. (1) (Weight)= (Lift by tension)

where 'V= density of water at the particular temperatur~ T = surface tension in g/cm

Then h = E1cosOC (2) C r¥

For pure water in clean glass, OC = 0 and cos <1... = l; for room temperature of 20°c, T = 0.073 and 'Y = 1, whence

h - 0.15 • C -~ (3) GWSC 5 Hydr9l. 2-Con.

For natural earth materials there are too maey yariables to express capillary raise in precise terms, but in general it increases as grain · size decreases«. Terzaghi ("Hydrology," chapt. 9) cites experimental measurements or capillary r_ise by Atterburg in seven sands at a temperature. • or 170c ove~ a term or 72 days. Porosities and void ratios were essentially the same in· all sE;?Ven-41 perce~t and o.69, respectively. The measurements, given pelo~, show that capilla.cy rise incr~ased ~nversely to the first power of the grain size (approximat~ly) .

Grain size, mm 5-2 2-1 1-0.5 o.5-0.2 0.2-0. 1 0.1-0. • 05 0 . 05-0. 02 he, cm 2.5 6.5 13.1 24.6 42 . 8 105 .5 - 20~ * Still rising after 72 days.

If the capillary tube of the preceding sketch is raised vertically from the liquid, drainag~ ld.11 cease when the menisc~s falls to a point about h0 above the l~wer end or the tube. At the same time a pennanent droplet will form at the lower end of the tube as in the sketch at the left. As before, surface tension in the meniscus sustains the weight of -the liquid colunm he• Near the lowe.r end <:>f the tube, stress changes from tension in the column to compression in the droplet. Tension in the surface of the droplet acts like an elastic CQntainer and transfers the weight pf the drople,t to the lower end of the tube. Condttions analogous • to this example exist in stratified, granular earth materials which are not co~tinuously saturated and in which water is percolating downward from a fine~grained material above to a coarser-grained material below. -

Let the sketch at the left represent an idealized section across the wall of a p= atrn well that taps uncQn.fined ground water, with the water-bearing material replac~d by a bundle of vertical capillary tubes of h c various di~eters.. 'Ihen, the upper surface

Movement of ground water

Critic.al velocity.- Index · commonly used is the ~o-called Reynolds • number R=~ (4)

where d er mean diameter of grains 'V = mean velocity of the moving fluid 'Y = density ( specific weight) of the fluid .,Ji,= viscosity of the fluid

If R is less than about 1, the flow is "viscous" or laminar and velocity varies as the first power of the hydraulic gradient. If R is greater than about 10, the flow is turbulent and velocity varies as the one-half' po_wer (square root) of the hydraulic gradient. At values of R b~tween 1 and 101 ,flow may be either laminar or turbulent, depending on the range in size and shape of grains • • Darcy's law.- FQr laminar flow in permeable media (5)

where Q = quantity of now in a given interval of time K = a constant A~ cro~s~sectional area through which flow take~ place h1 and h2 = hydrostatic heads at either eµd of the flow reach Jt = length of the reach

Because movement is in the direction of dizrunj.shing head, (h1-h2) is considered negative and Darcy's law for unit cross---sectional area may be generalized

q = £ • -k.dh/dP, when dh/dt = 0 (6) A -

Disregarding dimensions, q is the mean velocity of movement and we may ·also write • (7) swsc 5 Hydrol. 3-Cqn.

Coefficient of lermeability.- In equation (5) the constant K ~ the coefl'folent o permeability or the transmission constant, a • characteristic of the permeable med.imn. K Cl q • A(¥). Q or k dh/~ (8)

13 Thus, K an:i k ha:ve dim!lilBiona of' T rl- L/L = ~ which is a velocity-,

Meinzer 1 s coefficient of p.erm.eabili ty

p = nQ (9)

where Q =- quantity of flow in gallons a day, at 6o°F I = h1draulic gradient (1) a~ a ratiQ ~ H/ AL or (2) in feet per mile . A • cross-s.ectioru.u ar~ in (l) square feet or • (2) foot-miles

'lbua, P has dimensions of

f{gal/day)/(rt/rt)_sq ft 1: (gal/day)/sq rt = 1. l(gal/day)/(.rt/mile)ft~~ T

which again is a velocity. In the abov~ equation of di111en;:1ions,. tt/ft is unity- or 100 percent hydraulic gradient-that is.r H •I ~ · .

. ~L= l SliQhter1s transmission constant dilf'ers from Mei11$er 1s coefficient o:r permeability only in that Q is e:x:presa8(l in ~ubic feet a minute. Thus, using subscript.a s and iii to identii\r the Slicbter and Meinz~ dimensions,. respectively-~ we may write

(10) • Coefficient or transm;ssibility.- The coefficient 9f tranamissibility · or transmissivity t'fii~is) measures the capa~ity or an _entire aquifer to transmit water at the prevailing temperature.. II\ simpleat terms it is Meinz~r•s co~ffici~t of penneability (corrected fo~ temperature) • multiplied by- the sa1;urated thicknes~ or the aquif~r, Thus T=pt=I (11)

where t = thickness of the aq,ui.ter, in fe~t

12 Thus, T has dimensions of (gal/day) ft/(.tt/ft) sq .rt= (ga.1/rl;ay)/tt c.,-

'!he coefficients P and T now aJ;98 T(ell e.ntrenched in our lit$rature. However, they conf'orm to neither the f09t-pound:-.aecond no~e cent:ilnet~­ gram-second systems. other t,orkers who de.al with movement of f'luids through permeable media have established Qther units of' ~rmeability, some of which introduce propertie,s of the flu.id (such as viscosity). Some of these uni ts are more logical than ours; theref·Qre, we should n9t • quarrel with them.

Relation .or permeabilitt to grain size.- According to Jacob (Engineering Hydrology, cllap • 5, p-. 324., 1950), a ~o~fficient _of permeability may be ~xpres~ed in the f'onn

(12)

where C = a dimensionless constant depending on physical characteristics of the pe:nn.eable medium (porosity, range and distTibution or grain sizes, shapes o.f grains, eic.) · d =- mean diameter of grains Y = apeci.f'ic weight (density) of' tne fluid JJ, = viscosity 0£ the fiuid

Thus, penneabilit,y vari_es as the square of g~ain diameter • • GWSC 5 Hydrol. 4

Compressibility and elasticity of aquifers and water

• 'Iheis_ 1 coefficient of storage.- 'Ihe coefficient of storage (Theis, C. v., The significance and nature of the cone of depression in ground­ water bodies: Econ. Geol., vol. 33, p. 894, 1938) is that volume of water discharged £rom storage withi.n a vertical column extending the full thickness of a saturated aquifer and having a cross-sectional area of unity, simultaneously with a decline in head of unity. Such discharge is due to compression of the aquifer and expansion of the contained water as the h~ad diminishes. By convention, the dimensions are taken in feet and pounds. For conftned or artesian aquifers the coefficient of storage ranges about from 10-!:> to 10-3.

Jacob (Trans. Am. Geophysical Union 19hO, pt. 2, PP• 576-577) confirms Th~is I equation by fundamental hydrologic concepts. His general equation is ·

(13)

where f' = density of the water g = standard mass 0£ a cubic foot of water 8 = porosity of the aquifer • m = thickness of the aquifer Ew,- = bulk,.;nodulus of elasticity of water (about 3x1Q.? lb in-2 or 4.3x107 lb ft-2) b a proportionate part of the aquifer that I".esponds elastically. For an uncemented granular aquifer bis unity; for?, non­ granular aquifer having tubular channels, such as limestone1 bis apparently equal to porosity; _for a sandstone, b doubtless ranges between these limits. Es a bulk modulus of elasticity of the aquifer · K = a dimensionless quantity depending largely · on the thiclmes,s, configuration, and · distribution of int~rcalated clay beds Ee = bulk modulus of compressic;,n of the clay • GWSC 5 Hydrol. 4-Con.

Within the parenthesis of e~uation (13), the first term indicates storage derived from expansion of the confined water and the second term indicates that from compression ot the aquif~r. Together these two account fQr all the water derived from storage within an ideal • and elastic aquifer bounded by impermeable planes. For practical applications, if the· time interval invQlved. in a determination of S is sufficiently long, the third term within the parenthesis 'ordinarily may be ignored. Then, for granular aquifers b = 1 and equation (13) .can be simplified into

(14)

7 2 where f& = -t = l/4. Jxl0 lb ft-

= 2 • 3xlQ-B lb-l ft 2

For an example of storage release from expansion of the water alone, · assume 8 = o.·3 and m = 1 foot.

• .4· -8 -1 2 Th:en S::::: 6 2. lb x 0.3 x 1 ft x 2. 3x10 lb ft

= 4.3x10~1 ft~

If m = 100 ft

• CliSC 5 Hydrol. 5

Subsiden9e due to withdrawal o:r water

Subsidence of the lal\d surface owing ~o nthdr~val of ~ound water or oil is a fairly common phenomeJ10n. .Among wat~r !ields, subsidenc_e • of same 6 feet n~ar San Jose~ ·ca1if., and 4 feet near_T~xas City, Tex. , has ,occurz-¢ (alth:ough attri:buted largely to :P-last_ic com.pr~ssion _of clay). Am.Qng oil fields, subside,nce of some 2 feet had occurr.ed by 1925 at Goo~e Creek, Tex.; of some 6 feet between 1938 and °1947 and 16 feet· by 1952 near Wilmi~on ;m.d Long Beach, Calif. (Se~ Gillul.7_, James, and Grant, u. s., Subsidence in the Long ~ch harbor area, Cali£.: ~1.· Soco .Ame,rica Bllll • .l. vol. 60, PP• 461-530, 1949 . ) . LohD,an propof:}:es a basis far computing ~<;t~ subsidence as follows: , · ·

FrQm equation (1:4) (15)

'Ih~., from Hooke's la~ that strain is prqpor~ional to stress (within the elastic- limit)~- we may write_ ·

m ;m - dm dm • r dp or 1;- dp (16) • ~

where dm = sub.siden<;~ dp • diminution of heap.

1.Ihen s e +dm --g e mAr -dp 0~ (17)

In praQtice, s would b~ detennin~_:rram a p.unping teat (reasonably l®g if much clay is present in the water-yielding zone, but not so long as to ~olve boundary e.ffec.ts); a WOJJld be measured from a core or samp~et and m would be taken from a drill~1s log or an electric log~ Fer example, take the Fox Hills sa.nd~to.n~ of the Denver basin. For t.h~s Lohman. gives · · · -

S = 2x10-1' (believed fairly elastic) m = 100 f'~t · - a= 0.3 • dp ~ 100 lb in-2 (231 feet of head.J assumed) GWSC~--~n. 5 • Then

Thus, _sU?sid~~ce o!_0 ,,~o4 toot is re,asonable for fairly elastj.c ~and, small S 1_ thiakn~sa lQO .feet, a,nd ~sur8- drop 100 lb 1n-2.,

Assume an oil field whos~ strata include ~IUJi4erabl~ clq, Se 10-3, 8 = 0-.3, m = l,._000 fee:t, and dp = 1,000 lb _in- • Th~n dm = Bubsidence owing to elastic 4efqnnation = 1.3 ft. Actual subsidenoe might be ~onsid~rably ~r~~ ol!ing ~o flasti~ deformation ~f clay_• .

If a subsidence has been identified and measqred, it.av-al~ can be inaert.ed into equation (14) or (16) t<> determine ' a cor:r.espqnding valu~ of E3• If. the latter value proves to be 0£ reas9.nable magnitude,- then elastic defoI"Jl)a.tion of the strata becan~s a cQD.p~tent expl~tion of • the measured subsidence•

• GWSC 5 Hydrol. 6

Steady and non-steady stream fl ·,_w from adjacent terranes

• I

I

A

M,dd~ Loup River near s~~K~1 Nebfas<, j ) ·~~. I1\ A ~ I/ ,Or.image, .l'H lJ4·j f.Q ':Un.· . A A.- ,,,,, . ·--ffd•I/ ;\ YIM IV ,1~ . ~. . I"" ---,,, ."'\. I\ .A - '"'-r-'V v V V nv"'v-1--J '-V v\_,...,..,.."'-""\... "''"',~./•./ II I ~ . ~ 1 I I I Wh,i. R,- nur 0&1N. South OoliOi. J'ij ~f--'----"__J \__ '.J""\. - ~ ~ LA ~"' I ~w 0<1 Doc Jon f•b , Apr .. .,, June July AUi s.111 "°" ...

. A • ~ " IOO JO#N DAY RIVCR Ar '\ 'J\ MCDONALD FCRRY \J ... ~ ~ ~ I ~ - KI\ ~ ~ ~ I -I\ ✓.,.. -. ►--..... - .. w ro, IUS /II/VCR Ar .• '· MONTC _,_ ~ \ OM::~ /IIAr ,..-- 1/-lf'~ ' i-/ .... , _,,, :; ...... _,,,.,_ / ~- ... ,-- - fr' ~ V '"' ... , .... - ~ R r) ", DCSCHUrC/1 RIVCR Ar ~ I? MOODY ( Pt.US CA/IIALS) ' I\ A v--.. ' r-, ,_ ,. r' ~ ~ .J'\ l/'-v~~ µ\ ... ~ \ '\ '\. \J - ~ i - ~ I I • u~ ~ ~Jr 'DA ) RIVCi ,.,. A 1 ,., ,u~ ,u, ,,u Ill$ l,U ,u, IU, ,,n IUO ,,,, IUI ,,,., IIJ# ,,,s ,,,, ,,,,, ,,,, Alfl#O lfl41\_j '141 IH# IHS ''"' I ,..., ""' Fi1. 2--Accwnulated monthly deviations from uniform fiow in three streams of central Oregon, • la pHCHl&&e of Ille mean for the 25 years endiflK September 30, 1921-1945 · GWSC 5 Hydrol. 6-Con.

or the preceding two diagrams, the upper (after Lohman) contrasts relatively steady flow of the Middle Loup River, Nebr., with flashy flow of the White River, S. Dak . The Middle Loup is ·one of several branches of a stream that drains the Sam Hills, a ground-water • reservoir of very great volume, whereas the White drains a shale terrane, 'Iha two streams are in the same climatic environment. Yet during much of the year the flow of the Middle Loup is 10 times the greater. ihe ratio of greatest flow to least flow (during the ye~ shown) is 1~6 to 1 fQr the Middle Loup, but is 27.5 to 1 for the White .

'Iha lower diagram (after Piper, A. M.: .AmQ Ge9physical Union Trans., v~l. 29, pp . 511-520, 1948) contrasts the John Day, Deschutes, and Metolius Rivers of central Oregon. The John Day drains 7,580 sq mi of rather impermeable terrane. Its flow fluctuates considerably each year and diminished progressively during the recurrent droughts of 1929-1941; its minimum flow has been less than 1 percent of its mean flow. 'Iha Deschutes drains 10, 500 sq mi . Its flow is strikingly uniform, the minimum of record having been 58 percent of the mean; this uniformity is a~ eff'ect of large perennial ground-water runoff. The ground-water runoff of the Deschutes canes largely frQm a part of its basin that is exceptionally permeable. 'Ihis part is drained largely by a tributary stream, the Metolius River, whose minimum flow of record is 76 percent of the mean. In this tributary, flow seems to lag at least 5 years after fluctuations of precipitation; it actually increas~ • slightly from 1933 into 1938, during a prolonged drought •

• GWSC 5 Hydrol. 7

Relation of fresh ground wat~r to salt water along sea coasts

Ghyben-Herzberg princi~le.- Small oceanic islands and coastal spits, • if formed of material that is c~ntinuously and moderately permeable, c~only are underlain by a lens-shaped mass of .fresh ground water "floating" upon underlying salt water. If hydrostatic ·equilibrium were attained, the form of the fresh-water mass would accord with Archimedes' principle th!li; a floating b~gy displaces its own weight o.f fluid. Thus, Badon Ghyben1/ an_d Herzber~ found, apparently independently, that the 1/ Badon Ghyben, w., Nota in verband met de voorgenomen put b~ring nab!j Amsterdam& K. Inst. Ind. Tijdschr, 1888-89, p. 21, The Hague, 1889. y Herzberg, Baurat, Die Wasser:versorgung einiger Nordseebader: Jour. Gasbeleuchtung und Wasserversorgung, Jahrg. 44, Munich,_ 1901.

depth ~o salt water was r_oughly a function of the height of the water table above ·mean sea level, and of the density of the sea water. In the sketch below, ,

• / / ' / \. Fresh water / ' \ __ .,, / \ h H .,, I ,,,,,,. ' / ' \ ,,,, Salt wate r / ' / / ' / ' / ' / ..... --- /

let H = total thickness of fresh water h1 = depth of .fresh water below mean sea level h2 = height of fresh water above mean sea level o/ = specific g!avity of sea water (specific gravity of fresh ground water assumed to be 1) ·

Then H = h1 + h2 = ,Vh1 (18)

whence h2 = ,Y-h1-h1 = h1('Y-l) (19) h2 • er- and h1 ,Y-1 (20) GWSC 5 Hydrol. 7-Cqn.

(An average value of 'Y' is about 1,025, when,c~ h1 = 40 h2 (appro~imate average) • The foregoing assumes hydrostatic equilibrium, which apP.lie~ • approximately near the center of the lens but does not apply near points ot fresh-water discharge into wells or at the c_oast. Actually, a dynamic equilibrium exists between recharge ~l}d discharge, with · fresh water moving over the body 0£ salt water1/. 'JI Hubbert, M. K., 'Ihe theory of g~ound-water motion: Jour. Geol. , vol. 48, PP• 882-884, 924-926, 1940. Effect of fllmPing wells.- A well drilled into a "Ghyben-Her~berg" lens may or may not yield fresh wate~, depending on the depth ot the - · well and of its cone of pumping depression. Sketch A, below·, diagrams three unpumped wells which pene~rate an equal depth below the water tableJ well~ at the extreme right, extends into the underlying salt water and evidently would not yield wholly fresh w:ater no matter how lightly it might be pumped.

C • -- _siter. table __ __ _ ---

C b ------...... ' ' ' ' ' ' A - ', J\ I '...._ , __ ./ I , ...... ,, B

C

--- __.,,... ..------, ---- .... ----- • GWSC 5 Hytirol. 7-Con.

In s~etch B, wells 2, and .E. are ~eing _pumped with c~nes of depressi~n of eq~ bqt moderate depth, At well!?, the r~sultant cone 9f salt-water rise is sufficiently high (~eor.eticuly about 40 times as high as the cone of depression is deep) that it over-_reaches ~e bot~om of the ~ell~ • which must yield salty ~ater. In sketch c, lf8ll c yields salty water when pumped with a greater draw-down than i~ B. - continental snelf.- In the sketc e ow, _e e ar esian aq er . e end to an offshore outcrop. Be~ under greater head, ·the fresh water in that aquifer. would extend beyond the Gh.yben-Herzberg interfaGe in the enclosing materials • . l.f the well shown w_ere all0J1ed to flow._ or were pumped, the fresh-water head in ~he aquifer would ~e diminish~ apd the inter.face with salt water would move lanµwarp.~ If draft i_s ~x~essive and co.ntinll;&l, the interface eventually will reach the well, which then will becQme salted. ·

_P..Qt e'J tlo.!]] etr. ___ W~te~- t~Je __ su r--fac e~- ___ _ Se ------a • __ tevel

• GWSC 5 1qdrol. 8

"'lhe aource or water derivq

Under the preceding caption as a title, c. v. Theis (Civil Eng., vol. 10, PP• 277~280, 1940) has epitPJlli:zed the h~ologic principles • on which our present __quant~tative'approach to gr~und-water probl811ls so largely depends. 'lhe hard core of this epitome follows. 1.be essential factors that determine the response of an aquifer tQ dev~lopment by wells are: 1. Distance to, and charact~r or, the recharge 2. Dis~ance to the lo~ali.ty of natural discharge 3. CliaraQter of the cone of depressiQn in the give~ aquifer, which depends on coefficients of transmissibilitf and or storage

Prior to any developnent by well~, an aquifer is in a state of apprqximate dynamic equilibrium. Draft f'rQm w:ells becanes an~ discharge super-imposed on the naturally stable system; it ~ust be compensated by one or mo;re of the _f.ollowing: . 1. Increase in recharge 2. Decr~ase in natural discharge J. Loss or storage . •. in the,, aquife:x: The formula for the cone of dep:x:es~ion in a homogeneous am isotropic • aquifer is ' h • 114T6 Qioo (e-U/u)du (21) l.87_r 2s/~

in which h = drawdown at any point, in ft Q s rate of discharge- Qf the well~ in gpm T = coefficient of transmissibility of the aqui.fer r = dista~oe between pumped well and _the point of d.rawdown, in rt S = coefficient of s~or•ge or the aquifer t = tim~ well has been discharging, 'in days ~=a dimensio:D].ess quantity varying betve~n the limits in4i~ated ·

From equation (21), it follows that drawdown is directly proportional ~o the rate of discharge {Q) and inversely proportional to the coefficient of ~ransmissibility {T).

A.rte~ any given interval of ~umping (excepting those that are very short), th~ radius of _the cone of depression, and the ra~e of enlargement or that radius, are indeJ!ende~t of the rate of discharge and inversely • proportional to the coefficient or storage (S). · GWSC 5 Hydrol. 8-Con.

In an artesian aquifer, the c~efficient of stor_age is no more than a few percent of that in a pon-~rtesian aquifer. Henc~, a cone of depression in an artesian ·a(luifer gr.Qws ab9ut 100 times as .fast as in a npn-artesian aquifer. Thus., excepting those that are very • ex~ensive~ an art~sian aquifer reaches a new equil~brium very ·soon after a gro~-water d_eve_lopment. I,!1- other words J within a shQrt time each well reaches its maximum e.ftect on the whole of such an aquifer, and derives most of its water QY increasing recharge or cfimiiµshing natural dfscharge. Such an aquifer ca,n be treated as a unit in _any measure~ for conservation of the ground water.

Conversel71 in an ext~nsive non-artesian aquifer, it water is withdrawn at great distances from the areas of recharge and of natural discharge1 for a considerable tim.e each n.ew well deriyes most of its water from storage within a rather small radius from that well. Tilus, a new equilibrium is reached s~owly, at best. A large ground~wate~ body of this sort can not be treated as a unit under conservation measuresJ rather, it must be treated as a number of dis~inct sub-units • •

,. • GWSC 5 Hydrolo 9.

'lhiessen polygons

For computing mean height of water table, change in ground water storage, and the like, it is a common practice to weight the observed • data from each observation well according to a polygonal area of influence for that well. "Thiessen polygons" are simple to construct, although procedures differ in some details. The writer's method is as f_qllows:

/ / \ ,/' ~- -~ \ If \ I I \I / \ __):Y' / • \ I "-- In the typical array above, join observation wells by rays (dashed lines) dividing the area into a n~twork of triangles whose sides are as short as possible, and whose angles ordinarily are not obtuse. At the mid­ point of each ray, erect a perpendicular and extend these perpendiculars to intersect one another (solid lines)o The intersecting perperdiculars define the polygon of influence around each well. Areas of the polygons are detenniried readily by planimeter. Storage change in a given area may be computed at intervals of a quarter, half year,_ o_r year. Here the same polygonal areas should be used in each successive computation, but a complication arises wherever an observation well is not represented in the observed data. In this ev:ent,. the writer p~efers not to modify the polygons; rather, ~o interpolate the missing data from the observations at adjacent wells. End result is essent_ially the same as would have resul. ted fr.om constructing new polygons. other complications arise where the water table or potentiometric surface is uneveno Here, it is und~sirable that a polygon span a sharp ridge or deep trough of that surface. Considerable judgment ·can be • exercised in building up the observation-well ~et to a~oid this contingency • GroUDd-W&ter Oeolog Course No. 27570 Section 2J Loo. 2J 3 oredit houri

Br.1.~t outline ot eubJect, 11&tter1 Introduction Definition ot 1ro_wld••ter poloa Bel&t1on to other fielda ot geoloa Bel.&tion'"to other fielda ot ioience and engineering !qdroloa and bJ'drologio 0¥01• Relation of lvdroloa to al.oael.7 related ec1encea Ground-water poloa teobm.que• and tho•• et related acienoea CleopbJaica Oeoohemiatry ~OQdraulJ.ca -Qeologio control• on ocaurranoe and lltWe•nt ot ground water Bock tn,•• Poroait7 or1g1n&l NOondary Particle aize (Mchanical.) analyeia Stratigrap~ related to depoa1t1on Structure related to deformation 11\e water table and wter-uble aq111ten The piesaaetric aurtaoe and artesian Coon.tined) aq,uiten Zones of.Qbeurtaoe water Capui•nty-ina ita erreot• ly1roecopic water and the }q'groeaopic ooetfioient Water yielding, storage, and retention oapacities ot geologic 11&teriall Hoveaant ot gl'Ouncl water turblllent now J.em4nar flow Critical nlocit1 Daro7'1 Lav P1raaabl.l1t7 ad tbe coetticient of peraeab1l1\7 TftUIU.aail:d.lity and the ooett1cien\ of trana!.aaibilit7 8ton.p and the coetfialst ot 1torage Compariaon ot water-table• va. contined aquifer - Bl.aeticity of compre■aib1lit7 of arteaian eysteau nutic deformation lxpaalion ot water Subaidenoe pbenoanora LNkap troa OODfiDing or oontined beda Geolo17 ot atreu now Aquilera and their oontrola Surtan (topograpblo) teat.urea and their control• Ra1ntall and oliMtio oontrola Relation to rook tne• Oeololio control.a of qullt1 ot •ter Connate vater1 Residual waters lttects ot rock typea Efteota of rook structure• Ettecte ot taulta, dikea, river eroaion, e\o •. Man-made controle ot, or etfecta on, ground vat.er Killing practices Induatrial wastes Intenaive dnelopm.ent Irrigation praotioea DraiD&ge practice• 11eld methods Laborator7 methoda Planning, ■tart.1n1, and auppoJ'\illa a 1ro\1Dd-vater innatigation Plaooing, writing and gettillg in tona the publication, ground-vat.er reporta.

Texts a u. s. Oeologioal Surye7 W&tei---Suppq Paper 489, •occurreue ot Ground Water in the United State••• 0onl'DINDt Pr1Dting Ottioe, t2.2S u. s. Oeologioal 8vn7 V&ter-hl,pl7 Paper 491a, •0ut11De ot Ground­ Water B7drology, wi\b Det1nit1om", Gonrnment Printing Ottioe to.20.

Oarald0. Parker GRO'C!fD WATER SHORT COURSE • Ground-Water Hydraulics Ot11'LINE

Flow nets and the circulation ot ground water in aquifers Bead versus depth relations: 1n areas ot discharge 1n areas of recharge

fioving wells in water-table aquifer• Bead distribution near partially-penetrating pumped wells Elasticity of artesian aquifers Barometric effects Railroad train effects Tidal effects Ocean, lake, or stream tides Earth or crustal tides • Earthquake effects Excavations overlying artesian aquifers Coefficient ot storage and its relation to the elasticity of artesian aquifers Porosity of artesian aquifer determined from coefficient of storage and seismic velocity data Potential theory and applications Introduction Assumptions necessary to mathematical formulation versus field conditions generally encountered The significance of T and S determinations by field methods Reconciling well performance versus the concept of effective­ average T and S coefficients Entrance losses at wells • Well developnent •

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