Water Well Manual (USAID).pdf - The Water, Sanitation and Hygiene

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Flow Toward Wells Converging j&w: When a well is at rest, that is, when there is no flow taking place from it, the water pressure within the well is the same as that in the formation outside the well. The level at which water stands within the well is known as the static water level. This level coincides with the water table for a water-table aquifer or the piezometric surface for an artesian aquifer. Should the pressure be lowered within the well, by a pump for example, then tire greater pressure in the aquifer on the outside of the well would force water into the well and flak thereby results. This lowering of the pressure within the well is also acz$ *nanied by a lowering of the water level in and around the well. Water fl,j~ Through the aquifer to the well from all directions in what is known as ~0 ergingflow. This flow may be considered to take place through successit lindrical sections which become smaller and smaller as the we!1 is ap y’ ied (Fig. 2.10). This means that the area across which t&e flow takes r also becomes successively smaller as the R, -2R, A, = 2A2 v, ‘2V, Fig. 2.10 F L 0 W CONVERGES TO- WARD A WELL, PASSING THROUGH IMAGINARY CYLINDRKAL SURFACES THAT ARE SUCCESSIVELY SMALLER AS THE WELL IS APPROACHED. well is approached. With the same quantity of water flowing across these sections, it follows from equation (2.3) that the velocity increases as the area becomes smaller. Darcy’s Law, equation (2.2), tells us that the hydraulic gradient varies in direct proportion to the velocity. The increasing velocity to- wards the well is, therefore, ac- companied by an increasing hydraulic gradient. Stated in other terms, the water surface or the piezometric surface develops an in- creasingly steeper slope toward the well. In an aquifer of uniform shape and texture, the depression of the water table or piezonetric surface in the vicinity of a pumped or freely flowing well takes the form of an inverted cone. This cone, known as the cone of depression (Fig. 2.1 l), has its apex at the water level in the well during pumping, and its base at the static water level. The water level in the well during pumping is known as the pumping water level. The difference in levels between the static water level and the surface of the cone of depression is known as the drawdown. Drawdown, therefore, increases from zero at the outer limits of the cone of depression to a maximum in the pumped weft. The radius of influence is the distance from the center of the well to the outer limit of the cone of depression. Fig. 2.12 shows how the transmissibility of an aquifer affects the shape of the cone of depression. The cone is deep, with steep sides, a large drawdown, 16
-- Rodlus of Influence --+ Static water level _------ -- .-- T Drowdown in we8 C--Well Screen Fig. 2.11 CONE OF DEPRESSION IN VICINITY OF PUMPED WELL. FRadius =IS,OCO ft-- and a small radius ot‘ influence when the aquifer transmissibility is low. With a high transmissibility, the cone is wide and shallow, rhe drawdown being small, and the radius of influence large. Rechg~ md bortndar-y ejfects: When pumping commences at ‘I well. the initial quantity of water discharged comes from the aquifer storage immediately surrounding the well. The cbne of depression is then small. As pumping continues, the cone expands to meet the increasing demand for water from the aquifer storage. The radius of influence increases and, with it, the drawdown in the well in order to provide the additional pressure head required to move the water through correspondingly greater distances. If the rate of pumping is kept constant, then the rate of Transmissibility - IO.OCO gpd/ft Radius = 40,000 ft Transmissibi!ity - IOO.000 gpd/ft - - Fig. 2.12 EFFECT OF DIFFERING COEFFICIENTS OF TRANSMISSIRILITY UPON THE SHAPE, DEPTH AND EXTENT OF THE CONE c)F DEPRESSION, PUMPING RATE AND OTHER FACTORS BEING THC SAME IN BOTH CASES. 17
Page 1 and 2: A PRAGTICAL GUIDE FOR LOCATI CONSTR
Page 4 and 5: hmier Pwss Editorial Advisory Boani
Page 6 and 7: WATER EL1 MANUAL Covers Copyright @
Page 8 and 9: Page ACKNOWLEDGEMENTS ii FOREWORD 1
Page 10 and 11: S. PUMPING EQUIPMENT 114 CONSTANT D
Page 12 and 13: While man has always recognized ihe
Page 14 and 15: An understanding of the processes a
Page 16 and 17: Bsit of Soil Water tntermediate Bel
Page 18 and 19: and loess may be limited by both th
Page 20 and 21: deposition of large aprons of mater
Page 22 and 23: the pc>:ti,sity. This quautity is r
Page 24 and 25: permeability, P, we see from equati
Page 28 and 29: expansion and deepening of the cone
Page 30 and 31: yield of the individual wells (Fig
Page 32 and 33: Multiple well or well-point systems
Page 34: 10 ppm of iron means that in every
Page 37 and 38: ground waters in some parts of Arge
Page 39 and 40: Geologic Maps Geologic maps, of whi
Page 41 and 42: depth. thickness. and description o
Page 43 and 44: CHAPTER 4 Generally, the aim of eng
Page 45 and 46: lodged in them and thus restrict fl
Page 47 and 48: Fig. 4.3 THE Y-SHAPED OPENINGS OFTH
Page 49 and 50: Fig. 45 CONTBNUOUSSLOT T Y P E OF W
Page 51 and 52: Manufacturers make well screens in
Page 53 and 54: The limiting size of material to be
Page 55 and 56: too 90 E 60 z t 50 : .L 40 2 30 E (
Page 57 and 58: prime concern in small we!ls. Gener
Page 59 and 60: otherwise unsatisfactory water into
Page 61 and 62: The object of formation stabilizati
Page 63 and 64: Pump unit Sanitary well seal I / ,R
Page 65 and 66: There are four basic operations inv
Page 67 and 68: Ham? driver ----k- Htle backfilled
Page 69 and 70: single wlley block : /Tripod Fig. 5
Page 71 and 72: Fig,..8 MAN ON SCAFFOLDING RAISES H
Page 74 and 75: Cutting edges Galvanized iron pipe
Page 76 and 77:
inexperienced driller because of th
Page 78 and 79:
string are usually joined together
Page 80 and 81:
.I Fig. 5.18 CAStbiG DRIVE SHOE. of
Page 82 and 83:
Fig. 5.22 A GRAVITY PLACEMENT METHO
Page 84 and 85:
Fig. 5.24 OUI’SIDE-TUBING METHOD
Page 86 and 87:
Pull-back Method The pull-back meth
Page 89 and 90:
Wash line- .Cemsnt grout ,’ Exoan
Page 91 and 92:
to the surface with the return flow
Page 93 and 94:
-Inner Carm~ Fig. 5.36 DOUBLE-CASIN
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Lead packer Pulhg pipe Sand join1 S
Page 97 and 98:
saving that sbandunmcnt ot‘ the b
Page 99 and 100:
esult, tools lost in a hole do not
Page 101 and 102:
Tapered Tap Die Overshot Circulatin
Page 103:
If the hold is secure, continue lif
Page 106 and 107:
CHAPTER 6 WE11 C6MPLETION Well comp
Page 108 and 109:
‘N E L VI E L
Page 110 and 111:
Static water :evel -m----.-e Solid
Page 112 and 113:
The procedure is to lower the tool
Page 114 and 115:
wells. The thinner the gratlel pack
Page 116 and 117:
Wells, like all other engineering s
Page 118 and 119:
of the wells to determine whether s
Page 120 and 121:
Black iron or plastic pipe Well scr
Page 122 and 123:
,&ting technique is used to agitate
Page 124 and 125:
Drilling and completing a well form
Page 126 and 127:
container is termed the srrctiorl h
Page 128 and 129:
plunger on the tijrward stroke p~~s
Page 130 and 131:
or deep well type and are usually d
Page 132 and 133:
Fig. 8.9 VOLUTE-TYPE C’ENTRIFU- C
Page 134 and 135:
pre y.,,:~ 1; +-.b to, rourT the no
Page 136 and 137:
Check valve Radial bearing lmpetfer
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To storage ha I 3 Power unit - Stat
Page 140 and 141:
Provision may also be made for pump
Page 142 and 143:
132
Page 144 and 145:
OF Too great stress can never be pl
Page 146 and 147:
feet before final disappearance at
Page 148 and 149:
REFERENCES Acme Fishing Tool Compan
Page 150 and 151:
T OF PE ICITY The coefficient of pe
Page 152 and 153:
Unit TABLE B.3 VOLUME Equivalents o
Page 154 and 155:
- B-8 PRESSURE 1 Atmosphere = 760 m
Page 156 and 157:
TABLE B-14 ESTIMATING DISCHARGE FRO
Page 158 and 159:
-z- TABLE B.16 DRILLING CABLE ROPE
Page 160 and 161:
A Abandoned well, I37 Acid. hydroch
Page 162 and 163:
Gelling, 64 Geologic cross-sections
Page 164 and 165:
s Sand, 7,9? 119, 126, 129, 137 --
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