8/18/2019 Ch 2 WS Sources of Water Supply
1/100
DBU Cha ter two Sources of Water Su
CHAPTER TWO:
Sources of Water Supply
DBU, Institute of Technology
College of Engineering
Department of Civil Engineering
Abraham Atnafu
8/18/2019 Ch 2 WS Sources of Water Supply
2/100
DBU Cha ter two Sources of Water Su
Nature of water source determines the components of thewater supply system
Factors to be considered to select source:
Quantity
Quality
Reliability
Safety of sourceWater rights
Environmental impacts…
Introduction
8/18/2019 Ch 2 WS Sources of Water Supply
3/100
DBU Cha ter two Sources of Water Su
Hydrologic Cycle
8/18/2019 Ch 2 WS Sources of Water Supply
4/100
DBU Cha ter two Sources of Water Su
The water cycle, also known as the hydrologic cycle, describes the continuous
movement of water on,above and below the earth surface. The sun, which
drives the water cycle, radiates solar energy on the oceans and land.Key Hydrological Processes
Precipitation : Condensed water vapor that falls to the earth surface. Most
precipitation occurs as rain, but also includes snow, hail, fog drip, sleet, etc
Runoff: The variety of ways by which water moves across the land. Thisincludes both surface runoff and channel runoff. As it flows, the water may
infiltrate into the ground, evaporate into the air, become stored in lakes or
reservoirs, or be extracted for agricultural or other human uses.
Infiltration: The flow of water from the ground surface into the ground.
Once infiltrated, the water becomes soil moisture or groundwater.
Hydrological Cycle
8/18/2019 Ch 2 WS Sources of Water Supply
5/100
DBU Cha ter two Sources of Water Su
Subsurface Flow: The flow of water underground, in the vadose zone and
aquifers. Subsurface water may return to the surface (e.g. as a spring or by
being pumped) or eventually seep into the oceans. Water returns to the
land surface at lower elevation than where it infiltrated, under the force of
gravity or gravity induced pressures. Groundwater tends to move
slowly, and is replenished slowly, so it can remain in aquifers for thousand
of years.
Evaporation and transpiration: The transformation of water from liquid to
gas phases as it moves from the ground or bodies of water into the
overlying atmosphere. The source of energy for evaporation is primarilysolar radiation. Evaporation often implicitly includes transpiration from
plants, though together they are specifically referred to as
evapotranspiration.
8/18/2019 Ch 2 WS Sources of Water Supply
6/100
DBU Cha ter two Sources of Water Su
Types of water supply sources
Surface Water Sources
Rain Water
Lakes and reservoirs
River Water
Sea water
Ground Water Sources
Spring Water
Wells
Infiltration galleries
8/18/2019 Ch 2 WS Sources of Water Supply
7/100DBU Cha ter two Sources of Water Su
Rain water might contain dust, smoke, bacteria, carb
dioxide… as falling from high altitude
RW Harvesting- roofs are most effective and can be integra
with tanks
Rain water
8/18/2019 Ch 2 WS Sources of Water Supply
8/100DBU Cha ter two Sources of Water Su
8/18/2019 Ch 2 WS Sources of Water Supply
9/100DBU Cha ter two Sources of Water Su
Advantages of rainwater collection:◦ Quality of RW is high
◦ Independent
◦ Local materials can be used for collection
◦ No energy costs
◦ Easy to maintain◦ Time saving and convenient
Disadvantages◦ High initial cost (i.e. for a family)
◦ Quantity of water is dependent on the roof area and rainy seasons
◦ Flat taste
Rain water…
8/18/2019 Ch 2 WS Sources of Water Supply
10/100
A A i T ,
Z e r i h u n
A l e m a y e h
u
Lakes and reservoirs
Lake Tana
Store water in wet seasons for usage in dry seasons
It is a standing water; because of this:
◦ Quality is very low: turbidity, bacteria and pollutants
◦Thermal stratification i.e. for deep lakes/reservoirs)
8/18/2019 Ch 2 WS Sources of Water Supply
11/100DBU Cha ter two Sources of Water Su
River water
Abay river
8/18/2019 Ch 2 WS Sources of Water Supply
12/100DBU Cha ter two Sources of Water Su
River water
Abay river
A stream or river is a body of running water othe surface of the earth, from higher to lowe
ground.
Their capacity is dependent on minimum flow peday
Development of rivers requires :
submerged intake structuresmall diversion dams (i.e. for small streams)
8/18/2019 Ch 2 WS Sources of Water Supply
13/100DBU Cha ter two Sources of Water Su
Groundwater source
Aquifer
8/18/2019 Ch 2 WS Sources of Water Supply
14/100DBU Cha ter two Sources of Water Su
Advantages :It is likely to be free of pathogenic bacteria
free from turbidity and colour
It can be used without further treatmentIt can be found in the close vicinity
It is economical to obtain and distribute
The water-bearing stratum provides a naturalstorage at the point of intake.
Groundwater sources
8/18/2019 Ch 2 WS Sources of Water Supply
15/100DBU Cha ter two Sources of Water Su
Disadvantages
often have high in mineral content;
It usually requires pumping.
CATIONS: calcium, magnesium, iron and manganese
ANIONS: bicarbonate, carbonate, and chloride
Groundwater sources…
8/18/2019 Ch 2 WS Sources of Water Supply
16/100
DBU Cha ter two Sources of Water Su
SpringsSpring water is a groundwater that
outcrops from ground due to impervious
base that prevents percolation.
Mostly found from sand or gravel aquife
8/18/2019 Ch 2 WS Sources of Water Supply
17/100
DBU Cha ter two Sources of Water Su
Gravity springs◦ GW flows over an impervious stratum onto the ground
surface◦
The yield varies with the position of the water table◦ May dry up during or immediately after a dry season
Gravity overflow spring Gravity depression spring
8/18/2019 Ch 2 WS Sources of Water Supply
18/100
DBU Cha ter two Sources of Water Su
Artesian springs◦ High quality water due to confinement◦ High discharge due to high pressure in the confinement
◦ Yield is likely uniform and nearly constant over the seasof the year
Artesian depression spring Artesian fissure spring
8/18/2019 Ch 2 WS Sources of Water Supply
19/100
DBU Cha ter two Sources of Water Su
Horizontal wells that collect water over practically thei
entire lengths. Simple means of obtaining naturally filtered water
Infiltration gallery
8/18/2019 Ch 2 WS Sources of Water Supply
20/100
DBU Cha ter two Sources of Water Su
Replenishment (filling) of aquifers is known as recharge Unconfined aquifers are recharged by precipitation
percolating down from the land’s surface
Confined aquifers are generally recharged where the
aquifer materials are exposed at the land’s surface -called
an outcrop.
Recharge of aquifers
8/18/2019 Ch 2 WS Sources of Water Supply
21/100
DBU Cha ter two Sources of Water Su
Recharge of aquifers
8/18/2019 Ch 2 WS Sources of Water Supply
22/100
DBU Cha ter two Sources of Water Su
When surface water loses water to the adjacent
aquifer, the stream is called a losing stream.
water flows from the ground water to the stream, it is
called a gaining stream.
Recharge of aquifers…
Aquifer
Impervious layer
Groundwatertable
8/18/2019 Ch 2 WS Sources of Water Supply
23/100
DBU Cha ter two Sources of Water Su
To evaluate and classify raw water quality physical, chemical, and bacteriological parameters
raw water can be classified as having poor, fair, and good quality.
To identify sources of pollution
Surface water: urban runoff, agricultural runoff, industrialdischarge, and leachate from landfills;
Groundwater: infiltration from pit-latrines and septic tanks, landfill
leachate, and infiltration from polluted areas.
To assess the treatment required for beneficial uses level of treatment and unit process required are dependent on the
raw water quality
Water quality considerations
Water quality considerations of sources are required for the following purposes.
8/18/2019 Ch 2 WS Sources of Water Supply
24/100
DBU Cha ter two Sources of Water Su
Treatment types
Well Aeration Disinfection Fluoridation
WellRapid sand
filtrationAeration Disinfection Fluoridation
For groundwater having excellent quality
For groundwater having moderate quality
8/18/2019 Ch 2 WS Sources of Water Supply
25/100
8/18/2019 Ch 2 WS Sources of Water Supply
26/100
DBU Cha ter two Sources of Water Su
Surface water sources◦ Safe water yield during the drought years
◦ Urbanization and land development in the watershed
◦ Proposed impoundments on tributaries
◦
Water quality◦ Assessment of reliability
◦ Requirements for construction of water supply system components
◦ Economics of the project
◦
Environmental impacts of the project◦ Water rights
Source selection
8/18/2019 Ch 2 WS Sources of Water Supply
27/100
DBU Cha ter two Sources of Water Su
Ground water sources Aquifer characteristics (depth, geology)
Safe aquifer yield
Permissible drawdown
Water quality
Source of contamination(gasoline, oil, chemicals)
Saltwater intrusion(areas near to seas or oceans)
Type and extent of recharge area
Rate of recharge
Water rights
Source selection…
R
http://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPG
8/18/2019 Ch 2 WS Sources of Water Supply
28/100
DBU Cha ter two Sources of Water Su
An artificial lake formed by the
construction of a dam across a valley
o Contain dam to hold water
o A spillway to allow excess water to flow
o A gate chamber with valves to regulate flo
Reservoirs
http://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPGhttp://upload.wikimedia.org/wikipedia/commons/e/e0/Taiwan_JungHua_Dam.JPG
8/18/2019 Ch 2 WS Sources of Water Supply
29/100
DBU Cha ter two Sources of Water Su
The area of land draining to the dam site is called a
catchment or watershed.
Reservoirs
Outlet
8/18/2019 Ch 2 WS Sources of Water Supply
30/100
DBU Cha ter two Sources of Water Su
The following investigations are required for reservoir
planning:
A. Topographic surveying- to produce a topo-map which will
be used as a base for
preparing water surface area vs. elevation curve
plotting storage volume vs. elevation
indicating man-made and natural features that may be
affected
Reservoirs
8/18/2019 Ch 2 WS Sources of Water Supply
31/100
DBU Cha ter two Sources of Water Su
B. Geologic investigationsWater tightness of the reservoir basin
Suitability of foundations for the dam
Geological and structural features, such as faults, fissures, etc
Type and depth of overburden
Location of permeable and soluble rocks if any
Ground water conditions in the region
Location and quantity of materials for the dam construction
Reservoirs
8/18/2019 Ch 2 WS Sources of Water Supply
32/100
DBU Cha ter two Sources of Water Su
C. Hydrological investigationsdetermination of rainfall, runoff, seepage, and
evaporation in the reservoir catchment from long
years of data.
These information are essential for estimating the reservoir
capacity and design of spill way.
Reservoirs…
8/18/2019 Ch 2 WS Sources of Water Supply
33/100
DBU Cha ter two Sources of Water Su
Catchment geology- minimum percolation losses and high runoffpotential
Dam site- strong foundation with minimum seepage loss under thedam.
Narrow valley- sites that resulting lesser dam length
Topography- should be such that large area and valuableproperties are not submerged
Site that creates deep reservoirs- this has the advantages ofminimizing the evaporation loss and submerged area whencompared to shallow reservoirs
Sites that ensure good water quality- avoid sites that are
downstream of waste discharges and tributaries with high silt loads
Criteria for Selecting reservoir sites
8/18/2019 Ch 2 WS Sources of Water Supply
34/100
DBU Cha ter two Sources of Water Su
Yield is the amount of water that can be supplied from areservoir within a specified interval of time.
Safe yield or firm yield: is the maximum quantity of
water that can be guarantied during a critical dry
period. the safe yield from a reservoir > maximum day demand
Methods to determine the storage volume of reservoirs:
◦
mass curve method(Rippl) Method.◦ analytical method.
Volume of reservoirs
M h d
8/18/2019 Ch 2 WS Sources of Water Supply
35/100
DBU Cha ter two Sources of Water Su
reservoir capacity is determined from accumulated mass inflow andaccumulated demand curves.
Net Inflow= total Inflow-outflow (evaporation, seepage, d/s flow)
Procedure
Prepare accumulated mass inflow curve from the stream hydrograph Prepare the accumulated demand curve on the same scale
Draw tangent lines that are parallel to the accumulated demand curve
at the high points of the accumulated mass curve (P1, P2, P3, etc)
Measure the vertical distances between the tangent lines and the mass
inflow curve (V1, V2, V3, etc.)
Determine the required reservoir storage capacity as the largest of the
vertical distances (V1, V2, V3, etc.)
Mass curve method
M h d
8/18/2019 Ch 2 WS Sources of Water Supply
36/100
DBU Cha ter two Sources of Water Su
Mass curve method
Time, Year (month)
Volume
(m3)
V1
V2
Accumulated demand
Accumulated inflow
Spill
Analytic method
8/18/2019 Ch 2 WS Sources of Water Supply
37/100
DBU Cha ter two Sources of Water Su
Calculate the net inflow from the given hydrological data Calculate the deficiency (demand – net inflow)
Compute the cumulative deficiency. If the cumulative
deficiency is negative, take the cumulative deficiency as zero
Determine the required reservoir capacity as the maximumcumulative deficiency
Analytic method
(1) (2) (3)= (2)-(1) (4) if CF is – ve, take 0
Net inflow
(m3)
Demand (m3) Deficiency
(m3)
Cumulative deficiency
(m3)
I1 D1 F1 CF1 = F1I2 D2 F2 CF2 = CF1 + F2I3 D3 F3 CF3 = CF2 + F3
E l 2 1Inflo
8/18/2019 Ch 2 WS Sources of Water Supply
38/100
DBU Cha ter two Sources of Water Su
Compute the storage requirement
needed for an impounding reservoir for
a constant draft of 23 ML/km2/months
of 30.4 days with the given monthly net
river inflow for a critical year.
Example 2.1 MonthInflo
(ML/
1 94
2 12
3 454 5
5 5
6 2
7 0
8 29 16
10 7
11 72
12 92
13 214 55
15 33
A l ti l S l ti
8/18/2019 Ch 2 WS Sources of Water Supply
39/100
DBU Cha ter two Sources of Water Su
Month inflow
draft/
demand
Cummulative
Demand Cummulative inflow Defficiency
cummulative
Deficiency
1 94 23 23 94 -71 0
2 122 23 46 216 -99 0
3 45 23 69 261 -22 0
4 5 23 92 266 18 18
5 5 23 115 271 18 36
6 2 23 138 273 21 577 0 23 161 273 23 80
8 2 23 184 275 21 101
9 16 23 207 291 7 108
10 7 23 230 298 16 124
11 72 23 253 370 -49 75
12 92 23 276 462 -69 613 21 23 299 483 2 8
14 55 23 322 538 -32 0
15 33 23 345 571 -10 0
Analytical Solution
Graphical Solution
8/18/2019 Ch 2 WS Sources of Water Supply
40/100
DBU Cha ter two Sources of Water Su
0
100
200
300
400
500
600
0 2 4 6 8 10 12 14
C u m m u l a t i v e Q
Month
Cummulative Demand
Cummulative inflow
419-294=124
Graphical Solution
R e s e
r v o i r f u l l
Start of
Dry period
End of
Dry period
Res. Draw down period
Depletion of Res. Replenishment
of Res.
R e s .
f u l l
Exercise
8/18/2019 Ch 2 WS Sources of Water Supply
41/100
DBU Cha ter two Sources of Water Su
Exercise
Safe yield from a given reservoir capacity
8/18/2019 Ch 2 WS Sources of Water Supply
42/100
DBU Cha ter two Sources of Water Su
Prepare the mass inflow curve.
From the apices A1, A2, A3 etc. of the mass curve, draw
tangents in such a way that their maximum departure fro
the mass curve does not exceed the specified reservo
capacity. The ordinates E1D
1, E
2D
2, E
3D
3, etc. are all equa
to the reservoir capacity (say 1500 ha.m)
Measure the slopes of each of these tangents. The slope
indicate the yield which can be attained in each year fro
the reservoir of given capacity. The slope of the flattedemand line is the firm yield.
Safe yield from a given reservoir capacity
8/18/2019 Ch 2 WS Sources of Water Supply
43/100
Cross section of Dam
8/18/2019 Ch 2 WS Sources of Water Supply
44/100
DBU Cha ter two Sources of Water Su
Cross section of Dam
Types of Dams
8/18/2019 Ch 2 WS Sources of Water Supply
45/100
DBU Cha ter two Sources of Water Su
Types of Dams
Impoundments: Embankment dams
8/18/2019 Ch 2 WS Sources of Water Supply
46/100
DBU Cha ter two Sources of Water Su
Embankment dam-A dam constructed from natural materialsexcavated or obtained nearby. The natural fill materials are placed
and compacted without the addition of any binding agent. Two types-
Earth fill dam ( if compacted soil constitutes over 50% of the dam
volume) and
Rock fill dam (over 50% of the material is coarse-grained material ocrushed rock with impervious membrane).
Advantages: For sites in wide valleys and steep-sided gorges
Adaptability to a broad range of foundation conditions
Use of locally available natural materials
Impoundments: Embankment dams
Impoundments: Concrete Dam
8/18/2019 Ch 2 WS Sources of Water Supply
47/100
DBU Cha ter two Sources of Water Su
Disadvantages: Easily damaged or destructed by overflow
leakage and internal erosion
They are gravity dam, arch dam, buttress dam, etc.
Gravity dam
Dependent upon its own mass for stability.
For gorges with very steep side slopes
It can be constructed by Masonry(stone or brick)
Shape: straight or curved Dam height: can be very high for sound foundation
Impoundments: Concrete Dam
Impoundments: Concrete Dams...
8/18/2019 Ch 2 WS Sources of Water Supply
48/100
DBU Cha ter two Sources of Water Su
Arch dam Functions structurally as a horizontal arch, transmitting the
major portion of the water load to the abutments or
valley sides rather than to the floor of the valley.
structurally more efficient, needs less concrete volume
Buttress dam
consists of a continuous upstream face supported at
regular intervals by downstream buttresses.
Impoundments: Concrete Dams...
Catchment protection
8/18/2019 Ch 2 WS Sources of Water Supply
49/100
DBU Cha ter two Sources of Water Su
Activities that take place within the reservoir catchment have impacts on the quality and quantity
of water stored behind the dam. Catchment protection primarily focuses on maintaining thewater quality and capacity of the reservoir. It involves activities that include
Minimization of diffuse pollution from urban runoff
Minimization of agricultural diffuse pollution
Controlling discharges from point sources such aswastewater treatment plant, industries, etc
Limitation of soil erosion through soil conservation
measures, such as afforestation, etc.
Providing corridors along tributary streams, rivers, and thereservoir
Catchment protection
8/18/2019 Ch 2 WS Sources of Water Supply
50/100
DBU Cha ter two Sources of Water Su
Ground water
hydraulics
8/18/2019 Ch 2 WS Sources of Water Supply
51/100
Groundwater
8/18/2019 Ch 2 WS Sources of Water Supply
52/100
DBU Cha ter two Sources of Water Su
Groundwater is the water beneath the ground surface contained in void spaces (pore spaces between
rock and soil particles, or bedrock fractures).
Basic Terms
Aquifer
An aquifer is an underground layer of water-bearing permeable rock or unconsolidated
materials(gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water
well. Water table
The water table is the level at which the groundwater pressure is equal to atmospheric pressure.
Aquitard
An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another.
Aquitards comprise layers of either clay or non-porous rock with low hydraulic conductivity.
Groundwater
8/18/2019 Ch 2 WS Sources of Water Supply
53/100
DBU Cha ter two Sources of Water Su
Unconfined aquifer
It is an aquifer with the water table as its upper boundary. Because the aquifer is not under pressure the
water level in a well is the same as the water table outside the well.
Confined aquifer
It is an aquifer found between two relatively impermeable layers.
Artesian aquifer/well
It is a confined aquifer containing groundwater that will flow upward through a well, called an artesian
well, without the need for pumping. Water may even reach the ground surface if the natural pressure is
high enough, in which case the well is called a flowing artesian well.
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling
to access groundwater in underground aquifers.
8/18/2019 Ch 2 WS Sources of Water Supply
54/100
DBU Cha ter two Sources of Water Su
Borehole
It is a narrow shaft drilled in the ground as part of a groundwater site assessment.
Piezometric surface
The imaginary surface that everywhere coincides with the piezometric head of the water in the aquifer.In
areas of artesian ground water, it is above the land surface.
Base flow
Base flow is the portion of stream flow that comes from groundwater. It sustains flows in a river
during the dry periods between rainstorms.
Groundwater Recharge
The natural or intentional infiltration (percolation) of surface water into the groundwater system.
Fossil water
Fossil water is groundwater that has remained in an aquifer for thousands or even millions of years.
When geologic changes seal the aquifer off from further recharging, the water becomes trapped inside.
8/18/2019 Ch 2 WS Sources of Water Supply
55/100
Aquifer parameters
8/18/2019 Ch 2 WS Sources of Water Supply
56/100
DBU Cha ter two Sources of Water Su
(The water yield capacity of aquifers depends on different parameters)
Aquifer parameters
8/18/2019 Ch 2 WS Sources of Water Supply
57/100
DBU Cha ter two Sources of Water Su
Storage coefficient (S) : the volume of water that an aquifer
releases from or takes into storage per unit surface area of theaquifer per unit change in head
Hydraulic gradient (dh/dx ): the slope of the piezometric surface
or water table line in m/m. The magnitude of the head
determines the pressure on the groundwater to move and its
velocity.
q p
Examples
8/18/2019 Ch 2 WS Sources of Water Supply
58/100
DBU Cha ter two Sources of Water Su
p
Aquifer parameters
8/18/2019 Ch 2 WS Sources of Water Supply
59/100
DBU Cha ter two Sources of Water Su
Hydraulic conductivity(K): ratio of velocity to hydraulic
gradient, indicating permeability of porous media.
Transmissivity: the capacity of an aquifer to transmit watermeasure of how easily water in a confined aquifer can flow through
the porous media.
q p
T = Kb, b = saturated thickness
K =QdL
Adh
Aquifer Types
8/18/2019 Ch 2 WS Sources of Water Supply
60/100
DBU Cha ter two Sources of Water Su
Unconfined and confined aquifers(An unconfined aquifer does not have confining unit and is defined by water-table. Confined aquifer is overlain by a confining unit that has a lower hydraulic conductivity.)
q yp
Groundwater flow
8/18/2019 Ch 2 WS Sources of Water Supply
61/100
DBU Cha ter two Sources of Water Su
Groundwater flows in the direction of decreasing head. equipotential lines lines showing points having equal
pressure.
Flow direction is perpendicular to equipotential lines
Aquifer boundary130 m
135 m
140 m
145 m150 m
155 m
Equipotential lineFlow direction
Velocity of GW
8/18/2019 Ch 2 WS Sources of Water Supply
62/100
DBU Cha ter two Sources of Water Su
Velocity can be determined by Darcy’s law V = kS
Darcy law :Q through porous media is proportional to the head loss and inverselyproportional to the length of the flow path.
K = hydraulic conductivity and h is the head loss
Porous medium
Q
h
L
Area = A
elementsmallfor very;K V
or
L
ΔhK
A
QV
dLdh
Determination of K
8/18/2019 Ch 2 WS Sources of Water Supply
63/100
DBU Cha ter two Sources of Water Su
Determination of K
8/18/2019 Ch 2 WS Sources of Water Supply
64/100
DBU Cha ter two Sources of Water Su
Laboratory methods
Constant head permeameter
V = volume water flowing in time t through of area A, length L, and withconstant head h.
Variable head permeameter
r = radius of the column in which the water level drops
rc = radius of the sample
h1, h2 are heads at times t1 and t2, respectivelyt = t2 – t1
AthVL K
2
12
2
lnhh
t r Lr K
c
Problems
8/18/2019 Ch 2 WS Sources of Water Supply
65/100
DBU Cha ter two Sources of Water Su
Determination of K...
8/18/2019 Ch 2 WS Sources of Water Supply
66/100
DBU Cha ter two Sources of Water Su
Field Methods
Pumping test: constant removal of water from a single well
and observations of water level declines at several adjacent
wells.
This is the most accurate way
For anisotropic aquifers, the combined horizontal hydraulic
conductivity:
Where, Ki = K in layer i; Zi = thickness of layer I
i
ii
Z
Z K K
Example
8/18/2019 Ch 2 WS Sources of Water Supply
67/100
DBU Cha ter two Sources of Water Su
Determination of K...
8/18/2019 Ch 2 WS Sources of Water Supply
68/100
DBU Cha ter two Sources of Water Su
ield Methods…
Slug test or piezometer test the simplest method
some volume of water is taken out from the piezometer and the
subsequent rise of the water back to its original position is recorded
in time.
ri-inside radius,
L- the length of the screen section,
ro-the outside radius to- characteristic time interval
Hydraulics of water wells
8/18/2019 Ch 2 WS Sources of Water Supply
69/100
DBU Cha ter two Sources of Water Su
Well: hydraulic structure utilized to access water-bearing aquifers
Allows estimation of aquifer hydraulic properties
Provides direct access to ground water conditions
1) Sampling
2) Testing3) Resource Extraction
4) Environmental Restoration
Hydraulics of water wells
8/18/2019 Ch 2 WS Sources of Water Supply
70/100
DBU Cha ter two Sources of Water Su
Aquifer test : studies involving analyzing the change, with
time, in water levels in an aquifer caused by withdrawalsthrough wells.
Drawdown/cone of depression : is the difference between the
water level at any time during the test and the original
position. Ground
Cone of depression Drawdown
Well
Original GWT
Impervious
stratum
Radius of influence of steady state pumping
wells
8/18/2019 Ch 2 WS Sources of Water Supply
71/100
DBU Cha ter two Sources of Water Su
wells
Piezometric head
8/18/2019 Ch 2 WS Sources of Water Supply
72/100
DBU Cha ter two Sources of Water Su
Steady state Radial flow to a wellassumptions:
8/18/2019 Ch 2 WS Sources of Water Supply
73/100
DBU Cha ter two Sources of Water Su
• Cone of depression remains in equilibrium
• The water table is only slightly inclined
• Flow direction is horizontal
• Slopes of the water table and the hydraulic gradient are equal• Aquifer: isotropic, homogeneous and infinite extent
• Well fully penetrating the aquifer
Steady Radial Flow to a Well-Confined
8/18/2019 Ch 2 WS Sources of Water Supply
74/100
DBU Cha ter two Sources of Water Su
dr
dhrT
dr
dhrbK Q 22
In a confined aquifer, the drawdown curve or cone of depression varies with distance from a
pumping well
For horizontal flow, Q at any radius r equals, from Darcy’s law,
Steady Radial Flow to a Well-Confined
8/18/2019 Ch 2 WS Sources of Water Supply
75/100
DBU Cha ter two Sources of Water Su
Integrating after separation of variables, with h = h w at r = r w at the well, yields Thiem Equation.
Near the well, transmissivity, T , may be estimated by observingheads h1 and h2 at two adjacent observation wells located at r1and r2, respectively, from the pumping well.
)(2
ln
12
1
2
hhr
r
QT
w
w
r
r
hhT Q
ln
2
Steady Radial Flow to a Well-Unconfined
8/18/2019 Ch 2 WS Sources of Water Supply
76/100
DBU Cha ter two Sources of Water Su
radial flow in an unconfined, homogeneous, isotropic, and
horizontal aquifer yields:dr dH rHK Q 2
Steady Radial Flow to a Well-Unconfined
8/18/2019 Ch 2 WS Sources of Water Supply
77/100
DBU Cha ter two Sources of Water Su
1
2
2
1
2
2
ln
)(
r
r
hh K Q
Integrating, the flow rate in a unconfined aquifer from 2 to 1
Solving for K,
1
2
2
1
2
2
ln)( r
r
hh
Q K
Example
8/18/2019 Ch 2 WS Sources of Water Supply
78/100
DBU Cha ter two Sources of Water Su
A 0.5 m well fully penetrates an unconfined aquifer of 30 m
depth. Two observation well located 30 and 70 m from the
pumped well have drawdowns of 7 m and 6.4 m, respectively. If
the flow is steady and K = 74 m/d.
what would be the discharge
Estimate the drawdown at the well
Solution
8/18/2019 Ch 2 WS Sources of Water Supply
79/100
DBU Cha ter two Sources of Water Su
For unconfined well Q is given as
h1= 30-7 = 23 m, and h2 = 30 – 6.4 = 23.6 m
r1 = 30 m and r2 = 70 m
1
2
2
1
2
2
ln
)(
r
r
hh K Q
daymQ /54.7671
30
70
ln
)236.23(74
322
Solution
8/18/2019 Ch 2 WS Sources of Water Supply
80/100
DBU Cha ter two Sources of Water Su
Drawdown at the well,
using the h1=23 m and r w=0.5m/2=.25 m, we have hw
daymh
r
r
hh K Q w
w
w /54.7671
25.0
30ln
)23(74
ln
)( 322
1
22
1
Solving for hw, we have h w = 19.26 m
So the drawdown would be 30.0 – 19.26 = 10.74 m
8/18/2019 Ch 2 WS Sources of Water Supply
81/100
Solution
8/18/2019 Ch 2 WS Sources of Water Supply
82/100
DBU Cha ter two Sources of Water Su
For confined aquifer Q is given by
Taking between the well and at the radius of influence(R) we
have
h - h w = 6 m
b = 25 m
R = 250 m
w
w
r
r
hh
bK Q ln2
wr
m
day
daymmmQ
250ln
6
sec/86400
/70252sec/1.0 3
Solving for r w, we get r w = 0.12 m or 12 cm
Thus, diameter of the well is 24 cm or 25 cm
Exercise
8/18/2019 Ch 2 WS Sources of Water Supply
83/100
DBU Cha ter two Sources of Water Su
A well 60cm in diameter in a confined aquifer was pumped at asteady rate of 0.0311 m3/s.When the well level remained
constant at 85.48 m, the observation well level at a distance of
10.4 m was 86.52 m. Calculate the transmissivity.
Solution
8/18/2019 Ch 2 WS Sources of Water Supply
84/100
DBU Cha ter two Sources of Water Su
Interference of wells
8/18/2019 Ch 2 WS Sources of Water Supply
85/100
DBU Cha ter two Sources of Water Su
The combined drawdown at a point is equal to the sum of the
drawdowns caused by individual wells.
Reduced yield for each of the wells.
Resultant drawdown
8/18/2019 Ch 2 WS Sources of Water Supply
86/100
A A i T ,
Z e r i h u n
A l e m
a y e h u
Pumping and recharging wells
8/18/2019 Ch 2 WS Sources of Water Supply
87/100
DBU Cha ter two Sources of Water Su
T
Well construction
8/18/2019 Ch 2 WS Sources of Water Supply
88/100
DBU Cha ter two Sources of Water Su
Well construction depends
on
the flow rate,
depth to groundwater,
geologic condition,
casing material, and
economic factors
Shallow and deep well
construction
Shallow well construction
8/18/2019 Ch 2 WS Sources of Water Supply
89/100
DBU Cha ter two Sources of Water Su
Shallow wells are less than 30 m deep
constructed by
digging,
boring,
driving, or jetting methods.
Shallow well construction
8/18/2019 Ch 2 WS Sources of Water Supply
90/100
DBU Cha ter two Sources of Water Su
Dug wells: excavated by hand and
are vertical wells.
diameter > 0.5 m and depth < 15 m.
Lining and casing :concrete or brick.
D i ll i f i l th d i ti ll
Shallow well construction
8/18/2019 Ch 2 WS Sources of Water Supply
91/100
DBU Cha ter two Sources of Water Su
Driven wells: a series of pipe lengths driven vertically
downward by repeated impacts into the ground. diameters 25 – 75 mm
Length below 15 m.
Shallow well construction
8/18/2019 Ch 2 WS Sources of Water Supply
92/100
DBU Cha ter two Sources of Water Su
Bored wells : constructed with
hand-operated or power-drivenaugers.
Diameters of 25 to 900 mm
depths up to 30 m
Shallow well construction
8/18/2019 Ch 2 WS Sources of Water Supply
93/100
DBU Cha ter two Sources of Water Su
Jetted wells: a high-velocity stream
of water directed verticallydownward, while the casing that is
lowered into the hole conducts the
water and cuttings to the surface.
Small-diameter holes, up to 10
depths up to 15 m
useful for observation wells and well-
point systems for dewatering
purposes.
8/18/2019 Ch 2 WS Sources of Water Supply
94/100
Percussion drilling
8/18/2019 Ch 2 WS Sources of Water Supply
95/100
DBU Cha ter two Sources of Water Su
Pulley
Casing pipe
Rope
Tripod
8/18/2019 Ch 2 WS Sources of Water Supply
96/100
DBU Cha ter two Sources of Water Su
Deep well construction
8/18/2019 Ch 2 WS Sources of Water Supply
97/100
DBU Cha ter two Sources of Water Su
Rotary method: consists of drilling with a hollow, rotating
bit, with drilling mud or water used to increase efficiency. Nocasing is required with drilling mud because the mud forms a
clay lining on the wall of the well. Drilling mud consists of a
suspension of water, bentonite clay, and various organic
additives. A rapid method for drilling in unconsolidated formations
Air rotary methods use compressed air in place of drilling mud and
are convenient for consolidated formations.
Drilling depths can exceed 150 m
Hydraulic rotary drilling
8/18/2019 Ch 2 WS Sources of Water Supply
98/100
DBU Cha ter two Sources of Water Su
Mud to settling tank
Tripod
Drilling mud
http://www.dando.co.uk/images/uploads/rotary.htm
8/18/2019 Ch 2 WS Sources of Water Supply
99/100
DBU Cha ter two Sources of Water Su
http://www.dando.co.uk/images/uploads/rotary.htm
8/18/2019 Ch 2 WS Sources of Water Supply
100/100
DBU Cha ter two Sources of Water Su
END of
chapter 2:
By:Abraham
Atnafu
Top Related