Chapter 13 water resources_Dr. Inoka Widanagamage

Chapter 13  water resources_Dr. Inoka Widanagamage


Water resources. Chapter 13. This is a case history. Long Island, the
groundwater pollution. A serious problem on the
western end of island since the beginning
of 20th century. Groundwater below Nassau County
is tremendous, yet intensive pumping causing as much as 15
meter decline in water levels. So the salt water intrusion due
to declination in water level. So, urbanization triggered
more serious water pollution. Urban runoff, sewage and
fertilizers, road salt , industrial and other
waste, and landfills. So most of them
have been closed. So this case history you
can read from the book. And this is the
place that you can see the picture of Long Island
in Nassau County and mixing of these salt and
fresh interface. So right here you can see
the fresh groundwater. And the salty
groundwater so this is where the problem comes in. So when we talk about
water resources, we talk about water pollution. And that’s another
chapter that we’re going to cover in this class. But, this is just the beginning,
and the very first time that we’re going to talk
about the water resources. So we need to make sure that
we understand what is water? And what is the process
that we are getting water? And what are the different
processes or the components that water involve? So the cyclic nature
similar to other elements on the earth crust. Like you may heard
about the carbon cycle. You may heard of sulfur
cycle, nitrogen cycle. Likewise, the water
has its own cycle. It’s a cyclic nature. The water cycle, or it’s
known as hydrologic cycle. This is– in definition,
is global movement of water between different
water storage compartments. So when we think
about compartments, maybe clouds, maybe lakes,
maybe oceans, maybe atmosphere. So likewise, in
different water storage, in different compartments. So that is the global
movement of water between these
different compartments. When it comes to global
distribution of water, the abundance not a problem. The distribution in space
and over time, a problem. So we have polar regions,
polar caps enough. Large amounts of water but
the distribution in space is the problem. It’s not distributed,
similarly, equally in the places that we really need water. So supply versus use,
a problem, for sure. So we have limited
supply in some places, but it’s heavily used. So this is where
the problem comes. This is where the water is a
resource and it’s nonrenewable. And we need to protect it. More than 99% of Earth’s water
is unavailable or unsuitable for beneficial human use. Either salt or ice. All people compete for less
than 1% of Earth’s water supply. So you can imagine water
is already a resource. So that is precipitation. Water’s horizontal movement. Either surface runoff,
like rivers or streams, and shallow subsurface through
flow, and the groundwater flow. So this is where you talk
about the horizontal movement. If you think about the
groundwater flow patterns, that’s a horizontal
movement until you reach the water table. The water from the
place where they get infiltrated, from
the surface water, they get into the pore spaces
in between soil particles. And they’re [INAUDIBLE] through
and coming to the groundwater table. And then from
groundwater it’s moving every different
direction horizontally. So that’s the horizontal
movement of water. So the world’s water supply. So here is the
chart that you can refer to when we need
to talk about the water volumes, surface area, location,
and percentage of total water, and estimated, average,
residence time. So what is the residence time? You know from your
first or second chapter we have talked about what
is the residence time. That means how many
years or how long this world is going to survive
in that particular place, in simple explanation. So oceans, thousands of years. Atmospheres, 9 days. So that residence
time is much shorter. And lakes is like 10 years. And icecaps, or glaciers, up
to tens of thousands of years and longer. So that’s why we
always have the ice in the water in the ice caps. So you can clearly
think about this. And that’s easy to
understand, what is the residence time means. And when it comes to
the surface area– so oceans cover a large surface
area and also groundwater. You would never think about
it but the groundwater covers a large area as well. The water volume. The highest water volume,
obviously, in the oceans. And then the
icecaps and glaciers when it comes to
the groundwater. OK? So the percentage of
total water is mainly the oceans; have the highest
percentage of total water. Surface water, that’s also
known as surface runoff, has important effects on both
the transportation and erosion. So surface runoff is responsible
to transport the sediments, at the same time
eroding the sediments. They’re taking
sediment particles from one place to another. So that’s called erosion. And also drainage
network is something that we need to talk about. So the surface runoff– there are different types
of drainage patterns that you talk about. We talked about drainage
basin and different patterns like rectangular,
trellis, or radial. They are different
drainage patterns. Drainage network that
you’re talking about. So that all contributes
towards the surface runoff. Drainage basin or watershed. It’s an area of land
that contributes water to a particular stream or river. A basic unit of landscape. So that’s a drainage
basin or the watershed. So that’s where
rivers starting from. And, basically, these
are mountainous regions where you can have the springs. And they start forming the
water and then the runoff. They’re moving away from
that watershed area. Drainage divide. That is the boundary
or imaginary line between drainage basins. So two drainage
basins are demarcated or is separated by this divide. So divide is important. That’s an imaginary line
between two drainage basins. Stream order and the size
of the drainage basin. So this is something we’re not
going to talk in much detail. However, that’s also important. It’s in the order one drainage,
or two, or three, likewise. And the size of
the drainage basin is also important to get an
idea about how much water that exists in that
particular drainage basin. Factors affecting runoff
and sediment yield. Geological factors,
topographic factors, climatic factors, vegetation
factors, and, of course, the land-use practice factors. So, geological factors. The type and structure
of soil and rocks. That’s also important and
that determines the runoff and the sediment yield. When you think about the
permeability of soils versus impermeable layers of
soils; so that kind of changes the surface runoff. And also topographic
factors, the high relief versus low relief. Steep angle or
gentle, slope angle. So that also contributes
towards the runoff. And climatic factors; the
type, intensity, duration, and distribution
of precipitation. That’s also important when it
comes to the surface runoff. Vegetation factors; the type,
size, and the distribution of vegetation is
also important when it comes to surface runoff. Groundwater. When it comes to the
groundwater profile, I’ll show you a picture
later the next slide, but there are a couple of words
that you should understand. And you should be able
to define what it is. Vadose zone, also known
as zone of aeration. So that’s the unsaturated zone. And you can have the
water vapor in here. But mostly you have air
within the soil particles. Zone of saturation is where
you have the soil particles completely saturated
with the water molecules. The water table is the boundary
between the zone of aeration and zone of saturation. Perched water table. That is the local water table
above a regional water table. So that is more temporary
water table, I should say. We need more rainfall then
you have perched water table. When there’s a
drought, so it kind of disappears or
something like that. And here is the picture to
show you zone of aeration, or the vadose zone, versus zone
of saturation and the water table. So the flow of ground water,
like we mentioned before, is horizontal. Aquifer– these words
are also important, and you should know the
definitions and examples for each different terms. So aquifer, a unit
capable of supplying water at an economically useful rate. So in this case the aquifer
could be water rich aquifer, or sometimes it could
be oil rich aquifer. So that unit is capable
of supplying water at an economically useful rate. Aquitard, or acquiclude, is
a confining layer or unit restricting and retarding
groundwater flow. So, for example, if you are
thinking about the clay layer. So that’s impermeable
layer and that considered as the aquitard or acquiclude. Aquifer, for example,
sandstorms are good aquifers because they are highly
porous and highly permeable. So they considered
as the aquifers where you can store oil or
water within the soil particles. Unconfined aquifer. That is no overlying,
confining layer. The confining aquifer is with
an overlying aquitard layer. So we’ll look at
some examples later. So perched aquifer,
like I mentioned, that’s a local
zone of saturation above the regional water table. Here you can see
the vadose zone, and the zone of saturation,
and the water table. And if you look at these
two different areas– so it’s sandy soil, not
saturated and this is sandy soil, saturated– you can see the blue
shade to this picture. So that’s giving you
an idea about water. Enriched area was this no
water area, or really less, just the water vapor in here. And the groundwater
recharge and discharge. So the recharge zone. Area where water
infiltrates downward from surface to groundwater. That is where you’re going to
recharge the groundwater table. Discharge zone. That’s the area
where groundwater is removed from an aquifer,
such as spring, well or river. Influent stream is
above the water table. Recharge water to groundwater,
may be intermittent. Effluent stream. That is the perennial
stream with the addition of groundwater when
precipitation is low. So these are some terms
that you need to understand. If you have any question
about these, let me know. Groundwater pressure surface. So generally
declining from source along the flow from recharge
area to discharge area. Artesian well. The water self-rising
about the land surface in a confined aquifer. So cone of depression
is drawdown cone of groundwater in a well. Hydraulic gradient. The gradient of water
table, generally following the topographic gradient. So, for example,
if you have a hill. And the high elevation
to low elevation. So the gradient is– you’re going to see
the water table is changing from high
elevation to low elevation. The elevation of
water table is also changing according
to the topography. So the gradient is always– you consider like
high versus low. So it’s usually
higher water table and it’s going to flow towards
the topographically lower area. And the water table
follows the same pattern. Hydraulic conductivity is
the ability of rock materials to allow water to move
through cubic meters per day per square meter. So hydraulic conductivity
is very important concept in hydro-geologist especially. So we’ll be talking about
that later in depth, but not for this class. So this is just more
introductory level environmental geology class. When you talk about this
groundwater movement we should talk about what
is hydraulic conductivity. But we’re not going to
calculate or we’re not going to talk about any Darcy’s Laws. But they all come after the
hydraulic conductivity concept. So that’s the ability
of raw materials to allow water to move through. So if you think about sandstone,
that the hydraulic conductivity is higher compared
to clay stone. Porosity, the percentage
of void space in sediment, or rock, to store water or oil. So that’s porosity. Permeability is the
measuring the interconnection of pores in a rock material. So that’s permeability. So porosity and
hydraulic conductivity. If you have high
porosity you should expect to see higher
hydraulic conductivity. So, for example, the sand,
the porosity is high. But at the same time it depend
on the size of the material, too. For example, the clay has
high porosity, like 50%. Very, very tiny particles. But the conductivity
is really low because there’s no pore spaces. Even though they’re pore spaces,
they’re not interconnected. So they need to
be interconnected in order to transmit the water,
in order to conduct the water. So that’s the idea. But sand, you have porosity
35% but having these pores connected to each other. So hydraulic
conductivity increases. And in granite
high porosity is 1% and the conductivity
is very, very low. Sandstone, hydraulic
conductivity is 28.7 meters per day. That is higher. Because you have
more space in there. But the gravel, look at the
gravel, so it’s 25% porous. The hydraulic
conductivity is very high because you have
these pore spaces. The 25% of porosity
is interconnected. So this interconnection
of these pore spaces is important when you talk
about hydraulic conductivity. Available groundwater
estimated above the total flow of the Mississippi during
the last 200 years. The groundwater as primary
drinking water source for nearly 50% of US population. Groundwater overdraft problems,
like extraction rate exceeding recharging rate, like no
precipitation but more extraction, in many
parts of the country. In particular, some states
in the Great Plains region. Estimated 5% of
groundwater depleted, but water level declined more
than 15 meter in some areas. So the groundwater is
the basic water supply for most of the places
that you go within the US or in other countries. But the recharge and
the discharge rate needs to be matched up. So if you have more
and more discharge, more and more extraction
of the groundwater, but no recharge or less recharge
that can cause the problem. And that’s one of
the problems that you can see in this picture. So that’s called the
cone of depression. So you get depressed when
you don’t have things. But the same way, so the water
table, it gets depressed. This is called the
cone of depression. And that because of the over
discharge from the water well and the groundwater trying
to form this kind of, all these groundwater
flows towards this well. And that’s kind of creating
the cone of depression. So that’s a feature
that you can observe if you have higher discharge
and no or less recharge. Overdraft of groundwater
leads to a lower water levels of streams, lakes,
reservoirs, et cetera. Overuse of surface water
that yields lower discharge rates of groundwater. Effluent stream in
groundwater discharge zone tends to be perennial. And influent stream
in groundwater recharge zone above
the water table often intermittent or ephemeral. Special linkage areas, like
sinkholes and cavern systems in the karst terrains. So the karst topography,
what does that mean? So those are carbonate
environments. So the karst topography where
you talk about limestone caves, for example. So that’s where you’re
going to have sinkholes. That’s these limestones. These are carbonates. So they react with the liquids. Especially the acidic or
slightly acidic liquids. And they’re forming these holes. And with that you should
think about, like, the sinkholes in
these areas are not good for building
up any structures. However, for the
groundwater, this can be good places that
they can transmit water to one place to other
easily because of this less strength in the rocks. Especially the carbonates. So interactions between
surface water and groundwater. So here is a picture showing
you that the springs, and the lakes,
the groundwater is kind of recharging the
lakes or these wells. And then wherever you have
cut the groundwater table. And that’s where you’re going
to see this water exposed in different places as a river,
or as a lake, or as a well. So karst topography problems. The water pollution occurs
where sinkholes have been used for waste disposal. So people used to use the
sinkholes as the waste disposal sites. Which is not good. Because the carbonate is not
a very strong or very strength rock. So that’s a very weak rock. And that can do
a lot of leakages because they get dissolved. As I mentioned, slightly
acidic conditions they can dissolve because
these are carbonates. So that can cause
leakages if you dispose the waste that’s not protected. So carvern systems
are prone to collapse. Producing sinkholes
that may form in areas that damage buildings
on the ground surface, roads, and other facilities. In many areas
underlined by limestone, such as Edwards
Plateau in Texas, groundwater is being mined. As a result of the mining,
important karst springs, where water emerges from
caverns, are being changed. Causing a reduction
in biodiversity. So that’s a big
environmental issue. And water use. So offstream use is a
removal or diversion from its surface water
or groundwater sources temporarily. So example, we use it for
irrigation, thermoelectric, industrial use. The consumptive use is type
of offspring use of water without immediate return to the
surface water or groundwater, such as transpiration
and human use. Instream use is navigation,
fish and wildlife, and recreational uses. So these are different
types of water uses. In major urban areas, over
withdrawal of groundwater can be an issue. So that’s over
discharging water. Overuse of local surface
water can be an issue. So threats of local urban
landfill so the water supply, for example
Long Island, New York. That’s a problem. So water import
issues and problems. So what is distance
to transport? How much water available? From where? So conflicts with other
areas, litigations, and long-range planning. So these things come into play
when we talk about the water management actually. So trends in water use. Based on the data
from 1950 to 1995 surface water use far
greater than groundwater use. The rate of water use decreased
and leveled off since 1980. Irrigation and thermoelectric
are major fresh consumptive water use. Less fresh water use since
1980 due to new tech and water recycling. So here is the
chart that you can see the population increasing. And the groundwater
versus surface water versus total water. And you can see from 1950 to
2005, population increases and the water usage increases. And especially using
the groundwater, it kind of decreases. But using the surface
water increases. But the total usage
of water increases. The withdrawals in billions
of gallons per day. So that number is increasing. So here is another chart. The withdrawals in
billions of gallons per day in y-axis, and x-axis. The years are 1950 to 2005. So total withdrawals,
it’s kind of equaled out after 1980 to 2005. Because people
use other systems, other supply of
water rather than this particular groundwater. So water conservation. Improved agricultural irrigation
could reduce water withdrawals by between 20% and 30%. Engineering technology and
structure regulating irrigation and reducing evaporation. So better technologies in power
plants and other industries. So less use of water due
to improve efficiency. So domestic use of water,
like urban and rural, accounts for only 10% of the
total national withdrawals. Can be reduced at a relatively
small cost with more efficient bathroom and sink fixtures. You can imagine how much
water that we waste when we go to bathroom or at the sink. Global water conservation
is a virtual water budget. Conservation of water
at the global scale. So this is import
and export plan. So you can see some
countries they have enough water they can import– I’m sorry, they can export. And then the other
countries who needs water, they can import the water. So this has become global
scale conservation plan. Water management. So needs for water management. Increasing demand for water use. And water supply problems in
semiarid and arid regions. Water supply problems in
mega-cities of humid regions. And water treated as commodity. Capital, market,
and regulations. So these things needs
to be discussed when it comes to water management. And aspects to be considered
is the natural, environmental factors. Geologic, geographic,
and climatic. Human environmental factors
like economic factors, social, and political. And some of the strategies
would be more surface water use in wet years. And more groundwater
use in dry years. And also you reuse and recycle
water regular basis, as well as emergencies, like fires. Managing the rivers. So dam construction
could save water and using useful projects
like hydro-power projects. And impact on flood frequency. And impact on
sediment distribution, particularly downstream. And impact on wildlife habits. And control the planned floods. So when it comes to
the river management these are the things that
we need to pay attention. And also the water
and ecosystems. Changes in response to climate,
nutrient, inputs, soils, and hydrology. And general tendencies to
increase human use of water, increase degradation
of natural ecosystems. So overall reconciliation
between multiple water uses. Water resources development,
that’s dam, reservoirs, canals, and associated impact
on surface water environment. For reconciling
the uses of water in agriculture, industry,
urbanization, and recreation. And the protection of
wetland and water resources. That’s also [INAUDIBLE] facts. The wetlands, like
swamps, or marshes, bogs, prairie potholes, vernal pools. And the wetlands are one of
the nature’s natural filters. So the plants in wetlands may
effectively trap sediments, nutrients, and pollutants. Freshwater wetlands are a
natural sponge during floods. They store water, helping to
reduce downstream flooding. And release water
after the flood, nourishing low flows
of river systems. And wetlands are
highly productive lands where many nutrients
and chemicals are naturally cycled
while providing habitat for a wide variety of
plants and animals. Freshwater wetlands are often
areas of groundwater recharge to aquifers. Some of them, a spring-fed
marsh, for example, are points of
groundwater discharge. So emerging global
water shortage. Isolated shortage
of water, that’s indication of a global
pattern of water shortage. So depleted water resources. Over-drafted aquifers. Dried lakes, like Aral Sea. And troubled streams, like
Colorado and Yellow River, not reaching seas some years. And polluted limited water
resources due to development and increased waste. And the demands for water
resources tripled as populated more doubled last 50 years. And growing fast next 50 years. The global warming, that’s
causing more problems. So these are some of
the critical thinking points as your take home
message from this chapter. And with that we’re going
to conclude the Chapter 13. If you have any
questions, please feel free to email me or
put in the discussion bot.

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