Objective; Students will be able to describe the hydrologic cycle
Only 1% of all the available water constitutes our freshwater. Where do we find it? Freshwater is found underground, in rivers, in lakes, in ponds and in the atmosphere. In New Haven, the majority of our fresh water comes from Lake Whitney, Lake Saltonstall, Lake Gaillard, West River and groundwater sources. But remember, water is continually evaporating, condensing, and falling as precipitation in what is called the
hydrologic
cycle
.
(figure available in print form)
Because of the hydrologic cycle, enough precipitation falls each year to cover the entire surface of the earth 85 cm deep in water. However, the amount of water that evaporate, condenses, and returns as precipitation is not the same over the oceans as over the land.
During evaporation all salt and minerals are left behind, thus purifying sea water. Off all the water that evaporates approximately 84% comes from the oceans and approximately 16% comes from land sources. However, more precipitation over land occurs than evaporates, 23% precipitation on land and 77% over and oceans. Therefore, the hydrologic cycle is continuously replenishing the freshwater on land from the vast supply of water in the ocean.
What happens to water that falls on land? Basically three things happen to water that falls as rain. One, two-thirds may evaporate back into the atmosphere; Two, some soaks into the ground; Three, the rest flows across the surface of the land.
The amount of water that soaks into the ground depends on how dry the ground is and what kind of soil is present. Some soils have space in between the soil particles called a
pore
space
. The more pore space a soil has, the more water it will hold.
The total amount of pore spaces in a volume of materials is called
porosity
. The porosity of rock layers is and important property to consider when studying groundwater. Another important property of rock layers is
permeability
. Permeability is a measure of how well water flows through the pores and cracks in rock layers. The amount of permeability depends on the size and shape of the pore spaces and how they are connected. Highly permeable rock layers are able to transport groundwater over great distances.
ACTIVITY 1
POROSITY
Materials: 4 large containers (beakers) they should be the same size, sand, clay, gravel, garden soil, 100 ml graduated cylinder, water
Fill each container with the same amount of soil (about three quarters full) then add water till the container is full. Be sure to measure the amount of water added to each container. This exercise show the porosity of each type of soil.
ACTIVITY 2
PERMEABILITY
Materials: 5 larger filters, sand, clay, gravel, garden soil, 4 beakers, and a watch with a second hand and filter paper
Put filter paper in each filter and fill 4 out of the 5 filters with different soils. Saturate each sample then add 30 ml of water into each filter successively and time how long it takes for the water to filter through each type of soil and the filter paper. This activity shows the permeability of each soil.
When water moves across the earth’s surface, it is called
surface
runoff
. Surface runoff occurs when the rain falls faster than the water can move through the soil, the water begins to collect on the surface. This water may move downhill across the surface of the land.
Surface runoff moves on land from high places to lower places. It collects in small streams and drains into larger streams and into major rivers. The area of land drained by a river is called the river’s
watershed
. It is this area that must be carefully guarded against contamination.
PROBLEMS:
-
1. The water source of a spring-fed lake is
-
2. A permeable rock layer containing water that is trapped between 2 impermeable layers is called a(n) .
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3. A trapped aquifer will form a(n)
.
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4. One way to prevent water shortages is by damning rivers to form
.
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5. The hydrologic cycle continuously replenishes the freshwater on land from the supply of water in:.
|
(A) wells
|
(C) ice caps
|
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(B) oceans
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(D) underground streams
|
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6. Which of the following does
not
happen to water that falls as rain?
-
(A) It evaporates back into the atmosphere
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(B) It soaks into the ground
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(C) It condenses onto grass
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(D) It flow across the surface of the land
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7. The amount of water a rock layer can hold depends on its:.
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(A) soil type
|
(C) amount of precipitation
|
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(B) pore space
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(D) texture
|
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8. Wells are found in:
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(A) reservoirs
|
(B) watersheds
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(C) aquifers
|
(D) lakes
|
answers:.
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1. groundwater
|
5. B
|
|
2. aquifer
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6. C
|
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3. well
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7. B
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4. reservoirs
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8. C
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