lab_3_ex_6__1_
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Grand Rapids Community College *
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106
Subject
Geography
Date
Feb 20, 2024
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docx
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8
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1
Exercise
6
Streams and Flooding
In this lab you will:
James S. Reichard
Georgia Southern University
Student Name
Section
learn to identify drainage divides and floodplains on a map in order to access the potential for flooding at a given location. You will also examine the historical discharge record of a stream and learn how to calculate the recurrence interval of flood events.
Background Reading and Needed Supplies
Prior to doing this exercise you should read Chapter 6 in the textbook.
With respect to supplies, you will need a calculator, ruler, and colored pencil.
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54
Part II
–
Floodplains
Recall from the textbook that a floodplain (Figure 6.3) is the relatively flat area that lies
adjacent to a stream or river. During high discharge events, a stream will overflow its banks and
inundate its floodplain. Also recall that in downstream areas where the gradient decreases and the channel approaches base level, rivers tend to meander more and produce wider floodplains.
Floods here are referred to as downstream floods
. In contrast to flash floods, downstream floods occur slowly and involve greater volumes of water. Of course the level to which any floodplain becomes inundated will depend on the amount of discharge.
Figure 6.3
To minimize the risk of flooding, a building should be located as far above the elevation of the channel as is practical. Since placing a building on an active floodplain virtually guarantees damage from a flood, it is important to recognize the uppermost edge of a floodplain. As can be
seen in Figure 6.3, the floodplain's edge is marked by an abrupt increase in slope. On a topographic map, this abrupt slope increase occurs where the contour lines become closely spaced. For example, the purple lines on the topographic map in Figure 6.4 coincide with the upper edge of the floodplain where the slope abruptly increases. Note that due to erosion, this change in slope is oftentimes more gradual and, therefore, not as obvious on a map.
4) Using a purple-colored pencil or marker, carefully trace the edge of the floodplain along the north-south flowing stream on the eastern side of the map in Figure 6.4. Note that part of the
floodplain has already been mapped for you.
5) Are there any buildings or roads within the floodplain? Explain why.
There are no buildings or roads within the floodplain because the probability of having property or
vehicle damage is evitable in high risk flood zones especially on the valley floor. A floodplain
represents the base level of all water flow. So, because of the greater amount of water volume in
that flat surface, any building or road in its path will unundate the area. This could leave buildings
or roads underwater for a long period of time.
6) In Figure 6.4, part of the drainage divide on the south side of the tributary named Big Branch
has already been mapped for you. Continue tracing this drainage divide (in red) until you come to the southern most edge of the map.
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from CourseHero.com on 02-01-
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