RUNNING WATER 16
INTRODUCTION
Running Water
CHAPTER OUTLINE
2.
253
3.
254
4.
255
5.
256
6.
257
7.
8.
258
9.
259
LEARNING OBJECTIVES/FOCUS ON CONCEPTS
16.2 Describe
16.4 Outline
16.6 Contrast
.
16.8 Sketch and explain
260
TEACHING STRATEGIES
Clicker Questions:
Muddiest Point:
A. Stream Calculations
B. The 100-Year Flood
261
C. Do I live on a floodplain?
TEACHER RESOURCES
Web Resources:
USGS Resources:
262
EPA Resources:
NOAA Resources:
PhysicalGeogrpahy.net
oThe Geologic Work of Streams
263
Examples of Flooding Events:
o April 2001 Mississippi River Flood
Imagery, Animations, and Videos:
Images
264
Animations
FEMA Levee Simulator
Video
ANSWERS TO QUESTIONS IN THE CHAPTER:
CONCEPT CHECKS
16.1 EARTH AS A SYSTEM: THE HYDROLOGIC CYCLE
1. Sketch should be similar to Figure 16.2. Once precipitation falls on land, it may be infiltrated
2. is a collective term for water evaporating from Earths surface AND water
being released from plants.
3. The water cycle is in balance, meaning that the overall amount of water in system remains
265
16.2 RUNNING WATER
1. The amount of water that infiltrates into the ground versus runs off over the land depends on
many factors including: the intensity and duration of rainfall; the amount of water already in
2. Drawing should be similar to Figure 16.3.
3. The three main zones of river systems are: sediment production, sediment transport, and
16.3 STREAMFLOW
1. Streams cut channels into bedrock through quarrying (removal of blocks from the bed of the
2. Streams transport their load as dissolved materials, particles suspended in the water column,
and as bed load, or particles moved along the stream bed.
3. Capacity is the maximum load of solid particles a stream can transport per unit time.
4. Settling velocity is the speed at which a particle falls through a still fluid. The larger the
particle, the more rapidly it settles. The shape and specific gravity of a particle also affects its
16.4 THE WORK OF RUNNING WATER
1. Student drawing should be similar to Figure 16.13 and show the curved surface of rupture of a
slump as well as scarps created from the moved block of material.
2. Rockslides occur when blocks of bedrock break loose and slide down a slope along a relatively
3. The massive rockslide at Gros Ventre, Wyoming, was triggered by heavy rains and melting
snow. Here, a great mass of sandstone, shale, and soil moved along a saturated clay bed,
4. A lahar is a type of debris flow common on steep slopes of some volcanoes. Lahars are caused
when unstable layers of ash and debris become saturated with water and flow down steep
266
5. Earthflows are different from debris flows in that they are often more viscous, and thus move
16.5 STREAM CHANNELS
1. Bedrock channels are more likely to be found near the headwaters of a stream where streams
2. Figure should be similar to Figure 16.16 and 16.17.
3. Braided channels are characterized by large bed loads of coarse particles. A stream may
16.6 SHAPING STREAM VALLEYS
1. Base level is the lowest elevation to which a stream can erode its channel. Ultimate base level
2. A graded stream is one that has the necessary slope and other channel characteristics to
3. V-shaped valleys are those that are actively downcutting; these valleys often have rapids and
4. See Figure 16.23. Erosional floodplains develop as the continuous side-to-side erosion of
5. Incised meanders may form where a change in base level causes a stream to begin
downcutting, or where uplift of the land on which the river is flowing initiates downcutting.
16.7 DEPOSITIONAL LANDFORMS
1. See Figure 16.26. Foreset beds form where coarse particles deposits soon after entering the
2. As a delta grows outward from the shoreline, the streams gradient continually decreases. This
circumstance eventually causes the channel to become choked with sediment. As a
3. The Mississippi River used to regularly overflow its banks in seasonal floods; these floods
delivered huge quantities of sediment to the delta. Flood control efforts by humans has
4. A natural levee forms parallel to a river channel where flooding deposits coarse materials
5. Alluvial fans form where sediment-laden mountain streams emerge onto flat lowlands. When
16.8 DRAINAGE PATTERNS
2. Dendritic patterns develop on relatively uniform surface materials. Rectangular patterns
3. The formation of a water gap may be due to an antecedent or super posed streams. Antecedent
streams are those that exist in an area before a ridge or mountain is uplifted. Here, the stream
4. Stream piracy is the capture of drainage that previously flowed to another stream. Headward
erosion can narrow and breach a divide, causing stream piracy to occur.
16.9 FLOODS AND FLOOD CONTROL
1. Regional floods are usually seasonal and occur in association with rapid snow melt and/or
heavy spring rains; can also result from numerous heavy rain events. Flash floods occur with
2. 100-year floods do not necessarily occur every 100 years. The term 100-year flood means
3. Flood control is attempts to eliminate or lessen the catastrophic impact of floods on life and
the environment. Artificial levees are earthen mounds built on river banks to increase the
volume of water a channel can hold. These artificial structures are not built to withstand
4. Nonstructural approaches integrate sound floodplain management by identifying high-risk
flood areas and implementing appropriate zoning regulations to minimize development in
EYE ON EARTH
EOE #1 THOUSAND SPRINGS, IDAHO
1. Springs represent locations where water flows to the surface from the underground. This
2.
a. Water likely fell onto this surface as rainfall or snow, and infiltrated through the rock
to become groundwater. Alternatively, water might have entered the groundwater
supply through an influent stream nearby.
EOE #2 WHITE RIVER, ARKANSAS
1. The suspended load of this river gives it its brown color.
3. The flow velocity would increase due to a straightening of the stream channel.
EOE #3 MIDDLE FORK, SALMON RIVER, IDAHO
2. Valley deepening is the dominant process here; we see the beginnings of valley widening at
the base of the mountains, in the foreground of this image.
EOE #4 YUKON RIVER, BRITISH COLUMBIA
1. When this river meets the Bering Sea, it deposits its load as the gradient drops. Eventually,
2. The channels that radiate across the delta are called distributaries.
269
1. The dam here creates a temporary base level for this stream. Upstream of the dam, the
river likely slowed and possibly began depositing sediment.
2. Downstream of the dam, increased flow velocities may scour and deepen the channel. The
3. Over time, the sediment delivered by the Colorado River will fill the reservoir, reducing its
GIVE IT SOME THOUGHT
1. The amount of water that runs off or infiltrates the surface depends on (1) the intensity and
3. The suspended load of the jar will settle to the bottom. The dissolved load will likely stay in the
4. A mass wasting event such as a debris flow could influence a streams flow. Debris flows are
water-saturated accumulations of sediment that travel downslope. If this flow reaches a
5. River #1 represents (d) an alluvial braided channel. River #2 represents (b) a meandering
6.
a) River #4 is downcutting its channel into the bedrock.
7. During drought, a streams ability to erode would be decreased due to less water present in the
channel. Heavy precipitation would increase the amount of water in a stream, thus increasing
8. Base level for the Wabash River is the Ohio River, into which it flows. Base level for the Ohio
River is the Mississippi River, into which it flows. Neither of these is considered ultimate base
9.
a) The formation of large ice sheets locks water from the hydrologic cycle into glacial ice.
10. Over the past 6000 years, the river has built deltas progressively further east and southeast.
Cities, commerce, and transportation have grown around the current path of the Mississippi
11. A stream may lengthen its course by headward erosion, by increased erosion on the outer bends
12. The term does not mean a flood only happens once every 100 years. This phrase
13. The heavy rains that fell in the region may have been concentrated to the watershed (drainage
basin) that feeds the Connecticut River, and not the basin of the Thames River. Therefore,
271