Chapter 11 Streams and Floods 1 Humans and

Chapter 11: Streams and Floods 1. Humans and Rivers 2. The Hydrologic Cycle 3. Drainage Networks and Patterns 4. Factors Affecting Stream Flow 5. The Work of Streams 6. Floods 7. Flood Control Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Learning Objectives • • Students will explain concepts related to streams and floods. Students will synthesize all the components and processes of the hydrologic cycle. Students will describe and distinguish among various stream drainage patterns. Students will identify the factors that influence stream velocity. Students will explain the erosion, transport, and deposition of streams. Students will list factors that contribute to flooding. Students will identify examples of flood protection and adjustment.

Humans and Rivers What is going on here, and what does it have to do with streams and floods? The Good Earth/Chapter 11: Streams and Floods

Humans and Rivers A stream is any flow of water through a channel (defined by its banks), from the smallest creek to the largest river. The Nile River Basin: The Nile is 6, 825 km long and drops 1, 800 meters in elevation from its source to its mouth. Flows from Burundi to the Mediterranean Sea, covering 35 degrees of latitude. Egypt became one of the earliest sites of civilization because of the Nile. Humans began diverting water from the Nile for irrigation over 5, 000 years ago. The Pyramids were built during a time of ample water in the Nile. The Good Earth/Chapter 11: Streams and Floods

Humans and Rivers The history of the Nile illustrates how organisms in the vicinity of a stream can be placed under considerable stress when significant changes occur in stream systems. We tend to take streams/rivers for granted, but they perform many positive functions in today's society: - Bring water to irrigate crops - Provide drinking water - Supply coolant for power plants - Transportation (barges) - Provide ecosystems for wildlife - Recreation sites The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Self Reflection Survey Answer the following questions as a means of uncovering what you already know bout streams and floods. 1. What river is nearest to where you live? Where does the river begin and where does it end? 2. How do people interact with streams? How do streams fit within the context of biology, economics, culture, politics, history, recreation, and aesthetics? The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: The Hydrologic Cycle The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle The hydrologic cycle. Water evaporates from oceans, rises through atmosphere, condenses to form clouds, is then released as precipitation that may flow over land in streams, sink underground, or be absorbed by plants. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Water moves in and around the earth system, changing from one physical state (liquid, solid, vapor) to another, in a process called the hydrologic cycle. Water in streams doesn’t just come from rainfall! The majority of precipitation reenters the atmosphere as water vapor through evaporation. Water vapor can enter the air when it released from plants through transpiration. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle The vast majority of Earth’s water is in the oceans (97%) with only about 3% on land. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Most of the water on land is stored in ice or groundwater. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Land receives more moisture by precipitation than it supplies by evaporation. The balance comes from evaporation from the oceans. This excess water is returned to oceans via surface streams. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 1 Sort the following twelve terms into six pairs of terms that most closely relate to one another. groundwater plants transpiration stream ice infiltration rainfall precipitation water vapor gas melt water run off The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Where do streams come from? Many (such as the Colorado river) come from small streams on the slopes of mountains. Their source water can be snowmelt from the mountains or rainwater running off the slopes. The source of the mighty Mississippi is a small lake in Minnesota! The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Rivers often come together to form another river. In the image above, the Allegheny (left) and the Monongahela (right) join to form the Ohio river in Pittsburg, PA. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle The majority of precipitation on land runs off to the oceans in streams. On average, the length of time that a given volume of water remains in streams is about 14 days. Only a small amount of precipitation on land sinks into the ground, as infiltration rates are slow compared to run off rates. However, the volume of water stored in groundwater is 70 times greater than the volume of water in streams and lakes. Ice stores about 3 times the volume of water found in groundwater. Many rivers have their sources in springs that bring groundwater to the surface (e. g. the Nile). Many rivers have sources in glacial melt water (e. g. Brahmaputra, Ganges). The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 2 Use the hydrologic cycle to suggest a hypothesis about why rivers in South America carry approximately twice as much fresh water as do rivers in North America. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 2 Draw a concept map that identifies the links among the components of the earth system and the hydrologic cycle. The Good Earth/Chapter 11: Streams and Floods

The Hydrologic Cycle Regardless of where or how they start, streams: - flow down slope. - often join other streams to form a network. - empty into another body of water (another stream, a lake, an ocean, a reservoir, a wetland). This lowest point to which a stream flows is called the base level. The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: Drainage Networks and Patterns The Good Earth/Chapter 11: Streams and Floods

Drainage Networks and Patterns What controls the amount of water in a stream channel? The size of the area it drains The average precipitation over the area The Nile and the Mississippi have the larges drainage basins, each covering over 1 million sq mi. Drainage basin = the area drained by a stream and its smaller streams (tributaries). Above, the Mississippi drainage basin is composed of several smaller drainage basins (colored areas). It takes up half the land area of the U. S. The Good Earth/Chapter 11: Streams and Floods

Drainage Networks and Patterns Drainage divides are found along the high ground separating drainage basins. Left – drainage divide and drainage basins, Ohio. Streams north of the divide flow into the Great Lakes. Streams south of the divide flow to the Ohio River, which joins the Mississippi and flows to the Gulf of Mexico. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 5 Why is the volume of water in the Mississippi River about 10 times greater than the volume of water in the Nile River? a) The Mississippi River drainage basin is ten times bigger than the Nile basin. b) The Mississippi River drainage basin receives more rain. c) The Mississippi River is a longer stream. d) There is less vegetation to absorb rainfall in the Mississippi River drainage basin. The Good Earth/Chapter 11: Streams and Floods

Drainage Networks and Patterns Why do stream patterns look like the branches of a tree? Streams will follow the path of least resistance, forming valleys where rock is most readily eroded or following the steepest slope. Dendritic drainage patterns are characteristic of areas where the geology is relatively uniform. The tips of the v’s where streams come together point down stream. The Good Earth/Chapter 11: Streams and Floods

Drainage Networks and Patterns Trellis patterns – streams intersect at right angle forming rectangular drainage patterns. Found in areas of alternating layers of weak and resistant rocks. Main streams flow parallel to ridges, cutting across at water gaps. Smaller streams flow down slope perpendicular to the course of the main stream. The Good Earth/Chapter 11: Streams and Floods

Drainage Networks and Patterns Rectangular patterns – occur in regions where the streams are controlled by joints, fractures in the underlying bedrock. Streams exploit these fractures and flow in them. Radial patterns – typically found on the flanks of volcanoes, where streams flow downhill from the summit. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 8 What type of drainage patterns can you observe in this map of part of the Appalachian Mountains and adjacent areas? Explain any differences in patterns that you observe in different parts of the map. The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: Factors Affecting Stream Flow The Good Earth/Chapter 11: Streams and Floods

Factors Affecting Stream Flow Gradient = the slope of a stream. It is the change in elevation of the stream over a horizontal distance. Where is a stream’s gradient highest, near the headwaters or near the mouth? The Good Earth/Chapter 11: Streams and Floods

Factors Affecting Stream Flow How might the features you see in this picture compare to what you would observe in a low-gradient river? Rocky banks and channel As you continue down stream a channel becomes less rock, changing to gravel, then sand, and eventually fine-grained silt and mud = channel roughness. Which would you expect to flow faster, the high gradient part of a stream or the low gradient part? Why? The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 9 Explain why stream velocity would change along the same section of a stream at different times of the year. The Good Earth/Chapter 11: Streams and Floods

Factors Affecting Stream Flow Cross-sectional area and hydraulic radius affect rates of flow. The wetted perimeter = the length of the surface of the channel banks and bed in contact with the water. A large cross-sectional area compared to wetted perimeter = large hydraulic radius, and therefore a relatively high stream velocity. Higher hydraulic radius = higher velocity The Good Earth/Chapter 11: Streams and Floods

Factors Affecting Stream Flow Downstream, channel roughness is generally reduced and hydraulic radius increases. Therefore, stream velocity increases downstream. Stream discharge = volume of water that passes a given point in one second. Discharge (m 3/s) = width (m) x depth (m) x velocity (m/s) Fun fact: 50 million gallons of water discharge into the Atlantic ocean from the Amazon river every second! The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 11 Some scientists predict that global warming will result in a corresponding increase in evaporation from the oceans. How would this affect the discharge of the Amazon River? a) Discharge would increase b) Discharge would decrease c) Discharge would stay the same The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: The Work of Streams The Good Earth/Chapter 11: Streams and Floods

The Work of Streams All streams erode particles from channel beds and banks and carry them downstream. a. About 5 months after the eruption of Mt. St. Helens this channel of the upper Muddy river had formed in the soft erupted materials. b. Note the increase in width and depth of the channel 12 months later. The Good Earth/Chapter 11: Streams and Floods

The Work of Streams Erosion produces stream load, which is the combination of bed load, suspended load, and dissolved load. How is stream color affected by load? Suspended load increases when discharge increases (higher velocity = more energy to move particles). The Good Earth/Chapter 11: Streams and Floods

The Work of Streams The Amazon River has 10 times the discharge of the Mississippi but it carries only 3 times the load. Why might this be? What factors account for this difference? Source materials are different – soils with different characteristics. Different weathering histories of the two regions. The area of the Amazon is much more densely vegetated – vegetation protects the underlying soil from erosion. Yellow River, China – carries more sediment relative to its discharge than any other major river on Earth! A braided channel, Alaska The Good Earth/Chapter 11: Streams and Floods

The Work of Streams As a stream slows down it drops some of its load. Heavier particles drop out first. When a stream has a heavy load, sediment is often deposited in the stream channel itself to form bars or islands. These deposits split the channel into smaller channels forming a braided channel. The Good Earth/Chapter 11: Streams and Floods

The Work of Streams As a meander becomes larger the channel migrates across the flood plain in the direction of erosion. Meanders = broad curves in a stream. Velocity of the stream varies as it moves through these large bends. The Good Earth/Chapter 11: Streams and Floods

The Work of Streams The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 15 Examine the image of part of the lower Mississippi River. This picture was taken from the space shuttle. The long axis of the image is about 67 miles long. This region is characterized by rich farmland (purple) where a variety of crops are grown. The gray regions bordering the river are undeveloped forested areas. The river is the black band that curves across the image. The river flows from north to south. 1. Interpret the image and discuss the geologic history of this section of the river. 2. Identify where erosion and deposition are occurring. 3. Use the blank map to draw an earlier course of the channel. The Good Earth/Chapter 11: Streams and Floods

The Work of Streams Rivers dump much of their sediment, forming a delta, where they enter the relatively quiet waters of an ocean or lake. Velocity rapidly declines as the river hits the ocean causing the drop of sediment. At right – Mississippi River delta. Constant dredging is required in order for oceangoing ships to navigate the main river channel. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 16 Create a concept map that links together the components of erosion, transportation, and deposition in a stream channel. The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: Floods The Good Earth/Chapter 11: Streams and Floods

Floods Flood = a temporary overflow of a river onto adjacent lands not normally covered by water. The Good Earth/Chapter 11: Streams and Floods

Floods usually occur when the amount of water on the land surface exceeds the volume of water that can be transported in stream channels and absorbed into the surrounding soil. Flooding is caused/influenced by: - Magnitude, timing, and type of precipitation - Human modifications of the physical landscape - Capability of the ground to absorb water - Evaporation rates - Physical characteristics of the stream system The Good Earth/Chapter 11: Streams and Floods

Floods a. Graph of monthly rainfall for Cedar Rapids, Iowa. b. Distribution and magnitude of precipitation (cm) associated with a single storm over southern Iowa July 4 and 5. The most common cause of flooding is excess precipitation. 1993 Mississippi River flood – caused by both long term and short term precipitation. Jan – July several midwestern states received over 150% of their normal precipitation. Heavy storms added large amounts of rainfall at once The Good Earth/Chapter 11: Streams and Floods

Floods This was spatially the largest flood in U. S. history! It covered 44, 000 square km or 17, 000 square miles. The Good Earth/Chapter 11: Streams and Floods

Floods In arid southwestern states, floods occur because channels often have no surface water in them most of the year and brief, intense storms cause flash flood. In areas with lots of snow and ice, floods occur when temperature rises sufficiently to cause rapid snow melt. When streams of snow melt flow from warmer to colder regions ice jams can form blocking flow and making the flooding worse. Ice jam flooding along the Red River, North Dakota. Ice blocked the flow, backing up the river and forming a temporary lake. The Good Earth/Chapter 11: Streams and Floods

Floods How do humans influence flooding? - Paving covers or alters natural surfaces that otherwise might absorb water. - Storm sewers that divert water from surfaces dump it into natural streams causing them to flood. - Housing developments or agricultural fields replace natural wetlands, which act as water storage reservoirs. - The collapse of constructed dams. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 17 List five factors that influence flooding. Use one sentence to briefly describe the role of each factor in flooding. The Good Earth/Chapter 11: Streams and Floods

Floods We can assess the potential of a stream to flood: -Stream gauges measure the stream stage, depth of water in a channel relative to a starting point for measurement -Data from most stream gauges become available via satellite for scientists -USGS has over 7000 stream gauges across the U. S. The Good Earth/Chapter 11: Streams and Floods

Floods Stage and discharge relationships for the Cuyahoga River, Akron, Ohio, for the stream gauge in figure 11. 26. Hydrograph for the Cuyahoga River, Akron, Ohio. Graph shows stage measurements for the gauging station in Figure 11. 26. Red arrows show measurements for figure b and c. The Good Earth/Chapter 11: Streams and Floods

Floods U. S. stream discharge information is available at http: //water. usgs. gov Historical flood information can be used to determine how frequently flooding has occurred in the past and to estimate the likelihood of future floods. Historical discharge data is arranged in order from largest flood discharge to smallest, assigned a rank based on size, and graphed. Recurrence interval = the average time in years between floods of the same size. Scientists can use graphs of maximum stream discharge versus recurrence interval to estimate the discharge of 100 -year floods. The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 20 An analysis of flood data in metropolitan areas over the last century suggests that floods, caused by similar volumes of precipitation are actually larger and more devastating today than in the past, despite advances in flood monitoring. Provide some potential explanations for this apparent paradox. The Good Earth/Chapter 11: Streams and Floods

Go back to the Table of Contents Go to the next section: Flood Control The Good Earth/Chapter 11: Streams and Floods

Flood Control Effects of the Mississippi River flood. a. The city of Des Moines, Iowa was inundated by the flood waters. b. A corn crop in Missouri was destroyed by the flooding. Why should we care about flood control? The Good Earth/Chapter 11: Streams and Floods

Flood Control • Cities located on flood plains suffer the most economic losses • Floodwaters can carry contaminated water (sewage, agricultural chemicals) • Roads get submerged and have to be closed and repaired after the flood • Farmland submerged – production falls • Floods can deposit thick layers of sediment where it should not be • Can halt barge traffic for months • People die and are uprooted and evacuated The Good Earth/Chapter 11: Streams and Floods

Flood Control In 2000 700 people were killed by the floods in the Limpopo River drainage basin in Mozambique. a) The river during a normal year and b) during the floods. The width of the river swelled to more than 80 miles in some locations. The Good Earth/Chapter 11: Streams and Floods

Flood Control We can try to stop floods (prevention) or adjust our lifestyle to deal with them effectively (adjustment). Levees. (a) Artificial levees are raised embankments along a stream channel constructed to protect neighboring lands from rising floodwaters. (b) A levee in West Virginia protects homes from potential flooding of the Potomac River. Levees and floodwalls protect cities and fields on the floodplain. Is this prevention or adjustment? The Good Earth/Chapter 11: Streams and Floods

Flood Control A floodway is a diversion channel that will transport floodwaters away from inhabited areas. Approximately 500, 000 people live at the confluence of the Assiniboine and Red Rivers in Winnipeg, Manitoba, Canada. Is this an example of prevention or adjustment? The Good Earth/Chapter 11: Streams and Floods

Flood Control Dams are used for flood control under the premise that floodwaters can be stored in reservoirs to be released slowly when the threat of flooding has receded. Prevention or adjustment? Potential problem? Storage facility must be big enough to accommodate the excess. Wilson Lake dam, central Kansas. The Good Earth/Chapter 11: Streams and Floods

Flood Control Examples of adjustment tactics: -Relocate settlement to higher ground -Sales tax increases to fund projects that modify land use patterns in floodplains -Restoration of wetlands along river banks -Avoid development in areas prone to flooding -FEMA created to provide financial assistance to those affected by natural disasters, including floods The Good Earth/Chapter 11: Streams and Floods

Streams and Floods Checkpoint 11. 22 Place a check mark in the appropriate column for each action listed at left indicating whether it is a prevention or adjustment tactic. Characteristic Flood control by. . . prevention adjustment Levee is constructed Newspaper publishes flood evacuation route New housing developments are elevated on pilings above ground Dredging removes sediment from streams Flood zone maps are available in local library Buildings are relocated outside of flood zone Dam is constructed upstream from the community Zoning regulations are enacted to prevent new construction in floodplain The Good Earth/Chapter 11: Streams and Floods

The End Go back to the Table of Contents The Good Earth/Chapter 11: Streams and Floods