Lecture_14_Ch_7_Rivers and Flooding

Lecture_14_Ch_7_Rivers and Flooding - 10/5/2011 Rivers and...

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10/5/2011 1 Rivers and Flooding Chapter 7 You will learn What watersheds are and the role they play in the natural history of rivers How scientists describe and measure rivers, including their discharge, flow, base level (datum), and longitudinal profile How rivers erode, carry, and deposit sediment What causes floods and how rivers develop floodplains How people measure and forecast floods How people attempt to control or mitigate flooding The Rock Cycle Classification: process of formation
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10/5/2011 2 The Water Cycle Hydrosphere interacts with other Earth systems in the water cycle; cycle transfers a prized resource among its reservoirs (oceans, atmosphere, on and under land) Atmosphere over the oceans is a key part of the water cycle; ~ 86% of its water vapor obtained through evaporation from seas When air rises, it cools, causing water vapor to turn into tiny droplets to form clouds. Where air temperature falls, as when air rises along mountains, the liquid water droplets condense and fall to Earth’s surface. Precipitation of rain, snow, or ice (hail) transfers water to the land Figure 2.17 The Water Cycle The water cycle transfers matter and energy among Earth systems. Moving out of the Floodplain Great 1993 Mississippi River Flood Figure 7-1 Illinois: Summer 1993 The Mississippi River floods of1993 submerged many towns, including Valmeyer and nearby Kaskaskia (shown here). Water locally reached 6.5 m (21 ft) depth in floodplain communities. Figure 7-2 Valmeyer’s New Location The 1993 flood at Valmeyer, Illinois, was the last straw for this community. The town of 900 citizens moved Valmeyer to high bluffs. Here the town’s mayor introduces the new community plan. Basic River Concepts Watersheds and divides Flow, discharge, and channel shape Base level Longitudinal profile and gradient Erosion, sediment transport, and deposition Floodplains You can find any watershed and find out its many measurements in your backyard by “surfing your watershed” on the Web.
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10/5/2011 3 Figure 7-3 The Amazon River Watershed The Amazon and its tributaries from the Andes Mountains headwaters flows east to the Atlantic Ocean. This huge watershed covers ~ 40% of South America: the main trunk of the Amazon is between 6300 and 6800 km (3900 and 4200 mi) long and 1/5 of all freshwater entering the world’s oceans comes from the Amazon . Figure 7-4 Rivers Are a Product of Their Watersheds Rivers develop, flow, and change through their watersheds—the area that contributes water to a river. Watersheds Come in Many Sizes All Earth systems interact in watersheds Its flood may exceeds (175000cms(6 M cfs) 7m sq. km (2.7 sq. mi) Flow, Discharge, and Channels Figure 7-5 Channel Cross-Sectional Area River channels of different shapes can have the same cross-sectional area. Discharge (m
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Lecture_14_Ch_7_Rivers and Flooding - 10/5/2011 Rivers and...

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