Streams - Geol 111 Incised meanders(bends of San Juan River...

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1 Streams and Flooding Geol 111 Incised meanders (bends) of San Juan River Introduction • Water is the single most important agent in shaping the earth’s surface • Wears down mountains, carves valleys, levels plains (all part of erosion) & transports sediment • Civilization developed along rivers and on flood plains • Flood plains formed by sedimentation during periods of channel overflow (flooding) • U.S.: ~$1 billion/yr in damage & ~100 lives Hydrologic Cycle • Hydrosphere – all water at or near the surface of the earth •Cy c l e s between several reservoirs • Evaporation – Precipitation : into and out of atmosphere is a major process • Infiltration : into the ground • Runoff : over the surface • 100 million billion gallons per year move through the hydrologic cycle; humans use only a small portion Hydrologic cycle: processes & reservoirs Streams and their Features •S t r e am : water flowing in a channel • Drainage basin : surface area drained by a stream • Discharge : volume of water flowing past a point in a specified length of time – Depends on drainage basin size, climate, vegetation & geology
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2 Streams and drainage basins 6 North American Major Drainage Basins North American Major Drainage Basins While the Mississippi basin is the largest river basin, the basins in Canada that feed Hudson Bay and the Arctic Ocean are also sizable. The Great Basin, west of the continental divide, does not drain into a sea or ocean, but instead exits into lakes and playas 7 12 Stream Discharge Discharge (Q) – the volume of water moving past a given point in a stream (3D volume-units usually cubic feet per second [ft 3 /sec]) Velocity (v) - the “speed” of the water (units feet per second [ft/sec]) Area (A) – the cross-sectional area of the stream channel Qv A = * Discharge (measure of stream size) Stream Velocity, Gradient, and Base Level • Velocity : “speed” of flowing water; related to discharge and gradient • Gradient : steepness of slope down which a stream flows; usually steep near source and low near mouth • Longitudinal profile : elevation change along length of stream, usually concave upward • Base level : lowest elevation to which a stream can erode downward
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Streams - Geol 111 Incised meanders(bends of San Juan River...

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