Earth Science, 10th edition
Chapter 4: Running Water and Groundwater
I. Earth as a system: the hydrologic cycle-illustrates the circulation of Earth’s water supply, shows the pathways and the resivours.
B. Processes involved in the cycle-the principle components of the water cycle are precipitation, evaporation and transpiration, and infiltratin and runoff.
C. Cycle is balanced-hydrologic cycle is a closed system (97 percent in oceans, approx. 3% fresh).
II. Running water
A. Streamflow-the ability of a stream to erode is largely dependant upon its velocity.
1. Factors that determine velocity
a. gradient-steepness usually measured in ft/mile
b. channel characteristics-shape, size, and roughness (friction)
c. discharge-the volume of water flowing past in a given unit of time (cubic feet per second)
B. Upstream-downstream changes – Most often, the gradient and roughness of a stream decrease downstream, while the width, depth, discharge, and velocity increase
C. Base level-lowest level to which a stream will erode it’s channel. Ultimate is ocean, but stream may have local (dam or reservoir).
D. The work of streams-water is the largest erosional agent
1. Erosion-mostly by abrasion
2. Transportation-three ways
a. dissolved-ions and molecules, usually expressed in ppm
b. suspended-largest transportation component, usually, sand, silt, and clay except in flood
c. bed-most important in stream erosion, moves by saltation.
3. Deposition-when velocity decreses, deposition occurs, particles are sorted according to mass. The general term for well sorted deposits of a stream is alluvium. Alluvial fans and deltas are depositional features of a stream or river.
E. Stream valleys-shaped by erosion.
1. Characteristics of narrow valleys-downcutting towards base level leaves charestic “v” shaped stream valley. Rapids and waterfalls are common.
2. Characteristics of wide valleys-after steam has accomplished downcutting, and has reached base level the valley becomes wide. Floodplains (flat low-lying portion of stream valley subject to inundation), and meander (looplike bend in stream or river).
F. Floods and flood control-several strategies include dams, artificial levees, and river channelization.
G. Drainage basins and patterns-the area of land that contributes water to a stream is called the drainage basin. Usually the drainage basin of one stream is separated from another by a divide (usually a ridge). Four patterns are produced by drainage systems
1. dendritic
2. radial
3. rectangular
4. trellis
III. Water beneath the surface (groundwater)
A. Largest freshwater reservoir for humans
B. Geological roles
C. Distribution and movement of groundwater
D. Features associated with groundwater
E. Environmental problems associated with groundwater
F. Geologic work of groundwater