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Study Guide for Exam 3

Study Guide for Exam 3 - GS 100 Winter 2003 Running Water...

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GS 100 Winter 2003 Answers to the Review Questions Running Water Chapter 9 1. Evaporation, primarily from the ocean, transport via the atmosphere, and eventually precipitation back to the surface. If the water falls on the continents, much will find its way back to the atmosphere by evaporation and transpiration. However, some water will soak in (infiltration) and runoff. 2. Most precipitation originates by evaporation from the oceans. Over time, water evaporated from the oceans is replenished by inflow of freshwater from rivers and streams. Continental ice sheets and glaciers have a strong effect on sea level changes. Expanding glacial ice volumes result in lowered sea level, shrinking ice sheets and glaciers effect rising sea level. 3. Textural properties of the surface material, kinds and abundance of vegetation, topography, and delivery mode of the moisture all have important effects on infiltration capacity. Permeable, initially unsaturated, highly porous regolith can hold up to 30 percent or more of its volume as water when fully saturated. Of course, the infiltration capacity of any porous material declines as the percentage of unsaturated pore space declines. Impermeable, surficial materials such as massive bedrock and asphalt paving prevent infiltration so moisture runs off or evaporates. Water infiltrates more readily into moist, unsaturated regolith than into dry regolith. Dense, vegetative cover enhances infiltration because soils are typically moist and porous, thus runoff is retarded. In forested areas, trees slow down the rate at which precipitation is delivered to the land surface, and considerable moisture is temporarily stored in humus and forest litter. On gentle tree covered slopes and flat lying terrain, slow runoff enhances infiltration. Runoff is accelerated on steep slopes and in areas with sparse vegetation, and infiltration decreases accordingly. Dense, vegetative cover enhances infiltration because soils are typically moist and porous, thus runoff is retarded. In forested areas, trees slow down the rate at which precipitation is delivered to the land surface, and considerable moisture is temporarily stored in humus and forest litter. On gentle tree covered slopes and flat lying terrain, slow runoff enhances infiltration. Runoff is accelerated on steep slopes and in areas with sparse vegetation, and infiltration decreases accordingly. 4. The gradient is the drop in elevation of the stream divided by the length of the flow path. Thus the gradient is 2000 m/250 km or 8 m/km. 5. The new gradient would be 2000 m/500 km or 4 m/km. If a fairly straight channel should develop meanders, the flow path would lengthen without any change in the elevation drop; thus the gradient is lowered. In this example, the length of the stream doubled so the gradient decreased by 50%.
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