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Surface Water Movement & Stream Development Chapter 9.1 - 9.2 Surface Water Movement • Once water reaches the Earth, what happens to it? –Runoff – water flowing downslope along Earth’s surface • Can reach a stream • Can evaporate • Can infiltrate Earth’s surface to become groundwater Surface Water Movement • What conditions determine whether water will infiltrate the surface? – Soil composition • Pore spacing & percentage of particles – Soils w/ lots of sand, infiltrate; lots of clay – harder to infiltrate – Rate of precipitation • Light, gentle infiltrates more than heavy downpour. – Vegetation – more is better – Slope – gentle to no slope is better for infiltration Stream Systems • Streams – surface water channels • Tributaries – streams that flow into other streams • Watersheds – all of the land area whose water drains into a stream system Georgia Riverbasins Stream Load & Carrying Capacity • Stream Load: the amount of material a stream carries • Load is carried in 3 ways – Materials in suspension • Particles small enough to be held up by the turbulence of the moving water – Bed load • Sediment too big to be suspended, but is rolled or pushed along by the moving water – Materials in solution • Materials dissolved in the stream’s water • Expressed in parts per million (ppm) • Carrying capacity is the stream’s ability to transport material. – Depends on velocity and amount of water in stream – affected by channel’s slope, depth, and width Stream Development • Headwaters – region where water first accumulate to supply a stream – Usually high in mountains • Stream channels – the path of a stream, with water held within its banks • Meanders – bend or curve in a stream channel caused by moving water Visualizing Erosion & Deposition in a Meander Click on picture to animate Visualizing Stream Development Click on picture to animate Deposition of Sediment • The velocity of a stream determines how much sediment it will transport and subsequently the loss of velocity dictates how much of that sediment will deposit out of the stream • Alluvial fans – in mountainous regions where the gradient suddenly decreases, the sediment is dropped quickly at the base of the mountain in a fan-shaped deposit. • Deltas - triangular deposit that forms where a stream enters a larger body of water