Running Water and Groundwater Oceans – 97 % Glaciers/ice – 2 % Freshwater - < 1 % Water cycle = the continuous circulation of earth’s water supply It is powered by the sun
Evaporation = liquid to gas Condensation = gas to liquid (forms clouds) Precipitation = water (s,l ) returns to earth Infiltration = water that soaks into ground Runoff = water that flows across the ground Transpiration = water that plants release into the atmosphere (gas to liquid)
Earth’s water cycle is balanced Balanced = earth’s annual precipitation = the amount that evaporates Local imbalances do exist like droughts and floods
Stream Flow Velocity is the distance that water travels in a period of time. (some slow some fast) Highest velocities in the center of channel Velocity fastest on the outside bank/bend when a steam bends/curves The ability of a stream to erode & transport materials depends largely on its velocity
5 Stream Velocity Factors Gradient = slope (how steep or flat) Shape = crooked vs straight Size = wide vs narrow & deep vs shallow Roughness = smooth vs rough Discharge = the volume of water flowing past a certain point per unit of time (m3/s)
Stream Profile Changes • Profile - a cross-sectional stream view • Gradient and roughness decrease as you go downstream • Discharge, velocity, depth, and width increases as you move downstream • The ability of a stream to erode increases as the discharge increases.
Stream Terms • Tributary – anything that empties into another stream • Base level – the lowest point to which a stream can erode its channel • Meander – bends/curves in a river/stream • Oxbow lake – a meander that gets cut off from the main stream and form a small lake.
Stream Erosion • The ability of stream to carry a load is dependent upon 2 factors: • Competence - the largest particles the stream is transporting • Capacity – the maximum load it can carry • Steams generally erode “V” shaped valleys & channels in three ways • Abrasion • Grinding • Dissolving soluble materials
Stream Deposition • As the stream slows down material/alluvium begins to settle out • Larger materials settle out first • Delta – a triangular accumulation of sediment formed where a stream enters a lake/ocean • Levee – accumulation of sediment along the river banks • Rivers carve
3 Stages of Stream Development 1 Young – fast, straight, narrow, rapids 2 Mature – slower, meanders, wider 3 Old – slowest, meanders/oxbows, widest
Flooding • Flood plain – flat areas along rivers that occasionally flood • Flood contribution factors: • Paving • Excess precipitation • Methods of control • Dams and levees • Limiting development
Drainage basin - the land area that contributes water to a stream • Divide – imaginary line that separates one drainage basin of one stream from another • Drainage patterns • Dendritic • Radial • Braided • Trellis/rectangular
Groundwater • Zone of saturation – area below ground where all the pore spaces are completely filled with water • Zone of aeration – all the pore spaces are not completely filled with water • Water table – the line that divides the two
Groundwater • Porosity – the percentage of the total volume of rock (or sediment) that consists of pore spaces • Permeability – how well water moves through the rock/sediment • Well rounded and well sorted grains = high porosity • Aquifer – rock layers or sediment that allow groundwater to flow freely (sandstone) • Aquitard – does not allow groundwater freely to flow freely (shale)
Springs – form whenever the water table intersects the surface of the ground • Hot springs – water is heated from magma just below the surface • Geysers – intermittent hot spring/fountain that periodically erupts (Old Faithful) • Wells – a hole bored into the zone of saturation • A pump is needed • Cone of depression • Artesian wells – groundwater rises on its own under pressure and no pump is needed • Read pages 175/176 (env probs)
Caverns • A naturally formed underground chamber • Usually forms in limestone from carbonic acid dissolving the rock • Travertine – Calcium carbonate deposits • Stalactites, stalagmites, soda straws, curtains/ribbons, flowstone, etc • Karst topography – limestone areas with many caves and sinkholes (collapsed caves)