10 3 Sources of Fresh Water Precipitation becomes

10. 3 Sources of Fresh Water • Precipitation becomes run-off as gravity pulls water down into the groundwater, a lake or an ocean basin. • Run-off increases if: w precipitation falls on rock, as soils allow water to soak in w heavy rainfall saturates the ground so water can’t soak in w long periods of rainfall saturate the ground so water can’t soak in w water can flow quickly down a steep slope, not having time to soak in w there is no vegetation, as plants help to absorb water and hold soil with their root systems w there is human development and no soils See page 376 - 377 • Human development often alters run-off (c) Mc. Graw Hill Ryerson 2007

Drainage Basins • Drainage basins are large areas where surface water all moves towards one main river w Run-off flows into streams and smaller rivers, which are tributaries of large rivers, forming a branching system w Large rivers are separated by very high ground called divides § The Rocky Mountains form the Continental Divide, which divides BC and Alberta See page 379 (c) Mc. Graw Hill Ryerson 2007

Ground Water • Ground water is water that soaks into the ground w Rock/ground with good porosity allows more water to enter w More pores (spaces in the rock/soil), the better the porosity w An aquifer is a layer of porous rock that allows ground water to flow, almost like a river below the surface. • Humans get fresh water from w Reservoirs, natural or man-made w Wells, drilled into aquifers down to the water table, which is the top level of the zone of saturation. w The water table is very deep in See page 380 deserts, but near the surface in swamps (c) Mc. Graw Hill Ryerson 2007 w The water table rises during wet seasons

Glaciers • Almost 66% of all fresh water on Earth is in glaciers w Glaciers form from layers of snow falling over many years w Glaciers melt slowly under their own weight, and slowly flow downhill w Glaciers cover about 10% of the Earth’s surface w Alpine glaciers (aka valley) found in mountains See page 381 (c) Mc. Graw Hill Ryerson 2007

Glaciers w Continental glaciers (aka ice sheets) cover huge areas of land. § Eg. Greenland Antarctia w Glaciers flow until they § reach an ocean, where crevasses open and icebergs fall off § reach an area where warm temps allow as much melting as re-freezing, or recede if they melt faster than they can freeze Take the Section 10. 3 Quiz (c) Mc. Graw Hill Ryerson 2007