(c) McGraw Hill Ryerson 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:  precipitation falls on rock, as soils allow water to soak in  heavy rainfall saturates the ground so water can’t soak in  long periods of rainfall saturate the ground so water can’t soak in  water can flow quickly down a steep slope, not having time to soak in  there is no vegetation, as plants help to absorb water and hold soil with their root systems  there is human development and no soils Human development often alters run-off See page

(c) McGraw Hill Ryerson 2007 Drainage Basins Drainage basins are large areas where surface water all moves towards one main river  Run-off flows into streams and smaller rivers, which are tributaries of large rivers, forming a branching system  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) McGraw Hill Ryerson 2007 Ground Water Ground water is water that soaks into the ground  Rock/ground with good porosity allows more water to enter  More pores (spaces in the rock/soil), the better the porosity  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  Reservoirs, natural or man-made  Wells, drilled into aquifers down to the water table, which is the top level of the zone of saturation.  The water table is very deep in deserts, but near the surface in swamps  The water table rises during wet seasons See page 380

(c) McGraw Hill Ryerson 2007 Glaciers Almost 66% of all fresh water on Earth is in glaciers  Glaciers form from layers of snow falling over many years  Glaciers melt slowly under their own weight, and slowly flow downhill  Glaciers cover about 10% of the Earth’s surface  Alpine glaciers (aka valley) found in mountains  Continental glaciers (aka ice sheets) cover huge areas of land.  Eg. Greenland and Antarctia  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 See page 381 Take the Section 10.3 Quizction 10.3 Quiz