3Recap Task : Explain the water budget graph for Athens, Greece. What implications would there be for water management in the Athens region?How will infiltration rates differ between an area of dense grassland and an urban area?RecapWater Balance
4Learning Objectives To create a storm hydrograph To interpret a storm hydrograph-linking ideas to the drainage basin
5Do you know how much water we need? Cooking, washing and flushingAnswer: 150 litresTo grow wheat needed for ½ loaf of breadAnswer: 500 litresTo grow a kilogram of riceAnswer: 2000 litresTo raise a chicken for Sunday roastAnswer: 6000 litresTo provide enough feed for a cow to make a quarter pound hamburgerAnswer: litres
6The fact is...The natural water cycle is struggling to meet our demands.½ Billion people are eating rice and wheat irrigated using water from reserves that are not being replenished.By 2025 three billion people will face chronic water shortages.
7Key DefinitionRiver discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second (cumecs).In other words, the amount of water passing through a river in a second
9Draw a Storm Hydrograph Draw on the graph:Rainfall- bar chartDischarge- line graphDraw on the Base flow line (what was it like at the start and had it returned to that at the end? A straight line will do nicely!)Now add the labels from the sheet to your graph- write them around the actual graph and draw lines to the correct part.
12Rivers & people A living graph makes you look further at a graph and link it topeople and events that liebehind it.Look at the living graph and read through the statementsDecide where the statements will fit on to the living graph.Discuss results and highlight the variety of positions which statements may fit into.Explain why the statements were put into certain places.
14Physical Factors Basin size If a basin is small it is likely that rainfall will reach the main channel more rapidly than in a larger basin where the water has much further to travel.Types of precipitationFlooding most frequently occurs after a long period of heavy rainfall, when the ground has become saturated and infiltration has been replaced by runoff.When heavy rain occurs, the rainfall intensity may be greater than the infiltration capacity of the soil, resulting in surface runoff.Heavy snowfall means that water is held in storage and river levels drop. When temperatures rise rapidly, meltwater soon reaches the main river.
15Physical FactorsRelief – in steep upland valleys, water is likely to reach the river more quickly than in gently sloping lowland areas.Rock type – if a basin has permeable rocks (ie limestone) there will be rapid infiltration and little surface runoff. If a basin has impermeable rocks (ie granite) water will not be able to pass through them and so there will be greater surface runoff.Soil type – sandy soils, with large pore spaces, allow rapid infiltration and do not encourage flooding. Clays have much smaller pore spaces; this reduces infiltration and throughflow, but encourages surface runoff and increases the flood risk.
17Geology Which rock will cause the most overland flow and why? Which rock might slow down the passage of water the most? A or B hydrograph shape?
18GeologyWhich one might be pervious?Which one would slow down the passage of water the most? A or B hydrograph shape?Which one would be most likely to flood?
19Urban Flooding. Effect of urbanization on a typical stream hydrograph Urban Flooding. Effect of urbanization on a typical stream hydrograph. Normal base flow is indicated with a dark blue line. The purple line indicates discharge after a storm, before urbanization. Following urbanization, stream discharge dramatically increases, as shown by the light blue line.