Presentation on theme: "Topic 8: Water Cycle and Climate"— Presentation transcript:
1 Topic 8: Water Cycle and Climate What is the water cycle?~The water cycle is also called the hydrologic cycle. It is a model used to illustrate the movement and the phase changes of water at and near the Earth's surface.~It is fueled by the sun.
2 What happens when precipitation falls on the ground? ~It can be stored or retained on the surface as ice or snow (water retention).~It can infiltrate or seep (sink into) the Earth’s surface.~It can flow over the Earth’s surface as runoff.~It can be evaporated or transpired (both of these together is called evapotranspiration).
3 Factors Affecting Infiltration ** Remember: Infiltration means to sink into. **Ex: Watering a plantSlope of the LandSortingDegree of SaturationShapePorosityCapillarityPermeabilityVegetationPackingLand Use
4 Slope of the Land The steeper the slope (gradient), the less the infiltration or seepage--- inverse or indirect relationship
5 Degree of Saturation The more saturated the loose Earth materials are, the less the infiltration--- inverse or indirect relationshipWater infiltrates into the ground until it meets the interface between the zone of saturation and the zone of aerationThis interface is the WATER TABLEThe depth of the water table below the surface varies with the amount of infiltrationSubsurface water below the water table is called GROUND WATER
6 PorosityPorosity is the percentage of open space (pores and cracks) in a material compared to its total volumeGenerally: the greater the porosity, the greater the amount of infiltration that can occur---Direct RelationshipDependent upon shape
7 Shape Well rounded particles have a greater porosity. Round particles = more pore space, higher porosity, and more infiltration Angular particles = less pore space, less porosity, and less infiltration
8 PackingThe closer the particles are packed together, the lower the porosityTherefore if you have a lower porosity, infiltration will also be lower.
9 Sorting Sorted = higher porosity or pore space If all the particles in a material are about the same size, they are said to be sortedIf the particles are of mixed sizes, they are said to be unsortedSorted = higher porosity or pore spaceUnsorted = lower porosity because the smaller particles fill in the pore space
10 PermeabilityThe ability of a material to allow fluids such as water to pass through it. Larger particles will increase permeability, because pore space is larger.**Impermeability may be due to tight packing or cementing of particles, which seals off the pores from one another.ex: ice in the winter
11 CapillarityThe process by which water is drawn into openings due to the attractive force between water molecules and the surrounding earth materials. As the particles decrease, capillarity increases.When water moves upward against gravity, it is called capillary action.ex: How plants take water from the soil
12 VegetationGrasses, trees and other plant types capture falling precipitation on leaves and branches, keeping that water from being absorbed into the EarthIf any water gets through the vegetation, the velocity of the water will be reduced and this will give the ground more time to absorb the waterGround without vegetation usually has high runoff and low infiltration rates
13 Land UseRoads, parking lots, and buildings create surfaces that are not longer permeable.These impermeable surfaces often channel runoff.Farming, cutting down trees and grazing animals will reduce vegetation and therefore decrease permeability.
14 Factors Affecting Runoff and Stream Discharge Runoff can occur when:The rate of precipitation exceeds the permeability rateThe pore space of loose material or rock is saturated with waterThe slope of the surface is too great to allow infiltrationThe water on the surface has not evaporated**The greater the runoff, the greater the amount of stream discharge (volume of water flowing past a certain spot in a stream in a specific amount of time.)**UNITS FOR STREAM DISCHARGE = meters/sec**Flooding occurs when a stream overflows its normal channel**