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Department
Geography
Course
GGR206H1
Professor
Romila Verma
Semester
Fall

Description
The Importance of Hydrological Cycle  Water has a basic role in the climate system through the hydrologic cycle. Hydrological cycle is the interdependence and continuous movement of all phases of water (ie liquid, solid, and gas form the basis of the hydrology cycle) It is also a key process upon which other cycles operate.  water is indestructible so the total quantity of water in the hydrological cycle cannot be diminished as it changes from water vapor to liquid or solid and back again  The processes of streamflow, groundwater flow and evaporation ensure the never ending transfer of water b/w land, ocean and atmosphere, followed by its return as precipitation to the earth’s surface  The really mobile fresh water, which contributes frequently and actively to rainfall, evaporation and streamflow, represents only about 0.3% of the global total, and is distributed unevenly in both space and time  Water as a form of precipitation and water vapour, provides the following functions to the earth:  water vapour in the atmosphere condenses and forms clouds. This may give rise to precipitation and helped the earth’ heat balance because of its high albedo nature.  Water, because of its nature of high specific heat capacity, act as a cushion in extreme climate  As a source of fresh water : be stored in the forms of pools, puddles and surface water or flow over the surface into streams and lakes, from where it will move either by evaporation into the atmosphere, or by seepage toward the groundwater, or by further surface flow into the oceans  Agriculture/Plant use: the groundwater component will eventually be removed either by upward capillary movement to the soil surface or to the root zone of the vegetation covers, whereas it will be returned by evapotranspiration.  The high albedo of ice and snow help to reflect sunlight back to the universe. It is stored as snow and ice before melting or sublimation occurs, possibly after the lapse of many years or even centuries.  Water management for the planner in the future can bring different benefits and threat to human life and livelihood as between the developed and the developing world  10% of the world’s pop is now affected by chronic water scarcity  there is an urgent need for a must clearer understanding of the physical, economic, social, and political consequences of large-scale water resource development and of major irrigation and flood defense schemes which are designed to reduce the impact of drought and flood disasters  the need for sustainable development, and increasing recognition that water must be used more efficiently 7.7 In the light of growing information about climate variability and climate change, discuss the following concepts: river regimes; mean annual flow; the 100-year flood River regimes are an expression of seasonal conditions averaged over many years.  Simple Regimes  are driven largely by climate and are a reflection of the balance between rainfall and evaporation  Many small river exhibit comparatively simple regimes having one period of high water and one period of low water each year. Such regimes may result from the spring/summer melting of snowpacks or glaciers followed by a period of near zero flow during the winter months when temperatures are low and icemelt is negligible  When rainfall is evenly distributed throughout the year, low flow coincides with the peak of evaporation during the summer months and high runoff values occur during the winter months when evaporation is small  In tropical areas evaporation tends to be high throughout the year, so that the rainfall distribution is the main determinant of river regimes, with high runoff during the wet season  Complex I Regimes  characterized by four distinct phases throughout the year: two low flow and two high flow periods  The high runoff period result from snowmelt, may occur in spring and then be followed by a period of low runoff  Later in the year, a second period of high water levels and runoff may occur in the summer as a result of convectional rainfall over a ‘continental’ area, or in the autumn as a result of Mediterranean storms, or in the winter as a result of an excess of rainfall over evaporation in an oceanic area  Complex II regimes  Large rivers may flow through several distinct relief and climatic regions and may receive the waters of large tributaries which themselves flow over varied terrain. The regimes of such rivers tend to change with distance downstream.  Normally have simple or complex I regimes in their headwater reaches but downstream are gradually influenced by a variety of factors such as snow or glacier melt, rainfall and evaporation regimes.  These different inflows may either reinforce the trends found in the headwater regime or may cancel each other out. Mean Annual Flow  average amount of water that flows down a particular river, per year, expressed either as a depth (in millimetres) of water spread evenly across the entire drainage basin, or as a volume (in cubic metres) of water flowing past a given point.  are driven largely by climate and are a reflection of the balance between rainfall and evaporation 100 year Flood  A one-hundred-year flood is calculated to be the level of flood water expected to be equaled or exceeded every 100 years on average. The 100-year flood is more accurately referred to as the 1% annual probability flood, since it is a flood that has a 1% chance of being equaled or exceeded in any single year. 5.1 Discuss the role of groundwater in the hydrological cycle.  Most of the precipitation that reaches the ground surface is absorbed by the surface layers of the soil  Groundwater sustains streamflow during period of dry weather and is a major source of water in many arid regions. Due to its long residence time, areas that currently have an arid climate where there is little opportunity for water to percolate deeply, may nevertheless have significant groundwater reserves which are the result of recharge in former pluvial periods  Almost all of it is composed of precipitated atmospheric moisture that has percolated downwards through the zone of aeration  Only small quantities of groundwater are derived from connate water, which originated as sea water trapped in some rocks at the time of their deposition  Groundwater is the earth’s largest accessible store of fresh water and excluding ice-sheets and glaciers, has been estimated to account for 94 per cent of all fresh water.  The role of groundwater as a vast regulator in the hydrological cycle can be seen from the large residence time, averaging about 300 years 5.2 What types of materials make good aquifers and aquitards?  Layers of rock or unconsolidated deposits that contain sufficient saturated material to yield significant quantities of water are known as aquifers and less permeable formations that transmit water more slowly than the adjacent aquifers are commonly known as aquitards.  Aquitards restrict the movement of ground water into and out of adjacent aquifers.  A silt bed would be an aquitard in a stratigraphic sequence of alternate sand and silt layers but, if interlayered with less permeable clay beds, the silt would be an aquifer.  Most of the major aquifers are composed of sedimentary deposits formed from the erosion contrast, igneous and metamorphic rocks, formed under conditions of high temperatures and pressures, generally have few interconnected pore spaces and consequently most have only low water-bearing capacities.  The lower limit of groundwater occurs at a depth where interstices are so few and so small that further downward movement is virtually impossible. This groundwater boundary is frequently formed by a stratum of very dense rock, such as clay, slate or granite, or by the upper surface of the parent rock where the groundwater body occurs within a surface deposit of weathered material.  Alternatively, the compression of strata with depth, which results from the increasing weight of the overly rocks, means that a depth is eventually reached beyond which the interstices have been so reduced in both size and number that further water movement is effectively prevented.  The number of interstices tends generally to decrease with depth, and below about 10km all rocks may be considered to be impermeable  The depth at which this occurs will depend on the nature of the water-bearing rock, and would be shallower in a dense granite than in a deep porous sandstone 5.3 Explain, with the help of diagrams, what is meant by unconfined, confined and perched groundwater.  The upper boundary of the zone of saturation, water table, varies according to whether the groundwater is confined or unconfined. Unconfined groundwater  An unconfined aquifer has no confining bed above it and is usually open to infiltration from the surface  this boundary is normally known as the water table, which is defined as the level where the porewater pressure is equal to atmosphe
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