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GGR206H1 Study Guide - Midterm Guide: Lapse Rate, Groundwater Recharge, Water Cycle

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Romila Verma
Study Guide

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Chapter 1: Introduction:
1.1 Water-facts and figures
Hydrology is the science dealing with the waters of the earth, their occurrences,
distributions and circulation, their chemical and physical properties and their
interaction with the environment.
about 97% occurs as saline water in the seas and oceans -> only the remaining 3% is
fresh water (more that half is locked up in ice-sheets and glaciers and another
substantial volume occurs as virtually immobile deep groundwater)
the really mobile fresh water, which contributes frequently and actively to rainfall,
evaporation and streamflow, thus represents only about 0.3% of the global total
important to recognize that the small volume of mobile fresh water is itself distributed
unevenly in both space and time
wetland and prairie, forest and scrub, snowfield and desert, each exhibits different
regimes of precipitation, evaporation and streamflow, each offers different challenges
of understanding for the hydrologist and of water management for the planner an
engineer, and each poses different benefits and threats to human life and livelihood as
between the developed and the developing world
1.2 The changing nature of hydrology
the greatest advances came largely through work of Perrault and Mariotte, whose work
on the Seine drainage basin in northern France demonstrated that contrary to earlier
assumption, rainfall was more than adequate to account for river flow
and Halley showed that the total flow of springs and rivers could be more than
accounted for by evaporation from the oceans
challenge of modeling the global atmospheric and hydrosphere circulation in order to
better predict the hydrological and other consequences of climate variability and
climate change
another challenge is the need to respond to the ever increasing demands for water
the margin b/w global available stocks of fresh water and the amount used by human
activities will diminish further in the future -> already 10% of the world’s population is
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 floor disasters
the need for sustainable development (ie development that meets the needs of the
present without compromising the ability of future generations to meet their own
increasing recognition that water must be used more efficiently -> one way is to regard
water as both a natural resource and an economic commodity incurring costs of
abstraction, treatment and transportation to where it is required

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1.3 The hydrological cycle and system
the interdependence and continuous movement of all phases of water (ie liquid, solid,
and gas form the basis of the hydrology cycle)
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
instead 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
water vapour in the atmosphere condenses and may give rise to precipitation
the precipitation that reaches the ground surface may:
o be stored in the forms of pools, puddles and surface water which are usually
evaporated into the atmosphere quite quickly
o be stored as snow and ice before melting or sublimation occurs, possibly after
the lapse of many years or even centuries
o 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
o infiltrate through the ground surface to join existing soil water
o -> either by evaporation from the soil and vegetation cover or by throughflow
towards stream channels or by downward percolation to the underlying
groundwater where it may be held for periods ranging from weeks to millennia
o -> the groundwater component will eventually be removed either by upward
capillary movement to the soil surface or to the root zone of the vegetation
cover, whence it will be returned by evaporation to the atmosphere or by
groundwater seepage and flow into surface streams and into the oceans
a short burst of hydrological activity for a week or so may be followed by a long period
of virtual inactivity, apart from a slow redistribution of groundwater at some depth
below the surface
in cold climates the time delay b/w snowfall and the active involvement of the
precipitated moisture, after melting, in the subsequent phases of the hydrological cycle,
may range from months (seasonal snowpacks) through centuries (valley glaciers) to
millennia (Antarctic icecap) -> also increasingly the cycle us interrupted and modified
by human activities
Inflow = Outflow +/- Storage
each drainage basin can be regarded as an individual system receiving quantifiable
inputs of precipitation and transforming these via various flows and storages, into
quantifiable outputs of evaporation and stream flow
virtually every component of the drainage basin hydrological system may be modified
by human activity. The most important of these modifications result from:
o large scale modifications of channel flow and storage, for example by means of
surface changes such as afforestation, deforestation, and urbanization, which
affect surface runoff and the incidence or magnitude of flooding
o the widespread development of irrigation and land drainage

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o the large scale abstraction of groundwater and surface water for domestic and
industrial uses
Chapter 2 (Sections 2.1-2.3, 2.7): PRECIPITATION
2.1: Introduction and Definitions p.14
Precipitation controls the hydrology of a region
Knowledge of precipitation patterns in space and time is essential to understand soil
moisture, ground water recharge and river flows
Hydrologists are interested in the distribution itself... how much precipitation
occurs and when and where it falls.
Hail: special case of precipitation since even though it falls to the ground a solid, it
normally does so in temperature conditions which favour rapid melting. Therefore,
hydrologically it acts like a heavy rain shower.
Vapour: gas that is below its critical temperature so it may be easily condensed or
liquefied by small change in temperature or pressure
Vapour pressure: amount of water vapour in the air
o the warmer the air the greater amount of water vapour it can hold. Once max
amount is exceeded (by such factors of cooling) then condensation can occur.
Degree of saturation: max amount of water vapour that the air can hold before it is
Mainsource of atmospheric moisture is oceans
At any given moment the total amount of water vapour in the atmosphere
represents only 0.001% of the worlds total.
o Yet this source serves as a continuing source of supply in the form or
Environmental lapse rate: variation of air temp with height
Adiabatic: no exchange of heat
Clouds: mass of minute water droplets/ice crystals suspended in the atmosphere
appearing white and gray.
o at any given time ~1/2 of the earth’s surface is covered by clouds
o have a very important effect on the radiation balance due to their high albedo
o cloud appearance expresses air movement and different weather conditions
o in warm clouds the main cause for droplet growth are collision and
o precipitation happens when a body of moist air is cooled sufficiently for it to
become saturated and if condensation nuclei are present for water
droplets/ice crystals to form to a certain size
o common for several cloud types to occur together
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