Hydrology (Finals) Flashcards
is the process in which a liquid change to the gaseous state at the free surface, below the boiling point through the transfer of heat energy
evaporation
evaporation from water bodies and soil masses together with transpiration from vegetation
evapotranspiration
rate of evaporation is dependent on:
- the vapor pressures at the water surfaces and air above
- air and water temperatures
- wind speed
- atmospheric pressure
- quality of water
- size of the water body
rate of evaporation is proportional to the difference between the saturation vapor pressure (SVP) at the water temperature (ew) and the actual vapor pressure in the air (ea)
vapor pressure
John Daltonโs law of evaporation
rate of evaporation increases with an increase in the water temperature
temperature
the amount of water evaporated from a water surface is estimated by the following methods:
- using evaporimeter data
- empirical evaporation equations
- analytical methods
are water-containing pans which are exposed to the atmosphere and the loss of water by evaporation measured in them at regular intervals
evaporimeters
a pan of diameter 1210 mm and depth 255 mm and made of unpainted GI sheet
class A evaporation pan
the pan is placed on a wooden platform of height 15 cm above ground level to allow free air circulation below the pan
class A evaporation pan
a pan of diameter 1220 mm and depth 255 mm and is made of copper sheet 0.9 mm thick, tinned inside and painted white outside
ISI standard pan
the pan is placed on a square wooden platform of width 1225 mm and heigh 100mm above the ground level below the pan
ISI standard pan
920 mm square pan made of unpainted GI sheet, 460 mm deep, and buried into the ground within 100 mm of the top
colorado sunken pan
a square pan of 900 mm sides and 450 mm deep
us geological survey floating pan
supported by drums float in the middle of a raft of size 4.25 m x 4.87m, it is set a float in a lake with a view to simulate the characteristics of a large body of water
us geological survey floating pan
lake evaporation = cp x pan evaporation
class a land pan - 0.700, 0.60-0.80
ISI pan (modified class A) - 0.875, 0.65-1.10
colorado sunken pan - 0.805, 0.75 - 0.86
USGS floating pan - 0.760, 0.70-0.82
empirical evaporation equation
๐ธ๐ฟ = ๐พ๐(๐ข)( ๐๐ โ ๐๐)
f(u) = wind speed
meyerโs formula
๐ธ๐ฟ= ๐พ๐( ๐๐โ ๐๐)(๐ + ๐๐/16 )
water budget method
๐ + ๐๐๐ + ๐๐๐ = ๐๐๐ + ๐๐๐ + ๐ธ๐ฟ + ฮ๐ + ๐๐ฟ
analytical methods of evaporation
- water-budget method
- energy-balance method
- mass-transfer method
simplest but the least reliabe
water-budget method
is application of law of conservation of energy
energy-budget method
water volume lost due to evaporation from a reservoir
๐๐ธ = ๐ด๐ธ๐๐๐ถ๐
methods to reduce evaporation losses
- reduction of surface area
- mechanical covers
- chemical films
as the area increases the rate if evaporation also increases
reduction of surface area
permanent rods over the reservoir, temporary rods and floating roof such as rafts and light -weight floating particles
mechanical cover
application of cetyl alcohol (heaxdecanol) and stearyl alcohol (octadecanol)
chemical films
process by which water leaves the body of a living plant and reaches the atmosphere as water vapor
transpiration
important factors affecting transpiration are:
atmospheric vapor pressure
temperature
wind
light intensity
characteristics of the plants
the total amount of water loss in the form of water vapors into the atmosphere from surface of the soil. canopy interception, water bodies as well as from the aerial parts of the plants
evapotranspiration
if sufficient moistureis always available to completely meet the needsof vegetayion full covering the area
potential evapotranspiration
the real evapotranspiration occurring in a specific situation
actual evapotranspiration
is the maximum quantity of water that the soil retain against the force gravity
field capacity
is the moisture content of a soil at which the moisture is no longer available in sufficient quantity to sustain the plants
permanent wilting point
hydrologic budget
๐ทโ ๐น๐โ๐ฎ๐โ๐ฌ๐๐๐=ฮ๐บ
is a special watertight tank containing a block of a soil and seat in a field of growing plants
lysimeters
measurement are usually confined to precipitation, irrigation input, surface runoff, and soil moisture
field plots
it is calculated by multiplying the reference crop evapotranspiration by coefficient K, the value of which changes with the stage of the crop
potential evapotranspiration of any other crop
potential evapotranspiration of any other crop
๐ธ๐=๐พ(๐ธ๐๐)
Blaney - Criddle Formula
๐ธ๐=2.54๐พ๐น and ๐น= ฮฃ๐โ๐ฬ ๐/100
can be defined as a flow channel into which the surface runoff from a specified basin drains
stream
the science and practice of water measurement
hydrometry
streamflow measurement techniques
direct determination stream discharge
indirect determination stream flow
direct determination stream discharge
- area-velocity methods
- dilution techniques
- electromagnetic methods
- ultrasonic method
indirect determination stream flow:
- hydraulic structures
- slope-area
classifications of stream
- perennial streams
- intermittent streams
- ephemeral streams
water flows in these streams through out the year. the primary water source can be from ground water, surface water, or combination of both
perennial streams
For part or most of the year but may carry no water during the dry season
intermittent stream
there streams flow only for a short time, usually after a large storm or snowmelt when there is an increase in water runoff
ephemeral streams
the simplest of stage measurements are made by noting the elevation of the water surface in contact with a fixed graduated staff
staff gauge
is made of a durable material with a low coefficient of expansion with respect to the both temperature and moisture
staff
it is a gauge used to measure the water-surface elevation from the above the surface such as from a bridge or similar structure
wire gauge
it overcomes this basic objection of manual staff gauge and find considerable use in stream-flow measurement practice
automatic stage recorders
is the most common type of automatic stage recorder in a stilling well is balanced by means of a counterweight over the pulley of a recorder
float-gauge recorder
in this gauge, compressed air or gas is made to bleed out at a very small rate through an outlet placed at the bottom of the river
bubble gauge
methods of streamflow measurement
volumetric method and gravimetric method
slop-area method
are applicable if the channel or the stream cross-sectional area is small and the flow is relatively slow/laminar
volumetric method and gravimetric method
it is the simplest and quickest method of determining the flow, thus may cause inaccuracies on flow measurement of large channel
volumetric method and gravimetric method
this method is used by civil engineers in the design of channels.
slope-area method
manningโs rational equation
๐ฃ=1/๐(๐ ^2/3)(๐^1/2)
r= area/perimeter
current meter
๐ฃ=๐(๐๐ )+๐
Ns = number of revolutions per seconds of the meter
a, b = constants
the use of these structures is that these structures provide a unique control section in the flow such that the discharge will become a function of the water surface elevation
control-section method
control-section method
Q = f(H)
H = water surface elevation
means the draining of flowing off of precipitation from a catchment area through a surface channel
runoff
is the portion of rainfall which flows through the rivers, streams, etc
runoff
types of runoff
surface runoff
subsurface runoff
base flow
portion of rainfall that enters streams immediately after occurring rainfall
surface runoff
amount of rainfall first enter into soil and then flows laterally towards streams without joining water table
subsurface runoff
delayed flow. water that meets the groundwater table and joining the streams or ocean
base flow
factors affecting runoff
climate factor
direction of prevailing wind
physiological factors
shape of watershed
fan shaped
fan shaped (elongated)
broad shaped
peak runoff is less
fan shaped
peak flow is more
broad shaped
which results due to an isolated storm, is typically single peaked skew distribution of discharge and is known variously as storm hydrograph, flood hydrograph or simply, hydrograph
hydrograph
it consists of flow in all the three phases of runoff, viz, surface runoff, interflow and baseflow
hydrograph
components of a hydrograph
rising limb
crest segment
recession limb
also known as, the concentration curve, represent the increase in discharge due to the gradual building u of storage in channel and over the catchment surface.
rising limb
is one of the most important parts of hydrograph as it contains the peak flow
crest segment
which extends from the point of inflection at the end of the crest segment
recession limb
it is the time from the beinning to end of the direct runoff
time base of Hydrograph (Tb)
it is the difference in time between the center of mass of net rainfall and center of mass runoff
lag time (TL)
it is the time difference between the beginnings of direct runoff
time to peak (Tp)
it is the effective rainfall duration, which causes direct runoff.
rainfall duration (Tr)
In this method, the separation of the base flow is achieved by joining with a straight line the beginning of the surface runoff to a point on the recession limb representing the end of the direct runoff.
method I
is obtained from the total storm hydrograph by separating the quick-response flow from the slow response runoff.
surface-flow hydrograph
In this method, the base flow curve existing prior to the commencement of the surface runoff is extended until it intersects the ordinate drawn at the peak.
method II
In this method, the base flow recession curve after the depletion of the flood water is extended backwards till it intersects the ordinate at the point of inflection
method III
is that part of the rainfall that becomes direct runoff at the outlet of the watershed.
effective rainfall or excess rainfall
is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells.
Groundwater
The study of the distribution and movement of groundwater
hydrogeology or groundwater hydrology.
The area where water fills the aquifer
saturated zone (or saturation zone)
this zone also known as groundwater zone is the space in which all the pores of the soil are filled with water.
Saturated Zone or phreatic zone
in this zone the soil pores are only partially saturated with water.
Zone of Aeration
this lies close to the ground surface in the major root band of the vegetation from which the water is lost to the atmosphere by evapotranspiration.
soil water zone
in this water is held by capillary action. This zone extends from the water table upwards to the limit of the capillary rise.
capillary zone
this lies between the soil water zone and the capillary fringe.
intermediate zone
is a saturated formation of earth material which not only stores water but yields it in sufficient quantity.
aquifer
it is a formation through which only seepage is possible and thus the yield is insignificant compared to aquifer
aquitard
it is a geological formation which is essentially impermeable to the flow of water.
aquiclude
it is a geological formation which is neither porous nor permeable.
aquifuge
the top surface of the saturated zone
water table
is the processes of infiltration and migration or percolation by which ground water is replaced
recharge
occurs where ground water flows into a stream, escapes at the surface in a spring, or otherwise exits the aquifer.
groundwater recharge
region above water table where water rises due to capillary forces in the porous medium.
capillary fringe
rock and water
saturated zone, phreatic zone
a geologic unit that stores and transmits water
aquifer
water is in contact with atmospheric pressure โ drill and well hit the water table
unconfined aquifer
recharge upgradient forces water to flow down and get trapped under an aquiclude.
confined aquifer
Percentage volume occupied by voids. is independent of scale
porosity
Measures the transmission property of the media and the interconnection of the pores
permeability
was a French engineer who lived in the mid-16th century.
darcy
is the water table slope and its determined by dividing the vertical difference between the recharge and discharge points by the length if flow between these points.
hydrauic gradient
๐= ๐พ๐ด(โ1โโ2)/๐
h1 - h2 = hydrauloc gradient
K = hydraulic conductivity factor
Q = discharge
Rock types such as carbonate rocks or beds of rock salt or gypsum, chemical sediments deposited in shallow seas, are extremely soluble in water
karst and sinkholes
is a hole drilled into the ground to access water contained in an aquifer.
well
are used to pull water out of the ground, and a screen filters out unwanted particles that could clog the pipe
pipe and pump
are usually bored into an unconfined water source, generally found at depths of 100 feet or less.
bored or shallow wells
are drilled into a formation consisting entirely of a natural rock formation that contains no soil and does not collapse. Their average depth is about 250 feet.
consolidated or rock wells
are drilled into a formation consisting of soil, sand, gravel or clay material that collapses upon itself.
unconsoidated or sand wells
different categories of hydraulic structures
thin plates structure
long base weirs
flumes
made of concrete, masonry, metal sheets
flumes
