Review in Hydrology

7/30/2019 Review in Hydrology

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HYDROLOGY

Roldan Q. Pineda

June 26, 2013


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Water is the most abundant substance on earth,the principal constituent of all the living things, and a

major force constantly shaping the surface of the

earth. It is also a key factor in air-conditioning the

earth for human existence and in influencing theprogress of civilization. Hydrology, which treats all

phases of the earths water, is a subject of great

importance for people and their environment.

Introduction


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The world's total volume of water is in manydifferent forms:

Liquid- oceans, rivers and rain

Solid- glaciers Gas- invisible water vapor in the air

Water changes states as it is moved

around the planet by wind currents.

Understanding the Water Cycle


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Changes in the distribution, circulation, ortemperature of the earths waters can have far-reaching

effects.

Changes may caused by human activities.

Water Cycle


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Applications of Hydrology

Design and operations of hydraulic structures

Water supply

Wastewater treatment and disposal

Irrigation

Drainage Hydropower generation

Flood control

Navigation

Erosion and sediment control Salinity control

Pollution abatement

Recreational use of water

Fish and wildlife protection


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Water Resources

Fresh water

3%

Saline (Oceans)

97%

Earths water

Groundwater

30.1%

Icecaps and Glaciers68.7%

Surface water

0.3%Others

0.9%

Freshwater

Lakes

87% Swamps

11%

Rivers

2%

Fresh surface water

Source: en.wikipedia.org


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Surface Water Groundwater Seawater Rainwater

Sources of Natural Drinking Water

- is water in a

river, lake or freshwater wetland.

Surface water is

naturally

- is fresh water

located inthe pore space

of soil and rocks

- water that is

flowing within

aquifers below

the water table

- is precipitation

that is collectedfrom relatively

clean, above-

ground surfaces -

usually rooftops.

- is water that

has the propertyof salinity and

temperature

which controls

the density of

the water.


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There are several

forces acting on a

water droplet or ice

crystal in a cloud Winds

Atmospheric stability

Gravity

Drag (friction)

When a droplet

reaches a certain

critical mass the force

of gravity will exceedthe other forces and

precipitation will fall

Rain drops are 100X

larger than clouddroplets

Precipitation


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standard rain gauges

automated rain gauges

Measurement of Precipitation


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Measuring Precipitation with Weather

Radar

Tipping bucket rain gauge

http://en.wikipedia.org/wiki/File:Close_up_chart.JPGhttp://en.wikipedia.org/wiki/File:Tipping_Bucket_Recorder.JPG


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A disdrometer is an instrument used to

measure the drop size distribution and velocity

of falling hydrometeors. Some disdrometerscan distinguish between rain, graupel, and hail.

Measuring PrecipitationUsing Weather Satellites



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Averaging

Thiessen Polygon Method

Isohyetal Method

Interpretation of Precipitation Data


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Example: A small urban watershed has four rainfall gages as located in the figure. Total rainfall recorded at

each gage during a storm event is listed. Compute the mean aerial rainfall for this storm using Theissens

Method.

Gage Stn. Rainfall

A 81.50 mm

B 73.00 mm

C 75.25 mm

D 76.25 mm

A

D

CB

400 m 400 m

400 m

400 m

400 m

100 m

100 m

400 m400 m

300 m

300 m

300 m

200 m

A

A2 A3

A1

A4


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Rainfall Depth and Intensity

30 min 1 hour 2 hours

0 0

5 0.02 0.02

10 0.34 0.36

15 0.1 0.46

20 0.04 0.5

25 0.19 0.69

30 0.48 1.17 1.17

35 0.5 1.67 1.65

40 0.5 2.17 1.81

45 0.51 2.68 2.22

50 0.16 2.84 2.34

55 0.31 3.15 2.46

60 0.66 3.81 2.64 3.81

65 0.36 4.17 2.5 4.15

70 0.39 4.56 2.39 4.2

75 0.36 4.92 2.24 4.46

80 0.54 5.46 2.62 4.96

85 0.76 6.22 3.07 5.53

90 0.51 6.73 2.92 5.56

95 0.44 7.17 3 5.5

100 0.25 7.42 2.86 5.25

105 0.25 7.67 2.75 4.99

110 0.22 7.89 2.43 5.05

115 0.15 8.04 1.82 4.89

120 0.09 8.13 1.4 4.32 8.13

125 0.09 8.22 1.05 4.05 8.2

130 0.12 8.34 0.92 3.78 7.98

135 0.03 8.37 0.7 3.45 7.91

140 0.01 8.38 0.49 2.92 7.88

145 0.02 8.4 0.36 2.18 7.71

150 0.01 8.41 0.28 1.68 7.24

Max depth 0.76 3.07 5.56 8.2

Max int. in/hr 9.12 6.14 5.56 4.1

Time (min)

Rainfall

(in)

Cumulative

rainfall

Running totals


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1. Determine number of years of data, n

2. Set rainfall duration for analysis (5 minutely, hourly, daily, etc.)

3. Find maximum depth for duration in each year

4. Rank the depths from highest to lowest for all years

Greatest amount at top of list, rank = m = 1

Partial duration series algorithm swaps out maximum for year during n

years with with n maximum in n years (e.g., more than 1 value per year

allowed)

5. Compute return period

Return Period


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The return period or recurrence time interval T is

where n is number of years of data, m is rank of data from highest

(m=1) to lowest (m=n)

Corresponding probability = 1 / T (e.g., for t = 100 year event, the

probability = 0.01)

m

nT

1

TP

1

Return Period


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Return Period

Year

Max.

Rainfall

depth(cm)

Rankeddata rank

Return

period,

T=(n+1)/m

n=20

numberof data

Prob,P=1/T Prob in %

1931 150 222 1 21.00 0.048 5%

1932 141 205 2 10.50 0.095 10%

1933 184 192 3 7.00 0.143 14%

1934 147 184 4 5.25 0.190 19%

1935 131 184 5 4.20 0.238 24%

1936 222 182 6 3.50 0.286 29%1937 181 181 7 3.00 0.333 33%

1938 205 179 8 2.63 0.381 38%

1939 133 165 9 2.33 0.429 43%

1940 135 159 10 2.10 0.476 48%

1941 119 156 11 1.91 0.524 52%

1942 184 150 12 1.75 0.571 57%

1943 159 150 13 1.62 0.619 62%1944 150 147 14 1.50 0.667 67%

1945 192 142 15 1.40 0.714 71%

1946 179 141 16 1.31 0.762 76%

1947 142 135 17 1.24 0.810 81%

1948 165 133 18 1.17 0.857 86%

1949 156 131 19 1.11 0.905 90%

1950 182 119 20 1.05 0.952 95%


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Terminology

Evaporation process by which liquid water

passes directly to the vapor phase

Transpiration - process by which liquid water

passes from liquid to vapor through plant

metabolism

Sublimation - process by which water passesdirectly from the solid phase to the vapor phase

Evaporation


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Vapor pressure water vapor normally behaves as an

ideal gas

Partial pressure of water (vapor pressure) adds topartial pressures of the other gaseous constituents

- Water vapor is about 1-2% of total pressure

Humidity quantity of water vapor present in air

(absolute, specific or a relative value)

Specific Humidity ratio of mass of water vapor in moistair - to mass of air

Dew point temperature temperature at which air

becomes saturated at a given specific humidity

Evaporation


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Energy supply for vaporization (latent heat)

Solar radiation

Transport of vapor away from evaporative surface

Wind velocity over surface

Specific humidity gradient above surface

Vegetated surfaces

Supply of moisture to the surface

Evapotranspiration (ET)

Potential Evapotranspiration (PET) moisture supply is not limited

Factors Influencing Evaporation


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Energy Balance Method

Aerodynamic Method

Combined Method

Priestly-Taylor Method

Method Estimating Evaporation


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In any area, most rocks below a particular depth are saturated.

At equal pressure (zero pressure), water flows towards lower elevation

(downhill).At equal elevation, water flows towards lower pressure. (Pipe to faucet)

Water flows at different rates through different materials: larger holes->faster flow

Groundwater


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Direct use of groundwater

About half the domestic water use is from groundwater. Varies

regionally.

Advantages of using groundwater

much less subject to seasonal variations in availability than

surface water

slow movement leads to high biological purity

temperature is remarkably constant

available virtually everywhere if you go deep enough

Stream flow usually comes from groundwater discharge whichmeans the other half of the water supply is from groundwater

indirectly

Groundwater controls erosion, influences mass wasting, soil

processes, etc.

Importance of Groundwater


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Important processes Infiltration creating soil moisture

Subsurface flow through soil

Groundwater flow

Saturation = % of void space occupied bywater

Zone of aeration (pores contain water &

air) Soil water zone

Water moves down (up) during infiltration(evaporation)

Vadose zone Water held in place by capillary forces

Saturation is at or near field capacity exceptduring infiltration

Capillary zone Completely saturated at base

Near field capacity at the top

Water is pulled up from the water table bycapillary forces

Zones of Saturation


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Factors determining movement include Soil texture

Size soil particles

Pore space

Soil moisture content

Slope of soil or rock layer relative to direction of force

of gravity

Movements very complicated and hard to predict

Soil Water Movement


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Typical bulk groundwater flow rates range from 0.01 m/yr to 100 m/yr,

mostly in the low range. Because much groundwater flow is

channeled, the actual rates of flow are often much higher or lower.

Permeability varies tremendously. Clean sandstone may have K=0.1

m/s, while clay can have K=1E-10 m/s.

Most of the movement happens in the most permeable materials, and

the bulk of most materials act as storage. (Its sort of like roads and

parking lots/street parking).

Rates of Flow


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These are situational terms. Aquifer- a layer that yields sufficient water to

be worth pumping. Should be permeable.

Aquitard - the opposite of an aquifer, it does

not yield enough water to be worth pumping.

Rates of Flow


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Water Table and Topography


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About half the domestic water use is from groundwater. Variesregionally.

Why groundwater is good

much less subject to seasonal variations in availability than

surface water

slow movement leads to high biological purity

temperature is remarkably constant

available virtually everywhere if you go deep enough

Use of Groundwater


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Drawdown: depression of a piezometric surface (including watertable) due to pumping. Since pumping water out means lifting it,

this is important.

Cone of depression is lowering of piezometric surface due to

pumping around a well. Much more depressed near the well and

less depressed further away. For a given amount of water

withdrawal, the shape (width vs. depth) depends on hydraulic

conductivity, storativity, and layer thickness. Other things beingequal, a higher-permeability aquifer will have a broader, shallower

cone of depression. A higher-storativity aquifer will also have a

broad, shallow cone of depression. A thicker aquifer has a broader,

shallower cone of depression.

Use of Groundwater


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Use of Groundwater


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Aquifer - store & transmit Unconsolidated deposits sandand gravel, sandstones etc.

Aquicludestore, dont transmit Clays and less shale Impervious boundaries of

aquifers

Aquitardtransmit dont store Shales and less clay Leaky confining layers of

aquifers

Confined aquifer (underpressure) Bounded by impervious layers

Unconfined aquifer (phreatic,water table) Bounded by a water table

Types of Aquifer


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Hydraulic conductivity (K)

Ability of a formation to transmit

water

Storativity (S) Ability of a formation to store

water

Porosity (n)

Percent of total pore spaceoccupied by voids

Sedimentary

Material

Porosity (%)

Peat Soil 60-80

Soils 50-60

Clay 45-55

Silt 40-50

Med. to Coarse Sand 35-40

Uniform Sand 30-40

Fine to Med Sand 30-35

Gravel 30-40

Gravel and Sand 30-35

Sandstone 10-20Shale 1-10

Limestone 1-10

Aquifer Properties


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General

Process of waterpenetrating from groundinto soil

Factors affecting

infiltration Condition of soil surface,

vegetative cover, soilproperties, hydraulicconductivity, antecedentsoil moisture

Four zones

Saturated, transmission,wetting, and wetting front

depth

Wetting Zone

TransmissionZone

Transition ZoneSaturation Zone

Wetting Front

Infiltration


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Infiltration rate Rate at which water enters the soil at the surface

Cumulative infiltration

Accumulated depth of water infiltrating during given

time period

Infiltration


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- water which travels over the ground surface to a channel.

Surface Runoff


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What is a Stream? What are

its boundaries? Where doesit begin? Where does itend?

A stream is a current ofwater or other fluid. It is

anything flowing out of

a source; river, rivulet

Streamflow


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Streams are like the capillaries and blood vessels that

connect to the major arteries, the rivers. But unlikeour body's circulation system, the smaller channelsdeliver most of the water and food to the bigger ones.Without feeder streams, our rivers would not exist.

You could say a stream begins at its headwaters, oftenin the mountains, fed by an underground spring or the

runoff from rain and snow melt. Rivulets of water flowdownhill, merging together to become a stream whichcontinues, mixing with other tributaries, until they allbecome a river flowing to the sea. The mouth of ariver usually opens into the ocean in a broad baywhere fresh water and salt water mix, called an

estuary. The length of a stream may be only a few feetfrom where it emerges until it joins another stream,or it may traverse hundreds of miles, from themountains to the sea. Some streams flow year-round,others only after a storm or when snow melts in thespring.

Streamflow


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What could be more dynamic than a stream? It is

constantly changing its flow, its depth, even its bed, asanyone knows who has observed a stream in differentseasons or at different places along its course. Itscours, shifts channels, meanders, floods, erodes,carries and deposits silt. Squeeze a stream in oneplace, and like a water balloon, it bulges in another.

Where it is restricted, the stream speeds up tocompensate, eroding downstream banks or spreadingout to flood adjacent property.

Many factors shape the character of a stream as itprogresses from its headwaters to its mouth: theslope and current, the amount of water being

transported, its temperature and water chemistry.These, in turn, influence the vegetation, the animals,the bottom sediments, and the shape of the channelat any point along the stream's journey.

Streamflow

f


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Streamflow

fl


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What exactly is a Streamflow?

Stream flow is a measure of the water volume transported by a stream. It is measuredby determining the volume of water that moves by a point in a set period of time (e.g.,

cubic feet per second or gallons per hour). Flow is affected by weather and groundwater

interactions: it increases during wet seasons and decreases during dry seasons.

Stream flow or discharge is the volume of water that moves through a specific point in a

stream during a given period of time. Discharge is usually measured in units of cubic feet

per second (cfs). To determine discharge, a cross-sectional area of the stream or river is

measured. Then, the velocity of the stream is measured using a Flow Rate Sensor. The

discharge can then be calculated by multiplying the cross-sectional area by the flow

velocity.

Stream flow is an important factor in the stream ecosystem and is responsible for many

of the physical characteristics of a stream. Stream flow can also modify the chemical and

biological aspects of a stream. Aquatic plants and animals depend upon stream flow to

bring vital food and nutrients from upstream, or remove wastes downstream.

Streamflow

S fl


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Factors Influencing Flow

Velocity

Depth of stream channel

Width of stream channel

Roughness of stream

bottom

Slope or incline of

surrounding terrain

Factors Influencing

Stream Volume

Weather or climate

Seasonal changes

Merging tributaries

Human impact

Streamflow

M i S fl


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The amount of water flowing in a river is called the discharge.

Specifically, discharge is the volume of water that flows past a point during aspecific time. Discharge is usually reported as the number of cubic feet of

water passing a point each second, abbreviated as cfs (cubic feet per

second).

Across the country, discharge is measured in many ways. On some

rivers, devices called stilling wells are installed. The height of water in the

well is proportional to the discharge.

Discharge can also be measured using weirs, small "walls" built

across rivers to force the flow through a V-notch at the top. The height of the

water level in the notch indicates the amount of discharge.

Current meters can be used to measure river velocity. The measured

velocity must be multiplied by the river's cross section to calculate discharge.

Measuring Streamflow

M i St fl


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Stilling well used to measure streamflow Schematic of a stilling well and shelter at

a stream-gauging station.

The height of water passing through

the notch in the weir can be used to

measure discharge.

Current meter and weight suspended

from a bridge crane.

Measuring Streamflow

P k R ff E ti ti b R ti l M th d


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Relates peak runoff to rainfall intensity

Assumes entire catchment contributing, rainfall distributed evenly, alllosses are in coefficient

Qp = C i A

C is runoff coefficient, i is rainfall intensity (m/s), A is watershed area

(m2) and Qp is peak runoff (cms)

Note that peak runoff is important for sizing storm water conveyance

structures such as sewer pipes and culverts

Limitations of Rational Method

Runoff coefficient is not likely dependent of rainfall rate and

antecedent moisture conditions

Rainfall is not likely uniform over the catchment area so should

limit application to areas smaller than 80 has.

Higher coefficients should be used for less frequent storms given

smaller percentage of rainfall abstraction

Peak Runoff Estimation by Rational Method

W t h d


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Area draining to a stream

Streamflow generated by water

entering surface channels

Affected by

Physical, vegetative, andclimatic features

Geologic considerations

Stream Patterns

Dry periods Flow sustained from

groundwater (baseflow)http://www.epa.gov/owow/watershed/whatis.html

Watershed

St fl


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Atmospheric Water

Evapotranspiration

Precipitation

Subsurface Water Infiltration

Groundwater

Surface Water

Atmospheric Moisture

Interception

Snowpack

Surface

Soil Moisture

Groundwater

Streams and Lakes

Runoff

RainSnow

Evaporation

Evapotranspiration

Evaporation

Throughfall and

Stem Flow

Snowmelt

Infiltration

Overland

Flow

Percolation

Groundwater Flow

Channel Flow

Pervious Impervious

Energy

Watershed

Boundary

Streamflow

St fl Di h H d h


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- graph showing the flow rate as a function of timeat a given location on a stream.

-- an integral expression of the physiographic and

climatic characteristics that govern the relations

between rainfall and runoff of a particular drainage

basin.

-- two types: annual hydrograph and stormhydrograph

Streamflow or Discharge Hydrographs

Annual Hydrograph


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http://www.ncdc.noaa.gov/paleo/ctl/hydrograph.html

Annual Hydrograph

Storm Hydrograph


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Peak

Time

Discharge,

Q

Beginning of

Direct Runoff

Baseflow

RecessionBaseflow

Recession

Centroid of

Precipitation

Basin Lag

Time

of Rise

End of

Direct Runoff

Inflection

Point

Storm Hydrograph

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Review in Hydrology