FLORIDA INTERNATIONAL UNIVERSITY Department of Civil and Environmental Engineering

College of Engineering and Computing Miami, Florida

Civil Engineering PE Exam Refresher

Hydrologic Engineering

Fernando R. Miralles-Wilhelm, Ph.D., P.E., D.E.E.

Associate Professor of Water Resources Engineering PN: (305) 348-3653 FN: (305) 348-2800

E-mail: miralles@fiu.edu

Hydrology Concepts, Principles and Applications

1) Hydrologic Cycle

2) Hydrologic Cycle Components

a) Precipitation b) Evaporation and transpiration c) Infiltration d) Surface Runoff e) Groundwater Flow

3) Hydrologic Calculations

a) Rainfall data b) Runoff depth c) Time of Concentration d) Rational formula e) CN-method f) Infiltration data g) Evapotranspiration data h) Groundwater flow i) Well hydraulics

It never stops moving, it never goes away

Hydrologic EngineeringPE Refresher Course

Review OutlineReview Outline

Hydrologic CycleHydrologic Cycle Rainfall data

S f R ff Surface Runoff Evaporation and Transpiration Infiltration and Groundwater Flow Water balance calculationsWater balance calculations

The Hydrologic CycleThe Hydrologic Cycle

Lets take it from the top: RainfallLets take it from the top: Rainfall

How much rain does my site get?How much rain does my site get?

D l k t h t t ( i l i f ll Do we look at short term (single rainfall events) or longer term (seasonal, annual)?

What aspect of my design is affected by p y g yrainfall?

Rainfall: sources of dataRainfall: sources of data

National/International: NOAA NationalNational/International: NOAA, National Weather Service, World Climate

State: SFWMD in Florida

Local: county water agencies (Boston y g (Water and Sewer)

Rainfall DataRainfall DataAnnual Rainfall in the Continental US, 1895-2003Source: NOAA (www noaa gov)Source: NOAA (www.noaa.gov)

Rainfall DataRainfall DataAnnual Rainfall in Key West, FL, 1895-2003Source: NOAA (www noaa gov)Source: NOAA (www.noaa.gov)

Rainfall DataRainfall DataBAGHDAD, IRAQWeather station BAGHDAD is at about 33 22N 44 20EWeather station BAGHDAD is at about 33.22 N 44.20 E. Average Rainfall

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year

mm 27.1 27.5 26.9 18.8 7.3 0.0 0.0 0.2 0.1 2.6 20.0 26.3 154.8

inches 1.1 1.1 1.1 0.7 0.3 0.0 0.0 0.0 0.0 0.1 0.8 1.0 6.1es

Source: BAGHDAD data derived from GHCN 1. 967 months between 1888 and 1990

Are there regulatory requirements?Are there regulatory requirements?Figure 1: SFWMD 25-Year 72-Hour Design Storm

11 50012.00012.50013.00013.50014.00014.50015.000

7.5008.0008.5009.0009.500

10.00010.50011.00011.500

3 0003.5004.0004.5005.0005.5006.0006.5007.000

0.0000.5001.0001.5002.0002.5003.000

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00

Ti m e ( H our s)

Rainfall CharacteristicsRainfall Characteristics

Depth: volume of rainfall per unit area ofDepth: volume of rainfall per unit area of watershed

Duration: elapsed time of a rainfall event Duration: elapsed time of a rainfall event Intensity: instantaneous rate of change of

i f ll d th ith tirainfall depth with time Return Period: statistical average of

separation time between events of similar depth, duration and intensity

I t it D ti FIntensity-Duration-Frequency (IDF) Curves(IDF) Curves

ai cd bt

i)( += d )(

a, b, c are coefficients fitted to datatd is the rainfall duration

Following water: Surface RunoffFollowing water: Surface Runoff

Depends on type of soil and slopeDepends on type of soil and slope Should be a fraction of rainfall, since other

fractions either infiltrate into the soilfractions either infiltrate into the soil, evaporate or are transpired by vegetation

Surface RunoffSurface RunoffFound as: The Rational Method

Q = C x i x AQ C x i x A

Where:

Q = Maximum (or Peak) Surface Runoff Rate (cfs)C = Runoff CoefficientC = Runoff CoefficientI = Rainfall Intensity (in/hr)A = Site Area (acre)A Site Area (acre)

Surface RunoffSurface RunoffSoil Classification Groups

A: Sand and siltsB: Sandy loam (muddy) soilsC: Clayey loam (muddy) soilsC: Clayey loam (muddy) soilsD: Clay (swell when wet)

Source: McCuen [1998]: Hydrologic Analysis and DesignHydrologic Analysis and Design,Prentice Hall

Are there regulatory requirements?Are there regulatory requirements?

Typically, the post-development surface runoffTypically, the post development surface runoff should not exceed pre-development values

Figure I-1Figure I 1 Comparison of Pre- and Post-development Hydrographs in an Upstream Catchment

50

30

35

40

45

c

f

s

)

Pre-development

10

15

20

25

F

l

o

w

(

c

Post-development with peak flow control

0

5

5 10 15 20 25 30Time (hours)

Where do we put the excess ?water?

Development typically means moreDevelopment typically means more impervious areas (increase C more runoff))

If we are not allowed to increase the peak surface runoff, there will be excess water post-development

Need to store water in storage basins, gdetention ponds, or reservoirs (canals, ponds, lakes); this is known as t t tstormwater management

Stormwater ManagementStormwater Management

Henderson Creek (Belle Meade, FL)

Stormwater ManagementStormwater Management

Stormwater drainage system, Immokalee, FL

Stormwater ManagementStormwater Management

Stormwater drainage canal, Kingston, Jamaica

How much storage do I need?How much storage do I need?

The volume of excess water will be theThe volume of excess water will be the difference between the surface runoff volumes post-prevolumes post pre

This is the volume of storage you will need to insure that peak runoff is not exceededto insure that peak runoff is not exceeded

Do you have it or do you need to build it? Thi t i t itti ith l l dThis gets into permitting with local and state agencies

Runoff CharacteristicsRunoff Characteristics

Depth: volume of runoff generated per unitDepth: volume of runoff generated per unit watershed area

Time of concentration: travel time of water Time of concentration: travel time of water from the furthermost point in the watershed to the outletwatershed to the outlet

Runoff hydrograph

Runoff DepthRunoff Depth

Calculated using the NRCS (formerlyCalculated using the NRCS (formerly SCS) TR-55 Method

Curve Number (CN) is calculated based Curve Number (CN) is calculated based on soil type and land useCN i dj t d f t d t ff CN is adjusted for antecedent runoff conditions

Runoff depth is calculated from the adjusted CN

Runoff DepthRunoff DepthII

I CNCNCN058010

2.4=I: Dry soilsIICN058.010

II: Normal moisture conditions (from table)III: Soil is wet; at or near saturation

Runoff Depth (in) is calculated as:II

IIIII CN

CNCN13.010

23+=

Runoff Depth (in) is calculated as:

)8.0()2.0( 2

SPSPR +

=)8.0( SP +

Where P is the rainfall depth in inches, and S is given by:

101000S 101000 =CN

S

Time of ConcentrationTime of Concentration6.0)(996 nL

3.00

4.0

)(99.6SqnLtC =

tC = minutesn = Manning roughness coefn = Manning roughness coefL = flow path lengthq= excess rainfall (mm/hr)S l d lS0 = land slope

Runoff HydrographRunoff Hydrograph

NRCS Triangular HydrographNRCS Triangular Hydrograph

Note: QP from RationalMethod and tP is time ofconcentration.

NRCS Dimensionless Unit Hydrograph

EvaporationEvaporation

Linkage between the hydrologic andLinkage between the hydrologic and energy (sun) cycles; energy is transformed to moisture (humidity)( y)

The rate of evaporation (how much, howThe rate of evaporation (how much, how quick) depends primarily on temperature

Requires knowing how much energy is required to evaporate (dry) a drop of waterrequired to evaporate (dry) a drop of water

EvaporationEvaporationFound by evaporation pans

Actual Evaporation =

Pan Evaporation x 0.70

TranspirationTranspiration

Vegetation uptake and release of water forVegetation uptake and release of water for metabolic (growth) purposes

Uptake takes place through the roots

Release takes place through the leaves (stomata)(sto ata)

Vegetation functions as a pass-through forVegetation functions as a pass through for water

EvapotranspirationSource: Laio et al., AdvancesIn Water Resources 24, p. 708, 2001

Evapotranspiration

2001

Source: Hanson U S GeologicalSource: Hanson, U.S. Geological Survey Water-Supply Paper 2375,1991

InfiltrationInfiltration

Leakage of water through the groundLeakage of water through the ground surface and into aquifers

Soil tends to hold-up some of the water; d d i lsoda and ice analogy

Actual infiltration does not exceed the soils infiltration capacityp y

Infiltration Capacity MeasurementInfiltration Capacity MeasurementVery site specific !!!

Double-Ring Infiltrometer

Groundwater FlowGroundwater Flow Aquifers and aquifer properties Darcys equation Well drawdownWell drawdown

AquifersAquifers Portion of geologic porous material that is

able to store and transmit waterable to store and transmit water

Aquifer propertiesAquifer properties

Porosity (n): fraction of porous material volumePorosity (n): fraction of porous material volume that is void (%)

Permeability (k): measure of typical pore size y ( ) yp p(units of L2)

Hydraulic conductivity (K): ability of the media to y y ( ) ytransmit water (units of LT-1)

Storage coefficient (S): capacity of porous media to store water, expressed as volume of water stored per unit media volume (dimensionless)

About k and KkgK =About k and K

Darcys EquationDarcy s EquationhKAQ =

K: hydraulic conductivityL

KAQ = K: hydraulic conductivity A: cross sectional area (perpendicular to

flow);flow); h/L = hydraulic gradient (head change

per unit length of flow)per unit length of flow) Notice that flow occurs from higher to

lower head (basic hydraulics)lower head (basic hydraulics)

Groundwater drawdown near a wellGroundwater drawdown near a well

Pumping near a well creates a localizedPumping near a well creates a localized depression in the groundwater level (water table)table)

This depression diminishes with distance from the pumping location (r)from the pumping location (r).

Drawdown (s) is defined as the head diff b t th b f d ftdifference between the before and after pumping, i.e., s = h-y

Calculating groundwater drawdownCalculating groundwater drawdown

)(2 yyKY22 )( yyK

=2

12

ln

)(2

rr

yyKYQ

=2

12

ln

)(r

yyKQ

1r 1rUnconfined Aquifer Confined Aquifer

Water Budget for a SiteWater Budget for a SiteRainfall

EvaporationTranspiration

Surface RunoffSITE

I filt ti

Surface Runoff

Infiltration

Water BudgetWater Budget

[INs] [OUTs] = [Net][INs] [OUTs] = [Net]

[IN ] R i f ll [INs] = Rainfall

[OUTs] = Evap + Trans + Inf + Runoff

[Net] = Change in surface water depth = dd

Water BudgetWater Budget

So we have:So, we have:

d = R (Q + E + T + I)

This budget must be made over a defined ti i d ( th d )time period (year, season, month, day)

What you need to knowWhat you need to know

R: rainfall intensity (i)R: rainfall intensity (i)

Surface Runoff: runoff coefficient (C) site Surface Runoff: runoff coefficient (C), site area (A)

Evapotranspiration: www.usgs.gov

Infiltration: local site measurement

Calculation Example: Las Vegas, NVNV

Site area: 5000 acre, Soil Type B, flat slopeSite area: 5000 acre, Soil Type B, flat slope Rainfall Intensity = 7 in/yr Evapotranspiration Rate (E) = 4 5 in/yrEvapotranspiration Rate (E) = 4.5 in/yr Change in surface water depth d= 0 (arid area) Before development: 82% open land; 18% Before development: 82% open land; 18%

paved roads; After development: 52% residential; 18% paved After development: 52% residential; 18% paved

roads; 16% open land; 14% parking lots, schools, commercial,

Calculation ExampleCalculation Example Before: C = 0.82 x 0.08 + 0.18 x 0.85 =

0 220.22

After: C = 0.52 x 0.17 + 0.18 x 0.85 + 0.16 x 0.08 + 0.14 x 0.85 = 0.37

So, development increases the surface runoff coefficient, and therefore the runoff water (lesser water availability, higher fl d i k)flood risk)

Calculation ExampleCalculation ExampleBefore water budget (annual basis): Rainfall: 7 in/yr x 1 ft/12 in = 0.58 ft/yrRunoff: 0.22 x 0.58 ft/yr = 0.13 ft/yrET: 4.5 in/yr x 1 ft/12 in = 0.38 ft/yrInfiltration: I = R - Q ET (d=0)

Before: 0.58-0.13-0.38 =0.06 ft/yr = 0.7 in annually

After: 0.58-0.22-0.38=-0.02 ft/yr = -0.2 in annually

Conceptual SolutionConceptual Solution

Need to capture excess surface runoffNeed to capture excess surface runoff generated by development.

To break even (no net water loss due to d l t) ld d t b ilddevelopment), you would need to build a 0.9 in x 5000 acre = 375 acre-ft reservoir,

hi h ld l i h th i filt ti twhich would replenish the infiltration water