Travel Time Calculation

8/2/2019 Travel Time Calculation

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Travel Time Calculation

Dr. T. Brikowski, Geosciences Dept., UTD

Spring 2007

Introduction

o Introduction

o Velocity Method

o Graphical Velocity Method

o Upland Velocity Method

o Sheetflow Observations

o Kinematic Wave Equationo Empirical Formulas

o SCS Lag Formula

o Kirpich Method

Runoff Curves

o SCS Runoff Curve Numbers

o Infiltration-Soil Groups

o Textural Criteria for Hydrologic Soil Groups

o Runoff Curve Numbero Part II: Runoff Curve Number

o Part III: Runoff Curve Number

o Antecedent Moisture Condition

o Antecedent Rainfall Limits

o Composite CN Curves

o Connected Impervious Area Graphical Composite CN

o Unconnected Impervious Areas

o Unconnected Impervious Area Graphical Composite CN

Bibliography

About this document ...

Introduction
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Introduction.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Introduction.html#SECTION0001100000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Graphical_Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Upland_Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Sheetflow_Observations.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kinematic_Wave_Equation.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Empirical_Formulas.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Lag_Formula.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_II_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Moisture_Conditi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Rainfall_Limits.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Composite_CN_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.html#SECTION00021200000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/About_this_document.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/About_this_document.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/footnode.html#foot85http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Introduction.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Introduction.html#SECTION0001100000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Graphical_Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Upland_Velocity_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Sheetflow_Observations.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kinematic_Wave_Equation.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Empirical_Formulas.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Lag_Formula.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_II_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Moisture_Conditi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Rainfall_Limits.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Composite_CN_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.html#SECTION00021200000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/About_this_document.html


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Flood hazard often depends on the time distribution of runoff, i.e. a given amount

of precipitation can yield a large flood over urban areas, or a minimal flood over

agricultural areas

This time distribution is characterized by estimates oftravel time, usually given as

time of concentration

Time of concentration is defined as the time required for water to travel from thefarthest point of the watershed to its outlet

Typically Manning Equation or ``Velocity Method'' are used to obtain , with

different parameters for each flow regime (sheet flow, concentrated flow, channel

and pipe flow, seesummary table)

Velocity Method

Noting that velocity = , solve for time:

Velocity is usually determined using the Manning Equation

(1)

Note that the factor of ` 1.49'' is for length measured in feet, use 1.0 for metric

length. For multiple flow segments, add up the times:

Graphical Velocity Method

for convenience assume there is a relationship between roughness and hydraulicradius , then (1) can be simplified to

(3)

then is a function of land cover (for sheet flow)
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Watershed_Dynamics/Time_Parameter_Classificati.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Watershed_Dynamics/Time_Parameter_Classificati.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.html#e-Manninghttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Watershed_Dynamics/Time_Parameter_Classificati.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.html#e-Manning


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by fitting to observations, lines of velocity vs. slope can be plotted for various land

covers, and used to graphically estimate velocity

this is termed the ``Upland Method'' (Fig.1), and is really just a simplification ofthe Manning Equation

Upland Velocity Method
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Upland_Velocity_Method.html#f-uplandhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Upland_Velocity_Method.html#f-uplandhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Upland_Velocity_Method.html#f-upland


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Figure 1: Upland method, graphical velocity estimation (McCuen, 2004).

Sheetflow Observations
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#McCuen-2004http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#McCuen-2004


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Figure 2: Raindrop impact erosion and sheetflow on bare soil (Dunne and Leopold, 1978).

Note transition to channel flow at edge of field (foreground). Other examples include USGS

Everglades Factsheet .
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#Dunne-Leopold-1978http://pubs.usgs.gov/fs/2004/3123http://pubs.usgs.gov/fs/2004/3123http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#Dunne-Leopold-1978http://pubs.usgs.gov/fs/2004/3123http://pubs.usgs.gov/fs/2004/3123


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Kinematic Wave Equation

for sheet flow (Fig. 2) can often assume that hydraulic radius equals product of

rainfall intensity and travel time, then

substitute that into Manning Equation (1) and solve for travel time (in minutes),

using length in feet:

(4)

this equation is solved iteratively, since is needed only for the time of

concentration

note the equation assumes no local inflow (precip. is only water source), noponding or backwater effects, no storage effects, and that discharge is only a

function of depth.

These assumptions are only true for sheet-flow in the most distal parts of awatershed.

Generally it is better to use the Manning instead

Empirical Formulas

a variety of empirical formulas have been developed to predict for specific

watershed types, most are specialized forms of Manning equation

o FAA equation: developed from airfield drainage data, 1970

o Espey-Winslow equation, developed in 1974 predicting time to peak flow

for overland+channel flow, Houston area was main data source

o SCS lag formula (see next page), estimates time from center of mass of

excess rainfall to the peak discharge. (the lag time, where )

Many other methods exist, e.g.McCuen (1998, sec. 3.6.5)

in many wase these are obsolete with the advent of computers, but are important for

comparison purposes to older results
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Sheetflow_Observations.html#f-sheet_flow_photohttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.html#e-Manninghttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#McCuen-1998http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#McCuen-1998http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Sheetflow_Observations.html#f-sheet_flow_photohttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Velocity_Method.html#e-Manninghttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#McCuen-1998


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SCS Lag Formula

used for small watersheds ( acres) where overland flow dominates

built into the SCS TR-55 and TR-25 urban watershed models

the formula is (where is watershed length in ft, slope , and is the SCS

runoff curve number):

(5)

Kirpich Method

One important empirical method (at least in WMS) is the Kirpich Method (Kirpich, 1940).

These are simply formulas that depend only on basin length and slope, and hencecan be calculated directly from WMS-computed basin parameters:

(6)

(7)

where is channel length in ft and is channel slope ( )

Equation (6) is for small watersheds in Pennsylvania. (7) was developed for

watersheds from 1-112 acres, slope 3-10% in Tennessee.

Computed is multiplied by 0.4 for overland flow path that are concrete or

asphalt, and by 0.2 where the channel is concrete lined

Runoff Curves
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#Kirpich-1940http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.html#e-Kirpich_Penns.%23e-Kirpich_Penns.http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.html#e-Kirpich_Tenn%23e-Kirpich_Tennhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#Kirpich-1940http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.html#e-Kirpich_Penns.%23e-Kirpich_Penns.http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Kirpich_Method.html#e-Kirpich_Tenn%23e-Kirpich_Tenn


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Subsections

SCS Runoff Curve Numbers

Infiltration-Soil Groups

Textural Criteria for Hydrologic Soil Groups

Runoff Curve Number Part II: Runoff Curve Number

Part III: Runoff Curve Number Antecedent Moisture Condition

Antecedent Rainfall Limits

Composite CN Curves

Connected Impervious Area Graphical Composite CN

Unconnected Impervious Areas

Unconnected Impervious Area Graphical Composite CN

SCS Runoff Curve Numbers

the Soil Conservation Service developed curve number ( ) as an index

combining hydrologic soil group and land use factors (cover and condition)

Soil Group (Figs. 3-4) best identified using SCS County soil conservation surveys

o really represents typical infiltration rate

o modern access usually via USGS STATSGO database, land-use data also

included

earlier applications used Curve Number tables (Figs. 5-7)

Infiltration-Soil Groups
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_II_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Moisture_Conditi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Rainfall_Limits.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Composite_CN_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.html#SECTION00021200000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.html#f-soil_groups_infilthttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.html#f-soil_groups_texturehttp://water.usgs.gov/GIS/metadata/usgswrd/XML/ussoils.xmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.html#f-cn1http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.html#f-cn3http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/SCS_Runoff_Curve.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_II_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Moisture_Conditi.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Antecedent_Rainfall_Limits.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Composite_CN_Curves.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.htmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Unconnected_Impervious_Area.html#SECTION00021200000000000000000http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Infiltration_Soil_Groups.html#f-soil_groups_infilthttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Textural_Criteria_Hydrologi.html#f-soil_groups_texturehttp://water.usgs.gov/GIS/metadata/usgswrd/XML/ussoils.xmlhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.html#f-cn1http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.html#f-cn3


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Figure 3: Infiltration rate criteria for SCS Hydrologic Soil Groups (McCuen, 2004).

Textural Criteria for Hydrologic Soil

Groups


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Figure 4: Textural Criteria for SCS Hydrologic Soil Groups (McCuen, 2004).

Runoff Curve Number


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Figure 5: Runoff curve numbers for typical land use types (McCuen, 2004).

Part III: Runoff Curve Number


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Figure 7: Runoff curve numbers for typical land use types (cont.) (McCuen, 2004).

Part II: Runoff Curve Number


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16/21


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Figure 8: Seasonal rainfall limits (left) and CN adjustment (right) for antecedent moisture

conditions (McCuen, 2004).

Composite CN Curves

in urban areas, percent imperviousness highly variable


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a weighted approach is used for transitional values of imperviousness not

shown in standard tables (Figs. 5-7)

can be computed mathematically, where is the fraction of impervious area, and

98 is the curve number of completely impervious material:

(8)

or use graphical method (Fig. 9)

Connected Impervious Area Graphical

Composite CN

Figure 9: Graphical computation of composite CN curves for all impervious surfacesconnected to storm drain (SCS, 1986, Fig. 2-3).

Unconnected Impervious Area Graphical

Composite CN
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.html#f-cn1http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.html#f-cn3http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.html#f-composite_CN_connectedhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#SCS-TR55-1986http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Runoff_Curve_Number.html#f-cn1http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Part_III_Runoff.html#f-cn3http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Connected_Impervious_Area.html#f-composite_CN_connectedhttp://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#SCS-TR55-1986


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Figure 10:Graphical computation of composite CN curves for impervious surfaces not connected tostorm drain (SCS, 1986, Fig. 2-4). To use, enter right half of diagram with unconnected fraction of total

impervious area (total ) and the ratio of total unconnected impervious area to total impervious area.

Then move left to the appropriate pervious CN and read down to find the composite CN.

Bibliography

T. Dunne and L. B. Leopold.

Water in Environmental Planning.W. H. Freeman, New York, 1978.

ISBN 0-7167-0079-4.Z. P. Kirpich.

Time of concentration in small agricultural watersheds.

Civil Engineering, 10 (6): 362-, 1940.

R. H. McCuen.Hydrologic Analysis and Design.

Prentice Hall, Upper Saddle River, New Jersey, 07458, 2nd edition, 1998.

ISBN 0-13-1345958-9.URLhttp://www.prenhall.com.

R. H. McCuen.Hydrologic Analysis and Design.Prentice Hall, Upper Saddle River, New Jersey, 07458, 3rd edition, 2004.

ISBN 0-13-142424-6.

URLhttp://www.prenhall.com.

SCS.
http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#SCS-TR55-1986http://www.prenhall.com/http://www.prenhall.com/http://www.prenhall.com/http://www.prenhall.com/http://www.utdallas.edu/~brikowi/Teaching/Applied_Modeling/SurfaceWater/LectureNotes/Travel_Time/Bibliography.html#SCS-TR55-1986http://www.prenhall.com/http://www.prenhall.com/


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Urban hydrology for small watersheds.

Technical Release TR-55, Soil Conservation Service, Hydrology Unit, June 1986.

URLhttp://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.html.
http://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.htmlhttp://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.htmlhttp://www.wcc.nrcs.usda.gov/hydro/hydro-tools-models-tr55.html

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Travel Time Calculation

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