Watershed Modeling using
HEC-HMS and EPA-SWMM
©T. G. Cleveland, Ph.D., P.E.
10 July 2012
Lesson 3
Outline
•
•
•
•
Precipitation
Hyetographs
Design Storms
Precipitation in HEC-HMS
– Exercise: Minimal HMS Model and Texas DDF
Precipitation
• Driver of rainfall-runoff models
– Event
– Continuous
Hyetographs
• The plot of depth versus time (or intensity
versus time) is a hyetograph.
Hyetographs
• The plot of depth versus time (or intensity
versus time) is a hyetograph.
Design Storms
•
Precipitation pattern defined for use in
the design of hydrologic system
–
–
Serves as an input to the hydrologic system
Can by defined by:
•
•
Hyetograph (time distribution of rainfall)
Isohyetal map (spatial distribution of rainfall)
Design Storm Estimates
• Could use observed data and prepare your
own Depth-Duration-Frequency relationship
– Outside scope of this course.
• Use existing Depth-Duration-Frequency (DDF)
or Intensity-Duration-Frequency (IDF) tools for
a study area
– These produce point estimates!
– If area on the large side, consider ARF.
Module 11: Design Storms
•
WRI 99-4267 ARF for
Texas Design Storms
–
–
A design storm for a point is
the depth of precipitation that
has a specified duration and
frequency (recurrence
interval).
The effective depth often is
computed by multiplying the
design-storm depth by a
“depth-area correction factor”
or an “areal-reduction factor.”
ARF in Texas
Region of Unit Hydrograph applicability
ARF in Texas
Concept of IDF for Design
• Estimate intensity for
5-yr return period for a
30-minute duration
i ~ 2.75 inches/hour
Design Storms for Texas
• TP-40 - Maps of storm depths for different
storm durations and probabilities
Design Storms for Texas
• HY-35 Maps of storm depths for different
storm durations and probabilities
TP40, HY35 both have
interpolation guidance to
construct values between
mapped values.
Design Storms for Texas
• TxDOT spreadsheet that tabulates information
in the maps. Beware it is units dependent!
http://onlinemanuals.txdot.gov/txdotmanuals/hyd/ebdlkup.xls
Design Storms for Texas
• Link is good (verified 5 AUG 11)
– Reports intensity instead of depth. Multiply by
time to recover depth.
Author added this row, not in on-line version
http://onlinemanuals.txdot.gov/txdotmanuals/hyd/ebdlkup.xls
Design Storms (elsewhere)
• NOAA Atlas-14
– On-line collection
of interactive
maps.
– Select a location,
and the atlas
generates DDF
information.
Design Storms for Texas
• What the spreadsheet and the maps
represent is a hyperbolic model that relates
time and intensity.
b
I
e
(TC  d)
• The values e,b, and d parameterize the model.
• The value Tc has meaning of averaging time, although usually treated as a
time of concentration.

Design Storms for Texas
D moves this “knee” LEFT/RIGHT
• The values e,b, and d
parameterize the
model.
• The shaded polygon is
a hull that encloses
TP-40 and HY-35 for
Harris Co., TX (barely
visible open circles)
• The “design
equation” curve is the
EBDLKUP.xls curve for
Harris Co., TX
B moves this curve UP/DOWN
E changes slope of the curve
Design Storms for Texas
D moves this “knee” LEFT/RIGHT
• Aside:
– The “blue” cloud is a
simulation using the
empirical hyetographs
and PP1725 for Harris
Co.
– The solid red dots are
maximum observed
intensity regardless of
location (some dots
are from Texas)
– The empirical curves
represent an
alternative model.
B moves this curve UP/DOWN
E changes slope of the curve
Design Storms for Texas
• DDF Atlas
– Alternative to TP40, HY35, and
EBDLKUP.
– Includes more recent data (20 years)
than these other tools
– Provides guidance for interpolation
and extrapolation
– Works in depth – the native unit in
HMS
Rainfall Depth
• Look up depths by
recurrence interval, STORM
duration, and location.
Local Information
• DDF for Austin, TX
Local Information
• IDF for Houston, TX
• Most Metropolitan areas in
Texas (USA) have similar
DDF/IDF charts and tables
published.
• Serve as a basis for Design
Storms
Design Precipitation Hyetographs
•
Ultimately are interested in entire
hyetographs and not just the depths or
average intensities.
–
Techniques for developing design precipitation
hyetographs
1.
2.
3.
4.
SCS method
Triangular hyetograph method
Using IDF relationships
Empirical Hyetographs (Texas specific)
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS Method
•SCS
(1973) analyzed DDF to develop dimensionless rainfall
temporal patterns called type curves for four different regions
in the US.
•SCS type curves are in the form of percentage mass
(cumulative) curves based on 24-hr rainfall of the desired
frequency.
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS Method
•SCS
(1973) analyzed DDF to develop dimensionless rainfall
temporal patterns called type curves for four different regions
in the US.
•SCS type curves are in the form of percentage mass
(cumulative) curves based on 24-hr rainfall of the desired
frequency.
•If a single precipitation depth of desired frequency is known,
the SCS type curve is rescaled (multiplied by the known
number) to get the time distribution.
•For durations less than 24 hr, the steepest part of the type
curve for required duration is used
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS Method
If a single precipitation depth of desired
frequency is known, the SCS type curve is
rescaled (multiplied by the known number) to
get the time distribution.
•
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS Method
•For
durations less than 24 hr, the steepest part of the
type curve for required duration is used (i.e. 6-hour as
shown)
•HEC-HMS
has SCS built-in, but does not rescale time – storm must be 24hours (or analyst rescales external to the program)
1.0
0.0
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS type curves for Texas (II&III)
SCS 24-Hour Rainfall Distributions
SCS 24-Hour Rainfall Distributions
T (hrs)
T (hrs)
Fraction of 24-hr
rainfall
Type II
Type III
Fraction of 24-hr rainfall
Type II
Type III
0.0
0.000
0.000
11.5
0.283
0.298
1.0
0.011
0.010
11.8
0.357
0.339
2.0
0.022
0.020
12.0
0.663
0.500
3.0
0.034
0.031
12.5
0.735
0.702
4.0
0.048
0.043
13.0
0.772
0.751
5.0
0.063
0.057
13.5
0.799
0.785
6.0
0.080
0.072
14.0
0.820
0.811
7.0
0.098
0.089
15.0
0.854
0.854
8.0
0.120
0.115
16.0
0.880
0.886
8.5
0.133
0.130
17.0
0.903
0.910
0.922
0.928
0.938
0.943
9.0
9.5
Not 0.147
much difference
in the two 18.0
0.148
curves
space!19.0
0.163in dimensionless
0.167
9.8
0.172
0.178
20.0
0.952
0.957
10.0
0.181
0.189
21.0
0.964
0.969
10.5
0.204
0.216
22.0
0.976
0.981
11.0
0.235
0.250
23.0
0.988
0.991
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
24.0
1.000
1.000
SCS Method Steps
•
Given Td and frequency/T, find the design
hyetograph
1. Compute P/i (from DDF/IDF curves or equations)
2. Pick a SCS type curve based on the location
3. If Td = 24 hour, multiply (rescale) the type curve with P to
get the design mass curve
1.
If Td is less than 24 hr, pick the steepest part of the type curve
for rescaling
4. Get the incremental precipitation from the rescaled
mass curve to develop the design hyetograph
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
Example 9 – SCS Method
• Find - rainfall hyetograph for a 25-year, 24-hour duration SCS
Type-III storm in Harris County using a one-hour time
increment
• a = 81, b = 7.7, c = 0.724 (from Tx-DOT hydraulic manual)
i
a
81

 0.417in / hr
c
t  b 24* 60  7.70.724
• Find
P  i *Td  0.417in / hr * 24 hr  10.01in
– Cumulative fraction - interpolate SCS table
– Cumulative rainfall = product of cumulative fraction * total 24-hour
rainfall (10.01 in)
– Incremental rainfall = difference between current and preceding
cumulative rainfall
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
SCS – Example (Cont.)
(hours)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Cumulative
Fraction
Cumulative
Precipitation
Incremental
Precipitation
Pt/P24
Pt (in)
(in)
0.000
0.010
0.020
0.032
0.043
0.058
0.072
0.089
0.115
0.148
0.189
0.250
0.500
0.751
0.811
0.849
0.886
0.904
0.922
0.939
0.957
0.968
0.979
0.989
1.000
0.00
0.10
0.20
0.32
0.43
0.58
0.72
0.89
1.15
1.48
1.89
2.50
5.01
7.52
8.12
8.49
8.87
9.05
9.22
9.40
9.58
9.69
9.79
9.90
10.01
0.00
0.10
0.10
0.12
0.12
0.15
0.15
0.17
0.26
0.33
0.41
0.61
2.50
2.51
0.60
0.38
0.38
0.18
0.18
0.18
0.18
0.11
0.11
0.11
0.11
3.00
2.50
Precipitation (in)
Time
2.00
1.50
1.00
0.50
0.00
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Time (hours)
If a hyetograph for less than 24 needs to be prepared,
pick time intervals that include the steepest part of the
type curve (to capture peak rainfall). For 3-hr pick 11 to
13, 6-hr pick 9 to 14 and so on.
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
32
Alternating block method
•
Given Td and T/frequency, develop a hyetograph in Dt
increments
1. Using T, find i for Dt, 2Dt, 3Dt,…nDt using the IDF curve for the
specified location
2. Using i compute P for Dt, 2Dt, 3Dt,…nDt. This gives cumulative P.
3. Compute incremental precipitation from cumulative P.
4. Pick the highest incremental precipitation (maximum block) and place
it in the middle of the hyetograph. Pick the second highest block and
place it to the right of the maximum block, pick the third highest
block and place it to the left of the maximum block, pick the fourth
highest block and place it to the right of the maximum block (after
second block), and so on until the last block.
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
35
Example: Alternating Block Method
Find: Design precipitation hyetograph for a 2-hour storm (in 10
minute increments) in Denver with a 10-year return period 10minute
Duration
(min)
10
20
30
40
50
60
70
80
90
100
110
120
Td 
e
Intensity
(in/hr)
4.158
3.002
2.357
1.943
1.655
1.443
1.279
1.149
1.044
0.956
0.883
0.820
f

Td 
Cumulative
Depth
(in)
0.693
1.001
1.178
1.296
1.379
1.443
1.492
1.533
1.566
1.594
1.618
1.639
i  design rainfall intensity
96 .6
0.97
 13 .90
Incremental
Depth
(in)
0.693
0.308
0.178
0.117
0.084
0.063
0.050
0.040
0.033
0.028
0.024
0.021
Td  Duration of storm
c, e, f  coefficien ts
0.8
Time
(min)
0-10
10-20
20-30
30-40
40-50
50-60
60-70
70-80
80-90
90-100
100-110
110-120
Precip
(in)
0.024
0.033
0.050
0.084
0.178
0.693
0.308
0.117
0.063
0.040
0.028
0.021
0.7
0.6
Precipitation (in)
i
c
0.5
0.4
0.3
0.2
0.1
0.0
0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90
Time (min)
This slide adapted from: www.ce.utexas.edu/prof/maidment/GradHydro2010/.../DesignStorms.ppt
36
90100
100110
110120
• Dimensionless
Hyetograph is
parameterized to
generate an input
hyetograph that is 3 hours
long and produces the 5year depth.
– For this example, will use
the median (50th
percentile) curve
Rescale Depth
Empirical Hyetograph
Average Intensity
Rescale Time
• Tabular values in the
report.
– This column scales TIME
– This column scales DEPTH
Dimensional Hyetograph
Dimensional Hyetograph
• Use interpolation to generate uniformly
spaced cumulative depths.
Other Design Storms
• Frequency Design Storm
– Enter a frequency (probability)
– Enter intensity “duration” (lengths of pulses)
– Enter storm “duration”
– Enter accumulated depths at different portions of
the storm (dimensional hyetograph)
– Enter storm area (HMS uses this value for its own
ARF computations)
Summary - I
• Design storms are precipitation depths for a location
for a given storm duration and a given probability.
– DDF Atlas
– EBDLKUP.xls, TP40, HY35
• Design hyetographs are the time-redistribution of
these depths.
– SCS
– Triangular
– Empirical
Summary - II
• Intensities are average intensities that produce to
observed depth.
– DDF, IDF curves convey same information. Depth is the
natural (and measured) variable.
• Area Reduction Factors may be appropriate for larger
watersheds represented by point gages.
– Theissen weights are for spatial distribution of gages
– ARFs are computed externally and applied to the time series before
areal weighting.
HEC-HMS Overview
• History
– Evolved from HEC-1 as part of “new-generation”
software circa 1990
– Integrated user interface to speed up data input
and enhance output interpretation
• HMS is a complex and sophisticated tool
– Intended to be used by a knowledgeable and
skilled operator
– Knowledge and skill increase with use
HEC-1 (Predecessor to HEC-HMS)
• Separate (individual) programs in 1967 (L. R.
Beard)
• Unified into a single program in 1973
• Revised in 1981: kinematic wave
• PC full version in 1988
• Revised 1991: Extended memory support
• Final release 1998
– 32 years development until final release
HEC-HMS
•
•
•
•
Evolved from HEC-1
Project begun in 1990
HEC-HMS “released” in 1998
Current version is 3.5
– 21 years of development to date.
– Include the HEC-1 period and have nearly 50 years
of development – The program “engine” is
mature!
HEC-HMS
• Purpose
– Replacement for HEC-1
• Foundation for future hydrologic software
– Improved interface (GUI), graphics, and reporting.
– Newer hydrologic computation methods
imbedded
– Integration of hydrologic capabilities
Rainfall-Runoff Process
•
Precipitation
– Meterology, Climate
• Watershed
•
Runoff
– Fraction of precipitation signal
remaining after losses
–
–
–
–
Losses
Transformation
Storage
Routing
HEC-HMS
• Hydrologic Cycle Components in HEC-HMS
(circa 2008)
Rainfall, P(t)
Snowfall
Evapotranspiration
Snowpack
Snowmelt
Infiltration Loss
Land Surface and Vegetation
Runoff
Percolation Loss
Channels
Runoff
Reservoirs
Discharge, Q(t)
HEC-HMS
• Conceptualizes precipitation, watershed
interaction, and runoff into major elements
– Basin and sub-basin description
• Supply how the system components are interconnected
– Loss model
• Supply how rainfall is converted into excess rainfall
– Transformation model
• Supply how the excess rainfall is redistributed in time
and moved to the outlet
HEC-HMS
• Conceptualizes precipitation, watershed
interaction, and runoff into major elements
– Meterological model
• Raingage specifications and assignment to different
sub-basins
– Time-series models
• Supply input hyetographs
• Supply observed hydrographs
– Simulation control
• Supply instructions of what, when, how to simulate
HEC-HMS
• Precipitation
• Abstractions
– Fraction of precipitation that does not contribute
to runoff (and ultimately discharge)
• Routing
– Watershed routing
– Stream (Channel) routing
– Reservoir (Storage) routing
HEC-HMS
• Data management
– Graphical User Interface (GUI)
– Multiple input files
– Multiple output files
– Time-series in HEC-DSS
• All files arranged in a “Project”
– Paths to individual files
– Can e-mail entire project folders and have them
run elsewhere
HEC-HMS, IO Files
• project-name.hms
– List of models, descriptions, project default
methods
• basin-model-name.basin
– Basin model data, including connectivity
• meterologic-model-name.met
– Meterologic model data
HEC-HMS, IO Files
• control-specifications-name.control
– Control specifications
• run-name.log
– Run log; messages, warnings, etc. during a run.
• project-name.run
– List of runs, includes recent execution time.
HEC-HMS
• Introduction to HMS
• Minimal Model
– Rainfall models
Exercise
• Exercise 3
– Interpret Texas DDF Atlas
– Explore HEC-HMS Minimal Model
Hydrologic Models
• Require engineering judgment
– Experience helps
– Results can be difficult to interpret
• Require accurate input data
– Judgment here too, some data have marginal
influence on results, other data are vital.
• Require quality control procedures
Documenting Your Work
• This exercise is a bit more complex than filling
out a table (although that is part of the
exercise).
• This exercise you will complete the table and
hand in a report with relevant screen captures
of the HMS model and the written component
for the last problem.