Example9

Report
Example 9
Design Storms in HEC-HMS
Purpose
• Illustrate the steps to create a design
storm in HEC-HMS.
– The example will create a variety of design
storms for a particular Texas location.
– Focus on HOW to construct the hyetograph
(for design storms requiring external
processing) and the two built-in methods
Learning Objectives
• Generate an input hyetograph design
storm using several different methods.
– External processed storms
• Generate an SCS and Frequency Storm
using HEC HMS
– Internal processed storms
• Generate rapid generic HMS models for
creating input data (for later export).
Problem Statement
• Generate a 24-hour, 25-year design storm
for Harris Co. Texas using
– SCS Design Storm Approach and EBDLKUP
– 0-4194-3 Empirical Hyetograph
• Generate a 6-hour, 25-year design storm
for Harris Co. Texas using
– SCS Design Storm Approach and EBDLKUP
– 0-4194-3 Empirical Hyetograph
Problem Statement
• Generate a 24-hour, 25-year design storm
for Harris Co. Texas using
– Frequency Storm and DDF Atlas
Required Tools
• TP-40, HY35, DDF Atlas, or EBDLKUP
– This example will use both the DDF Atlas
and EBDLKUP to illustrate use of the two
tools, you don’t need both.
• 0-4194-3 Empirical Hyetographs
Precipitation Depth
• Using EBDLKUP
– 24 hr, 25 yr Depth = 10.01 inches
– 6 hr, 25 yr Depth = 6.75 inches
Rapid HMS Model
• Create a new project
– Basin model
• Dummy subbasin
• No loss
• No UH transform
Rapid HMS Model
• Create a new project
– Meterological model
• SCS Storm
Rapid HMS Model
• Meterological model
– SCS Storm
• Select Type
• Insert Depth
Rapid HMS Model
• Control Specifications
– Time Window
• 24 hours for SCS storm
Rapid HMS Model
• Run the model
Rapid HMS Model
• We will want the SCS 24-hour storm for the later
work, so lets get a copy from HMS.
– Observe that element time series has no rain – storm
is produced directly, but we can convert the 1 sq.mi.
discharge into watershed inches/hour in Excel
HEC-HMS Output
• Convert the No-transform hydrograph into the
SCS Type 2 storm (AREA=1 sq. mi.)
SCS Type-2 Storm
6-Hour Storm
• Now we will figure out the 6 hour SCS
storm.
– Idea is to use the most intense part of the
storm.
– Use the 6 hours centered on 12:00 of the
storm, rescale these to the correct depth and
we have a 6-hour storm.
SCS 6-hour
SCS 6-hour, Unscaled
• Pick the 6-hour
period.
– Then set remainder to
zero
– Compute total depth
– Adjust to get the
required total depth of
6.75 inches
SCS 6-hour, Unscaled
• Pick the 6-hour
period.
– Then set remainder to
zero
– Compute total depth
– Adjust to get the
required total depth of
6.75 inches
SCS 6-hour, Unscaled
• Pick the 6-hour
period.
– Then set remainder to
zero
– Compute total depth
– Adjust to get the
required total depth of
6.75 inches
SCS 6-hour, Scaled
• Pick the 6-hour
period.
– Then set remainder to
zero
– Compute total depth
– Adjust to get the
required total depth of
6.75 inches
SCS 6-hour, Scaled
• Cut and past into
HMS
– Time series data
manager
HEC-HMS Model
• Run the model
HEC-HMS Model
• Summary
– SCS 24-hr is “built-in”, specify storm type and depth.
– SCS 6-hr is processed externally
• Results
– 24 hr, Qp = 9340 cfs, Tp = 11:52 , V= 10.01 in.
– 6 hr, Qp = 8905 cfs , Tp = 2:52 , V = 6.75 in
– Recall the Qp are not true “runoff” in this example –
they represent “excess precipitation” expressed in
units of watershed discharge for a 1 sq. mi.
watershed.
Using DDF Atlas
• Repeat the example using the DDF atlas
– Need two maps; 25 yr – 24 hr and 25 yr – 6 hr.
Rainfall Depth
• Use DDF atlas to find depths would
produce nearly identical results
– 25 yr, 24 hr ~ 9-10 inches
– 25 yr, 6 hr ~ 6-7 inches depth
• Building an HMS model would be the same for
SCS Type 2 storm.
• Use these values instead in the empirical
hyetograph approach
• Dimensionless
Hyetograph is
parameterized
to generate an
input
hyetograph
that is 6 or 24
hours long and
produces the
25-year depth.
0 – 6.5 inches
Or
0 – 9.5 inches
Generate a Hyetograph
– For this
example, will
use the
median (50th
percentile)
curve
0 – 6 hours
Or
0 – 24 hours
• We won’t actually use
the graph, instead use
the tabular values in the
report.
– This column scales TIME
– This column scales
DEPTH
• We saw this same chart
in example 2
Dimensional Hyetograph
Dimensional Hydrograph
• Use interpolation to generate uniformly
spaced in time cumulative depths.
• This example will use the HMS fill feature
Input Hyetograph
•
•
Cut-paste-fill
to create the
hyetograph
Considerable
time required
(will illustrate
“live”)
Empirical 24-hr, 25-yr
•
Cut-paste-fill
to create the
hyetograph
Data Preparation
• Discovered in this example that using the
dimensionless hyetograph requires a
tedious cut-paste-fill process to put the
data into the uniform spaced time series
structure.
– Need a better way, that is some kind of
interpolator that will take non-uniform spaced
paired data and produce uniform spaced data.
Interpolation in Excel
• Use Excel to interpolate by use of INDEX
and MATCH functions.
– Takes a bit of programming, but will make
empirical hyetographs easier to manage and
will save time.
Interpolation in Excel
• Copy the dimensionalized hyetograph to a
different worksheet (as values).
– Use MATCH and INDEX to locate the nearest values
in the dimensional TIME and DEPTH to the arbitrary
TIME
– Equation to interpolate depth is
Dinterpolated 
( Dhi  Dlow )(Tinterpolated  Tlow )
(Thi  Tlow )
Interpolation in Excel
Dinterpolated 
( Dhi  Dlow )(Tinterpolated  Tlow )
(Thi  Tlow )
6-hr, 25 yr Empirical
• Now that we have an interpolator, we can
prepare a six hour storm with less data
entry effort in HMS.
– Depth ~ 6-7 inches, lets use 7
– Duration is 6 hours
• Back to the Excel sheet (we already built)
6-hr, 25 yr Empirical
Change these values as appropriate
Copy to the interpolate sheet
6-hr, 25 yr Empirical
Change these values as appropriate
6-hr, 25 yr Empirical
Copy the interpolated series into HEC-HMS
Copied the interpolated depths here
Frequency Storm
• HEC-HMS has a “frequency” storm option
built-in to the meterological manager.
• It requires a set of depths for different
times in a storm (kind of like the empirical
hyetograph).
• It is a way to directly enter DDF values into
HMS without the interpolation issues.
• Will illustrate with the 24-hour Harris
County example.
Frequency Storm
• From the DDF atlas we will need a series of
depths
Frequency Storm
• From the DDF atlas we will need a series of
depths
Read these from the Atlas Maps pp 47-54
Frequency Storm
• Run the model
Comparison of Results
• Several different design storms
– SCS, Empirical Hyetograph, Frequency
Storms
• Different durations
– Compare the 24-hour
• Anticipate different results because storm
“shapes” are different.
• Anticipate about same total depths
Comparison of Results
Design Storm
Model
Total Depth IPeak Tpeak
SCS-3 +EBDLKUP
10.01
3723
12:00
DDF+Empirical
9.49
2219
~ 00:30
DDF+Frequency
9.00
4356
12:05
Summary
• Illustrated a 24-hour SCS storm
parameterized using EBDLKUP
• Illustrated how to “export” that storm from
HMS and convert into a 6-hour storm
• Illustrated how to use the DDF Atlas and
Empirical Hyetograph to generate 24-hour
and 6-hour storms.
• Illustrated the Frequency storm
parameterized by the DDF Atlas
Summary
• Storm depths similar (anticipated result)
• Time of peak intensity different for
Empirical Hyetograph
– Anticipated
– empirical are front-loaded storms
– SCS and Frequency are “balanced” about the
½ storm duration
Summary
• As an aside, the choice of 1-minute time
steps was dumb – but this example was
about storms and not how well the
hypothetical 1 sq. mi. converted those
storms into excess.

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