Example 4
HEC-HMS Simulation
Adding a detention pond at the
outlet
Purpose
• Illustrate data preparation and entry to
model storage devices in HEC-HMS
– Uses Example 3B as basis.
Learning Objectives
• Learn how to select canopy and depression
storage abstractions.
– Will use to examine effects
• Learn how to prepare storage-discharge tables.
– Use Excel and typical hydraulics considerations to
build the table.
• Learn how to import the storage-discharge table
into HEC-HMS
– Paired-Data manager
Problem Statement
• Simulate the response of the Ash Creek
watershed at Highland Road for 20 May
1978 historical conditions.
– Use Example 3B as the base “model”
– Use Example 3B output hydrograph as a
comparison hydrograph to examine effect of
different abstractions on simulation
– Treat the entire watershed as a single subbasin.
Background and Data
• Watershed Outlet
– Highland Road and
Ash Creek, Dallas,
TX.
– Area is residential
subdivisions, light
industrial parks, and
some open
parkland.
– White Rock Lake is
water body to the
North-West
Physical Properties
• Watershed
Properties
– AREA=6.92 mi2
– MCL=5.416 mi
– MCS=0.005595
– CN=86
– R=0
Loss Model: Green-Ampt
• Parameter estimation
– Initial water content. 0.187
– Saturated water content: 0.464
– Saturated hydraulic conductivity: 0.04 in/hr
– Soil suction: 8.27 inches
Preparing Example 4
• “Clone” Example 3B and
rename the project.
– Select path
– “Save-As”
Example 4
• Run Example 4
– Export the simulation hydrograph to a file.
– Re-import that file as a discharge gage.
– We will use this hydrograph to examine effect of
abstraction changes.
• Will use skills developed in Example 3
– External hydrograph import
• Develop new skill – exporting results
Prepare a Base-Case
• Run Example 4
– Export the simulation hydrograph
to a file.
Export/Import Base Case
• Run Example 4
– Import the result hydrograph to a
discharge gage.
Verify Import
• Re-Run Example 4
– Set the result
hydrograph as the
“observation” discharge
gage.
– Observe “perfect” fit
• Diagnostic in practical
models, perfect fits mean
analyst chose wrong time
series.
Canopy Abstraction
• Set canopy abstraction
to some non-zero
value.
– What do we expect
discharge to do?
Canopy Abstraction
• Set canopy abstraction
to some non-zero
value.
– What do we expect
discharge to do?
• Storing up to ½ inch of
precipitation – anticipate
that peak is reduced and
a loss of early runoff.
Canopy Abstraction
• Set canopy abstraction to
some non-zero value.
– What do we expect
discharge to do?
• Storing up to ½ inch of
precipitation – anticipate
that peak is reduced and a
loss of early runoff
• Run the new model and
examine results
Depression Abstraction
• Similar procedure and
data-entry items.
– What do we expect
discharge to do?
• Storing even more
precipitation, anticipate
further reduction in peak.
– Run the new model and
examine results
Reservoir Storage
• Now will return to more
reasonable canopy
and depression values
– Canopy = 0.05 in
– Depression = 0.25 in
• Will use as a basis
before adding a
reservoir element
Reservoir Storage
• Reservoir element
– Locate on the basin
• Use toolbars in HEC-HMS
– Identify connection
• Use connections in HEC-HMS
– Specify a storage-discharge relation
• Build table externally (in Excel) then import information into
HEC-HMS
Example 4
• Reservoir element
– Locate on the basin
• Use toolbars in HECHMS
Reservoir Storage
• Connections in HEC-HMS
– Hydrologic/Hydraulic Elements are “connected” by
assigning to an element its downstream receiving
element.
• Rainfall thus connects “downstream” to a subbasin.
• In this example, the sub-basin will drain
“downstream” to the reservoir
• The reservoir will then drain “downstream” to our
outlet of interest (i.e. its output is the outlet)
Reservoir Storage
• Reservoir element
– Identify the reservoir
as “downstream” of
the sub-basin
– In the sub-basin
editor, we select the
reservoir as the
downstream element
Reservoir Storage
• Reservoir element
– Identify the reservoir
as “downstream” of
the sub-basin
– In the sub-basin
editor, we select the
reservoir as the
downstream element
– If successful, then the
connection is shown
on the GUI
Reservoir Storage
Flow from Sub-Basin
• Reservoir element
– Need to build the
storage-discharge
table
– External to HMS
– Analyze the reservoir
hydraulics
– This example, pretend
an 8-foot deep
detention basin fit into
the outlet somehow
Reservoir Storage
• Reservoir element
– Analyze the reservoir
hydraulics
storage
discharge
Reservoir Storage
• Storage-Discharge is
entered in the “Paired
Data “ structure
– Components
– Paired Data
– New
Example 4
• Storage-Discharge
Table by cut-paste
from the worksheet
– Need storage in AcreFeet
Reservoir Storage
• Run the model
– Turned off the
canopy and
depression storage
so can compare
effect of reservoir.
Reservoir Storage
• What if Reservoir is
increased to 16X larger
– about 0.5% of entire
drainage area?
– Notice the shifting in peak
location and magnitude
• Changed:
– Multiplied the storage by
16.
– Used the watershed outlet
as the source for
reference curve
HEC-HMS Example 4
• Learning Points
– Copy entire projects to keep different models
organized.
– Canopy and Depression Storage are
abstractions – impact the excess precipitation.
– Reservoir Storage attenuates the runoff
signal, and if sufficient delays peak arrival.
• Stream routing will look similar to reservoir
behavior, parameterization is different.
HEC-HMS Example 4
• Learning Points
– Used external analysis to build the storagedischarge table
• Simplified hydraulics to account for weir and orifice
flow.
• Excel to produce the STORAGE-DISCHARGE
table.
– Paired Data manager for HMS table
• Imported the Excel table into the StorageDischarge table in HMS
HEC-HMS Example 4
• Learning Points
– Used output time series to build comparison
hydrographs to examine effect of changes
• Use of a hand-written simulation log and some
forethought could allow multiple comparisons in a
single project directory – file count could get large,
naming convention would be important.
HEC-HMS Example 4
• Learn more
– HEC HMS user manual
– FHWA-NHI-02-001 Highway Hydrology
• Next module
– Routing