HEC-HMS Simulation

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Example 4

• HEC-HMS Simulation
• Adding a detention pond at the outlet

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Purpose

• Illustrate data preparation and entry to model
  storage devices in HEC-HMS
• Uses Example 3B as basis.

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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

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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 sub-basin.

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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

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Physical Properties

• Watershed Properties
• AREA6.92 mi2
• MCL5.416 mi
• MCS0.005595
• CN86
• R0

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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

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Preparing Example 4

• Clone Example 3B and rename the project.
• Select path
• Save-As

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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

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Prepare a Base-Case

• Run Example 4
• Export the simulation hydrograph to a file.

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Export/Import Base Case

• Run Example 4
• Import the result hydrograph to a discharge gage.

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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.

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Canopy Abstraction

• Set canopy abstraction to some non-zero value.
• What do we expect discharge to do?

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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.

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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

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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

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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

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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

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Example 4

• Reservoir element
• Locate on the basin
• Use toolbars in HEC-HMS

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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
  sub-basin.
• 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)

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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

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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

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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

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Reservoir Storage

• Reservoir element
• Analyze the reservoir hydraulics

storage
discharge
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Reservoir Storage

• Storage-Discharge is entered in the Paired Data
  structure
• Components
• Paired Data
• New

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Example 4

• Storage-Discharge Table by cut-paste from the
  worksheet
• Need storage in Acre-Feet

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Reservoir Storage

• Run the model
• Turned off the canopy and depression storage so
  can compare effect of reservoir.

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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

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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.

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HEC-HMS Example 4

• Learning Points
• Used external analysis to build the
  storage-discharge 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
  Storage-Discharge table in HMS

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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.

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HEC-HMS Example 4

• Learn more
• HEC HMS user manual
• FHWA-NHI-02-001 Highway Hydrology
• Next module
• Routing