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 sub-basin.

7 1 2 0 0 0 . 0 0 7 1 4 0 0 0 .0 0 7 1 6 0 0 0 .0 0 7 1 8 0 0 0 .0 0 7 2 0 0 0 0 . 0 0 7 2 2 0 0 0 . 0 0

3 6 2 6 0 0 0 .0 0

3 6 2 8 0 0 0 .0 0

3 6 3 0 0 0 0 .0 0

3 6 3 2 0 0 0 .0 0

3 6 3 4 0 0 0 .0 0

3 6 3 6 0 0 0 .0 0

3 6 3 8 0 0 0 .0 0

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

7 1 2 0 0 0 . 0 0 7 1 4 0 0 0 .0 0 7 1 6 0 0 0 .0 0 7 1 8 0 0 0 .0 0 7 2 0 0 0 0 . 0 0 7 2 2 0 0 0 . 0 0

3 6 2 6 0 0 0 .0 0

3 6 2 8 0 0 0 .0 0

3 6 3 0 0 0 0 .0 0

3 6 3 2 0 0 0 .0 0

3 6 3 4 0 0 0 .0 0

3 6 3 6 0 0 0 .0 0

3 6 3 8 0 0 0 .0 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 HEC-HMS

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)

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• 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

Flow from Sub-Basin

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 Acre-

Feet

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 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

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