HEC-HMS Simulation Adding a detention pond at the outlet Example 5 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 4B 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 4B as the base “model” Use Example 4B output hydrograph as a comparison hydrograph to examine effect of different abstractions on simulation Treat the entire watershed as a single sub-basin.

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 4B New Import Basin/Met/Control

Example 5 Run Example 5 Will use skills developed in 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 4 External hydrograph import Develop new skill – exporting results

Prepare a Base-Case Run Example 5 Export the simulation hydrograph to a file.

Export/Import Base Case Run Example 5 Import the result hydrograph to a discharge gage.

Verify Import Re-Run Example 5 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 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 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 5 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 5 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 5 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 5 Learn more Next module HEC HMS user manual FHWA-NHI-02-001 Highway Hydrology Next module Routing