example 3 hec-hms simulation 3 different loss models
TRANSCRIPT
Example 3
HEC-HMS Simulation
3 Different Loss Models
Purpose
• Illustrate different loss models in a HEC-HMS precipitation-runoff simulation– The example is “minimal” in the sense that
only a small set of HEC-HMS capabilities are employed
– Realistic parameter values are employed from public-domain references, but the example is fabricated for pedagogical simplicity.
Learning Objectives
• Learn how to copy a “project” so can modify without damage to original files. – Reinforce the concepts of “Projects” as a data-storage
paradigm.
• Learn how to import observations.– Use of measured rainfall and discharge. Where
available can use to “calibrate” a watershed model.
• Learn how to parameterize different loss models– Initial loss and constant rate loss model– NRCS CN runoff generation (loss)– Green-Ampt loss model
Problem Statement
• Simulate the response of the Ash Creek watershed at Highland Road for a the XXXX historical conditions.– Use Example 2 as the base “model”, modify
by substitution of the real rainfall time series and the observed runoff time series.
– 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
This was used in IaCl specification-- will examine source of number-- will also need GA values
Historical Data
• Precipitation and Runoff– May 20, 1978– Total depth about
3-inches, close to Example 2 depth (much different time scale)
Historical Data
• Precipitation– Note start time
• Runoff– Note start time
Start Time
• Start time is important– The start time of rainfall time series and runoff time
series should be same– A common error is time mismatch, usually obvious in
the simulation but not always.
Using “Real” Data
• Need to prepare the data– Uniform time steps (no 17 hour gap)– Rainfall and runoff data should have same start
times, use zero-padding to make happen
• Data become “time-series” elements– Rainfall => With a “rain-gage” in HEC-HMS– Runoff => With a “discharge-gage” in HEC-HMS
Building The Model – Create a New Project
• Use Example 2 as the base model– Start Example 2– Select “Save-As”– Save to a new project name and file
Building The Model – Create a New Project
• Use Example 2 as the base model– Start Example 2– Select “Save-As”– Save to a new project name and file
Name
Path
Check these to create duplicate files
Building The ModelVerify the copy
• Run a simulation– Convince self that
have a working copy
Data Preparation
• Now prepare the external hyetograph from the historical data– Use Excel to prepare the time series– Specify a long enough time window in the
time-series manager– Use HEC-HMS “fill” to fill in the 17 hours
Data Preparation: Rainfall
• Use Excel to prepare the time series
• Specify a long enough time window in the time-series manager– 5-20-1978 to 5-22-
1978 should cover the rainfall and allow an entire day for runoff
– Can refine if needed
Data Preparation:Rainfall
• Specify a long enough time window in the time-series manager– 5-20-1978 to 5-22-
1978 should cover the rainfall and allow an entire day for runoff
Data Preparation: Rainfall
• Use Excel to prepare the time series– Identify non-uniform time
step sections– line up with input table in
HEC-HMS– One-time only is easiest to
enter blocks, then use HMS tools to fill in values
– Many storms, worth writing code to interpolate (external to HMS)
Not every 15 minutes here
Data Preparation: Rainfall
• Use Excel to prepare the time series– Identify non-uniform time
step sections– line up with input table in
HEC-HMS– One-time only is easiest to
enter blocks, then use HMS tools to fill in values
– Many storms, worth writing code to interpolate (external to HMS)
Data Preparation: Rainfall
• One-time only is easiest to enter blocks, then use HMS tools to fill in values– Enter value first line
(not displayed)– Highlight fill block– Right-click block and
select fill method
Data Preparation: Rainfall
• One-time only is easiest to enter blocks, then use HMS tools to fill in values– Enter value first line
(not displayed)– Highlight fill block– Right-click block and
select fill method
Completed data fill (zero padding in this case)
Data Preparation: Rainfall• Continue for remaining non-uniform spaced blocks.
– When complete, plot the time-series and Excel and HEC-HMS; should look the same (padded the Excel file to start/end same elapsed time)
• This plot is QA/QC only, once data are entered, won’t need further Excel plots.
Loss Model Parameters• IaCl model in TxDOT 0-4193-7
Data Preparation: Runoff
• Use Excel to prepare the time series
• Specify a same time window as rainfall
• Copy, paste, fill by same process.
Data Preparation: Runoff
• Create discharge gage– Time series manager.
Data Preparation: Runoff
• Specify time window
Data Preparation: Runoff
• Use same process as for rainfall– Insert blocks– Use fill tool to insert
missing values– Plot results to
compare
Data Preparation: Runoff• Continue for remaining non-uniform spaced blocks.
– When complete, plot the time-series and Excel and HEC-HMS; should look the same (padded the Excel file to start/end same elapsed time)
• This plot is QA/QC only, once data are entered, won’t need further Excel plots.
Example 3: IaCl Loss Model
• Leave remainder of model unchanged– Represents the IaCl model– Represents the NRCS DUH transformation model
• Run the simulation using the real rainfall (in contrast to a hypothetical input)– Compare simulation output with discharge gage– Assess how well the estimation methods worked– Try different loss models (Run 2 and Run 3)
Example 3: IaCl Loss Model
• Instruct the program to plot the observed gage with the simulation gage.– Basin/Options
Example 3: IaCl Loss Model
• Dotted curve is observed runoff, solid is simulation– Timing ~ 70 minutes late– Peak ~ 50% low– Volume ~ 20% high
• One could “calibrate” but that is for a later module.
• Stipulate that simulation is a bit off, and explore different loss models.
Example 3B : Green-Ampt
• Requires some added knowledge about the Ash Creek locale– Soil types and tables of values– Prior study (if lucky – in this example
available)
Example 3B : Green-Ampt
• Soil Types – Texas available from
TAMU– Nationwide from
NRCS• This example will
download the NRCS map, it is more assessable to hydrologists, the TAMU database is specialized for soil scientists.
Example 3B : Green-Ampt
• NRCS Soil Map
Zoom to this area
Read description
Example 3B : Green-Ampt
• NRCS Soil Map : Type 2
Example 3B : Green-Ampt
• NRCS Soil Map : Type 2– Loamy and clayey soils
Example 3B : Green-Ampt
• Compare description with published soil behavior– Use middle
description.– Other arrows
indicate reasonable bounding ranges
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
Example 3B: Green-Ampt
• Results– Timing ~ 70 minutes
late– Peak ~ 50% low– Volume ~ 9% high
(good!)
Example 3A : NRCS Loss Model
• Example 3A will substitute the NRCS Loss Model for the IaCl model
• Clone the project again (Save As …) to preserve structure and reduce chance of a data specification error
• Change the loss model specification, enter curve number and re-simulate.
Example 3A : NRCS Loss Model
• Curve number selection– Determine hydrologic soil classification– Uses same soil map as in Green-Ampt– Soil Group C or D appropriate based on
saturated hydraulic conductivity.
Example 3A : NRCS Loss Model•Make an assessment of “open space”, residential, and commercial industrial.
•Then decide fraction impervious for a composite number.
•Subjective, but most analysts will be within +/- 10.
Example 3A : NRCS Loss Model
• Look up CN for the different parts, I choose lowest value in C group soil.– 10% of area is the stream drainage, essentially open
space CN ~ 79, %IC=0– 30% of area is commercial-business (note the general
aviation airport is included) CN ~ 91, %IC ~ 85– 60% of area is some kind of residential, CN ~ 83,
%IC~40
• Composite these to a value of CN=90 for the watershed, IC is already considered.
Example 3A : NRCS Loss Model
• Clone the project again (Save As …) to preserve structure and reduce chance of a data specification error
• Change the loss model specification, enter curve number and re-simulate.
Example 3A : NRCS Loss Model
• Results with different loss model.– Timing ~ 70 minutes
late– Peak ~ 50% low– Volume ~ 50% high
HEC-HMS Example 3
• Learning Points– Copy entire projects to keep different models
organized.– Used Excel to prepare data for import into
Time-Series-Manager; allows use of measured values where available.
– IaCl, Green-Ampt, NRCS CN perform differently but require similar data preparatory effort.
HEC-HMS Example 3
• Learning Points– Used external data sources
• NRCS soil maps (internet)• Texas A&M Soil Database (didn’t use, but know
available)• Used a Green-Ampt soil property correlation in
SWMM (but from the soils literature)• Used TxDOT hydraulic design manual for CN
estimation. NEH 630 Chapter 9-10 would have produced similar values.
HEC-HMS Example 3
• Learning Points– Assembly of external data sources is vital to
the hydrologist• Most practicing hydrologist’s offices are a mess of
old reports – that’s where they find the data.• Many useful external data sources are available in
PDF reports from a variety of sources, need to get in the habit of citing the data source should one need to defend input value choices.
HEC-HMS Example 3
• Learn more– HEC HMS user manual– FHWA-NHI-02-001 Highway Hydrology
• Next example– Calibration tools