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HydroCAD
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TR-20
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TR-55
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Runoff
methodology
|
Unit
hydrograph procedure (unlimited points), Santa Barbara Urban Hydrograph,
Rational Method
|
Unit hydrograph
procedure (301 points)
|
Tabular method derived from
TR-20
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Rainfall types
|
Extensive rainfall library, user-defined storms,
& synthetic rainfall distributions generated from local precipitation frequency
data.
|
SCS type I, IA, II & III
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SCS type I, IA, II & III
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Unit
hydrograph
|
Extensive UH library including
SCS, Delmarva, and others.
|
SCS Unit Hydrograph or
user defined curve
|
SCS Unit Hydrograph only
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Curve number
entry
|
Automatic curve number lookup and
weighting, with adjustment for unconnected impervious areas
|
Requires direct entry of
composite curve number
|
Automatic curve number
lookup and weighting, with adjustment for unconnected impervious areas.
|
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Curve number
weighting |
Area-weighted, or separate runoff for
each CN with weighted flow. |
Requires direct entry of
composite curve number |
Area-weighted curve number |
Curve number
limitations
|
No restrictions
|
No restrictions
|
Reduced accuracy as CN
differs from 75
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Time of
concentration
calculations
|
All TR-55 methods plus common
channel shapes, upland method,
CN method, and Kerby/Kirpich method
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Contains no Tc
calculations: Requires
direct entry of Tc
|
Calculates Tc for sheet,
shallow concentrated, &
channel flow
|
Tc limitations
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No restrictions
|
Must be greater than zero
|
Limited to .1 to 2 hrs
|
Tc precision
|
1/10 minute or 1/600 hour
|
1/100 hour
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Rounded to nearest step
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Subarea
limitations
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None
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None
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Must not differ by more than
factor of 5
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Runoff accuracy
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Within 1% of 1982 TR-20 release
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“The standard”
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Within +25% of TR-20
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Reach routing
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Muskingum-Cunge or Storage-indication method with
optional routing delay (translation)
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Modified Att-Kin procedure
|
No routing, separate tables
for travel times of 0 to 3
hours
|
Reach hydraulics
|
Automatic calculation for common
shapes or custom cross-sections
|
None. Requires entry of
routing coefficients.
|
n/a, no reach routing
|
Pond routing
|
Storage-indication method, dynamic
storage-indication method, or
simultaneous routing
|
Storage-indication
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None, only estimates ponding
effects
|
Pond hydraulics
|
Automatic calculations for
orifice, weir, culvert, etc, used alone or combined for outlet structures
|
Must be entered directly,
no calculations provided
|
n/a, no pond routing
|
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Tailwater |
Dynamic tailwater handling with all
standard outlet devices
|
none - uses static stage-discharge
curves |
none - uses static stage-discharge
curves |
|
Dam Breach |
Progressive dam breach triggered at
specified time or WSE |
none |
none |
|
Pumps |
Full pump simulations including pipe
loses and tailwater effects |
none |
none |
Pond Sizing
Estimate
|
Using actual inflow hydrograph
|
none
|
Using assumed hydrograph
shape
|
Detention Time
|
By plug-flow and center-of-mass
methods
|
not calculated
|
not calculated
|
Pond storage
calculations
|
Automatic calculation from pond
dimensions or surface areas, plus
direct entry
|
Direct entry only
|
n/a, no pond routing
|
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Underground
Storage |
Automatic chamber layout and modeling,
including embedded storage calculations |
requires external calculations |
requires external calculations |
Flow diversions
(split flows)
|
Automatic diversion of outflow from
specified pond outlet(s)
|
Separate “Divert”
procedure based on user-defined curve
|
n/a
|
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Pollutant
Loading |
Automatic land-use reporting and
pollutant loading calculations. |
none |
none |
Routing
diagram
|
Interactive, on-screen, with labels
and background image
|
none
|
none
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Calculation
procedure
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Automatically calculated as required
|
“Batch mode” calculation of
entire watershed
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Manual initiation of each
calculation
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Units system
|
US/English, Metric, or custom, plus
split input/output units
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US/English only
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US/English only
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Graphics
capabilities
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Full graphics to screen, printer,
or file
|
none
|
none
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Reports
|
Automatic reports with headings,
graphics, etc.
|
Manual
|
Manual
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Data Storage
|
Automatic by job name
|
Manual
|
Manual
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