WMS

1
WMS

• Infiltration and Evapotranspiration Considerations

2
Tools

• Infiltration
• HEC-1 Loss Methods
• Rational Method
• HSPF
• TR-20 TR-55
• Evapotranspiration
• CASC2D
• All event based

3
HEC-1 LOSS METHODS

• Uniform
• Exponential
• Green-Ampt
• Holtan
• SCS Curve Number

4
HEC-1 Input
5
Initial Uniform Loss Rate

• Initial loss (in)
• Uniform loss rate (in/hr)
• Useful when you can calibrate values from an
  actual event
• Some tables in Hands on HEC-1 manual show loss
  rate relation to storm frequency, soil type, CN

6
Exponential Loss Method

• Empirical method
• Relates loss rate to rainfall intensity and
  accumulated losses
• Determined using optimization routines with
  actual event data

7
Green-Ampt

• Initial loss
• Volumetric moisture deficit
• Wetting front suction
• K at natural saturation
• USDA tables
• Soil type and land use coverages
• Automated computation in WMS

8
Holtan

• Use where agriculture is dominant use
• Growth index (infiltration capacity maturity of
  ground cover)
• Long term equilibrium loss rate
• Initial avail. soil moisture capacity (in)
• Typical values in Hands on HEC-1

9
SCS Curve Number

• Initial Abstraction (based on CN)
• Curve Number
• Soil-type land use data
• Automated computation for composite CN

10
Composite Curve Number Calculations
11
RATIONAL METHOD QCiA

• Required parameters
• C runoff coefficient
• various standard tables, land use coverage
• I rainfall intensity (in/hr)
• IDF curves, NOAA maps (avail on line)
• A basin area (ac)
• automated computation in WMS
• tc time of concentration (min)
• automated computation (several methods)

12
HSPF

• Water Quality Model
• WMS interface can read in HSPF input files
  created in other programs
• Soil type and land use data used in computing non
  point source runoff

13
TR-55

• Urban runoff model
• Parameters
• Basin area, CN, tc, rainfall data
• TR-20 is similar
• Not for urbanizing watersheds
• Specify reservoir data

14
CASC2D

• Physically based 2D finite difference
  rainfall/runoff model
• Uses rectangular grid cells to represent
  distributed watershed and rainfall domains
• Includes an advanced soil moisture accounting
  procedure based on Green-Ampt

15
CASC2D Evapotranspiration Options

• Deardorf
• Land surface albedo
• Wilting point water content
• Penman
• Above parameters
• Vegetation height
• Vegetation radiation coefficient
• Canopy stomatal resistance