~ ~ ~ PURPOSE ~ ~ ~
This subroutine computes variables related to the watershed hydrology:
the time of concentration for the subbasins, lagged surface runoff,
the coefficient for the peak runoff rate equation, and lateral flow travel
time.
~ ~ ~ INCOMING VARIABLES ~ ~ ~1
name |units |definition
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
ch_n(1,:) |none |Manning's "n" value for the tributary channels
ch_s(1,:) |m/m |average slope of tributary channels
gdrain(:) |hrs |drain tile lag time: the amount of time
|between the transfer of water from the soil
|to the drain tile and the release of the
|water from the drain tile to the reach.
hru_km(:) |km2 |area of HRU in square kilometers
lat_ttime(:)|days |lateral flow travel time
slsoil(:) |m |slope length for lateral subsurface flow
slsubbsn(:) |m |average slope length for subbasin
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ OUTGOING VARIABLES ~ ~ ~
name |units |definition
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
lat_ttime(:)|none |Exponential of the lateral flow travel time
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ SUBROUTINES/FUNCTIONS CALLED ~ ~ ~
SWAT: Ttcoef
~ ~ ~ ~ ~ ~ END SPECIFICATIONS ~ ~ ~ ~ ~ ~
calculate composite usle value
should be beginning month of simulation and not 12 (December)
set fraction of field capacity in soil
set initial soil water and temperature for each layer set day length threshold for dormancy and initial dormancy 365/2pi = 58.09 sdlat will be >= 1. if latitude exceeds +/- 66.5 deg in winter latitude exceeds +/- 66.5 deg in summer set maximum depth in soil to maximum rooting depth of plant compute lateral flow travel time unit conversion: xx = m/(mm/h) * 1000.(mm/m)/24.(h/d) / 4.