~ ~ ~ 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
S-curve equation Jeff made up. 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.