~ ~ ~ PURPOSE ~ ~ ~
this subroutine controls the grass waterways
~ ~ ~ INCOMING VARIABLES ~ ~ ~
name |units |definition
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
ihru |none |HRU number
surfq(:) |mm H2O |amount of water in surface runoff generated
grwat_l(:) |km |Length of Grass Waterway
grwat_w(:) |none |Width of grass waterway
grwat_s(:) |m/m |Slope of grass waterway
grwat_spcon(:) |none |sediment transport coefficant defined by user
tc_gwat(:) |none |Time of concentration for Grassed waterway and its drainage area
surfq(:) |mm H2O |surface runoff generated on day in HRU
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ OUTGOING VARIABLES ~ ~ ~
name |units |definition
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ LOCAL DEFINITIONS ~ ~ ~
name |units |definition
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
qp_cms |m^3/s |peak runoff rate for the day
rcharea |m^2 |cross-sectional area of flow
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ ~ ~ SUBROUTINES/FUNCTIONS CALLED ~ ~ ~
~ ~ ~ ~ ~ ~ END SPECIFICATIONS ~ ~ ~ ~ ~ ~
do this only if there is surface runoff this day
compute channel peak rate using SCS triangular unit hydrograph
Calculate average flow based on 3 hours of runoff
if peak rate is greater than bankfull discharge find the crossectional area and depth for todays flow by iteration method at 1cm interval depth find the depth until the discharge rate is equal to volrt Sediment yield (kg) from fraction of area drained by waterway
Calculate sediment losses in sheetflow at waterway sides
calculate area of sheeflow in m^2 assumne *:1 side slope 8.06 = (8^2+1^2)^.5 Adjust Area to account for flow nonuniformities White and Arnold 2009 found half of flow in VFS handled by 10% of VFS area. Waterways likely even more concentrated Assume only 20% of sideslope acts as filters calculate runoff depth over sheetflow area in mm Calculate sediment load on sheetflow area kg/ha Calculate runoff and sediment losses taken from mostly from filter.f surq_remove = 75.8 - 10.8 * Log(sf_depth) + 25.9 & * Log(sol_k(1,j)) Simpler form derived from vfsmod simulations. r2 = 0.57 Publication pending white and arnold 2008
calculate flow velocity
compute deposition in the waterway
if there is significant flow calculate Calculate sediment concentration in inflow mg/m^3 Calculate sediment transport capacity mg/m^3 Calculate deposition in mg Calculate sediment out of waterway channel Calculate total fraction of sediment and surface runoff transported Subtract reductions from sediment, nutrients, bacteria, and pesticides NOT SURFACE RUNOFF to protect water balance Calculate pesticide removal based on the sediment and runoff removal only