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bmp_sand_filter.f
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bmp_sand_filter.f
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subroutine sand_filter(kk,flw,sed)
!! ~ ~ ~ PURPOSE ~ ~ ~
!! this subroutine routes water and sediment through sand filters in the subbasin
!! ~ ~ ~ INCOMING VARIABLES ~ ~ ~
!! name |units |definition
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! hru_sub(:) |none |subbasin in which HRU/reach is located
!! i_mo |none |current month of simulation
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! ~ ~ ~ OUTGOING VARIABLES ~ ~ ~
!! name |units |definition
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! pnd_sed(:) |kg/L |ratio of sediment to water in pond
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! ~ ~ ~ LOCAL DEFINITIONS ~ ~ ~
!! name |units |definition
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! sb |none |subbasin or reach number
!! kk |none |filter id number in the subbasin
!! ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
!! ~ ~ ~ SUBROUTINES/FUNCTIONS CALLED ~ ~ ~
!! Intrinsic: Min
!! SWAT: pipeflow coded in bmp_sed_pond.f90
!! ~ ~ ~ ~ ~ ~ END SPECIFICATIONS ~ ~ ~ ~ ~ ~
use parm
implicit none
integer :: sb, ii
integer, intent(in) :: kk
real*8 :: tsa,ffsa,vfiltr,mxvol,pdia,ksat,por,dp,dc,pden,alp,
& wetfsh,whd,sub_ha,dt,qcms,effct,effl,effg,effbr,vpipe,phead,hpnd,
& tmpw,qloss,fsat,qpipe,mu,pipeflow,splw,hweir,tst,kb,qintns,qq,
& qfiltr,sloss,spndconc,sedpnd,qpndi,qpnde,sedrmeff,sed_removed,
& sedconc,qevap,hrd
real*8, dimension(:) :: qpnd(0:nstep),qsw(0:nstep),qin(0:nstep),
& qout(0:nstep),fc(0:nstep),f(0:nstep)
real, dimension(3,0:nstep), intent(inout) :: flw, sed
sb = inum1
sub_ha = da_ha * sub_fr(sb)
dt = real(idt) / 60. !time interval in hours
qin = 0.; qout = 0.;qevap=0
flw(2,:) = 0.; sed(2,:) = 0.;f=0
qpnd = 0.; qsw = 0.; qpndi = 0.; qpnde = 0.; fc = 0.;qfiltr = 0.
kb = 1.38e-16 !Boltzmann constant, g-cm^2/s^2-K
!! Initialize parameters, coefficients, etc
tsa = ft_sa(sb,kk) !total surface area of filter (m^2)
if (tsa>sub_ha*10000.*0.5) tsa = sub_ha*10000.*0.5 !sandfilter should be smaller than 0.5 times the subbasin area
ffsa = ft_fsa(sb,kk) !fraction of infiltration bed in the filtration basin (m2/m2)
mxvol = ft_h(sb,kk) / 1000. * tsa !max. capacity of the basin (m^3)
pdia = ft_pd(sb,kk) !outflow orifice pipe diameter (mm)
splw = ft_bpw(sb,kk) !spillway overflow weir width (m)
ksat = ft_k(sb,kk) !saturated hydraulic conductivity (mm/hr)
por = ft_por(sb,kk) !filter porosity
dp = ft_dp(sb,kk) / 10. !median diameter of TSS particle (cm)
dc = ft_dc(sb,kk) / 10. !median diameter of filter media (cm)
pden = tss_den(sb,kk) !density of tss particle (g/cm3)
alp = ft_alp(sb,kk) !filter attachment efficiency (0-1)
vfiltr = ft_dep(sb,kk) / 1000. * tsa * ffsa * por !actual volume of filter column (m^3)
!! wetting front suction head (mm)
wetfsh = 10. * Exp(6.5309 - 7.32561 * por + 3.809479 * por ** 2 -
& 0.049837 * por * 100. + 0.001608 * por ** 2 * 100. ** 2 -
& 0.000799 * 100. ** 2 * por)
!! Get initial values from previous day
qpnd(0) = ft_qpnd(sb,kk)
qsw(0) = ft_qsw(sb,kk)
qin(0) = ft_qin(sb,kk)
qout(0) = ft_qout(sb,kk)
sedpnd = ft_sedpnd(sb,kk)
fc(0) = ft_fc(sb,kk)
do ii=1,nstep
qloss = 0.
qin(ii) = flw(1,ii) * 10. * (sub_ha - tsa / 10000.) +
& precipdt(ii) * tsa / 1000. !m^3
qout(ii) = qout(ii-1)
If (qin(ii)<0.001.and.qpnd(ii-1)<0.001)then
if (qsw(ii-1)<0.001) then
!No flow
qout(ii) = 0.
qloss = 0.
else
qout(ii) = ksat * dt * qsw(ii-1) / vfiltr / 1000.* tsa
& * ffsa !m^3
! outflow control
if (sf_ptp(sb,kk)==1) then
phead = (qsw(ii-1)/(tsa*ffsa)/por) * 1000. !mm
! If (phead>pdia/2.) then
qpipe = pipeflow(pdia,phead) * dt *3600. !m^3
! else
! qpipe = qout(ii) * 2. !pipe flow does not affect outflow
! endif
!recalculate water balance if orifice pipe limits outflow
if(qout(ii) > qpipe) qout(ii) = qpipe
end if
qsw(ii) = max(0.,qsw(ii - 1) - qout(ii)) ! m^3
endif
Else
qpnd(ii) = qpnd(ii-1) + qin(ii) !m^3
hpnd = qpnd(ii) / tsa * 1000. !ponding depth on the filter surface, mm
!spillway overflow
If (hpnd > ft_h(sb,kk)) Then
qloss = max(0.,qpnd(ii) - mxvol) !weir outflow
hpnd = ft_h(sb,kk)
qpnd(ii) = max(0.,qpnd(ii) - qloss)
End If
qpndi = qpnd(ii) + qsw(ii-1)
! estimate unsaturated filter flow
if(qsw(ii-1)<0.99*vfiltr) then
if (qpnd(ii)>0) then
whd = (wetfsh + hpnd)
tst = ksat
Do !green and ampt infiltration
fc(ii) = fc(ii - 1) + ksat * dt + whd * Log((tst + whd)
& / (fc(ii - 1) + whd))
If (Abs(fc(ii) - tst) < 0.001) Then
Exit
Else
tst = fc(ii)
End If
End do
!infiltration rate
f(ii) = ksat * (1 + whd / fc(ii)) !mm/hr
!water infiltrated, m^3
qfiltr = f(ii) * dt / 1000. * tsa * ffsa
!infiltration limited by the total available water
If (qfiltr > qpnd(ii)) then
qfiltr = qpnd(ii)
qpnd(ii) = 0.
else
qpnd(ii) = qpnd(ii) - qfiltr
endif
hpnd = qpnd(ii) / tsa * 1000. !mm
!update soil water
qsw(ii) = qsw(ii-1) + qfiltr
else
f(ii) = 0.
qfiltr = 0.
end if
!soil water no more than saturation
if (qsw(ii) > vfiltr) then
hrd = qsw(ii) / vfiltr
qout(ii) = ksat * hrd * dt / 1000. * tsa * ffsa !m3
qsw(ii) = qsw(ii) - qout(ii)
qpnd(ii) = qpndi - qsw(ii) - qout(ii)
else
if (qpnd(ii)>=qpnd(ii-1).and.qout(ii-1)<0.001) then
!rising hydrograph, no outflow
qout(ii) = 0.
else
!receding or continuing hydrograph
qout(ii) = ksat * qsw(ii) / vfiltr * dt / 1000.
& * tsa * ffsa !m3
if (qout(ii)>qout(ii-1)) qout(ii) = qout(ii-1)
qsw(ii) = qsw(ii) - qout(ii)
endif
endif
else
!darcy flow when saturated
qfiltr = ksat * (hpnd + ft_dep(sb,kk)) /
& ft_dep(sb,kk) * dt / 1000. * tsa * ffsa
qout(ii) = qfiltr
qpnd(ii) = qpnd(ii) - qfiltr
if(qpnd(ii)<0) then
qpnd(ii) = 0.
qsw(ii) = qsw(ii-1)+qin(ii)+qpnd(ii-1)-qfiltr
qfiltr = qin(ii) + qpnd(ii-1)
else
qsw(ii) = vfiltr
qfiltr = qout(ii)
endif
end if
!Evapotranspiration loss
qevap = tsa * sub_etday(sb) / 1000. / 1440. * idt !m^3
if(qevap<1e-6) qevap = 0.
qpnd(ii) = qpnd(ii) - qevap
If (qpnd(ii)<0) then
qpnd(ii) = 0.
qevap = 0.
endif
!check if orifice pipe limits outflow in case outflow control exists
if (sf_ptp(sb,kk)==1) then
phead = (qsw(ii)/(tsa*ffsa)/por + qpnd(ii)/tsa) * 1000. !mm
qpipe = pipeflow(pdia,phead) * dt *3600. !m^3
!recalculate water balance if orifice pipe limits outflow
if(qout(ii) > qpipe) then
qout(ii) = qpipe ! m^3
if (qout(ii)<qin(ii)+qpnd(ii-1)+qsw(ii-1)) then
if (qout(ii)<qin(ii)+qpnd(ii-1)) then
qfiltr = qout(ii)
else
qfiltr = qin(ii) + qpnd(ii-1)
endif
qsw(ii) = qsw(ii-1) + qfiltr - qout(ii)
qpnd(ii) = qin(ii) + qpnd(ii-1) - qfiltr
else
qout(ii) = qin(ii) + qpnd(ii-1) + qsw(ii-1)
qfiltr = qin(ii) + qpnd(ii-1)
qsw(ii) = 0.
qpnd(ii) = 0.
endif
qloss = max(0.,qpnd(ii) - mxvol)
qpnd(ii) = max(0.,qpnd(ii) - qloss)
endif
end if
qpnde = qpnd(ii) + qsw(ii)
Endif
! no outlet control: all the infiltration water is added to shallow aquifer recharge for next day\
if (sf_ptp(sb,kk)==0) then
bmp_recharge(sb) = bmp_recharge(sb)
& + qout(ii) / (sub_ha*10000.- tsa) *1000.
qout(ii) = 0. !effluent from the filter unit (through-flow+overflow), normalized to subbasin area
end if
! store the flow output
flw(1,ii) = qin(ii) / (sub_ha *10000. - tsa) * 1000. !mm
flw(2,ii) = qout(ii) / (sub_ha*10000.- tsa) *1000. !mm
flw(3,ii) = qloss / (sub_ha *10000. - tsa) * 1000. !mm
! write(*,'(2i3,20f7.3)') iida, ii, qin(ii),qout(ii),qpnd(ii),
! & qsw(ii),qloss
!--------------------------------------------------------------------------------------
! TSS removal
sloss = 0.; sedrmeff = 0.
! sediment bypass in spillway overflow
if (qloss>0) then
if(qin(ii)>0) then
sedconc = sed(1,ii) / qin(ii) !tons/m3
else
sedconc = sedpnd / qpnd(ii) !tons/m3
endif
sloss = sedconc * qloss !tons
sedpnd = sedpnd + sed(1,ii) - sloss !tons
end if
if (qpndi>0.001) then
spndconc = sedpnd / qpndi ! tons/m^3
else
spndconc = 0.
end if
If (qout(ii)<0.001)then
! no outflow through filter media
if (qloss>0.001) then
sed(2,ii) = sloss
else
sed(2,ii) = 0.
end if
Else
! water temperature, C
tmpw = sub_hhwtmp(sb,ii)
! water viscosity (g/cm-s) using 3rd order polynomial interpolation
mu = -3.e-6 * tmpw ** 3 + 0.0006 * tmpw ** 2 -
& 0.0469 * tmpw + 1.7517
mu = mu * 1.e-2
!filter flow, cm/s
qcms = qout(ii) / (tsa * ffsa) * 100. / dt / 3600.
If (qcms > 0.001) Then
!sedimentation efficiency
effg = (pden - 1) * 981 * dp ** 2 / (18 * mu * qcms)
if (effg<0.001) effg = 0.001
!brownian motion efficiency
effbr = 0.905 * (kb * (tmpw+273.) / (mu * dp * dc *
& qcms)) ** 0.6667
Else
effg = 0.999
effbr = 0.999
End If
!interception efficiency
effl = 1.5 * (dp / dc) ** 2
If (effl > 0.999) effl = 0.99
If (effg > 0.999) effg = 0.99
If (effbr > 0.999) effbr = 0.99
!contact efficiency
effct = effl + effg + effbr
If (effct > 0.999) effct = 0.99
! sediment removal efficiency
sedrmeff = 1. - Exp(-1.5 * (1. - por) * alp * effct *
& ft_dep(sb,kk) / ft_dc(sb,kk))
! sediment removed during the time step
sed_removed = spndconc * qout(ii) * sedrmeff
! sediment through filter, tons
sed(2,ii) = spndconc * qout(ii) * (1. - sedrmeff)
sedpnd = sedpnd - spndconc * qout(ii) !tons
sed(3,ii) = sloss
if (sedpnd<0) sedpnd = 0.
! write cumulative amount of sediment removed
ft_sed_cumul(sb,kk) = ft_sed_cumul(sb,kk) + sed_removed !tons
End if
! write(*,'(3i6,20f10.3)') iyr,iida,ii,qin(ii),
! & qout(ii),qsw(ii),qpnd(ii),qloss,qevap
! write(*,'(3i5,20f10.3)') iyr,iida,ii,precipdt(ii),qin(ii),
! & qout(ii),qloss,qpndi,qpnde,qpnd(ii),qsw(ii),f(ii),sed(1,ii)*1000,
! & sed(2,ii)*1000,sloss*1000
end do
! store end-of-day values for next day
ft_qpnd(sb,kk) = qpnd(nstep)
ft_qsw(sb,kk) = qsw(nstep)
ft_qin(sb,kk) = qin(nstep)
ft_qout(sb,kk) = qout(nstep)
ft_sedpnd(sb,kk) = sedpnd
ft_fc(sb,kk) = fc(nstep)
return
end subroutine