SWAT+ Documentation
  • Introduction to SWAT+
  • Watershed Configuration
    • Spatial Objects
  • Calibration
  • SWAT+ Input Files
    • Input File Format
    • Master File (file.cio)
    • Simulation Settings
      • object.cnt
      • time.sim
        • day_start
        • yrc_start
        • day_end
        • yrc_end
        • step
      • print.prt
        • nyskip
        • interval
        • aa_int_cnt
        • hydcon
        • object
      • object.prt
        • obj_typ
        • obj_typ_no
        • hyd_typ
    • Climate
      • weather-sta.cli
        • name (weather_sta.cli)
        • wgn
        • pcp
        • tmp
        • slr
        • hmd
        • wnd
        • pet
        • atmo_dep
      • weather-wgn.cli
        • name (weather_wgn.cli)
        • yrs_pcp
        • tmp_max_ave
        • tmp_min_ave
        • tmp_max_sd
        • tmp_min_sd
        • pcp_ave
        • pcp_sd
        • pcp_skew
        • wet_dry
        • wet_wet
        • pcp_days
        • pcp_hhr
        • slr_ave
        • dew_ave
        • wnd_ave
      • pcp.cli and pcp data files
      • tmp.cli and tmp data files
      • hmd.cli and hmd data files
      • slr.cli and slr data files
      • wnd.cli and wnd data files
      • atmo.cli
        • timestep
        • num_aa
    • Basin
      • codes.bsn
        • pet
        • crack
        • swift_out
        • rte_cha
        • nostress
        • carbon
        • lapse
        • uhyd
        • tiledrain
        • wtable
        • soil_p
        • gampt
        • qual2e
        • gwflow
      • parameters.bsn
        • sw_init
        • surq_lag
        • adj_pkrt
        • prf
        • orgn_min
        • n_uptake
        • p_uptake
        • n_perc
        • p_perc
        • p_soil
        • p_avail
        • rsd_decomp
        • pest_perc
        • msk_co1
        • msk_co2
        • msk_x
        • nperco_lchtile
        • evap_adj
        • denit_exp
        • denit_frac
        • adj_uhyd
        • cn_froz
        • dorm_hr
        • plaps
        • tlaps
        • n_fix_max
        • rsd_decay
        • urb_init_abst
        • uhyd_alpha
        • splash
        • rill
        • surq_exp
        • cov_mgt
        • co2
    • Landscape Units
      • ls_unit.def
        • id (ls_unit.def)
        • name (ls_unit.def)
        • elem_tot
        • elements
      • ls_unit.ele
        • id (ls_unit.ele)
        • name (ls_unit.ele)
        • obj_typ
        • obj_typ_no
        • bsn_frac
    • Routing Units
      • rout_unit.rtu
        • id (rout_unit.rtu)
        • name (rout_unit.rtu)
        • define
        • topo
        • field
      • rout_unit.def
        • id (rout_unit.def)
        • name (rout_unit.def)
        • elem_tot
        • elements
      • rout_unit.ele
        • id (rout_unit.ele)
        • name (rout_uni.ele)
        • obj_typ
        • obj_id
    • Hydrologic Response Units
      • hru-data.hru
        • id (hru-data.hru)
        • name (hru-data.hru)
        • topo
        • hydro
        • soil
        • lu_mgt
        • soil_plant_init
        • surf_stor
        • snow
        • field
      • hru-lte.hru
        • id (hru-lte.hru)
        • name (hru-lte.hru)
        • area
        • cn2
        • cn3_swf
        • t_conc
        • soil_dp
        • perco_co
        • slp
        • slp_len
        • et_co
        • aqu_sp_yld
        • alpha_bf
        • revap
        • rchg_dp
        • sw_init
        • aqu_init
        • aqu_sh_flo
        • aqu_dp_flo
        • snow_h2o
        • lat
        • soil_text
        • trop_flag
        • grow_start
        • grow_end
        • plnt_typ
        • stress
        • pet_flag
        • irr_flag
        • irr_src
        • t_drain
        • usle_k
        • usle_c
        • usle_p
        • usle_ls
    • Hydrology
      • topography.hyd
        • name (topography.hyd)
        • slp
        • slp_len
        • lat_len
        • depos
      • hydrology.hyd
        • name (hydrology.hyd)
        • lat_time
        • lat_sed
        • can_max
        • esco
        • epco
        • orgn_enrich
        • orgp_enrich
        • cn3_swf
        • bio_mix
        • perco
        • lat_orgn
        • lat_orgp
        • pet_co
        • latq_co
      • snow.sno
        • name (snow.sno)
        • fall_tmp
        • melt_tmp
        • melt_max
        • melt_min
        • tmp_lag
        • snow_h2o
        • cov50
        • snow_init
      • field.fld
        • name (field.fld)
        • len
        • wd
    • Soils
      • soils.sol
        • name (soils.sol)
        • hyd_grp
        • dp_tot
        • anion_excl
        • perc_crk
        • texture
        • bd
        • awc
        • soil_k
        • carbon
        • clay
        • silt
        • sand
        • rock
        • alb
        • usle_k
        • ec
        • caco3
        • ph
      • soil_plant.ini
        • name (soil_plant.ini)
        • sw_frac
        • nutrients
        • pest
        • salt
      • nutrients.sol
        • name (nutrients.sol)
        • exp_co
        • lab_p
        • nitrate
        • fr_hum_act
        • hum_c_n
        • hum_c_p
    • Landuse and Management
      • landuse.lum
        • name (landuse.lum)
        • cal_grp
        • plnt_com
        • mgt
        • cn2
        • cons_prac
        • urban
        • urb_ro
        • ov_mann
        • tile
        • sep
        • vfs
        • grww
        • bmp
      • plant.ini
        • name (plant.ini)
        • plnt_cnt
        • rot_yr_ini
        • plnt_name
        • lc_status
        • lai_init
        • bm_init
        • phu_init
        • plnt_pop
        • yrs_init
        • rsd_init
      • management.sch
        • name (management.sch)
        • op_typ
        • op_data1
        • op_data2
        • op_data3
      • cntable.lum
        • name (cntable.lum)
        • cn_a
        • cn_b
        • cn_c
        • cn_d
      • cons_practice.lum
        • name (cons_practice.lum)
        • usle_p
        • slp_len_max
      • ovn_table.lum
        • name (ovn_table.lum)
        • ovn_mean
        • ovn_min
        • ovn_max
    • Decision Tables
      • "name".dtl
        • var
        • obj
        • obj_num
        • lim_var
        • lim_op
        • lim_const
        • alt
        • act_typ
        • obj
        • obj_num
        • name
        • option
        • const
        • const2
        • fp
        • outcome
    • Management Practices
      • harv.ops
        • name (harv.ops)
        • harv_typ
        • harv_idx
        • harv_eff
        • harv_bm_min
      • graze.ops
        • name (graze.ops)
        • fertname
        • bm_eat
        • bm_tramp
        • man_amt
        • grz_bm_min
      • irr.ops
        • name (irr.ops)
        • irr_eff
        • surq_rto
        • irr_amt
        • irr_dep
        • irr_salt
        • irr_no3n
        • irr_po4
      • chem_app.ops
        • name (chem_app.ops)
        • app_eff
        • inject_dp
        • surf_frac
      • fire.ops
        • name (fire.ops)
        • chg_cn2
        • frac_burn
      • sweep.ops
        • name (sweep.ops)
        • swp_eff
        • frac_curb
    • Structural Practices
      • tiledrain.str
        • name (tiledrain.str)
        • dp
        • t_fc
        • lag
        • rad
        • dist
        • drain
        • pump
        • lat_ksat
      • filterstrip.str
        • name (filterstrip.str)
        • fld_vfs
        • con_vfs
        • cha_q
      • grassedww.str
        • name (grassedww.str)
        • mann
        • sed_co
        • dp
        • wd
        • len
        • slp
      • bmpuser.str
        • name (bmpuser.str)
        • sed_eff
        • ptlp_eff
        • solp_eff
        • ptln_eff
        • soln_eff
        • bact_eff
      • septic.str
        • name (septic.str)
        • typ
        • yr
        • operation
        • residents
        • area
        • t_fail
        • dp_bioz
        • thk_bioz
        • cha_dist
        • sep_dens
        • bm_dens
        • bod_decay
        • bod_conv
        • fc_lin
        • fc_exp
        • fecal_decay
        • tds_conv
        • mort
        • resp
        • slough1
        • slough2
        • nit
        • denit
        • p_sorp
        • p_sorp_max
        • solp_slp
        • solp_int
    • Databases
      • plants.plt
        • name (plants.plt)
        • plnt_typ
        • gro_trig
        • nfix_co
        • days_mat
        • bm_e
        • harv_idx
        • lai_pot
        • frac_hu1
        • lai_max1
        • frac_hu2
        • lai_max2
        • hu_lai_decl
        • dlai_rate
        • can_ht_max
        • rt_dp_max
        • tmp_opt
        • tmp_base
        • frac_n_yld
        • frac_p_yld
        • frac_n_em
        • frac_n_50
        • frac_n_mat
        • frac_p_em
        • frac_p_50
        • frac_p_mat
        • harv_idx_ws
        • usle_c_min
        • stcon_max
        • vpd
        • frac_stcon
        • ru_vpd
        • co2_hi
        • bm_e_hi
        • plnt_decomp
        • lai_min
        • bm_tree_acc
        • yrs_mat
        • bm_tree_max
        • ext_co
        • leaf_tov_min
        • leaf_tov_max
        • bm_dieoff
        • rt_st_beg
        • rt_st_end
        • plnt_pop1
        • frac_lai1
        • plnt_pop2
        • frac_lai2
        • frac_sw_gro
        • aeration
        • rsd_pctcov
        • rsd_covfac
      • urban.urb
        • name (urban.urb)
        • frac_imp
        • frac_dc_imp
        • curb_den
        • urb_wash
        • dirt_max
        • t_halfmax
        • conc_totn
        • conc_totp
        • conc_no3
        • urb_cn
      • tillage.til
        • name (tillage.til)
        • mix_eff
        • mix_dp
      • fertilizer.frt
        • name (fertilizer.frt)
        • min_n
        • min_p
        • org_n
        • org_p
        • nh3_n
      • pesticide.pes
        • name (pesticide.pes)
        • soil_ads
        • frac_wash
        • hl_foliage
        • hl_soil
        • solub
        • aq_reac
        • aq_volat
        • mol_wt
        • aq_resus
        • aq_settle
        • ben_act_dep
        • ben_bury
        • ben_reac
      • septic.sep
        • name (septic.sep)
        • q_rate
        • bod
        • tss
        • nh4_n
        • no3_n
        • no2_n
        • org_n
        • min_p
        • org_p
        • fcoli
    • Aquifers
      • aquifer.aqu
        • id (aquifer.aqu)
        • name (aquifer.aqu)
        • aqu_init
        • gw_flo
        • dep_bot
        • dep_wt
        • no3_n
        • sol_p
        • carbon
        • flo_dist
        • flo_max
        • alpha_bf
        • revap
        • rchg_dp
        • spec_yld
        • hl_no3n
        • flo_min
        • revap_min
      • initial.aqu
        • name (initial.aqu)
        • org_min
        • pest
        • path
        • hmet
        • salt
    • GWFlow
    • Channels
      • channel-lte.cha
        • id (channel-lte.cha)
        • name (channel-lte.cha)
        • ini
        • hyd
        • nut
      • initial.cha
        • name (initial.cha)
        • org_min
        • pest
        • salt
      • hyd-sed-lte.cha
        • name (hyd-sed-lte.cha)
        • wd
        • dp
        • slp
        • len
        • mann
        • k
        • erod_fact
        • cov_fact
        • sinu
        • eq_slp
        • d50
        • clay
        • carbon
        • dry_bd
        • side_slp
        • bed_load
        • fps
        • fpn
        • n_conc
        • p_conc
        • p_bio
      • nutrients.cha
        • name (nutrients.cha)
        • plt_n
        • plt_p
        • alg_stl
        • ben_disp
        • ben_nh3n
        • ptln_stl
        • ptlp_stl
        • cst_stl
        • ben_cst
        • cbn_bod_co
        • air_rt
        • cbn_bod_stl
        • ben_bod
        • bact_die
        • cst_decay
        • nh3n_no2n
        • no2n_no3n
        • ptln_nh3n
        • ptlp_solp
        • q2e_lt
        • q2e_alg
        • chla_alg
        • alg_n
        • alg_p
        • alg_o2_prod
        • alg_o2_resp
        • o2_nh3n
        • o2_no2n
        • alg_grow
        • alg_resp
        • slr_act
        • lt_co
        • const_n
        • const_p
        • lt_nonalg
        • alg_shd_l
        • alg_shd_nl
        • nh3_pref
    • Reservoirs and Ponds
      • reservoir.res
        • id (reservoir.res)
        • name (reservoir.res)
        • init
        • hyd
        • rel
        • sed
        • nut
      • initial.res
        • name (initial.res)
        • org_min
        • pest
        • salt
      • hydrology.res
        • name (hydrology.res)
        • yr_op
        • mon_op
        • area_ps
        • vol_ps
        • area_es
        • vol_es
        • k
        • evap_co
        • shp_co1
        • shp_co2
      • sediment.res
        • name (sediment.res)
        • nsed
        • d50
        • carbon
        • bd
        • sed_stl
        • stl_vel
      • nutrients.res
        • name (nutrients.res)
        • mid_start
        • mid_end
        • mid_n_stl
        • n_stl
        • mid_p_stl
        • p_stl
        • chla_co
        • secchi_co
        • theta_n
        • theta_p
        • n_min_stl
        • p_min_stl
      • weir.res
        • name (weir.res)
        • linear_c
        • exp_k
        • width
        • height
    • Wetlands
      • wetland.wet
        • id (wetland.wet)
        • name (wetland.wet)
        • init
        • hyd
        • rel
        • sed
        • nut
      • hydrology.wet
        • name (hydrology.wet)
        • hru_ps
        • dp_ps
        • hru_es
        • dp_es
        • k
        • evap
        • vol_area_co
        • vol_dp_a
        • vol_dp_b
        • hru_frac
    • Nutrient initialization
      • om_water.ini
        • name (om_water.ini)
        • vol
        • sed
        • part_n
        • part_p
        • no3
        • solp
        • chl_a
        • nh3
        • no2
        • cbn_bod
        • dis_ox
        • sand
        • silt
        • clay
        • sm_ag
        • l_ag
        • gvl
        • tmp
    • Constituents
      • constituents.cs
      • pest_water.ini
      • pest_hru.ini
      • salt_water.ini
      • salt_hru.ini
    • Point Sources and Inlets
      • recall.rec
        • id (recall.rec)
        • rec_typ
        • file
      • 'filename'.rec
    • Connectivity
      • 'object'.con
        • id
        • name
        • gis_id
        • area
        • lat
        • lon
        • elev
        • 'obj'
        • wst
        • cst
        • ovfl
        • rule
        • out_tot
        • obj_typ
        • obj_id
        • hyd_typ
        • frac
      • aqu_cha.lin
      • chan_surf.lin
    • Water Allocation
      • water_allocation.wro
        • rule_typ
        • cha_ob
        • ob_typ (source)
        • limit_mon
        • ob_typ (demand)
        • withdr
        • amount
        • right
        • rcv_ob
        • rcv_num
        • srcs
        • src
        • frac
        • comp
    • Calibration
      • codes.sft
      • wb_parms.sft
      • water_balance.sft
      • cal_parms.cal
      • calibration.cal
  • SWAT+ Output Files
    • Output File Format
    • Debugging Outputs
    • Soil
    • Management
    • Flow Duration Curve
    • Water Balance
    • Nutrient Balance
    • Losses
    • Plant and Weather
    • Channel
    • Aquifer
    • Reservoir
    • Recall
    • Hydrographs
    • Routing Unit
    • Pesticides
    • Object Outputs
  • Theoretical Documentation
    • ☁️Section 1: Climate
      • 🟰Chapter 1:1 Equations: Energy
        • ☀️1:1.1 Sun-Earth Relationships
          • 1:1.1.1 Distance between Earth and Sun
          • 1:1.1.2 Solar Declination
          • 🌄1:1.1.3 Solar Noon, Sunrise, Sunset, and Daylength
        • 1:1.2 Solar Radiation
          • 👽1:1.2.1 Extraterrestrial Radiation
          • 1:1.2.2 Solar Radiation under Cloudless Skies
          • 1:1.2.3 Daily Solar Radiation
          • 1:1.2.4 Hourly Solar Radiation
          • 1:1.2.5 Daily Net Radiation
        • 1:1.3 Temperature
          • 1:1.3.1 Daily Air Temperature
          • 1:1.3.2 Hourly Air Temperature
          • 1:1.3.3 Soil Temperature
          • 1:1.3.4 Water Temperature
        • 1:1:4 Wind Speed
      • Chapter 1:2 Atmospheric Water
        • 1:2.1 Precipitation
        • 1:2.2 Maximum Half-Hour Rainfall
        • 1:2.3 Water Vapor
        • 1:2.4 Snow Cover
        • 1:2.5 Snow Melt
          • 1:2.5.1 Snow Pack Temperature
            • Snow Melt Equation
      • Chapter 1:3 Weather Generator
        • 1:3.1 Precipitation
          • 1:3.1.1 Occurrence of Wet or Dry Day
          • 1:3.1.2 Amount of Precipitation
        • 1:3.2 Maximum Half-Hour Rainfall
          • 1:3.2.1 Monthly Maximum Half-Hour Rain
          • 1:3.2.2 Daily Maximum Half-Hour Rain Value
        • 1:3.3 Distribution of Rainfall Within Day
          • 1:3.3.1 Normalized Intensity Distribution
          • 1:3.3.2 Generated Time to Peak Intensity
          • 1:3.3.3 Total Rainfall and Duration
        • 1:3.4 Solar Radiation & Temperature
          • 1:3.4.1 Daily Residuals
          • 1:3.4.2 Generated Values
          • 1:3.4.3 Adjustment for Clear/Overcast Conditions
            • Maximum Temperature
            • Solar Radiation
        • 1:3.5 Relative Humidity
          • 1:3.5.1 Mean Monthly Relative Humidity
          • 1:3.5.2 Generated Daily Value
          • 1:3.5.3 Adjustment for Clear/Overcast Conditions
        • 1:3.6 Wind Speed
      • Chapter 1:4 Climate Customization
        • 1:4.1 Elevation Bands
        • 1:4.2 Climate Change
    • Section 2: Hydrology
      • Surface Runoff
        • Runoff Volume: SCS Curve Number Procedure
        • SCS Curve Number
        • Soil Hydrologic Groups
        • Antecedent Soil Moisture Condition
        • Retention Parameter
        • Slope Adjustments
        • Runoff Volume: Green & Ampt Infiltration Method
        • Peak Runoff Rate
        • Time of Concentration
          • Overland Flow Time of Concentration
          • Channel Flow Time of Concentration
        • Runoff Coefficient
        • Rainfall Intensity
        • Modified Rational Formula
        • Surface Runoff Lag
        • Transmission Losses
      • Chapter 2:2 Evapotranspiration
        • 2:2.1 Canopy Storage
        • 2:2.2 Potential Evapotranspiration
          • 2:2.2.1 Penman-Monteith Method
            • Soil Heat Flux
            • Aerodynamic Resistance
            • Canopy Resistance
            • Combined Term
          • 2:2.2.2 Priestley-Taylor Method
          • 2:2.2.3 Hargreaves Method
          • 2:2.2.4 Reading Measured or Estimated PET
        • 2:2.3 Actual Evapotranspiration
          • 2:2.3.1 Evaporation of Intercepted Rainfall
          • 2:2.3.2 Transpiration
          • 2:2.3.3 Sublimation and Evaporation from the Soil
            • Sublimation
            • Soil Water Evaporation
          • 2:2.3.4 Evaporation from Ponded Water
      • Soil Water
        • Soil Structure
        • Percolation
        • Bypass Flow
        • Perched Water Table
        • Lateral Flow
          • Lateral Flow Lag
      • Groundwater
        • Groundwater Systems
        • Shallow Aquifer
          • Recharge
          • Partitioning of Recharge Between Shallow and Deep Aquifer
          • Groundwater/Base Flow
          • Revap
          • Pumping
          • Groundwater Height
        • Deep Aquifer
    • Section 3: Nutrients/Pesticides
      • Nitrogen
        • Nitrogen Cycle in the Soil
          • Initialization of Soil Nitrogen Levels
        • Mineralization & Decomposition / Immobilization
          • Humus Mineralization
          • Residue Decomposition & Mineralization
        • Nitrification & Ammonia Volatilization
        • Denitrification
        • Atmospheric Deposition
          • Nitrogen in Rainfall
          • Nitrogen Dry Deposition
        • Fixation
        • Upward Movement of Nitrate in Water
        • Leaching
        • Nitrate in the Shallow Aquifer
      • Phosphorus
        • Phosphorus Cycle
          • Initialization of Soil Phosphorus Levels
        • Mineralization & Decomposition / Immobilization
          • Humus Mineralization
          • Residue Decomposition & Mineralization
        • Sorption of Inorganic P
        • Leaching
        • Phosphorus in the Shallow Aquifer
      • Pesticides
        • Wash-off
        • Degradation
        • Leaching
      • Bacteria
        • Wash-off
        • Bacteria Die-off/Re-growth
        • Leaching
      • Carbon
        • Sub-model Description
        • Changes from previous version
        • Analytical Solutions
    • Section 4: Erosion
      • Sediment
        • MUSLE
          • Soil Erodibility Factor
          • Cover and Management Factor
          • Support Practice Factor
          • Topographic Factor
          • Coarse Fragment Factor
        • USLE
          • Rainfall Erodibility Index
        • Snow Cover Effects
        • Sediment Lag in Surface Runoff
        • Sediment in Lateral & Groundwater Flow
      • Nutrient Transport
        • Nitrate Movement
        • Organic N in Surface Runoff
          • Enrichment Ratio
        • Soluble Phosphorus Movement
        • Organic & Mineral P Attached to Sediment in Surface Runoff
          • Enrichment Ratio
        • Nutrient Lag in Surface Runoff and Lateral Flow
      • Pesticide Transport
        • Phase Distribution of Pesticide
        • Movement of Soluble Pesticide
        • Transport of Sorbed Pesticide
          • Enrichment Ratio
        • Pesticide Lag in Surface Runoff and Lateral Flow
      • Bacteria Transport
        • Bacteria in Surface Runoff
        • Bacteria Attached to Sediment in Surface Runoff
          • Enrichment Ratio
        • Bacteria Lag in Surface Runoff
      • Water Quality Parameters
        • Algae
        • Carbonaceous Biological Oxygen Demand
          • Enrichment Ratio
        • Dissolved Oxygen
          • Oxygen Saturation Concentration
    • Section 5: Land Cover/Plant
      • Growth Cycle
        • Heat Units
          • Heat Unit Scheduling
        • Dormancy
        • Plant Types
      • Optimal Growth
        • Potential Growth
          • Biomass Production
            • Impact of Climate on Radiation-Use Efficiency
            • Modification of Biomass Calculation for Trees
          • Canopy Cover and Height
          • Root Development
          • Maturity
        • Water Uptake by Plants
          • Impact of Low Soil Water Content
          • Actual Water Uptake
        • Nutrient Uptake by Plants
          • Nitrogen Uptake
            • Nitrogen Fixation
          • Phosphorus Uptake
        • Crop Yield
      • Actual Growth
        • Growth Constraints
          • Water Stress
          • Temperature Stress
          • Nitrogen Stress
          • Phosphorus Stress
        • Actual Growth
          • Biomass Override
        • Actual Yield
          • Harvest Index Override
          • Harvest Efficiency
    • Section 6: Management Practices
      • General Management
        • Planting/Beginning of Growing Season
        • Harvest Operation
        • Grazing Operation
        • Harvest & Kill Operation
        • Kill/End of Growing Season
        • Tillage
          • Biological Mixing
        • Fertilizer Application
        • Auto-Application of Fertilizer
        • Continuous Application of Fertilizer
        • Pesticide Application
      • Water Management
        • Irrigation
          • Manual Application of Irrigation
          • Auto-Application of Irrigation
        • Tile Drainage
        • Impounded/Depressional Areas
        • Water Transfer
        • Consumptive Water Use
        • Point Source Loadings
      • Urban Areas
        • Characteristics of Urban Areas
        • Surface Runoff from Urban Areas
        • USGS Regression Equations
        • Build Up/Wash Off
          • Street Cleaning
      • Septic Systems
        • Biozone Algorithm
          • Buildup of Live Bacterial Biomass
          • Fate and Transport of Bacterial Biomass
          • Field Capacity
          • Clogging Effect on Hydraulic Conductivity
          • Soil Moisture and Percolation
          • Nitrogen, BOD, Fecal Coliform
          • Phosphorus Removal
          • Model Assumptions
        • Integration of Biozone Algorithm
          • Simulating Active and Failing Systems
      • Filter Strips and Grassed Waterways
        • Filter Strips
          • Empirical Model Development
          • Sediment Reduction Model
          • Nutrient Reduction Models
            • Total Nitrogen
            • Nitrate Nitrogen
            • Total Phosphorus
            • Soluble Phosphorus
          • VFS SWAT+ Model Structure
        • Grassed Waterways
    • Section 7: Main Channel Processes
      • Water Routing
        • Channel Characteristics
        • Flow Rate and Velocity
        • Variable Storage Routing Method
        • Muskingum Routing Method
        • Transmission Losses
        • Evaporation Losses
        • Bank Storage
        • Channel Water Balance
      • Sediment Routing
        • Landscape Contribution to Subbasin Routing Reach
        • Sediment Routing In Stream Channels
          • Simplified Bagnold Equation (Default method)
          • Physics Based Approach for Channel Erosion
        • Channel Erodibility Factor
        • Channel Cover Factor
        • Channel Downcutting and Widening
      • In-Stream Nutrient Processes
        • Algae
          • Chlorophyll a
          • Algal Growth
            • Local Specific Growth Rate of Algae
            • Local Respiration Rate of Algae
            • Local Settling Rate of Algae
        • Nitrogen Cycle
          • Organic Nitrogen
          • Ammonium
          • Nitrite
          • Nitrate
        • Phosphorus Cycle
          • Organic Phosphorus
          • Inorganic/Soluble Phosphorus
        • Carbonaceous Biological Oxygen Demand
        • Oxygen
          • Oxygen Saturation Concentration
          • Reaeration
            • Reaeration By Fickian Diffusion
            • Reaeration By Turbulent Flow Over A Dam
      • In-Stream Pesticide Transformations
        • Pesticide In The Water
          • Solid-Liquid Partitioning
          • Degradation
          • Volatilization
          • Settling
          • Outflow
        • Pesticide In The Sediment
          • Solid-Liquid Partitioning
          • Degradation
          • Resuspension
          • Diffusion
          • Burial
        • Mass Balance
      • Bacteria Routing
        • Bacteria Decay
        • Bacteria Sediment
      • Heavy Metal Routing
    • Section 8: Water Bodies
      • Impoundment Water Routing
        • Reservoirs
          • Surface Area
          • Precipitation
          • Evaporation
          • Seepage
          • Outflow
            • Measured Daily Outflow
            • Measured Monthly Outflow
            • Average Annual Release Rate For Uncontrolled Reservoir
            • Target Release For Controlled Reservoir
        • Ponds/Wetlands
          • Surface Area
          • Precipitation
          • Inflow
          • Evaporation
          • Seepage
          • Outflow
            • Pond Outflow
            • Wetland Outflow
        • Depressions/Potholes
          • Surface Area
          • Precipitation
          • Inflow
          • Evaporation
          • Seepage
          • Outflow
            • Overflow
            • Release Operation
            • Tile Flow
      • Sediment In Water Bodies
        • Mass Balance
        • Settling
        • Sediment Outflow
      • Nutrients In Water Bodies
        • Nutrient Transformations
        • Total Balance
        • Eutrophication
          • Phosphorus/Chlorophyll a Correlations
      • Pesticides In Water Bodies
        • Pesticide In The Water
          • Solid-Liquid Partitioning
          • Degradation
          • Volatilization
          • Settling
          • Outflow
        • Pesticide In The Sediment
          • Solid-Liquid Partitioning
          • Degradation
          • Resuspension
          • Diffusion
          • Burial
        • Mass Balance
      • Bacteria In Water Bodies
        • Bacteria Decay
    • References
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The amount of soluble, inorganic phosphorus in the stream may be increased by the mineralization of organic phosphorus and diffusion of inorganic phosphorus from the streambed sediments. The soluble phosphorus concentration in the stream may be decreased by the uptake of inorganic P by algae. The change in soluble phosphorus for a given day is:

7:3.3.4

where is the change in solution phosphorus concentration (mg P/L), is the rate constant for mineralization of organic phosphorus (day or hr), is the organic phosphorus concentration at the beginning of the day (mg P/L), is the benthos (sediment) source rate for soluble P (mg P/m-day or mg P/m-hr), is the depth of water in the channel (m), is the fraction of algal biomass that is phosphorus (mg P/mg alg biomass), is the local growth rate of algae (day or hr), is the algal biomass concentration at the beginning of the day (mg alg/L), and is the flow travel time in the reach segment (day or hr). The local rate constant for mineralization of organic phosphorus is calculated with equation 7:3.3.2. Section 7:3.1.2.1 describes the calculation of the local growth rate of algae. The calculation of depth and travel time is reviewed in Chapter 7:1.

The user defines the benthos source rate for soluble P at 20C. The benthos source rate for soluble phosphorus is adjusted to the local water temperature using the relationship:

7:3.3.5

where is the benthos (sediment) source rate for soluble P (mg P/m-day or mg P/m-hr), is the benthos (sediment) source rate for soluble phosphorus at 20C (mg P/m-day or mg P/m-hr), and is the average water temperature for the day or hour (C).

Table 7:3-3: SWAT+ input variables used in in-stream phosphorus calculations.

Variable Name
Definition
File Name
  1. Theoretical Documentation
  2. Section 7: Main Channel Processes
  3. In-Stream Nutrient Processes
  4. Phosphorus Cycle

Inorganic/Soluble Phosphorus

ΔsolPstr=(βP,4∗orgPstr+σ2(1000∗depth)−α2∗μa∗algae)∗TT\Delta solP_{str}=(\beta_{P,4}*orgP_{str}+\frac{\sigma_2}{(1000*depth)}-\alpha_2*\mu _a*algae)*TTΔsolPstr​=(βP,4​∗orgPstr​+(1000∗depth)σ2​​−α2​∗μa​∗algae)∗TT
ΔsolPstr\Delta solP_{str}ΔsolPstr​
βP,4\beta_{P,4}βP,4​
−1^{-1}−1
−1^{-1}−1
orgPstrorgP_{str}orgPstr​
σ2\sigma_2σ2​
2^22
2^22
depthdepthdepth
α2\alpha_2α2​
μa\mu_aμa​
−1^{-1}−1
−1^{-1}−1
algaealgaealgae
TTTTTT
°\degree°
σ2=σ2,20∗1.074(Twater−20)\sigma _2 =\sigma_{2,20} *1.074^{(T_{water}-20)}σ2​=σ2,20​∗1.074(Twater​−20)
σ2\sigma_2σ2​
2^22
2^22
σ2,20\sigma_{2,20}σ2,20​
°\degree°
2^22
2^22
TwaterT_{water}Twater​
°\degree°

AI2

α2\alpha_2α2​: Fraction of algal biomass that is phosphorus (mg P/mg alg biomass)

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RHOQ

ρa,20\rho_{a,20}ρa,20​: Local algal respiration rate at 20°\degree°C (day−1^{-1}−1)

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BC4

βP,4,20\beta_{P,4,20}βP,4,20​: Local rate constant for organic phosphorus mineralization at 20°\degree°C (day−1^{-1}−1)

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RS5

σ5,20\sigma_{5,20}σ5,20​: Local settling rate for organic phosphorus at 20°\degree°C (day−1^{-1}−1)

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RS2

σ2,20\sigma_{2,20}σ2,20​ : Benthos (sediment) source rate for soluble phosphorus at 20°\degree°C (mg P/m2^22-day)

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