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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  1. Theoretical Documentation
  2. Section 3: Nutrients/Pesticides
  3. Bacteria

Bacteria Die-off/Re-growth

Last updated 3 years ago

Chick’s Law first order decay equation is used to determine the quantity of bacteria removed from the system through die-off and added to the system by regrowth. The equation for die-off/re-growth was taken from Reddy et al. (1981) as modified by Crane and Moore (1986) and later by Moore et al. (1989). The equation was modified in SWAT+ to include a user-defined minimum daily loss. Die-off/re-growth is modeled for the two bacteria populations on foliage, in the surface soil solution and sorbed to surface soil particles. The equations used to calculate daily bacteria levels in the different pools are:

bactlpfol,i=bactlpfol,i−1∗exp(−μlpfol,net)−bactmin,lpbact_{lpfol,i}=bact_{lpfol,i-1}*exp(-\mu _{lpfol,net})-bact_{min,lp}bactlpfol,i​=bactlpfol,i−1​∗exp(−μlpfol,net​)−bactmin,lp​ 3:4.2.1

bactpfol,i=bactpfol,i−1∗exp(−μpfol,net)−bactmin,pbact_{pfol,i}=bact_{pfol,i-1}*exp(-\mu _{pfol,net})-bact_{min,p}bactpfol,i​=bactpfol,i−1​∗exp(−μpfol,net​)−bactmin,p​ 3:4.2.2

bactlpsol,i=bactlpsol,i−1∗exp(−μlpsol,net)−bactmin,lpbact_{lpsol,i}=bact_{lpsol,i-1}*exp(-\mu _{lpsol,net})-bact_{min,lp}bactlpsol,i​=bactlpsol,i−1​∗exp(−μlpsol,net​)−bactmin,lp​ 3:4.2.3

bactpsol,i=bactpsol,i−1∗exp(−μpsol,net)−bactmin,pbact_{psol,i}=bact_{psol,i-1}*exp(-\mu _{psol,net})-bact_{min,p}bactpsol,i​=bactpsol,i−1​∗exp(−μpsol,net​)−bactmin,p​ 3:4.2.4

bactlpsorb,i=bactlpsord,i−1∗exp(−μlpsorb,net)−bactmin,lpbact_{lpsorb,i}=bact_{lpsord,i-1}*exp(-\mu _{lpsorb,net})-bact_{min,lp}bactlpsorb,i​=bactlpsord,i−1​∗exp(−μlpsorb,net​)−bactmin,lp​ 3:4.2.5

bactpsorb,i=bactpsorb,i−1∗exp(−μpsorb,net)−bactmin,pbact_{psorb,i}=bact_{psorb,i-1}*exp(-\mu _{psorb,net})-bact_{min,p}bactpsorb,i​=bactpsorb,i−1​∗exp(−μpsorb,net​)−bactmin,p​ 3:4.2.6

where bactlpfol,ibact_{lpfol,i}bactlpfol,i​ is the amount of less persistent bacteria present on foliage on day iii (#cfu/m2^22), bactlpfol,i−1bact_{lpfol,i-1}bactlpfol,i−1​ is the amount of less persistent bacteria present on foliage on day i−1i-1i−1 (#cfu/m2^22), μlpfol,net\mu _{lpfol,net}μlpfol,net​ is the overall rate constant for die-off/re-growth of less persistent bacteria on foliage (1/day), bactmin,lpbact_{min,lp}bactmin,lp​ is the minimum daily loss of less persistent bacteria (#cfu/m2^22), bactpfol,ibact_{pfol,i}bactpfol,i​ is the amount of persistent bacteria present on foliage on day iii (#cfu/m2^22), bactpfol,i−1bact_{pfol,i-1}bactpfol,i−1​ is the amount of persistent bacteria present on foliage on day i−1i-1i−1(#cfu/m2^22), μpfol,net\mu_{pfol,net}μpfol,net​ is the overall rate constant for die-off/re-growth of persistent bacteria on foliage (1/day), bactmin,pbact_{min,p}bactmin,p​ is the minimum daily loss of persistent bacteria (#cfu/m2^22), bactlpsol,ibact_{lpsol,i}bactlpsol,i​ is the amount of less persistent bacteria present in soil solution on day iii (#cfu/m2^22), bactlpsol,i−1bact_{lpsol,i-1}bactlpsol,i−1​ is the amount of less persistent bacteria present in soil solution on day i−1i-1i−1 (#cfu/m2^22), μlpsol,net\mu_{lpsol,net}μlpsol,net​ is the overall rate constant for die-off/re-growth of less persistent bacteria in soil solution (1/day), bactpsol,ibact_{psol,i}bactpsol,i​ is the amount of persistent bacteria present in soil solution on day iii (#cfu/m2^22), bactpsol,i−1bact_{psol,i-1}bactpsol,i−1​ is the amount of persistent bacteria present in soil solution on day i−1i-1i−1(#cfu/m2^22), μpsol,net\mu_{psol,net}μpsol,net​ is the overall rate constant for die-off/re-growth of persistent bacteria in soil solution (1/day), bactlpsorb,ibact_{lpsorb,i}bactlpsorb,i​ is the amount of less persistent bacteria sorbed to the soil on day iii (#cfu/m2^22), bactlpsorb,i−1bact_{lpsorb,i-1}bactlpsorb,i−1​ is the amount of less persistent bacteria sorbed to the soil on day i−1i-1i−1 (#cfu/m2^22), μlpsorb,net\mu _{lpsorb,net}μlpsorb,net​ is the overall rate constant for die-off/re-growth of less persistent bacteria sorbed to the soil (1/day), bactpsorb,ibact_{psorb,i}bactpsorb,i​ is the amount of persistent bacteria sorbed to the soil on day iii (#cfu/m2^22), bactpsorb,i−1bact_{psorb,i-1}bactpsorb,i−1​ is the amount of persistent bacteria sorbed to the soil on day i−1i-1i−1 (#cfu/m2^22), and μpsorb,net\mu_{psorb,net}μpsorb,net​ is the overall rate constant for die-off/re-growth of persistent bacteria sorbed to the soil (1/day).

The overall rate constants define the net change in bacterial population for the different pools modeled. The impact of temperature effects on bacteria die-off/re-growth were accounted for using equations proposed by Mancini (1978). The user defines the die-off and growth factors for the two bacterial populations in the different pools at 20°C. The overall rate constants at 20°C are then calculated:

μlpfol,net,20=μlpfol,die,20−μlpfol,grw,20\mu_{lpfol,net,20}=\mu_{lpfol,die,20}-\mu_{lpfol,grw,20}μlpfol,net,20​=μlpfol,die,20​−μlpfol,grw,20​ 3:4.2.7

μpfol,net,20=μpfol,die,20−μpfol,grw,20\mu_{pfol,net,20}=\mu_{pfol,die,20}-\mu_{pfol,grw,20}μpfol,net,20​=μpfol,die,20​−μpfol,grw,20​ 3:4.2.8

μlpsol,net,20=μlpsol,die,20−μlpsol,grw,20\mu_{lpsol,net,20}=\mu_{lpsol,die,20}-\mu_{lpsol,grw,20}μlpsol,net,20​=μlpsol,die,20​−μlpsol,grw,20​ 3:4.2.9

μpsol,net,20=μpsol,die,20−μpsol,grw,20\mu_{psol,net,20}=\mu_{psol,die,20}-\mu_{psol,grw,20}μpsol,net,20​=μpsol,die,20​−μpsol,grw,20​ 3:4.2.10

μlpsorb,net,20=μlpsorb,die,20−μlpsorb,grw,20\mu_{lpsorb,net,20}=\mu_{lpsorb,die,20}-\mu_{lpsorb,grw,20}μlpsorb,net,20​=μlpsorb,die,20​−μlpsorb,grw,20​ 3:4.2.11

μpsorb,net,20=μpsorb,die,20−μpsorb,grw,20\mu_{psorb,net,20}=\mu_{psorb,die,20}-\mu_{psorb,grw,20}μpsorb,net,20​=μpsorb,die,20​−μpsorb,grw,20​ 3:4.2.12

where μlpfol,net,20\mu_{lpfol,net,20}μlpfol,net,20​ is the overall rate constant for die-off/re-growth of less persistent bacteria on foliage at 20°C (1/day), μlpfol,die,20\mu_{lpfol,die,20}μlpfol,die,20​ is the rate constant for die-off of less persistent bacteria on foliage at 20°C (1/day), μlpfol,grw,20\mu_{lpfol,grw,20}μlpfol,grw,20​ is the rate constant for re-growth of less persistent bacteria on foliage at 20°C (1/day), μpfol,net,20\mu_{pfol,net,20}μpfol,net,20​ is the overall rate constant for die-off/re-growth of persistent bacteria on foliage at 20°C (1/day), μpfol,die,20\mu_{pfol,die,20}μpfol,die,20​ is the rate constant for die-off of persistent bacteria on foliage at 20°C (1/day), μpfol,grw,20\mu_{pfol,grw,20}μpfol,grw,20​ is the rate constant for re-growth of persistent bacteria on foliage at 20°C (1/day), μlpsol,net,20\mu_{lpsol,net,20}μlpsol,net,20​ is the overall rate constant for die-off/re-growth of less persistent bacteria in soil solution at 20°C (1/day), μlpsol,die,20\mu_{lpsol,die,20}μlpsol,die,20​ is the rate constant for die-off of less persistent bacteria in soil solution at 20°C (1/day), μlpsol,grw,20\mu_{lpsol,grw,20}μlpsol,grw,20​ is the rate constant for re-growth of less persistent bacteria in soil solution at 20°C (1/day), μpsol,net,20\mu_{psol,net,20}μpsol,net,20​ is the overall rate constant for die-off/re-growth of persistent bacteria in soil solution at 20°C (1/day), μpsol,die,20\mu_{psol,die,20}μpsol,die,20​ is the rate constant for die-off of persistent bacteria in soil solution at 20°C (1/day), μpsol,grw,20\mu_{psol,grw,20}μpsol,grw,20​ is the rate constant for re-growth of persistent bacteria in soil solution at 20°C (1/day), μlpsorb,net,20\mu_{lpsorb,net,20}μlpsorb,net,20​ is the overall rate constant for die-off/re-growth of less persistent bacteria attached to soil particles at 20°C (1/day), μlpsorb,die,20\mu_{lpsorb,die,20}μlpsorb,die,20​ is the rate constant for die-off of less persistent bacteria attached to soil particles at 20°C (1/day), μlpsorb,grw,20\mu_{lpsorb,grw,20}μlpsorb,grw,20​ is the rate constant for re-growth of less persistent bacteria attached to soil particles at 20°C (1/day), μpsorb,net,20\mu_{psorb,net,20}μpsorb,net,20​ is the overall rate constant for die-off/re-growth of persistent bacteria attached to soil particles at 20°C (1/day), μpsorb,die,20\mu_{psorb,die,20}μpsorb,die,20​ is the rate constant for die-off of persistent bacteria attached to soil particles at 20°C (1/day), and μpsorb,grw,20\mu_{psorb,grw,20}μpsorb,grw,20​ is the rate constant for re-growth of persistent bacteria attached to soil particles at 20°C (1/day).

The overall rate constants are adjusted for temperature using the equations:

Table 3:4-2: SWAT+ input variables that pertain to bacteria die-off/re-growth.

Variable Name
Definition
Input File

WDPQ

.bsn

WGPQ

.bsn

WDLPQ

.bsn

WGLPQ

.bsn

WDPS

.bsn

WGPS

.bsn

WDLPS

.bsn

WGLPS

.bsn

WDPF

.bsn

WGPF

.bsn

WDLPF

.bsn

WGLPF

.bsn

THBACT

.bsn

BACTMINLP

.bsn

BACTMINP

.bsn

μlpfol,net=μlpfol,net,20∗θbact(T‾av−20)\mu_{lpfol,net}=\mu_{lpfol,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μlpfol,net​=μlpfol,net,20​∗θbact(Tav​−20)​ 3:4.2.13

μpfol,net=μpfol,net,20∗θbact(T‾av−20)\mu_{pfol,net}=\mu_{pfol,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μpfol,net​=μpfol,net,20​∗θbact(Tav​−20)​ 3:4.2.14

μlpsol,net=μlpsol,net,20∗θbact(T‾av−20)\mu_{lpsol,net}=\mu_{lpsol,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μlpsol,net​=μlpsol,net,20​∗θbact(Tav​−20)​ 3:4.2.15

μpsol,net=μpsol,net,20∗θbact(T‾av−20)\mu_{psol,net}=\mu_{psol,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μpsol,net​=μpsol,net,20​∗θbact(Tav​−20)​ 3:4.2.16

μlpsorb,net=μlpsorb,net,20∗θbact(T‾av−20)\mu_{lpsorb,net}=\mu_{lpsorb,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μlpsorb,net​=μlpsorb,net,20​∗θbact(Tav​−20)​ 3:4.2.17

μpsorb,net=μpsorb,net,20∗θbact(T‾av−20)\mu_{psorb,net}=\mu_{psorb,net,20}*\theta_{bact}^{(\overline T_{av}-20)}μpsorb,net​=μpsorb,net,20​∗θbact(Tav​−20)​ 3:4.2.18

where θbact\theta_{bact}θbact​ is the temperature adjustment factor for bacteria die-off/re-growth, T‾av\overline T_{av}Tav​ is the mean daily air temperature, and all other terms are as previously defined.

: Die-off factor for persistent bacteria in soil solution at 20°C (1/day)

: Growth factor for persistent bacteria in soil solution at 20°C (1/day)

: Die-off factor for less persistent bacteria in soil solution at 20°C (1/day)

: Growth factor for less persistent bacteria in soil solution at 20°C (1/day)

: Die-off factor for persistent bacteria adsorbed to soil particles at 20°C (1/day)

: Growth factor for persistent bacteria adsorbed to soil particles at 20°C (1/day)

: Die-off factor for less persistent bacteria adsorbed to soil particles at 20°C (1/day)

: Growth factor for less persistent bacteria adsorbed to soil particles at 20°C (1/day)

: Die-off factor for persistent bacteria on foliage at 20°C (1/day)

: Growth factor for persistent bacteria on foliage at 20°C (1/day)

: Die-off factor for less persistent bacteria on foliage at 20°C (1/day)

: Growth factor for less persistent bacteria on foliage at 20°C (1/day)

: Temperature adjustment factor for bacteria die-off/growth

: Minimum daily loss of less persistent bacteria (# cfu/m)

: Minimum daily loss of persistent bacteria (# cfu/m)

μpsol,die,20\mu_{psol,die,20}μpsol,die,20​
μpsol,grw,20\mu_{psol,grw,20}μpsol,grw,20​
μlpsol,die,20\mu_{lpsol,die,20}μlpsol,die,20​
μlpsol,grw,20\mu_{lpsol,grw,20}μlpsol,grw,20​
μpsorb,die,20\mu_{psorb,die,20}μpsorb,die,20​
μpsorb,grw,20\mu_{psorb,grw,20}μpsorb,grw,20​
μlpsorb,die,20\mu_{lpsorb,die,20}μlpsorb,die,20​
μlpsorb,grw,20\mu_{lpsorb,grw,20}μlpsorb,grw,20​
μpfol,die,20\mu_{pfol,die,20}μpfol,die,20​
μpfol,grw,20\mu_{pfol,grw,20}μpfol,grw,20​
μlpfol,die,20\mu_{lpfol,die,20}μlpfol,die,20​
μlpfol,grw,20\mu_{lpfol,grw,20}μlpfol,grw,20​
θbact\theta_{bact}θbact​
bactmin,lpbact_{min,lp}bactmin,lp​
2^22
bactmin,pbact_{min,p}bactmin,p​
2^22