SWAT+ Documentation
  • INTRODUCTION
    • 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
      • 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
    • Initialization
      • soil_plant.ini
        • name (soil_plant.ini)
        • sw_frac
        • nutrients
        • pest
        • salt
      • 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
      • pest_water.ini
      • pest_hru.ini
      • salt_water.ini
      • salt_hru.ini
    • Constituents
      • constituents.cs
    • 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 7: Main Channel Processes
  3. Sediment Routing
  4. Sediment Routing In Stream Channels

Simplified Bagnold Equation (Default method)

Williams (1980) used Bagnold’s (1977) definition of stream power to develop a method for determining degradation as a function of channel slope and velocity. In this version, the equations have been simplified and the maximum amount of sediment that can be transported from a reach segment is a function of the peak channel velocity. The peak channel velocity, vch,pkv_{ch,pk}vch,pk​, is calculated:

vch,pk=qch,pkAchv_{ch,pk}=\frac{q_{ch,pk}}{A_{ch}}vch,pk​=Ach​qch,pk​​ 7:2.2.1

where qch,pkq_{ch,pk}qch,pk​ is the peak flow rate (m3^33/s) and AchA_{ch}Ach​ is the cross-sectional area of flow in the channel (m2^22). The peak flow rate is defined as:

qch,pk=prf∗qchq_{ch,pk}=prf*q_{ch}qch,pk​=prf∗qch​ 7:2.2.2

where prfprfprf is the peak rate adjustment factor, and qchq_{ch}qch​ is the average rate of flow (m3^33/s). Calculation of the average rate of flow, qchq_{ch}qch​, and the cross-sectional area of flow, AchA_{ch}Ach​, is reviewed in Section 7, Chapter 1.

The maximum amount of sediment that can be transported from a reach segment is calculated:

concsed,ch,mx=csp∗vch,pkspexpconc_{sed,ch,mx}=c_{sp}*v_{ch,pk}^{spexp}concsed,ch,mx​=csp​∗vch,pkspexp​ 7:2.2.3

where concsed,ch,mxconc_{sed,ch,mx}concsed,ch,mx​ is the maximum concentration of sediment that can be transported by the water (ton/m3^33 or kg/L), cspc_{sp}csp​ is a coefficient defined by the user, vck,pkv_{ck,pk}vck,pk​ is the peak channel velocity (m/s), and spexp is an exponent defined by the user. The exponent, spexpspexpspexp, normally varies between 1.0 and 2.0 and was set at 1.5 in the original Bagnold stream power equation (Arnold et al., 1995).

The maximum concentration of sediment calculated with equation 24.1.3 is compared to the concentration of sediment in the reach at the beginning of the time step, concsed,ch,iconc_{sed,ch,i}concsed,ch,i​. If concsed,ch,i>concsed,ch,mxconc_{sed,ch,i}>conc_{sed,ch,mx}concsed,ch,i​>concsed,ch,mx​, deposition is the dominant process in the reach segment and the net amount of sediment deposited is calculated:

seddep=(concsed,ch,i−concsed,ch,mx)∗Vchsed_{dep}=(conc_{sed,ch,i}-conc_{sed,ch,mx})*V_{ch}seddep​=(concsed,ch,i​−concsed,ch,mx​)∗Vch​ 7:2.2.4

where seddepsed_{dep}seddep​ is the amount of sediment deposited in the reach segment (metric tons), concsed,ch,iconc_{sed,ch,i}concsed,ch,i​ is the initial sediment concentration in the reach (kg/L or ton/m3^33), concsed,ch,mxconc_{sed,ch,mx}concsed,ch,mx​ is the maximum concentration of sediment that can be transported by the water (kg/L or ton/m3^33), and VchV_{ch}Vch​ is the volume of water in the reach segment (m3^33 H2_22​O).

If concsed,ch,i<concsed,ch,mxconc_{sed,ch,i}<conc_{sed,ch,mx}concsed,ch,i​<concsed,ch,mx​, degradation is the dominant process in the reach segment and the net amount of sediment reentrained is calculated:

seddeg=(concsed,ch,mx−concsed,ch,i)∗Vch∗KCH∗CCHsed_{deg}=(conc_{sed,ch,mx}-conc_{sed,ch,i})*V_{ch}*K_{CH}*C_{CH}seddeg​=(concsed,ch,mx​−concsed,ch,i​)∗Vch​∗KCH​∗CCH​ 7:2.2.5

where seddegsed_{deg}seddeg​ is the amount of sediment reentrained in the reach segment (metric tons), concsed,ch,mxconc_{sed,ch,mx}concsed,ch,mx​ is the maximum concentration of sediment that can be transported by the water (kg/L or ton/m3^33), concsed,ch,iconc_{sed,ch,i}concsed,ch,i​ is the initial sediment concentration in the reach (kg/L or ton/m3^33), VchV_{ch}Vch​ is the volume of water in the reach segment (m3^33 H2_22​O), KCHK_{CH}KCH​ is the channel erodibility factor, and CCHC_{CH}CCH​ is the channel cover factor.

Once the amount of deposition and degradation has been calculated, the final amount of sediment in the reach is determined:

sedch=sedch,i−seddep+seddegsed_{ch}=sed_{ch,i}-sed_{dep}+sed_{deg}sedch​=sedch,i​−seddep​+seddeg​ 7:2.2.6

where sedchsed_{ch}sedch​ is the amount of suspended sediment in the reach (metric tons), sedch,ised_{ch,i}sedch,i​ is the amount of suspended sediment in the reach at the beginning of the time period (metric tons), seddepsed_{dep}seddep​ is the amount of sediment deposited in the reach segment (metric tons), and seddegsed_{deg}seddeg​ is the amount of sediment reentrained in the reach segment (metric tons).

The amount of sediment transported out of the reach is calculated:

sedout=sedch∗VoutVchsed_{out}=sed_{ch}*\frac{V_{out}}{V_{ch}}sedout​=sedch​∗Vch​Vout​​ 7:2.2.7

where sedoutsed_{out}sedout​ is the amount of sediment transported out of the reach (metric tons), sedchsed_{ch}sedch​ is the amount of suspended sediment in the reach (metric tons), VoutV_{out}Vout​ is the volume of outflow during the time step (m3^33 H2_22​O), and VchV_{ch}Vch​ is the volume of water in the reach segment (m3^33 H2_22​O).

In this method, the erosion is assumed to be limited only by the transport capacity, i.e., the sediment supply from channel erosion is unlimited. If the bedload entering the channel is less than the transport capacity, then channel erosion is assumed to meet this deficit. On the other hand if the bedload entering the channel is more than the transport capacity, the difference in the load will get deposited within the channel. Hence, in the default method, the bed load carried by the channel is almost always near the maximum transport capacity given by the simplified Bagnold equation and only limited by the channel cover and erodibility factors (eq. 7:2.2.11). During subsequent floods, the deposited sediments will be resuspended and transported before channel degradation.

If this method is chosen for sediment transport modeling, it does not keep track of particle size distribution through the channel reaches and all are assumed to be of silt size particles. Further, the channel erosion is not partitioned between stream bank and stream bed and deposition is assumed to occur only in the main channel; flood plain deposition of sediments is also not modeled separately.

Last updated 3 years ago