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 7: Main Channel Processes
  3. Sediment Routing
  4. Sediment Routing In Stream Channels

Physics Based Approach for Channel Erosion

Last updated 3 years ago

For the channel erosion to occur, both transport and supply should not be limiting, i.e., 1) the stream power (transport capacity) of the water should be high and the sediment load from the upstream regions should be less than this capacity and 2) The shear stress exerted by the water on the bed and bank should be more than the critical shear stress to dislodge the sediment particle. The potential erosion rates of bank and bed is predicted based on the excess shear stress equation (Hanson and Simon, 2001):

ξbank=kd,bank∗(τe,bank−τc,bank)∗10−6\xi_{bank}=k_{d,bank}*(\tau_{e,bank}-\tau_{c,bank})*10^{-6}ξbank​=kd,bank​∗(τe,bank​−τc,bank​)∗10−6 7:2.2.8

ξbed=kd,bed∗(τe,bed−τc,bed)∗10−6\xi_{bed}=k_{d,bed}*(\tau_{e,bed}-\tau_{c,bed})*10^{-6}ξbed​=kd,bed​∗(τe,bed​−τc,bed​)∗10−6 7:2.2.9

where ξ\xiξ – erosion rates of the bank and bed (m/s), kdk_dkd​ – erodibility coefficient of bank and bedbedbed (cm3^33/N-s) and τc\tau_cτc​ – Critical shear stress acting on bank and bed (N/m2^22). This equation indicates that effective stress on the channel bank and bed should be more than the respective critical stress for the erosion to occur.

The effective shear stress acting on the bank and bed are calculated using the following equations (Eaton and Millar, 2004):

τe,bankγ∗depth∗slpch=SFbank100((W+Pbed)∗sinθ4∗depth)\frac{\tau_{e,bank}}{\gamma*depth*slp_{ch}}=\frac{SF_{bank}}{100}(\frac{(W+P_{bed})*sin\theta}{4*depth})γ∗depth∗slpch​τe,bank​​=100SFbank​​(4∗depth(W+Pbed​)∗sinθ​) 7:2.2.10

τe,bedγW∗depth∗slpch=(1−SFbank100)(W2∗Pbed+0.5)\frac{\tau_{e,bed}}{\gamma_{W}*depth*slp_{ch}}=(1-\frac{SF_{bank}}{100})(\frac{W}{2*P_{bed}}+0.5)γW​∗depth∗slpch​τe,bed​​=(1−100SFbank​​)(2∗Pbed​W​+0.5) 7:2.2.11

logSFbank=−1.4026∗log(PbedPbank+1.5)+2.247logSF_{bank}=-1.4026*log(\frac{P_{bed}}{P_{bank}}+1.5)+2.247logSFbank​=−1.4026∗log(Pbank​Pbed​​+1.5)+2.247 7:2.2.12

where SFbankSF_{bank}SFbank​ – proportion of shear stress acting on the bank, τe\tau_eτe​ – effective shear stress on bed and bank (N/m2^22), γW\gamma_WγW​ – specific weight of water (9800 N/m3^33), depthdepthdepth – Depth of water in the channel (m), WWW – Top width of channel (m), PbedP_{bed}Pbed​ – Wetted perimeter of bed (bottom width of channel) (m), PbankP_{bank}Pbank​ – Wetted perimeter of channel banks (m), θ\thetaθ – angle of the channel bank from horizontal, slpchslp_{ch}slpch​ – Channel bed slope (m/m).

The effective shear stress calculated by the above equations should be more than the critical shear stress or the tractive force needed to dislodge the sediment. Critical shear stress for channel bank can be measured using submerged jet test (described later in this chapter). However, if field data is not available, critical shear stress is estimated using the third-order polynomial fitted to the results of Dunn (1959) and Vanoni (1977) by Julian and Torres (2006) :

τc=(0.1+0.1779∗SC+0.0028∗SC2−2.34∗10−5∗SC3)∗CCH\tau_c=(0.1+0.1779*SC+0.0028*SC^2-2.34*10^{-5}*SC^3)*C_{CH}τc​=(0.1+0.1779∗SC+0.0028∗SC2−2.34∗10−5∗SC3)∗CCH​ 7:2.2.19

where SCSCSC – percent silt and clay content and CCHC_{CH}CCH​ – channel vegetation coefficient (range from 1.0 for bare soil to 19.20 for heavy vegetation; see table 7:2-1):

Table 7:2-1. Channel vegetation coefficient for critical shear stress (Julian and Torres, 2006)

Channel erodibility coefficient (kdk_dkd​) can also be measured from insitu submerged jet tests. However, if field data is not available, the model estimates kdk_dkd​ using the empirical relation developed by Hanson and Simon (2001). Hanson and Simon (2001) conducted 83 jet tests on the stream beds of Midwestern USA and established the following relationship between critical shear stress and erodibility coefficient:

kd=0.2∗τc−0.5k_d=0.2*\tau_c^{-0.5}kd​=0.2∗τc−0.5​ 7:2.2.13

where kdk_dkd​ – erodibility coefficient (cm3^33/N-s) and τc\tau_cτc​ – Critical shear stress (N/m2^22).

Using the above relationships, the bank/bed erosion rate (m/s) can be calculated using eqns. 7:2.2.14 and 7:2.2.15. This has to be multiplied by the sediment bulk density and area exposed to erosion to get the total mass of sediment that could be eroded. Due to the meandering nature of the channel, the outside bank in a meander is more prone to erosion than the inside bank. Hence, the potential bank erosion is calculated by assuming erosion of effectively one channel bank:

Bnkrte=ξbnk∗(Lch∗1000∗depth∗1+Zch2)∗ρb,bank∗86400Bnkrte=\xi_{bnk}*(L_{ch}*1000*depth*\sqrt{1+Z_{ch}^2})*\rho_{b,bank}*86400Bnkrte=ξbnk​∗(Lch​∗1000∗depth∗1+Zch2​​)∗ρb,bank​∗86400 7:2.2.14

Similarly, the amount of bed erosion is calculated as:

Bedrte=ξbed∗(Lch∗1000∗Wbtm)∗ρb,bed∗86400Bedrte=\xi_{bed}*(L_{ch}*1000*W_{btm})*\rho_{b,bed}*86400Bedrte=ξbed​∗(Lch​∗1000∗Wbtm​)∗ρb,bed​∗86400 7:2.2.15

where Bnkrte,BedrteBnkrte,BedrteBnkrte,Bedrte – potential bank and bed erosion rates (Metric tons per day), LchL_{ch}Lch​– length of the channel (m),depthdepthdepth– depth of water flowing in the channel (m), WbtmW_{btm}Wbtm​– Channel bottom width (m), ρb,bank,ρb,bed\rho_{b,bank},\rho_{b,bed}ρb,bank​,ρb,bed​– bulk density of channel bank and bed sediment (g/cm3^33or Metric tons/m3^33 or Mg/m3^33). The relative erosion potential is used to partition the erosion in channel among stream bed and stream bank if the transport capacity of the channel is high. The relative erosion potential of stream bank and bed is calculated as:

Bnkrp=BnkrteBnkrte+BedrteBnk_{rp}=\frac{Bnkrte}{Bnkrte+Bedrte}Bnkrp​=Bnkrte+BedrteBnkrte​ 7:2.2.16

Bedrp=1−BnkrpBed_{rp}=1-Bnk_{rp}Bedrp​=1−Bnkrp​ 7:2.2.17

SWAT+ currently has four stream power models to predict the transport capacity of channel. The stream power models predict the maximum concentration of bed load it can carry as a non-linear function of peak velocity:

concsed,ch.mx=f(peakconc_{sed,ch.mx}=f(peak concsed,ch.mx​=f(peak velocity)velocity)velocity) 7:2.2.18

where concsed,ch.mxconc_{sed,ch.mx}concsed,ch.mx​ – maximum concentration of sediment that can be transported by the water (Metric ton/m3^33). The stream power models currently used in SWAT+ are 1) Simplified Bagnold model 2) Kodatie model (for streams with bed material size ranging from silt to gravel) 3) Molinas and Wu model (for primarily sand size particles) and 4) Yang sand and gravel model (for primarily sand and gravel size particles).

  1. Simplified Bagnold model: (same as eqn. 7:2.2.9)

concsed,ch,mx=csp∗vch,pkspexpconc_{sed,ch,mx}=c_{sp}*v_{ch,pk}^{spexp}concsed,ch,mx​=csp​∗vch,pkspexp​ 7:2.2.19

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, vch,pkv_{ch,pk}vch,pk​ is the peak channel velocity (m/s), and spexpspexpspexp 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).

2. Kodatie model

Kodatie (2000) modified the equations developed by Posada (1995) using nonlinear optimization and field data for different sizes of riverbed sediment. This method can be used for streams with bed material in size ranging from silt to gravel:

concsed,ch,mx=(a.vchb∗yc∗SdQin)∗(W+Wbtm2)conc_{sed,ch,mx}=(\frac{a.v_{ch}^b*y^c*S^d}{Q_{in}})*(\frac{W+W_{btm}}{2})concsed,ch,mx​=(Qin​a.vchb​∗yc∗Sd​)∗(2W+Wbtm​​) 7:2.2.20

where vchv_{ch}vch​ – mean flow velocity (m/s), y – mean flow depth (m), S – Energy slope, assumed to be the same as bed slope (m/m), (a,b,c and d) – regression coefficients for different bed materials (Table 7:2-1), QinQ_{in}Qin​ – Volume of water entering the reach in the day (m3^33), W – width of the channel at the water level (m), WbtmW_{btm}Wbtm​ – bottom width of the channel (m).

3. Molinas and Wu model:

Molinas and Wu (2001) developed a sediment transport equation for large sand-bed rivers based on universal stream power. The transport equation is of the form:

CW=MΨNC_W=M\Psi^NCW​=MΨN 7:2.2.21

where CWC_WCW​ – is the concentration of sediments by weight, Ψ\PsiΨ – universal stream power, MMM and NNN are coefficients. This equation was fitted to 414 sets of large river bed load data including rivers such as Amazon, Mississippi. The resulting expression is:

CW=1430∗(0.86+Ψ)∗Ψ1.50.016+Ψ∗10−6C_W=\frac{1430*(0.86+\sqrt \Psi)*\Psi^{1.5}}{0.016+\Psi}*10^{-6}CW​=0.016+Ψ1430∗(0.86+Ψ​)∗Ψ1.5​∗10−6 7:2.2.22

where Ψ\PsiΨ – universal stream power is given by:

Ψ=Ψ3(Sg−1)∗g∗depth∗ω50∗[log10(depthD50)]2\Psi=\frac{\Psi^3}{(S_g-1)*g*depth*\omega_{50}*[log_{10}(\frac{depth}{D_{50}})]^2}Ψ=(Sg​−1)∗g∗depth∗ω50​∗[log10​(D50​depth​)]2Ψ3​ 7:2.2.23

where SgS_gSg​ – relative density of the solid (2.65), ggg – acceleration due to gravity (9.81 m/s2^22), depthdepthdepth – flow depth (m), ω50\omega_{50}ω50​ – fall velocity of median size particles (m/s), D50D_{50}D50​ – median sediment size. The fall velocity is calculated using Stokes’ Law by assuming a temperature of 22ºC and a sediment density of 1.2 t/m3:

ω50=411∗D5023600\omega_{50}=\frac{411*D_{50}^2}{3600}ω50​=3600411∗D502​​ 7:2.2.24

The concentration by weight is converted to concentration by volume and the maximum bed load concentration in metric tons/m3^33 is calculated as:

concsed,ch,mx=CWCW+(1−CW)∗Sg∗Sgconc_{sed,ch,mx}=\frac{C_W}{C_W+(1-C_W)*S_g}*S_gconcsed,ch,mx​=CW​+(1−CW​)∗Sg​CW​​∗Sg​ 7:2.2.25

4. Yang sand and gravel model

Yang (1996) related total load to excess unit stream power expressed as the product of velocity and slope. Separate equations were developed for sand and gravel bed material and solved for sediment concentration in ppm by weight. The regression equations were developed based on dimensionless combinations of unit stream power, critical unit stream power, shear velocity, fall velocity, kinematic viscosity and sediment size. The sand equation, which should be used for median sizes (D50D_{50}D50​) less than 2mm is:

logCW=5.435−0.286logω50D50υ−0.457logV∗ω50+(1.799−0.409logω50D50υ−0.3141logV∗ω50)log(vchSω50−VcrSω50)logC_W=5.435-0.286log\frac{\omega_{50}D_{50}}{\upsilon}-0.457log\frac{V_*}{\omega_{50}}\\+(1.799-0.409log\frac{\omega_{50}D_{50}}{\upsilon}-0.3141log\frac{V_*}{\omega_{50}})log(\frac{v_{ch}S}{\omega_{50}}-\frac{V_{cr}S}{\omega_{50}})logCW​=5.435−0.286logυω50​D50​​−0.457logω50​V∗​​+(1.799−0.409logυω50​D50​​−0.3141logω50​V∗​​)log(ω50​vch​S​−ω50​Vcr​S​) 7:2.2.26

and the gravel equation for D50 between 2mm and 10mm:

logCW=6.681−0.6331logω50D50υ−4.816logV∗ω50+(2.784−0.305logω50D50υ−0.282logV∗ω50)log(vchSω50−VcrSω50)logC_W=6.681-0.6331log\frac{\omega_{50}D_{50}}{\upsilon}-4.816log\frac{V_*}{\omega_{50}}+\\(2.784-0.305log\frac{\omega_{50}D_{50}}{\upsilon}-0.282log\frac{V_*}{\omega_{50}})log(\frac{v_{ch}S}{\omega_{50}}-\frac{V_{cr}S}{\omega_{50}})logCW​=6.681−0.6331logυω50​D50​​−4.816logω50​V∗​​+(2.784−0.305logυω50​D50​​−0.282logω50​V∗​​)log(ω50​vch​S​−ω50​Vcr​S​) 7:2.2.27

where CWC_WCW​ – Sediment concentration in parts per million by weight, ω50\omega_{50}ω50​ – fall velocity of the median size sediment (m/s), vvv – Kinematic viscosity (m2^22/s), V∗V_*V∗​ - Shear velocity (gRS)(\sqrt{gRS})(gRS​)(m/s), vchv_{ch}vch​ – mean channel velocity (m/s), VcrV_{cr}Vcr​ – Critical velocity (m/s), and SSS – Energy slope, assumed to be the same as bed slope (m/m).

From the above equations, CWC_WCW​ in ppm is divided by 106^66 to convert in to concentration by weight. Using eq. 7:2.2.32,CWC_WCW​ is converted in to maximum bed load concentration(concsed,ch,mxconc_{sed,ch,mx}concsed,ch,mx​) in metric tons/m3^33.

By using one of the four models discussed above, the maximum sediment transport capacity of the channel can be calculated. The excess transport capacity available in the channel is calculated as:

SedEx=Vch∗(concsed,ch,mx−concsed,ch,i)SedEx=V_{ch}*(conc_{sed,ch,mx}-conc_{sed,ch,i})SedEx=Vch​∗(concsed,ch,mx​−concsed,ch,i​) 7:2.2.28

If SedEXSedEXSedEX is < 0 then the channel does not have the capacity to transport eroded sediments and hence there will be no bank and bed erosion. If SedEXSedEXSedEX is > 0 then the channel has the transport capacity to support eroded bank and bed sediments. Before channel degradation bank erosion, the deposited sediment during the previous time steps will be resuspended and removed. The excess transport capacity available after resuspending the deposited sediments is removed from channel bank and channel bed.

Bnkdeg=SedEX∗Bnkrp,SedEX∗Bnkrp≤BnkrteBnkdeg=Bnkrte,SedEX∗Bnkrp>BnkrteBnk_{deg}=SedEX* Bnk_{rp}, SedEX*Bnk_{rp} \le Bnkrte \\ Bnk_{deg}=Bnkrte, SedEX*Bnk_{rp}>Bnkrte Bnkdeg​=SedEX∗Bnkrp​,SedEX∗Bnkrp​≤BnkrteBnkdeg​=Bnkrte,SedEX∗Bnkrp​>Bnkrte 7:2.2.29

Beddeg=SedEX∗Bedrp,SedEX∗Bedrp≤BedrteBeddeg=Bedrte,SedEX∗Bedrp>BedrteBed_{deg}=SedEX*Bed_{rp},SedEX*Bed_{rp}\le Bedrte \\ Bed_{deg}=Bedrte , SedEX*Bed_{rp}>BedrteBeddeg​=SedEX∗Bedrp​,SedEX∗Bedrp​≤BedrteBeddeg​=Bedrte,SedEX∗Bedrp​>Bedrte 7:2.2.30

seddeg=Bankdeg+Beddegsed_{deg}=Bank_{deg}+Bed_{deg}seddeg​=Bankdeg​+Beddeg​ 7:2.2.31

where BnkdegBnk_{deg}Bnkdeg​ – is the amount of bank erosion in metric tons, BeddegBed_{deg}Beddeg​ – is the amount of bed erosion in metric tons, seddegsed_{deg}seddeg​ – is the total channel erosion from channel bank and bed in metric tons. Particle size contribution from bank erosion is calculated as:

Bnksan=Bnkdeg∗BnksanfriBnksil=Bnkdeg∗BnksilfriBnkcla=Bnkdeg∗BnkclafriBnkgra=Bnkdeg∗BnkgrafriBnksan=Bnk_{deg}*Bnksanfr_i \\ Bnksil=Bnk_{deg}*Bnksilfr_i \\ Bnkcla=Bnk_{deg}*Bnkclafr_i \\ Bnkgra=Bnk_{deg}*Bnkgrafr_iBnksan=Bnkdeg​∗Bnksanfri​Bnksil=Bnkdeg​∗Bnksilfri​Bnkcla=Bnkdeg​∗Bnkclafri​Bnkgra=Bnkdeg​∗Bnkgrafri​ 7:2.2.32

where BnksanBnksanBnksan – is the amount of sand eroded from bank in metric tons, BnksilBnksilBnksil – is the amount of silt eroded from bank, BnkclaBnkclaBnkcla – is the amount of clay eroded from bank, BnkgraBnkgraBnkgra – is the amount of gravel eroded from bank; BnksanfriBnksanfr_iBnksanfri​, BnksilfriBnksilfr_iBnksilfri​,BnkclafriBnkclafr_iBnkclafri​, and BnkgrafriBnkgrafr_iBnkgrafri​ – fraction of sand, silt, clay and gravel content of bank in channel iii. Similarly the particle size contribution from bed erosion is also calculated separately.

The particle size distribution indicated in Table 7:2-3 for bank and bed sediments is assumed by the model based on the median sediment size (BnkD50BnkD_{50}BnkD50​,BedD50BedD_{50}BedD50​) input by the user. If the median sediment size is not specified by the user, then the model assumed BnkD50BnkD_{50}BnkD50​ and BedD50BedD_{50}BedD50​ to be 50 micrometer (0.05 mm) equivalent to the silt size particles.

Table 7:2-3. Particle size distribution assumed by SWAT+ based on the median size of bank and bed sediments

Deposition of bedload sediments in channel is modeled using the following equations (Einstein 1965; Pemberton and Lara 1971):

Pdepz=(1−1ex)∗100Pdep_z=(1-\frac{1}{e^x})*100 Pdepz​=(1−ex1​)∗100 wherewhere \\ where

x=1.055∗Lch∗1000∗ωvch∗depthx=\frac{1.055*L_{ch}*1000*\omega}{v_{ch}*depth}x=vch​∗depth1.055∗Lch​∗1000∗ω​ 7:2.2.33

where PdepPdepPdep - is the percentage of sediments (zzz - sand, silt, clay, and gravel) that get deposited, LchL_{ch}Lch​ – length of the reach (km), ω\omegaω – fall velocity of the sediment particles in m/s (eq. 7:2.2.31), vchv_{ch}vch​ – mean flow velocity in the reach (m/s), and depthdepthdepth – is the depth of water in the channel (m).The particle size diameters assumed to calculate the fall velocity are 0.2mm, 0.01mm, 0.002mm, 2 mm, 0.0300, 0.500 respectively for sand, silt, clay, gravel, small aggregate and large aggregate.

It should be kept in mind that small aggregate and large aggregates in the bedload are contributed only from overland erosion and routed through the channel. Gravel is contributed only from channel erosion. Only sand, silt and clay in the bedload is contributed both from overland and channel erosion. If the water in the channel enters the floodplain during large storm events, then silt and clay particles are deposited in the floodplains and the main channel in proportion to their flow cross-sectional areas. Silt and clay deposited in the flooplain are assumed to be lost from the system and is not resuspended during subsequent time steps as in the main channel. The complete mass balance equations for sediment routing are as follows:

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

sedch,i=sanch,i+silch,i+clach,i+grach,i+saggch,i+laggch,ised_{ch,i}=san_{ch,i}+sil_{ch,i}+cla_{ch,i}+gra_{ch,i}+sagg_{ch,i}+lagg_{ch,i}sedch,i​=sanch,i​+silch,i​+clach,i​+grach,i​+saggch,i​+laggch,i​

seddep=sanch,i∗Pdepsan+silch,i∗Pdepsil+clach,i∗Pdepcla+grach,i∗Pdepgra+saggch,i∗Pdepsagg+laggch,i∗Pdeplaggsed_{dep}=san_{ch,i}*Pdep_{san}+sil_{ch,i}*Pdep_{sil}+cla_{ch,i}*Pdep_{cla}+gra_{ch,i}*Pdep_{gra}+sagg_{ch,i}*Pdep_{sagg}+lagg_{ch,i}*Pdep_{lagg}seddep​=sanch,i​∗Pdepsan​+silch,i​∗Pdepsil​+clach,i​∗Pdepcla​+grach,i​∗Pdepgra​+saggch,i​∗Pdepsagg​+laggch,i​∗Pdeplagg​

seddeg=Bnkdeg+Beddegsed_{deg}=Bnk_{deg}+Bed_{deg}seddeg​=Bnkdeg​+Beddeg​ wherewherewhere

Bnkdeg=Bnksan+Bnksil+Bnkcla+BnkgraBnk_{deg}=Bnksan+Bnksil+Bnkcla+BnkgraBnkdeg​=Bnksan+Bnksil+Bnkcla+Bnkgra

Beddeg=Bedsan+Bedsil+Bedcla+BedgraBed_{deg}=Bedsan+Bedsil+Bedcla+BedgraBeddeg​=Bedsan+Bedsil+Bedcla+Bedgra 7:2.2.34

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 entering 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 contribution from bank and bed erosion 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​​ 7:2.2.35

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).