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title: structural BMPs description: Structural best-management-practice files: tile drains, septic systems, filter strips, grassed waterways, user-defined BMPs, urban areas. status: review verified_against: - src/input_file_module.f90 - src/sdr_read.f90 - src/sep_read.f90 - src/septic_parm_read.f90 - src/scen_read_filtstrip.f90 - src/scen_read_grwway.f90 - src/scen_read_bmpuser.f90 - src/sat_buff_read.f90 - src/urban_parm_read.f90 verified_at_commit: 8a1edd4a23915a2cac1cd90c788f0d521404700e

Purpose

This page documents the structural BMP parameter files referenced by HRUs and landscape units: tiledrain.str, septic.str, filterstrip.str, grassedww.str, and bmpuser.str. File names for the first five are set in type input_structural in src/input_file_module.f90. The page also covers two closely related files declared elsewhere: septic.sep (effluent quality, named in type input_parameter_databases), urban.urb (urban land-cover parameters, same type), and satbuffer.str (saturated buffer, file name hard-coded in the reader).

Each file is optional. If the slot in file.cio is null or the file is missing, the reader allocates a zero-length array and skips on. Every reader skips two header lines, then reads one record per parameter set.

Records in tiledrain.str, filterstrip.str, grassedww.str, and bmpuser.str are referenced by name from hru-data.hru (columns tiledrain, vfsfield, grassww, bmpuser). Records in septic.str are referenced from the management schedule when a septic operation is scheduled.

Source

tiledrain.str

Subsurface drain parameter sets. Read into sdr (type subsurface_drainage_parameters in src/hru_module.f90). Referenced by the tiledrain column of hru-data.hru.

# Column Type Units Default Description
1 name char(40) none "null" parameter set name
2 depth real mm 0.0 depth of drain tube from soil surface
3 time real hours 0.0 time to drain soil to field capacity
4 lag real hours 0.0 drain tile lag time
5 radius real mm 0.0 effective radius of drains
6 dist real mm 0.0 distance between two drain tubes or tiles
7 drain_co real mm/day 0.0 drainage coefficient
8 pumpcap real mm/hr 0.0 pump capacity
9 latksat real none 0.0 multiplication factor for lateral saturated hydraulic conductivity

Example from refdata/Osu_1hru/tiledrain.str:

tiledrain.str: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                        dp          t_fc           lag           rad          dist         drain          pump      lat_ksat  
mw24_1000           1000.00000      24.00000      96.00000     100.00000      30.00000      10.00000       1.00000       2.00000

Editor column names (dp, t_fc, rad, drain, pump, lat_ksat) differ from source field names. The reader uses position only.

septic.str

Per-HRU septic system parameter sets (geometry, biozone properties, decay coefficients). Read into sep (type septic_system in src/septic_data_module.f90).

# Column Type Units Description
1 name char(13) none parameter set name
2 typ int none septic system type
3 yr int year year the septic system became operational
4 opt int none operation flag (1 = active, 2 = failing, 0 = not operated)
5 cap real none number of permanent residents
6 area real m^2 average drainfield area per septic system
7 tfail int days time until failing system gets fixed
8 z real mm depth to top of biozone layer
9 thk real mm thickness of biozone layer
10 strm_dist real km distance to stream
11 density real per km^2 number of septic systems per square kilometre
12 bd real kg/m^3 density of biomass
13 bod_dc real m^3/day BOD decay rate coefficient
14 bod_conv real none mass conversion factor between bacterial growth and BOD degraded
15 fc1 real none linear coefficient for biozone field capacity
16 fc2 real none exponential coefficient for biozone field capacity
17 fecal real m^3/day fecal coliform decay rate coefficient
18 plq real none plaque conversion factor from TDS
19 mrt real none mortality rate coefficient
20 rsp real none respiration rate coefficient
21 slg1 real none slough-off calibration parameter
22 slg2 real none slough-off calibration parameter
23 nitr real none nitrification rate coefficient
24 denitr real none denitrification rate coefficient
25 pdistrb real L/kg linear P sorption distribution coefficient
26 psorpmax real mg P/kg soil maximum P sorption capacity
27 solpslp real none slope of linear effluent soluble P equation
28 solpintc real none intercept of linear effluent soluble P equation

Example from refdata/Osu_1hru/septic.str:

septic.str: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                   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  
standard                 1         0         0       2.50000     100.00000        70     500.00000      50.00000       0.50000       1.50000    1000.00000       0.50000       0.32000      30.00000       0.80000       1.30000       0.10000       0.50000       0.16000       0.30000       0.50000       1.50000       0.32000     128.00000     850.00000       0.04000       3.10000
failing                  1         0         0       2.50000     100.00000         1     500.00000      50.00000       0.50000       1.50000    1000.00000       0.50000       0.32000      30.00000       0.80000       1.30000       0.10000       0.50000       0.16000       0.30000       0.50000       1.50000       0.32000     128.00000     850.00000       0.04000       3.10000

septic.sep

Effluent quality database. One record per effluent type. Records are referenced by index from elsewhere (no name resolution in the reader). Read into sepdb (type septic_db in src/septic_data_module.f90). File name is in in_parmdb%septic_sep.

# Column Type Units Description
1 sepnm char(20) none effluent set name
2 qs real m^3/day flow rate per capita
3 bodconcs real mg/L biological oxygen demand
4 tssconcs real mg/L total suspended solids
5 nh4concs real mg/L NH4-N concentration
6 no3concs real mg/L NO3-N concentration
7 no2concs real mg/L NO2-N concentration
8 orgnconcs real mg/L organic N concentration
9 minps real mg/L mineral P concentration
10 orgps real mg/L organic P concentration
11 fcolis real mg/L fecal coliform concentration

The source comment on nh4concs reads "concentration of total phosphorus"; the field is the NH4-N concentration based on column position and downstream use. Example from refdata/Osu_1hru/septic.sep (first two records shown):

septic.sep: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                    q_rate           bod           tss         nh4_n         no3_n         no2_n         org_n         min_p         org_p         fcoli  description
gcon                   0.22700     170.00000      75.00000      42.40000       0.00000       0.00000      10.00000       6.00000       1.00000  10000000.00000  1Generic
gadv                   0.22700      22.00000      14.00000      18.90000       9.60000       0.00000       3.00000       5.10000       0.90000     543.00000  2Generic

filterstrip.str

Vegetative filter strip parameter sets. Read into filtstrip_db (type filtstrip_operation in src/mgt_operations_module.f90). Referenced by the vfsfield column of hru-data.hru.

# Column Type Units Default Description
1 name char(40) none "" parameter set name
2 vfsi int none 0 on/off flag for vegetative filter strip
3 vfsratio real none 0.0 drainage-area to filter-strip-area ratio
4 vfscon real none 0.0 fraction of total runoff from the entire field
5 vfsch real none 0.0 fraction of flow entering the most concentrated 10% of the VFS that is fully channelized

Example from refdata/Osu_1hru/filterstrip.str:

filterstrip.str: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                  flag       fld_vfs       con_vfs         cha_q  description
field_border             0       0.10000       0.00300       0.20000  Field_border
high_engineered          0       0.10000       0.00100       0.05000  Highly_engineered_low_channelized

grassedww.str

Grassed waterway parameter sets. Read into grwaterway_db (type grwaterway_operation in src/mgt_operations_module.f90). Referenced by the grassww column of hru-data.hru.

# Column Type Units Default Description
1 name char(40) none "" parameter set name
2 grwat_i int none 0 on/off flag for waterway simulation
3 grwat_n real none 0.0 Manning's n for grassed waterway
4 grwat_spcon real none 0.0 sediment transport coefficient
5 grwat_d real m 0.0 depth of grassed waterway
6 grwat_w real m 0.0 width of grassed waterway
7 grwat_l real km 0.0 length of grassed waterway
8 grwat_s real m/m 0.0 slope of grassed waterway

Example from refdata/Osu_1hru/grassedww.str:

grassedww.str: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                  flag          mann        sed_co            dp            wd           len           slp  description
grwway_high              0       0.05000       0.02000       1.00000       4.00000       0.50000       0.10000  Slope_>8
grwway_med               0       0.05000       0.02000       0.75000       3.00000       0.75000       0.03500  Slope_2-5
grwway_low               0       0.05000       0.02000       0.50000       2.00000       1.00000       0.01000  Slope_0-2

bmpuser.str

User-defined upland BMP removal-efficiency sets. Read into bmpuser_db (type bmpuser_operation in src/mgt_operations_module.f90). Referenced by the bmpuser column of hru-data.hru.

# Column Type Units Default Description
1 name char(40) none "" parameter set name
2 bmp_flag int none 0 on/off flag
3 bmp_sed real percent 0.0 sediment removal
4 bmp_pp real percent 0.0 particulate P removal
5 bmp_sp real percent 0.0 soluble P removal
6 bmp_pn real percent 0.0 particulate N removal
7 bmp_sn real percent 0.0 soluble N removal
8 bmp_bac real percent 0.0 bacteria removal

Example from refdata/Osu_1hru/bmpuser.str:

bmpuser.str: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                  flag       sed_eff      ptlp_eff      solp_eff      ptln_eff      soln_eff      bact_eff  description
bmpusr1                  1       0.20000       0.20000       0.20000       0.20000       0.20000       0.20000

Note: a second type bmpuser_operation1 in the same module exposes a wider parameter set (surface, subsurface, tile flow and constituents). The reader populates bmpuser_db (bmpuser_operation); the wider type is not read here.

satbuffer.str

Saturated buffer source-receiver pairs. Read into satbuff_db (type saturated_buffer_parameters in src/hru_module.f90). The file name is hard-coded as "satbuffer.str" in the reader, not listed in type input_structural. The file is loaded only when it exists.

# Column Type Description
1 name char(40) parameter set name
2 hru_src int source HRU contributing tile inflow
3 frac_src real fraction of source HRU contributing to tile flow
4 flocon_dtbl char(40) flow-control decision table name (resolved against dtbl_flo)
5 hru_rcv int receiving (buffer) HRU
6 lyr int soil layer for incoming tile flow (0 = surface)

After reading, the reader copies the parameter set into hru(hru_src)%sb%sb_db and hru(hru_rcv)%sb%sb_db, then resolves flocon_dtbl against the loaded flow-control decision tables (dtbl_flo) to set hru(hru_src)%sb%dtbl.

urban.urb

Urban land-cover parameter database (build-up, wash-off, percent impervious, urban CN). Read into urbdb (type urban_db in src/urban_data_module.f90). File name is in in_parmdb%urban_urb. Urban parameter sets are referenced from landuse.lum for HRUs flagged as urban.

# Column Type Units Default Description
1 urbnm char(16) none "" urban land-cover name
2 fimp real fraction 0.05 fraction of HRU area that is impervious
3 fcimp real fraction 0.05 fraction of HRU classified as directly connected impervious
4 curbden real km/ha 0.0 curb length density
5 urbcoef real 1/mm 0.0 wash-off coefficient for removal of constituents from an impervious surface
6 dirtmx real kg/curb-km 1000.0 maximum amount of solids allowed to build up on impervious surfaces
7 thalf real days 1.0 time for solids on impervious areas to build up to half the maximum
8 tnconc real mg N / kg sed 0.0 total nitrogen concentration in suspended-solid load from impervious areas
9 tpconc real mg P / kg sed 0.0 total phosphorus concentration in suspended-solid load from impervious areas
10 tno3conc real mg NO3-N / kg sed 0.0 NO3-N concentration in suspended-solid load from impervious areas
11 urbcn2 real none 98.0 moisture condition II curve number for impervious areas

Example from refdata/Osu_1hru/urban.urb (first three records shown):

urban.urb: written by SWAT+ editor v2.2.0 on 2023-03-22 04:25 for SWAT+ rev.60.5.4
name                  frac_imp   frac_dc_imp      curb_den      urb_wash      dirt_max     t_halfmax     conc_totn     conc_totp     conc_no3n        urb_cn  description
urhd                   0.60000       0.44000       0.24000       0.18000     225.00000       0.75000     550.00000     223.00000       7.20000      98.00000  Residential-High Density
urmd                   0.38000       0.30000       0.24000       0.18000     225.00000       0.75000     550.00000     223.00000       7.20000      98.00000  Residential-Medium Density
urml                   0.20000       0.17000       0.24000       0.18000     225.00000       0.75000     460.00000     196.00000       6.00000      98.00000  Residential-Med/Low Density
  • file.cio. The structural and hru_parm_db lines select which of these files are read.
  • hru-data.hru. References tiledrain.str, filterstrip.str, grassedww.str, and bmpuser.str by name.
  • landuse.lum. References urban.urb entries for urban HRUs.