There are a number of SWAT+ files that control the simulation of channel processes. The file channel-lte.cha summarizes the main channel information and references several other files that specify the details:

• initial.cha references several files, which specify the initial contents of nutrients and constituents in the water,

• hyd-sed-lte.cha controls the channel hydrology and sediment properties, and

• nutrients.cha controls the channel nutrient properties.

The SWAT+ Editor assigns a name to every object, which is typically the abbreviation of the object type followed by the object number in QSWAT+. However, the name of the channel is not used by SWAT+, so the user may change it.

The pointer to the channel hydrology and sediment file is a foreign key referencing name in hyd-sed-lte.cha.

The pointer to the channel initialization file is a foreign key referencing name in initial.cha.

The ID of the channel is a primary key referenced by lcha in chandeg.con.

The pointer to the channel nutrient file is a foreign key referencing in .

The name of the channel initialization record is a primary key referenced by ini in channel-lte.cha.

The pointer to the pesticide initialization file is a foreign key referencing in .

The pointer to the organic-mineral initialization file is a foreign key referencing name in om_water.ini.

The name of the channel hydrology and sediment record is a primary key referenced by hyd in channel-lte.cha.

The channel slope is calculated by QSWAT+ based on the DEM.

The channel length is calculated by QSWAT+ based on the DEM.

Channel sinuosity is a measure of how much a river or stream channel deviates from a straight line between two points. It is calculated by dividing the length of the channel by the straight-line distance between its endpoints.

For rivers, the conventional classes of sinuosity are:

• sinu <1.05: almost straight

• 1.05 ≤ sinu <1.25: winding

• 1.25 ≤ sinu <1.50: twisty

• 1.50 ≤ sinu: meandering

The table below lists the D50 values of different sediment classes:

The name of the channel nutrient record is a primary key referenced by in .

If routing is performed on an hourly time step, the units of alg_stl are converted to m/hr by the model.

If routing is performed on an hourly time step, the units of ben_disp are converted to mg P/m2*hr by the model.

If routing is performed on an hourly time step, the units of ptlp_stl are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of ptln_stl are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of ben_nh3n are converted to mg N/m2*hr by the model.

If routing is performed on an hourly time step, the units of cbn_bod_co are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of air_rt are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of ben_bod are converted to mg/m2*hr by the model.

If routing is performed on an hourly time step, the units of nh3n_no2n are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of ptlp_solp are converted to 1/hr by the model.

Qual2E provides three different options for computing the algal growth rate:

1. Multiplicative: The multiplicative option multiplies the growth factors for light, nitrogen and phosphorus together to determine their net effect on the local algal growth rate. This option has its biological basis in the multiplicative effects of enzymatic processes involved in photosynthesis.

2. Limiting nutrient: The limiting nutrient option calculates the local algal growth rate as limited by light and either nitrogen or phosphorus. The nutrient/light effects are multiplicative, but the nutrient/nutrient effects are alternate. The algal growth rate is controlled by the nutrient with the smaller growth limitation factor. This approach mimics Liebig’s law of the minimum.

3. Harmonic mean: The harmonic mean is mathematically analogous to the total resistance of two resistors in parallel and can be considered a compromise between the multiplicative and limiting nutrient options. The algal growth rate is controlled by a multiplicative relation between light and nutrients, while the nutrient/nutrient interactions are represented by a harmonic mean.

Qual2E defines four light averaging options:

1. Depth-averaged algal growth attenuation factor for light (FL) is computed from one daylight average solar radiation value calculated in the steady state temperature heat balance.

2. FL is computed from one daylight average solar radiation value supplied by the user.

3. FL is obtained by averaging the hourly daylight values of FL computed from the hourly daylight values of solar radiation calculated in the steady state temperature heat balance.

4. FL is obtained by averaging the hourly daylight values of FL computed from the hourly daylight values of solar radiation calculated from a single value of total daily, photosynthetically active, solar radiation and an assumed cosine function.

The only option currently active in SWAT+ is 2.

If routing is performed on an hourly time step, alg_grow is converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of no2n_no3n are converted to 1/hr by the model.

If routing is performed on an hourly time step, the units of ptln_nh3n are converted to 1/hr by the model.

The Michaelis-Menton half-saturation constant for P defines the concentration of phosphorus, at which algal growth is limited to 50% of the maximum growth rate.

If routing is performed on an hourly time step, alg_resp is converted to 1/hr by the model.

The Michaelis-Menton half-saturation constant for N defines the concentration of nitrogen, at which algal growth is limited to 50% of the maximum growth rate.