Please enable JavaScript.
Coggle requires JavaScript to display documents.
WQ3.3Computational Steps - Coggle Diagram
WQ3.3Computational Steps
Paragraph1
-
They are made at each runoff time step for each subcatchment immediately after surface runoff has been computed.
-
Paragraph2
Note，a pollutant’s buildup constants, vary by land use, not by subcatchment
example, if residential land is assigned a set of buildup constants, then, those constants apply to the residential portion of all subcatchments
the buildup mB (in mass units), at the start of the current time period
not initially, available, for each pollutant on each land use in the subcatchment
initially at time zero, 2ways to get m_B
user specified an initial buildup, of the pollutant, over the entire subcatchment
user-supplied antecedent dry days, with Equation 3-1, to get an initial buildup per area, multiplied by the area associated with the land use, to obtain an initial mass m_B
Paragraph3
computational steps, to update the buildup, over a single time step
- runoff rate >0.001 in/hr, time step belong to a wet weather event, no buildup addition occurs, as is reduced by washoff described in Chapter 4
- If buildup for the pollutant has been designated to occur only when snow is present and the current snow depth is less than 0.001 inches then no buildup addition occurs.
- total mass of buildup mB ——> normalized mass b, by dividing it by fL_UA/fL_UL if buildup is normalized with respect to area /curb length.
- Use Equation 3-2 to find the time t corresponding to normalized buildup b.
- change time step to t, use this value in Equation 3-1, find an updated value for b
- Convert the new normalized buildup b back to total mass mB by multiplying it by the normalizing factor (either fLUA or fLUL).
Paragraph4
produce a new set of pollutant mass buildups mB, at the end of the runoff time step. mB will be used to compute washoff loads when the next wet period occurs(as described in Section 4)