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WQ4.2.5 Wet Deposition and Runon - Coggle Diagram

- - - - The instantaneous loading rates from these two streams
        
        a wrong way
        
        simply be added onto the loads computed from the washoff functions described earlier
        
        because they must first be routed through the volume of water (shallow as it may be) that ponds atop the surface of the subcatchment
        
        See Volume I for a description of how SWMM uses a nonlinear reservoir model to describe surface runoff.
        
        condtion
        
        Consistent with the way that the flow from direct rainfall and runon is treated
        
        these pollutant streams are completely mixed with the current contents of the ponded water
        
        and a mass balance is performed to find the pollutant mass from these sources leaving the ponded surface water over the computational time step.
        
        This mass flux is added to the mass flux computed from the washoff functions to arrive at a total washoff amount.
        
        two-stream approach
        
        to handling washoff from both pollutant buildup and from rainfall/runon
        
        Figure 4-3 depicts
        
        written of mass balance for the pollutant and volume of the washoff stream
        
        originating from the ponded surface water that receives upstream run-on and direct deposition can be
        
        note1
        
        applied to the subcatchment as a whole
        not to its separate impervious and pervious sub-areas
        
        Precipitation, infiltration, and evaporation rates have been converted from their more conventional units of inches/hr to cfs
        
        by multiplying by the subcatchment’s area
        
        Infiltration removes a proportional amount of mass
        
        regardless of constituent
        
        Evaporation removes volume but not mass causing Cponded to increase
        
        Qout
        
        It can be lower than the Qrunoff used in the buildup washoff functions
        
        1 more item...
        
        is the total runoff flow leaving the subcatchment.
        
        The only unknown to solve for is Cponded
        
        all flow rates and volumes are known from the runoff calculations done prior to washoff analysis
        
        W_washoff is total washoff rate
        
        by adding together the washoff rates w
        
        computed for the buildup on each land use
        
        Wponded
        
        is the runoff load from ponded surface storage
        
        is Qout ×Cponded.
        
        Wout
        
        is the total mass flow rate of pollutant leaving the subcatchment
        
        is Wwashoff + Wponded
        
        Wout / Qout.
        
        is the concentration of pollutant in the subcatchment’s runoff
        
        note2
        
        this scheme requires
        
        an additional set of state variables be kept track of over a simulation
        
        namely the ponded mass (mp=Vponded×Cponded) for each pollutant in each subcatchment