SWMM5 inflow.c Summary

Below is a step-by-step explanation of the inflow.c file in EPA SWMM5. This file manages any external (direct) or dry-weather flow (DWF) inflows assigned to nodes in the drainage network. It covers:

• Direct/External Inflows: e.g., time series flows or concentrations added directly to a node.
• Dry-Weather Flows (DWF): e.g., constant or pattern-based baseline inflows for a node (like average daily sewage flows).

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1. Overview of inflow.c

EPA SWMM5 allows you to specify additional inflows entering a drainage system node, beyond normal subcatchment runoff. They can be:

1. External inflows:

   • Typically from time series, e.g., industrial wastewater discharges or other user-defined flows.
   • Can be flows, or pollutant concentrations/mass loads.

2. Dry Weather Flows (DWF):

   • Typically average flows that vary by monthly/daily/hourly patterns.
   • E.g., base sanitary flows in a network.

The inflow.c file implements reading and storing these inflows, plus computing their actual flow/concentration at a given time step.

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2. Data Structures

2.1 TExtInflow

typedef struct ExtInflow {
    int    param;        // -1 for FLOW or pollutant index
    int    type;         // type of inflow: FLOW_INFLOW, CONCEN_INFLOW, MASS_INFLOW
    int    tSeries;      // index of time series for inflow
    double cFactor;      // units conversion factor
    double sFactor;      // scaling factor
    double baseline;     // baseline inflow value
    int    basePat;      // baseline time pattern
    struct ExtInflow* next;
}  TExtInflow;

• param: Which inflow parameter is assigned (either flow or pollutant). If -1, it’s FLOW; otherwise it’s a pollutant index.
• type: Tells if it’s FLOW_INFLOW, CONCEN_INFLOW, or MASS_INFLOW.
• tSeries: Index of a time series controlling the inflow variation over time.
• cFactor, sFactor: Additional conversion and scaling factors.
• baseline and basePat: A constant baseline inflow plus an optional time pattern multiplier.
• Linked together in a linked list via next.

2.2 TDwfInflow

typedef struct DwfInflow {
    int     param;                // -1 for FLOW or pollutant index
    double  avgValue;             // average baseline DWF
    int     patterns[4];          // up to 4 pattern indexes
    struct  DwfInflow* next;
} TDwfInflow;

• For dry-weather flow:
  • param = -1 for flow, otherwise pollutant index.
  • avgValue = average DWF. For flow, it’s eventually converted to user’s flow units.
  • patterns = monthly/daily/hourly/weekend patterns. The code sorts them by pattern type for speed.

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3. Reading Inflow Inputs

3.1 inflow_readExtInflow()

int inflow_readExtInflow(char* tok[], int ntoks)

• Parses a line of input data describing an external (direct) inflow.
• Data line format:
  1. nodeID
  2. FLOW | pollutID
  3. tSeriesID (time series name, could be blank)
  4. (optional) CONCEN/MASS for pollutant, plus numeric fields:
     • A unitsFactor if MASS,
     • A scaleFactor,
     • A baseline,
     • A basePat (pattern).
• If the parameter is FLOW, then param=-1; otherwise, it’s the pollutant index.
• If it’s mass inflow, an additional factor in cf (conversion factor) is read.
• This eventually calls inflow_setExtInflow() to create or update the TExtInflow object and link it into the node’s list of external inflows.

Key: The code sets:

• Type = FLOW_INFLOW, CONCEN_INFLOW, or MASS_INFLOW.
• Time Series reference.
• Baseline flow or concentration.
• Optional time pattern.

3.2 inflow_setExtInflow()

int inflow_setExtInflow(int j, int param, int type, int tseries, int basePat,
                        double cf, double baseline, double sf)

• Actually allocates (or re-uses) a TExtInflow struct for a node j.
• Fills in the parameters for external inflow:
  • param, type, tseries, cFactor, sFactor, baseline, basePat.
• Returns 0 if success, or error code otherwise.

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3.3 inflow_readDwfInflow()

int inflow_readDwfInflow(char* tok[], int ntoks)

• Reads a line describing dry weather flow for a node.
• Format:
  1. nodeID
  2. FLOW or pollutant name
  3. avgValue
  4. Up to 4 pattern IDs
• Identifies the node, the param (flow or pollut index), the average value.
• Finds up to 4 pattern references.
• Creates a TDwfInflow object and attaches it to Node[j].dwfInflow.

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4. Managing Inflow Lists

4.1 Deleting Inflows

• inflow_deleteExtInflows(int j): frees the linked list of external inflows on node j.
• inflow_deleteDwfInflows(int j): frees the linked list of dry-weather inflows on node j.

These are typically called at the end of a run or if the user re-initializes objects.

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5. Computing Inflow Rates

During a simulation step, SWMM needs to compute the actual inflow from these data. Two main calls:

1. inflow_getExtInflow(): for external inflows
2. inflow_getDwfInflow(): for dry-weather flows

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5.1 inflow_getExtInflow()

double inflow_getExtInflow(TExtInflow* inflow, DateTime aDate)

• For a given date/time, returns the current external inflow.
• Steps:
  • Possibly apply the baseline pattern multiplier (monthly/daily/hourly/weekend).
  • If time series is present, lookup the time series value at aDate and scale it.
  • Then combine those plus the conversion factor: $$\text{flow or conc.} = cFactor \times (\text{TimeSeriesValue} \times sFactor + baseline)$$

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5.2 inflow_getDwfInflow()

double inflow_getDwfInflow(TDwfInflow* inflow, int month, int day, int hour)

• For the current time’s month, day, hour, it collects pattern multipliers from up to 4 patterns:
  • monthly,
  • daily,
  • hourly,
  • weekend hourly.
• A final factor f is then multiplied by inflow->avgValue.
• Returns that product as the current DWF for the parameter (flow or pollutant).

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5.3 Pattern Lookups

getPatternFactor(int p, int month, int day, int hour)

• Takes pattern index p plus the current date/time, returns the pattern factor.
• The code checks if pattern type is monthly/daily/hourly/weekend, picks the right factor from the pattern array. If out of range, defaults to 1.0.

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6. Dry-Weather Flow Patterns

inflow_initDwfPattern(int j)

• Initializes the Pattern[j] object with all factors = 1.0, no ID. Called when a Time Pattern is first created.

inflow_readDwfPattern(char* tok[], int ntoks)

• Reads lines defining a pattern’s values.
• Sets the pattern type = monthly/daily/hourly/weekend, then reads the numeric factors for up to 24 slots (for hourly) or 12 slots (monthly), etc.

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7. Summary

1. Reading Inputs:

   • External inflows from lines containing node, pollutant, time series, scaling, baseline, etc.
   • DWF inflows from lines containing node, pollutant, average value, up to 4 patterns.

2. Managing Node Inflow Lists:

   • Each node has a linked list of TExtInflow objects and a linked list of TDwfInflow objects.
   • inflow_delete...() frees them.

3. Using Patterns:

   • Patterns can adjust baseline or time series inflow by monthly/daily/hourly/weekend multipliers.

4. Computing Inflows:

   • External inflows use inflow_getExtInflow() => time series + baseline pattern.
   • DWF inflows use inflow_getDwfInflow() => average flow + pattern multipliers.

In short, inflow.c parses inflow inputs and manages their time-dependent retrieval so that SWMM’s hydraulic/quality engine can incorporate these flows and pollutant loads at each node in each time step.