The Runoff Job Control dialog allows the entry of all data which is used to control the Runoff simulation. The following section provide details on the Job Control parameters for Runoff mode.

If Runoff Mode has not been solved, do not check Global Storms.

Job Control data consists of:

Title

The first title line is used across all modes. The second title line, the Runoff Title, is specific to the Runoff mode.

Evaporation

Enter the monthly evaporation rates in this section. 

Evaporation is used to renew surface depression storage and is also subtracted from rainfall and/or snowmelt at each time step. It has a negligible effect on single event simulation (ie. less than a week long), but is important for continuous simulation.

This function is not used to deplete the snow pack; ie, it does not act as sublimation, nor does it affect regeneration of infiltration capacity. The evaporation input in Runoff acts as an upper bound for evapo-transpiration losses from groundwater and soil moisture. Evaporation also occurs from open channels, ie., trapezoidal, parabolic or natural channels.

Direct Input (B1 - IVAP = 1 or 2)

This option provides for entering evaporation rates directly, as either a daily rate or a total monthly rate.

Evaporation (F1 - VAP). Evaporation rate for the given month, expressed either as an average daily rate or a monthly rate (in./day [mm/day] or in./month [mm/month]).

Daily Values (B1 - IVAP = 1). This option specifies a daily evaporation rate in units of in./day [mm/day]. This option is ignored if 'Direct Input' has not been selected.

Monthly Values (B1 - IVAP = 2). This option specifies a monthly evaporation rate in units of in./month [mm/month]. This option is ignored if 'Direct Input' has not been selected.

Temperature Interface File (B1 - IVAP = 4)

This option allows the evaporation rates to be read from the TEMP interface file.

Default Evaporation (B1 - IVAP = 0)

This option uses a default evaporation rate of 0.1 in/day [3 mm/day].

Water Quality (Runoff)

If the water quality simulation flag (this flag) is ON water quality data can be optionally entered at each subcatchment and the water quality related Global Databases are enabled. Otherwise water quality data cannot be selected from a subcatchment or defined in the water quality Global Databases (ie. Buildup/Washoff, Erosion, Initial Loads, Pollutants and Landuses).

The generation of non-point source water quality constituents (ie. pollutants) in storm water can only be included from the Runoff module.

Several methods constitute the genesis of stormwater quality, most notably Buildup and Washoff. In an impervious urban area it is usually assumed that a supply of constituents is built up on the land surface during dry weather preceding a storm. With the storm the material is then washed off into the drainage system.

As an alternative to the use of a buildup-washoff formulation, quality loads may be generated by a rating curve approach. Another quality source is catchbasins. These are treated as a reservoir of constituents in each subcatchment available to be flushed out during a storm. Erosion of "solids" may be simulated directly by the Universal Soil Loss Equation. SWMM adapts this method for storm events. A final source of constituents is in the precipitation itself. SWMM permits a constant concentration of constituents in precipitation.

Many constituents can appear in either dissolved or solid forms and may be absorbed into other constituents. To treat this situation, any constituent may be computed as a fraction ("potency factor") of another.

When conduits are included, quality constituents are routed through them assuming complete mixing within each conduit at each time step. No scour, deposition, or decay-interaction during routing is simulated in the Runoff module.

Several methods constitute the genesis of stormwater quality, most notably Buildup and Washoff. In an impervious urban area it is usually assumed that a supply of constituents is built up on the land surface during dry weather preceding a storm. With the storm the material is then washed off into the drainage system.

As an alternative to the use of a buildup-washoff formulation, quality loads may be generated by a rating curve approach. Another quality source is catchbasins. These are treated as a reservoir of constituents in each subcatchment available to be flushed out during a storm. Erosion of "solids" may be simulated directly by the Universal Soil Loss Equation. SWMM adapts this method for storm events. A final source of constituents is in the precipitation itself. SWMM permits a constant concentration of constituents in precipitation.

Many constituents can appear in either dissolved or solid forms and may be absorbed into other constituents. To treat this situation, any constituent may be computed as a fraction ("potency factor") of another.

When conduits are included, quality constituents are routed through them assuming complete mixing within each conduit at each time step. No scour, deposition, or decay-interaction during routing is simulated in the Runoff module.

Water Quality parameters

Pollutant List

List of pollutants to be used in the simulation. Any number of pollutants may be defined, but a maximum of 20 may be used in any particular simulation (This is the typical configuration but if errors are encountered the SWMM.PAR file should be checked for the actual maximum number allowed).

The pollutants to be used are chosen from those defined in the 'Pollutants' Global Database. To add a pollutant to the "Use Pollutants" list, highlight the pollutant required in the Pollutant list (left-hand list), then select the "Add" button. To remove a pollutant from the list select the pollutant you wish to delete from the "Use Pollutants" list (right-hand list), then select the "Delete" button.

Land Use List

List of landuses to be used in the simulation. Any number of landuses may be defined, but normally a maximum of 10 may be used in any particular simulation (This is the typical configuration but if errors are encountered the SWMM.PAR file should be checked for the actual maximum number allowed).

The available land uses are those defined in the 'Land Use' Global Database. Land uses for the subcatchment 'Water Quality' dialog are chosen from this list. To add a landuse to the "Use Landuses" list, highlight the landuse required in the Landuse list (left-hand list), then select the "Add" button. To remove a landuse from the list select the landuse you wish to delete from the "Use Landuse" list (right-hand list), then select the "Delete" button.

Erosion (Optional)

Flag indicating erosion of suspended solids is to be simulated using the Universal Soil Loss Equation. When this flag is ON, the Erosion Global Database is enabled and the subcatchment erosion data is used.

 

Erosion is added as an additional water quality constituent, so that one fewer Pollutants can be simulated. Futhermore, if Erosion is simulated, at least one other (arbitrary) pollutant must be simulated. No particular soil characteristics (eg. particle size distribution) are assigned to the erosion parameter, and its name is "EROSION", with units of "mg/l".

Add Erosion to Constituent. Flag indicating erosion is to be added to the pollutant whose name appears in the button on the right (often suspended solids). This list of possible Pollutants is defined by the 'Pollutant' Global Database. This addition is done before pollutant fractions are distributed (see the Runoff Pollutant Global Database). If this flag is OFF, erosion is not added to any pollutant, but is accounted for separately.

Maximum 30 minute storm intensity (J1 - RAINIT). Highest average 30 minute rainfall intensity during the year, in./hr [mm/hr].

Catchbasin

This typical catchbasin will be used as the single unit catchbasin when defining subcatchments. Each subcatchment may have a multiple number of the catchbasins.

Catchbasins generally have a negligible effect on most simulation results. Although catchbasins contribute to a first flush effect, the most important task in most simulations is to obtain a correct total storm load, to which catchbasins are seldom strong contributors. Hence, excessive effort to define catchbasin parameters is seldom required.

Storage Volume (J1 - CBVOL). Average individual catchbasin storage volume, ft^3 [m^3].

Recharge Time (J1 - DRYBSN). Dry days required to recharge catchbasin concentrations to initial values from a zero load. The initial concentrations are defined in the Pollutant-Landuse Dialog under the Pollutant Global Database.

Street Sweeping (Optional)

Street sweeping data for calculating dust and dirt removal.

Start Month (J1 - KLNBGN). Month of the year when street sweeping starts, 1 - 12.

Start Day (J1 - KLNBGN). Day of the month when street sweeping starts, 1 - 31.

Stop Month (J1 - KLNEND). Month of the year when street sweeping finishes, 1 - 12.

Stop Day (J1 - KLNEND). Day of the month when street sweeping finishes, 1 - 31.

Street Sweeping Efficiency (J1 - REFFDD). Percentage of dust and dirt removed by Street Sweeping. This removal efficiency is applied during the mini-simulation that occurs prior to the initial storm or start of simulation.

Dry Days Before Simulation

Number of dry days before the start of simulation. A 'dry day' is not well defined but may be considered as the number of days prior to the start of simulation in which the cumulative rainfall is less than a specified value, eg. 0.1 in. [2.5 mm].

Snow Melt

If the snow melt flag (this flag) is ON, snow melt data can optionally be entered for each subcatchment. Otherwise snow melt data will not be able to be entered from a subcatchment or from the Snowmelt Global Database.

The general snow melt data defines the overall mode and degree of sophistication of computations as either single event or continuous, the holding capacity of snow in general, and the average wind speed effects of the whole area.

Snowmelt Parameters

Simulation Type: Single Event

For single event SWMM, snow covered areas are constant (areal depletion curves are used only for continuous SWMM) and input parameters are fewer. In addition, snowfall quantities are not computed on the basis of air temperatures but may only be input, if desired, as negative precipitation intensities. Melt coefficients are constant and there is no maintenance of the cold content of the snow pack, nor is there redistribution (that is, plowing) for normally bare areas.

For single-event mode, air temperatures are entered directly on a constant time interval basis.

Air Temperature (C5 - TAIR). Air temperature during the given time interval, F [C]. Air temperatures are considered constant over the air time step.

Time Interval (C5 - DTAIR). Time interval in hours between air temperature readings. This time interval is independent of the simulation time steps.

Simulation Type: Continuous

For continuous SWMM, areal depletion curves are used to compute snow-covered areas. Snowfall quantities are computed on the basis of air temperatures. Melt coefficients vary daily, from a maximum on June 21 to a minimum on December 21 (or vice-versa for the Southern Hemisphere). Melt coefficients vary daily, from extremes on June 21 and December 21. The snow pack cold content is maintained and redistribution (ie. plowing) for normally bare areas occurs. Both models use the same melt equations and melt routing procedures.

In continuous mode, air temperatures are read from the TEMP interface file.

The parameters used to define continuous event snow melt are:

Areal Depletion Curve

The areal depletion curve (ADC) accounts for the variation in actual snow covered area that occurs following a snowfall. In most snowmelt models, it is assumed that there is a depth above which there will always be 100% cover. In SWMM, this depth (call it SI) remains constant. The ADC is a non-dimensional plot of relative area that is snow-covered against snow depth (water equivalent) relative to SI.

The ADC curves are employed when the snow depth becomes less than the depth for 100% cover (SI).

Areal depletion curves are used to compute snow-covered areas. Snowfall quantities are computed on the basis of air temperatures. Melt coefficients vary daily, from extremes on June 21 and December 21. The snow pack cold content is maintained and redistribution (ie. plowing) for normally bare areas occurs.

Relative Snow Depth. This parameter is the ratio of the depth (water equivalent) of snow over the snow covered areas of the catchment to the depth required for 100% cover.

Area Snow Cover (Perv) ASC (C4 - ADCP). Fraction in the range 0.0 - 1.0 of the pervious area covered by snow.

Area Snow Cover (Imperv) ASC (C3 - ADCI). Fraction in the range 0.0 - 1.0 of the impervious area covered by snow.

Dividing Temperature (C1 - SNOTMP)

Dividing temperature between snow and rain, F [C]. Precipitation occurring at air temperatures above this value will be rain, at or below will be snow.

In natural areas, a temperature of 34-35F (1-2C) provides the dividing line between equal probabilities of rain and snow. However, this parameter may need to be somewhat lower in urban areas, due to warmer surface temperatures.

Snow Gauge Correction Factor (C1 - SCF)

The snow gauge correction factor accounts for the error in snow gauge measurement.

The factor is usually greater than 1.0 (the gauge tends to underestimate the catch) and increases as a function of wind speed. In practice, the snow gauge correction factor can be used as a calibration factor to account for gains or losses of snow that cannot be determined from the available data. For example, snow losses such as interception and sublimation can be accounted for.

Antecedent Temperature Weighting Index (C1 - TIPM)

During non-melt periods the temperature of the snow pack follows the temperature of the air, but with a delay, since temperature changes cannot occur instantaneously. The Antecedent Temperature Weighting Index is an indicator of the surface layer of the snow pack and is used to account for this time delay.

Values of TIPM <= 0.1 give significant weight to temperatures over the past week or more and would indicate a deep 'surface layer' (thus inhibiting heat transfer). Values of TIPM greater than 0.5 would essentially only give weight to temperatures during the past day. The pack will both warm and cool faster (ie. track the air temperature) with higher values of TIPM. A value of 0.5 has been shown to give reasonable results for natural catchments (Anderson, 1973).

Negative Melt/Melt Coefficient Ratio (C1 - RNM)

Ratio of negative melt coefficient to melt coefficient. "Negative melt coefficient" is used when snow is warming or cooling below the base melt temperature without producing runoff.

Heat transfer within the snow pack is less during non-melt periods due to the presence of liquid water in the pack for the latter case. This parameter multiplies the normal melt coefficients to produce a lower coefficient for use during non-melt periods. The negative melt coefficient is usually <= 1.0 with a typical value of 0.6 for natural areas. Values for urban areas are likely to be somewhat higher because of the higher density of urban packs. The higher the value, the more rapid the heat gain or loss of the pack in response to air temperature changes.

Hemisphere

The hemisphere option is used to indicate whether the average latitude is in the Northern or Southern Hemisphere.

Average Latitude (C1 - ANGLAT)

Average latitude of watershed, in degrees north or south from the equator. This parameter is used to compute daylight hours for the catchment.

Longitudinal Correction (C1 - DTLONG)

Longitude correction, standard time minus mean solar time, minutes (of time). This parameter is used to compute the hours of daylight for the catchment. Moderate errors in this parameter have little effect on the results.

Compute DTLONG as follows: Determine standard meridian (SM) for the time zone of the catchment (eg. in the USA EST=75°W, CST=90°W, MST=105°W and PST=120°W). Let theta = average longitude of catchment, and delta = theta - SM. Then DTLONG = 4 x delta. Eg. Minneapolis at theta = 93°W has DTLONG = +12 minutes (of time). Note that one degree of longitude is equal to 4 minutes of time.

Free Water Holding Capacity Ratio (C1 - FWFRAC3)

Percentage of free water holding capacity to snow depth (in. [mm] water equivalent) for snow on normally bare impervious area.

Using this parameter the snow is treated by the model as a reservoir for liquid melt before it is released as runoff.

Free Water Holding Capacity

The free water holding capacity of a snow pack is the volume of water (as a depth) within the pack that can be held as liquid melt prior to releasing runoff. It acts as an intermediate reservoir; the larger its volume, the greater the delay in the appearance of runoff following the conversion of snow to liquid water. Some available information is given in the following table (from Anderson, 1973; Corps of Engineers, 1956).

Snowpack Conditions Ratio of free water-covered area holding capacity to snow depth on snow:

Typical deep pack (> 10 in.) 0.02-0.05

Typical shallow early winter pack 0.05-0.25

Typical shallow spring pack 0.20-0.30

or with slush layer

Note that the fraction increases as pack density increases, pack depth decreases, slush layer increases, or ground slope decreases. Snowpack depths are in units of water equivalent; one inch of snow water equivalent equals a depth of approximately 11 inches of new snow on the ground surface.

Percentage of free water holding capacity is entered for both  Pervious and Impervious areas.

Wind Speed Data

Wind speeds are used for melt calculations during periods of precipitation. The higher the values of wind speed, the greater are the convective and condensation melt terms. Of course, if the simulation covers a large area, the wind speeds can only be considered as gross estimates of highly variable speeds.

TEMP Interface File. Read wind speed data from the TEMP interface file defined in Utilities.

Monthly Wind Speeds. Average monthly speeds are often available from climatological summaries.

Wind speed is averaged for the given month, in miles/hr or km/hr.

Average Watershed Elevation (C1 - ELEV)

Average watershed elevation in ft [m]. This is used only to compute average atmospheric pressure, and has a minimal effect on results.

Regeneration of Horton Infiltration Capacity

Selecting this requires that a regeneration value is entered in the field. If this flag is OFF, then no regeneration of infiltration capacity occurs.

For continuous simulation, infiltration capacity is regenerated using the Horton type exponential rate constant equal to REGEN*DECAY, where DECAY is the Horton rate constant read in for each infiltration Global Database. This flag has no effect if Green-Ampt infiltration is used for a catchment.

Time Control (Runoff)

Time control allows the entry of the simulation start/stop date and time and time step durations.

The Use Simulation Start Time for Rainfall Event check box applies to user input Constant Time Intervals and Variable Time Intervals rainfall data. When checked the rainfall date and time from the Rainfall Global Database record is ignored and the rainfall will automatically start with the simulation start time.

Dry Time Step. Dry time step in seconds. Must be greater than or equal to the wet time step. The dry time step is used to update the infiltration parameters, generate groundwater flow, and to produce a time step value for the interface file. The dry time step should be 1 day to a week and generally longer in drier climates.

A dry time step is used when there is no precipitation or surface storage. However, there may be groundwater flow.

Transition Time Step. Transition time step in seconds. Must be less than or equal to the Dry time step and greater than or equal to the Wet time step.

A transitional time step is used when there is no precipitation input on any subcatchment, but the subcatchment(s) still have water remaining in surface storage. The Runoff overland flow routing technique loses water through infiltration, evaporation, and surface water outflow during the transition periods

Wet Time Step. Wet time step in seconds. Must be greater than or equal to 1.0 and less than or equal to the transition time step.

A wet time step is used when any of the subcatchments have precipitation input. Typically the WET time step should be a fraction of the rainfall interval. Five minute rainfall should have wet time steps of 1, 2.5 or 5.0 minutes, for example. It can be longer but information is lost by averaging over a longer time period.

Simulation Start/End. Enter the Year, Month, Day, Hour, Minute, and Second of the simulation start and end. 

Print Control (Runoff)

This dialog controls all the 'general' (not node or conduit specific) output options.

 

Inlet Results

This parameter controls the amount of output generated for each inlet in the system. An inlet is the drainage point for any sub-network.

Print Summary at end of Simulation (B2 - IPRN3 = 0). Do not print daily, monthly, or yearly totals.

Print Monthly and annual totals (B2 - IPRN3 = 1). Print monthly and annual totals only, one year per page.

Print Daily, monthly and annual totals (B2 - IPRN3 = 2). Print daily, monthly and annual totals, two months per page. Daily totals are printed whenever there is non-zero precipitation and/or runoff.

General results

These parameters control the output of non-zero flows and concentrations from conduits or nodes flagged for output. All printed values are instantaneous at the end of the preceding time step. Zero flows are not printed to avoid voluminous output in long simulations.

Statistical summary only (M1 - INTERV = 0). Print a statistical summary only, rather than detailed time step printouts.

Print every 'x' time steps (M1 - INTERV > 0). Print detailed output to the text output file at the interval defined here.

Define Print Periods (M2 - NDET > 0)

Set the print periods to the periods entered below, for General Results.

Start Date (M2 - STARTP). The print period start and end dates must be entered in a specific format. The date format is set by the DATE_FORMAT variable in the SWMM.CFG file.

End Date (M2 - STARTPR). The print period start and end dates must be entered in a specific format. The date format is set by the DATE_FORMAT variable in the SWMM.CFG file.

Plot Hyetographs and Inlet Hydrographs (B2 - IPRN2)

Flag for whether or not to plot to a line printer, an inlet hydrograph and a hyetograph for each rain gauge.

Save ALL Results for Review

This flag will save all the results for nodes and conduits from analysis to a special file for later graphical post-processing.

Gauged Pollutants List

This flag and the associated dialog allows the definition of the list of pollutants to be used in the Gauged Pollutant List. If this flag is OFF, no gauge pollutants are shown. If this flag is ON, a list of pollutants is selected from the list of gauged pollutants shown in the Pollutants Global Database.

The pollutants to be used are chosen from those defined in the Pollutants Global Database. Any number of pollutants may be defined. To add a pollutant to the "Use Pollutants" list, highlight the pollutant required in the Pollutant List (left-hand list), then select the "Add" button. To remove a pollutant from the list select the pollutant you wish to delete from the "Use Pollutants" list (right-hand list), then select the "Delete" button.

The pollutant load and concentrations may be generated in the Hydraulics, Runoff or Sanitary Layer, or read in from an interface file.

Global Storms


Name. This field is used in the Review Results display and also in XP Tables. Further, this name is appended to the model name when writing the output files, i.e. modelname_globalstormname.out. For this reason it is important to not use any special punctuation or symbols in the name as this can cause issue properly reading/writing the given files.

Return Period. This field is used for display purposes only.

Rainfall. The Rainfall Global Database record corresponding to the storm to be analyzed.

Override Multiplier. The value entered in this field replaces (overrides) the value entered in the Constant Time Interval dialog of the global database. This value will only be active if the rainfall type is Absolute Depth or Cumulative Depth.

Multiplier. The new multiplier for the Absolute or Cumulative Depth.

The maximum number of Global Storms allowed in a single model is 200 for the 2013 version and beyond

Rational Formula Settings

 

The Rational Formula data is selected from the Rational Formula settings in the Global Database.

Return Period to Analyze is the Recurrence Interval of the storm being analyzed.

Use Partial Area. If enabled this option uses the partial area hydrology effects to locate the critical storm duration that produces the maximum peak flow draining to each node. This may result in a storm duration less than the time of concentration for the total catchment above a node, and hence the term partial area. For large contributing areas this approach will generally yield higher peak flows.

If disabled, the program uses a storm duration corresponding to the time of concentration for each contributing subcatchment in the calculation of peak flows. 

Colorado Urban Hydrograph Procedure (CUHP) 

The CUHP program was originally developed in 1971 by Ben Urbonas and Stewart McGuire (URS/KEN R. WHITE COMPANY). The program has been regularly revised for the Urban Drainage and Flood Control District by a number of companies and individuals including, Gary Walkovitz (URS COMPANY), Ben Urbonas and David Lombard (UDFCD), C. R. Wuerz (Merrick and Company), Young S. Yoon and Nien Sheng Hsu (Boyle Engineering Corporation).

Read more about the Job Control options for CUHP  in the Regional Hydrology Methods section.

Sacramento Hydrology Methods

Use this dialog to specify start and stop times of the simulation and the parameters for the Nolte or Sacramento County methods.


Read more about Sacramento Hydrology Methods in the Regional Hydrology Methods Section.

Los Angeles County Method Job Control

If LAC_HYDROLOGY=ON has been set in the swmxp.ini file, the LA County Hydrology Job Control dialog will become available. 

Days To Analyze

Either the fourth day or all four days of the LA County Modified Rational Method procedure may be analyzed by selecting the suitable radio button. The factor applied to the dimensionless storm is entered in the appropriate fields for Days 1 through 4.

Storm Frequencies

The base frequency and the rainfall multiplier is entered in this field.

Simulation Start Time

The starting year, month, day, hour, minute, and second of the simulation. This data is only used by the Interface File when you are simulating the hydraulics using XPSWMM. The duration of the run is determined by the number of days being analyzed. 

Rainfall Template

Opens a dialog where a  dimensionless (normalized) rainfall pattern can be entered. Read more about this function in the 24 Hr Rainfall Template section of the LA County Method page

Runoff/Infiltration

The infiltration data is entered in the LA County Runoff/Infiltration dialog.

Pollutants

Ticking the check box will load the Pollutants List dialog. Available pollutants are selected from what has been entered in the Pollutants section of the Global Database.

Load Location Points

This option allows you to load data from an existing MORA file. The format of this file is shown below.

Location Card Data (Refer to Figure D-6 of LA County Hydrology Manual


ColumnEntryDescription
1-3006 Card code number.
4-9numeric 

Location number of point in the watershed where a calculation is to be made. Location numbers must be listed in the sequence calculations are to be made.

10-14numeric If hydrograph in main line of the drainage system located in primary storage.
15 

alphabetic

The alphabetic code identifies the drain where flow rate is to be modified by: (1) addition of a hydrograph from a lateral or subarea; (2) separation of flow junction with relief drain; or (3) flood routing and channel storage effects. A letter must be listed on each data card.
  • A If hydrograph In principle Lateral B located in primary storage.
  • B If hydrograph in Lateral C located in primary storage.
  • C If hydrograph in Lateral O located in primary storage
  • D If hydrograph in Lateral E located in primary storage.
  • F If hydrograph in Lateral F located in primary storage. 
16

alphabetic

 For relief drains (see Column 53-59) the alphameric code indicates the lateral receiving flow separated from the primary drain.
  • C If hydrograph in Lateral C to be combined with hydrograph in Line A or B.
  • D If hydrograph in Lateral D to be combined with hydrograph in Lines A, B, or C.
  • E If hydrograph in Lateral E to be combined with hydrograph in Lines A, B, C, or D.
  • F If hydrograph in Lateral F to be combined with hydrograph in Lines A, B, C, D, or E. 
 17-19 numeric Soil type number. (See Figures C-6,) A soil type number must be listed on all cards.
 20-22 numeric Effective imperviousness of subarea in percent.
 23-26 numeric Subarea tributary drainage in acres.
 

27-28

 numeric Time of concentration in minutes. An arbitrary time for a zero acre subarea in
Column 23-26must be shown if flood routing through a reach with no tributary area is desired.
 29  alphabetic If storm pattern:
  • A through I for other than design storm rainfall to be used.
  • J If J zone design storm rainfall pattern to be used.
  • K If K zone design storm rainfall pattern to be used.
  • L If L zone design storm rainfall pattern to be used.
  • M If M zone design storm rainfall pattern to be used.
  • T If thunderstorm (convective storm) design rainfall pattern to be used. 

The letter must be listed in Column 29 of each data card.

30-31

numeric

If A through I storm pattern to be used, an identification number between 1 and 99
must also be used.

  • 01 If thunderstorm (convective storm) design rainfall pattern to be used.
  • 10 If 10-year frequency rainfall for J, K, L, M zone rainfall to be used.
  • 25 If 25-year frequency rainfall for J, K, L, M zone rainfall to be used.
  • 50 If 50-year frequency rainfall for J, K, L, M zone rainfall to be used.

The number must be listed in Column 30-51 of each data card.

32numeric
  • 1 If mountain channel reach to be used. (See Figure C-12.5.)
  • 2 If natural valley channel reach to be used. (See Figure C-12.4.)
  • 3 If typical 36-foot road width--8-inch curb street to be used. (See Figure C-12.3.)
  • 4 If circular pipe size to be specified, or if street flow is undesirable.
  • 5 If rectangular channel base width or depth to be specified. (Trapezoidal section side slope can be specified.)
  • 6 If trapezoidal channel side slope, maximum peak velocity, and either width or depth to be specified.
32blank

If the system is to begin flood routing in street section:

  • Change from street to pipe section when flow depth reaches the property line, From pipe to rectangular channel when pipe diameter of 8 feet is exceeded, and from the hydraulically most efficient rectangular section to a maximum depth of 13 feet when that depth is reached. (This change in conveyance is also automatic if either street (3) or pipe (4, with no size listed) is specified.)
  • The trapezoidal channel (6) may involve composite lining with unlined bottom to facilitate channel percolation, or for economic or other design considerations. In steeper areas where scour of the channel bottom could occur, the system routes flow by adjusting channel slope as necessary (drop structures assumed) to not exceed the specified maximum velocity at peak flow rate. Specified values would be: (1) maximum velocity and maximum depth; or (2) maximum velocity and base width.
33-37 numeric Length of channel reach between subarea collection points in feet.
38-43 numeric Slope of drain in feet per foot.
44-46numeric 

If trapezoidal channel (6 in Column 32), computed as horizontal projection of channel wall divided by depth in feet per foot.

blank If rectangular section.

47-52 

numeric If specified circular pipe diameter in feet is to be used (4 in Column 32).
numeric If specified bottom width of rectangular channel in feet is to be used (5 in Column 32).
numeric If specified bottom width of trapezoidal channel in feet is to be used (6 in Column 32).

53-59 
  • Numeric Peak flow rate in second feet to remain in main line or lateral listed in Column 15 at junction with relief drain specified (1, 3, 4 in Column 60).
  • Numeric Percent to be applied to hydrograph ordinate to obtain the hydrograph to remain in the main line or lateral listed in Column 15 at junction with relief drain (2 in Column 60). 
60   numeric
  •  1 If hydrograph in drain listed in Column 15 to be proportioned on percentage basis, such that hydrograph remaining in drain has peak flow listed in Column 53-59 with residual flow transferred to relief drain listed in Column 16. 
  • 2 If hydrograph in drain listed in Column 15 to be proportioned on percentage basis, such that hydrograph remaining in drain has percentage of total Flow specified in Column 53-59 with excess flow transferred to relief drain listed in Column 16. 
  • 3 If hydrograph in drain listed in Column 15 to be separated such that all flow up to peak flow rate listed in Column 53-59 remains in the drain with excess flow transferred to relief drain listed in Column 16. 
  • 4 If hydrograph in drain listed in Column 15 to be separated such that only Flow above a base value (equal to the peak flow rate minus the flow rate listed in Column 53-59) remains in the drain with all flow below the base value transferred to relief drain listed in Column 16.
 61 
  • 1 If hydrograph for all four days of a four-day design storm to be computed.
  • 2 If hydrograph for second, third, and fourth days of four-day design storm to be computed. 
  • 3 If hydrograph for third and fourth days of four-day design storm to be computed.
  • Blank If hydrograph for only fourth day (maximum day rainfall) of four-day design storm to be computed, or hydrograph for thunderstorm, or other selected storm rainfall to be computed
 62 
  • 1 If hydrograph print-out only desired. (See Figure E-5.7.) 
  • 2 If hydrograph print-out plus card punched hydrograph desired.
 63 
1 if Confluence Q print-out listing peak flow and time for each lateral and combined peak and time at downstream end of confluence. (See Figure E-5.6.)
 64 
  • A If hydrograph stored in Line A to be erased.
  • B If hydrograph stored in Line B to be erased.
  • C If hydrograph stored in Line C to be erased.
  • D If hydrograph stored in Line D to be erased.
  • E If hydrograph stored in Line E to be erased.
  • F If hydrograph stored in Line F to be erased.
  • G If all hydrographs stored in system to be erased.
65 
  • 1 If project description heading at beginning of print-out and heading for hydrograph print-out (See D-3.4.) sheets desired.
  • 2 If end of job.
66 
A if Hydrograph data cards read into main line or lateral listed in Column 15. (See D-3.5.)
67
  • 1 If main line flow to be recomputed using area reduction factor for total drainage area and initially computed drain sizes.
  • 2 If Lateral B flow to be recomputed using area reduction factor for total drainage area and initially computed drain sizes.
  • 3 If Lateral C flow to be recomputed using area reduction factor for total drainage area and initially computed drain sizes.
  • 4 If Lateral D Flow to be recomputed using area reduction factor for total drainage area and initially computed drain sizes.
  • 5 If Lateral E flow to be recomputed using area reduction factor for total drainage area and initially computed drain sizes.
  • 7 If area reduction to be set at 1.0.
68-70 
  • blank If n of .O14 to be used for channel bottom.
  • numeric If higher n value for rougher channel bottom to be used.
71-73
  • blank If n of .014 to be used for channel side walls.
  • numeric If higher n value for rougher surface to be used.
74-75
  • blank If rectangular or trapezoidal channel maximum depth of 13 feet to be used.
  • numeric If rectangular or trapezoidal channel, maximum channel depth in whole feet other than 13 feet to be used.
76-77numeric 

Maximum velocity in whole feet per second when trapezoidal channel (6) specified in Column 32.


Read more about LA County Procedure in the Regional Hydrology Methods section.