Hydrology in SWMM5

Hydrologic Modeling Features

SWMM accounts for various hydrologic processes that produce runoff from urban areas. These include:

·	time-varying rainfall
·	evaporation of standing surface water

·	snow accumulation and melting
·	rainfall interception from depression storage

·	infiltration of rainfall into unsaturated soil layers
·	percolation of infiltrated water into groundwater layers

·	interflow between groundwater and the drainage system
·	nonlinear reservoir routing of overland flow

·	capture and retention of rainfall/runoff with various types of low impact development (LID) practices.

Spatial variability in all of these processes is achieved by dividing a study area into a collection of smaller, homogeneous Subcatchment areas, each containing its own fraction of pervious and impervious sub-areas. Overland flow can be routed between sub-areas, between Subcatchments, or between entry points of a drainage system.

Hydrology

Aside from rain gages and Subcatchments, the following hydrology-related objects are used by SWMM:

·

Aquifers

·	Snow Packs

·	Unit Hydrographs

·	LID Controls
Surface Runoff

The conceptual view of surface runoff used by SWMM is illustrated in the figure below.

Each Subcatchment surface is treated as a nonlinear reservoir. Inflow comes from precipitation and the runoff from any designated upstream Subcatchments. Outflows consist of infiltration, evaporation, and surface runoff. The capacity of this "reservoir" is the maximum depression storage, which is the maximum surface storage provided by ponding, surface wetting, and interception. Surface runoff, Q, occurs only when the depth of water d in the "reservoir" exceeds the maximum depression storage, ds, in which case the outflow is given by Manning's equation. Depth of water over the Subcatchment (d) is continuously updated with time by solving numerically a water balance equation over the Subcatchment.

Subcatchments

Subcatchments are hydrologic units of land whose topography and drainage system elements direct surface runoff to a single discharge point. The user is responsible for dividing a study area into an appropriate number of Subcatchments, and for identifying the outlet point of each Subcatchment. Discharge outlet points can be either nodes of the drainage system or other Subcatchments.

Subcatchments are divided into pervious and impervious subareas. Surface runoff can infiltrate into the upper soil zone of the pervious subarea, but not through the impervious subarea. Impervious areas are themselves divided into two subareas - one that contains depression storage and another that does not. Runoff flow from one subarea in a Subcatchment can be routed to the other subarea, or both subareas can drain to the Subcatchment outlet.

Infiltration of rainfall from the pervious area of a Subcatchment into the unsaturated upper soil zone can be described using five different models:

·	Classic Horton infiltration
·	Modified Horton infiltration

·	Green-Ampt infiltration
·	Modified Green-Ampt Infiltration

·	SCS Curve Number infiltration

To model the accumulation, re-distribution, and melting of precipitation that falls as snow on a subcatchment, it must be assigned a Snow Pack object. To model groundwater flow between an aquifer underneath the subcatchment and a node of the drainage system, the subcatchment must be assigned a set of Groundwater parameters. Pollutant buildup and washoff from subcatchments are associated with the Land Uses assigned to the subcatchment. Capture and retention of rainfall/runoff using different types of low impact development practices (such as bio-retention cells, infiltration trenches, porous pavement, vegetative swales, and rain barrels) can be modeled by assigning a set of predesigned LID controls to the subcatchment.

The other principal input parameters for subcatchments include:

·	assigned rain gage
·	outlet node or subcatchment

·	assigned land uses
·	tributary surface area

·	imperviousness
·	slope

·	characteristic width of overland flow
·	Manning's n for overland flow on both pervious and impervious areas

·	depression storage in both pervious and impervious areas
·	percent of impervious area with no depression storage.

See Also

Subcatchment Properties

Infiltration

Land Uses

LID Controls

Aquifers

Snow Packs

Shaping a Subcatchment

Subcatchments are drawn on the Study Area Map as closed polygons. To edit or add vertices to the polygon, follow the same procedures used for links (see Shaping a Link). If the subcatchment is originally drawn or is edited to have two or less vertices, then only its centroid symbol will be displayed on the Map.

Subcatchment Properties
Name	User-assigned subcatchment name.
X-Coordinate	Horizontal location of the subcatchment's centroid on the Study Area Map. If left blank then the subcatchment will not appear on the map.
Y-Coordinate	Vertical location of the subcatchment's centroid on the Study Area Map. If left blank then the subcatchment will not appear on the map.
Description	Click the ellipsis button (or press Enter) to edit an optional description of the subcatchment.
Tag	Optional label used to categorize or classify the subcatchment.
Rain Gage	Name of the rain gage associated with the subcatchment.
Outlet	Name of the node or subcatchment that recieves the subcatchment's runoff.
Area	Area of the subcatchment, including any LID controls (acres or hectares).
Width	Characteristic width of the overland flow path for sheet flow runoff (feet or meters). An initial estimate of the characteristic width is given by the subcatchment area divided by the average maximum overland flow length. The maximum overland flow length is the length of the flow path from the outlet to the furthest drainage point of the subcatchment. Maximum lengths from several different possible flow paths should be averaged. These paths should reflect slow flow, such as over pervious surfaces, more than rapid flow over pavement, for example. Adjustments should be made to the width parameter to produce good fits to measured runoff hydrographs.)
% Slope	Average percent slope of the subcatchment.
% Imperv	Percent of the land area (not including any LIDs) which is impervious.
N-Imperv	Manning's n for overland flow over the impervious portion of the subcatchment (Typical Values).
N-Perv	Manning's n for overland flow over the pervious portion of the subcatchment (Typical Values).
Dstore-Imperv	Depth of depression storage on the impervious portion of the subcatchment (inches or millimeters) (Typical Values).
Dstore-Perv	Depth of depression storage on the pervious portion of the subcatchment (inches or millimeters) (Typical Values).
% Zero-Imperv	Percent of the impervious area with no depression storage.
Subarea Routing	Choice of internal routing of runoff between pervious and impervious areas: IMPERV: runoff from pervious area flows to impervious area PERV: runoff from impervious flows to pervious area OUTLET: runoff from both areas flows directly to outlet
Percent Routed	Percent of runoff routed between subareas.
Infiltration	Click the ellipsis button (or press Enter) to edit infiltration parameters for the subcatchment.
LID Controls	Click the ellipsis button (or press Enter) to edit the use of low impact development controls in the subcatchment.
Groundwater	Click the ellipsis button (or press Enter) to edit groundwater flow parameters for the subcatchment.
Snow Pack	Name of snow pack parameter set (if any) assigned to the subcatchment.
Land Uses	Click the ellipsis button (or press Enter) to assign land uses to the subcatchment. Only needed if pollutant buildup/washoff modeled.
Initial Buildup	Click the ellipsis button (or press Enter) to specify initial quantities of pollutant buildup over the subcatchment.
Curb Length	Total length of curbs in the subcatchment (any length units). Used only when pollutant buildup is normalized to curb length.
N-Perv Pattern	Name of optional monthly Time Patternadjustments applied to pervious Manning's n (N-Perv). Leave blank if not applicable.
Dstore Pattern	Name of optional monthly Time Patternadjustments applied to both depression storage (Dstore) values. Leave blank if not applicable.
Infil. Pattern	Name of optional monthly Time Patternadjustments applied to the pervious area's hydraulic conductivity. Leave blank if not applicable.

Note:

The adjustment factors provided in a subcatchment's Infiltration Pattern will override those supplied for Conductivity in the project's Climate Adjustment factors.

Infiltration Editor

The Infiltration Editor dialog is used to specify values for the parameters that describe the rate at which rainfall infiltrates into the upper soil zone of a subcatchment's pervious area. It is invoked when editing the Infiltration property of a Subcatchment. The infiltration parameters depend on which infiltration model was selected for the project: Horton and Modified Horton, Green-Ampt and Modified Green-Ampt, or Curve Number. The choice of infiltration model can be made either by editing the project's Simulation Options or by changing the project's Default Properties.

·	Horton Infiltration Parameters

·	Green-Ampt Infiltration Parameters

·	Curve Number Infiltration Parameters

Infiltration

Infiltration is the process of rainfall penetrating the ground surface into the unsaturated soil zone of pervious subcatchments areas. SWMM offers four choices for modeling infiltration:

Classical Horton Method

This method is based on empirical observations showing that infiltration decreases exponentially from an initial maximum rate to some minimum rate over the course of a long rainfall event. Input parameters required by this method include the maximum and minimum infiltration rates, a decay coefficient that describes how fast the rate decreases over time, and the time it takes a fully saturated soil to completely dry (used to compute the recovery of infiltration rate during dry periods).

Modified Horton Method

This is a modified version of the classical Horton Method that uses the cumulative infiltration in excess of the minimum rate as its state variable (instead of time along the Horton curve), providing a more accurate infiltration estimate when low rainfall intensities occur. It uses the same input parameters as does the traditional Horton Method.

Green-Ampt Method

This method for modeling infiltration assumes that a sharp wetting front exists in the soil column, separating soil with some initial moisture content below from saturated soil above. The input parameters required are the initial moisture deficit of the soil, the soil's hydraulic conductivity, and the suction head at the wetting front. The recovery rate of moisture deficit during dry periods is empirically related to the hydraulic conductivity.

Modified Green-Ampt Method

This method modifies the original Green-Ampt procedure by not depleting moisture deficit in the top surface layer of soil during initial periods of low rainfall as was done in the original method. This change can produce more realistic infiltration behavior for storms with long initial periods where the rainfall intensity is below the soil’s saturated hydraulic conductivity.

Curve Number Method

This approach is adopted from the NRCS (SCS) Curve Number method for estimating runoff. It assumes that the total infiltration capacity of a soil can be found from the soil's tabulated Curve Number. During a rain event this capacity is depleted as a function of cumulative rainfall and remaining capacity. The input parameters for this method are the curve number and the time it takes a fully saturated soil to completely dry (used to compute the recovery of infiltration capacity during dry periods).

SWMM also allows the infiltration recovery rate to be adjusted by a fixed amount on a monthly basis to account for seasonal variation in such factors as evaporation rates and groundwater levels. This optional monthly soil recovery pattern is specified as part of a project's Evaporation data.

SCS Curve Numbers

SCS Runoff Curve Numbers (Antecedent moisture condition II)1

Hydrologic Soil Group
Land Use Description	A	B	C	D
Cultivated land
Without conservation treatment	72	81	88	91
With conservation treatment	62	71	78	81
Pasture or range land
Poor condition	68	79	86	89
Good condition	39	61	74	80
Meadow
Good condition	30	58	71	78
Wood or forest land
Thin stand, poor cover, no mulch	45	66	77	83
Good cover2	25	55	70	77
Open spaces, lawns, parks, golf courses, cemeteries, etc.
Good condition: grass cover on 75% or more of the area	39	61	74	80
Fair condition: grass cover on 50 - 75% of the area	49	69	79	84
Commercial and business areas (85% impervious)	89	92	94	95
Industrial districts (72% impervious)	81	88	91	93
Residential3
Average lot size (% Impervious4)
1/8 ac or less (65)	77	85	90	92
1/4 ac (38)	61	75	83	87
1/3 ac (30)	57	72	81	86
1/2 ac (25)	54	70	80	85
1 ac (20)	51	68	79	84
Paved parking lots, roofs, driveways, etc.5	98	98	98	98
Streets and roads
Paved with curbs and storm sewers5	98	98	98	98
Gravel	76	85	89	91
Dirt	72	82	87	89

1.	Source: SCS Urban Hydrology for Small Watersheds, 2nd Ed., (TR-55),

June 1986.

2.	Good cover is protected from grazing and litter and brush cover soil.

3.	Curve numbers are computed assuming that the runoff from the house

and driveway is directed toward the street with a minimum of roof water

directed to lawns where additional infiltration could occur.

4.	The remaining pervious areas (lawn) are considered to be in good

pasture condition for these curve numbers.

5.	In some warmer climates of the country a curve number of 95 may be used.

Default Subcatchment Properties

The Subcatchment page of the Project Defaults dialog sets default property values for newly created subcatchments. These properties include:

·	Subcatchment Area
·	Characteristic Width

·	Slope
·	% Impervious

·	Impervious Area Roughness
·	Pervious Area Roughness

·	Impervious Area Depression Storage
·	Pervious Area Depression Storage

·	% of Impervious Area with No Depression Storage
·	Infiltration Method.

Explanations of these properties can be found in the Subcatchment Properties topic.

The default properties of a subcatchment can be modified later by using the Property Editor.

Depression Storage

Typical Depression Storage Values

Impervious surfaces	0.05 - 0.10 inches
Lawns	0.10 - 0.20 inches
Pasture	0.20 inches
Forest litter	0.30 inches

(Source: ASCE,(1992), Design & Construction of Urban Stormwater Management Systems, New York, NY)

Soil Group Definitions

NRCS Hydrologic Soil Group Definitions

Group	Meaning	Saturated Conductivity (in/hr)
A	Low runoff potential. Water is transmitted freely through the soil. Group A soils typically have less than 10 percent clay and more than 90 percent sand or gravel and have gravel or sand textures.	> 1.42
B	Moderately low runoff potential. Water transmission through the soil is unimpeded. Group B soils typically have between 10 percent and 20 percent clay and 50 percent to 90 percent sand and have loamy sand or sandy loam textures.	0.57 - 1.42
C	Moderately high runoff potential. Water transmission through the soil is somewhat restricted. Group C soils typically have between 20 percent and 40 percent clay and less than 50 percent sand and have loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures.	0.06 - 0.57
D	High runoff potential. Water movement through the soil is restricted or very restricted. Group D soils typically have greater than 40 percent clay, less than 50 percent sand, and have clayey textures.	< 0.06

Source: Hydrology National Engineering Handbook, Chapter 7, Natural Resources Conservation Service, U.S. Department of Agriculture, January 2009.

Soil Characteristics
Soil Texture Class	K	Ψ	ϕ	FC	WP
Sand	4.74	1.93	0.437	0.062	0.024
Loamy Sand	1.18	2.40	0.437	0.105	0.047
Sandy Loam	0.43	4.33	0.453	0.190	0.085
Loam	0.13	3.50	0.463	0.232	0.116
Silt Loam	0.26	6.69	0.501	0.284	0.135
Sandy Clay Loam	0.06	8.66	0.398	0.244	0.136
Clay Loam	0.04	8.27	0.464	0.310	0.187
Silty Clay Loam	0.04	10.63	0.471	0.342	0.210
Sandy Clay	0.02	9.45	0.430	0.321	0.221
Silty Clay	0.02	11.42	0.479	0.371	0.251
Clay	0.01	12.60	0.475	0.378	0.265

K = hydraulic conductivity, in/hr

Ψ = suction head, in.

ϕ = porosity, fraction

FC = field capacity, fraction

WP= wilting point, fraction

Source: Rawls, W.J. et al., (1983). J. Hyd. Engr., 109:1316.

Note: The following relation between Ψ and K can be derived from this table:

Ψ = 3.237K-0.328 (R2 = 0.9)

Horton Infiltration Parameters
Parameter	Description
Max. Infil. Rate	Maximum infiltration rate on the Horton curve (in/hr or mm/hr) (see table below)
Min. Infil. Rate	Minimum infiltration rate on the Horton curve (in/hr or mm/hr). Equivalent to the saturated hydraulic conductivity. See the Soil Characteristics Table for typical values.
Decay Const.	Infiltration rate decay constant for the Horton curve (1/hours). Typical values range between 2 and 7.
Drying Time	Time in days for a fully saturated soil to dry completely. Typical values range from 2 to 14 days.
Max. Infil. Vol.	Maximum infiltration volume possible (inches or mm, 0 if not applicable). Can be estimated as the difference between a soil's porosity and its wilting point times the depth of the infiltration zone.

Representative Values for Max. Infiltration Rate

1. DRY soils (with little or no vegetation): Sandy soils: 5 in/hr Loam soils: 3 in/hr Clay soils: 1 in/hr 2. DRY soils (with dense vegetation): Multiply values given in A. by 2 3. MOIST soils Soils which have drained but not dried out (i.e., field capacity): divide values from A and B by 3. Soils close to saturation: choose value close to min. infiltration rate. Soils which have partially dried out: divide values from A and B by 1.5 - 2.5.

o use a previously saved rainfall interface file, but cannot find any data for one of its rain gages in the interface file. It can also occur if the gage uses data from a user-prepared rainfall file and the station id entered for the gage cannot be found in the file.

ERROR 323:

cannot open runoff interface file xxx.

A runoff interface file could not be opened, possibly because it does not exist or because the user does not have write privileges to its directory.

ERROR 325:

incompatible data found in runoff interface file.

SWMM was trying to read data from a designated runoff interface file with the wrong format (i.e., it may have been created for some other project or actually be some other type of file).

ERROR 327:

attempting to read beyond end of runoff interface file.

This error can occur when a previously saved runoff interface file is being used in a simulation with a longer duration than the one that created the interface file.

ERROR 329:

error in reading from runoff interface file.

A format error was encountered while trying to read data from a previously saved runoff interface file.

ERROR 331:

cannot open hot start interface file xxx.

A hotstart interface file could not be opened, possibly because it does not exist or because the user does not have write privileges to its directory.

ERROR 333:

incompatible data found in hot start interface file.

SWMM was trying to read data from a designated hotstart interface file with the wrong format (i.e., it may have been created for some other project or actually be some other type of file).

ERROR 335:

error in reading from hot start interface file.

A format error was encountered while trying to read data from a previously saved hotstart interface file.

ERROR 336:

no climate file specified for evaporation and/or wind speed.

This error occurs when the user specifies that evaporation or wind speed data will be read from an external climate file, but no name is supplied for the file.

ERROR 337:

cannot open climate file xxx.

An external climate data file could not be opened, most likely because it does not exist.

ERROR 338:

error in reading from climate file xxx.

SWMM was trying to read data from an external climate file with the wrong format.

ERROR 339:

attempt to read beyond end of climate file xxx.

The specified external climate does not include data for the period of time being simulated.

ERROR 341:

cannot open scratch RDII interface file.

SWMM could not open the temporary file it uses to store RDII flow data.

ERROR 343:

cannot open RDII interface file xxx.

An RDII interface file could not be opened, possibly because it does not exist or because the user does not have write privileges to its directory.

ERROR 345:

invalid format for RDII interface file.

SWMM was trying to read data from a designated RDII interface file with the wrong format (i.e., it may have been created for some other project or actually be some other type of file).

ERROR 351:

cannot open routing interface file xxx.

A routing interface file could not be opened, possibly because it does not exist or because the user does not have write privileges to its directory.

ERROR 353:

invalid format for routing interface file xxx.

SWMM was trying to read data from a designated routing interface file with the wrong format (i.e., it may have been created for some other project or actually be some other type of file).

ERROR 355:

mis-matched names in routing interface file xxx.

The names of pollutants found in a designated routing interface file do not match the names used in the current project.

ERROR 357:

inflows and outflows interface files have same name.

In cases where a run uses one routing interface file to provide inflows for a set of locations and another to save outflow results, the two files cannot both have the same name.

ERROR 361:

could not open external file used for Time Series xxx.

The external file used to provide data for the named time series could not be opened, most likely because it does not exist.

ERROR 363:

invalid data in external file used for used for Time Series xxx.

The external file used to provide data for the named time series has one or more lines with the wrong format.

Format Errors
ERROR 200:	one or more errors in input file.

This message appears when one or more input file parsing errors (the 200-series errors) occur.

ERROR 201:

too many characters in input line.

A line in the input file cannot exceed 1024 characters.

ERROR 203:

too few items at line n of input file.

Not enough data items were supplied on a line of the input file.

ERROR 205:

invalid keyword at line n of input file.

An unrecognized keyword was encountered when parsing a line of the input file.

ERROR 207:

duplicate ID name at line n of input file.

An ID name used for an object was already assigned to an object of the same category.

ERROR 209:

undefined object xxx at line n of input file.

A reference was made to an object that was never defined. An example would be if node 123 were designated as the outlet point of a subcatchment, yet no such node was ever defined in the study area.

ERROR 211:

invalid number xxx at line n of input file.

Either a string value was encountered where a numerical value was expected or an invalid number (e.g., a negative value) was supplied.

ERROR 213:

invalid date/time xxx at line n of input file.

An invalid format for a date or time was encountered. Dates must be entered as month/day/year and times as either decimal hours or as hour:minute:second.

ERROR 217:

control rule clause out of sequence at line n of input file.

Errors of this nature can occur when the format for writing control rules is not followed correctly (see Control Rule Format).

ERROR 219:

data provided for unidentified transect at line n of input file.

A GR line with Station-Elevation data was encountered in the [TRANSECTS] section of the input file after an NC line but before any X1 line that contains the transect's ID name.

ERROR 221:

transect station out of sequence at line n of input file.

The station distances specified for the transect of an irregular cross section must be in increasing numerical order starting from the left bank.

ERROR 223:

Transect xxx has too few stations.

A transect for an irregular cross section must have at least 2 stations defined for it.

ERROR 225:

Transect xxx has too many stations.

A transect cannot have more than 1500 stations defined for it.

ERROR 227:

Transect xxx has no Manning's N.

No Manning's N was specified for a transect (i.e., there was no NC line in the [TRANSECTS] section of the input file.

ERROR 229:

Transect xxx has invalid overbank locations.

The distance values specified for either the left or right overbank locations of a transect do not match any of the distances listed for the transect's stations.

ERROR 231:

Transect xxx has no depth.

All of the stations for a transect were assigned the same elevation.

ERROR 233:

invalid treatment function expression at line n of input file.

A treatment function supplied for a pollutant at a specific node is either not a correctly formed mathematical expression or refers to unknown pollutants, process variables, or math functions.

Property Errors
ERROR 108:	ambiguous outlet ID name for Subcatchment xxx.

The name of the element identified as the outlet of a subcatchment belongs to both a node and a subcatchment in the project's data base.

ERROR 109:

invalid parameter values for Aquifer xxx.

The properties entered for an aquifer object were either invalid numbers or were inconsistent with one another (e.g., the soil field capacity was higher than the porosity).

ERROR 110:

ground elevation is below water table for Subcatchment xxx.

The ground elevation assigned to a subcatchment's groundwater parameters cannot be below the initial water table elevation of the aquifer object used by the subcatchment.

ERROR 111:

invalid length for Conduit xxx.

Conduits cannot have zero or negative lengths.

ERROR 112:

elevation drop exceeds length for Conduit xxx.

The elevation drop across the ends of a conduit cannot be greater than the conduit's length. Check for errors in the length and in both the invert elevations and offsets at the conduit's upstream and downstream nodes.

ERROR 113:

invalid roughness for Conduit xxx.

Conduits cannot have zero or negative roughness values.

ERROR 114:

invalid number of barrels for Conduit xxx.

Conduits must consist of one or more barrels.

ERROR 115:

adverse slope for Conduit xxx.

Under Steady or Kinematic Wave routing, all conduits must have positive slopes. This can usually be corrected by reversing the inlet and outlet nodes of the conduit (i.e., right click on the conduit and select Reverse from the popup menu that appears). Adverse slopes are permitted under Dynamic Wave routing.

ERROR 117:

no cross section defined for Link xxx.

A cross section geometry was never defined for the specified link.

ERROR 119:

invalid cross section for Link xxx.

Either an invalid shape or invalid set of dimensions was specified for a link's cross section.

ERROR 121:

missing or invalid pump curve assigned to Pump xxx.

Either no pump curve or an invalid type of curve was specified for a pump.

ERROR 131:

the following links form cyclic loops in the drainage system.

The Steady and Kinematic Wave flow routing methods cannot be applied to systems where a cyclic loop exists (i.e., a directed path along a set of links that begins and ends at the same node). Most often the cyclic nature of the loop can be eliminated by reversing the direction of one of its links (i.e., switching the inlet and outlet nodes of the link). The names of the links that form the loop will be listed following this message.

ERROR 133:

Node xxx has more than one outlet link.

Under Steady and Kinematic Wave flow routing, a junction node can have only a single outlet link.

ERROR 134:

Node xxx has illegal DUMMY link connections.

Only a single conduit with a DUMMY cross-section or Ideal-type pump can be directed out of a node; a node with an outgoing Dummy conduit or Ideal pump cannot have all of its incoming links be Dummy conduits and Ideal pumps; a Dummy conduit cannot have its upstream end connected to a storage node.

ERROR 135:

Divider xxx does not have two outlet links.

Flow divider nodes must have two outlet links connected to them.

ERROR 136:

Divider xxx has invalid diversion link.

The link specified as being the one carrying the diverted flow from a flow divider node was defined with a different inlet node.

ERROR 137:

Weir Divider xxx has invalid parameters.

The parameters of a Weir-type divider node either are non-positive numbers or are inconsistent (i.e., the value of the discharge coefficient times the weir height raised to the 3/2 power must be greater than the minimum flow parameter).

ERROR 138:

Node xxx has initial depth greater than maximum depth.

Self-explanatory.

ERROR 139:

Regulator xxx is the outlet of a non-storage node.

Under Steady or Kinematic Wave flow routing, orifices, weirs, and outlet links can only be used as outflow links from storage nodes.

ERROR 141:

Outfall xxx has more than 1 inlet link or an outlet link.

An outfall node is only permitted to have one link attached to it.

ERROR 143:

Regulator xxx has invalid cross-section shape.

An orifice must have either a CIRCULAR or RECT_CLOSED shape, while a weir must have either a RECT_OPEN, TRAPEZOIDAL, or TRIANGULAR shape.

ERROR 145:

Drainage system has no acceptable outlet nodes.

Under Dynamic Wave flow routing, there must be at least one node designated as an outfall.

ERROR 151:

a Unit Hydrograph in set xxx has invalid time base.

The time base of a Unit Hydrograph cannot be negative and if positive, must not be less than the recording interval for its rain gage.

ERROR 153:

a Unit Hydrograph in set xxx has invalid response ratios.

The response ratios for a set of Unit Hydrographs (the short-, medium-, and long-term response hydrographs) must be between 0 and 1.0 and cannot add up to a value greater than 1.0

ERROR 155:

invalid sewer area for RDII at Node xxx.

The sewer area contributing RDII inflow to a node cannot be a negative number.

ERROR 156:

inconsistent data file name for Rain Gage xxx.

If two Rain Gages use files for their data sources and have the same Station IDs then they must also use the same data files.

ERROR 157:

inconsistent rainfall format for Rain Gage xxx.

If two or more rain gages use the same Time Series for their rainfall data then they must all use the same data format (intensity, volume, or cumulative volume).

ERROR 158:

time series for Rain Gage xxx is also used by another object.

A rainfall Time Series associated with a Rain Gage cannot be used by another object that is not also a Rain Gage.

ERROR 159:

recording interval greater than time series interval for Rain Gage xxx.

The recording time interval specified for the rain gage is greater than the smallest time interval between values in the Time Series used by the gage.

ERROR 161:

cyclic dependency in treatment functions at Node xxx.

An example would be where the removal of pollutant 1 is defined as a function of the removal of pollutant 2 while the removal of pollutant 2 is defined as a function of the removal of pollutant 1.

ERROR 171:

Curve xxx has its data out of sequence.

The X-values of a curve object must be entered in increasing order.

ERROR 173:

Time Series xxx has its data out of sequence.

The time (or date/time) values of a time series must be entered in sequential order.

ERROR 181:

invalid Snow Melt Climatology parameters.

The ATI Weight or Negative Melt Ratio parameters are not between 0 and 1 or the site latitude is not between -60 and +60 degrees.

ERROR 182:

invalid parameters for Snow Pack xxx.

A snow pack's minimum melt coefficient is greater than its maximum coefficient; the fractions of free water capacity or impervious plowable area are not between 0 and 1; or the snow removal fractions sum to more than 1.0.

ERROR 183:

no type specified for LID xxx.

A named LID control has layers defined for it but its LID type was never specified.

ERROR 184:

missing layer for LID xxx.

A required design layer is missing for the specified LID control.

ERROR 185:

invalid parameter value for LID xxx.

An invalid value was supplied for an LID control's design parameter.

ERROR 187:

LID area exceeds total area for Subcatchment xxx.

The area of the LID controls placed within the subcatchment is greater than that of the subcatchment itself.

ERROR 188:

LID capture area exceeds total impervious area for Subcatchment xxx.

The amount of impervious area assigned to be treated by LID controls in the subcatchment exceeds the total amount of impervious area available.

ERROR 191:

simulation start date comes after ending date.

Self-explanatory.

ERROR 193:

report start date comes after ending date.

Self-explanatory.

ERROR 195:

reporting time step is less than routing time step.

Self-explanatory.

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