Runoff Surface Data Fields (InfoWorks)

Runoff Surface data can be edited on either the Runoff Surface Grid Window of the Subcatchments Grid or the Runoff Surface Property Sheet.

Most data can be edited on the grid, but some fields cannot be displayed in the grid format.

To view and edit all runoff surface data, use the Property Sheet.

The following describes all the data which can be used to define a runoff surface.

Common Data Fields

Fields that are common to the majority of objects can be found in the Common Fields topic.

Runoff Surface Data

Database Table Name: hw_runoff_surface

Show Columns	Database Names
	Size, Type and Units
	Defaults and Error Limits

Field Name

Help Text

Database Field

Data Type

Size

Units

Precision

Default

Error Lower Limit

Error Upper Limit

Warning Lower Limit

Warning Upper Limit

Runoff surface ID

An integer that identifies this runoff surface. Each surface ID must be unique.

runoff_index

Long Integer

99999

Description

Description of Runoff Surface. Maximum 80 characters.

surface_description

Text

Surface type

Database Value	Description	Help Text
Impervious	Impervious	for example, roads
Pervious	Pervious	for example, grassed areas
Unknown	Unknown	surface conditions unknown

surface_type

Text

Unknown

Routing model

Further information on these routing models is given in the Runoff routing models section.

Database Value	Description
Clark	Clark
Desbordes	Desbordes
HEC Snyder (Snyder Alameda)	HEC Snyder
Kadoya	Kadoya
LargeCatch	LargeCatch
Non-linear	Non-Linear
ReFH	ReFH
SCS Unit	SCS Unit
Snyder	Snyder Unit
Sprint	Sprint
SWMM	SWMM
Unit	Unit
Wallingfrd	Wallingfrd
Rational	Rational
Cascade	Cascade
RAFTS	RAFTS

routing_model

Text

User-specified RAFTS B

A check (x) in the box indicates that the RAFTS B value to be used by InfoWorks ICM is specified by the user in the Runoff routing value field.

An unchecked box indicates that InfoWorks ICM calculates the RAFTS B value. See the RAFTS Routing Model for details about how this is calculated.

rafts_user_b

Boolean

Runoff routing type

Choose one of the following. This determines the nature of the runoff routing value you give.

Database Value	Description	Help Text
Rel	Rel	Relative. The Runoff Routing Value is a factor to multiply the default value of the routing factor.
Abs	Abs	Absolute. The Runoff Routing Value is the routing factor.

runoff_routing_type

Text

Runoff routing value

This is either the storage delay time coefficient (RAFTS B), or depending on the runoff routing type you chose it is:

Runoff Routing Type	Runoff Routing Value
Relative	A factor to multiply the default value of the routing factor.
Absolute	The routing factor.

When using SWMM routing, the value represents the Manning roughness, regardless of the type.

When using Kadoya routing, the value represents the Kadoya C value, regardless of the type.

When using RAFTS routing, this field is editable if the User-specified RAFTS B box is checked, enabling you to specify the RAFTS B value to be used. If unchecked, the RAFTS B value is calculated by InfoWorks ICM. See the RAFTS Routing Model for details about how this is calculated.

runoff_routing_value

Double

Ground slope

InfoWorks ICM uses the ground slope when calculating runoff rate and initial losses. If a value is not entered, or a value of zero is entered, InfoWorks ICM will attempt to obtain a value for slope in the following ways:

The slope will be taken as the Slope value specified for the Subcatchment, if available.
If there is no subcatchment slope but the subcatchment slope flag is set to #D (default) InfoWorks ICM calculates a slope from:

((ground level at node to which subcatchment is attached) - (ground level at d/s node of .1 link from node to which subcatchment is attached)) / length of .1 link from node to which subcatchment is attached

If the slope flag is not set to #D, or the subcatchment is not connected to a node in the system, or there is no .1 link from the node, or the .1 link is a control, the default slope is 0.0. However, in practice, the simulation engine will apply a minimum slope value of 0.002 to prevent divide by zero errors.

ground_slope

Double

0.1

Runoff volume type

Choose a runoff volume model from the drop-down menu.

Further information on these routing models is given in the Runoff volume models section.

Database Value	Description
Fixed	Fixed PR Model
Wallingfrd	Wallingford Procedure Model
NewUK	New UK PR Model
SCS	SCS Model
Horton	Horton Infiltration Model
GreenAmpt	Green-Ampt Model
ConstInf	Constant Infiltration Model
CN	SCS Model
Horner	Horner Model
ReFH	ReFH Model
HortonSWMM	Horton Infiltration Model (using method implemented in SWMM)
SRM	Simple Runoff Model
PDM	Probability Distributed Model
DefConLoss	Deficit and Constant Loss Model
UKWIRPaved	UKWIR Model
UKWIRPerv	UKWIR Model
f1-Rsa	f1-Rsa Model
DWA (Grenzwertmethode)	DWA Model
CNSWMM	CNSWMM Model

runoff_volume_type

Text

Initial abstraction factor

The quantity of rainfall required to just cause overland flow is the initial loss. The initial part of a rainstorm is assumed to cause no runoff because it is lost in wetting the ground surface and in forming puddles.

This field is only enabled if you set the Initial loss type field to SCS, and its value represents:

Type

Value

SCS

The proportion of the storage depth that is retained on the surface before runoff occurs.

The original SCS approach recommended an Initial abstraction factor value (k) of 0.2. However other studies suggest k values between 0.05 and 0.1 may be more appropriate. See SCS Model for further information.

The software currently has a default value of zero for initial abstraction factor for runoff surfaces with an Initial loss type set to SCS; you may wish to override this. Alternatively, you can specify an initial abstraction value directly by setting the Initial loss type to Abs, and setting the Initial loss value to the value you want to use for the Initial abstraction.

initial_abstraction_factor

Double

Fixed runoff coefficient

This is a proportion. For example, 0.1 indicates 10% runoff from this surface.

Used for Runoff volume type of Fixed or ConstInf.

runoff_coefficient

Double

Maximum deficit

Amount of water that the soil layer can hold (depth).

Used for Runoff volume type of DefConLoss

maximum_deficit

Double

Infiltration loss coefficient

Used to calculate the infiltration loss when Runoff volume type is set to ConstInf.

See Sustainable Urban Drainage Systems for more information.

Infiltration rate when soil layer is saturated when runoff volume type is set to DefConLoss.

infiltration_coeff

Double

Green Ampt conductivity

The minimum or asymptotic infiltration rate of the soil. This is equivalent to limiting infiltration rate in Horton.

Used when Runoff volume type is set to GreenAmpt.

saturated_hydraulic_conductivity

Double

Green Ampt suction

This is the average capillary suction at the wetting front. It depends on the soil type. Typical values in mm:

Soil Type	Average Capillary suction (mm)
Sand	100
Sandy loam	200
Salt loam	300
Loam	200
Clay Loam	250
Clay	175

Used when Runoff volume type is set to GreenAmpt.

average_capillary_suction

Double

Horner alpha

Parameter used to define loss coefficient.

Used when Runoff volume type is set to Horner.

halpha

Double

Horner beta

Parameter used to define loss coefficient.

Used when Runoff volume type is set to Horner.

hbeta

Double

Horner recovery (min)

Time to recover to initial conditions.

Used when Runoff volume type is set to Horner.

hrecovery

Double

Decay factor (1/hour)

Exponential term (k) (1/hr) from the equation to calculate rate:

Used when Runoff volume type is set to Horton, HortonSWMM or DWA.

decay_factor

Double

Initial infiltration

Initial infiltration () from the equation to calculate rate:

Used when Runoff volume type is set to Horton, HortonSWMM or DWA.

initial_infiltration

Double

Limiting infiltration

Limiting infiltration () from the equation to calculate rate:

Used when Runoff volume type is set to Horton, HortonSWMM or DWA.

limiting_infiltration

Double

Recovery factor

The value (or lack of value) in this field determines how the simulation recovers infiltration capacity during dry periods.

If the value is zero or blank then the simulation recovers infiltration capacity with a linear function.

(1)

where:

sms - the soil moisture store (m)

- the limiting infiltration capacity (m/s)

dt - the run timestep (s)

t - time (s)

until sms is zero or rainfall occurs.

If the value is non-zero then recovery is exponential, like SWMM.

(2)

where:

sratio - the ratio of current sms to limiting sms

sms_limiting - the sms at the limiting infiltration rate () (m)

- the maximum infiltration rate (m/s)

k - the decay coefficient for infiltration (s-1)

krecovery - the recovery coefficient (s-1)

sms, , dt, t as above.

until sms is zero or rainfall occurs.

The exponential function for infiltration capacity recovery can also be written as:

(3)

where:

- the current infiltration rate (m/s)

tw - the hypothetical projected time at which on the recovery curve (s)

Used when Runoff volume type is set to Horton or DWA.

recovery_factor

Double

Horton drying time

Time in days for a fully saturated soil to dry completely. Typical values range from 2 to 14 days.

Used when Runoff volume type is set to HortonSWMM.

drying_time

Double

Horton max infiltration volume

Maximum infiltration volume possible.

Used when Runoff volume type is set to HortonSWMM.

max_infiltration_volume

Double

SCS depth

The storage depth is the maximum potential storage depth, S (in metres), for this surface. Used when Runoff volume type is set to SCS.

storage_depth

Double

Wal. proc. distribution

This is the weighting factor for dividing the runoff calculated by the Wallingford runoff model between pervious and impervious areas:

1.0 for paved and roof surfaces
0.1 for pervious surfaces

Used when Runoff volume type is set to Wallingfrd.

runoff_distribution_factor

Double

Initial loss porosity

The initial loss porosity can be used to represent a runoff surface where the initial storage volume (as defined using the Initial loss type and Initial loss value fields) actually contains some sort of fill material such as sand, gravel or rocks.

The fill material reduces the potential capacity for water storage. An Initial loss porosity of 0.3 represents 30% air volume in the structure (70% of the volume is taken up by fill material).

This feature is particularly useful when using a runoff surface to represent a permeable pavement. See Sustainable Urban Drainage Systems.

initial_loss_porosity

Double

0.001

Initial loss type

The initial loss type determines the nature of the value in the Initial loss value or Initial abstraction factor fields.

Database Value	Description	Help Text
Abs	Absolute	The value for this type of initial loss can be set in the Initial loss value field.
Slope	Depression storage is related to ground slope
SCS	See the SCS Model.	The value for this type of initial loss can be set in the Initial abstraction factor field.
DWA	See the DWA Model.	The value for this type of initial loss can be set in the Initial loss value field.

initial_loss_type

Text

Initial loss value

This field is only enabled if the Initial loss type field is set to Absolute, Slope or DWA, and its value represents:

Type

Value

Absolute

The depression storage depth

Slope

Depression storage is related to ground slope by the expression

where:

s is the ground slope

If you are using the Wallingford Model for runoff and routing, the default (recommended) values are:

Impervious surfaces	0.000071
Pervious surfaces	0.00028

DWA

The depression storage depth. Initial loss factors due to monthly variations are included in the software and will be used when running a simulation.

initial_loss_value

Double

Equivalent Manning's n

Enabled when Routing model is set to RAFTS and the User-specified RAFTS B box is unchecked but is only used if the Per-surface RAFTS box is checked on the subcatchment which uses this runoff surface.

Used in the calculation of RAFTS B on a per runoff surface basis. The specified value must be within the range of 0.01 to 0.1. A default value of 0.025 is used if no other value is specified. See the RAFTS Routing Model for further information.

equivalent_roughness

Double

RAFTS adapt factor

Enabled when Routing model is set to RAFTS and the User-specified RAFTS B box is unchecked but is only used if the Per-surface RAFTS box is checked on the subcatchment which uses this runoff surface.

A calibration factor used to calculate the storage factor that is output for the runoff surface in the subcatchment. See the RAFTS Routing Model for further information.

rafts_adapt_factor

Double

New UK depth

The moisture depth parameter, PF, is one factor which determines the volume of runoff form pervious surfaces in the variable PR (New UK) runoff model. Calibration of this model suggests that you should normally use a value of 200mm. Larger values will yield less runoff from pervious surfaces, smaller values will yield more runoff.

Used when Runoff volume type is set to NewUK.

moisture_depth_parameter

Double

Green Ampt deficit

This is the fraction difference between the soil porosity and actual moisture content.

Used when Runoff volume type is set to GreenAmpt.

initial_moisture_deficit

Double

Saturated rainfall

Amount of rainfall required for saturation.

Used when Runoff volume type is set to f1-Rsa.

saturated_rainfall

Double

Maximum runoff

This is a proportion indicating the maximum amount of runoff this surface will contribute. For example, 0.8 indicates no more than 80% runoff of the rainfall from this surface.

Used when Runoff volume type is set to Wallingfrd, f1-Rsa or DWA.

maximum_runoff

Double

Minimum runoff

This is a proportion indicating the minimum amount of runoff this surface contributes. For example, 0.2 indicates at least 20% runoff of the rainfall from this surface.

Used when Runoff volume type is set to Wallingfrd, f1-Rsa or DWA.

Surface Type	Wal. Proc minimum recommended value
Impervious	0.2
Pervious	0.0

minimum_runoff

Double

Effective impermeability, IF

Effective impermeability factor used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPaved.

effective_impermeability

Double

0.65

0.5

Precipitation decay coefficient, Cpv

Paved decay constant used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPaved.

precipitation_decay

Double

0.1

0.001

0.1

0.2

Power coefficient for PI, Beta

Paved power factor used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPaved.

power_coeff_paved

Double

0.5

0.001

0.5

Storage depth, PFpv

Storage depth for paved and roof surfaces used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPaved.

storage_depth_paved

Double

0.001

Wetness decay for NAPI, Cs

Wetness decay constant used by the UKWIR Model.

Used when Runoff volume yype is set to UKWIRPerv.

napi_decay_coeff

Double

0.8

0.001

0.7

0.9

Power coefficient, Cr

Pervious power factor used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPerv.

power_coeff_pervious

Double

0.8

0.001

0.8

Storage depth, PFs

Soil store depth used by the UKWIR Model.

Used when Runoff volume type is set to UKWIRPerv.

storage_depth_pervious

Double

0.001

100

Minimum NAPI

Minimum value of NAPI that will be used during the simulation. Used to set a cap on negative values of NAPI when using the UKWIR Model.

Used when Runoff volume type is set to UKWIRPerv.

minimum_napi

Double

-15

Depression loss

The depth of rainfall, in depressions (resevoirs), which is lost to runoff. This must be equal or greater than 0 (≥0).

See the DWA Model for further information.

Used when Runoff volume type is set to DWA.

depression_loss

Double

Number of reservoirs

The number of reservoirs.

Used when Routing model is set to Cascade.

If set to 0, no routing will be performed.

number_of_reservoirs

Integer

Runoff Surfaces

Subcatchments Grid

Property Sheets

Runoff Routing Models

Runoff Volume Models