Runoff Volume Models
Runoff volume models are used in InfoWorks networks determine how much of the rainfall runs off the catchment into the drainage system after accounting for any initial losses.
The Runoff Volume Model to be used is set in the Runoff Volume Type field of the Runoff Surface. The runoff surface is then associated with one or more Land Use objects which are in turn associated with one or more subcatchments.
Surfaces of different types may be mixed in the same model. (For example Horton infiltration, GreenAmpt infiltration and New UK percentage runoff (Variable PR) surfaces may be mixed in the same model.) Appropriate initial conditions information must be set in the Rainfall Event for each surface type used.
There are two types of runoff volume models: total catchment models and individual models. Total catchment models must be applied to all the surface types in a subcatchment. Whereas an individual model can be applied to one surface type in a subcatchment.
Model  Type  Comments  Runoff Surface Data Fields Used  Appropriate for: 

Individual 
The ConstInf model allows you to set a constant infiltration from the surface into groundwater. This is effectively a loss to the system. When the storage capability of the surface is fully used, the surface acts as a fixed runoff surface.

Fixed Runoff Coefficient Infiltration Loss Coefficient Fixed Runoff Coefficient 


DefConLoss  Individual 
The Deficit and Constant Loss Model is based on the HECHMS model described in the HECHMS Users's Manual (2010). 
Maximum Deficit Infiltration Loss Coefficient 

f1Rsa  Individual 
The f1Rsa model is used to calculate effective rainfall when using the Quasi Linear Reservoir Method. See the Japanese Runoff Methodology technical paper for further information. 
Minimum runoff Maximum runoff Saturated rainfall 
This model is a standard runoff model used in Japan. 
Individual 
You supply the figure for the percentage of rainfall that actually runs off into the system. Enter the percentage runoff required. A value of 0.1 represents 10% runoff. If using the SWMM, Desbordes or SPRINT runoff routing models you would typically define fixed runoff surfaces with runoff coefficients of 1.0 for the impervious surfaces. You could set the pervious surfaces as fixed runoff with runoff coefficients of 0.0 or use the Horton or GreenAmpt models. If you wish to use the New UK model for pervious surfaces, then you should set up the impervious surfaces as fixed runoff surfaces with the runoff coefficient equal to the effective impervious area factor (IF). 
Fixed Runoff Coefficient 
Catchments where you a good estimate of the percentage runoff can be made. 

Individual 
GreenAmpt runoff volumes can only be used on pervious surfaces. The GreenAmpt surface must always be defined as the last surface. Define initial soil moisture deficit(s) as a percentage in the initial condition fields in catchment runoff data. The software resets the value to the initial moisture deficit value defined in the Runoff Surfaces tab if this is lower. 
Green Ampt Conductivity Green Ampt Suction Green Ampt Deficit Green Ampt SMD (rainfall event initial condition) 
Rural surfaces and pervious surfaces within a catchment. This model is associated in the US in conjunction with the Storm Water Management Model (SWMM) runoff routing model. 

Individual 
A runoff volume model used to determine the net rainfall on urban subcatchments. 
Horner Alpha Horner Beta Horner Recovery 
Impervious surfaces in medium sized urban subcatchments. 

Individual 
The Horton Infiltration model can only be used on pervious surfaces. More than one Horton surface may be defined for a land use. Horton surfaces can be mixed with fixed runoff volume surfaces, SCS or GreenAmpt. If the last surface at a node is defined as a Horton surface the software adds the noncontributing areas from the fixed runoff volume surfaces on the subcatchment to the area of the last (Horton) surface. The noncontributing area is defined as follows for each fixed runoff surface: (1  Runoff Coefficient) * Surface area 
Decay factor Initial infiltration Limiting infiltration Recovery factor Horton SMS (rainfall event initial condition) 
Rural surfaces and pervious surfaces within a catchment. This model can be used with all routing models. It is usually associated with the Desbordes or the SWMM runoff routing models. 

HortonSWMM  Individual 
The HortonSWMM Infiltration model can only be used on pervious surfaces. More than one HortonSWMM surface may be defined for a land use. HortonSWMM surfaces can be mixed with fixed runoff volume surfaces, SCS or GreenAmpt. If the last surface at a node is defined as a HortonSWMM surface the software adds the noncontributing areas from the fixed runoff volume surfaces on the subcatchment to the area of the last (HortonSWMM) surface. The noncontributing area is defined as follows for each fixed runoff surface: (1  Runoff Coefficient) * Surface area 
Decay factor Initial infiltration Limiting infiltration Horton Drying Time Horton Max Infiltration Volume Horton SMS (rainfall event initial condition) 
Rural surfaces and pervious surfaces within a catchment. This model can be used with all routing models. It is usually associated with the Desbordes or the SWMM runoff routing models. 
Total catchment 
This is a UK model, which represents the condition of the catchment changing throughout the simulation for a pervious surface. 
New UK Depth API30 (rainfall event initial condition) 
UK pervious catchments where it is important to take account of the change in catchment wetness during long storms. 

PDM  Total catchment 
Simulations using PDM functionality can only be run if the PDM option is enabled on your licence. The Probability Distributed Model (PDM) is a rainfallrunoff model developed by the Centre for Ecology and Hydrology (CEH). 
  
ReFH  Individual 
The ReFH Model is a rainfallrunoff model based on procedures developed by the Center for Ecology and Hydrology (CEH) to update the FSR/FEH Rainfall Runoff Method, in response to concerns that the FSR/FEH design model tended to overestimate design floods. Note
For any simulation that includes ReFH direct runoff calculations for closing the water balance, these will be calculated for the specified duration, regardless of whether timestep control is active or not. Therefore, when scheduling a run, it is advisable to use a duration that reflects the longest anticipated duration (instead of, for example, 99999 minutes) to reduce the time taken for the runoff phase of the simulation. 
ReFH Cini (rainfall event initial condition) ReFH BF0 (rainfall event initial condition) 
Most UK subcatchments. 
SRM  Total catchment 
Simulations using PDM functionality can only be run if the PDM option is enabled on your licence. A simplified runoff model that uses a soil moisture deficit time series in conjunction with a constant runoff coefficient to modify input rainfall to get an effective rainfall. 
  
UKWIR  Total catchment  Runoff model using the UKWIR equation developed by HR Wallingford as a replacement to the New UK PR Model defined previously. 
Effective impermeability, IF Precipitation decay coefficient Cpv Power coefficient for PI, Beta Storage depth, PFpv Wetness decay for NAPI, Cs Power coefficient, Cr Storage depth, PFs, Minimum NAPI NAPI (rainfall event initial condition) Initial UKWIR paved precipitation index (rainfall event initial condition) 
UK catchments 
Individual 
A rural catchment model, which is intended for use in single storm simulations. The CNSWMM model can be used for multiple storm simulations. 
SCS Depth SCS Index (rainfall event initial condition) 
Rural catchments and pervious surfaces within a catchment. 

Total catchment 
The default model, which is calibrated for the UK. 
Fixed Runoff Coefficient Wal. Proc Distribution Mimimum runof Maximum runoff 
Urban catchments in or close to the UK. 

CN 
Individual 
A rural catchment model. This is the similar to the SCS method but where the Curve number, specified as a subcatchment property, is used determine storage depth. The CN model is intended for use in single storm simulations. The CNSWMM model can be used for multiple storm simulations. 
Curve number (Subcatchment Data Fields) SCS Index (rainfall event initial condition) 
Rural catchments and pervious surfaces within a catchment. 
Individual 
An initial loss and runoff model used in Germany. 
Decay factor Initial infiltration Limiting infiltration Recovery factor Mimimum runof Maximum runoff Depression Loss 
Catchments in Germany 

CNSWMM  Individual 
The SWMM Curve Number infiltration model developed by the US Environment Protection Agency (EPA), and is intended for use in multiple storm simulations. Only one CNSWMM surface may be defined for a land use. CNSWMM surfaces can be mixed with fixed runoff volume surfaces. 
Curve number (Subcatchment Data Fields) SCS Index (rainfall event initial condition) 
Rural surfaces and pervious surfaces within a catchment. This model can be used with all routing models. It is usually associated with the Desbordes or the SWMM runoff routing models. 