Setting Antecedent Wetness Conditions for the New UK Runoff Model in InfoWorks ICM

Initial NAPI Values in InfoWorks ICM

Initial NAPI Values in InfoWorks ICM

In the New UK runoff model was calibrated against a variety or urban catchments in the UK. It uses a value of the antecedent wetness conditions (NAPI) which can vary depending on the soil type. The soil type is defined as part of the subcatchment data or as part of the user defined defaults. In the UK, the soil type classification is derived from Maps. There are 5 different soil types although commonly soil type 5 is not used. The soil type effects the value of a constant which is used in the calculation of NAPI. It is common to set an initial value of NAPI which as above can vary depending on the soil type.

A feature of InfoWorks ICM which has been inherited from InfoWorks CS and its predecessor HydroWorks, is that it is only possible to use one value of NAPI with any one rainfall profile. This is a problem in catchments with different soil types where a different value of NAPI is needed for each soil type. This blog describes how it is possible to represent the effect of different soil types on NAPI values within subcatchments.

Download Paper Initial NAPI Values in InfoWorks ICM

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    About Duncan Kitts

    Duncan Kitts is a Senior Support Engineer with Innovyze in the United Kingdom, specializing in River modelling and 2D modelling. He has over 9 years experience of modeling the key hydraulic processes involved in both fluvial systems and urban drainage environments. Duncan is responsible for providing support of both infoworks ICM and Infoworks RS.
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