This forum is shutting down! Please post new discussions at

NDR - Values for crit_len out of grasslands/forests ?


I am using NDR model, which requires input for "crit_len" parameter (length after which the maximum retention efficiency "eff" is reached). 

This parameter is relatively easy to assess for grassland and forest (which are commonly used for riparian retention), eg. Zhang et al. 2010. But it is far more complicated to evaluate for fields, and urban areas. Intuitively, one would input higher values for crit_len on these land uses, since they don't retain nutrients as well as grasslands. However, InVEST online documentation suggests to set it at the pixel's size - which, in my model, is smaller (5m) than grassland's crit_len (10-15m).
So, should I keep this odd parameterization ? Or should I rather take a fictive, high crit_len (such as 300m, which is a maximum according to online documentation) ?

Many thanks in advance,



  • RichRich Administrator, NatCap Staff
    Hi Emmanuel, only set the critical length to a pixel if you want to reach full retention within a pixel. If you know your critical length is 10-15m, then use that value!
  • Hi Rich,
    Thanks for your answer. Problem is, I don't want to reach full retention within a urban pixel: it's just that I don't know which value to take ! Are there any standard values, used in other studies ?
  • swolnyswolny Member, NatCap Staff
    Hi Emmanuel -

    Just letting you know that I've asked the hydrologist who wrote the model to chime in, but she's been away traveling. Hopefully she'll have more insights for you when she returns.

    ~ Stacie
  • Hello Stacie,
    Thanks a lot for asking. I'm looking forward to hearing from her !

Sign In or Register to comment.