Limitations of L-THIA

The SCS CN method, which is a core component of many traditional hydrologic models, has been used in a straightforward simple fashion to assess the long term hydrological impacts of land use change.

With the intention of minimizing the complexity of the SCS CN method certain elements were simplified by:

• Neglecting the contributions of snowfall to precipitation
• Neglecting the effect of frozen ground that increases stormwater runoff during cold months
• Neglecting variations in antecedent moisture conditions

These simplifications are necessary to keep the technique straightforward and accessible but could be removed if a more sophisticated analysis was required.

L-THIA has been developed as a tool to asess the long term impact that changes in land use have on hydrology of an area. It is to be used with data that is readily available to planners and decision makers. It is not meant to assess the details for requirements of a storm water drainage system and other such urban planning concerns.