The hydrological behaviour of natural catchments and the ability to model it adequately is a significant element to be considered for any integrated stormwater management plan in an urban context. As the basic objective of sustainable drainage systems is to replicate the pre-development hydrology, it becomes essential to be able to confidently evaluate the discharge and runoff volume being produced in natural conditions. Unlike urbanized areas where overland flow on the surface is the predominant mechanism generating runoff, many other processes like interflow and groundwater flow are more significant as runoff processes for undeveloped conditions. The interaction between overland flow and groundwater flow also becomes more and more important to consider as many low impact development practices involve infiltration to minimize surface runoff.
This paper will examine the capabilities of SWMM5 to model natural and rural catchments and the newly added options in PCSWMM to overcome some of the perceived deficiencies of SWMM5. Following a recent development program, the new version of PCSWMM has integrated many interesting features for rural hydrology that could be used to more easily model hydrological features in natural catchments. After a review of the concepts that have to be considered, the presentation will discuss the analyses for two small catchments that have been used to assess the capabilities of SWMM5 and PCSWMM5. The first one is a small undeveloped and forested basin just north of Quebec City and it will be used to discuss the principles of pre-development conditions as a basis for stormwater management criteria. The second catchment is a small rural area that has been monitored for 3 years during an extensive research program led by Agriculture and Agri-Food Canada to manage runoff from cultivated parcels.