Catchment typology is a link indicator to help identifing the dominant water pathways of contaminants in each system.
Catchment typology is a catchment classification framework aiming to group catchments according to their hydrogeological functions. Catchments, therefore, can be classified in many different ways depending on interests and applications (Wagner et al., 2007 and references therein). Here we focus on the catchment typology, which has been developed to evaluate agriculture impacts on water quality.
Rittenburg et al. (2015) propose a conceptual framework of catchment typologies to evaluate the effectiveness of best management practice in agricultural catchments. They define three catchment typologies (A, B1 and B2) by: 1) the budget between precipitation intensity and soil infiltration capacity and 2) the thickness of the soil – i. e. permeable layer (Table 7.1).
Table 7.1: Catchment typology and dominant flow paths (modified from Figure 1 of Rittenburg et al., 2015)
|Type A||Type B1||Type B2|
|Hydro-geological criteria||Hydrological factor||Precipitation intensity > soil infiltration capacity||Precipitation intensity < infiltration capacity||Precipitation intensity < infiltration capacity|
|Geological factor||Regardless of soil* thickness||Thin soil||Deep soil|
|Dominant pathways||Overland flow||Overland flow, interflow, tile drainage||Groundwater, tile drainage|
* Soil refers to a permeable layer.
In type A catchments, precipitation intensity is greater than soil infiltration capacity; therefore, water cannot infiltrate in the subsurface. Then, water and contaminants will run over the ground surface (i. e. overland flow).
In type B1 catchments, soil infiltration capacity is greater than precipitation intensity while the thickness of permeable layer is thin. In this case, the unsaturated zone may become saturated quickly; consequently, overland flow, interflow, and tile drainage may be the dominant pathways.
In type B2 catchments, soil infiltration capacity is greater than precipitation intensity and the thickness of permeable layer is large. In this case, water may infiltrate into the deeper subsurface. Groundwater and tile drainage may be the dominant pathways.