Spatial-temporal assessment of water and sediment connectivity through a modified connectivity index in a subtropical mountainous catchment

The concept of connectivity aims to understand the hydrosedimentological (water and sediments) processes that occur in the catchment and influence the water and sediment transfer at different spatial-temporal scales. Connectivity is often assessed through connectivity indexes, commonly considering only structural features of the landscape. The present study proposes the insertion of the precipitation and surface runoff characteristics as functional components to the connectivity index (IC). Its main goal is to evaluate the space-time variation of water and sediment connectivity in a subtropical catchment. To achieve this goal, two parameters, extracted from precipitation data, were inserted in the IC and resulted in the hydrosedimentological connectivity index (IHC), which concerns the runoff generation and the characteristics of the antecedent precipitation event. The IHC was tested on a catchment scale for 7 individual precipitation events. For each event, the index provided values and maps that reflected the dynamic processes of the catchment, regarding the functional and structural components of connectivity. The performance analysis of the index was qualitative, and it was carried out by means of a visual interpretation using field data on processes and sediment paths. The IHC map was coherent with the field data and it showed a satisfactory representation of the sediment transfer patterns. It was observed that the debris flow scars corresponded to the flow paths with higher IHC values and the deposition areas with the lower IHC values. In addition, the IHC values showed a positive correlation with the catchment flow values. Statistical analysis indicated a correlation between the mean IHC and the total runoff volume (+0.69) as well as between the mean IHC and the peak flow (+0.63). The IHC was able to estimate the space-time variation of water and sediment connectivity in a catchment, identifying locations of sediment transfer and deposition for precipitation events with different magnitudes. The modified method was able to bring advances to connectivity representation, however, it presented some limitations, such as the incapability to represent the sediment exhaustion in the catchment. Even so, the IHC allows its application in areas with little data and it can be a useful tool in identifying relevant sites on watershed management.

Automated summary

By introducing precipitation and surface runoff characteristics as functional components into the connectivity index, a hydrosedimentological connectivity index (IHC) was proposed to evaluate the space-time variation of water and sediment connectivity in a subtropical catchment. The IHC proved to be a useful tool for identifying sediment transfer and deposition locations in catchments with limited data, providing a satisfactory representation of sediment transfer patterns and showing positive correlations with catchment flow values.