The Topographic Wetness Index (TWI) is a terrain analysis technique used to quantify the potential for wetness of a particular area. The TWI can provide information about the amount of water that is likely to accumulate in a location and the flow patterns of water across the terrain. TWI quantifies the potential wetness of a landscape based on topography and slope, it is not a direct measure of wetness, it is a measure of potential wetness based on an analysis of terrain data. The formula for TWI involves two components: slope and contributing area. The slope is computed from the DTM. It represents the change in elevation between neighboring cells. Flow accumulation identifies the flow direction of water across the landscape. It accumulates the contributing area for each cell. The contributing area represents the upstream area that contributes flow to a specific cell. Contributing area is only considered up to a maximum of 180 meters away from an analysis pixel (areas in the landscape for which no Lidar data has been collected are not considered). Cells with higher contributing area are more likely to be wetter due to water accumulation. The TWI combines slope and contributing area. Wetlands, depressions, and valleys typically have high TWI values. Uplands, ridges, and steep slopes have lower TWI values.

The Rangeland Department in the Kamloops District from the Government of British Columbia has recently raised concerns regarding the observation on the reduction of the number and the surface area of the grassland ponds in the Lac du Bois Grasslands Protected Area. This study aims to distinguish between the ponds with stable groundwater inputs (i.e. connected ponds) and the ponds with unstable groundwater inputs (i.e. perched ponds) to assist the government in determining reliable water sources. This research started by categorizing ponds with different surface areas as either low resilience or threatened resilience. Different terrain models were created using Light Detection and Ranging (LiDAR) data in addition to the calculation of the topographic wetness index (TWI). The classifications were validated using Google Earth and drone imagery. An overall of 121 ponds was discovered with 86 of them considered as low resilience, while the remaining 27 ponds being threatened resilience. For the low resilience ponds, 19 of them were identified as perched ponds, 47 as connected ponds, and 20 as intermediate ponds with the risk of having unstable groundwater connection that requires further analysis in the field. For the threatened resilience ponds, 5 of them were found to be perched ponds, 17 as connected ponds, and 5 as intermediate ponds. The outcome of the pond distribution indicates that the perched ponds were more likely to be found in an area with a flat slope, surrounded by grass, and low canopy coverage. Additionally, the calculated TWI was unable to differentiate between the pond types as the median groundwater levels are spatially dependent on the local topographic features.

Calculation results of weights for all conditioning factors.