Hydrologic Response of a Bog Cascade with a Dynamic Contributing Area in Discontinuous Permafrost

English Abstract:

Flows from river basins in the lower Liard River valley in northwestern Canada have been rising in the last two decades as a result of climate warming. Changes in precipitation account for only about 30% of this increase. In the wetland-dominated basins that characterise the southern margin of permafrost, permafrost thaw and disappearance, and resulting land-cover change, is occurring at an unprecedented rate. Permafrost thaw has the potential to fundamentally alter the processes giving rise to streamflow in this region by altering the type and relative proportions of biophysical terrains. Field studies were conducted at the Scotty Creek Research Basin, a 152 km² watershed, located about 50 km south of Fort Simpson, NT. Scotty Creek is typical of other basins in the region and is underlain by discontinuous permafrost. There are three major land-cover types in the basin, each exhibiting a distinct hydrological function. Channel fens convey water to the basin outlet, while permafrost plateaus are runoff generators. Flat bogs have been shown to be primarily storage features, however ephemeral channels have been observed to cut through permafrost plateaus and allow for hydrologic interaction between bogs. These channels create series of bog cascades that drain adjacent peat plateaus and ultimately flow into the channel fen. It is shown that the transmission of water through bogs and into the fen is a mechanism that changes the effective contributing area based on antecedent moisture conditions. The dynamic contributing areas are shown to be controlled by storage thresholds. Field data indicates that transmission of water through bogs is dependent on storage levels. Sharp crested v-notch weirs and flume boxes were installed in the channels to create a continuous stage-discharge relationship to gauge runoff entering the channel fen through the bog cascades. In this study we attempt to quantify the amount of runoff produced from bog cascades and determine how the contributing area varies in time and space. The hydrological model Raven will be used to simulate this system and explore how the contributing area changes in response to storms of varying magnitudes.