Application of the Fill-and-Spill Concept in Permafrost Hydrology

摘要

The fill-and-spill concept for runoff generation and flow delivery postulates that outflow occurs only when water held in storage exceeds the storage capacity (or rises above the outflow threshold). Each flow production process has its threshold, and in permafrost areas seasonal freeze-thaw and the accumulation-ablation of snow and ice change the storage capacity of the active layer and above ground. Unique to permafrost regions, not only the status of storage (governed by water gains and losses), but also the water-holding capacity (including considerations of the space that can retain water and the outflow threshold elevation) changes during the thaw season. Examples of subsurface, surface, and channel flow production are reviewed in light of the fill-and-spill concept. Permafrost areas are particularly amenable to the realization of this concept as the shallow but uneven active layer allows ready responses to water gains and losses, while seasonal snow and ice in channels create blockages that have to be overcome by spillage before segments of the flow network are hydrologically united for water delivery.