Babbage River delta and lagoon; hydrology and sedimentology of an Arctic estuarine system

Inputs, transfer processes, and storage characteristics of water and sediment have been investigated in a 40-km² estuarine system on the central Yukon coast. The setting is transgressive, microtidal, and high-latitude (69°N). The Babbage Estuary system can be subdivided into fluvial, tidal-distributary, delta-plain, intertidal, lagoon, marginal-supratidal, and barrier subsystems, each associated with one or more distinctive depositional environments and characteristic lithofacies assemblages. The structure of the system has been examined in terms of links between subsystems and overall system response to input perturbations. Although the propagation of tide and surge within the estuary may be treated as a quasi-linear stochastic process, transfers of fluvial water and sediment through the system are highly non-linear. Furthermore, the parameters of the system change dramatically on an annual cycle. Inputs and associated system responses are dominated in the short run by seasonal- and synoptic-scale variance, the former reflecting major seasonal adjustments in the phase distribution, circulation process, iand input regime of the estuary. The annual salinity cycle, with a range of at least 60 ppt, exhibits a short reaction and long relaxation response to major snowmelt runoff inputs in May or June, when salt water is flushed completely out of the estuary. Wind-generated waves are effectively absent from the system during 8-9 months of the year, but play a major role during the open-water season. Although direct transport of sediment by ice is relatively unimportant, ice effects are pervasive; they include, in addition to restriction of winter runoff and surface wave generation, creation of hypersaline conditions, control of the sedimentologically important flood events on deltaic supratidal flats, enhanced rates of coastal recession due to thermal degradation of ground ice, and production of distinctive thermokarst morphology on supratidal surfaces. Water level, storage volume, salinity, and suspended sediment series during the open-water season in the lagoon are dominated by synoptic-scale wind effects. In the delta, the major synoptic-scale anomalies of sediment concentration are related to storm runoff. At long time scales, the estuarine system has been dominated by rising sea level and coastal recession; Holocene climatic fluctuations may also have been important. A transgressive sequence has developed, including various distinctive features, notably the absence or limited development of aeolian, backbarrier-margin, tidal-delta, and intertidal marsh facies, a largely afaunal intertidal component, and deltaic deposits with poorly developed levees and abundant lake basins. The basal fluvial component includes a sinuous gravel channel assemblage of a hitherto poorly documented type. The Babbage Estuary barrier sequence is primarily transgressive, but incorporates localized elements of progradational and inlet-migration models. Examples of major transgressive, progradational, and inlet-fill barrier sequences occur in close proximity on the central Yukon coast.

Organization: Government of Yukon | Gouvernement du Yukon