Ninth International Conference on Permafrost ... - IARC Research

Examining the Temporal Variation in Headwater Drainage Networks and Potentialfor Thermokarst Using Remote Sensing in the Imnavait BasinErin D. TrochimUniversity of Alaska FairbanksDouglas L. KaneUniversity of Alaska FairbanksAnupma PrakashUniversity of Alaska FairbanksIntroductionSurficial drainage networks underlain by a confining layersuch as permafrost are characterized by significant amountsof overland flow, manifesting features such as water tracksand incised channels as the dominant complex. Variations inrouting can occur in the Arctic fresh water hydrological cycleas feedback mechanisms between vegetation and permafrostdistribution. Predicting and characterizing potential responseis an important component for engineering infrastructureappropriate for the climatic conditions. The Imnavait basinnorth of the Brooks Range in Alaska is part of a long-termmonitoring effort, and provides an opportunity to pairhydrological studies and high-resolution topography modelswith remotely sensed data, to create a qualitative, spatiallydistributed perspective.Water tracks are saturated areas mantled with organicsoils which may or may not connect to the channel network(McNamara et al. 1999). Flows are perpendicular to elevationcontours, and they often develop a parallel distribution withspacing of approximately tens of meters. The vegetationassociated with water tracks is proportional to quantity ofwater typically present within the channel (Walker et al.1994). Well-developed water tracks contain the Eriophorumangustifolium-Salix pulchra willow community while watertracks of intermittent flow, which are poorly defined, containshrub facies of the Sphagno-Eriophoretum vaginati. subass.typicum.Thawing of ice-rich permafrost or thermokarsting(van Everdingen 1998) in foothills or mountainous areastypically occurs along water tracks; determining the thermalregime of the water tracks will allow the prediction of (if)when a thermokarst may occur. Assessment of whether thewater tracks are experiencing shrub expansion, one of thestrongest indicators of ecosystem change due to climatechange measured to date (Stow et al. 2004), is important forprediction of the future thermal state. Changes in vegetationcan result in feedbacks to the thermal state of the associatedpermafrost, as an increase in density and spatial expansionlower the albedo and allow more energy to be absorbed intothe ground (Callaghan et al. 2004). Coupling this effect withpotential alterations to landscape as a result of thermokarstactivity, including changes in groundwater flow and storage,relief, and discharge patterns and amounts (Grosse et al.2006), results in the potential to significantly alter thelandscape.The Imnavait basin covers an area of 2.2 km 2 . Till froma glacial advance in the middle Pleistocene covers theslopes (Hamilton 1989). Thick permafrost reaching 300 mdeep (Osterkamp & Payne 1981), and lack of springs in thebasin effectively isolate the basin from deep groundwatersources. Maximum depths of thaw are typically 25 to 50 cm,but can extend to 100 cm with variation in environmentalfactors including soil type, slope, aspect, and soil moisture(Hinzman et al. 1991).Aerial photographs from July of 1956, 1978, and 2007were georeferenced and used to digitize water tracks intothree classes to examine the temporal variation in both areaand texture over this 61-year period. Water tracks that wereleast, moderately, and well developed were buffered by 2,5, and 7.5 m, respectively, to approximate area. Zonal GISanalysis using a 5 m digital elevation model acquired in2001 was used to examine the variations in slope, aspect,and elevation.300000Poorly DevelopedMod. DevelopedWell Developed200000Sum Area (m 2 )100000Figure 1. Water tracks in the Kuparuk River basin.01956 1978 2007Figure 2. Imnavait Basin water track distribution: 1956, 1978, and2007.315