Horacio Toniolo

Arctic Landscapes in Transition: Responses to Thawing Permafrost

Observations indicate that over the past several decades, geomorphic processes in the Arctic have been changing or intensifying. Coastal erosion, which currently supplies most of the sediment and carbon to the Arctic Ocean [Rachold et al., 2000], may have doubled since 1955 [Mars and Houseknecht, 2007]. Further inland, expansion of channel networks [Toniolo et al., 2009] and increased river bank erosion [Costard et al., 2007] have been attributed to warming. Lakes, ponds, and wetlands appear to be more dynamic, growing in some areas, shrinking in others, and changing distribution across lowland regions [e.g., Smith et al., 2005]. On the Arctic coastal plain, recent degradation of frozen ground previously stable for thousands of years suggests 10–30% of lowland and tundra landscapes may be affected by even modest warming [Jorgenson et al., 2006]. In headwater regions, hillslope soil erosion and landslides are increasing [e.g., Gooseff et al., 2009].

The importance of flow and turbulence characteristics for hydrokinetic energy development on the Tanana River at Nenana, Alaska

The site selection for the installation of hydrokinetic devices along a river reach is an issue of fundamental importance. While it is acknowledged that multiple factors such as accessibility, navigation, safety, and hydraulics, among many others, must be considered in the final decision, this article focuses on the influence of river morphology on turbulence flow parameters. Specifically, continuous high-resolution velocity measurements from a hydrokinetic resource assessment on the Tanana River near Nenana in the interior of Alaska are analysed to estimate, kinetic energy (KE), turbulent kinetic energy (TKE) as well as KE partition at particular locations. To accomplish these tasks, two different methods used to rotate the coordinate systems into the main flow direction are correlated and compared in order to extract the turbulent parameters from the main flow. The coordinate system methods include the streamline coordinate rotation and the extraction of statistical fluctuations from the average flow. The streamline coordinate rotation method is chosen to extract the TKE in temporal series. The calculated TKE was up to 30 per cent of the total flow KE in measurements located in pools and dissipated downstream, beyond the highly turbulent locations of bathymetric depressions and river bends. The overall KE increased over a bed free of major macro-obstacles and reduced depth, where the TKE fraction accounted for only 2 per cent of the total KE. The visualizations of the KE and TKE are compared with the river morphology, leading to identification of helical flow, flow separation, and turbulent flow structures along the river bend and in pools to help the decision-making process in hydrokinetic planning.

Hydraulic and Sedimentological Characterizations of a Reach on the Anaktuvuk River, Alaska

Rivers located on the North Slope of Alaska’s Brooks Range are typically not well characterized with respect to basic hydraulic and sedimentological data. In order to obtain basic hydrosedimentological information on the Anaktuvuk River, a pristine stream located in the Colville River basin, we conducted an extensive field campaign from late May to early June 2009. The study reach was located at N69°27.78 5′ , W151°09.85 8′ , latitude and longitude, respectively. The Anaktuvuk River flows north from the Brooks Range to the Colville River, drains an area of 7,058  km2 , and encompasses 2,063 m of vertical relief. During the field campaign, the field crew measured discharge and water-surface slope, collected water samples, and characterized bed sediment. As a result of fieldwork and laboratory work, we present an initial rating curve for the Anaktuvuk River, as well as the calculated roughness coefficient and suspended sediment concentrations. In addition, we compare the observed bankfull discharges with th...

Numerical simulation of sedimentation processes in reservoirs as a function of outlet location.

Abstract This paper builds on a recently published one-dimensional moving-boundary model of the coevolution of topset, foreset and bottomset in a reservoir that captures the dynamics of the internal muddy pond typical to reservoirs. This model was modified to account for different outlet locations at the reservoirs downstream end. This model considers a river carrying two sustained phases of sediments: coarse (sand) and fine (mud). The coarse phase deposits in the topset and delta foreset, while the fine phase forms a dilute suspension of wash load in the river. As the river enters the reservoir, the muddy water plunges on the foreset to form a Froude-supercritical (purely depositional) turbidity current. This turbidity current emplaces the bottomset. The modified numerical model was tested against five laboratory experiments previously reported by the author. The model successfully locates the muddy-water/clear-water interface. In addition, modeled and measured bed deposits are in good agreement. Results clearly indicate that the location of the internal hydraulic jump plays a key role in the final bed deposit.

Thermokarst Evolution in Sub-Arctic Alaska: A Study Case

Several landscape modifications are indicative of a warming climate in Arctic arid Sub-arctic regions. Preliminary results of detailed analyses on the development of a thermokarst are presented here. Thermokarst occur when massive ice buried in permafrost thaws allowing the surface to rapidly subside. Although thermokarst is a natural process that often happens when ice-rich permafrost is disturbed, the cause of the recent acceleration in the initiation of new thermokarsts is believed to be the changing climate, which has warmed markedly in Interior Alaska in recent decades. The study site is located in the Caribou-Poker Creeks Research Watershed (CPCRW). The watershed is situated in Central Alaska, 50 km northeast of Fairbanks, Alaska. The permafrost distribution is discontinuous in the area and the ice-rich nature of these frozen soils makes them particularly susceptible to thermokarsting and erosion. The research involves both field and laboratory analyses. Direct measurements of water flowing into the thermokarst and suspended sediment sampling were conducted from spring to fall, 2004. Two topographical surveys were performed in the same period. Suspended sediment concentrations and grain size distributions were obtained in laboratories at the University of Alaska Fairbanks. Initial results indicate: a) high flow rate and low sediment concentration during breakup, and b) a reduction in the water discharge and high sediment concentration values during the summer, in spite of the unusually dry conditions that occurred during this period. Substantial morphologic changes were observed along the summer months. For example, the upstream end of the thermokarst migrated approximately 2.5 meters by successive collapsing events. A new pond was created and partially filled with sediments from the soil matrix. In a pre-existent depression the bed sediment deposit thickness was, on the average, in the order of 60 cm. Thus, the local topography was intensely altered. As a consequence of these modifications, the flow patterns were also changed in the area. It is expected that a new small stream will develop in the site.

Antecedent Conditions and Damage Caused by 2015 Spring Flooding on the Sagavanirktok River, Alaska

AbstractAlaska’s economy is tied to oil production, with most of the petroleum coming from the Prudhoe Bay oil fields through the Trans-Alaska Pipeline System. Deadhorse, an industrial town located...

Numerical vorticity quantification in the Kvichak River, Alaska (USA)

Hydrokinetic turbine deployment locations have historically been sited based on the power density and theoretical hydraulic power. Neither of these parameters account for the turbulence within the fluid column. It is the goal of this paper to quantify the vorticity magnitude, based on previously collected Acoustic Doppler Current Profiler data, associated with transects of the Kvichak River near Igiugig, Alaska (USA). The Kvichak River is a proposed site for the deployment of a hydrokinetic turbine, where three siting recommendations have previously been made by others. Vorticity magnitude results are plotted in cross-sectional, two-dimensional contour format and are utilized to further the analysis and recommendations of the deployment site along the study area. A vector system rotation is applied to correlate Acoustic Doppler Current Profiler data output to a regional coordinate system. Results indicate that higher levels of vorticity magnitude are associated with two of the primary recommended turbine deployment sites and provide confidence in the suitability of the sole remaining proposed turbine deployment location.